Authors: Moritz Kretzschmar, M.D., Ph.D., D.E.S.A. et al
Anesthesiology 11 2017, Vol.127, 800-812.
Background: Increasing numbers of patients with obstructive lung diseases need anesthesia for surgery. These conditions are associated with pulmonary ventilation/perfusion (VA/Q) mismatch affecting kinetics of volatile anesthetics. Pure shunt might delay uptake of less soluble anesthetic agents but other forms of VA/Q scatter have not yet been examined. Volatile anesthetics with higher blood solubility would be less affected by VA/Q mismatch. We therefore compared uptake and elimination of higher soluble isoflurane and less soluble desflurane in a piglet model.
Methods: Juvenile piglets (26.7 ± 1.5 kg) received either isoflurane (n = 7) or desflurane (n = 7). Arterial and mixed venous blood samples were obtained during wash-in and wash-out of volatile anesthetics before and during bronchoconstriction by methacholine inhalation (100 μg/ml). Total uptake and elimination were calculated based on partial pressure measurements by micropore membrane inlet mass spectrometry and literature-derived partition coefficients and assumed end-expired to arterial gradients to be negligible. VA/Q distribution was assessed by the multiple inert gas elimination technique.
Results: Before methacholine inhalation, isoflurane arterial partial pressures reached 90% of final plateau within 16 min and decreased to 10% after 28 min. By methacholine nebulization, arterial uptake and elimination delayed to 35 and 44 min. Desflurane needed 4 min during wash-in and 6 min during wash-out, but with bronchoconstriction 90% of both uptake and elimination was reached within 15 min.
Conclusions: Inhaled methacholine induced bronchoconstriction and inhomogeneous VA/Q distribution. Solubility of inhalational anesthetics significantly influenced pharmacokinetics: higher soluble isoflurane is less affected than fairly insoluble desflurane, indicating different uptake and elimination during bronchoconstriction.
What We Already Know about This Topic
- Inhalational anesthetic arterial kinetics depends on not only alveolar ventilation and pulmonary perfusion but also their distribution, agent solubility, and mixed venous kinetics
- Methacholine inhalation causes bronchoconstriction, shifts mean ventilation to regions with higher ventilation/perfusion ratios, and broadens perfusion dispersion with increased perfusion in low ventilation/perfusion regions and interpulmonary shunt
- Inhaled methacholine delayed desflurane uptake and elimination in a piglet model
What This Article Tells Us That Is New
- Compared with the fairly insoluble desflurane, the uptake and elimination of the more soluble isoflurane in piglets was less affected by methacholine-induced bronchoconstriction and ventilation/perfusion scatter
THE rising prevalence of the chronic obstructive pulmonary disease and asthma may increase the number of patients suffering from these conditions who are in need of anesthesia for surgery. This is important for clinical anesthesia, because these diseases are associated with pulmonary ventilation/perfusion (VA/Q) mismatch that may affect uptake and elimination of volatile anesthetics.