Erroneous calibration of esophageal pressure in case of airway closure

Abstract

Airway closure results in a lack of communication between proximal and distal airways unless the airway pressure (Paw) overcomes the airway opening pressure (AOP). This has been described in patients undergoing mechanical ventilation with acute respiratory distress syndrome, obesity, hydrostatic pulmonary edema and during cardiopulmonary resuscitation. In these categories of patients, esophageal pressure (Pes) can guide the personalization of mechanical ventilation and calibration of the esophageal balloon is necessary to obtain reliable Pes measurements. The impact of airway closure has never been envisaged. This study investigated the impact of airway closure on the calibration of the esophageal balloon by the ∆Paw/∆Pes following a positive pressure occlusion test during passive mechanical ventilation. The calibration test was performed in twelve human cadavers with airway closure at end-expiration at different levels of positive end-expiratory pressure (PEEP) and at end-inspiration. The ∆Paw/∆Pes measured at end-expiration and at end-inspiration were significantly different when total PEEP was lower than AOP (estimated means 0.42 [0.40; 0.44] vs. 0.95 [0.92; 0.97], P < 0.001), while this difference was not observed when total PEEP was higher than AOP (estimated means 0.99 [0.92; 1.05] vs. 0.99 [0.92; 1.06], P = 0.854). These results were corroborated by observations during esophageal balloon calibration in two patients requiring Pes monitoring for clinical management. In case of airway closure, compression of the chest is not fully transmitted to the airways. This can lead to a conspicuous underestimation of the ∆Paw/∆Pes and poor reliability of this monitoring technique when the test takes place below AOP. Our results favor a positive pressure occlusion test performed during an end-inspiratory occlusion as the new standard of operative procedures for positioning and calibrating the esophageal balloon.

Keywords: ARDS; Acute respiratory distress syndrome; Airway closure; Airway opening pressure; Baydur test; Calibration; End-expiratory occlusion; End-inspiratory occlusion; Esophageal pressure; Positive pressure occlusion test.

Fig. 1

50 positive pressure occlusion tests performed by manual external compression during end-expiratory (end-exp.) versus end-inspiratory (end-insp.) occlusion at different positive end-expiratory pressure (PEEP) levels or trunk inclinations (0° vs. 30°) in 12 human cadavers. Results are presented overall (left) or sorted by total PEEP (PEEP_tot) below or above the airway opening pressure (AOP, right). P value stands for linear mixed effects model significance level. ∆Paw/∆Pes, ratio of changes in airway pressure over changes in esophageal pressure during positive pressure occlusion test. The dashed lines indicate the 0.8–1.2 target range for ∆Paw/∆Pes

Fig. 2

Esophageal pressure (Pes) calibration in two patients with airway closure (dashed lines). A In Patient #1, admitted to the Intensive Care Unit for acute respiratory distress syndrome associated to COVID-19 (c-ARDS), a low-flow inflation (left panel) revealed the presence of airway opening pressure (AOP). An esophageal balloon was correctly placed at the chest x-ray assessment. Although many attempts, it was not possible to obtain a ratio between airway and esophageal pressure swings (∆Paw/∆Pes) within 0.8 and 1.2 when performing the calibration maneuver (positive pressure occlusion test) during an end-expiratory occlusion starting from a total positive end-expiratory pressure (PEEP) of 7 cmH₂O (middle panel). However, when the test was performed during an end-inspiratory occlusion (right panel) from a plateau pressure of 24 cmH₂O, the calibration ratio was within the recommended values. B In Patient #2, requiring veno-arterial extracorporeal membrane oxygenation (V-A ECMO) after out-of-hospital cardiac arrest, AOP was found at 22 cmH₂O. An esophageal balloon was correctly placed at the chest x-ray assessment. A positive pressure occlusion test was performed at end-expiration to verify the correct positioning of the esophageal catheter. Total PEEP (extrinsic plus intrinsic) was measured during the occlusion. At 0 cmH₂O of extrinsic PEEP (total PEEP 10 cmH₂O), significant swings in Pes during chest compressions were observed in absence of correspondent changes in Paw (left panel). Repeating the calibration test after extrinsic PEEP was increased to 10 cmH₂O (total PEEP 13 cmH₂O), limited swings in Paw started to appear (middle panel). After a further increase of PEEP at 17 cmH₂O (total PEEP 20 cmH₂O), a clear swing in Paw was observed and was of the same size of the Pes swing. This allowed us to achieve a reliable ∆Paw/∆Pes ratio and balloon calibration (right panel)