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4th Year Drugs > Anaesthesia > Flashcards

Flashcards in Anaesthesia Deck (72):
1

What are the three stages of general anaesthesia?

  • Induction
  • Maintenance
  • Emergence

2

What are the three A's of general anesthesia?

  • AMNESIA - lack of response and recall to noxious stimuli – Unconsciousness
  • ANALGESIA - pain relief
  • AKINESIS - Immobilisation/paralysis

3

What are the three types of drugs that make up the 'triad of anaesthesia?'

  • Hypnotic agents
  • Analgesics
  • Muscle relaxants

4

What are induction agents and what is there aim? What are the two ways in which an individual can be induced?

Transition from an awake to an anesthetised state. 

  • IV - induce loss of consciousness in one-arm brain circulation time (10-20 secs; lasting for 4-10 mins)
  • Inhalational Induction - usually amnesia maintenance

5

What are the IV induction agents?

  • Propofol
  • Etomidate
  • Ketamine 
  • Thiopentone 

6

What are the characteristics of propofol?

  1. Dose
  2. Mechanism
  3. Advantages
  4. Disadvantages 
  5. CIs

'Milk' (MJ overdose!) - most common

1. 1.5 – 2.5 mg/kg: titrated against patient response (anaesthesia onset)

2. Enhances inhibitory function of the GABA through GABA-A receptors

3. - Rapid induction (<30 secs) and emergence (lasts 2-5 mins)

     - Anti-emetic properties (↓ incidence of postop N&V (PONV))

     - Excellent suppression of pharyngeal reflexes and good                         brochodilator

4. - Lipid based - pain on injection

    - Marked ↓BP (systemic vasodilatation), ↓HR  ↓RR (act on                  respiratory centre),

    - Involuntary movements

    - Allergies/rashes - contains soya, eggs

5. - Children - “propofol infusion syndrome

- metabolic acidosis, lipidaemia, cardiac, arrhythmias and     increased mortality

7

What are the characteristics of Thiopentone?

1 Dose
2Type of drug and Mechanism
3 Advantages
4 Disadvantages 
5 CIs

'Pale yellow powder'

1. 4-5 mg/kg

2. Barbituate - Binds to GABA-A receptor and enhances inhibitory effects of GABA 

3. - Rapid induction  (<30sec) (∴ main use = rapid sequence induction)  

    - Anticonvulsant properties

    - Can imprvoe neurological outcomes ( ↓cerebral blood flow            (↓ICP), ↓metabolic rate and ↓oxygen demand - 'Barbitutate            coma'

4. - Depresses heart contractile force (↓BP/Q BUT ↑HR) - caution in              hypovolaemia

    -  ↓RR

    - Airway reflexes well preserved (vs propofol) -                  coughing/laryngospasm

    -  Rash/bronchospasm (causes histamine release)

    - Intrarterial Injection - thrombosis and gangrene 

5. Porphyria (overproduction and excretion of porphyrins) - can precipitate prophyria due to hepatic enzyme induction

   

8

What are the characteristics of etomidate?

Dose
Mechanism
Advantages
Disadvantages/CIs

1. Non-barbituate - 0.3 mg/kg 

2. Binds to GABA-A receptor and enhances inhibitory effects of GABA

3. - Haemodynamic stability  - minimal ↓BP/Q

    - Lowest incidence of hypersensitivity reactions

4. - Pain on injection (lipid emulsion)

    - Involuntary movements 

    - High incidence of post-op N&V 

   - Adreno-cortical suppression (suppressed for up to 72hrs) - ∴

     CI in critically ill/septic shock patients (↑ mortality)

9

What are the characteristics of Ketamine?

