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4th Year Drugs > Anaesthesia > Flashcards

Anaesthesia Flashcards

1
Q

What are the three stages of general anaesthesia?

A
  • Induction
  • Maintenance
  • Emergence
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2
Q

What are the three A’s of general anesthesia?

A
  • AMNESIA - lack of response and recall to noxious stimuli – Unconsciousness
  • ANALGESIA - pain relief
  • AKINESIS - Immobilisation/paralysis
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3
Q

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

A
  • Hypnotic agents
  • Analgesics
  • Muscle relaxants
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4
Q

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

A

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
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5
Q

What are the IV induction agents?

A
  • Propofol
  • Etomidate
  • Ketamine
  • Thiopentone
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6
Q

What are the characteristics of propofol?

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

‘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
    • 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
    • Lipid based - pain on injection
      - Marked ↓BP (systemic vasodilatation), ↓HR ↓RR (act on respiratory centre),
      - Involuntary movements
      - Allergies/rashes - contains soya, eggs
    • Children - “propofol infusion syndrome”
      - metabolic acidosis, lipidaemia, cardiac, arrhythmias and increased mortality
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7
Q

What are the characteristics of Thiopentone?

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

A

‘Pale yellow powder’

  1. 4-5 mg/kg
  2. Barbituate - Binds to GABA-A receptor and enhances inhibitory effects of GABA
    • 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’
    • 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
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8
Q

What are the characteristics of etomidate?

Dose
Mechanism
Advantages
Disadvantages/CIs

A
  1. Non-barbituate - 0.3 mg/kg
  2. Binds to GABA-A receptor and enhances inhibitory effects of GABA
    • Haemodynamic stability - minimal ↓BP/Q
      - Lowest incidence of hypersensitivity reactions
    • 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)

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9
Q

What are the characteristics of Ketamine?

Dose
Mechanism
Advantages
Disadvantages/CIs

A

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
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10
Q

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

A
  • Sevoflurane
  • Desflurane
  • Isoflurane
  • Enflurane - rare
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11
Q

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

A
  • 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
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12
Q

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

A

Things that increase metabolism

  • Infancy (peaks at 6 months)
  • High temp
  • Pregnancy
  • Chronic Alcoholism
  • Stimulants (cocaine/amphetamine)
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13
Q

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

A

Things that REDUCE metabolism…

  • Hypoinatraemia
  • Hypothermia
  • Elderly
  • Acute alcohol intoxication
  • Pregnancy
  • Anemia
  • CNS depressant drugs e.g. benzo, opioids
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14
Q

What are the characteristics of Sevoflurane?

  1. Colour/characteristics
  2. Uses
  3. Route and MAC

4 Effects on CV, resp and CNS

SEs

A
  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)
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15
Q

What are the characteristics of Isoflurane?

  1. Colour/characteristics
  2. Uses
  3. Route and MAC

4 Effects on CV, resp and CNS

  1. SEs
A
  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.
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16
Q

What are the characteristics of Desflurane?

  1. Colour/characteristics
  2. Uses
  3. Route and MAC

4 Effects on CV, resp and CNS

  1. SEs
A
  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.
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17
Q

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

A
  • MAC: 1.6%
  • Potentially causes hepatotoxicity
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18
Q

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

A

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
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19
Q

What are the CFs of malignant hyperthermia?

A

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)

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20
Q

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

A
  • Short Acting - rapid acting, high potency (fentanyl = 100x more potent than morphine)
  • Long Acting
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21
Q

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

A
  • Fentanyl, Remifentanil, Alfentanil
  • Intra op analgesia - suppresses response to laryngoscope, reduces surgical pain
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22
Q

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

A
  • Morphine, Oxycodone
  • Intra-op and post-op analgesia
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23
Q

What other types of analgesics are commonly used?

A

Most commonly used analgesic

  • Paracetamol

Most commonly used oral opioid in adults

  • Codeine

Intravenous NSAIDS

  • Ketorolac, Parecoxib
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24
Q

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

A
  • 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
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25
Q
  • Name one depolarising muscle relaxant.

