A pilot study on the hemodynamic effects of negative pressure ventilation in patients after cardiac surgery focussing on right ventricular function

Abstract

Right ventricular dysfunction and right ventricular failure are important complications in cardiac surgical patients and typically observed after complex surgical cases. Treatment options for optimizing the hemodynamic status in patients presenting with these complications are limited. Negative pressure ventilation has been shown to ameliorate the effects of conventional positive pressure ventilation (PPV) and to improve cardiac output in patients with Fontan circulation and patients undergoing coronary artery bypass surgery. No data are available on the effects of negative pressure ventilation on systemic hemodynamics and right heart function after complex on-pump cardiac surgery. Hypothesis of the present study is that right ventricular function improves under condition of negative pressure ventilation after complex on-pump surgery. Thirty patients after complex cardiac surgery were examined using basic hemodynamic monitoring, transesophageal ultrasound, a 3rd generation pulmonary artery catheter, cerebral oximetry and arterial and venous blood gases. The first 15 patients were ventilated for 15 min using standard PPV followed by 15 min of extrathoracal continuous negative pressure ventilation (CNPV) combined with PPV, and 15 min of extrathoracal biphasic negative pressure ventilation (BCV, biphasic cuirass ventilation) combined with an as far as possible reduced PPV. In the second 15 patients, the sequence of negative pressure ventilation was changed and BCV was performed before CNPV. Finally, every patient was ventilated for 15 min with standard PPV again. A full dataset of hemodynamics and a respiratory dataset was collected during each observation period. CNPV und BCV reduced central venous pressure and pulmonary artery occlusion pressure by 2 mmHg. During BCV cardiac index increased by + 24% (+ 0.5 l/min/m²; 95% CI 0.2-0.8, p = 0.001) through an increase of stroke volume index by + 24% (p = 0.0003) without change of heart rate. This was accompanied by an increase of right ventricular ejection fraction (+ 18%, p = 0.008), pulmonary arterial pulsatility index (+ 30%, p = 0.0001), left ventricular ejection fraction (+ 15%, p = 0.01), and oxygen delivery DO₂ (+ 13%, p = 0.0006). Posthoc analysis in patients with reduced stroke volume index (< 27 ml/m² prior to the start of the study) revealed that mixed venous oxygen saturation and cerebral oxygen saturation increased by 7% (p = 0.005/p = 0.006). No adverse effects were observed. While CNPV has only moderate hemodynamic effects by reducing cardiac filling pressure, BCV improves systemic and right ventricular hemodynamics as well as global oxygen balance in patients after complex cardiac surgery. During both negative pressure ventilation modes, no immediate adverse events could be observed. These findings justify investigations if these treatment modalities may impact clinical outcomes in patients with right ventricular dysfunction or failure.Trial registration clinicaltrials.gov ID: NCT06088966, registered October 3rd, 2023.

Keywords: Cardiac surgery; Heart failure; Hemodynamic optimization; Negative pressure ventilation; Right ventricular failure.

Fig. 1

Consort chart.

Fig. 2

sequence of protocol steps.

Fig. 3

Changes of measurements via PAC over the time under condition of CNPV and BCV on the left and 15 min of conventional PPV as final treatment of every study on the right. All data is presented as relative changes referring to initial measurement before any treatment. Depicted are measurements of pulmonary artery catheter as percent of initial measurement under conditions of PPV (%) over the time. Different coloured curves show different ventilation modes. Ventilation modes are 15 min of continous negativ pressure ventilation and PPV (CNPV), 15 min of biphasic cuirass ventilation with reduced positive pressure ventilation (BCV) and 15 min of usual positive pressure ventilation as ending of treatment in every single patient (PPV); error bars show ± SEM; n = 30; compared to initial measurement under PPV: * = p < 0.05; ** = p < 0.005.