Tue28September1204PM 2

Which one of these anaesthetic agents is most likely to inhibit hypoxic pulmonary vasoconstriction (HPV)?

(Please select 1 option)

Propofol 6-12 mg/kg/hour

Desflurane 2 MAC Correct

Isoflurane 1 MAC

Sevoflurane 1 MAC

Fentanyl 50 mcg/kg

Explanation

Alveolar and airway hypoxia causes resistance pulmonary arteries to constrict, diverting blood to better-oxygenated alveoli.

Hypoxic pulmonary vasoconstriction optimises O2 uptake in atelectasis, pneumonia, asthma, and adult respiratory distress syndrome. During single-lung anaesthesia, hypoxic pulmonary vasoconstriction helps maintain systemic oxygenation.

The mechanism of hypoxic pulmonary vasoconstriction involves a redox-based O2 sensor within pulmonary artery smooth muscle cells. Pulmonary artery smooth muscle cells mitochondria vary production of reactive O2 species in proportion to PaO2. Hypoxic withdrawal of these redox second messengers inhibits voltage-gated potassium channels, depolarising the pulmonary artery smooth muscle cells.

Depolarisation activates L-type calcium channels, increasing cytosolic calcium and triggering hypoxic pulmonary vasoconstriction. Some anaesthetic agents attenuate this response with the potential for causing further deterioration in ventilation perfusion mismatch.

Agents that inhibit HPV

Ether

Halothane

Desflurane (>1.6 MAC)

Agents with minimal or no effect on HPV

Thiopentone

Fentanyl

Desflurane (1MAC)

Isoflurane (<1.5MAC)

Sevoflurane (1MAC)

Propofol.

Answer Statistics

1

12%

2

52%

3

13%

4

22%

5

4%

Times answered: 235