Experimental critical care in rats: gender differences in anesthesia, ventilation, and gas exchange

Objective: To compare normative ventilatory and gas-exchange data and anesthetic requirements in male and female rats subjected to critical care conditions. Design: Prospective study. Setting: Critical care research laboratory in a hospital. Subjects: Twenty-two age-matched young male and female rats (Sprague-Dawley, Long Evans strain). Interventions: Anesthesia was induced with 65 and 45 mg/kg pentobarbital in male and female rats, respectively. The rats were then tracheostomized and cannulated in one femoral vein and artery. Anesthesia was maintained using 8-15 mg/kg/hr pentobarbital (iv) and controlled by continuous hemodynamic monitoring. Measurements and Main Results: Normoxic baselines for breathing frequency, tidal volume, minute volume, inspiratory-to-expiratory ratio, inspiratory drive (tidal volume/inspiratory time), respiratory system compliance, peak airway pressure, and gas-exchange profiles were established. Ventilatory and gas-exchange responses to oxygen and CO 2 were then determined by exposure to 10 mins of hyperoxia (100% oxygen), two levels of mild and severe hypercapnic hyperoxia (inspired Pco 2 of 30 and 60 torr; 4 and 8 kPa), and two levels of mild and severe normocapnic hypoxia (inspired Po 2 of 81 and 48 torr; 10.7 and 6.3 kPa). The average anesthetic requirement (during a 5- to 6-hr experiment) was 30% less In the female rats than in the male rats (p