Weaning from ventilation

With the exception of fast-track patients, an expectant approach should be adopted. Guidelines for ventilatory weaning are outlined in Table 1 and TableZ It may be appropriate to start weaning before these criteria are met. For example, some patients may be weaned and extubated prior to removal of an intra-aortic balloon pump.

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Adequate analgesia is vital and can be provided by intravenous or extradural opiate infusions, or by small titrated doses of intravenous opiates, commonly administered via patient-controlled analgesia devices. As in all patients, regular clinical assessments are the key to the weaning process. A small group of patients with limited cardiac reserve may decompensate when challenged by the work of spontaneous breathing.

Patient extubation is a clinical decision and guidelines are listed in T§b!e...3.. At this stage, an elevated PaCO2 can be accepted in a hemodynamically satisfactory patient, and is indeed very common in a comfortable co-operative postsurgical patient in whom adequate narcotic analgesia has been achieved.

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After extubation many patients benefit from additional respiratory support in the form of humidified oxygen by mask or nasal cannula, continuous positive airway pressure by mask, and physiotherapy including the use of incentive spirometry. Nasal positive-pressure ventilation is not usually indicated in the early postoperative phase but may be the logical progression in a patient with limited cardiopulmonary reserve who undergoes a protracted weaning program.

In some patients weaning may be predictably or inadvertently inappropriate in the early postoperative period. Common associated factors include complex and prolonged surgery, re-exploration, perioperative infarction, left ventricular dysfunction, dysrhythmia, pulmonary edema or fluid overload, pulmonary hypertension, obesity, chronic pulmonary disease, neurological injury, and advanced age. Cardiovascular stability should be achieved before weaning is contemplated. In patients with poor left ventricular function, judicious use of diuretics, angiotensin-converting enzyme inhibitors, and phosphodiesterase inhibitors may be necessary during a protracted weaning phase. An early sign of decompensation in such a patient is a sudden rise in right atrial pressure when increased respiratory work demands are imposed. Pleural collections in excess of 250 ml should be drained, sometimes repeatedly and preferably with ultrasound guidance, in patients with limited reserve.

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