2008A01 An 80 year old woman is undergoing major emergency surgery.
Describe the maintenance inhaled concentration of sevoflurane you would choose
and the factors that might influence this.

List:

· Intro

· PD: age and illness

· Effect of adjuvant opioid

· Volatile kinetics: age and illness

· Anaesthetic and surgical factors

· The answer

Intro:

Aims	· Ensure amnesia, hypnosis, immobility · Prevent awareness (lower risk) · Minimise CVS toxicity (higher risk)
Problems	· Elderly · Acutely unwell · Major surgery
Maintenance inhaled concentration	· After 15 mins, close to equilibration between inhaled, alveolar exhaled partial pressure · Hence consider equivalent to MAC

Pharmacodynamics: age and illness

Values	· MAC-amnesia 0.25 · MAC-awake 0.33 · MAC (immobility) 1.0
Factors reducing all MAC values	· Age: note quite linear ↓6% per decade after 40yrs (at 80: 1.4%) · Severe illness: mAP<40mmHg, PaO2 <40mmHg, PaCO2 >80mmHg, ↓pH, ↓temp · Adjuvant drugs: opioids, benzodiazepines

Effect of adjuvant opioid:

	Sevo alone	Sevo + fentanyl 3ng/mL
MACBAR	4.15%	↓80%
MAC	1.85%	↓60%
MACawake (0.3)	0.6%	↓25%
Standard deviation	0.1	<0.1

Volatile pharmacokinetics kinetics: age and illness

Absorption	· ↓Cardiac output -> ↑rate of rise FA/FI
Distribution	· ↓Cardiac output (↑age) -> ↑rate of rise FA/FI · ↓Muscle mass ↑rate of rise FA/FI
Metabolism	· ↓Liver enzymatic activity -> ↓rate of consumption -> ↑rate of rise FA/FI
Excretion	· N/A

Anaesthetic and surgical factors:

e.g. fractured NOF	· Spinal anaesthetic-> ↓nociceptive activation of ARAS -> ↓↓MAC requirement
e.g. laparotomy, thoracotomy	· ↑↑Stimulation -> ↑MAC requirement

Answer:

Considerations	· Very low risk of awareness at 0.8 MAC = 1.1% · Significant reduction in MAC with age, illness, adjuvants · Likely rapid ↑FA/FI · However need to account for ΔFA/FI
Final answer	· Inspired concentration 1.5% · Recommend EEG monitoring e.g. BIS, aim 40-60 (I don’t know if this is the correct answer)

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