ANAESTHESIA - Standing Sedation and Equine Anaesthesia Flashcards
(154 cards)
1
Q
What can be done as an alternative to general anaesthesia in horses for particular procedures?
A
Standing sedation
2
Q
Where should you carry out a standing sedation in a horse?
A
Carry out the sedation in a quiet room and avoid stimulations such as light, noise and other horses. It can also be useful to put a blinder on the horse and swabs in their ears once they are sedated to reduce stimulation
3
Q
Why are equine standing sedations commonly converted to general anaesthesia?
A
Equine standing sedations often result in the sedation not working or there being oversedation and recumbency, both of which require conversion to general anaesthesia
4
Q
How should you prepare for the possibility of converting a standing sedation to general anaesthesia?
A
Have induction drugs at hand and doses already calculated
Move the horse to an appropriate area for recovery
5
Q
Which phenothiazine is licensed as a sedative in horses?
A
Acepromazine
6
Q
What is the clinical use of acepromazine in equids?
A
Acepromazine provides light sedation with no analgesia and thus tends not to be a sufficient sedative in horses when used on it’s own. However, it can be very useful to reduce the excitatory and locomotor effects of opioids as well as reduce α2 agonist doses required
7
Q
Which α2 agonists are licensed as sedatives in horses?
A
Xylazine
Detomidine
Romifidine
8
Q
What are the routes of administration for xylazine in horses?
A
Intravenous (IV) (has to be done under the cascade)
Intramuscular (IM)
9
Q
What are the routes of administration for detomidine in horses?
A
Intravenous (IV)
Intramuscular (IM)
Oral transmucosal gel (Dormosedan)
10
Q
What are the routes of administration for romifidine in horses?
A
Intravenous (IV)
Intramuscular (IM)
11
Q
Why is romifidine the best α2 agonist for procedures on the horse’s head?
A
Romifidine has the least muscle relaxing properties resulting in reduced ataxia which is ideal for head procedures
However not all practices have romifidine so detomidine is also a good choice
12
Q
Which α2 agonist provides the most reliable sedation in horses?
A
Detomidine
13
Q
Which opioid is commonly used in combination with α2 agonists in horses?
A
Butorphanol
14
Q
Why is butorphanol commonly used in combination with α2 agonists in horses?
A
Butorphanol has a potent synergistic effect on α2 agonists
15
Q
When would you not want to use butorphanol in horses?
A
Butorphanol can cause head shaking and twitching so is not ideal for head procedures
16
Q
Why should you be cautious when administering opioids to healthy horses?
A
Opioids cause increased excitability and locomotion in healthy horses
17
Q
Why are general anaesthetics particularly challenging in horses?
A
General anaesthetics can be challenging due to a horse’s fight or flight response. They tend to react before they think which can result in dangerous situations for both the handlers and the horse itself, especially when they are recovering from anaesthesia
18
Q
What information should you gather when taking a history prior to equine anaesthesia?
A
Signalement
Passport
Medical history
Information about previous anaesthetics and how the patient responded
Time of last meal
Any allergies/intolerances
19
Q
What is the maximum amount of time in which you should carry out field anaesthesia in horses?
A
You should carry out field anaesthesia for no more than 90 minutes
20
Q
What should you do if you anticipate equine field anaesthesia to take longer than 60 - 90 minutes?
A
Consider moving the horse to an equine hospital for anaesthesia
21
Q
Why is it not always necessary to fast a horse prior to anaesthesia?
A
Horses do not vomit so the risk of aspiration is not considered a primary risk when undergoing anaesthesia. Allowing the horse to eat prior to undergoing anaesthesia maintains normal gut motility which can decrease the risk of post-operative colic
22
Q
When should you never fast a horse prior to anaesthesia?
A
You should never fast a suckling foal prior to anaesthesia
23
Q
What should you carry out to prepare for equine field anaesthesia?
A
Get a patient weight
Establish intravascular access
Wash out the mouth with water
24
Q
Which three methods can you use to obtain a horse’s weight?
A
Weighing scales
Measuring band
Calculate using a formula
25
What is the formula that can be used to calculate a horse's weight?
Body weight (kg) = (Girth (cm2) x Length (cm)) / 11,877
26
Why should you wash out a horse's mouth prior to anaesthesia?
