Introduction
Postoperative pulmonary complications (PPCs) have undeniable clinical relevance because they are frequent and impose a significant burden of perioperative morbidity and mortality. The reported incidence of PPCs varies considerably among studies, from 2% to 40%, with several risk factors identified ( Table 9.1 ). Ambiguities in the definition of PPCs and lack of systematic studies have created more challenges to the perioperative pulmonary risk evaluation. However, in the last decade, definitions were improved and risk factors were comprehensively analyzed and included in validated outcome prediction models.
| Strong evidence a | Fair evidence a | Indeterminate | |
|---|---|---|---|
| Patient-related factors | Advanced age | History of smoking | Respiratory infection in the last month |
| ASA class > 2 | Impaired sensorium | GERD | |
| Congestive heart failure | Weight loss | Alcohol use | |
| Functional dependence | Alcohol use | Diabetes mellitus | |
| COPD | Weight loss | ||
| Obesity | |||
| Moderate/severe obstructive sleep apnea | |||
| Hypertension | |||
| Liver disease | |||
| Cancer | |||
| Sepsis | |||
| Asthma | |||
| Renal failure | |||
| Ascites | |||
| Diabetes mellitus Preoperative shock | |||
| Procedure-related factors | Aortic aneurysm | Transfusion | Prolonged hospitalization |
| Thoracic | Procedures with a high risk for ALI/ARDS | ||
| Abdominal | Procedures with a risk for UEPI | ||
| Upper abdominal | Perioperative nasogastric tube | ||
| Neurosurgery | Use of long-acting neuromuscular blockers | ||
| Prolonged surgery (> 3 hours) | Mechanical ventilation strategy | ||
| Head and neck | Open abdominal surgery (vs. laparoscopic) | ||
| Emergency | Neostigmine | ||
| Vascular | Failure to use peripheral nerve stimulator | ||
| General anesthesia | |||
| Blood transfusion | |||
| Lab/preoperative testing | Low serum albumin | Chest radiograph | Positive cough test |
| Blood urea | Low preoperative oxygen saturation | ||
| Anemia | |||
| Generic variations | |||
| Increased creatinine | |||
| Abnormal liver function test results | |||
| Predicted maximal oxygen uptake | |||
| FEV 1 /FVC < 0.7 and FEV 1 < 80% of predicted |
a Adapted from Smetana GW, Lawrence VA, Cornell JE. American College of Physicians: Preoperative pulmonary risk stratification for noncardiothoracic surgery: systematic review for the American College of Physicians. Ann Intern Med 2006;144(8):581.
Epidemiology
Approximately 1 million surgical patients have PPCs each year in the United States. Studies have shown that PPCs occur in 2%–12% of nonthoracic surgeries and in up to 38% of thoracic surgeries. In patients after major abdominal surgery, the incidence of PPCs was around 6%.
In a multicenter study, the 30-day mortality was estimated to be 19.5% in those with PPC as opposed to 0.5% in those without a PPC. A prospective cohort study on patients undergoing nonthoracic surgery showed that patients who developed a PPC had a mean hospital stay of 27.9 days as opposed to a mean value of 4.5 days in patients who did not have a PPC.
A study on US Medicare beneficiaries showed that pneumonia and respiratory failure respectively account for 2.8% and 1.4%, respectively, of causes of rehospitalization after surgery. The American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) analyzed Medicare inpatient claims and found that preventing postoperative complications would avoid 41,846 readmissions and save $620 million of public health expense every year.
Definition
Early studies lumped events with questionable clinical relevance, such as intraoperative bronchospasm or low-grade fever, together with more significant complications, such as pneumonia and respiratory failure. A more systematic approach should evaluate only those complications that are likely to affect mortality, prolong hospital stay, or require specific treatment. These clinical entities should be defined by criteria as stringent and univocal as possible, such as the criteria for nosocomial pneumonia. However, the reported rate of pulmonary complications is variable even when stricter criteria for the diagnosis of PPCs are used, probably due to the heterogeneity of the populations studied and of the surgical procedures performed ( Table 9.2 ). The large variability among studies is also due to difficulty in discriminating each of the complications because they have interdependent pathways.
| Procedure-related risk factor | Adjusted OR for PPCs (95% CI) | PPC rate a (%) |
|---|---|---|
| Surgical site | ||
| 6.90 (2.74–17.36) | – |
| 2.10 (0.81–5.42 | 25.5 |
| 2.21 (1.82–2.68) | 10.3 |
| 4.24 (2.89–6.23) | – |
| – | 18.9 |
| – | 19.7 |
| – | 5.1 |
| – | 7.7 |
| 2.53 (1.84–3.47) | – |
| – | 1.8 |
| 2.26 (1.47–3.47) | – |
| 2.52 (1.69–3.75) | – |
| 2.35 (1.77–3.12) | – |
a After multivariable adjustment for other patient-related and procedure-related risk factors.
