Background: The computerized noninvasive measurement of respiratory mechanics enables new prospects in the study of respiratory physiopathology in surgical repair of large incisional hernias.
Study design: We studied 10 patients with COPD ventilated with a Servo Ventilator 900C. We measured inspiratory flow by means ofa pneumotacograph, the volume by integrating the flow signal, and esophageal and airway opening pressure by means of two differential pressure transducers (an esophageal balloon measures, separately, chest wall and lung mechanical properties). The signals were sent by an analogic-digital converter to a personal portable computer to be analyzed. We calculated compliance of total respiratory system (Crs), chest wall (Ccw), and lung (CI); maximum resistance of the total respiratory system (Rmax, Rs), chest wall (Rmax, w), and lung (Rmax, L); and work of breathing (Wob). Statistics were performed using one-way analysis of variance and p = 0.05 was considered significant.
Results: At the closure of the peritoneum a reduction of Crs and Wob was recorded in seven patients in whom a PTFE prosthesis widening the abdominal cavity was used to restore the baseline value. Variations in respiratory compliance are from variations in Ccw with unaffected CI (Ccw varied from 0.180 to 0.130 L/cmH2O at peritoneal closure and from 0.130 to 0.170 L/cmH2O by prosthetic peritoneal widening). Respiratory resistances remained unchanged (11.3 cmH2O/ L/s) at any time of measurement.
Conclusions: The intraoperative assessment of respiratory mechanics is useful to evaluate and eventually to decrease the mechanical workload (prosthesis widening peritoneum or fascia incisions). The passive mechanical work performed by the ventilator needs to be kept constant or no higher than 10% basic data: if these conditions are maintained, mostly in patients with COPD, there is no risk of respiratory muscular fatigue during the postoperative period.