Background

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. The goal of perioperative pulmonary management is to identify patients at high risk of significant postoperative pulmonary complications, so that appropriate interventions can be provided to minimize that risk. In most cases, even in high-risk patients, the procedure can be performed safely as planned, but occasionally postponement, modification, or cancellation are warranted.

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]).

Procedure-related risk factors

Surgical site

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:

It is found that high rates of respiratory failure and other postoperative complications in patients undergoing general anesthesia compared with spinal or epidural anesthesia. Spinal or epidural anesthesia, in conjunction with general anesthesia, may be associated with a lower risk of postoperative pneumonia, venous thromboembolic disease, myocardial infarction, renal failure, and respiratory depression. Patients who received epidural analgesia following abdominal aortic aneurysm repair had fewer complications than those receiving parenteral opioids. The addition of neuraxial anesthesia, rather than avoidance of general anesthesia, may be the key to reducing pulmonary complications. In any case, spinal or epidural anesthesia is safe and should be considered in high-risk patients. Regional nerve block is associated with a low risk and, when feasible, should also be considered for high-risk patients. Residual neuromuscular blockade was more common with pancuronium than intermediate-acting agents.

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. Video-assisted thoracoscopic surgery uses much smaller incisions; consequently, the hospitalization time is substantially reduced. Smaller incisions, performed without separation of the ribs and resulting in less postoperative pain, lead to early ambulation and reduced pulmonary complications. Preparation for Surgery

Smoking cessation

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. Smoking cessation should be pursued in most patients in the preoperative period, even very close to the time of surgery. A longer duration of smoking cessation provides a greater risk reduction; patients should be counseled to abstain from smoking regardless of the time remaining before surgery. When feasible, counseling, nicotine replacement therapies, bupropion, and varenicline improve the quit rate and should be used aggressively.

COPD

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.

Asthma

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.

Preoperative antibiotics

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.

Patient education

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.

Summary

The following preoperative measures help minimize pulmonary complications in at-risk patients:

1. Educate patients on lung expansion maneuvers
2. Optimize COPD and asthma treatment regimens
   1. Course of systemic steroids if suboptimal control
3. Smoking cessation
4. Consider inspiratory muscle training or pulmonary rehabilitation in high-risk patient
5. Antibiotics for acute bronchitis

Intra-operative Strategies

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. Spinal anesthesia may be safer than general anesthesia; therefore, spinal anesthesia should be considered for high-risk patients. Depending on the type and duration of surgery, endotracheal intubation and mechanical ventilation may be preferable because of the ability to monitor and control the respiratory rate and tidal volume.

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.

Postoperative Strategies

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. In conclusion, lung expansion maneuvers, aside from early mobilization, may not be required in most patients. Other methods are likely equivalent in moderate- and high-risk patients, so selection should focus on cost, availability, and expertise. CPAP may be targeted to high-risk patients, particularly those who are not able to cooperate with other modalities. Preoperative initiation and/or patient education improve the efficacy of these exercises.

Pain control

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. Management of postoperative pain includes narcotics and narcotic-like medications administered peripherally into the epidural or intrathecal space. Intrathecal administration of narcotics is associated with a longer duration of analgesia (15-22 h), respiratory depression, and headaches. Inter-costal nerve blocks have also been shown to be beneficial in upper abdominal surgery. Epidural narcotics are morphine, fentanyl, sufentanil, and hydroxymorphine; the local anesthetics used for epidural analgesia are bupivacaine and ropivacaine. Adding small doses of local anesthetics to narcotics is a preferred approach. This potentiates pain relief, minimizes nerve blockade, and reduces adverse effects from both agents. Postoperative epidural analgesia and inter-costal nerve blocks improve pain control and help reduce postoperative complications, with little risk. Epidural hematoma is a rare complication, except when concomitant anticoagulation is prescribed. Epidural hematomas have been reported in patients receiving low molecular weight heparin (LMWH) who had epidural catheters. Perioperative use of nonsteroidal anti-inflammatory drugs (NSAIDs) may complement other pain management strategies. Nonsteroidal agents are known to decrease the narcotic requirement in the postoperative period. The agent ketorolac may be administered intramuscularly as needed. Other nonsteroidal agents are given orally or rectally.

Glycemic control

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.

Nasogastric decompression

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.

Summary

The following postoperative measures help minimize pulmonary complications in at-risk patients:

• Adequate pain control
• Selective use of nasogastric decompression and total parenteral nutrition
• Early mobilization
• Lung expansion maneuvers
  • Consider CPAP in high-risk patients
  • Consider epidural analgesia in at-risk patients
• DVT prophylaxis