What is:

  1. It used for
  2. It’s dose
  3. The SEs
A

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
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26
Q

What is the cause of suxamethonium apnoea?

A
  • 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!)
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27
Q

What drug is used to reverse Suxamethonium?

A

None!

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28
Q

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

A

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

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

Long: Pancuronium (11 letters!)

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29
Q

What are the SEs for non-depolarising muscle relaxants?

A
  • Slow onset and variable duration, therefore less side effects
  • Stimulate histamine release - ↓BP (vasodilation), ↑HR, Flushing
30
Q

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

A
  • Myasthenia gravis or myasthenic syndrome
    • Extremely sensitive to their effects.
31
Q

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

A

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
Q

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

A
  • 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
Q

What is the physiology of PONV?

A
34
Q

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

A

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
Q

What factors can increase the risk of PONV?

A

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
Q

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

A

Vasoactive agents

Commonly used:

  • Ephedrine
  • Phenylephrine
  • Metaraminol

Severe hypotension / ICU

  • Noradrenaline
  • Adrenaline
  • Dobutamine
37
Q

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

A
38
Q

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

A

Mech: Activates α1 (indirectly), β1, β2

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

SEs: Repeated doses less effective (tachyphylaxis)

39
Q

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

A

Mechs: α1 (weak α2, weak β1)

Effects: HR ↓, MAP ↑↑, CO ↓, PVR ↑↑

SEs:

40
Q

What are the: effects and mechanisms of Metaraminol?

A

Mechs: Activates α1 (indirectly), β1, β2

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

41
Q

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

A

Neonate - 80%

6 Months - 70%

1 yr - 60%

Young Adult - 60%

Elderly - 50%

42
Q

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

A
  • 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
Q

What is the definition of a solvent and solute?

A

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
Q
A
45
Q

What is the difference between osmolarity and osmolality?

A

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
Q

What is the definition of tonicity?

A
  • 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
Q

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

A
  • 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
Q

How does fluid move between different compartments?

a) Interstitial and intravascular

B) Intracellular and extracellular

A

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
Q

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

A
  • 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
Q

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

A
51
Q

What is the definition of insensible losses?

A
  • Loses from non-urine sources - insensible losses incease in unwell patients (febrile, tachypnoeic, increased bowel movements/stoma output)
52
Q
A
53
Q

What is the physiology of water and sodium homeostasis?

A
54
Q

How are IV fluids broadly categorised?

A
  • Crystalloids - NaCl 0.9%, Dextrose, Dex/Sal, Hartmanns
  • Colloids - gelatins (Gelofusine, voluven, Volulyte), RBCs, Albumin (HAS)
55
Q

What parameters are used to assess patient fluid status?

A
  • 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
Q

How is fluid loss classified?

A

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

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

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

57
Q

What are crystalloids? What are their uses?

A
  • 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
Q

What are the advantages and disadvanatges of crystalloids?

A

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
Q

What are the characteristics of saline solution NaCl 0.9%?

A
  • 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
Q

Name 4 crystalloid solutions

A
  • Normal saline (0.9% NaCl)
  • Hartmanns solution
  • Lactated Ringer’s
  • Hypertonic Saline (3, 5, 7.5%)
  • Ringer’s solution
61
Q

WHat are the characteristics of Hartmanns solution?

A
  • 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
Q

What are the characteristics of hypertonic solutions?

A
  • 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
Q

What are the characteristics of 5% dextrose?

A
  • 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
Q

What are colloids?

A
  • 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
Q

What are the main problems associated with colloids?

A
  • Anaphylactic reactions
  • Coagulopathy
  • Cost
66
Q

What are the five principles of clinical fuluid management?

A
  • Individualise to the particular patient
  • Assess current fluid status
  • Replace any deficit
  • Maintenance fluids / electrolytes
  • Replace ongoing losses
67
Q

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

A

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
Q

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

A
  • 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
Q

What are sources of fluid loss in patients?

A

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
Q

What is the fluid Tx for ongoing losses?

A
  • 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
Q

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

A
  • 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
Q

What is the dose for resus fluids?

A
  • 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

4th Year Drugs (7 decks)

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