Dose
Mechanism
Advantages
Disadvantages/CIs

Dose: 1 - 1.5 mg/kg. Slow onset (90 secs) and lasts 5-10 mins

Mech: 

  •  Anatagonises NMDA (↓effects of glutamate (main                             excitatory NT) ► dissociative anaesthesia (conscious                   but insensitive to pain) - anterograde amnesia
  • Acts on opioid and muscarinic receptors. Also effects                      Na/Ca movement across cell membranes  ► Profound                  analgesia
  • Inhibits monoamine reuptake ► anti-depressant effects

- Because of above, can be used as sole anaesthetic for                SHORT procedure 

Advan: 

  • minimal effect on resp drive, protective airway reflexes                = intact ∴ good preshopital
  • ↑HR/BP/Q - useful in shocked, unwell patients
  • Bronchodilator - role in management of severe asthma

Disadvan: 

  • Hypersalivation ► airway obstruction (Tx with anti-                          muscarinic e.g. glycopyrrolate)
  • N&V
  • Catalepsy - open eyes, slow nystagmus gaze. Intact corneal/light reflexes
  • Emergence phenomenon: vivid dreams,                                            hallucinations
  • Hypertonus, occassional purposeful movements

 

10

What are the inhalation/volatile agents for maintaining (usually) /inducing amnesia?

  • Sevoflurane
  • Desflurane
  • Isoflurane
  • Enflurane - rare

11

What is the definition of minimum alveolar concentration (MAC)?

  • Minimum alveolar concentration of vapour (%) at steady state
  • That prevents the reaction to a standard surgical stimulus (traditionally a set depth/width of skin incision)
  • In 50% of subjects

12

What factors can increase MAC? (i.e. anaesthesia requirements)

Things that increase metabolism

  • Infancy (peaks at 6 months)
  • High temp
  • Pregnancy
  • Chronic Alcoholism
  • Stimulants (cocaine/amphetamine)

13

What factors reduce the MAC (i.e. anaesthestic requirement)

Things that REDUCE metabolism...

  • Hypoinatraemia
  • Hypothermia
  • Elderly
  • Acute alcohol intoxication
  • Pregnancy
  • Anemia
  • CNS depressant drugs e.g. benzo, opioids

14

What are the characteristics of Sevoflurane?

1. Colour/characteristics

2. Uses

3. Route and MAC

4 Effects on CV, resp and CNS 

SEs

1. Clear, colourless, sweet smelling, non- irritant

2. Popular for inhalational induction. Maintenance. 

3. Route: Inhalation, via calibrated vaporiser. MAC: ~2%

4. ↓BP (vasodilation), ↓RR, minimal effect on cerebral blood flow

5. Malignant Hyperthermia, nephrotoxic (↓ renal blood flow)

15

What are the characteristics of Isoflurane?

1. Colour/characteristics

2. Uses

3. Route and MAC

4 Effects on CV, resp and CNS 

5. SEs

1. Clear, colourless liquid. Pungent smell 

2. Maintenance. Pungent smell limits use for induction.

3. Routes: Inhalation via calibrated vaporiser. MAC: 1.15%

4. Least effect on organ blood flow ↓BP (vasodilation), ↑HR, ↓RR, slight ↑cerebral blood flow/ICP

5. Malignant hyperthermia. 

16

What are the characteristics of Desflurane?

1. Colour/characteristics

2. Uses

3. Route and MAC

4 Effects on CV, resp and CNS 

5. SEs

1. Clear colourless liquid. Low lipid solubility (∴ rapid induction and elimination). High volatility.

2. Long operations e.g. organ donation. Unsuitable for induction. 

3. Inhaled via electrically heated vaporiser - dual circuit gas/vapour blender. MAC: 6%

4. ↓BP, ↑HR, ↓RR, min effect of cerebral blood flow/ICP

5. Malignant hyperthermia. Reduces renal blood flow.

 

17

What is  the MAC of Enflurane? Why isnt it really used anymore

 

- MAC: 1.6%

- Potentially causes hepatotoxicity 

18

What is the pathohpysiology of malignant hyperthermia? What triggers it?

Triggers: ALL volatile inhalation agents, Suxamethonium

Pathophysiology:

  • Autosomal genetic condition of ryanodine receptor gene 
  • Triggering agent causes uncontrolled release of cytoplasmic free calcium from skeletal muscle SR
  • Causes muscle rigidity ► ↑ metabolism  ► body temp

19

What are the CFs of malignant hyperthermia?

Due to uncontrolled ↑ in intracell Ca ion conc, there is:

-  Muscle rigidity 

- ↑ metabolism (↑ end tidal CO2 first, ↑ body temp occurs later )

- Rhabdomyolysis - renal failure

(Arrythmias, ↑K+, and DIC may develop)

 

20

What are the two types of general analgesias used in anaesthetics? 

