Monitoring and Maintenance of Anesthesia Flashcards
(217 cards)
1
Q
What is the definition of MAC?
A
- MAC is the Minimum Alveolar Concentration of an inhalational anaesthetic agent which is required to prevent movement in response to a noxious stimulus in 50% of animals.
- MAC studies are usually performed in experimental animals which have not received any other drugs for premedication or induction of anaesthesia.
2
Q
How do we use MAC in clinical anaesthesia?
A
- MAC gives us information about the POTENCY of different inhalational agents, ie. how much we need to give to an animal to produce anaesthesia.
- It can be thought of as the dose required of an inhalational agent.
- However, MAC studies are based on 50% of the population not moving in response to a painful stimulus: the other 50% of the population given MAC of an inhalational agent will move in response to a painful stimulus!
- For clinical anaesthesia, we would use 95% of the population as a guideline. To achieve clinical anaesthesia in 95% of the population, you need to give about 1.25 x MAC.
- Additionally, there are lots of factors that can increase or decrease MAC (or the amount of inhalational agent required) in an individual animal.
3
Q
MAC and Potency
A
The MAC of isoflurane in the dog is 1.3%. The MAC of sevoflurane in the dog is 2.3%. Potency is inversely proportional to MAC.
- This means that isoflurane is more potent than sevoflurane
4
Q
Blood:Gas
Desflurane
A
0.42
5
Q
Blood:Gas
Halothane
A
2.4
6
Q
Blood:Gas
Isoflurane
A
1.46
7
Q
Blood:Gas
Sevoflurane
A
0.6
8
Q
Blood:Gas
Nitrous Oxide
A
0.47
MAC: 200%
9
Q
you wanted to use an inhalation induction of anaesthesia using an induction chamber / box in an aggressive cat, which would be the best agent to choose?
A
- Sevoflurane has a low blood:gas solubility so induction will be fast. It is also non-irritant to the respiratory passages.
- However, it is not licensed in cats.
10
Q
Surgery then proceeds uneventfully and the procedure finishes shortly afterwards.
If you had used nitrous oxide, are there any special precautions you should take before recovery?
A
11
Q
In your assessment of the patient’s pulse which of the following could be classified as ‘peripheral’ pulses?
A
Dorsal pedal arterial pulse, Auricular arterial pulse, Digital arterial pulse
12
Q
normal PaCO2 for animal under anaesthesia
A
- 35-45 mm Hg
- lower would indicate a degree hyperventilation
13
Q
size A and H cylinders
A
- not used for medical gases
14
Q
size of cylinders attached to anaesthetic machines and the size used for manifolds
A
- size E usually attached to anaesthetic machines (have the Pin Index system for safety)
- each medical gas has a specific pin index configuration -prevents connection of wrong cylinder
- size J for those supplying manifolds (for supplying pipelines)
**now most practices use pipelines to a central gas line -more economical, much larger tanks!
15
Q
black cylinder with white top
A
- Oxygen
- stored at 13700kPa
- Gauge pressure indicates the gas volume left inside the cylinder
- Major gas used to maintain adequate oxygenation of a patient during procedures.
- Stored in black-bodied cylindrical containers with a white collar.
- This is being phased out, so soon they will be found in solid white containers with ‘Oxygen’ written in black lettering along the side.
16
Q
blue cylinder
A
- Nitrous Oxide
- stored in liquid phase with gas on top at 4400kPa (4.4 bar)
- Gauge pressure stays constant as long as there is some liquid left in the cylinder! - doesn’t indicate the volume remaining - must weigh for this!
- Used as a form of anaesthetic gas, though is uncommonly used in practice recently.
- Stored in solid blue cylindrical containers.
17
Q
grey cylinder with black/white quarters on top
A
Medical Air
- often used in procedures with high end anaesthesia
- the air contains N (like normal air we breath) which is responsible for keeping the alveoli of your lungs open
- Compressed regular air, containing standard atmospheric ratios of gases.
- Notable is nitrogen, used to aid in inflation of pulmonary alveoli.
- Stored in grey-bodied cylindrical containers with a white and black quartered collar.
18
Q
bodok seal
(sealing washer)
A
- makes a gas-tight joint!
- must be placed between cylinder and anaesthetic machine
- with make a very loud noise when turned if missing when cylinders are changed
19
Q
Schrader Valves
A
- special end terminal unit of pipeline from central gas supply
- non-interchangeable!
- i.e. an oxygen line cannot be plugged into Schrader valve for NO
- also color coded (with hoses)
20
Q
3 main components of anaesthetic machine
(positioned b/w cylinders and the anaesthetic machine)
A
- gas supply (oxygen +/- NO+/- air)
- pressure gauges
- pressure relief valve - reduces cylinder pressure to a safer operating pressure of about 400kPa (4 bar)
- gas is 5 times atmospheric pressure –> would blow lungs apart alone
- reduce this to normal atmospheric pressure so patient can breath normally
21
Q
Emergency Oxygen Flush and Common Gas Outlet
A
-bypasses flow meters and vaporizers: gives you 40-60L of oxygen per minute
- never push when an animal is connected! - will blow their lings apart!!
- this is for cleaning ONLY
- can be to dilute anaesthetic gases (e.g. if used to fill an empty reservoir bag during anaesthesia)
- button usually found next to the common gas outlet
22
Q
Pressure Relief Valve
A
23
Q
Vaporisers
A
- in order to deliver volatile agent, you need vaporizers
- isoflurane, etc.
- calibrated for one agent only
- only isoflurane vaporizers will take isoflurane
purple: isoflurane, red: halothane
isoflurane - saturated vapor pressure (240 mmHg, 32%)
- very accurate!
- most theaters are 20-21 degrees so they work well
- in very cold temps (farm in winter) they do not work well!- need to be at the right temperature
- Fresh gas is split: can go through bypass channel or pass through a vaporization chamber –> therefore mixes gas containing no vapor with containing fully saturated anaesthetic vapor to produce a final mixture with appropriate vapour concentration
-splitting ratio is adjusted by the control dial on the vaporizer
24
Q
Scavenging Systems
A
- all practices should have scavenging systems!
- DO NOT LET GAS JUST SPILL INTO ROOM
- if you don’t have the proper system to absorb the volatile agent, they will get filled with volatile agents
- needs to go in waste bin
- charcoal can be incinerated
- Portable Systems - activated charcoal absorbers
- Passive Systems - pollutes atmosphere
- Active Systems - connect to vacuum system, air brake must be utilised to limit suction
25
4 main functions of Anaesthetic Breathing Systems
26
Non- rebreathing systems vs. rebreathing systems
27
Non-rebreathing systems
| (5)
* T-piece **(0-10kg) - *IPPV*** - **class F -** class F being least efficient (higher flow rates required)
* Mini-Lack **(2-10kgs ) - Class A -** (lower flow rates required)
* Bain - **10-18kgs - *IPPV -class D***
* Lack - **10-35kgs - class A** (theoretically very efficient in fresh gas use)
* Magill - **10-35 kgs - class A**
Typically, low classification systems are less suited to animals that must be ventilated (cannot spontaneously breathe), as a much higher flow rate is required in these patients.