This is done to prevent the endotracheal tube carrying food material into the trachea and lungs
27
What is the standard premedication combination for horses?
α2 agonist and Butorphanol
28
Which two analgesia techniques are good to use in combination in horses?
Systemic analgesia
Locoregional analgesia
29
Which drug classification do you use for locoregional anaesthesia?
Local anaesthetics
30
Which three local anaesthetics are licensed in horses?
Lidocaine
Bupivacaine
Mepivacaine
31
What is the standard anaethesia induction protocol for horses?
Ketamine and Benzodiazepine
32
Which benzodiazepine is licensed in horses?
Midazolam
33
Which induction protocol would you use for short procedures (less than 20 minutes)?
Standard protocol
34
Which induction protocols are recommended for intermediate procedures (20 to 40 minutes)?
Standard protocol
Triple drip induction
35
What induction protocol is recommended for longer procedures (30 to 90 minutes)?
Triple drip induction
36
Which three drugs are used for triple drip induction?
α2 agonist *(usually the same one that you used for the premedication)*
Ketamine
Guaifenesin (GGE)
37
What is the purpose of guaifenesin (GGE) in the triple drip?
Guaifenesin is a muscle relaxant which counteracts the hypertonicity caused by ketamine
38
Why should guaifenesin (GGE) only be administered IV?
Guaifenesin (GGE) should only be administered IV as it is a perivascular irritant and can cause tissue necrosis
39
Why should Guaifenesin (GGE) only be infused at a concentration of less than 10% in horses?
Guaifenesin can cause thrombophlebitis in horses
40
What are the main advantages of a triple drip?
Easy
Increases cardiovascular and respiratory function
41
What are the two main disadvantages of a triple drip?
Can only be used for up to 90 minutes
Horse will appear light due to dissociative anaesthetic affect of ketamine
42
Why can you only use a triple drip for up to 90 minutes?
Due to the risk of drug accumulation and a prolonged and more ataxic recovery
43
How is anaesthesia maintained in equine field anaesthesia?
Total Intravenous Anaesthesia (TIVA)
44
What are the two advantages of intubating horses for field anaesthesia?
- Allows for airway maintenance and protection
- Intermittent positive pressure ventilation (IPPV) is possible if you have a large animal ventilator available
45
What are the two disadvantages of intubating horses for field anaesthesia?
- Large animal endotracheal tubes are expensive
- May not have a large animal ventilator available for intermittent positive pressure ventilation (IPPV)
46
According to veterinary evidence, identify nine risk factors that can increase anaesthetic risk in horses
Patient ASA grade
Procedural urgency
Major procedures
Duration of procedure
Patient signalement (age, breed, body weight/conditon)
Concurrent disease
Patient temperament
Inadequate pain management
Level of monitoring and degree of intervention by anaesthetist
47
Which two horse breeds are susceptible to more difficult anaesthetic recoveries?
Thoroughbreds
Arabian
48
How does inadequate pain management increase anaesthetic risk in horses?
Horses are flight animals and pain will result in an increased stress and flight response during the recovery period which increases their risk of post-operative injury
49
What are the three classifications of complications associated with equine inhalant anaesthesia?
Intra-operative complications
Post-operative (recovery) complications
Post-recovery complications
50
What are the three main organs systems affected by inhalant anaesthetic agents in equids?
Cardiovascular system
Respiratory system
Neuromusculoskeletal system
51
How should you assess a horse for cardiac arrhythmias prior to an anaesthetic?
Carry out a thorough auscultation on both sides of the heart. If you hear anything abnormal, use an ECG for further investigation
52
How can you tell the difference between physiological and pathological murmurs in horses?
Physiological murmurs tend to be low grade and localised over the base of the heart, whereas pathological murmurs and usually louder towards the apex of the heart
53
How do you determine if the second degree atrioventricular (AV) heart block is physiological or pathological in a horse?
The arrhythmia should stop during exercise, if the arrhythmia continues, this suggests that it is a pathological rather than physiological arrhythmia and an ECG should be carried out
54
When would a racehorse be classified as tachycardic at rest?
A racehorse would be classified as tachycardic with a heartbeat above **40bpm**
55
When would a small pony be classified as tachycardic at rest?
