Frequently asked questions about Perioperative management of pulmonary complication
Postoperative pulmonary complications contribute significantly to overall perioperative morbidity and mortality rates. Such complications account for about 25% of deaths occurring within 6 days of surgery. The frequency rate of these complications varies from 5-70%. This wide range is due to variations among studies in the definition of postoperative pulmonary complications, as well as variability in patient- and procedure-related factors.
One of the more comprehensive lists of postoperative pulmonary complications includes fever (due to microatelectasis), cough, dyspnea, bronchospasm, hypoxemia, atelectasis, hypercapnia, adverse reaction to a pulmonary medication, pleural effusion, pneumonia, pneumothorax, and ventilatory failure. Determining which complications fit this definition is challenging, but likely included are: atelectasis, infection (e.g., bronchitis, pneumonia), prolonged mechanical ventilation and respiratory failure, exacerbation of an underlying chronic lung disease, and bronchospasm. When such a definition is employed, postoperative pulmonary complications prolong the hospital stay by an average of 1-2 weeks, and are likewise associated with increased morbidity and mortality. The risk of postoperative complications varies with the type of surgery being performed. Pulmonary complications occur much more often than cardiac complications in patients undergoing elective surgery to the thorax and upper abdomen. Operations at sites farther from the diaphragm are associated with a much lower incidence of postoperative pulmonary complications. Preoperative evaluation for patients undergoing lung resection (i.e., for lung cancer) differs considerably from that for those undergoing nonresectional surgery. Postoperative pulmonary complications are also more common in patients with preexisting lung disease, medical co-morbidities, poor nutritional status, overall poor health, and in those who smoke. Not all of these risk factors are modifiable, although strategies exist to reduce the risk of postoperative pulmonary complications even among high-risk patients.
Perioperative Pulmonary Physiology
Respiratory effects of general anesthesia
Anesthetic agents are associated with marked alterations in respiratory drive. Such agents cause a diminished response to both hypercapnia and hypoxemia. In combination with neuromuscular blockers, anesthetic agents cause diaphragm and chest wall relaxation, which results in a marked reduction in the functional reserve capacity and, thereby, thoracic volume. This decrease in lung volume promotes atelectasis in the dependent lung regions and persists for more than 24 hours in 50% of patients. Consequently, arterial hypoxemia occurs from ventilation-perfusion (V-Q) mismatching and increased shunt fraction.
Postoperative respiratory physiology in upper abdominal and thoracic surgery
Thoracic and upper abdominal surgery is associated with a reduction in vital capacity by 50% and in functional residual capacity by 30%, Diaphragmatic dysfunction, postoperative pain, and splinting causes these changes. Following upper abdominal surgery, patients shift to a breathing pattern with which ribcage excursions and abdominal expiratory muscle activities increase. This shift is attributed to decreased central nervous system (CNS) output to the phrenic nerves, thus inhibiting diaphragmatic stimulation. A reflex mechanism arising from the sympathetic, vagal, or splanchnic receptors is thought to be responsible. In humans, this reflex inhibition is partially reversed by epidural anesthesia.
Following upper abdominal and thoracic surgery, patients maintain adequate minute volume, but the tidal volume is smaller and the respiratory rate increases (i.e., rapid shallow breathing). These breathing patterns, along with the residual effects of anesthesia and postoperative narcotics, inhibit cough, impair mucociliary clearance, and contribute to the risk of postoperative pneumonia. Other factors that may contribute to increased respiratory complications include electrolyte imbalance (e.g., hypokalemia, hypophosphatemia, hypocalcemia), general debilitation, and underlying lung disease (e.g., chronic obstructive pulmonary disease [COPD]).
The incidence of postoperative pulmonary complications is inversely related to the distance of the surgical incision from the diaphragm. Abdominal aortic aneurysm repair is associated with the highest risk of postoperative pulmonary complications.
Duration of surgery
Patients undergoing procedures lasting longer than 3-4 hours have a higher incidence rate of pulmonary complications compared with those undergoing surgeries lasting shorter than 2 hours.
Type of anesthesia:
Minimally invasive surgery
Laparoscopic abdominal surgery, particularly cholecystectomy, is associated with fewer postoperative pulmonary abnormalities and a shorter hospital stay. These techniques use small incisions, and the reduced manipulation of visceral organs minimizes the adverse effects on respiratory muscles. Laparoscopic surgery leads to a 23% decrease in forced vital capacity (FVC) and a 16% decrease in FEV1, and it is associated with a lower incidence of complications compared with laparatomy ; therefore, even patients with severe COPD can tolerate surgery.
