General anesthetics and regional hypoxic pulmonary vasoconstriction

Area of Science:

• Anesthesiology
• Pulmonary Physiology
• Pharmacology

Background:

• Hypoxic pulmonary vasoconstriction (HPV) is a physiological mechanism that diverts blood flow away from poorly oxygenated lung areas.
• Previous studies indicated that certain anesthetics administered to the left lower lobe (LLL) inhibit LLL HPV.

Purpose of the Study:

• To investigate the effects of whole-lung administration of various inhalation anesthetics on left-lower-lobe HPV in dogs.
• To compare the impact of localized versus whole-lung anesthetic administration on HPV.

Main Methods:

• Dogs anesthetized with pentobarbital were used.
• Selective ventilation of the LLL with N2 alone was performed to establish baseline blood flow.
• Inhalation anesthetics (N2O, fluroxene, isoflurane, halothane, enflurane) were administered to the whole lung at 1 and 2 MAC.
• LLL HPV responses were measured during anesthetic administration.

Main Results:

• Isoflurane and fluroxene progressively inhibited LLL HPV, halving it at 2 MAC.
• Nitrous oxide (N2O) at one-third MAC caused slight but significant inhibition of LLL HPV.
• Halothane and enflurane produced minimal, nonsignificant changes in LLL HPV.
• Effects of whole-lung administration mirrored those of localized administration.

Conclusions:

• N2O, isoflurane, and fluroxene locally inhibit regional HPV, increasing venous admixture.
• Halothane and enflurane do not exhibit significant inhibitory effects on regional HPV.
• Anesthetic-induced inhibition of HPV is primarily a local phenomenon.