Pneumonia is probably the single most important PPC because it has a definitive impact on outcomes. Postoperative pneumonia has been detected in 18.6% of 140 patients undergoing major surgery and is associated with mortality rates as high as 21%. Perioperative bronchospasm seems to occur in a surprisingly small portion of the population, even when patients with asthma are considered. However, bronchospasm was the most frequent complication in smokers with evidence of airway obstruction by spirometry. Recently, the European Perioperative Clinical Outcome definitions included a universal definition of PPCs with a comprehensive list of components ( Table 9.3 ).
| Measure | Definition by Canet et al. 2010 | Other definition |
|---|---|---|
| Respiratory failure | Postoperative PaO 2 < 60 mmHg on room air, a ratio of PaO 2 to FiO 2 < 300, or arterial oxyhemoglobin saturation measured with pulse oximetry < 90% and requiring oxygen therapy | Requires invasive or noninvasive mechanical ventilation |
| Suspected pulmonary infection | Treatment with antibiotics for a respiratory infection, plus at least one of the following criteria: | Clinical diagnostic criteria for nosocomial pneumonia |
| New or changed sputum | ||
| New or changed lung opacities on a clinically indicated chest radiograph | ||
| Temperature > 38.3°C | ||
| Leukocyte count > 12,000/mm 3 | ||
| Atelectasis | Suggested by lung opacification with shift of the mediastinum, hilum, or hemidiaphragm toward the affected area and compensatory overinflation in the adjacent nonatelectatic lung | Requires intervention (bronchoscopy, postural therapy) |
| Aspiration pneumonitis | Respiratory failure after the inhalation of regurgitated gastric contests | |
| Pneumothorax | Air in the pleural space with no vascular bed surrounding the visceral pleura | Requires drainage |
| Pleural effusion | Chest radiograph demonstrating blunting of the costophrenic angle, loss of the sharp silhouette of the ipsilateral hemidiaphragm | Requires drainage |
| Bronchospasm | Newly detected expiratory wheezing treated with bronchodilators | Requires bronchodilator therapy |
| ARDS | Acute onset < 1 week, bilateral infiltrates on CXR, hypoxemia as evidenced by PaO 2 /FiO 2 < 300, minimal evidence of left atrial fluid overload, PCWP < 18 cm H 2 O | |
| Tracheobronchitis | Purulent sputum with normal chest radiograph, no IV antibiotics | |
| Pulmonary edema | Pulmonary congestion/hypostasis, acute edema of lung, congestive heart failure | |
| Exacerbation of preexisting lung disease | Not further defined | |
| Pulmonary embolism | Not further defined |
Etiology and Pathophysiology
The mechanisms leading to PPCs are complex and only partially understood. Factors related to preexisting diseases, surgical trauma, and anesthesia interact in predisposing a patient to the development of PPC ( Fig. 9.1 ). Perioperative loss of lung volumes with consequent formation of atelectasis is widely accepted as one of the most important mechanisms leading to PPC. Atelectasis is initiated during anesthesia and mechanical ventilation and deteriorates gas exchange intraoperatively and in the early postoperative period. Using computed tomographic scans of the chest, Hedenstierna et al. observed small areas of alveolar collapse shortly after the induction of general anesthesia in healthy subjects but could not demonstrate the same phenomenon in patients receiving epidural anesthesia. The causes of the formation of atelectasis during general anesthesia are multiple. Lung tissue has a natural tendency to display gravity-dependent alveolar collapse during mechanical ventilation, as suggested by the fact that atelectasis is located in the recumbent parts of the lungs ( Fig. 9.2 ). Mechanical ventilation and muscle relaxation cause cephalad displacement and decreased respiratory excursion of the posterior part of the diaphragm, a finding that explains the dominant caudal distribution of the areas of atelectasis ( Fig. 9.3 ). High fraction of inspired oxygen and lower pulmonary distending pressures predispose to dependent airway closure and subsequent absorption atelectasis. The three mechanisms postulated for atelectasis during general anesthesia are compression of lung tissue, absorption atelectasis, and loss of surfactant.
