List indications for mechanical ventilation of postoperative patients.
Describe the initial ventilator settings for postoperative patients without prior pulmonary disease, with prior pulmonary disease, and patients with single lung transplantation.
Describe monitoring of the ventilated postoperative patient.
Discuss weaning of patients requiring postoperative ventilatory support.
A frequently encountered category of patients requiring ventilatory support are those in the immediate postoperative period. This is particularly true of patients following thoracic or cardiac surgery, although changes in surgical and anesthesia techniques have decreased the requirement for mechanical ventilation. Generally, these patients do not present complex ventilatory management problems and many are extubated within 24 hours. In addition, many of these patients who present with postoperative hypoxemia or hypercarbia can be successfully managed with mask continuous positive airway pressure (CPAP) or noninvasive ventilation (NIV).
It has been well established that surgical procedures that include general anesthesia, especially those affecting the thoracic or abdominal cavities, result in impairment of ventilatory function. The reasons for these impairments include the effects of general inhalation anesthetics on hypoxic pulmonary vasoconstriction and a blunting of hypoxemic and hypercapnic ventilatory drive when intravenous narcotics are used. As a result of alteration in the shape and motion of the diaphragm and chest wall, thoracic or cardiac surgery can decrease lung volume by 20% to 30% and upper abdominal surgery can reduce the vital capacity by up to 60%. Many thoracic surgical and cardiac surgical patients have radiographic evidence of atelectasis. In the patient with normal preoperative pulmonary function, this may not present significant postoperative problems. But in patients with preexisting pulmonary disease, some level of postoperative respiratory failure can be expected. Cardiac surgical patients are at risk of diaphragmatic dysfunction due to phrenic nerve injury. In patients with preexisting pulmonary disease, postoperative management can be complex. With the increased use of lung resection surgery, heart and lung transplantation, and complex cardiac surgery performed on older patients, postoperative ventilatory failure is a common reason for ventilatory support.
The primary reason for mechanical ventilation in this group is apnea as a result of unreversed anesthetic agents (Table 21-1). The primary reasons that anesthesia is not reversed are iatrogenic hypothermia, the need to reduce cardiopulmonary stress, or the presence of altered pulmonary mechanics. Some cardiac surgeons favor cold cardioplegia to reduce the likelihood of hypoxic injury. These patients receive narcotic anesthesia throughout the procedure and may require 8 to 16 hours for warming and full reversal of anesthesia. Transplant recipients (heart or lung) are ventilated to ensure cardiopulmonary stress is minimized during the initial acclimation period and to minimize any adverse effects of an increased work-of-breathing in the immediate postoperative period. The most difficult group of patients is those with preexisting lung disease whose pulmonary mechanics are adversely affected by surgery, who require ventilatory support because of ...