  • Short Acting - rapid acting, high potency (fentanyl = 100x more potent than morphine)
  • Long Acting 

21

Name three short acting analgesics. When/why are they used?

  • Fentanyl, Remifentanil, Alfentanil 
  • Intra op analgesia - suppresses response to laryngoscope, reduces surgical pain

22

Name two long acting analgesics. When/why are they used?

  • Morphine, Oxycodone
  • Intra-op and post-op analgesia

23

What other types of analgesics are commonly used? 

Most commonly used analgesic

  • Paracetamol

Most commonly used oral opioid in adults

  • Codeine

Intravenous NSAIDS

  • Ketorolac, Parecoxib

24

What are the two main groups muscle relaxants? How do they exert there action?

  • Depolarising
    • PHASE I: Cause depolarisation by mimicking the effect of Ach to nicotinic receptor. Contraction; fasciculations are seen and repolarisation is inhibited
      • Not hydrolysed by acetylcholinesterase, therefore...
    • PHASE II: 'Persistent depolarisation' = desensitisation (end plates lose sensitivity)
  • Non-depolarising 
    • ​Competitive antagonist - bind to nicotinic ACh receptors causing gradual muscle paralysis
    • Compete with ACh for nicotinic receptor binding, preventing end plate depolarisation and impulse propagation

25

- Name one depolarising muscle relaxant.

What is:

  1. It used for
  2. It's dose 
  3. The SEs 

Suxamethonium

Use: 1. Rapid intubation of the trachea and short periods of neuromuscular blockade. 2. Rapid sequence induction

Dose:  1 - 1.5 mg/kg

SEs: 

  • Bradycardia 
  • Muscle pains (due to fasciulations before paralysis)
  •  Hyperkalaemia 
  • ↑ICP, IOP and gastric pressure
  • Anaphylaxis - skin rash ► bronchospasm
  • Malignant hyperthermia
  • Suxamethonium apnoea

 

 

 

26

What is the cause of suxamethonium apnoea? 

  • Suxamethonium = metabolised by plasma cholinesterase (usually 5-10mins) - some PTs lack /have an altered enzyme ∴ ↓ metabolism
  • ∴ PTs may = paralysed for many hrs after administration
  • Pts must be anaesthetised/ventilated until after sux eliminated (slow!)

27

What drug is used to reverse Suxamethonium?

None!

28

Name the a) short, b) intermediate and c) long acting non-depolarising muscle relaxants

Short: Atracurium, mivacurium (aka nevercurium - hardly used!) (10 letters, earlier in alphabet!)

Intermediate: vecuronium, rocuronium** (10 letters, later in alphabet)

Long: Pancuronium (11 letters!) 

29

What are the SEs for non-depolarising muscle relaxants?

- Slow onset and variable duration, therefore less side effects

- Stimulate histamine release -  ↓BP (vasodilation), ↑HR, Flushing

 

 

30

Which population should you caution the use of non-depolarising muscle relaxants?

  • Myasthenia gravis or myasthenic syndrome
    •   Extremely sensitive to their effects.

31

What drug is used to reverse the action of ALL non-depolarising drugs? What is the mechanism and its SEs?

Neostigmine 

Mech: Reversible, anti-cholinesterase ► prevents ACh breakdown ∴ ↑ACH

SEs: Stimulates both nicotinic and muscarinic receptors (parasynp)

  • Nicotinic: low dose: muscle contraction. High dose: block neuromuscular transmission (↑↑↑acetylcholine)
  • Muscarinic: ↓HR, bronchoconstriction (↑bronchial secretions), miosis, salivation, ↑GI tone/secretions/motility, N&V,

32

What drug is neostigmine usually combined with to reverse the muscarinic SEs?

  • Anti-muscarinic agent: Glycopyrrolate
  • ∴ prevents muscarinic SEs ass with neostigmine:
    • ↓bradycardia 
    • ↓ salivary, tracheabronchial, pharyngeal, gastric, secretions
  • SEs: cant see, cant pee, cant spit, cant shit, 

33

What is the physiology of PONV?

