MIDAZOLAM-FENTANYL-ISOFLURANE ANESTHESIA IS SUITABLE FOR HEMODYNAMIC AND FLUID BALANCE STUDIES IN PIGS

The domestic pig is a useful model in certain areas of biomedical rese arch. Effective use of this species is often encumbered by lack of ref erence values in conscious as well as anaesthetized animals. Anaesthes ia itself influences physiological and biological variables; the anaes thetic technique often affects experimental results. The relationship between anaesthesia and haemodynamics is well characterized in man, bu t less established in pigs. We studied the effect of midazolam-fentany l-isoflurane anaesthesia in six immature, male, domestic pigs (Norwegi an landrace). Haemodynamic variables (heart rate, arterial systolic, m ean, diastolic pressures, pulmonary systolic, mean, diastolic pressure s, pulmonary capillary wedge pressure), tissue perfusion, lymph flow ( thoracic duct) were recorded for 3 h in animals with open chest throug h midline sternotomy. Variables relevant to fluid balance, e.g. inters titial hydrostatic pressure (Pi), serum-colloid osmotic pressure (s-CO P) and serum-albumin (s-albumin) and -protein (s-protein) concentratio ns were measured. With the chosen anaesthetic technique haemodynamic v ariables, including lymph flow, and laboratory variables remained cons tant during the study period. Most variables were similar to condition s in humans. In contrast to adult humans exposed to the same anaesthet ic technique, these pigs had lower haemoglobin-, s-albumin- and s-prot ein concentrations. A finding which may reflect immaturity. Liver and lung perfusion decreased significantly during the study period whereas perfusion of the other organs studied remained constant. Lack of resp onses to defined noxious stimuli during the study period suggest adequ ate analgesia. We conclude that midazolam, fentanyl and isoflurane pro vide cardiovascular stability including normal microvascular fluid exc hange, which are essential elements for securing the duality of result s obtained during cardiovascular research in anaesthetized pigs.