EVALUATION OF RESPIRATORY INDUCTIVE PLETHYSMOGRAPHY IN CONTROLLED VENTILATION - MEASUREMENT OF TIDAL VOLUME AND PEEP-INDUCED CHANGES OF END-EXPIRATORY LUNG-VOLUME

Study objective: To determine the accuracy of respiratory inductive pl ethysmography (RIP) with a respiratory monitor (Respitrace Plus; NIMS Inc., Miami) operating in the DC-mode for the measurement of tidal vol umes (VT) and positive end-expiratory pressure (PEEP)-induced changes of end-expiratory lung volume (Delta EELV) in patients with normal pul monary function, acute lung injury (ALI), and COPD during volume-contr olled ventilation. Design: Prospective comparison of RIP with pneumota chography (PT) for assessment of VT and with multibreath nitrogen wash out procedure (N-2,WO) for determination of Delta EELV as reference me thods. Setting: Mixed ICU at a university hospital. Patients: Thirty-o ne sedated and paralyzed patients: 12 patients with normal pulmonary f unction mechanically ventilated after major surgery, 10 patients with respiratory failure due to ALI, and 9 patients with a known history of COPD ventilated after surgery or because of respiratory failure due t o bronchopulmonary infection. Interventions;: Stepwise increase of PEE P from 0 to 5 to 10 cm H-2,O and reduction to 0 cm H-2,O again. On eac h PEEP level, N-2,WO was performed. Measurements and main results: The baseline drift of RIP averaged 25.4+/-29.1 mL/min but changed over a wide range even in single patient measurements. Determination of VT fo r Single minutes revealed that 66.5% and 90.0% of all values were accu rate within a range of +/-10% and +/-20%, respectively. The deviation for VT measurements between RIP and PT in patients with COPD was signi ficantly (p<0.05) higher compared to patients with ALI or normal pulmo nary function. The difference of Delta EELV between RIP and N2WO was 1 1.6+/-174.1 mt with correlation coefficients of 0.77 (postoperative an d COPD patients) and 0.86 (ALI patients). However, just 25.8% and 46.2 % were precise within +/-10% and +/-20%, respectively. Delta EELV dete rmination in COPD patients differed more between RIP and N-2,WO than i n the other groups, but this was not significant. Conclusion: In a mix ed group of patients undergoing controlled ventilation, RIP using the Respitrace Plus monitor was not consistently precise enough for quanti tative evaluation of VT and EELV when compared to our reference method s. This was most evident in patients with COPD. For long-term volume m easurements, a better control of the baseline drift of RIP should be a chieved.