The effect of respiratory alkalosis on oxygen consumption in anesthetized patients

Study Objective: To investigate whether hyperventilation significantly altered oxygen consumption in anesthetized and paralyzed patients undergoing surgery. Design: Open crossover trial with 1 hour of hyperventilation preceded and followed by 1 hour of normoventilation. Setting: University medical center. Patients: Eight patients (five men and three women) undergoing lengthy orthopedic surgery with general anesthesia and muscle paralysis. Interventions: After baseline normoventilationfor 1 hour (Period 1), the anesthetized patients were hyperventilated to an arterial carbon dioxide tension (PaCO₂) of 20 to 25 mmHg for 1 hour (Period 2). Patients then experienced another hour of normoventilation (Period 5). Measurements and Main Results: Hemodynamic variables, electrocardiography, temperature, end-tidal partial pressure of CO₂ (P_ETCO₂), oxygen consumption (VO₂), carbon dioxide production, and minute ventilation were continuously followed throughout the study, and arterial blood gases were drawn at the beginning and end of each study period. During the period of hyperventilation, pH was significantly higher and P._ETCO₂ and (PaCO₂) significantly lower compared with the periods of normoventilation. (VO₂), was significantly increased during hyperventilation compared with the periods of normoventilation. Hemodynamic variables and temperature were similar in the three study periods. Conclusions: In anesthetized paralyzed patients, there is an increase in whole-body (VO₂), with hypocapnic alkalosis.