Functional residual capacity declines after surgery, and the observed changes are bigger when the site of surgical incision is closer to the diaphragm. Pain and surgical trauma lead to limitation of inspiratory excursion and are important contributors to postoperative lung volume loss. Pain in the immediate postoperative period causes spinal reflex inhibition of the phrenic nerve due to nociceptive inputs to ventral and ventrolateral horns of the spinal cord, which affect the diaphragm function. There is also evidence that surgical manipulation of upper abdominal viscera results in a reflex dysfunction of the diaphragm muscle that is not related to pain, as shown in patients after laparoscopic cholecystectomy. Atelectasis is considered a relevant complication in itself, because it can cause hypoxemia and respiratory failure and also because it could predispose to pneumonia. However, a causative link between atelectasis and pneumonia remains undemonstrated. Experimental data showed limited bacterial growth following alveolar recruitment in an animal model of pneumonia, suggesting that collapsed lung provides a favorable environment for infection.
In addition to volume loss, other factors play a role in the genesis of PPC and of postoperative pneumonia. An important factor is probably mucous retention caused by decreased coughing resulting from pain and medications and by dysfunction of mucociliary transport in the airway mucosa. Mucociliary transport is an important mechanism of pulmonary defense, and its velocity is decreased by anesthesia and by endotracheal intubation with a cuffed tube. Smokers have a decreased mucociliary transport velocity during anesthesia compared with nonsmokers, a finding that may help to explain the high rate of PPC in these patients. It is not clear how long this functional impairment of mucous transport lasts after the end of anesthesia and extubation.
Aspiration of contaminated oropharyngeal secretions is thought to be a prominent mechanism leading to nosocomial and postoperative pneumonia. Residual subclinical muscle relaxation has been detected in patients who received long-acting muscle relaxants, and it was associated with an increased rate of pulmonary complications. Residual effects of neuromuscular blockers cause atelectasis in the postanesthesia care unit. Residual blockade is defined as a train-of-four ratio of < 0.9, which is associated with lower values of forced vital capacity and of peak expiratory flow rate as measured by pulmonary function testing (PFT). Poor airway protection and aspiration of secretions are probably even more common after certain procedures, such as transhiatal esophagectomy, explaining the 28.5% rate of PPCs observed after this surgery.
Finally, chronic obstructive pulmonary disease (COPD) causes gas exchange and respiratory mechanics abnormalities that reduce the patients’ ability to tolerate superimposed acute lung disease and render them prone to respiratory failure. Additionally, patients with COPD have dysfunction of the respiratory muscles due to chest wall deformation and to myopathy. These patients may be unable to withstand the increased ventilatory demand and the higher work of breathing required in the postoperative period and may require ventilatory support earlier than patients with normal muscle function.
Preoperative Pulmonary Evaluation for Nonthoracic Surgery
The preoperative pulmonary evaluation is an integral part of the general preoperative risk assessment. The evaluation should start by collecting information on the patient’s overall health status, then focus on the respiratory system and include a careful exam.
The majority of patients undergoing nonthoracic procedures are less likely to benefit from instrumental testing. They should proceed to have surgery, have it postponed, or have it denied without further evaluation. This approach should be the same, regardless of the type of planned surgery, and differs from the evaluation of the patient candidate for pulmonary resection, which is discussed later in this chapter.
For better understanding, the risk factors for PPC are grouped into patient factors and operative factors. Patient factors include pulmonary and extrapulmonary factors, while the operative factors include anesthesia and surgical factors, which are discussed separately.
Patient Factors
Pulmonary Factors
After an evaluation of the overall health status, history taking should elicit specific pulmonary risk factors, such as chronic or acute pulmonary diseases, smoking history, and sleep-related breathing disorders.
The presence of COPD was associated with an increased risk of PPCs in multiple studies. In the NSQIP population, a previous diagnosis of COPD was an independent risk factor for postoperative pneumonia (odds ratio [OR], 1.71), reintubation (OR 1.54), and failure to wean from the ventilator (OR, 1.45). Even when a history of COPD is not documented, its presence should be suspected on the basis of elements of the history, such as elevated sputum production. In a prospective study on 148 veterans undergoing nonthoracic surgery, the presence of elevated preoperative sputum production was an independent predictor of PPC by multivariate analysis. A systematic review by Smetana et al. in COPD patients undergoing nonthoracic surgery showed that the OR for PPCs attributable to COPD was 2.36.
It is unclear whether a history of asthma is associated with increased rates of clinically significant PPCs. In a review of records of 706 patients with asthma undergoing surgery, Warner et al. reported a small incidence (1.7%) of bronchospasm during or after surgery. The rate of this event was higher in patients who had a recent asthma exacerbation. However, the incidence of more severe complications and postoperative respiratory failure (PRF) was negligible in this study. In both prospective studies by McAlister et al., a history of asthma was not associated with a higher risk of PPCs.
