The Relationship Between Trans-diaphragmatic Pressure and Diaphragmatic Contraction

Summary

Participation Requirements

Description

Protocol The patients will enter a Spontaneous Breathing Trial (S.B.T.) for sixty minutes. During the S.B.T. the desirable measurements will be made: transdiaphragmatic pressure, diaphragm thickening, Tdi,pi , Tdi,ee , TFdi, Di,e, Maximal Inspiratory Pressure (M.I.P.) , Rapid Shallow Breathing Index...

Protocol The patients will enter a Spontaneous Breathing Trial (S.B.T.) for sixty minutes. During the S.B.T. the desirable measurements will be made: transdiaphragmatic pressure, diaphragm thickening, Tdi,pi , Tdi,ee , TFdi, Di,e, Maximal Inspiratory Pressure (M.I.P.) , Rapid Shallow Breathing Index (R.S.B.I.). If the S.B.T. is successful then the patient will be removed from the mechanical ventilator. For the next 48 hours the patient will be monitored for distress signs and thus be reintubated or if the weaning of the patient was successful extubation. Flow chart of the study The patient meets the S.B.T. criteria. The patient is placed in a semi recumbent position. A nasogastric tube attached with two balloons, which are connected with a pressure transducer, one placed in the stomach and the other one in the lower third of the esophagus. The balloons will be connected with a Hans Rudolph pneumotachograph for the measurement of the tidal volume, the flow and the esophageal pressure. An occlusion test will be performed to make sure the esophageal balloon is correctly placed. Measurement of Pes, Pgas, M.I.P., and simultaneous sonographic measurements (Diaphragm thickening,Tdi,pi, Tdi,ee, Di,e,TFdi) during the S.B.T. with the patient being in t-tube. Measurement of the same parameters during an S.B.T. with an airway of reduced diameter. The patient will be reintubated for 60 minutes. The S.B.T. is repeated and the R.S.B.I. will be calculated. If the S.B.T. is successful according to the R.S.B.I. the patient will be disconnected from the mechanical ventilation. Monitoring of the patient for the next 48 hours, for the extubation respiratory distress syndrome or reintubation for another reason. Further monitoring for 30 days in order to measure the time spent in mechanical ventilation Definitions Transdiaphragmatic pressure Pdi will be measured with the use of a nasogastric catheter which has 2 balloons attached at 25 cm and 10 cm from it's distal end. The balloons, of 7 cm length, will be connected with a pressure transducer and with the use of a linear pneumotachometer Hans Rudolph RSS 100HR the graphic representation of the pressures will be displayed in a computer monitor. The balloons will contain 0,5-1 ml of air and will be placed in the stomach and the lower third of the esophagus. To ensure the correct positioning of the balloons an occlusion test (Baydur test) will be performed ,where the similar fluctuations between the esophageal and the airway pressure will be affirmative. As long as the stomach balloon is concerned the positive pressures during the inspiration will be affirmative of the correct positioning. Pressure Time Index P.T.I. is the product of the ratio of the mean inspiratory pressure to the maximal inspiratory pressure (Pavg/Mip) and the ratio of the inspiratory time to the total duration of the inspiratory cycle (Ti/Ttot).The usefulness of the P.T.I. consists that it measures the total energy cost of breathing. P.T.I.=(Pavg/M.I.P.)x(Ti/Ttot) where as a Pavg is considered the airway pressure in the middle of the inspiratory phase (ti/2). Tension Time Diaphragm Index Ttdi is used as an index of diaphragmatic exhaustion. Measurements above 0,15 are indicative of the diaphragmatic incapability to maintain spontaneous breathing for more than 45 minutes, whence the naming of Ttdi critical Ttdi = (Pdi/Pdi,max)x(TixTtot) Rapid Shallow Breathing Index Rapid Shallow Breathing Index (R.S.B.I.) is a method used for predicting the weaning outcome. It is measured during spontaneous breathing and equates to the ratio of respiratory rate per minute (RR) to the tidal volume (Vt) expressed in liters. R.S.B.I. = RR/Vt It has been shown that an R.S.B.I. values below 105 breaths/min/L can predict a successful weaning. Maximal Inspiratory Pressure Maximal Inspiratory Pressure (M.I.P.) is used as a predictive factor of the weaning outcome. It is measured with a manometer placed in a fully occluded airway, while the patient tries to breathe through it for 20 seconds. The highest pressure value is named M.I.P. It has been shown that values below -25 cmH2O are indicative of a positive weaning outcome. Diaphragm Ultrasound The diaphragmatic function is assessed during spontaneous breathing and during breathing with an airway of reduced diameter. The diaphragmatic movement is assessed with ultrasound (Phillips iE33) using a Linear 3-11 MHz head. The ultrasound probe is placed in the mid axillary line perpendicular to the zone of apposition between the 8th-10th intercostal spaces. In this position, the diaphragm is shown as a non-echogenic layer between two echogenic layers which represent the diaphragmatic pleura and the abdominal peritoneum. With this technique the diaphragmatic thickening (Tdi,pi - Tdi,ee), diaphragmatic thickness at end-expiration (Tdi,ee) and end-inspiration (Tdi,pi), diaphragmatic excursion Di,e and diaphragmatic thickening fraction TFdi are measured. All the measurements are made using M-Mode Sonography.

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