Hence a higher classification system that already utilises a high flow rate would be better
28
Re-breathing system
* Circle - **10kgs ++++**
* **IPPV**
29
Calculation of **Minute Volume**
| (needing to know Tidal Volume)
**Minute Volume = Tidal Volume x respiration rate**
**\*\*make sure you convert to L per minute!!**
30
**How would you calculate the correct fresh gas flow (FGF) to use with your chosen breathing system?**
**FGF = Minute volume × circuit factor**
Firstly, estimate the minute volume. This can be done in two ways:
1. Minute volume = 200 ml/kg/minute (this is quicker and can be applied easily in daily veterinary practice)
2. Multiply the respiratory rate by the estimated tidal volume (10ml/kg).
The value for minute volume then needs to be multiplied by the appropriate **‘circuit factor’**. For the T-piece, the circuit factor is 2.5-3 × minute volume. For the 6kg dog in this case, if minute volume is 1200ml/minute, then FGF will need to be at least 3 litres/minute to **prevent rebreathing of previously exhaled alveolar (and hence CO2 containing) gas.**
31
**What are the main Mapleson class A anaesthetic systems**
**(3)**
All class A systems have a circuit factor of 1-1.5, so requiring a low flow rate.
Hence most are unsuitable for ventilated patients.
1. Coaxial Lack
2. Parallel Lack
3. Magill
32
Magill System
* **10-35 kgs**
* **system factor: 1-1.5**
* **NOT IPPV**
* **Mapleson Class A**
* Fresh gas passes through a tube with a reservoir bag, and into the patient.
* Exhaled gas from the patient fills this tube, and is then pushed out via the APL (adjusted pressure limiting) waste valve when fresh gas next passes through.
**Uncommonly used, as APL valve is close to the patient's face, and can be obstructive**
33
Coaxial Lack System
**10-35kg**
**1- 1.5 system factor**
**Not IPPV**
**Mapleson Class A**
* Fresh gas passes through a tube with a reservoir bag, and into the patient.
* Exhaled gas passes via a second, internal tube to the APL waste valve, located above the reservoir bag.
* **Commonly used in animals over 10kg**
* -essentially moved the valve as it became an issue in front of patients face
34
Parallel Lack System
* **10-35kg**
* **1 - 1.5 System Factor**
* **NOT IPPV**
* **Mapleson Class A**
Fresh gas passes through a tube with a reservoir bag, and into the patient.
Exhaled gas passes via a second, seperate tube that runs parallel to the first, to the APL waste valve located above the reservoir bag.
**Commonly used in animals over 10kg.**
***A mini version is also available for animals under 10kg.***
35
What are the main Mapleson class B-F anaesthetic systems
These systems typically have a circuit factor of 2.5-3, and so require a high flow rate.
These systems are more suitable for ventilated patients.
Due to high flow rates required, these systems are typically unsuitable for animals over 50kg
1. **T-piece (0-10kgs)**
2. **Bain (10-18kgs)**
In both systems, non-blind reservoir bag variants are uncommon, as these bags have the capability to twist, block gas expulsion, and cause pressure damage to the lungs.
36
T-piece breathing system
| (Ayres)
* **0-10kgs**
* **2..5-3 System Factor**
* **YES IPPV**
* **Mapelson Class F**
Fresh gas passes into a tube leading to the patient at a T-junction close to the patient's head.
Expired gas passes down this main tube to the scavenging system.
Some variants will have a reservoir bag at the end of this tube **(Ayres)** , which may be blind ended with an APL valve prior, or non-blind ended to allow gas to pass.
Bags began to twist in original- causes damage to lungs --\> next model
**this is really good for ventilating patients!** - not for spontaenously breathing patients like Class A's
* **Most commonly used high class system in small animals, as is suited to animals under 10kg.**
37
Breathing System for a good for a healthy, young and _small_ animal undergoing elective castration?
**T-piece (ayres)**
* **The T-piece has minimal apparatus deadspace and resistance to breathing, making it ideal for animals ~\<10kg**. Fresh gas flows for the T-piece must exceed 2.5 × the patient’s minute volume, otherwise expired gas will be rebreathed. Rapid respiratory rates with short expiratory pauses may require even higher flow rates (≥3×minute volume)
38
Bain System
* **10-18kgs**
* **2.5-3 System Factor**
* **YES IPPV**
* **Mapelson Class D**
* good for ventilating patients but again a very high circuit factor
Fresh gas passes through a small tube within a larger tube and into the patient.
* Exhaled air passes through the larger tube and into the scavenging system.
* Multiple variants, either with a reservoir bag and an APL valve adjacent to fresh gas inflow, or with a non-blind ended reservoir bag that allows gas to pass.
* Suitable for animals over 10kg, but uncommonly used due to high flow rates being uneconomical.
* Can come long or short
- fresh gas comes through inner green tube
- used gas flows in outer tube and goes into bag
- bag continues to a valve at the top
* **-how do you know if there is a hole in the inner tube?**
Only way to know is to occlude the inner tube with device provided
Bobbin will dip
If there were a hole in the tube, the gas would not cause the bobbin to dip
39
What is the **Humphrey ADE system**, how does it function, and when is it used?
* Variable non-rebreathing system that can be switched between Mapleson classes A, D, and E by the use of a lever.
* Also permits the attachment of an absorbent canister, converting it into a circle rebreathing system.
* The lever controls the circuit factor of the system, altering the flow rates for its function, and so allowing it to be used for both spontaneous and ventilated breathing patients.
* Suitable in small animals at a range of different weights.
40
What are the main **rebreathing systems** used in practice
1. Circle
2. Coaxial Circle
41
Circle Breathing System
* **10kg+++**
* **not good for smaller animals**
* **Doesn't have a system factor- Minimum flow rate is 10mls/kg**
* **Start at 100mls/kg then reduce to a maintenance setting of 50mls/kg**
* **YES- IPPV**
Fresh gas enters the system circuit, travelling to the patient for inhalation.
Exhaled gas passes through the second arm of the circuit, into the reservoir bag and into the absorbent cansister.
Carbon dioxide is removed, and the gas reenters the fresh gas arm of the circuit for rebreathing.
Backflow of gas is prevented by the presence of one-way valves in the inspiratory and expiratory arms of the circuit
42
Coaxial Circle Breathing System
* Fresh gas enters an inlet chamber above the absorbent canister and passes into a tube to the patient.
* Exhaled gas passes through a second tube that surrounds the inlet tube, and travels into the reservoir bag and the absorbent canister.
* Carbon dioxide is removed, and the gas reenters the inlet chamber and inspiratory limb of the circuit.
43
How are endotracheal tubes sized, and how are they selected for the individual patient?
* Sizing determined by the internal diameter of the tube in millimetres.
* **Should ideally use the largest tube that will fit through the larynx of the animal**.
* This maximises the airflow that a patient can receive.
44
Opioid commonly given with alpha-2 adrenoreceptor agonists in horses...
**Butorphanol**
* **less legislation involved**
* **helps prevent them fom kicking**
* can really see a difference in the way they stand as well - it is not analgesic effect, it removes some of their response to touch!
*
45
Usual premedication for the horse
* **Acepromazine & small amount of opioid** (Butorphanol) in the bix so it can walk calmly to the theater
* then give **Adrenoreceptor agonist (alpha 2 agonist) - Xylazine** once it is there or else it may not be able to walk to the theater
* Alpha 2 more usually used as a co-induction
* blurred lines between pre-med and sedation sometimes on what drug is given when
46
antinociception
| (analgesia)
the action or process of blocking the detection of a painful or injurious stimulus by sensory neurons --\> analgesia
- one of the purposes of GA
* SE's: causes CVS and respiratory depression
47
Balanced Anaesthesia
48
What type of pre-med would be best suited for a cat or dog with Mitral Valve Disease?
Which would you not use?
* Use: **ACP (Phenotiazines) -** useful for MVD **- vasodilation and hypotension (NOT GOOD FOR HCM)**
* may be able to use opioids as they are good for patients with cardiac disease
* Avoid: **Medetomidine** **(Alpha 2 agonist)**
49
What Pre-med(s) would be useful in a healthy, young, non-pre medicated animal?
