Circulatory effects of halothane and halothane-nitrous oxide anesthesia in the dog: spontaneous ventilation.

The cardiovascular effects of equipotent (minimum alveolar concentration; MAC) doses of halothane versus halothane plus 25% N2O (H25N2O) in spontaneously breathing dogs do not differe except that nitrous oxide increased mean arterial pressure (AP) and decreased arterial oxygen partial pressure (PAO2). When 75% nitrous oxide was added to halothane anesthesia, AP, mean pulmonary artery pressure (PAP), heart rate (HR), cardiac output (CO), stroke volume (SV), total peripheral resistance (TPR), and left ventricular work (LVW) increased and PAO2 and hemoglobin saturation decreased. Arterial oxygen tensions below 80 torr were common at moderate and deep anesthetic levels of halothane plus 75% N2O (H75N2O). The specific contribution of N2O, hypoxemia, hypercapnia, or temporal recovery (or a combination of these) in producing cardiovascular stimulation were not determined.