Cardiac Output Measurement by Partial Carbon Dioxide Rebreathing, 2-Dimensional Echocardiography, and Lithium-Dilution Method in Anesthetized Neonatal Foals

Abstract

The objective of this study was to assess 2 noninvasive methods of measuring cardiac output (CO) in neonatal foals by comparing results to that of the lithium-dilution method. Ten neonatal foals were anesthetized and CO was manipulated by varying the depth of anesthesia and infusion of dobutamine. Concurrent CO measurements were obtained by lithium dilution (reference method), partial carbon dioxide (CO 2 ) rebreathing, volumetric echocardiography (cubic, Teichholz, Bullet, area-length, and single and biplane modified Simpson formulas), and transthoracic Doppler echocardiography. Thirty pairs of lithium-dilution/noninvasive CO measurements were taken from the 10 foals. For each method, relative bias was calculated as a percentage of the average CO. Lithium determinations of CO ranged between 3.09 and 11.1 L/min (mean Ϯ SD ϭ 6.39 Ϯ 2.1 L/min), resulting in cardiac indices ranging between 79.0 and 209 mL/kg/min (mean Ϯ SD ϭ 131 Ϯ 35.9 mL/kg/min). Relative bias of Doppler echocardiography significantly increased (P Ͻ .05), whereas that of partial CO 2 rebreathing significantly decreased (P ϭ .03) with increasing CO. Other methods were not influenced by the level of CO. Among methods not influenced by the level of CO, relative bias of the Bullet method (Ϫ4.2 Ϯ 20.9%; limits of agreement Ϫ45.2 to 36.7%) was significantly lower (P Ͻ .05) than that of each of the other noninvasive methods evaluated. Volumetric echocardiography using the Bullet method provides an accurate and noninvasive estimate of CO in anesthetized neonatal foals and warrants investigation in critically ill conscious foals.

Determination of cardiac output in neonatal foals by ultrasound velocity dilution and its comparison to the lithium dilution method

“…Other authors have determined that UDCO compared favorably with pulmonary thermodilution 17 and aortic flow‐probe models 14,25 in mice, rats, and humans 14,17,26 . The mean bias and relative bias of the current study was similar to that reported with other methods evaluating CO in foals: trans‐thoracic echocardiogram versus LiDCO (−4.2±20.9%), 11 partial carbon dioxide rebreathing versus LiDCO (−17.3±57 mL/kg/min) 2 and pulmonary thermodilution versus LiDCO (47.5±49.2±mL/kg/min) 5 . It is widely accepted that calculation of bias and precision represents the best statistical method of comparing 2 techniques measuring the same physiological variable, such as CO.…”

“…It is widely accepted that calculation of bias and precision represents the best statistical method of comparing 2 techniques measuring the same physiological variable, such as CO. However, a review of the current literature assessing CO methodologies has revealed a notable lack of consistency regarding the criteria used to determine whether a newer technique can replace or be used interchangeably with an older or more established method 11 . It was demonstrated that by combining the errors of both the test and reference method that acceptance of a new method of measuring CO should rely on limits of agreement of up to approximately ±30% 27 .…”

“…In the current study, UDCO had few observations with a relative bias >30% 27 . Consequently, UDCO can be used interchangeably with the LiDCO method 11,27 . The negative bias found in this experiment (−7.7±23.4%) indicated that the use of UDCO tended to slightly overestimate CO when compared with LiDCO values.…”

“…Other established methods such as pulmonary thermodilution are not routinely used in foals due to invasiveness, technical difficulty, and risks involved 10 . Thus, there has been growing interest in less invasive techniques for continuous measurement of CO, such as application of the Fick principle, esophageal Doppler ultrasound, thoracic bioimpedance, and arterial pulse contour analysis 2,6,11–13 …”

Effects of dexmedetomidine and xylazine on cardiovascular function during total intravenous anaesthesia with midazolam and ketamine and recovery quality and duration in horses

“…; Giguère et al. ). The technique might show higher variability than transoesophageal measurement because parallel alignment between ultrasound beam and aortic blood flow is more difficult (Young et al.…”