Which one would not?
* use: **ACP (all young healthy dogs, cats 50/50) or Medetomadine (short procedures, aggressive cats, non-conventional species)**
* avoid: **Diazepam or Midazolam alone** (not great sedatives)
* don't use benzodiazepines in hepatic encephalopathy patients either (metabolized in the liver)
50
Good pre-med option for a seizure patient
* Benzodiazepines!
* **anti-convulsant**
* **Diazepam or Midazolam**
* **NOTE:** avoid overdosing though, antagonists are expensive unlike for alpha-2s
51
Midazolam is inhibited by.....
* **ERYTHROMYCIN**
52
Good pre-med for fracture repair
* **Benzodiazepines**
* **Myorelaxation**
53
Which pre-med would you avoid using in a cat with Myasthenia Gravis?
What is Myasthenia Gravis?
* **Myasthenia gravis** is a chronic autoimmune neuromuscular disease that causes weakness in the skeletal muscles, which are responsible for breathing and moving parts of the body, including the arms and legs
* Avoid the use of **Benzodiazepines (Diazepam, Midazolam)**
* **Myorelaxation can lead to decreased respiratory function and relaxation of intercostal and diaphragmatic muscles**
54
What should be best avoided as a pre-med in horses?
* Diazepam
* Benzodiazepines may scare horses as it is a muscle relaxant
55
Avoid the use of this pre-med in young, healthy cats
(use not indicated)
* Benzodiazepines
* **Diazepam**
56
Avoid the use of this pre-med in patients with hepatic encephalopathy
* Benzodiazepines
* Diazepam, Midazolam
57
Good choice in pre-med for brachycephalic breeds
* **Diazepam (IV)** -minimally affect CV and respiratory function, myorelaxation
* can use **ACP** in some cases
* likely avoid **opioids** (SE of Respiratory depression) and possibly medetomidine
58
some SE's of opioid use in horses
* spontaneous locomotor activity (in other animals also, but esp. horses)
* changes in gut motility! --\> can make horses colic
59
Good choice of opioid in dogs
| (that is licensed)
* **Methadone**
* does not cause vomiting and nausea like Morphine
* Onset 10 min, duration 2-4 hours
* No His release if given IV
60
Butorphanol
* K and u agonist
* **MILD** sedative
* poor analgesic
* used with sedative drugs in horses and dogs
* **not controlled**
61
a weak mu agonist used in SA practice commonly ...
* **Buprenorphine**
* licensed in SA, commonly used
* not as potent as Morphine, but better than Butorphanol
* **Schedule 3 -** less controlled than morphine
* **longest acting opioid (7 hr)**
62
Opioid that must be given IM
* **Pethidine**
* **mu agonist of short duration**
* IV will lead to increased Histamine release
* **shortest acting opioid (20 min)**
63
Fentanyl
* very potent mu agonist
* short acting opioid
* **now licensed for dogs (Fentadon)**
* used often as an infusion during Sx
* **HIGH POTENCY**
64
**Which patients should you used Opioids?**
**(3)**
* All patients in pain
* Invasive Sx's
* Patients with Cardiac Diseases
65
Which Patients should you be cautious with using opioids?
(4)
* **respiratory diseases (SE includes respiratory depression)**
* **Allergic conditions (asthma)** - morphine, pethidine --\> ***both high risk for undesired effects*** and also can cause Histamine release possibly - worsen condition
* patients with **laryngeal dysfunction** as a pre-med **--\> due to effects on respiration**
* **careful with rabbits and horses -** they can't vomit and it may cause gut stasis
66
Options for pre-med protocols
| (4)
* **Opioid, ACP, Benzodiazepine** or **alpha 2 agonist alone**
* **Opioid + ACP -** when sedation and analgesic effect called for
* **Opioid + alpha-2 agonist - (**ex: QUAD protocol)
* **Opioid + Benzodiazepine -** to achieve analgesic effect and lighter sedation in geriatrics, neonates, seizure Px's
67
Commonly used Injectable Anaesthetics
| (5)
* **Propofol**
* **Alfaxalone**
* **Ketamine**
**All--\> 100% bioavailability to the brain!**
_(not as much)_
* Thiopentane/Thiopental - not really used in SA clinics anymore
* Etomidate- only when REALLY sick. Does not cause CVS depression like others! (drop in CO, vasodilation, reduced BP)
68
goal of low dose anaesthetic
**Sedation**
ex: propofol
69
goal of high dose sedative
* Anaesthesia
70
What are some commonly used inhalational anaesthetics?
* **Isoflurane**
* **Sevoflurane - off license use in horses as good evidence for use** (only licensed for use in SA's)
* **Nitrous oxide -** use is fading**, NEVER USE IN THE HORSE** (hypoxia)
**others:**
* Halothane - not in production anymore
* Desflurane -used in horses sometimes, helps them get up faster, but not licensed for veterinary use
71
Common I/V Induction Protocol in Horses
**Ketamine and alpha 2 agonist**
works after 3 min, lasts for 15 min
**Give alpha 2 first! then ketamine --\> goes mad otherwise**
can add benzodiazepam for muscle relaxation if needed, but not super helpful as it is not very long acting
**Guaifenesin is used in the US:** works a similar way
another option: **Propofol and Alafaxalone (but crazy $$)**
72
4 phases (stages) of Anaesthesia
1. **Unconsciousness (part of the triangle)**
2. Signs of Excitement (often miss with IV induction!) = involuntary twitching/excitement
3. **Surgical Anaesthesia**
4. **Overdose**
73
Which anaesthetic gives analgesia?
**Ketamine**
74
What are the main effects of anaesthetic agents?
* **Cardiovascular depression (vasodilation, lower CO, and lower BP) - not HR**
* **Respiratory depression (lower RR, TV, and MV)**
also: dose- dependent (SE's), only some provide analgesia- cannot reach higher centers of the brain (ketamine does though), patients cannot feel pain but **still have nocioception**, **some of the drugs are lipophilic and will hide in fat**
75
Administration of Anaesthetic Agents
* **mostly IV**
* some may be IM - do not use injectable IM if the animal has poor perfusion! - does not reach the BBB quick enough
* some are **inhalational**
**\*\*uptake may be affected by the route of administration and there may be delay getting across the BBB**
Distribution into the tissues may be affected by disease as wel (depends on BF)
76
What is **propofol** and how is it administered?
(2-4mg/kg in pre-medded animals)
* Phenol - soya oil, egg, lecithin, placed in white emulsion --\> **contains lipid**
* **Must be given IV** - may not be good for aggressive animals! so lipophilic that if given IM, will not reach appropriate concentrations
* can be used for **induction and maintenance**
* Rapid onset and metabolism - cats cannot glucoronoconjugate well! - **they will go onto oxidation (Heinz body production and oxidative injury if used repeatedly) and therefore metabolize this drug slower** --\> slower recovery than dogs
* will get metabolized on guts, lungs, skin and kidney (extra - hepatic)
* **CV and resp depression** -if you induce fast, will get some degree of apnea or CVS reduction - especially since an alpha-2 that may have already been given can cause bradycardia --\> leading to slower onset due to slowed circulation
* can use for patients with liver issues or that cannot metabolize well due to extra-hepatic metabolization --\> **also good for C-sections because of this!! - immature livers**
* "propofol twitches"
77
What is a side effect of propofol and how do you counteract it?