34

What drugs and procedures are used to treat/prevent post operative N&V? 

Anti-emetic agents:

  • 5HT3 blockers: Ondansetron - prevention and Tx of PONV (esp chemo/RT)
  • Anti-histamine: Cyclizine - opioids, GA, RT and vestibular.
  • Steroids: Dexamethasone (8mg Adults, 150mg/kg children) ► unclear mech. Tx for chemo and PONV.
  • Dopamine antagonists: Phenothiazides (e.g. Prochlorperazine) 
  • Anti-dopaminergic: Metoclopramide
  • Benzodiazepines - Lorazepam - sedative/amnesic/antiemetic

 

Acupuncture 

  • Point P6 (2.5-5cm proximal to distal wrist crease. Between flexor carpi radialis and palmaris longus tendons).
  • 5 mins manual/electical stimulation ↓ vomiting incidence

35

What factors can increase the risk of PONV?

Patient factors - young, female, history motion sickness, anxious, non smoker

Anaesthetic factors - opioids, etomidate, N2O, volatile

Surgical factors - gynae, abdominal, middle ear, neurosurgery, ophthalmic (e.g. squint), prolonged op times, poor pain control post op

36

What types of drugs are used to Tx hypotension in A) commonly in surgery B) Severe Hypotension/ICU

 

Vasoactive agents

Commonly used:

  • Ephedrine
  • Phenylephrine
  • Metaraminol

Severe hypotension / ICU

  • Noradrenaline
  • Adrenaline
  • Dobutamine
     

37

What do alpha (I & II) beta (I & II) adreno receptors do?

 

 

38

What are the: effects, doses mechanisms and SEs of ephedrine? 

Mech: Activates α1 (indirectly), β1, β2

Effects: HR ↑, MAP ↑ (contractility), CO ↑ PVR ±

SEs: Repeated doses less effective (tachyphylaxis)

 

39

What are the: effects, doses mechanisms and SEs of Phenylephrine? 

Mechs: α1 (weak α2, weak β1)

Effects: HR ↓, MAP ↑↑, CO ↓, PVR ↑↑ 

SEs: 

40

What are the: effects and mechanisms of Metaraminol? 

Mechs:  Activates α1 (indirectly), β1, β2

Effects: Vasoconstriction - ↑ systolic/diastolic BP, ↑PVR

41

What is the total body water as % of total body weight in:

a) neonates

b) 6 months old

c) 1 yr olds

d) young adult

e) elderly

Neonate - 80%

6 Months - 70%

1 yr - 60%

Young Adult - 60%

Elderly - 50%

42

How is total body water distributed throughout the body? What are the different fluid compartments?

  • Distributed into different compartments/spaces - seperated by membranes that regulate flow of water between compartments 
    • Intracellular Fluid (ICF) - 2/3s (30L) of total body water
    • Extracellular Fluid (ECF) - 1/3 (15L) 
      • Interstitial fluid (ISF) (10L) - occupies spaces between cells
      • Intravascular fluid (3.5L) - blood plasma 
      • Transcellular Fluid (1.5L) - intraocular fluid, CSF, urine in bladder, fluid in bowel lumen 

 

43

What is the definition of a solvent and solute?

A liquid/ solid/gas which is able dissolve another solid/liquid/gas (solute*) to form a solution e.g. water + salt

 

Solute - a dissolved substance e.g. glucose 

 

44

45

What is the difference between osmolarity and osmolality?

Both quantify how much of a solute is dissolved in a solution i.e. the solute concentration of a solution

  • Osmolarity: the number of osmoles of solute particles per unit volume of solution (milliosmole)
  • Osmolality: the number of osmoles of solute particles per unit weight of solvent (milliosmoles/kg)

46

What is the definition of tonicity? 

  • Describes the relative solute concentration of two solutions seperated by a selectively permeable (semi-permeable) membrane (e.g. ICF and ECF)
  • Tonicity = influenced by number of solute particles within a solution (which cannot cross membrane)
    • Hypertonic (contains a higher concentration of solute on one side of the membrane)
    • Isotonic (contains the same concentration of solute on both sides of the membrane)
    • Hypotonic (contains a lower concentration of solute on one side of the membrane) 

47

What is the definition of osmosis? WHat is osmotic pressure? 

