The association of modifiable mechanical ventilation settings, blood gas changes and survival on extracorporeal membrane oxygenation for cardiac arrest

Abstract

Research question: Given the relative independence of ventilator settings from gas exchange and plasticity of blood gas values during extracorporeal cardiopulmonary resuscitation (ECPR), do mechanical ventilation parameters and blood gas values influence survival?

Methods: Observational cohort study of 7488 adult patients with ECPR from the Extracorporeal Life Support Organization (ELSO) Registry. We performed case-mix adjustment for severity of illness and patient type using generalized estimating equation logistic regression to determine factors associated with hospital survival accounting for clustering by center, standardizing variables by 1 standard deviation (SD) of their values. We examined non-linear relationships between ventilatory and blood gas values with hospital survival.

Results: Hospital survival was decreased with higher PaO₂ on ECMO (OR 0.69, per 1SD increase [95% CI 0.64, 0.74]; p < 0.001) and with any relative changes in PaCO₂ (pre-arrest to on-ECMO) in a non-linear fashion. Survival was worsened with any peak inspiratory pressure >20 cmH₂0 (OR 0.69, per 1SD [0.64, 0.75]; p < 0.001) and above 40% fraction of inspired oxygen (OR 0.75, per 1SD [0.69, 0.82]; p < 0.001), and with higher dynamic driving pressure (OR 0.72, per 1 SD increase [0.65, 0.79]; <0.001). Ventilation settings and blood gas values varied widely across hospitals, but were not associated with annual hospital ECPR case volume.

Conclusion: Lower ventilatory pressures, avoidance of hyperoxia, and relatively unchanged CO₂ (pre- to on-ECMO) were all associated with survival in patients after ECPR, yet varied across hospitals. Our findings represent potential targets for prospective trials for this rapidly growing therapy to test if these associations have causality.

Keywords: Blood gas changes; Extracorporeal cardiopulmonary resuscitation; Intensive care; Management; Mechanical ventilation; Post-cannulation care; Ventilation; Ventilatory management.

Figure 1. Enrollment Flowchart

Patient filtering for this study using data from the Extracorporeal Life Support Organization Abbreviations: Patient selection method for adult extracorpoeral cardiopulmonary resuscitation (ECPR) from the Extracorporeal Life Support Organization Registry

Figure 2. Predicted probability of hospital survival by ventilator peak inspiratory pressure at 24 hours of ECMO.

Case-mix adjusted predicted probability of hospital survival. Red line: Predicted survival curve across subjects by absolute values of ventilator peak inspiratory pressure (centimeters of water [cmH₂O]) using adjusted quadratic model. Grey dots: Predicted hospital survival for individual subjects. Black dots: Observed hospital survival for individual subjects. Abbreviations: ECMO-extracorporeal membrane oxygenation.

Figure 3. Predicted probability of hospital survival by delta P_aCO₂ starting ECMO.

Case-mix adjusted predicted probability of hospital survival. Red line: Predicted survival curve across subjects by absolute values of delta P_aCO₂ (24 hour values minus pre-arrest values) (in millimeters of mercury [mmHg]) using adjusted quadratic model. Grey dots: Predicted hospital survival for individual subjects. Black dots: Observed hospital survival for individual subjects. Abbreviations: ECMO-extracorporeal membrane oxygenation. P_aCO₂: arterial pressure of carbon dioxide.

Figure 4. Predicted probability of hospital survival by P_aO₂ at 24 hours of ECMO.

Case-mix adjusted predicted probability of hospital survival. Red line: Predicted survival curve across subjects by absolute values of P_aO₂ (in millimeters of mercury [mmHg]) at 24 hours of ECMO using adjusted quadratic model. Grey dots: Predicted hospital survival for individual subjects. Black dots: Observed hospital survival for individual subjects. Abbreviations: ECMO-extracorporeal membrane oxygenation. P_aO₂: arterial pressure of oxygen.