2000A09 Compare and contrast the effects of halothane and isoflurane on the heart.

(NOTE: I have not answered the question here, simply listed all the CVS effects of all the volatiles)

· Table

· Details of that table

· Guedel’s stage 2

	Halothane	Isoflurane	Enflurane	Desflurane	Sevoflurane
Contractility	↓↓↓(A)	↓	↓↓	-	↓
HR (A)	↓↓	↑↑	↑	↑	-
SVR	-/↓	↓↓	↓	↓↓	↓
mAP	↓↓	↓↓	↓↓	↓↓	↓
Cerebral blood flow(B)	↑↑↑	↑	↑	↑	↑
Splanchnic blood flow	↓↓↓ (risk T1HH)		↓
Sensitisation to catecholamines	↑↑↑		↑
SNS stimulation (C)				Y
Anaesthetic preconditioning (D)	Y	Y	Y	Y	Y
Prolonged QTc (insignificant)		Y	Y		Y

(A)Heart rate:

· Halothane -> ↑PSNS tone and direct depressant effect

· Others: ↓mAP -> reflex ↑HR (preserved baroreceptor reflex)

(B)Cerebral blood flow:

· <1MAC: ↓CBF (↓CMRO₂ predominates)

· >1MAC: ↑CBF (vasodilatation predominates)

· Halothane: ↑ICP if MAC >0.6

· Desflurane: least of all volatiles

· Rapid ↑[desflurane] -> SNS stimulation -> ↑HR/contractility/SVR

· Especially >1.5MAC

· ? Airway irritation ? Systemic effect (since occurs on CP bypass)

(D) Anaesthetic preconditioning

· Activation of mitochondrial and sarcolemmal ATP-sensitive K⁺ channels -> hyperpolarization

· Occurs at MAC >0.25

· Mimics ischaemic preconditioning

· ↑SNS output -> ↑HR, ↑cardiac output

· (Also irregular respiration, breath holding, laryngospasm etc.)