* **"Propofol twitches"**
* Tremors
* Give **ketamine or alfaxolone**
* can give Benzodiazapine as a muscle relaxant as well
* Give propofol slowly
* **happens to 15-20 % of patients and is a recurring phenomena**
78
Anaesthetic agent ok for induction in cats, but not for CRI
* **propofol**
* they metabolize it much slower than dogs! - they have issues metabolizing the triglycerides due to **LPL deficiency -** Lipoprotein lipase plays a critical role in breaking down fat in the form of triglycerides, which are carried from various organs to the blood by molecules called lipoproteins
* need to alternate agents in cats (could have Heinz bodies and oxidative damage after 3-5 days of repeated anaesthesia with propofol) --\> **alternate with ketamine**
79
When would you use propofol without a preservative or use a different agent?
* If suspect a prolonged anaesthetic
* **Propofol Plus is only licensed for induction!! - not good for CRI use over 30 min (mainly in cats)**
* for CRI need to use regular propofol
80
Propofol Plus
**contains benzyl alcohol to increase shelf-life! (28 days)**
* no pain on injection like Propoclear product
* does not need to be stored in fridge + little extravasation rxn
* **BUT,** cats struggle with it (prolonged recovery and hyperkinesia), neuro signs in dogs, **fatalities in both**
* **seems to be OK to use in dogs!**
* **lethal dosage dog:** admin per hour for **9 hours**
* **lethal dosage cat:** admin per hour for **6.5 hours**
81
What is alfaxalone?
## Footnote
**(2-5 mg/kg)**
**2 if given premed, 5 if not**
* anaesthetic agent
**Steroid** - can be used for both induction and maintenance
* Licensed IV in UK
* can be given IM (not licensed in the UK)
* Added solubilising agent - poorly soluble in water so margeted with solubilizing agent (cyclodextrin)
* Rapid onset and metabolism, short duration of action (excitement on recovery if not properly sedated)
* Excitement on recovery if not sedated
* **LESS CARDIOPULMONARY DEPRESSION THAN PROPOFOL** - good for cats with HCM!
* can be a nice sedation induction when given with other agents
* **Drug is CLEAR - do not confuse** (except now ketamine is color coded)
82
What is ketamine?
* Dissociative anaesthetic
* **Analgesic -** at sub- anaesthetic doses (binds NMDA receptors)
- NMDA receptor antagonists are a class of anesthetics that work to antagonize, or inhibit the action of, the N-Methyl-D-aspartate receptor (NMDAR). They are used as anesthetics for animals and humans; the state of anesthesia they induce is referred to as dissociative anesthesia
* **IM or IV** (only IM is licensed for dogs)
* Used for both induction and maintenance (only licensed in cats) - not greattt though as induction/maintenance agent
* Combine with sedative to avoid excitation and rigidity - **ALWAYS combine with other sedative** (ex: horses, give alpha 2 agonist prior to ketamine)
83
What is the triple combination for aggressive dogs and cats?
* IM injection
* Ketamine, medetomidine, opioid
* 3-5mg/kg
can make it a quad by adding **midazolam**
**AGGRESSIVE CATS AND DOGS-** short duration procedures
84
What do you need to remember when giving ketamine to horses?
* Only after profound sedation with a2 agonist
* Give with benzodiazepine to counteract ridigity
85
Why is placing an ET tube difficult with ketamine?
* one of the disadvantages with ketamine is that they retain a **gag reflex -** may need propofol with inhalation maintenance
* Cranial reflexes preserved
* Stimulates Sympathetic NS - mild hypertension/tachycardia, mild respiratory depression
* React to intubation, blinking and swallowing
* makes cats REAL DIFFICULT if using for induction
* as a baby vet - best to go with **propofol**
86
When is the use of **Ketamine** contraindicated in patients?
* animals with **cardiomyopathies!**
* **stimulation of sympathetic NS -** these patients will already have a high HR and Low Ventricular filling
* mild increase in BP and tachycardia
* **DIRECT MYOCARDIAL DEPRESSION**
* **mild respiratory depression**
87
Why is thiopentone/thiopental not used?
* No longer licensed
* Irritant extravascularly - extremely alkaline pH (10-14). Severe skin damage if you miss the vein
* USED to be a common induction agent
* **VERY lipophilic** --\> gets stored in the animal, makes them drowsy for long periods of time (repetitively drowsy) - especially if used for repetitive doses, not jsut loading
* **cumulative in the body fat**
* **slow recovery**
* **CVS depression** similar to that of propofol
88
When is thiopental/Thiopentone occassionally used??
* **Horses**
* **"top-up" during maintenance**
* **top up during anaesthesia**
* rapid onset, slower recovery
89
When is etomidate used?
* ECC patients -**emergency care**
* **Con**: **Depresses cortisol production** (by depressing adrenal gland fxn) - **be aware of Cushings Patients**
* Minimal CV and resp depression - **good for sick/compromised patients** (ex: pacemaker sx)
* Unlicensed (human drug)
90
What is a good combination injectable anesthetic for sick/compromised patients?
* Opioid and benzodiazepine
* Etomidate
91
Fentanyl/midazolam combo
* **opioid/benzodiazepine**
* **Not technically an anaesthetic -** not unconscious, animal must be v cooperative
* deep analgesia, no nociception and hence, no pain
* then benzodiazepine provides **retractive amnesia**
* **Sick and compromised patients!**
* high degree of mucle relaxation, not rendering animal unconscious
* not an issue intubating really, but they DO swallow!
* **good for GDV dogs and septic patients**
* **LESS EFFECT ON CVS SYSTEM THAN ANY OF THE OTHERS**
92
When is inhalational anaesthetic used?
(3)
* **Last resort in aggressive animals** - as the delivery of this inhalation agent can be very stressful for a patient
* **Small exotics when vein cannot be found**
* **Sevoflurane** preferred as _less irritant to nasal passages_, Iso irritation can lead to breath-holding
\*Sevoflurane and Isoflurane delivered in Oxygen (O2 first at very high flow)
93
Why is endotracheal intubation recommended?
* Deliver oxygen
* Deliver inhalational anaesthetic if required
* Protects airway from occlusion or aspiration
* Allows IPPV if needed - if resp. depressed
94
cons of Inhalation induction
* exposure of personel/pollution
* may see stress or excitement during induction (phase II which you generally bypass with IV injection)
* Isoflurane is more irritant to resp passages - **dogs absolutely hate it**
95
path of inhalation agent
**vaporizer --\> anaesthetic system --\> alveoli --\> blood --\> BRAIN**
need to create a good pressure from vaporizer to brain
-high partial pressure in lungs = high partial pressure in brain
* agents which are very soluble in blood have lower partial pressure in lungs, lower PP in brain
* **Speed of induction is SLOWER with more SOLUBLE agents**
96
**Blood: Gas Partition** coefficient
* #of parts gas in blood vs. alveolus
* **High no. -** agent v soluble in blood, takes longer to cross the BBB (e.g. **Halothane = 2.4 - v. high)**
* **Indicates length of induction and recovery (high number = longest)**
* Desflurane - .42
* NO - .47
* **Sevoflurane - .6 (quicker induction and recovery than iso)**
* **Isoflurane - 1.4**
* Halothane - 2.4
97
Making % solutions
* **1% sol'n** --\> 1000mg in 100cc or **10 mg/cc**
* **2.5 % sol'n = 25mg/ml**
* ex: bottle contains 2.5g (2500mg) --\> to make 2.5% sol'n (25mg/ml)
* you therefore need to add **100 ml** of water
* **_you want a 10mg/kg dose available for a 25kg dog?_**
* 25kg (dog BW) x 10mg/kg = 250 mg needed ready
* 2.5% sol'n strength **(25 mg/ml)**
* **10 ml dose!**
98
Inhalation Agents
(speed of induction agents - 5 in order )
Fastest to slowest
1. Desflurane - **most insoluble in blood**
2. NO - quite insoluble, once you stop induction, wants to leave through the lungs (alveoli) - therefore must give O2 when coming out of GA as the NO is taking room up in the lungs --\>**Avoid diffusion hypoxia**
3. Sevoflurane
4. Isoflurane
5. Halothane **- most soluble in blood**
99
Inhalation Agents and CVS/resp effects
* **iso causes more myocardial depression** than sevoflurane - affect contractility
* iso and sevo have similar effects on vasculature --\> **both SVR and result in vasodilation**
* neither sensitizes the heart to catecholamines (adrenaline/epinephrine)
* **both cause respiratory depression - but especially ISOFLURANE -** respiration is better maintained with sevoflurane
* for all inhalation agents --\> **potent dose-dependent cardiovascular depression --\> reduced BP**
100
When can you intubate an animal?
