Usefulness of the Recruitment-to-Inflation Ratio and Pulmonary Compliance for Assessing Pulmonary Recruitability in Cardiac Surgery Patients: A Prospective Study

Objective

To evaluate in cardiac surgery patients the potential for alveolar recruitment at 3 perioperative time points—after intubation, after cardiopulmonary bypass (CPB), and on arrival in the intensive care unit (ICU)—by collecting pulmonary compliance values and calculating the recruitment-to-inflation (R/I) ratio.

Design

An interventional cohort single-center study conducted in a department of anaesthesiology and critical care and an ICU

Setting

This interventional study was conducted in 41 patients undergoing noncomplex cardiac surgery. Ventilatory mechanics, blood gas analysis, and hemodynamic parameters were measured before, during, and after a lung recruitment maneuver (LRM) (3 minutes at a positive end-expiratory pressure [PEEP] of 12 cmH₂O). The R/I ratio was calculated retrospectively at 3 time points.

Participants

The study included patients scheduled for elective, nonurgent cardiac surgery requiring cardiopulmonary bypass (CPB), including coronary artery bypass grafting (CABG), valve replacement, and valve repair.

Interventions

R/I ratio measurement.

Measurements and Main Results

The proportion of recruitable patients (those with an R/I >0.5) decreased over time, from 61% (25 patients) postintubation (IOT), to 29% (12 patients) post-CPB and 17% (7 patients) in the ICU. After recruitment, lung compliance at all 3 time points was significantly higher in recruitable patients (R/I >0.5) compared to nonrecruitable patients (R/I <0.5) (p < 0.01). At all 3 time points, compliance before LRM did not differ significantly between the recruitable and nonrecruitable groups. Of the 123 LRMs performed in 41 patients, 11 (9%) were interrupted because of hemodynamic intolerance (defined as a >20% drop in mean arterial pressure).

Conclusions

In this study, an R/I ratio >0.5 identified up to 60% of patients as potentially recruitable. This parameter is particularly valuable given that PaO₂, partial pressure of oxygen in arterial blood (PaO₂), PaO₂:fraction of inspired oxygen ratio, and prerecruitment compliance did not predict a positive recruitment response. Further studies are needed to assess the utility of the R/I ratio in individualizing PEEP settings and reducing pulmonary complications in cardiac surgery patients.