Synchronized Intermittent Mandatory Ventilation With and Without Pressure Support Ventilation in Weaning Patients With COPD From Mechanical Ventilation: Patients
This prospective study was designed for male COPD patients, intubated and mechanically ventilated because of an acute exacerbation of their disease. All patients exhibited clinically a chronic bronchitis defined as a productive cough with sputum production for 3 months per year for a 2-consecutive-year period (American Lung Association criteria and an irreversible chronic airflow limitation on spirometric data obtained from a previous clinically stable period: FEVi/VC ratio less than 60 percent of predicted, and a chronic hyperinflation with a RV/TLC ratio of more than 130 percent of predicted. Asthmatic patients were excluded. We also excluded COPD patients with confounding medical or surgical problems (unstable cardiovascular disease, liver disease, diabetes, malignant disease, or recent surgery).
Patients with COPD in ARF were intubated (orotracheally or nasotracheally) with a tube with an internal diameter of more than 8 mm and started on MV in the control mode for at least 48 h (tidal volume of 10 ml/kg and a respirator rate that did not result in respiratory alkalosis). Then patients were placed under SIMV mode until the following criteria were satisfied: (1) cause of the exacerbation controlled; (2) SIMV rate <12 cycles/min; (3) spontaneous tidal volume (sVt) >5 ml/kg of body weight; (4) arterial oxygen saturation above 90 percent with FI02 <0.40; (5) pH >7.38; (6) maximal inspiratory force (MIF) < —20 cm H2O; and (7) airway occlusion pressure (P0.1) less than 5 cm H20.
Patients who appeared unable to tolerate discontinuation of MV at this time (respiratory acidosis for an SIMV rate <10 cycles/ min) were submitted to a randomization between SIMV/PSV (group 1) or SIMV (group 2) modes. Informed oral consent was obtained from the patient or the next of kin. Canadian health care mall Link A standard procedure was followed in both groups: the SIMV rate was reduced in steps of 2 cycles/min once or twice a day according to the patient’s tolerance (see further). When the SIMV rate had reached the 6 cycles/min step, short spontaneous breathing periods of 1 h were performed through the respirator circuitry (periods off machine-cycled breathing). If those spontaneous breathing trials (SBT) appeared clinically well tolerated, a spontaneous breathing period (SB) of at least 10 h was performed. When patients with COPD had successfully undergone this procedure, they were extubated.
In group 1, PSV was added throughout the weaning period and four decreasing levels, arbitrarily chosen, were used concurrently with the decrease in SIMV rate: 15 cm H2O at 10 cycles/ min step; 12 cm H2O at 8 cycles/min step; 9 cm H2O at 6 cycles/ min step; and 6 cm H2O during SBT and SB until the extubation. The SIMV and SIMV/PSV modes were always provided by a specific respirator (Puritan Benett 7200). With this respirator, the PSV delivery is ended when the patient’s inspiratory flow rate is less than 5 L/min or when the airways pressure exceeds the PSV level by 1.5 cm H2O. In both groups, appearance of clinical signs of respiratory muscle fatigue (increased in spontaneous breathing frequency [Sf], alternating abdominal and rib cage breathing, paradoxical inspiratory inward motion of the anterior wall of the abdomen, or sweats), and/or blood gases deterioration (respiratory acidosis with pH <7.35) led to return to the precedent ventilatory step. All patients were placed under a SIMV rate of 12 cycles/min during the night (10 pm to 5 am), group 1 with PSV and group 2 without PSV. The PEEP was never used and the level of the electrovan trigger was set at its minimal sensibility (0.4 cm H2O). No sedative, narcotic, or analeptic drugs were administered.