Lung recruitment during general anesthesia

Postoperative apnea, respiratory strategies, and pathogenesis mechanisms: a review

Recovery from anesthesia is ideally routine and uneventful. After extubation, the recovering postoperative patient ought to breathe without supportive care or additional oxygenation. It has been demonstrated in previous studies that postoperative pulmonary complications are clinically relevant in terms of mortality, morbidity, and length of hospital stay. Compromised postoperative ventilation can be described as the condition in which the postoperative patient does not have satisfactory spontaneous ventilation support and adequate oxygenation. Causes of impaired ventilation, oxygenation, and airway maintenance can be mechanical, hemodynamic, and pharmacologic. This review describes prevalence and differential diagnosis, including co-morbidities of postoperative apnea. The physiological mechanisms of breathing and prolonged postoperative apnea are also reviewed; these mechanisms include influences from the brainstem, the cerebral cortex, and chemoreceptors in the carotid and aortic body. Causes of prolonged postoperative apnea and management are also discussed.

Effects of positive end-expiratory pressure on anesthesia-induced atelectasis and gas exchange in anesthetized and mechanically ventilated sheep

OBJECTIVE

To evaluate the effects of 10 cm H(2)O of positive end-expiratory pressure (PEEP) on lung aeration and gas exchange in mechanically ventilated sheep during general anesthesia induced and maintained with propofol.

ANIMALS

10 healthy adult Bergamasca sheep.

PROCEDURES

Sheep were sedated with diazepam (0.4 mg/kg, IV). Anesthesia was induced with propofol (5 mg/kg, IV) and maintained with propofol via constant rate infusion (0.4 mg/kg/min). Muscular paralysis was induced by administration of vecuronium (25 microg/kg, bolus IV) to facilitate mechanical ventilation. After intubation, sheep were positioned in right lateral recumbency and mechanically ventilated with pure oxygen and zero end-expiratory pressure (ZEEP). After 60 minutes, 10 cm H(2)O of PEEP was applied for 20 minutes. Spiral computed tomography of the thorax was performed, and data were recorded for hemodynamic and gas exchange variables and indicators of respiratory mechanics after 15 (T(15)), 30 (T(30)), and 60 (T(60)) minutes of ZEEP and after 20 minutes of PEEP (T(PEEP)). Computed tomography images were analyzed to determine the extent of atelectasis before and after PEEP application.

RESULTS

At T(PEEP), the volume of poorly aerated and atelectatic compartments was significantly smaller than at T(15), T(30), and T(60), which indicated that there was PEEP-induced alveolar recruitment and clearance of anesthesia-induced atelectasis. Arterial oxygenation and static respiratory system compliance were significantly improved by use of PEEP.

CONCLUSIONS AND CLINICAL RELEVANCE

Pulmonary atelectasis can develop in anesthetized and mechanically ventilated sheep breathing pure oxygen; application of 10 cm H(2)O of PEEP significantly improved lung aeration and gas exchange.

[Peri-operative atelectasis and alveolar recruitment manoeuvres]

Respiratory complications are a significant cause of post-operative morbidity and mortality. Peri-operative atelectasis, in particular, affects 90% of surgical patients and its effects can be prolonged, due to changes in respiratory mechanics, pulmonary circulation and hypoxaemia. Alveolar collapse is caused by certain predisposing factors, mainly by compression and absorption mechanisms. To prevent or treat these atelectasis several therapeutic strategies have been proposed, such as alveolar recruitment manoeuvres, which has become popular in the last few years. Its application in patients with alveolar collapse, but without a previous significant acute lung lesion, has some special features, therefore its use is not free of uncertainties and complications. This review describes the frequency, pathophysiology, importance and treatment of peri-operative atelectasis. Special attention is paid to treatment with recruitment manoeuvres, with the purpose of providing a basis for the their rational and appropriate use.

Intraoperative ventilatory strategies for prevention of pulmonary atelectasis in obese patients undergoing laparoscopic bariatric surgery

BACKGROUND

Atelectasis occurs regularly after induction of general anesthesia, persists postoperatively, and may contribute to significant postoperative morbidity and additional health care costs. Laparoscopic surgery has been reported to be associated with an increased incidence of postoperative atelectasis. It has been shown that during general anesthesia, obese patients have a greater risk of atelectasis than nonobese patients. Preventing atelectasis is important for all patients but is especially important when caring for obese patients.

METHODS

We randomly allocated 66 adult obese patients with a body mass index between 30 and 50 kg/m(2) scheduled to undergo laparoscopic bariatric surgery into 3 groups. According to the recruitment maneuver used, the zero end-expiratory pressure (ZEEP) group (n = 22) received the vital capacity maneuver (VCM) maintained for 7-8 s applied immediately after intubation plus ZEEP; the positive end-expiratory pressure (PEEP) 5 group (n = 22) received the VCM maintained for 7-8 s applied immediately after intubation plus 5 cm H(2)O of PEEP; and the PEEP 10 group (n = 22) received the VCM maintained for 7-8 s applied immediately after intubation plus 10 cm H(2)O of PEEP. All other variables (e.g., anesthetic and surgical techniques) were the same for all patients. Heart rate, noninvasive mean arterial blood pressure, arterial oxygen saturation, and alveolar-arterial Pao(2) gradient (A-a Pao(2)) were measured intraoperatively and postoperatively in the postanesthesia care unit (PACU). Length of stay in the PACU and the use of a nonrebreathing O(2) mask (100% Fio(2)) or reintubation were also recorded. A computed tomographic scan of the chest was performed preoperatively and postoperatively after discharge from the PACU to evaluate lung atelectasis.

RESULTS

Patients in the PEEP 10 group had better oxygenation both intraoperatively and postoperatively in the PACU, lower atelectasis score on chest computed tomographic scan, and less postoperative pulmonary complications than the ZEEP and PEEP 5 groups. There was no evidence of barotrauma in any patient in the 3 study groups.

CONCLUSIONS

Intraoperative alveolar recruitment with a VCM followed by PEEP 10 cm H(2)O is effective at preventing lung atelectasis and is associated with better oxygenation, shorter PACU stay, and fewer pulmonary complications in the postoperative period in obese patients undergoing laparoscopic bariatric surgery.

[Atelectasis in general anesthesia and alveolar recruitment strategies]

Atelectasis occurs in most patients during general anesthesia and is the main cause of hypoxemia. The objective of this review is to examine the causes and diagnosis of atelectasis and the different strategies for reducing or preventing this complication and improving oxygenation. Pulmonary atelectasis is mainly caused by 3 factors: compression, gas absorption, and lack of surfactant. Compression and gas absorption are, however, the 2 most commonly implicated factors. Lung collapse is accentuated if pure oxygen is inhaled during induction or if the patient is morbidly obese. Laparoscopic, thoracic, and upper abdominal interventions also carry risk of lung collapse. Various techniques may be used to prevent atelectasis or to reopen collapsed lung tissue. These include using positive end-expiratory pressure or a high tidal volume-thus providing a higher airway pressure (vital capacity maneuver)-or both in combination. Alveolar recruitment strategies have been tried in bariatric surgery, single-lung ventilation, laparoscopy, and adult respiratory distress syndrome. Their application has reduced or prevented atelectasis, thereby reducing postoperative pulmonary complications.