* Suffieicent depth of anaethesia
* Eyes rotated ventrally
* Minimal, suggish palpebral reflex - **last one to be lost**
* Loose jaw tone - **very imp!!**
* No swallowing reflex on stimulation
* Pull tungue out, laryngoscope on tongue
* Don't touch epiglottis or larynx - can be reactive esp cats
* Visualise laryngeal opening
* (Local anaesthesia spray) - in cats spray LA to reduce laryngospasm (lidocaine spray) - **EASY TO OVERDOSE - LA toxicity**
* (Lubrication - if ET tube small fit)
101
102
aim for MAC
1.25-1.5 x MAC is goal for clinical anaesthesia (depends on previous sedation given so administered (generally at 1 or less))
**to achieve 95% of the population for clinical anaesthesia**
**MAC gives us the info on potency of different inhalation agents**
**\*\* can be thought of as the dose required of an inhalation agent**
potency is inversely proportional to MAC
**isoflurane is more _potent_ than sevoflurane**
**smaller animals--\> higher metabolism --\> higher MAC**
103
MAC for Isoflurane
* 1.3 % (in dogs)
* 1.6 % (in cats)
104
MAC for Sevoflurane
2. 3 % in the dog
2. 6 % in cats
105
* **Endobronchial intubation**
* Only intubating half of the lung
* Hypoxia
* Reduced anaesthetic agent delivery to the patient
* Can be desired effect (rarely)
* likely due to the ET tube being too long (should be nose to shoulder- connector tube a t level of the nose)
106
* Pressure on walls of trachea
* Increased risk of tracheal rupture
* E.g. overinflation of cuff, or moving animal without disconnecting ET tube
107
Describe intubation in cats
* Spray layrnx with local aeansthetic to desnsitise and reduce laryngospasm during intubation
* Lidocaine spray
* Care: easy to overdose - local anaesthetic toxicity - e.g. kitten, may use drop of normal lidocaine rather than spray
* Alternative options e.g. **Laryngeal mask (Vgel)** - tube that sits on top of oesophagus (pushing down the epiglottis), gas directed down trachea, so tube in **trachea avoids issues with damage and not reducing diameter of trachea**
* **CONS to VGel:** not very air tight and if the fit isn't good, epiglottis can move --\> partial airway obstruction
108
How can we maintain anaesthesia?
* **Inhalational**
* **IV: TIVA (Total IV anaesthesia)**
Intermittent boluses
Continuous rate infusion (CRI)
* **Combination of injectable and inhalational: "Balanced" technique - PIVA (partial IV anaesthesia)**
Injectable anaesthetic agent/analgesic drug
Occaisionally single IM injection sufficient - e.g. darting of wild or zoo animals
NOTE: **DO NOT FORGET ANALGESIA! most anaesthetics provide little analgesia (except ketamine)**
109
Graphically describe the plasma concentration of a intermitent or continuous dose of anaesthetic agent
* Intermittent boluses can be more stressful on the patient! benefit of CRI - plane of anaesthesia swings between toxic and subtherapeutic levels
* **CRI= constantly infused (MRI= minimum infusion rate) -** e.g. propofol, alfaxalone, ketamine
* Injectable agents for maintenance: Propofol (be wary with cats) , Alfaxalone, Ketamine (at low analgesic doses)
110
List injectable agents for maintenance and their use
* Propofol
* Alfaxalone
* Ketamine - not usually used alone
Analegesic doses with another agent - PIVA or part of TIVA
* Infusion pumps or syringe driver - easy to calculate and will automatically infuse over a period of time
* Can also do old-fashioned" counting drops
111
Comapre MAC values between common species
* MAC values often vary between different published studies
* MAC values tend to be be higher in birds
112
Metabolism of Inhalation Agents (%'s)
* **Isoflurane .2%**
* **Sevoflurane ~2%**
* Halothane 20%
* Desflurane 0.02%
113
If an animal has liver problems: which inhalation agent is safer to use?
## Footnote
**Sevoflurane or Isoflurane?**
**(the ones used in practice)**
* **Isoflurane!**
* 0.2 % metabolism
114
What is minimum alveolar concentration ***not*** affected by?
* gender
* length of anaesthesia
* blood pH
115
What is the mimum alveolar concentration affected by?
* Hypo/hyperthermia (hot --\> higher MAC)
* Age
V young: high
Old: low
* Severe anaemia - less RBC, less binding, more readily into tissues (Lower MAC)
* Severe hypotension - Lower MAC
* Hypoxia/Hypercapnia - will more readily take up O2 with agent (lower MAC)
* CNS depressant drugs
* Excitation
* Pregnancy (decreases)
* USe of opioids to provide analgesia during anaesthesia (decreases)
116
Compare the liver metabolism of different anaesthetic agents
Isofluane: 0.2%
Sevoflurane: 2%
(Halothan:20%)
Desflurane: 0.02%
**Lower = better for animals with liver dysfunction**
**Halothane --\> degree of hepatitis**
117
Describe the metabolism of Sevoflurane
* **Theoretically free fluoride ions released**
* Toxic to kidney - **Nephrotoxic**
* No problems reported clinically (experimental only)
* Compound A formed during rxn with hot and dry CO2 absober (esp Soda-lime)
* Nephrotoxic
* Newer absorbers prevent this rxn
* Low flow anaesthetisa potentiate these processes - can avoid this by increasing flow rate to high
* Recommended min fresh gas flow in humans 2L/min
118
Describe the use of nitrous oxide in anaesthesia
**MAC in animals ~200%** : cannot be used as sole anaesthetic agent (high MAC, low potency)
Mild analgesic properties-need to provide some background sedation and analgesia
* V insoluble in blood (low partition coefficient) , V fast onset
* Can speed onset of another agents (2nd gas effect) - less important now that insoluble agents are routinely used
* **"Diffusion hypoxia" at end of anaethetic** - diffuses rapidly out of blood into alveoli, displacing O2 in lungs - **give 100% O2 at this point for 15 min to avoid complication**
* Health risk with long-term exposure/pregnancy- **Vit b12 deficiency (important for the CNS) -** possible sensory neuropathy, myelopathy, encephalopathy
* **Atmostpheric pollution**: green house effect
* **mostly used to provide analgesia, until you have gone to get a more appropriate drug**
* Used to help carry halothane - help speed up induction
* Now it just provides extra sedation and analgesia
119
**when does anaesthetic mortality most often occur?**
(esp. in regards to healthy animals?)
* RECOVERY PERIOD
* **MUST MONITOR PATIENTS CLOSELY!**
* may need to extubate cats a bit earlier than when the swallowing reflex returns to prevent laryngospasm
* may extubate later if concerned about airway obstruction: Brachycephalics, vomiting risk, ruminants (prone to regurgitation) --\> have inflated cuff
120
3 types of pain
121
Pain Pathway
| (4 steps)
-free nerve endings will Will differentiate between different thresholds (hot/cold)
122
Transmission of pain via fibers
123
What type of fibers transmiss first pain?
