Respiratory physiopathology in surgical repair for large incisional hernias of the abdominal wall

BACKGROUND: The computerized noninvasive measurement of respiratory mechani cs enables new prospects in the study of respiratory physiopathology in sur gical repair of large incisional hernias. STUDY DESIGN: We studied 10 patients with COPD ventilated with a Servo Vent ilator 900C. We measured inspiratory flow by means of a pneumotacograph, th e volume by integrating the flow signal, and esophageal and airway opening pressure by means of two differential pressure transducers (an esophageal b alloon measures, separately, chest wall and lung mechanical properties). Th e signals were sent by an analogic-digital converter to a personal portable computer to be analyzed. We calculated compliance of total respiratory sys tem (Crs), chest wall (Ccw), and lung (Cl); maximum resistance of the total respiratory system (Rmax, Rs), chest wall (Rmax, w), and lung (Rmax, L); a nd work of breathing (Wob). Statistics were performed using one-way analysi s of variance and p = 0.05 was considered significant. RESULTS: At the closure of the peritoneum a reduction of Crs and Wob was re corded in seven patients in whom a PTFE prosthesis widening the abdominal c avity was used to restore the baseline value. Variations in respiratory com pliance are from variations in Ccw with unaffected Cl (Ccw varied from 0.18 0 to 0.130 L/cmH(2)O at peritoneal closure and from 0.130 to 0.170 L/cmH(2) O by prosthetic peritoneal widening). Respiratory resistances remained unch anged (11.3 cmH(2)O/L/s) at any time of measurement. CONCLUSIONS: The intraoperative assessment of respiratory mechanics is usef ul to evaluate and eventually to decrease the mechanical workload (prosthes is widening peritoneum or fascia incisions). The passive mechanical work pe rformed by the ventilator needs to be kept constant or no higher than 10% b asic data: if these conditions are maintained, mostly in patients with COPD , there is no risk of respiratory muscular fatigue during the postoperative period. (J Am Coll Surg 2001; 192:298-304. (C) 2001 by the American Colleg e of Surgeons).