Evaluation of transpulmonary ultrasound dilution cardiac output in piglets: accuracy, precision and trending ability with room temperature injectate

Objective Transpulmonary ultrasound dilution (TPUD) is a minimally invasive technique to measure cardiac output (CO) using a 1 mL kg -1 isotonic 37 degrees C saline injectate in-dicator. The objective was to evaluate the performance of TPUD using a room temperature saline injectate. Study design Prospective experimental trial. Animals A total of seven anesthetized male Yorkshire piglets.Methods Piglets aged 1 month and weighing 7.7-9.0 kg were anesthetized with detomidine-ketamine- hydromorphone-isoflurane and a pulmonary artery flow probe (PAFP) placed via a median sternotomy. The thoracic cavity remained open during measurement of CO by PAFP and TPUD. The TPUD indicators of 1 mL kg -1 0.9% saline at 37 degrees C and 20 degrees C were compared during infusions of phen-ylephrine and dobutamine, blood withdrawal and replace-ment. Bias, limits of agreement (LoAs) and percentage error (PE) between each iteration of PAFP and TPUD were measured with Bland -Altman plots. Trending ability via concordance, angular bias and radial LoA were compared. Results Bland -Altman plots showed negligible bias with varying LoAs. PEs of 22% and 38% were found for 37 degrees C and 20 degrees C saline injectates, respectively. In the four -quadrant plots, the concordance rate was 94% and 100% for measurements obtained with 37 degrees C and 20 degrees C saline injectates, respectively. Angular bias for both were < +/- 5 degrees, with radial LoA < +/- 7 degrees. Conclusions TPUD was accurate when using 1 mL kg -1 of isotonic saline at 37 degrees C in a range of CO within 0.2-0.8 L minute -1, and it reliably tracked positive and negative changes in CO. Room temperature (20 degrees C) indicator was less accurate but equally able to track direction of changes in CO.