Age, chronic obstructive pulmonary disease, and Innovar induced ventilatory depression during regional anesthesia

The effect of Innovar on ventilatory response to CO2 was studied in 35 patients undergoing peripheral surgery with regional anesthesia. The dosage schedule (per 70 kg body weight) was 2 ml intramuscularly, prior to the block, and 1 ml intravenously, after the block. The decrease in mean CO2 response slope (15 percent decrease from control 30 minutes after the first dose) was not statistically significant. Control slope varied inversely with age (r = 0.41, p less than 0.05), and (in 22 patients) directly with the FEV1/FVC ratio (r = 0.54, p less than 0.02) and with the combined variables (FEV1/FVC)/age (r = 0.58, p less than 0.01). Depression of CO2 response slope following Innovar did not vary with age or FEV1. We conclude that, in otherwise normal patients, these doses of innovar cause only minor depression of ventilatory response to CO2. However, in those patients who already have a depressed response (the elderly and those with a decreased FEV1/FVC ratio), this additional depression occasionally may be clinically important.