(fast, sharp, well localized pain)
**myelinated (Aδ) fibres**
124
What type of fibers transmiss second and visceral pain?
(slow, dull , poorly localized pain)
**unmyelinated (C) fibres**
125
What is the term "inflammatory soup" refering to in the process of nociception?
* during transduction of a noxious stimulus, **peripheral sensitization** can result in hyperalgesia due to cytokines/GFs being released simultaneously
* **Hyperalgesia** is a condition where a person develops an increased sensitivity to pain
* due to massive amount of inlammatory mediators
* think they are always painful on a limb or something
* where as central is a much more generalized, all over continuous pain
126
When will central sensitization occur?
* Failure of interneurons/ascending neurons to modulate a noxious stimulus at the dorsal horn in the SC
* Central sensitization is a condition of the nervous system that is associated with the development and maintenance of chronic pain. When central sensitization occurs, the nervous system goes through a process called wind-up and gets regulated in a persistent state of high reactivity
* **Trigger:** repeated stimuli
* this is why we give **Pre-emptive analgesia!!**
* NO involved with NMDA receptors - NMDA receptors can lead to **hyperalgesia effects**
* bc you have frequent stimulation, the central NS perceives that as constant pain
* will have hypersensitivity in the neck area but not elsewhere
127
By which tract does a noxious stimulus travel from the spinal cord to the brain?
**Spinothalamic**
* The anterior and lateral spinothalamic tracts. The former helps localize crude touch and pressure, the latter painful or temperature sensation.
* The spinoreticular tract, which is responsible for increasing our level of arousal/alertness in response to the pain or temperature.
128
What is the fourth vital sign in your clinical exam?
* **pain assessment**
129
What are some of the more common type of drugs we use for **analgesia**?
* NSAIDs
* opioids
* alpha 2 agonists
* local anaesthesia
* ketamine
130
Hyperalgesia and Allodynia
* innocuous = not harmful or offensive (like touch)
* In allodynia - receptors are really fucked, the mechanoreceptors meant to relay touch now relay pain --\> hard to treat and continues to spread
131
Three Domains of Pain Assessment
* use glasgow scale or Colorado scale
132
Cost of effective pain management
* The cost of pain is more than cancer and cardiomyopathies with chronic pain (at international level)
* **Long term treatment!**
133
What type of analgesia is the gold standard for severe/moderate pain control?
* **OPIOIDS**
134
Multi-modal Analgesia
Want to use as many drugs as possible in the lowest amount possible
But want to aim to treat as many receptors as possible - Tranduction, inhibit transmission, perception
LA's, corticosteroids, NSAIDS
**Modulation of spinal pathway (big one) :** inhibit central sensitization
Animal under GA has nocioception, but still doesn't percieve it! - they still have all the problems that a painful stimuli would cause
The animal is still painful but they just cannot perceive it
135
What is the reversal drug of opioids?
**Naloxone**
136
Opioids
* **Some conditions require it**
* **delta, kappa, and mu**
* But it is almost always part of our pre med
* Receptors are in CNS but also in the GIT! And other places
* This is why you get effects on other systems
* Reptiles --\> kappa
* Epsilon is a receptor that we think is linked and we are trying to alter drugs to aim for that
* We are trying for other receptors as our opioids have pretty adverse SE's
* **opioids works for the C -fibers --\> dull pain**
**Opioids are not good for sharp pain!! - common misconception**
137
## Footnote
**What is the reversal drug of etorphine [Immobilon] (opiod used in wild LA sedation)?**
Diprenorphine [Revivon]
138
Pure mu Agonists
* **Morphine**
* **Pethidine - do not give IV! (His release)**
* **Methadone** - only thing that doesnt make the animal vomit - bc it is more lipid soluble (won't affect CRTZ)
* **Fentanyl -** potent respiratory depressant. very potent analgesic, fast onset and short half life
* Cats lack specific pathways for hepatic metabolism
* Morphine lasts so much longer in these cats
* Propofol is also not a great idea either
* CANNOT HAVE PARACETAMOL
* Pethidine is the only one that increases HR
139
Partial Mu agonist
| (Buprenorphine)
* Has a higher affinity for the receptors
* If you give a strong dose of opioid by accident, you can give buprenophine to antagonize it
140
What opiods are full u-agonists?
| (6)
* morphine
* methadone
* pethidine
* fentanyl
* etorphine
* papaveretum
141
Tramadol
* **Tramadol** is used in human medicine for the management of osteoarthritis pain and is gaining acceptance in veterinary medicine to treat mild to moderate pain in dogs and cats. In addition to its analgesic properties, tramadol may also have some mild anti-anxiety effects
* weak u-receptor agonist (opiod-like)
inhibitor of serotonin and noradrenaline reuptake
NMDA receptor antagonist
142
Opioid Effects
| (6)
* thermoregulation - some hyperthermia
* Respiratory depression (mu mediated effect in resp center) - use naloxone. **esp. if co-admin of a sedative**
* **Bradycardia -** vagal stimulation. responsiveness to anticholinergics, pethidine an exception
143
NSAIDs in Pain Management
| (and 4 SE's)
144
What is the mixed agonist/antagonist opiod that is typically used for its sedative effects since it is a **poor analgesic**?
**Butorphanol**
145
What is the opiod that is a **partial u-agonist** typically used in SA medicine?
**Buprenorphine**
146
In what species do opiods have the side effect of CNS depression (sedation)?
dogs, humans, monkeys
147
In what species can opiods cause dyphoria/euphoria (CNS stimulation)?
cats, horses, ruminants
148
In which species can opiods cause hyperthermia?
* horses and cats
149
What are some universal side effects of opiods?
nausea, vomiting, respiratory depression, bradycardia
150
Effects of NSAIDs
151
What receptors does ketamine act on?
NMDA
152
Ketamine and Analgesia
153
Paracetamol
Easy to find
Minimal side effect which is true --\> UNLESS IT IS A CAT
Useful as long as liver function is fine! - don't give to animal with decreased hepatic metabolism
Make sure your animal has no liver disability
154
Define Local Anaesthesia
* **Implies that the local anaesthetic is used as the only means of anaesthesia**
* e.g. a cow that has a standing caesarian section performed under local anaesthesia
* High risk patients (geriatric, etc.) - using local anesthesia often
155
Define Local Analgesia
To provide **extra analgesia as a supplement to general anaesthesia**.
Local analgesia can be used to provide **multi-modal analgesia**, in association with e.g. opioids and/or NSAIDs
-most the time animals are under GA for local technique
156
How can we achieve local analgesia?
* Local anaesthetic drugs (more LA)
* Opioids
* Alpha 2 agonists
157
What are the order that the sensations are lost?
1. Pain
2. Cold
3. Warmth
4. Touch
5. Deep pressure
158
How does chemical structure affect pharmacology?
* **Lipid solubility** determines potency - axonal membranes predominantly lipid
* **Protein binding** determines duration of action - bind to protein (sodium channels) within axonal membranes - Longer, very attached to proteins, longer action
* **pKa determines speed of onset** - must diffuse across the axon sheath in uncharged base form
* -need to consider the pH of body
Pka closer to body pH has a faster onset
But also depends on the concentration of the drug you give
* **These drugs block the AP as they act mainly on Na channels**
Concentration depends on area
Not always easy to block
Cocaine was first used for ophthalmic surgery
Work on the interior and exterior of the cell
Want the **unionized one to be acting as it passes through better**
159
Which nerve types are most sensitive to local anaesthetics?
