Respiratory sites of action of propofol: absence of depression of peripheral chemoreflex loop by low-dose propofol
Nieuwenhuijs, D.; Sarton, E.; Teppema, L.J.; Kruyt, E.; Olievier, I.; van Kleef, J.; Dahan, A.
Anesthesiology 95(4): 889-895
2001
ISSN/ISBN: 0003-3022 PMID: 11605929 Document Number: 535564
Background: Propofol has a depressant effect on metabolic ventilatory control, causing depression of the ventilatory response to acute isocapnic hypoxia, a response mediated via the peripheral chemoreflex loop. In this study, the authors examined the effect of sedative concentrations of propofol on the dynamic ventilatory response to carbon dioxide to obtain information about the respiratory sites of action of propofol. Methods: In 10 healthy volunteers, the end-tidal carbon dioxide concentration was varied according to a multifrequency binary sequence that involved 13 steps into and 13 steps out of hypercapnia (total duration, 1,408 s). In each subject, two control studies, two studies at a plasma target propofol concentration of 0.75 mug/ml (Plow), and two studies at a target propofol concentration of 1.5 mug/ml (Phigh) were performed. The ventilatory responses were separated into a fast peripheral component and a slow central component, characterized by a time constant, carbon dioxide sensitivity, and apneic threshold. Values are mean +- SD. Results: Plasma propofol concentrations were approximately 0.5 mug/ml for Plow and approximately 1.3 mg/ml for Phigh. Propofol reduced the central carbon dioxide sensitivity from 1.5 +- 0.4 to 1.2 +- 0.3 (Plow; P < 0.01 vs. control) and 0.9 +- 0.1 1 cntdot min-1 cntdot mmHg-1 (Phigh; P < 0.001 vs. control). The peripheral carbon dioxide sensitivity remained unaffected by propofol (control, 0.5 +- 0.3; Plow, 0.5 +- 0.2; Phigh, 0.5 +- 0.2 l cntdot min-1 cntdot mmHg-1). The apneic threshold was reduced from 36.3 +- 2.7 (control) to 35.0 +- 2.1 (Plow; P < 0.01 vs. control) and to 34.6 +- 1.9 mmHg (Phigh; P < 0.01 vs. control). Conclusions: Sedative concentrations of propofol have an important effect on the control of breathing, showing depression of the ventilatory response to hypercapnia. The depression is attributed to an exclusive effect within the central chemoreflex loop at the central chemoreceptors. In contrast to low-dose inhalational anesthetics, the peripheral chemoreflex loop, when stimulated with carbon dioxide, remains unaffected by propofol.