Comparing Cardiac Output Differences in Patients With Fontan Physiology Between High and Low Tidal Volume Strategies:...

Single ventricle congenital heart disease patients palliated to Fontan physiology lack a ventricle to generate pulmonary blood flow. Positive pressure mechanical ventilation reduces pulmonary blood and therefore cardiac output as compared to regular, negative pressure ventilation. There is controversy as to whether lower or higher tidal volumes are optimal for mechanical ventilation.

This crossover trial aimed to determine whether higher versus lower tidal volumes would be optimal for systemic cardiac output.

The authors recruited Fontan patients < 18 years old presenting for cardiac catheterization who would require intubation and positive pressure ventilation. Patients were randomized to begin in either a high (10 mL/kg) or low (6 mL/kg) tidal volume strategy. Pressures and blood gases were obtained, the patient was transitioned to the alternate ventilation strategy, and the catheterization procedures were repeated. The authors derived a clinically significant difference of 0.7 L/min/m². Paired comparisons of systemic cardiac index, pulmonary blood flow, and vascular resistances were made between the high and low tidal volume conditions.

Thirty patients underwent the complete study protocol. Three out of nine (33%) patients who had a higher cardiac index in the high tidal volume strategy met the significant difference threshold compared to 8/19 (42%) of those who had a higher cardiac index in the low tidal volume strategy (Cohen's h = 0.186). There was no statistically significant difference in cardiac index between low (3.19 L/min/m², 95% CI 2.76-3.62 L/min/m²) and high (2.96 L/min/m², 95% CI 2.53-3.39 L/min/m²) tidal volume strategies, p = 0.062.

While there was no significant difference in cardiac index between the two ventilation strategies in the direct comparison, we did obtain data showing lower tidal volume may be favorable for maintaining cardiac index for some Fontan patients requiring positive pressure ventilation.