Authors: Hedov J et al.
Anesthesiology, February 25, 2026, 10.1097/ALN.0000000000006012
This experimental study evaluated how capnodynamic cardiac output monitoring behaves in the presence of a cardiac shunt. Capnodynamic monitoring estimates effective pulmonary blood flow (EPBF) using ventilatory variations in carbon dioxide elimination. Under normal physiologic conditions without significant shunts, EPBF approximates cardiac output. However, in patients with congenital heart disease or intracardiac shunts, it is unclear whether EPBF reflects pulmonary blood flow or systemic blood flow.
The investigators used a porcine model to simulate a left-to-right aorto-pulmonary shunt. Ten mechanically ventilated pigs underwent surgical construction of an artificial shunt between the aorta and pulmonary artery. This allowed the researchers to manipulate the proportion of shunt flow and measure the relationship between capnodynamic EPBF, systemic blood flow (Qs), and pulmonary blood flow (Qp).
Simultaneous measurements were performed at different shunt fractions. Agreement between EPBF and both systemic and pulmonary blood flow was evaluated using bias analysis, limits of agreement, percentage error, and correlation modeling.
When the shunt was open, EPBF showed relatively close agreement with systemic blood flow. The bias between EPBF and systemic blood flow was approximately 0.24 L/min, with a mean percentage error of about 30%. Concordance between these measurements was relatively strong, with Lin’s concordance correlation coefficient of 0.79.
In contrast, EPBF showed poorer agreement with pulmonary blood flow. The bias between EPBF and pulmonary blood flow was −1.28 L/min with a higher percentage error of approximately 38%. Concordance between EPBF and pulmonary flow was substantially weaker, with a correlation coefficient of 0.43.
Mixed-effects statistical modeling demonstrated that increases in EPBF were associated with increases in both systemic and pulmonary blood flow, but the relationship with systemic flow was stronger and more consistent. A 1.0 L/min increase in EPBF corresponded to a 1.0 L/min increase in systemic blood flow but approximately a 1.86 L/min increase in pulmonary blood flow.
These findings indicate that in the presence of a left-to-right shunt, capnodynamic EPBF more closely reflects systemic blood flow rather than pulmonary blood flow.
This distinction is clinically important because systemic blood flow is a key determinant of tissue oxygen delivery. In patients with congenital heart disease or shunt physiology, clinicians must often determine whether monitoring tools reflect systemic circulation or pulmonary circulation when guiding hemodynamic management.
The authors conclude that capnodynamic monitoring may still provide clinically meaningful estimates of systemic cardiac output even when significant shunt physiology is present. However, further studies in human patients with congenital heart disease will be necessary to confirm these findings.
What You Should Know
Capnodynamic monitoring estimates cardiac output by measuring carbon dioxide elimination during mechanical ventilation.
In patients without cardiac shunts, effective pulmonary blood flow approximates cardiac output.
In congenital heart disease with left-to-right shunts, it has been unclear whether capnodynamic monitoring reflects systemic or pulmonary flow.
This animal study suggests that capnodynamic monitoring more closely reflects systemic blood flow.
These findings may support the use of capnodynamic monitoring in complex cardiac physiology.
Key Points
Experimental study using a porcine model with surgically created aorto-pulmonary shunts.
Capnodynamic monitoring estimated effective pulmonary blood flow (EPBF).
EPBF showed better agreement with systemic blood flow than with pulmonary blood flow.
Bias between EPBF and systemic blood flow was small with acceptable percentage error.
Agreement between EPBF and pulmonary blood flow was significantly weaker.
Capnodynamic monitoring may provide useful estimates of systemic cardiac output even in the presence of left-to-right shunts.
Thank you to Anesthesiology for allowing us to summarize this article.