* **B fibers** - sympathetic
* then **A-delta fibers** - sensory and pain
160
Least sensitive nerve types to Local Anaesthetic
**A- beta**
**A -alpha**
* motor and proprioceptive
* **sensitivity of C fibers (unmyelinated) overlaps -** they have dull pain but are not very specific
161
What is the LA you can use in FA?
**Procaine**
**only licensed drug in UK - for cattle only**
**Mepivacaine:** mainly used in horses. any can be used in horses as long as they are licensed and are on the positive list
162
Esters - LA
| (2 examples)
**Procaine and tetracaine**
* allergenic
* don't see used in SA often
163
Amides: LA
Amides: metabolised in liver by amidases, **allergic reactions rare**
e. g. **lidocaine, bupivacaine, ropivacaine**
* metabolized in the liver, protein bound, need to be careful with doses and the liver
164
What has been reported when giving **lidocaine** to horses?
**Skin and subcutaneous swelling**
165
Using systemic Adrenaline after Lidocaine Administration
Applied directly on the site of your action
If you use **lidocaine sometimes use adrenaline with it as it constricts the area and keeps the lidocaine in the region desired**
**adrenaline -** It is a vasoconstrictor so can reduce local blood flow and increase the duration of action (by decreasing the rate of systemic absorption)
-be careful where you do it! - ear for example - can block arteries and block blood supply --\> necrosis
166
Common Complications of Local Anaesthesia
* **Nerve damage**
Low incidence in human anaesthesia
No intraneural injection (would destroy the nerve, and also require a very high pressure so if you feel a high pressure it is best to restart!)
Most local anaesthetics are done blind so it is possible to touch the nerve, but if you do function is very likely to return
* **Systemic toxicity**
Easily avoided by giving the correct dose
Always draw back before the injection in order to check you are not injecting into a blood vessel
* **Local toxicity**
Very rare
It's hard to control but be careful and keep an eye out for signs of it!
CNS signs, neurological signs
167
What are the normal and toxic doses (mg/kg) of local anaesthesia?
## Footnote
**Lidocaine**
**Bupivacaine**
**Ropivacaine**
**Normal:**
* 5
* 2 (never give more than 2, it is the most cardiotoxic)
* 1.5
**Toxic:**
* 10 - 20
* 3.5 - 4.5
* 1.5 - 5.0
168
Does cardiovascular toxicity occur at a higher or lower blood concentation than CNS toxicity with reference to local anaesthesia?
* **HIGHER**
* Cardiovascular Toxicity worse with Bupivicaine
* Don't want to block Na channels of the heart! - be aware!
1. **CNS toxicity**
2. **CVS toxicity**
3. **CV arrest**
169
Describe methaemoglobinaemia
* **Fe2+ in haemoglobin oxidised to Fe3+**
* Cannot bind and carry O2
* Results in cyanosis
* Especially **prilocaine (EMLA cream)- eutectic Mixture of LA's** - need to give time to work and also cover it
* Also benzocaine, lidocaine, procaine
* **take extreme care with lidocaine for cats and intubation!**
170
**What are the routes of administration of local anaesthesia?**
**(6)**
* Topical
* Regional
* Spinal or epidural
* Intra-articular (in the joint)
* IVRA - intravenous regional anaesthesia
* Systemic
171
What is the main problem with topical local anaesthesia for the eye?
* **Can slow corneal healing**
* If you have a corneal ulcer, LA there will decrease the healing so be aware!
1. Proparacaine
2. Tetracaine
172
**What eye drops can you use for local anaesthesia?**
* Proparacaine (proxymetacaine)
* Tetracaine (amethocaine)
173
Most potent local anaesthetic? (Lowest lipid solubility?)
* Procaine
* **0.5**
174
Least Potent Local Anaesthetic? (highest lipid solubility?)
* Tetracaine (can be used for eye)
* **80**
175
LA: Fastest onset in the body? (pka)
Slowest onset?
* Fastest (closest to pH of body): **Mepivacaine** (used in horses) - **7.6**
* Slowest: **Procaine - 8.9**
* Intermediate**: tetracaine - 8.6**
176
LA: longest duration in the body? **- protein binding %**
shortest?
**longest-** Bupivicaine - 95%
**Shortest-** Procaine - 6%
177
What is EMLA cream?
* **Eutectic Mixture of Local Anaesthetics**
* ***Lidocaine and prilocaine***
* Used for venous catheterisation
* Absorbed across intact skin
* Apply 30 minutes before
178
What is infiltrative anaesthesia?
* Lidocaine with or without adrenaline
* Lowest possible concentration
* 2-5mg/kg total dose
* Fine sharp needles
* Do not use adrenaline in tissues supplied by end arteries (ears, tails)
179
What are the problems with paravertebral anaesthesia?
* Fat animals
* Muscle spasm
* Damage to aorta
* Infection
180
Field Blocks
* **line blocks**
* **Inverted L block**
* **Skin, subcut, muscle**
* **Along incision or remote** - blocking supply to incision
181
Epidural Analgesia
* **Touch back of L7**
* **Drugs used:** Local Anaesthetics, Opioids, Alpha-2 agonists, ketamine, NSAIDs
182
Epidurals: Small v. Large animals
183
What is the only Local Anaesthetic you can use for a **IVRA?**
## Footnote
**(Biehrs Block)**
* **LIDOCAINE ONLY**
* do not use bupivicanine or ropivacaine unless you want to kill your patient
* also don't leave tornequet on longer than 2 hrs due to possible ischemia
184
Systemic Local Anaesthetics: Lidocaine
**Can be used IV! - can use systemically**
185
What procedures in farm animals requires general anaethesia?
* Umbilical hernia repair
* Urethrostomy
* Orthopaedia (not all)
* Enucleation (depends on species)
* Median laparotomy
* De-horning (adult)
186
Tabe 1 drugs licensed for use in all FA's
* **ketamine**
* **thaimylal**
* **thiopental** (not licensed in the UK atm)
if you go off license - the withdrawal period needs to be longer!
no positive inotropes in table 1 for use in FPAs- **be careful of hypotension under GA**
187
What proceudres in farm animals are done standing/ with sedation and local anaetshetic?
* Flank laparotomy
* C-section
* RDA or LDA
* Rumenotomy
* De-claw
* De-horning (young animals)
* Teat surgery
* Castration
188
Table 2 drugs
**SHOULD NOT BE GIVEN TO FPA's under ANY CIRCUMSTANCE**
- no anaesthetics included
- only **NSAIDS and azaperone** (tranq) have **Maximum Residue Limits** - -need to check the leaflet for withdrawal time to when the meat can be consumed
189
What causes regurgitation in the anaetshetised ruminant? Why is it so dangerous?
**Causes aspiration pneumonia**
Active regurgitation/ rumination- light plane of anaesthesia (commonly at intubation)
Passive regurgitation- during deep anaesthesia (cardia relaxation)
190
**What can you do to minimise regurgitation in an anaesthetised ruminant?**
* Reduce rumen fill- starve 18-24 hours (only in animals \>3months)
* Reduce rumen water- remove water for 12h (only in animals \>3months)
* Reduce fermentable amterial in the rumen BUT dehyrdration and starvation for 24h- **risk of ketoacidosis** (may do more harm than help)
* Ensure good depth of anaethesia when intubating
* Good fitting ET tube and immediate cuff inflation
* Postition of head- allow fluids to drain from the mouth
* Stomach tube/Orogastric tube - prevent aspiration or regurg by releasing fluid content of the rumen
191
## Footnote
**What is the physiological use for salivation in the ruminant? How can it cause problems during anaesthesia?**
Under GA they tend to just swallow the saliva
Can be aspirated when intubated - can provoke inflammation (need suction available) - won't cause as much irritation as stomach contents
Atropine - makes the saliva more mucus filled and thick (not recommended to give routinely anymore)
**saliva= Buffer for rumen function**
Large volume produced (50l daily in the cow)
Can cause electrolyte imbalances and aspiration at intubation
192
What causes rumen bloat/tympany and rumen atony? What are their potential effects during anaesthesia?
