Objective—To determine the hemodynamic effects
of nitrous oxide in isoflurane-anesthetized cats.
Animals—12 healthy adult domestic shorthair cats.
Procedure—Cats were anesthetized by administration
of isoflurane in oxygen. After instruments were
inserted, end-tidal isoflurane concentration was set at
1.25 times the individual minimum alveolar concentration,
and nitrous oxide was administered in a Latinsquare
design at 0, 30, 50, and 70%. Each concentration
was administered for 25 minutes before measurements
were obtained to allow for stabilization.
Heart rate; systemic and pulmonary arterial pressures;
central venous pressure; pulmonary artery occlusion
pressure; cardiac output; body temperature; arterial
and mixed-venous pH, PCO2, PO2, and hemoglobin
concentrations; PCV; and total protein and lactate concentrations
were measured before and during noxious
stimulation for each nitrous oxide concentration.
Arterial and mixed-venous bicarbonate concentrations
and oxygen saturation, cardiac index, stroke index,
rate-pressure product, systemic and pulmonary vascular
resistance indices, left and right ventricular stroke
work indices, arterial and mixed-venous oxygen contents,
oxygen delivery, oxygen consumption, oxygen
extraction ratio, alveolar-to-arterial oxygen difference,
and venous admixture were calculated.
Results—Arterial pressure, central venous pressure,
pulmonary arterial pressure, rate-pressure product,
systemic and pulmonary vascular resistance indices,
arterial PCO2, and PCV increased during administration
of 70% nitrous oxide. Arterial and mixed-venous pH,
mixed-venous PO2, and alveolar-to-arterial oxygen difference
decreased during administration of 70%
nitrous oxide. Results before and during noxious stimulation
Conclusions and Clinical Relevance—Administration
of 70% nitrous oxide to isoflurane-anesthetized
cats resulted in improved arterial pressure,
which was related to a vasoconstrictive effect. (Am J Vet Res 2003;64:273–278)