A small pony would be classified as tachycardic with a heartbeat above **60bpm**
56
How does tachycardia affect cardiac output?
Tachycardiac decreases cardiac output as the increased heart rate doesn't allow for sufficient ventricular filling, resulting in decreased stroke volume and cardiac output
57
What are the potential causes of tachycardia?
Hypotension
Hypoxaemia
Pain/nociception
Drug induced
58
When would a racehorse be classified as bradycardic?
A racehorse would be classified as bradycardic with a heartbeat below **28bpm**
59
When would a small pony be classified as bradycardic?
A small pony would be classified as bradycardic with a heartbeat below **30-35bpm**
60
What are the potential causes of bradycardia?
Hypertension
Hypoxaemia
Drug induced
61
Why is bradycardia particularly concerning in horses under anaesthesia?
Bradycardia is a precursor to asystole in horses
62
(T/F) CPR is almost always successful in treating cardiopulmonary arrest in horses
FALSE. CPR is very rarely successful in horses
63
How do inhalant anaesthetic agents cause hypotension in horses?
Anaesthetic agents decrease cardiac contractility, decrease heart rate and decrease systemic vascular resistance *(most significant change)*, all of which contribute to hypotension
64
What is the ideal mean arterial pressure (MAP) for horses?
Between 70 - 90mmHg
65
At what mean arterial pressure (MAP) will you begin to be concerned about muscle hypoperfusion in horses?
Mean arterial pressure (MAP) of less than 70mmHG
66
At what mean arterial pressure (MAP) will you begin to be concerned about organ hypoperfusion in horses?
Mean arterial pressure (MAP) of less than 60mmHG
67
What are the consequenses of hypotension in horses?
Hypotension results in reduced organ and tissue perfusion, conversion to anaerobic metabolism which results in hyperlacteraemia and an increased risk of post-anaesthetic myopathy
68
What is the preferred method for monitoring blood pressure during equine anaesthesia?
Direct blood pressure monitoring by placing an arterial catheter and connecting the catheter to a pressure transducer
69
Which arteries are used for direct monitoring of arterial blood pressure in horses?
Facial artery *(most common)*
Metatarsal artery
| The metatarsal isn't used very commonly due to the risk of sequestra
70
Why is it important not to insert an arterial catheter in the region of the facial artery near the eye?
The area needs to be surgically prepped to place an arterial catheter and the surgical sterilisation solutions can cause irritation and damage to the eye
71
What are the advantages of direct arterial blood pressure monitoring?
Allows for continuous, accurate blood pressure monitoring
Permits arterial blood sampling for blood gas analysis
72
What are the three main risks of direct arterial blood pressure monitoring?
Haemorrhage
Infection
Damage to the periosteum and risk of sequestra
73
Interpret this arterial pressure waveform
74
What is represented by the ascending slope of an arterial pressure waveform?
The slope of the ascending part of the curve represents myocardial contractility, if it is very steep the myocardium is contracting maximally and thus a higher systolic pressure is produced, if it is much more flat then this is a sign of reduced contractility as there is a lower systolic pressure
75
What is represented by the descending slope of an arterial pressure waveform?
The slope of the descending part of the waveform represents systemic vascular resistance. A steep downstroke with a low dicrotic notch indicates a low systemic vascular resistance (e.g. hypotension). A high dicrotic notch implies a high systemic vascular resistance (e.g. hypertension)
76
Which non-invasive technique can you use to monitor equine blood pressure?
Oscillometric blood pressure
77
Where can you place the cuff for oscillometric blood pressure monitoring in horses?
Tail
Distal limb
78
What is the main advantage of oscillometric blood pressure monitoring?
Oscillometric blood pressure monitoring is non-invasive with minimal risk of harm to the patient
79
What are the main disadvantages of oscillometric blood pressure monitoring?
Oscillometric blood pressure monitoring is less accurate and doesn't allow for continuous monitoring
80
What can you do to treat hypotension in horses under inhalant anaesthesia?
If possible, decrease the anaesthetic depth
Intravenous fluid therapy
Ionotropic and vasoconstrictive drugs
81
What is the fluid maintenance rate for equine anaesthesia?
5 ml/kg/hr
82
Give three examples of drugs you can administer to treat hypotension in anaesthetised horses
Dobutamine
Ephedrine
Phenylephrine
83
How does dobutamine help to treat hypotension?
