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

The cardiovascular effects of equipoxent (minimum alveolar concentration) doses of halothane versus halothane plus 25% N ₂O (H25N ₂O) in spontaneously breathing dogs do not differ except that nitrous oxide increased mean arterial pressure (AP) and decreased arterial oxygen partial pressure (Pao ₂). When 75% nitrous oxide was added to halothane anesthesia, AP, mean pulmonary artery pressure, heart rate, cardiac output, stroke volume, total peripheral resistance and left ventricular work increased and Pao ₂ and hemoglobin saturation decreased. Arterial oxygen tensions below 80 torr were common at moderate and deep anesthetic levels of halothane plus 75% N ₂O (H75N ₂O). The specific contribution of N ₂O, hypoxemia, hypercapnia, or temporal recovery (or a combination of these) in producing cardiovascular stimulation were not determined.