The Control of Breathing during Weaning from Mechanical Ventilation (7)

The Control of Breathing during Weaning from Mechanical Ventilation (7)Results
The ages of patients ranged from 56 to 87 years (mean age, 70 years) (Table 1). Various cardiopulmonary disorders were present. The majority of patients (9 of 14) had recently undergone major thoracic or abdominal surgery with secondary complications leading to prolonged respiratory failure. The most common complicating illnesses were obstructive lung disease (eight patients) and sepsis (four patients) combined with varying degrees of cardiac dysfunction. These complications had led to ventilator dependency for more than 1 week in 12 of 14 subjects.
A typical strip chart recording of the C02 concentration (Fco^ at the airway, Pao, and V is shown in Figure 1 (patient 4). In Figure 1A, the pressure and flow waveforms during mechanical ventilation with constant inspiratory flow are consistent with predictions derived from single compartment models of the respiratory system. All machine-delivered breaths meet relaxation criteria indicating that phasic respiratory motor activity had been suppressed. In contrast, the alteration of the pressure and flow tracings shown in Figure IB indicate that C02 supplementation to the inspired gas (note the increase in the baseline of the Fco2 tracing) has led to a recruitment of respiratory muscles. C02RT was defined on this basis.

Table 1—Patient Characteristics

PatientNo. Major Surgical Procedure(s)t Complicating Medical Condition(s) Sex/Age, yr Duration of Mechanical Ventilation, (Days)*
Group 1 1 CABG Sepsis, CHF M/65 70
2 CABG Sepsis, CHF, arrhythmia M/87 23
3 Laparotomy COPD, pancreatic abscess, sepsis M/64 8
4 COPD, alcoholism, pneumonia M/73 2
6 Tracheal reconstruction Upper airway obstruction F/56 42
Group 2 7 AAA repair, colectomy COPD, sepsis, DM M/69 7
8 Pneumonectomy, BPF repair Lung Ca, renal failure M/72 53
9 COPD, sepsis, MOF M/57 35
10 COPD F/72 2
11 MVR Cardiopulmonary arrest, arrhythmia F/78 22
12 COPD, pneumonia, Sz disorder M/86 32
13 Pancreatic surgical exploration COPD, adrenal Ca, pancreatitis, DM M/60 13
15 Metastatic prostate Ca, hyperkalemia, influenza b, arrhythmia M/75 32
16 AAA repair, colectomy COPD, renal failure M/68 31
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