Arterial and Mixed Venous Kinetics of Desflurane and Sevoflurane, Administered Simultaneously, at Three Different Global Ventilation to Perfusion Ratios in Piglets with Normal Lungs

• Background: Previous studies have established the role of various tissue compartments in the kinetics of inhaled anesthetic uptake and elimination. The role of normal lungs in inhaled anesthetic kinetics is less understood. In juvenile pigs with normal lungs, the authors measured desflurane and sevoflurane washin and washout kinetics at three different ratios of alveolar minute ventilation to cardiac output value. The main hypothesis was that the ventilation/perfusion ratio (V-A/Q) of normal lungs influences the kinetics of inhaled anesthetics.Methods: Seven healthy pigs were anesthetized with intravenous anesthetics and mechanically ventilated. Each animal was studied under three different V-A/Q conditions: normal, low, and high. For each V-A/Q condition, desflurane and sevoflurane were administered at a constant, subanesthetic inspired partial pressure (0.15 volume% for sevoflurane and 0.5 volume% for desflurane) for 45 min. Pulmonary arterial and systemic arterial blood samples were collected at eight time points during uptake, and then at these same times during elimination, for measurement of desflurane and sevoflurane partial pressures. The authors also assessed the effect of V-A/Q on paired differences in arterial and mixed venous partial pressures.Results: For desflurane washin, the scaled arterial partial pressure differences between 5 and 0 min were 0.70 +/- 0.10, 0.93 +/- 0.08, and 0.82 +/- 0.07 for the low, normal, and high V-A/Q conditions (means, 95% CI). Equivalent measurements for sevoflurane were 0.55 +/- 0.06, 0.77 +/- 0.04, and 0.75 +/- 0.08. For desflurane washout, the scaled arterial partial pressure differences between 0 and 5 min were 0.76 +/- 0.04, 0.88 +/- 0.02, and 0.92 +/- 0.01 for the low, normal, and high V-A/Q conditions. Equivalent measurements for sevoflurane were 0.79 +/- 0.05, 0.85 +/- 0.03, and 0.90 +/- 0.03.Conclusions: Kinetics of inhaled anesthetic washin and washout are substantially altered by changes in the global V-A/Q ratio for normal lungs.

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MEDICIN OCH HÄLSOVETENSKAP  -- Klinisk medicin -- Anestesi och intensivvård (hsv//swe)

MEDICAL AND HEALTH SCIENCES  -- Clinical Medicine -- Anesthesiology and Intensive Care (hsv//eng)

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