Abstract: Ventilation and perfusion matching have been well described, but never with clinically relevant parameters. We assumed that ventilatory approximate of cardiac output termed function cardiac output (fCO) calculated as a multiple product of MV * AFF (MV = Minute ventilation, AFF = EtCO2 to PaCO2 ratio) provides estimation of CO. We hypothesized that the product AFF * MV, termed functional CO (fCO), closely approximate measured CO in a porcine endotoxemic shock model.

Methodology: We performed secondary data analysis of a parent study of juvenile pigs in whom shock was induced with lipopolysaccharide from Escherichia Coli along with measurement of ultrasound dilution CO (UdCO) via CO Status (Transonic Systems Inc, New York). fCO was computed using MV and EtCO2 from Phillips Respironics NM3 device, and PaCO2 from a carotid artery catheter. Paired fCO and UdCO were available at baseline and at five 30-minute intervals after shock criteria were met. Paired measures we compared using Pearson’s regression, mixed-effects linear regression, Bland-Altman analysis, and equivalence with a priori margins of 30%.

Results: A total of 40 paired measurements of fCO and UdCO were obtained from 7 pigs. Mean (±SD) fCO and UdCO were 2.8 L/min (±0.86) and 2.7 L/min (±1.1), respectively. Pearson’s correlation coefficient between fCO and UdCO was r=0.51 (95% CI, 0.24 to 0.71), while mixed-effects correlation coefficient accounting for repeated measures within each pig was r=0.74 (95% CI, 0.53 to 0.86). The Bland-Altman plot showed fCO over-estimated UdCO at lower values and under-estimated UdCO at higher values. The mean ratio of fCO to UdCO was 1.08 (90% CI: 0.86 to 1.35).

Conclusion: fCO showed moderate correlation and agreement with UdCO in a porcine endotoxemic shock model. However, we could not exclude equivalence with a potential for fCO to overestimate UdCO, especially when CO is low. Further study is needed to determine the validity of fCO in human patients during health and, especially, shock states.

Jigar Chauhan is an assistant professor of pediatrics at Nemours Children's Hospital, Delaware, USA affiliated to Thomas Jefferson University, Philadelphia, Pennsylvania, USA. Dr. Chauhan serves as a faculty at a large 24 bed pediatric ICU at the hospital. His research interests include prediction of hemodynamics (CO) based on gas exchange, as a novel principle in physiology and medicine. He has this concept at society of critical care medicine annual congress and pediatric cardiac intensive care society conference, and continue to work of getting human data for ongoing work in the field.