Although smoking is a risk factor for postoperative pulmonary complications, one concern about smoking cessation in the immediate preoperative period is that abrupt removal of the irritant effect of cigarette smoke can inhibit coughing and lead to retention of secretions and small airway obstruction. As the beneficial effects of smoking cessation, including improvement in ciliary and small airway function and a decrease in sputum production, occur gradually over several weeks, a longer duration of abstinence before surgery would be expected to result in improved postoperative outcomes.
Aggressively treat patients with COPD to achieve the best possible baseline function. Bronchodilators, smoking cessation, antibiotics, and chest physical therapy may help significantly reduce pulmonary complications. Treat patients who have a persistent wheeze, functional limitation, or severe air flow obstruction with perioperative steroids.
Optimize asthma control before surgery. Perioperative systemic corticosteroids are recommended for persistent symptoms if the peak flow rate and FEV1 are less than 80% predicted or previous best. Such treatment has been shown to decrease the risk of bronchospasm. The safety of perioperative corticosteroids is well established in patients with asthma, and their use is not associated with death, serious infections, or adrenal suppression. Hypothalamic-pituitary-adrenal axis suppression should be assumed to be present in patients who have received systemic steroids for more than 3 weeks in the past 6 months. These patients should receive stress-dose coverage perioperatively.
Indiscriminate use of prophylactic antibiotics does not lead to a reduction in pulmonary complications. These drugs may be used in patients with a clinically apparent respiratory infection. Cancel elective surgery if the patient has an active infection.
Lung expansion, deep breathing and coughing, and incentive spirometry are best taught to the patient before surgery and are useful for postoperative reduction of atelectasis.
The following preoperative measures help minimize pulmonary complications in at-risk patients:
Type of anesthesia
The type of anesthesia and neuromuscular blockage affect the incidence of postoperative pulmonary complications. Intermediate- and shorter-acting agents (e.g., vecuronium, rocuronium) are preferred, because residual neuromuscular blockade from longer-acting agents may contribute to pulmonary complications.
Type of neuromuscular blockade
Pancuronium, a long-acting neuromuscular blocker, may lead to residual effects, cause hypoventilation, and increase complications. Use the intermediate-acting agents (e.g., vecuronium, atracurium) in high-risk pulmonary patients.
Duration and type of surgery
When available, a less ambitious, shorter procedure should be considered in extremely high-risk patients. The duration of the surgical procedure is known to affect the rate of postoperative complications. Because upper abdominal and thoracic operations carry the greatest risk, a percutaneous (laparoscopic) procedure should be substituted for an open procedure if possible.
Lung expansion maneuvers
Lung expansion maneuvers include incentive spirometry, deep breathing exercises, postural drainage, percussion and vibration, cough, suctioning, mobilization, intermittent positive pressure breathing (IPPB), and CPAP. A meta-analysis of 48 trials suggested that the routine use of incentive spirometry provides no benefit following abdominal and cardiac surgery.
Pain is a highly complex process involving specialized nociceptor fibers in the peripheral tissues; neurotransmitters and neuromodulators at all levels of neuraxis; integration of information in central nervous system; and learned behavior, affect, and cognitive status. Adequate postoperative pain control helps minimize pulmonary complications by encouraging earlier ambulation and performance of lung expansion maneuvers.
Glycemic control was associated with a reduced duration of mechanical ventilation in a mixed medical-surgical population, but the impact of this intervention specifically on postoperative pulmonary complications is unclear.
Routine use of nasogastric tubes until bowel function returns following abdominal surgery is associated with higher rates of pneumonia and atelectasis relative to selective use of nasogastric tubes in patients who develop postoperative nausea or vomiting, inability to tolerate oral intake, or symptomatic abdominal distention. Selective nasogastric use was associated with a shorter time to oral intake without an increase in the risk of aspiration.
Total parenteral nutrition
Although poor nutrition is a risk factor for postoperative pulmonary complications, the routine use of total parenteral nutrition demonstrates no benefit over total enteral nutrition or no hyperalimentation, except perhaps in patients with severe malnutrition (>10% weight loss over 6 mo) or prolonged (10-14 d) inadequate enteral feeding.
Prevention of thromboembolism
Although not technically considered a postoperative pulmonary complication, brief mention should be made of venous thrombo-embolic disease (VTE). Surgery is a well-recognized risk factor for the development of deep vein thrombosis and subsequent pulmonary embolism. Much as postoperative pulmonary complications, the risk of VTE is influenced by patient- and procedure-related factors. Risk assessment and recommendations for prevention of VTE in surgical patients have recently been updated.
The following postoperative measures help minimize pulmonary complications in at-risk patients: