The Control of Breathing during Weaning from Mechanical Ventilation (6)

Parameters Recorded during Spontaneous Breathing (‘Weaning): All patients were observed by an investigator during a T-piece weaning trial of 1 h maximal duration. The Flo, was adjusted to assure a Sa02 of 90 percent to 93 percent. Respiratory rate, tidal volume, and breathing patterns were determined from the respiratory inductive plethysmograph recordings. At 5 min intervals, the perception of dyspnea was scored on a modified Borg scale with values ranging between 6 (indicating no discomfort) and 20 (indicating extreme shortness of breath). The airway pressure 100 ms following the occlusion of the inspiratory port of a unidirectional balloon occlusion valve (P0,, Hans Rudolph 2400) was also recorded every 5 min. Symptom-limited failure to wean was defined prospectively as an increase in dyspnea score to 19 or greater and/or as a sustained increase in respiratory rate over 30 breaths per minute. At the end of 1 h or within 5 min of weaning failure, arterial blood gas tensions were measured, from which COzSB was determined.
Statistical Analysis
Patients were separated into two groups according to predefined weaning response criteria. Croup 1 consisted of patients who completed the full weaning trial, while patients in group 2 experienced weaning-induced respiratory distress. Within and across group comparisons between COaRT, COaSB, and C02MV were made using paired, two-tailed Student t tests. Group mean differences in respiratory muscle strength, parameters of mechanical load, and respiratory motor output during weaning were also evaluated. Statistical significance was assumed at a p value ^0.05. Correlations between variables were analyzed by least squares linear regression.

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