* Fermentation produces large volumes of gas
* **No eructation when anaesthetised**- position of animal and fluid in the way
* Reduces function residual capacity (FRC)
* Reduced venous return
* Continued fermentation can lead to pH shift and atony
Fermentation continues when under GA but they cannot eructate when under GA - gases cannot evacuate --\> the size of bloat will have effect on the amount the lungs can fill (impact gas exchange and ventilation)
193
What can you do to prevent rumen bloat during anaesthesia?
(2)
Adequete startvation and water withholding time
Placement of a rumen tube or trochar to evacuate gas
194
What support is required for rumiants in hypotension during anaetshesia?
Crystalloid IV fluids, cannot give colloids (prohibited for use in farm animals)
**hypertension as a result of GA is more common in ruminants-** may be a result of high CO2?
* Even if the patients are ventilated with IPPV - they high arterial blood pressure remains high
195
What has a greater risk in ruminant anaesthesia than in anaetshsia of other species?
* IPPV
Less fibrous connective tissue in ruminant lungs- increased risk of airway damage if IPPV pressure too high
scan have V/Q mismatch - not as bad as horses though
196
What are potential causes of hypoxaemia and hypoventillation in the anaesthetised ruminant?
* **Drug induced respiratory depression**
* **Chemoreceptor depression**
* **Large rumen (and any bloat) leads to:**
small tidal volume
increased rate
reduction in FRC
V/Q mismatch - not as bad as horses, but still
decreased venous return
decreased cardiac output -especially when applying IPPV
197
What can you do to reduce the risk of neuropathies in the anaesthetised ruminant?
Adequete positioning, padding, ABP, oxygenation and perfusion
198
What sedatives (pre-meds) are used in ruminants?
*Alpha 2 agonists*
sedation, anxiolysis, recumbency, analgesia, muscle relaxation
sheep and goats very sensitive
* **Xylazine**- cattle 0.05-0.3mg/kg IM, 0.03-0.1 mg/kg IV. shep and goats 0.05-0.1mg'kg IM, \<0.05mg/kg IV
* **Detomidine**- cattle 0.01-0.04mg/kg IV
* **much more sensitive to xylazine than horses, but about the same on detomidine**
199
What are potential side effects of alpha 2 agonists in ruminants?
* Xylazine can cause pulmonary oedema in sheep and goats by causing bronchocontriciton
* Reduces eructation- leads to tympany
* Reduces swallowing- saliva in oropharynx
* Copious urine production
* Oxytocin like effect- uterine contraction
200
What drugs are used in induction of anaestheia in ruminants?
(legal options)
* **Ketamine 2-5mg/kg**
dissociative anaestheitc- **IV or IM**
excellent analgesic
muscle rigidity
laryngeal reflexes remain
* **Thiopentone 7.5-15mg/kg**
very fast acting
no veterinary licensed product available in UK
**very irritant so must go IV**, **extravasation causes necrosis**
accumulation leads to prolonged recoveries
not in thin/debilitated animals
**\*\*benzodiazepines are NOT LICENSED FOR USE IN FPA-** can induce animal essentially but nothing given for the muscle rigidity
201
What licenced NSAIDs (cattle only) can be used for analgesia?
* Meloxicam
* Flunixin
* Ketoprofen (no milk withdrawal, 1-4d meat withdrawal)
* Carprofen (no milk withdrawal, 21d meat withdrawal)
* Tolfenamic acid
* Metamizol
* If not indicated these have milk and meat withdrawal periods
202
What opioid is licenced in the horse if it is **off of the food chain? or is a FP animal?**
* **Butorphanol**
203
What local anaetshetics are licenced in food producing animals?
* **Procaine 5-10mg/kg toxic dose - careful, can get close to toxic dose**
* Lidocaine 4-10mg/kg toxic dose -under the cascade only --\> **but tend to use lidocaine as it is the least cardiotoxic**
204
Inhalation Agents used in Ruminants
**Isoflurane -** under the cascade
smaller ruminants can be masked down
* **esp. if you want to avoid the use of alpha-2's for SE's**
205
Ruminants - LA blocks
206
What aspects of camelids' anatomy/physiology makes them ruminant like?
* 3 compartment stomach/ruminate
* Prone to bloat/regurgitation/salivation
* Projectile regurgitation can be seen
* Lingual torus obstructs view during intubation
207
What aspects of camelids' anatomy/physiology makes them horse like?
* Often placid but can be temperamental
* Obligate nasal breathers
* More prone to resp obstruction
* Can develop stomach ulcers with stress - consider prophylaxis
208
What issues come with anaesthatising camelids?
* Catheter placement problematic
* Intubation - larynx relatively far back
* need to protect eyes from ulceration
209
What drugs can be used for sedation, induction and maintenance in camelids?
_Similar to ruminants BUT some **non-FPAdrugs**:_
* **_Sedation_**
Xylazine
***Benzodiazepines***
* **_Induction_**
Ketamine
***Propofol***
* **_Maintenance_**
Isoflurane (se in small ruminants -under cascade)
***Sevoflurane***
210
What drugs can be used for analgesia in camelids?
Similar to ruminants but **some non-FPA**
* NSAIDs - flunixin
* Opioids
Butorphanol (licensed for horses as FA)
***Pethidine***
***Morphine***
***Methadone***
* Nerve blocks or epidural
211
What are pigs quite prone to with anaesthesia
**Malignant Hyperthermia (MH)**
* **Genetics - autosomal dominant gene**
Hypermetabolic syndrome
* **No control over Ca2+ efflux from sarcoplasmic reticulum**
Muscle contraction and heat production
* **Trigger factors: (should all be avoided)**
**Stress**
**Inhalant agents**
Caffeine
Suxamethonium
**CS's:** Muscle rigidity, Hot and pink/red skin, tachypnoea/tachycardia, high core T, high EtCO2
212
What drugs can be used for sedation in pigs?
* **Azaperone (tranq) 1-8mg/kg deep IM**
Cheap effective
Need to wait 20 minutes minimum
can cause penile prolapse in boars
* **Alpha-2s under the cascade (dose much higher, less potent)**
May cause vomiting
With ketamine/butorphanol for sedation/field anaesthesia -can provide short filed of anaesthesia
213
What drug can be used to induce pigs?
**Ketamine**
214
What drug can be used for pig maintenance?
* **Isoflurane (under the cascade)**
215
What analgesic drugs can be used in pigs?
* Butorphanol under the cascade
* Flunixine
* Ketoprofen
* Meloxicam
* Lidocaine under the cascade
216
What is the treatment for Malignant Hyperthermia?
* **Remove trigger**
New breathing circuit - iso gets absorbed in the tube
Ideally non rebreathing
* **Active cooling (water, ice)**
* **IV fluids to minimise renal insult (myoglobinuria from muscle damage)**
* **Ventilate to reduce CO2**
* **Bicarbonate to reduce acidodis**
* **Monitor K+ = hyperkalaemia from damaged muscle**
217
How should farm animals be monitored during anaesthesia?
* **Ruminant** - eyes roll down with deepening anaesthesia, rotate back to central when deep
* **Alpacas** - may still retain a blink reflex, chewing/swallowing
* **Pigs** - may retain laryngeal reflex until deep plane
* Use all normal monitoring equipment
