The effects of halothane and isoflurane on cardiovascular function in dorsally recumbent horses undergoing surgery.

Author(s): Blissitt KJ, Raisis AL, Adams VJ, Rogers KH, Henley WE, Young LE

Affiliation(s): Department of Veterinary Clinical Studies, Royal (Dick) School of Veterinary Studies, Easter Bush Veterinary Centre, Near Roslin, Midlothian, UK.

Publication date & source: 2008-02-18, Vet Anaesth Analg., [Epub ahead of print]

Objective To determine the haemodynamic effects of halothane and isoflurane with spontaneous and controlled ventilation in dorsally recumbent horses undergoing elective surgery. Study design Prospective randomized clinical trial. Animals Twenty-five adult horses, body mass 487 kg (range: 267-690). Methods Horses undergoing elective surgery in dorsal recumbency were randomly assigned to one of four treatment groups, isoflurane (I) or halothane (H) anaesthesia, each with spontaneous (SB) or controlled ventilation (IPPV). Indices of cardiac function and femoral arterial blood flow (ABF) and resistance were measured using transoesophageal and transcutaneous Doppler echocardiography, respectively. Arterial blood pressure was measured directly. Results Four horses assigned to receive isoflurane and spontaneous ventilation (SBI) required IPPV, leaving only three groups for analysis: SBH, IPPVH and IPPVI. Two horses were excluded from the halothane groups because dobutamine was infused to maintain arterial blood pressure. Cardiac index (CI) was significantly greater, and pre-ejection period (PEP) shorter, during isoflurane compared with halothane anaesthesia with both spontaneous (p = 0.04, p = 0.0006, respectively) or controlled ventilation (p = 0.04, p = 0.008, respectively). There was an association between CI and PaCO(2) (p = 0.04) such that CI increased by 0.45 L minute(-1)m(-2) for every kPa increase in PaCO(2). Femoral ABF was only significantly higher during isoflurane compared with halothane anaesthesia during IPPV (p = 0.0006). There was a significant temporal decrease in CI, but not femoral arterial flow. Conclusion The previously reported superior cardiovascular function during isoflurane compared with halothane anaesthesia was maintained in horses undergoing surgery. However, in these clinical subjects, a progressive decrease in CI, which was independent of ventilatory mode, was observed with both anaesthetic agents. Clinical relevance Cardiovascular function may deteriorate progressively in horses anaesthetized for brief (<2 hours) surgical procedures in dorsal recumbency. Although cardiovascular function is superior with isoflurane in dorsally recumbent horses, the need for IPPV may be greater.