Dobutamine is inotropic and thus increases cardiac contractility which will help to increase blood pressure
84
How does ephidrine help to treat hypotension?
Ephedrine is inotropic and a vasoconstrictor so increases cardiac contractility and systemic vascular resistance which increases bood pressure
85
How does phenylephrine help to treat hypotension?
Phenylephrine is a vasoconstrictor so increases systemic vascular resistance which increases blood pressure
86
Which two factors increase the risk of hypoventilation in anaesthetised horses?
Inhaled anaesthetic agents
Positioning the horse in dorsal recumbency
87
How do inhaled anaesthetic agents cause hypoventilation in anaesthetised horses?
Inhaled anaesthetic agents cause dose-dependent respiratory depression in horses through reducing the sensitivity of the respiratory centres in the brainstem and the chemoreceptors in the carotid body to changes in partial pressure of CO2 (PaCO2). This can result in a decreased tidal volume, resulting in hypoventilation
88
How does positioning in dorsal recumbency cause hypoventilation in anaesthetised horses?
In dorsally recumbent horses, thoracic wall movement is restricted and the lungs are compressed by the abdominal organs, leading to the atelectasis and collapse of the alveoli, resulting in hypoventilation
89
What are the consequences of hypoventilation?
Hypoventilation results in hypercapnia and respiratory acidosis as well as hypoxaemia and eventually hypoxia
90
What is the main cause of ventilation perfusion (V/Q) mismatching in anaesthetised horses?
Atelectasis and thus alveolar collapse due to dorsal recumbent positioning is the main cause of a ventilation perfusion (V/Q) mismatch in anaesthetised horses
91
What are the consequences of a low ventilation perfusion (V/Q) mismatch in anaesthetised horses?
A low V/Q ratio develops when the perfusion exceeds ventilation of the alveoli, resulting in hypoxaemia due to the decreased oxygen levels within the alveoli which subsequently decreases the oxygen levels in the blood. A low V/Q ratio however has little impact on the removal of CO2
92
What are the consequences of a high ventilation perfusion (V/Q) mismatch in anaesthetised horses?
A high V/Q ration develops when the ventilation of the alveoli is greater than the perfusion. This can result in difficulties regarding CO2 removal from the blood, resulting in hypercapnia, however, will have minimal influence on blood oxygen levels
93
Which physiological compensatory mechanism is used to correct a ventilation perfusion (V/Q) mismatch in horses?
Hypoxic pulmonary vasoconstriction which shunts blood away from unventilated alveoli to well ventilated alveoli to correct the V/Q mismatch
94
How is hypoxic pulmonary vasoconstiction affected by inhalant anaesthetic agents?
Hypoxic pulmonary vasoconstriction is abolished by inhalant anaesthetic agents
95
Which pieces of equipment are used to monitor the respiratory system in horses under anaesthetic?
Capnography
Blood gas analysis
96
What is the normal EtCO2 in horses?
40mmHg
97
What is indicated by this capnography waveform?
This indicates increasing EtCO2
98
What is indicated by this capnography waveform?
This indicates decreasing EtCO2
99
What is indicated by this capnography waveform?
This indicates rebreathing of CO2
100
What is indicated by this capnography waveform?
This indicates breathing system or airway obstruction
101
What can be done to treat hypoventilation in anaesthetised horses?
If possible, decrease the anaesthetic depth
Intermittent positive pressure ventilation (IPPV)
Drugs
102
What can be done to reduce the risk of a ventilation perfusion (V/Q) mismatch in anaesthetised horses?
1. Place the horse in lateral recumbency rather than dorsal recumbency *however there is still a risk of atelectasis*
2. Intermittent positive pressure ventilation (IPPV)
103
What are the three benefits of intermittent positive pressure ventilation (IPPV) in equine anaesthesia?
1. Can prevent a decrease in tidal volume *(if used from the start)*
2. Can help control CO2 levels and prevent hypercapnia and respiratory acidosis
3. Allows for the use of positive end expiratory pressure (PEEP)
104
What is positive end expiratory pressure (PEEP)?
