Conventional monitoring is not sufficient to assess respiratory effort during assisted ventilation

Objective: Study the relationship and concordance between calculated respiratory effort using the signals of the ventilator (Pmus) and that measured in esophageal pressure (Pes) on mechanical ventilation with different levels of respiratory assistance.

Design: Prospective cohort study.

Ambit: Intensive Care Unit of 2 universitary hospitals. Patients Patients on weaning time.

Procedure: Airway, esophageal and respiratory flow were recorded on CPAP, assist volume control (ACV) and pressure support (PS), with complete (ACV1,PS1) and partial assistance (ACV5,PS5).

Measurement: respiratory variations of Pes and Pmus (Δ: cmH₂O) and pressure time product (PTPm: cmH₂O·s/m).

Results: Fourty one records were studied, the assistance was in CPAP of 5cmH2O, PS1 of 15±5 reduced to 9±4cmH₂O. In ACV1 the inspiratory flow was 1±0.2l/s, reduced to 0.49±0.1l/s for ACV5. The increase in respiratory assistance decreases respiratory effort, measured in Delta Pes (CPAP, ACV5, ACV1, PS5, PS1): 11±3, 6±3, 5±3, 9±6, 7±7 and in Pmus 16±5, 10±6, 5±3, 10±6, 5±4cmH₂O (P<.001). The PTP per minute measured in Pes: 213±87, 96±91, 23±24, 206±121, 108±100 (P=.001) and in Pmus: 293±117, 156±84, 24±32, 233±121, 79±90 (P<.001). The measurements in Pes and Pmus showed the following correlation, in Delta: 0.72 and PTPm, 0.87. The Bland-Altman analysis indicates that the difference between Delta Pes-Pmus can be 16 and the PTPm of 264 and the systematic error in Delta: -0.98±4.4 and PTPm -23.69±66.3cmH₂O·s/m.

Conclusions: Calculated and measured parameters of respiratory effort showed unacceptable differences in clinical practice.