Lung volume and VA/Q distribution response to intravenous versus inhalation anesthesia in sheep

• Published in: Anesthesiology (Philadelphia) 1984-07, Vol.61 (1), p.55-65
• Main Authors: DUECK, R, RATHBUN, M, GREENBURG, A. G
• Format: Article
• Language: English
• Subjects: Anesthesia, Inhalation; Anesthetics. Neuromuscular blocking agents; Animals; Biological and medical sciences; Halothane - administration & dosage; Halothane - pharmacology; Injections, Intravenous; Lung - drug effects; Lung Volume Measurements; Medical sciences; Neuropharmacology; Nitrous Oxide - administration & dosage; Nitrous Oxide - pharmacology; Pentobarbital - administration & dosage; Pentobarbital - pharmacology; Pharmacology. Drug treatments; Sheep; Ventilation-Perfusion Ratio - drug effects; Wakefulness
• ISSN: 0003-3022; 1528-1175
• DOI: 10.1097/00000542-198407000-00010

The effects of intravenous pentobarbital versus nitrous oxide/halothane inhalation anesthesia on blood gases, distribution of ventilation-perfusion ratios (VA/Q), and lung volume (FRC) were compared in 8 tracheostomized sheep in the lateral decubitus position. Pentobarbital anesthesia produced no significant changes (from awake control) in arterial blood PO2 or PCO2, ventilation-perfusion inequality, intrapulmonary shunt, or FRC during either spontaneous breathing or mechanical ventilation with muscle paralysis. With inhalation anesthesia, PaO2 decreased from 132 +/- 13 mmHg awake to 106 +/- 11 mmHg and 104 +/- 6 mmHg (FIO2 all 0.3) during spontaneous and mechanical ventilation. Shunt increased from 1.4 +/- 1.0% awake to 10.6 +/- 4.5 and 13.9 +/- 5.3%, respectively. Mean VA/Q decreased from 0.39 +/- 0.07 awake, to 0.21 +/- 0.06 and 0.29 +/- 0.07. Log standard deviation of VA/Q increased from 0.66 +/- 0.12 awake to 0.83 +/- 0.28 and 0.89 +/- 0.15. FRC decreased from 1.66 +/- 0.65 1 to 1.46 +/- 0.62 and 1.22 +/- 0.63 1, respectively. Differences in response to intravenous versus inhalation anesthesia for the above variables all were statistically significant at P less than 0.05. FRC and shunt changes with anesthesia showed significant correlation for both spontaneous (r = -0.80) and mechanical ventilation (r = 0.77), P less than 0.005 for both. We therefore propose that the differences between lung volume and gas exchange effects of intravenous versus inhalation anesthesia in sheep may have been related causally.