The Science Journal of the American Association for Respiratory Care

1996 OPEN FORUM Abstracts

A COMPARISON OF TWO DIFFERENT MAXIMAL INSPIRATORY PRESSURE PROCEDURES

C. Worth Brooks. Ir., MEd. RRT Frank Dennison, MEd, RPFT, RRT, Shelley C. Mishoe, PhD, RRT, Rob Gillum, BS, RRT, Rick Hall, BS, RRT, Arthur Taft, MHS, RRT. Medical College of Georgia, Augusta, GA

The purpose of measuring maximal inspiratory pressure (MIP) is to determine respiratory muscle strength. Research literature suggests a MIP that is greater than -30cmH_{2}O indicated adequate respiratory muscle strength to sustain spontaneous ventilation and provide an effective cough. The purpose of this study was to compare two clinical methods of measuring MIP. The study included twenty mechanically ventilated patients in ICUs who were deemed weanable by the attending physician. Methods: The patients were tested by two methods using a coin toss to determine order of assignment for each method. One method, the manual method (MM), involved taking the patient off the Puritan Bennett 7200 (PB) Ventilator and performing the MIP with an OEM Manometer and Nif-Tee Non-Rebreathing T-Piece to permit exhalation while inspiration was occluded for twenty seconds. The other method was done by using the MIP procedure offered by the respiratory mechanics software through the PB. The PB method measures the most subPEEP inspiratory press created by the patient against a block airway over a three-second period. Each procedure was performed three times. The patients were monitored for changes in heart rate, blood pressure and O_{2} saturation. Results: Cronbach's Alpha was used to assess interprocedure variability. Our results show that there was high internal consistency within each of the three trials for both Methods: PB = 0.83, MM = 0.94. Independent samples t-test showed a significant difference in MIPs when comparing the PB method (-16±8.9) to the MM method (-42±18.5); but there were no statistically significant differences between methods in terms of success of extubation. However, we found clinically important differences between methods. In our sample, five patients (25%) were extubated the same day because we obtained satisfactory MIPs with the MM method. These patients would not have been extubated that day if only the PB method was used. There were no significant differences with either method on clinical outcomes such as heart rate, blood pressure, and oxygen saturation. Conclusions: Patients in the study would not have generated a MIP greater than -30cmH_{2}O if the procedure was done through the PB versus the MM. Research literature states occlusion of the airway for 20 seconds and the use of a one-way valve optimizes the negative values. Thus the MM produced higher MIPs which indicated greater respiratory muscle strength. Based on our data and similar studies, the PB method underestimates true MIP. The MM method is probably a better indicator of respiratory muscle strength.

OF-96-034

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