Changes in respiratory pattern and arterial blood gases during sedation with propofol or midazolam in spinal anesthesia

Study Objectives: To investigate changes in respiratory pattern and arteria l blood gases during sedation with, propofol or midazolam in spinal anesthe sia. Design: Randomized, placebo-controlled study. Setting: Operating room of a university-affiliated hospital. Patients: 40 ASA physical status I and II patients who required spinal anes thesia. Interventions: Spinal anesthesia with tetracaine and subsequent sedation wi th propofol (n = 15), midazolam (n = 15), or placebo (n = 10) was performed . Measurements: Respiratory pattern [rib cage contribution to the tidal volum e (%RC) and phase shift between rib cage and abdominal movements (PSrc-ab)] with a respiratory inductive plethysmograph (Respigraph(TM)) and arterial blood gas analysis (pH, pO(2), and pCO(2)) Were recorded. Main Results: Spinal anesthesia per se increased %RC by 35% without changin g PSrc-ab values (1.00). Sedation with propofol and midazolam decreased %RC by 60% and by 40%, respectively. PSrc-ab increased in both groups followin g sedation, and the increase in this parameter was higher in the propofol g roup (1.12) than in the midazolam group (1.04). In the placebo group, %RC d ecreased by 20% without ang change in PSrc-ab. The decrease in pO(2) was mo re significant in the propofol group (65.1 mmHg) than in the midazolam (74. 2 mmHg) and placebo (83.1 mmHg) groups. Conclusion: Significant decreases in %RC and pO(2) during propofol sedation seem to depend on paradoxical respiration due, in part, to upper airway ob struction; therefore, attention should be directed to the respiratory patte rn during sedation, especially with propofol. (C) 1999 by Elsevier Science Inc.