Clinical monitoring of cardiac output assessed by transoesophageal echocardiography in anaesthetised dogs: A comparison with the thermodilution technique

Abstract

Background: Cardiac output (CO) is an important haemodynamic parameter to monitor in patients during surgery. However, the majority of the techniques for measuring CO have a limited application in veterinary practice due to their invasive approach and associated complexity and risks. Transoesophageal echocardiography (TEE) is a technique used to monitor cardiac function in human patients during surgical procedures and allows CO to be measured non-invasively. This prospective clinical study aimed to compare the transoesophageal echocardiography using a transgastric view of the left ventricular outflow tract (LVOT) and the thermodilution (TD) technique for the assessment of CO during mean arterial pressure of 65-80mmHg (normotension) and <65mmHg (hypotension) in dogs undergoing elective surgery. Eight dogs were pre-medicated with acepromazine (0.05mg/kg, IM), tramadol (4mg/kg, IM) and atropine (0.03mg/kg, IM), followed by anaesthetic induction with propofol (3-5mg/kg IV) and maintenance with isoflurane associated with a continuous infusion rate of fentanyl (bolus of 3 μg/kg followed by 0.3μg/kg/min). The CO was measured by TEE (COTEE) and TD (COTD) at the end of expiration during normotension and hypotension (induced by isoflurane). Results: There was a strong positive correlation between COTEE and COTD (r=0.925; P<0.0001). The bias between COTD and COTEE was 0.14±0.29L/min (limits of agreement, -0.44 to 0.72L/min). The percentage error of CO measured by the two methods was 12.32%. In addition, a strong positive correlation was found between COTEE and COTD during normotension (r=0.995; P<0.0001) and hypotension (r=0.78; P=0.0223). Conclusions: The results of this study indicated that the transgastric view of the LVOT by TEE was a minimally invasive alternative to clinically monitoring CO in dogs during anaesthesia. However, during hypotension, the CO obtained by TEE was less reliable, although still acceptable.