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 65-80 mmHg (normotension) and <65 mmHg (hypotension) in dogs undergoing elective surgery. Eight dogs were pre-medicated with acepromazine (0.05 mg/kg, IM), tramadol (4 mg/kg, IM) and atropine (0.03 mg/kg, IM), followed by anaesthetic induction with propofol (3-5 mg/kg IV) and maintenance with isoflurane associated with a continuous infusion rate of fentanyl (bolus of 3 μg/kg followed by 0.3 μg/kg/min). The CO was measured by TEE (CO_TEE) and TD (CO_TD) at the end of expiration during normotension and hypotension (induced by isoflurane).

Results: There was a strong positive correlation between CO_TEE and CO_TD ​​(r = 0.925; P < 0.0001). The bias between CO_TD and CO_TEE was 0.14 ± 0.29 L/min (limits of agreement, -0.44 to 0.72 L/min). The percentage error of CO measured by the two methods was 12.32%. In addition, a strong positive correlation was found between CO_TEE and CO_TD 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.

Keywords: Aortic flow; Doppler; Minimally invasive; Swan Ganz; Transgastric.

Fig. 1

Transgastric view of the left ventricular outflow tract assessed by transoesophageal echocardiography. a The almost parallel alignment between the volume sampled by the pulsate Doppler and the aortic blood flow (arrow) was obtained through this view. b The velocity-time integral (VTI) of aortic flow was calculated by the outline of the aortic blood flow

Fig. 2

Graphical dispersion of cardiac output (CO) values obtained by transoesophageal echocardiography (TEE) and the thermodilution technique (TD) in anaesthetised dogs undergoing surgery

Fig. 3

Bland-Altman analysis of cardiac output (CO) measured by transoesophageal echocardiography (TEE) and thermodilution technique (TD) in eight dogs with a mean arterial pressure of 65–80 mmHg (normotension) and <65 mmHg (hypotension) arterial pressure. All comparisons were within the thresholds of agreement (dotted line)

Fig. 4

Cardiac output measured in anaesthetised dogs with an adequate (normotension) and low (hypotension) arterial pressure during surgery. The line within the box indicates the median of the observations. The top and low parts of the box indicate the first and the third quartile, respectively. There were no significant differences between the cardiac output measured by the thermodilution technique (TD) and the transoesophageal echocardiography (TEE) during arterial normotension (P = 0.9612) and hypotension (P = 0.0761), according to the results obtained with the Student paired t-test