Positve end expiratory pressure (PEEP) is a pressure applied to the ventilator at the end of a breath to reduce alveolar collapse and even reinflate already collapsed alveoli to increase the surface area for gaseous exchange
105
What is the main disadvantage of intermittent positive pressure ventilation (IPPV)?
Gas always takes the path of least resistance so it is likely that during intermittent positive pressure ventilation (IPPV), that the gas will flow into the already inflated alveoli and not into the collapsed alveoli. This will result in an increase in intrathoracic pressure which will impede venous return, contributing to the ventilation perfusion (V/Q) mismatch
106
Which bronchodilator drugs can be used in anaesthetised horses with a ventilation perfusion (V/Q) mismatch?
Salbutamol *(inhaled)*
Clenbuterol *(IV)*
107
(T/F) Salbutamol is not licensed in horses
TRUE.
108
List six common post-anaesthetic complications seen in horses?
Equine post-anaesthetic myopathy (EPAM)
Neuropathy
Traumatic injury
Airway obstruction
Post-anaesthetic colic
Catheter complications
109
When do the clinical signs of post-anaesthetic myopathy become evident?
The clinical signs of post-anaesthetic myopathy may become evident as soon as the horse tries the stand or the clinical signs may be delayed by a few hours
110
What are the possible clinical signs of equine post-anaesthetic myopathy (EPAM)?
Swollen muscle
Hard muscle
Painful muscle
Hot muscle
111
What are the biochemistry changes associated with equine post anaesthetic myopathy (EPAM)?
Increased serum creatine kinase (Ck) levels
112
What are the urinalysis changes associated with equine post anaesthetic myopathy (EPAM)?
Myoglobinuria *(in severe cases)*
113
Why do you get myoglobinuria in severe equine post-anaesthetic myopathy cases?
When the muscle breaks down, this releases myoglobin into the blood which will be excreted as urine, resulting in myoglobinuria
114
Why do you get increased serum creatine kinase (Ck) levels in equine post-anaesthetic myopathy?
Creatine kinase is released into the bloodstream when there is muscle damage
115
What causes equine post-anaesthetic myopathy?
Equine post-anaesthetic myopathy is caused by muscle hypoperfusion
116
Which factors increase the risk of post-anaesthetic myopathy?
Increased duration of anaesthetic
Hypotension
Hypoxaemia
Heavy horses
Positioning of the horse resulting in muscle and blood vessel compression and stretch occlusion which reduces blood flow to the muscles
117
Which breeds of horse are at an increased risk of post-anaesthetic myopathies?
Double muscled breeds and quarter horses
118
What can you do to prevent post-anaesthetic myopathy?
1. Minimise the duration of anaesthesia
2. Carefully position and pad the patient
3. Maintain the mean arterial pressure (MAP) above 70mmHg *(can be done using fluid therapy)*
119
What can you do to manage and treat post-anaesthetic myopathy?
Analgesia
IV fluid therapy
Splints *(to support the patient's weight)*
120
What is the purpose of IV fluid therapy in managing equine post anaesthetic myopathies (EPAM)?
IV fluid therapy is used to maintain blood pressure and muscle perfusion as well as increase renal excretion of myoglobins as myoglobins can cause renal tubular necrosis
121
Give three examples of genetic muscular diseases
Equine polysaccharide storage myopathy (EPSM)
Hyperkalaemic periodic paralysis (HYPP)
Malignant hyperthermia
122
What causes equine polysaccharide storage myopathy (EPSM)?
Equine polysaccharide storage myopathy (EPSM) is caused by a mutation is the glycogen processing gene
123
What causes hyperkalaemic periodic paralysis (HYPP)?
Hyperkalaemic periodic paralysis (HYPP) is an inherited autosomal dominant disorder which affects sodium channels in the muscle and the ability to regulate blood potassium levels
124
What can trigger hyperkalaemic periodic paralysis (HYPP)?
Stress *(i.e. can be triggered due to anaesthetic stress)*
125
What causes malignant hyperthermia?
Malignant hyperthermia is caused by an inherited Ryanodine receptor mutation
126
What two factors can trigger malignant hyperthermia?
Stress *(i.e. can be triggered due to anaesthetic stress)*
Inhalant anaesthetics
127
What are the two classifications of neuropathies?
Peripheral neuropathy
Central neuropathy
128
What is peripheral neuropathy?
