Hemodynamic Effects of Altering Tidal Volume During Positive Pressure Ventilation in the Fontan Circulation: A Randomized Crossover Trial.

Abstract

Background: Primary determinants of pulmonary blood flow in the Fontan circulation are low transpulmonary gradient and pulmonary vascular resistance (PVR). Changes in intrathoracic pressure during intermittent positive pressure ventilation can influence the transpulmonary gradient, PVR, pulmonary blood flow, and cardiac output. The aim of this study was to evaluate the effect of low (5 mL/kg) versus high (10 mL/kg) tidal volume (V_T) ventilation on Fontan circulation hemodynamics.

Method: Postoperative patients with a Fontan circulation were enrolled in this single-center, randomized crossover trial. Patients, randomized to group 1 or 2, underwent a ventilation study sequence (baseline ventilation [7 mL/kg], then high V_T [10 mL/kg] or low V_T [5 mL/kg], then washout ventilation [7 mL/kg], followed by low [5 mL/kg] or high V_T [10 mL/kg]) in the operating room at the end of the cardiac surgical procedure. Respiratory, hemodynamic, and transesophageal (TEE) measurements were recorded after 5 min in each ventilation condition. The primary aim of this study was to evaluate the effect of low V_T ventilation (5 mL/kg) versus high V_T ventilation (10 mL/kg) on transpulmonary gradient (Fontan pressure minus left atrial pressure). The secondary aim was to compare TEE measurements of pulmonary blood flow, stroke volume, and Fontan flow between low and high V_T ventilation. We also compared standard hemodynamic and ventilation parameters for all ventilation conditions. Analysis was of paired data, calculating the between-treatment difference within participants across ventilation conditions.

Results: Eleven patients were included in the final data analysis with a median [IQR] age of 5 [4, 11] years and weight of 16.3 [13.8, 31.6] kg. The mean (±SD) peak inspiratory pressure during low and high V_T ventilation was 15.3 (±2.9) cmH₂O and 22.2 (±3.7) cmH₂O, respectively (difference -6.9, 95% CI -7.8, -5.9, p < 0.001). The mean airway pressure during low and high V_T ventilation was 7.3 ± 0.8 and 8.7 ± 0.9 (difference -1.5, 95% CI -2.1, -0.8, p = 0.001) with a mean inspiratory time of 0.62 (±0.22) s and 1.21 (±0.55) s (difference -0.59, 95% CI -0.84, -0.34, p < 0.001), respectively. During low V_T ventilation, the mean Fontan pressure was 13.3 (±1.8) mmHg compared to 12.3 (±2.5) mmHg for high V_T ventilation (difference 0.8, 95% CI -0.5, 2.1, p = 0.18). The mean transpulmonary gradient was 7.0 ± 1.3 mmHg compared to 6.8 ± 1.2 mmHg during low and high V_T ventilation, respectively (difference 0.2, 95% CI -0.2, 0.6, p = 0.21). We found no significant differences between low and high V_T ventilation in TEE measures of pulmonary blood flow, stroke volume, and Fontan flow.

Conclusions: This randomized, crossover pilot trial of Fontan patients showed that a low V_T ventilation (5 mL/kg) resulted in significantly lower peak and mean airway pressure compared with a high V_T ventilation (10 mL/kg). However, there were no significant changes in transpulmonary gradient, mean Fontan pressure, or TEE parameters of stroke volume, pulmonary blood flow, or Fontan flow.

Clinical trials registration number: NCT04633343.

Principal investigator: Manchula Navaratnam.

Date of registration: November 11, 2020. Clinical Trials Registration Registry URL: https://clinicaltrials.gov/study/NCT04633343?term=Fontan%20ventilation&rank=3.

Prior presentations: Congenital Cardiac Anesthesia Society Annual Meeting Top Oral Abstract Presentation.

Presenter: Alexander R Schmidt, March 30th, 2023.