  • Movement of water from less concentrated solution (hypotonic) to a more concentrated (hypertonic) solution across a semipermeable membrane 
  • Semi-permeable membrane - allows free passage of water, but NOT any solutes

 

Osmotic pressure - minimum pressure which needs to be applied to a solution to prevent the inward flow of its solvent across a semi-permeable membrane 

48

How does fluid move between different compartments?

a) Interstitial and intravascular

B) Intracellular and extracellular 

 

Interstitial and intravascular compartments 

  • Seperated by capillary wall (water crosses via gaps/through cell membrane)
  • Movement of H2O/solutes = largely passive (simple diffusion/filtration)

Cell membrane - allows passive movement 

  • Water/small uncharged/lipid soluble molecules able to cross via passive diffusion
  • Ions, glucose (facilitated diffusion), proteins via transmembrane proteins or ion channels (act to provide different permeability to different solutes)
    • Steady state - ECF and ICF = isotonic
    • Any difference in EC/IC tonicity = due to change in solute concentration in either fluid compartment
    •  H2O then moves from area of relative hypertonicity ► hypotonicity 

49

What is the main ion that governs movement of fluid between ICF and ECF compartments? What controls its conc?

  • Na+ - memebrane = impermeable to Na+ ions so extracell conc governs movement between ECF and ICF 
  • Extracell Na conc = controlled by kidneys and neuroendocrine controls 
  • K+ = major intracell ion

50

What are the sources of fluid input and output? (70kg man)

51

What is the definition of insensible losses?

  • Loses from non-urine sources - insensible losses incease in unwell patients (febrile, tachypnoeic, increased bowel movements/stoma output)

52

53

What is the physiology of water and sodium homeostasis?

54

How are IV fluids broadly categorised?

  • Crystalloids - NaCl 0.9%, Dextrose, Dex/Sal, Hartmanns
  • Colloids - gelatins (Gelofusine, voluven, Volulyte), RBCs, Albumin (HAS)

55

What parameters are used to assess patient fluid status? 

  • Thirst
  • Dry mucous membranes
  • ↓Skin turgor (sturnum)
  • Urine output <0.5ml/kg/hr (Oliguria)

Ongoing losses

  • ↑Cap refill time
  • ↓BP ↑HR
  • ↓JVP/CVP

Monitor fluid input-output chart, daily weight chart and U&Es regularly

56

How is fluid loss classified?

Mild - ↓weight (4%), ↓skin turgor, dry mucous membranes

Moderate - ↓weight (5-8%), oliguria, ↓BP ↑HR

Severe - ↓weight (>8%), profound oliguria, CVS collapse 

57

What are crystalloids? What are their uses?

  • Balanced salt/electrolyte solutions. Forms true solution and is capable of passing through semi-permeable membranes
  • Can be isotonic, hypertonic or hypotonic
  • Uses: Plasma expanders
    •  ↑ the intravascular/circulatory volume via movement of intracellular and interstitial water into intravascular space 
    •  e.g. haemorrhage, dehydration or surgical fluid loss

58

What are the advantages and disadvanatges of crystalloids?

Advantages

  • Short half life (30-60mins)
  • Inexpensive, readily avaliable 
  • Non-allergenic 

Disadvantages

  • 3x volume needed for replacement (Molecules = small enough to freely cross capillary walls ∴ 2/3s of infused volume fluid will move into tissues)
    • Excessive use: peripheral and pulmonary oedema 

59

What are the characteristics of saline solution NaCl 0.9%?

 

• 9 g of NaCl/L water 
• 154 mmol/L sodium
• 154 mmol/L chloride
• Osmolality = 308 mosm/L

  • Does not contain the same electrolytes in the same concentrations as extracellular fluid (135- 145)

• Potential problem = hyperchloraemic metabolic acidosis, more likely with renal insufficiency

60

Name 4 crystalloid solutions

  • Normal saline (0.9% NaCl)
  • Hartmanns solution
  • Lactated Ringer's
  • Hypertonic Saline (3, 5, 7.5%)
  • Ringer's solution

61

WHat are the characteristics of Hartmanns solution?