Peripheral neuropathy is the temporary or permanent loss of motor and sensory function due to peripheral nerve compression/traction
129
What is the main cause of periperal neuropathy due to equine anaesthesia?
Positioning of the horse resulting in compression/traction of the peripheral nerves
130
What can you do to prevent peripheral neuropathy in horses?
Carefully position and pad the patient
131
Give an example of a central myopathy
Spinal cord myelomalacia
132
(T/F) Spinal cord myelomalacia is very rare in horses
TRUE
133
What is the signalement that is more prone to spinal cord myelomalacia?
Young, male horses
134
Give three examples of common musculoskeletal injuries that can occur post-anaesthetic
Skin abrasions/cuts
Fractures
Disarticulations
135
Give three examples of common ocular injuries that can occur post-anaesthetic
Ocular bruising
Ocular foreign body entrapment
Dessication of the cornea
136
How can you prevent dessication of the cornea in anaesthetised horses?
Apply eye lubricant regularly during anaesthesia to prevent dessication of the cornea
137
What are the five possible signs of an post anaesthetic airway obstruction in a horse?
Stridor
Stertor
Nostril flaring
Paradoxical breathing
Absence of airflow at the nostrils
138
What are the possible causes of a post anaesthetic airway obstruction in a horse?
Nose stuck in the corner of the recovery stable
Nasal congestion
Laryngeal paralysis
Airway swelling
139
Why do horses experience nasal congestion due to anaesthesia?
When horses are positioned in dorsal recumbency, gravity causes blood to pool in the nasal region causing an increase in the hydrostatic pressure in the nasal vascular beds, resulting in nasal oedema and congestion
140
Which techniques can be used to reduce nasal congestion in anaesthetised horses?
Elevate the head
Place a nasopharangeal tube
Recover with the endotracheal tube secured in place
Vasoconstrictive intranasal spray 10 minutes before recovery
141
Which vasoconstrictive intranasal spray can be administered to horses to reduce nasal congestion?
Diluted phenylephrine intranasal spray
142
What are the possible causes of laryngeal paralysis in horses?
Pre-existing condition
Due to manipulation of the larynx during intubation
Due to over stretching of the laryngeal nerve when the horse is positioned in dorsal recumbency
143
Which six techniques can be used to reduce the risk of post-anaesthetic airway obstruction in horses?
Gentle intubation and extubation
Elevate the head during anaesthesia
Prevent overextension of the neck during anaesthesia
Administer diluted phenylephrine intranasal spray
Carefully position the horse in the recovery stable
Diligent monitoring of the horse during recovery
144
How should you treat a post-anaesthetic airway obstruction?
Re-intubate
Emergency tracheostomy
145
What can airway obstruction progress to?
Pulmonary oedema
146
What is a characteristic sign of pulmonary oedema in horses?
Red foam at the nostrils
147
What should be administered if a horse shows signs of post-anaesthetic pulmonary oedema?
Furosemide
148
How long should you monitor a horse for post-anaesthetic colic?
You should monitor a horse for post-anaesthetic colic for 24 hours
149
What are the ten requirements for a recovery stable?
Quiet
Adjustable lighting
Padded and non-slip
No corners
Facilities for observation
Close to the operating theatre
Oxygen supplementation
Scavenging system
Escape route for staff
Wall rings and ceiling hooks for if you have to secure the horse
150
How much oxygen should you provide a horse during anaesthetic recovery?
15 litres of oxygen per minute
151
List two examples of anaesthetic recovery methods in horses
Hand recovery
Head and tail ropes recovery
152
Describe the hand recovery method
Hand recovery involves people assisting the horse in recovery. This can be done in a field or large area and usually involves two or three people who are experienced and can work well together. This technique cannot be done in a confined space as it will risk the safety of the personnel involved
153
Describe the head and tail ropes recovery method
The head and tail ropes method requires a tight fitting head collar attached to a rope through a high ring and pulley system and a second similarly run rope tied to the tail. One person usually takes each rope and supports and guides the horse as it stands, allowing for support and some restraint from a safe distance. This is not a suitable method for lifting a horse that cannot stand on its own.
154
What should you provide horses with post anaesthetic recovery?
Allow free access to water
Withold food for 3-4 hours after recovery and reintroduce slowly
