Medicine of the Future in America

Automatic Weaning From Mechanical Ventilation Using an Adaptive Lung Ventilation Controller: Data

Three groups of patients were studied: group 1—normal lungs; group 2—pulmonary parenchymal abnormality; and group 3—chronic obstructive pulmonary disease (Table 1). The patients were initially ventilated for at least 30 min using the same mode and settings on which each patient had been ventilated during the mechanical ventilatory period. In this baseline condition, gross alveolar ventilation (V’gA in liters per minute) was measured as respiratory rate (f) times tidal volume (Vt) minus series dead space ventilation (f°VT—f’VdS) at baseline. The ventilator was then switched to ALV with a target V’gA identical to the baseline condition.

After 30 min, the target V’gA was reduced by 66% to encourage weaning. If after 2 h a patient required no more than 5 cm of pressure support and no more than four mechanical ventilatory breaths while still meeting the standard weaning criteria, the patient was considered to be weaned. He or she was then placed on a T-piece for another 24 h. The wean was documented as being successful if the patient required no further ventilatory support and continued to meet the standard wean criteria after 24 h. The wean was considered to have failed if the patient continued to require more than 5-cm pressure support or more than four mechanical breaths or no longer met the weaning criteria, eg, PaC02 increased to >6 kPa, respiratory rate increased to >30/ min, etc. The wean was also documented as having failed if the patient required further ventilatory support after an apparently successful wean.
To document the weaning process, recordings of ventilatory parameters (see below), hemodynamic parameters, and arterial blood gases were made at baseline, after 5 min on ALV, at 30 min, and then at 2 h intervals. The patients were also continuously monitored by ECG, pulse oximetry, and capnography. website

Results are reported as median values and were compared using the Mann-Whitney U test with Bonferroni correction where appropriate with a level of significance of 0.05.

Table 1—Patient Grouping, Outcome, and Primary Diagnoses

Group Outcome PatientNo. Age,yr VentilatorDays Diagnosis
Normal S 19 53 13 Meningitis/septicemia
Normal S 5 25 5 Postop vent/trauma
Normal S 31 58 6 Staphylococcal septicemia
Normal S 2 20 1 Postop vent/thymectomy
Normal S 17 32 6 Head injury/trauma
Normal S 20 74 3 Fat embolism syndrome
Normal Failed 16 59 9 Staphylococcal septicemia
Normal S 18 21 5 Guillain-Barre syndrome
Normal S 1 20 1 Postop vent/thymectomy
Parenchymal abnormality S 4 49 11 ARDS / Septicemia
Parenchymal abnormality S 10 35 7 Pneumonia/septicemia
Parenchymal abnormality S 6 29 11 ARDS/GPH
Parenchymal abnormality S 7 57 3 ARDS/tuberculosis
Parenchymal abnormality S 21 49 7 Pulmonary edema/renal failure
Parenchymal abnormality S 11 46 5 Legionnaires’ disease
Parenchymal abnormality Failed 30 35 19 ARDS / septicemia
Parenchymal abnormality t 12 52 2 Septicemia/fibrosing alveolitis
Parenchymal abnormality S 27 47 15 ARDS/trauma/aspiration
COPD S 3 68 6 Congestive heart failure in COPD
COPD s 9 71 3 Blunt chest trauma in COPD
COPD s 33 58 6 Pneumonia in COPD
COPD s 13 61 4 Pneumonia in COPD
COPD s 32 28 2 Bronchiectasis in COPD
COPD Failed 24 35 7 Pneumonia in COPD
COPD Failed 23 33 4 Pneumonia in COPD
COPD Failed 28 42 30 Pneumonia in COPD
COPD S 29 55 18 Pneumonia in COPD
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