  • Na+: 131 mmo/l
  • Cl = 111 mmol/l
  • Lactate = 29 mmol/l
  • K = 5 mmol/L
  • Ca = 2mmol/L
  • Isotonic - distributes across extravascular space
  • Potential SEs: K+ may accumulate 

62

What are the characteristics of hypertonic solutions? 

  • Hypertonic saline solutions include 1.8%, 3%, 5%, 7.5% and 10% sodium chloride solutions
  • Osmolality = exceeds intracellular water. the extracellular fluid (ECF) becomes slightly hyperosmolar thus gradient formed i.e. cell water ► extravascular space
  • Comps: ↓intracellular volume (cellular dehydration), hypernatraemia?

63

What are the characteristics of 5% dextrose?

  • Only water and dextrose (5% i.e. 50g/L) - Glucose taken up by cells and water distributes quickly across all fluid compartments 

  • Contains no electrolytes so decreases blood osmolality by dilution

  • 1 g Dextrose 3.4 Kcal

  • Calorific value approx. 170 kcal

64

What are colloids?

  • Contain NaCl and large chemicals (proteins/starches) which are incapable of    passing across a semi-permeable membrane.
  • Thought to increase oncotic pressure ► increase intravascular volume
  • Synthetic:
    • Gelatine based - dextrans
    • Starch based - Glesofusin (banned in 2013 - hyperoncotic ►AKI; anaphylaxis, coagulopathy)
  • Human protein products
    • Blood products: RBS, platelets, FFP
    • Human Albumin Solution (HAS)

 

65

What are the main problems associated with colloids?

  • Anaphylactic reactions

  • Coagulopathy

  •  Cost

66

What are the five principles of clinical fuluid management?

  • Individualise to the particular patient
  • Assess current fluid status
  • Replace any deficit
  • Maintenance fluids / electrolytes
  • Replace ongoing losses

67

What are the daily requirements? (Water, Na, K+, Energy, glucose)

Water - 30-40 ml/kg (35ml/kg if elderly)

Energy - 30-40 kcal/kg

Na - 1-2 mmol/kg

K - 1mmol/kg

Glucose - 50g/day

68

What arenthe daily requirements for a 70kg man? What would be a typical maintenance fluid regime?

  • Water = 70 x 40 = 2800ml
  • Na = 70 x 1-2 = 70-140 mmol
  • K = 70 mmol
  • 50g Glucose/day

1st bag: 1L 0.9% saline/Hartmanns over 8hrs 

2nd Bag: 1L of 5% dextrose + 20mmol/L K

3rd: 1L of 5% dextrose + 20mmol/L K

Total:

- 3000ml Water

- Saline: 154 mmol Na/Hartmanns: 131 mmol Na

- 40 mmol K

69

What are sources of fluid loss in patients? 

Reduced intake (high urea:creartinine, high PCV)

  • Elderly, dysphagia, unconscious

Increased Requirements

  • Trauma, burn, post-operative

Increased Loss

  • Fever/sweating
  • Hyperventilation
  • GI loss: vomiting (low K, low Cl, alkolosis), diarrhoea (low K, acidosis)
  • Renal loss (↑ diuresis - e.g. diuretics)
  • Third space losses e.g. lumen (bowel obstruction), retroperitoneum (e.g. pancreatitis), 

70

What is the fluid Tx for ongoing losses? 

  • Prescribe for routine maintenance requirement plus additional fluid and electrolyte supplements to replace the ‘measured’ abnormal ‘ongoing’ losses
  • (refer to table and prescribe according to source of loss)

71

What are the 2 main ways in which fluid resuscitation is used? What is the aim?

  • To maintain intravascular volume (in order to maintain blood pressure) e.g. hypovolaemic/cardiogenic/distributive shock 
  • To replace massive fluid losses (may require blood transfusion + other blood products)
  • AIM: ↑volume to ↑BP  

72

What is the dose for resus fluids?

  • Crystalloids (0.9% sodium chloride) 500 ml fluid bolus over less than 15 minutes. 
  • If fluid resus still required, repeat bolus. 
  • If >2000ml given and fluid resus still required, seek expert help