The infusion of catecholamines in dogs under general anaesthesia with fentanyl. The effects on intrapulmonary shunt.

Abstract

The pulmonary venous admixture, PaO2, and pulmonary and systemic haemodynamics were studied in six mongrel dogs during infusion of dobutamine (infusion rate 7.5 micrograms . kg-1 . min-1), dopamine (7.5 micrograms . kg-1 . min-1) and isoproterenol (0.1 microgram . kg-1 . min-1). Anaesthesia was performed by a single injection of Fentanyl (0.35 mg/kg). The carbon dioxide tension and body temperature were strictly maintained within limits. Only isoproterenol produced a significant change in pulmonary arterial pressure from an average of 1.2 +/- 0.4 kPa to 1.6 +/- 0.2 kPa (P less 0.05). There was no significant change in systemic haemodynamics with any of the three drugs. The use of catecholamines in dogs with healthy lungs does not induce any development in pulmonary venous admixture when haemodynamics are unchanged. Changes in these variables are dependent upon changes in pulmonary blood flow rather than being direct effects of the catecholamine.