Weaning parameters (spontaneous ventilatory measurements) were obtained by the respiratory therapist at the beginning of each 8-h shift. Acceptable weaning parameters included: (1) minute ventilation (Ve) <12 L/min, and two of the following four parameters: (2) maximum voluntary ventilation (MW) > two times Ve; (3) tidal volume (Vt) >5 ml/kg body weight; (4) forced vital capacity (FVC) >10 ml/kg body weight; and (5) negative inspiratory force (NIF) ^ — 20 cm HfO. When weaning parameters were satisfied, the patient was randomized immediately, according to hospital number, into either an IMV (even) or T-piece weaning mode (odd). The time from having acceptable weaning parameters to completion of a successful wean was recorded as weaning time (WT). Total ventilation time (TVT) was defined as the time from initiation of mechanical ventilation to completion of a successful wean. A successful wean was defined as discontinuation of mechanical ventilation for more than 48 h. The decision to extubate the patient was made by the attending physicians.
During the weaning trials acceptable blood gases had to be maintained using a fixed FIos (<0.45): (1) PaO, 55 mm Hg; (2) PaC02 increase of ^10 mm Hg; and (3) pH between 7.28 and 7.55. The following vital sign criteria had to be maintained during weaning: (1) respiratory rate (RR) >40 or no increase above 50 percent of the baseline RR; (2) heart rate (HR) ^140 beats/min or no increase above 30 percent of the baseline HR; and (3) a systolic blood pressure above 90 mm Hg or no decrease below 20 percent of baseline. so
If the patient failed to meet the above blood gas or vital sign criteria during weaning, the patient was removed from protocol, returned to mechanical ventilation on the original ventilator settings, and the primary physician notified. If the patient was stable clinically by the beginning of the next 8-h shift, weaning parameters were measured again and, if acceptable, the patient was assigned to a second or third trial of the protocol. Patients were placed into three study groups: (1) group A patients required mechanical ventilation in a stabilization mode for <72 h; (2) group B patients required mechanical ventilation in a stabilization mode for 2:72 h; and (3) group C patients either never met proposed weaning criteria and were stable clinically after seven days or had failed three weaning attempts at 2-h and 7-h wean. To maintain the same potential weaning time, the following weaning protocols were assigned to each of the three groups (Table 1).
Table 1—Summary cf Weaning Steps for IMV and T-Piece
|Croup A (2-h wean)||Group B (7-h wean)||Group C (3-day wean)(Never Satisfied Weaning Parameter or failed 3 weaning attempts)|
|Stabilization (<72 h)||Stabilization (>72 h)|
|Rate 6:30 min||T-Piece :30 min||Rate 8:2 h||T-Piece:30 minq2 hx 3||Day l:Rate 8||Day 1 T-Piece:15 min q 4 h x 2 T-Piece:30 min q 4 h x 2|
|Rate 4:30 min||Mechanical vent:30 min||Rate 6:2 h||Day 2:Rate 6||Day 2 T-Piece: 15 min q 2 h x 4 T-Piece:30 min q 2 h X 4|
|Rate 0:1 h||T-Piece: 1 h||Rate 4:2 h||T-Piece: 1 h||Day 3:Rate 4||Day 3 T-Piece:l h q 2 h x 4 T-Piece:2 h q 4 h x 2|
|Rate 0:1 h||Day 4:Rate 0||Day 4 T-Piece: 1 h|