A history of recent acute pulmonary process or exacerbation of preexisting lung disease is a high-yield finding because these patients are prone to airway hyperreactivity and to altered immune responses, which are often related to antibiotic use or to the infection itself. Such history is considered a risk factor for developing PPCs and is thought to be an adequate reason to postpone elective surgery. In the NSQIP study, the presence of preexisting pneumonia had an OR of 1.7 for developing PRF. For patients who have had a recent or have an ongoing upper respiratory infection, postponing the operation is probably appropriate in the setting of elective surgery, but the evidence supporting this decision is relatively weak. Studies reported more frequent episodes of oxygen desaturation but no major pulmonary complications or morbidity. For example, a recent upper respiratory infection significantly complicated the postoperative course in children after cardiac surgery, but there is little evidence that this problem also occurs in adults. In the study by Warner et al., asthmatic patients with recent upper respiratory infections were not at increased risk of PPC compared with the rest of the population. In a prospective study, a history of upper or lower respiratory infection was not associated with a higher risk of PPC. Similarly, recent upper respiratory infections were not associated with PPCs in both studies by McAlister et al. Recently, however, Canet et al. included in their study patients who had recent upper and lower respiratory tract infections with a history of fever and recent antibiotic use. They found that 17.2% of the study population ( n = 2464) developed one or more PPCs, and recent respiratory infection was an independent risk factor.
The presence of dyspnea and exercise intolerance should be investigated during the preoperative evaluation because these symptoms have been related to the risk of PPCs. The association between dyspnea and PPCs was not confirmed in the previous studies. In fact, this was not a criterion in the risk index proposed by Arozullah. However, dyspnea was included in the Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT) risk score model proposed by Canet et al., which was validated in a prospective multicenter observational cohort study.
Having a history of tobacco use is probably the most solid risk factor for PPC, because smoking has been established to be an independent predictor of PPC by several studies. In patients who are not current smokers, the risk of contracting a PPC decreases with time from smoking cessation, but it is unclear how much time is required for this risk to decrease optimally. Warner et al. reported that patients who quit smoking less than 8 weeks prior to surgery had a higher rate of PPC than patients who quit earlier. However, a longer smoke-free period seems to be needed to reduce the risk of PPCs to the level of the nonsmoking population, as suggested by the study by Arozullah et al., which showed that having smoked within 1 year before surgery increased the risk of pneumonia compared with the remaining patients. On the basis of study results, it has been suggested that smokers who do not quit entirely or who quit less than 8 weeks before surgery may have an increased risk of PPC not only compared with the nonsmoking population but also compared with patients who did continue to smoke. The results of the studies by McAlister et al. suggested that the extent of previous tobacco consumption may be a more important risk factor for PPCs than the timing of smoking cessation. Canet et al. observed that the PPC was related to the number of pack-years smoked and that history of smoking more than 40 pack-years was associated with PPCs in bivariate analysis. In a recent meta-analysis, preoperative smoking was found to be associated with PPCs (relative risk [RR]= 1.73; 95% confidence interval [CI], 1.35–2.23) but not with postoperative mortality.
Obstructive sleep apnea (OSA) is a sleep-related breathing disorder with a relatively high prevalence in the population and with a significant impact on health. The prevalence of symptomatic OSA has been estimated to be around 5%, while the prevalence of asymptomatic OSA is likely to be near 20%. Sleep-related breathing disorders are diagnosed and graded by measuring the apnea–hypopnea index by polysomnography. However, only a minority of patients with OSA present with a previous instrumental diagnosis. Finkel et al. screened surgical patients who were at high risk of OSA and noted that 81% of patients were unaware that they had sleep apnea prior to surgery.
The presence of sleep apnea may be associated with an increased rate of perioperative complications. In fact, OSA is accompanied by a cluster of comorbidities that can affect surgical outcomes. These include systemic hypertension and pulmonary hypertension (PH), right heart failure, diabetes, obesity, and stroke. However, it is also a common perception that OSA per se may independently increase the risk of complications of surgery and anesthesia. Patients with sleep-related breathing disorders have decreased control of airway muscle tone and of ventilation during sleep, which is exacerbated by long-acting narcotics and by residual anesthetic effects in the postoperative period. Airway problems, postoperative hypoxemia, and ventilatory failure occur in a severity-dependent manner in OSA patients undergoing upper airway surgery. However, there is limited evidence that OSA is associated with morbidity in other types of surgery. Memtsoudis et al. analyzed a national database to evaluate the effect of sleep-disordered breathing on pulmonary outcomes in orthopedic and general surgical populations and found an increased risk of worse pulmonary outcomes, including aspiration pneumonia, acute respiratory distress syndrome (ARDS), and emergent endotracheal intubation, but not pulmonary embolism.
STOP-Bang Questionnaire
In a Canadian study of surgical patients, a STOP-Bang score of 5–8 identified patients with high probability of moderate/severe OSA with high specificity ( Table 9.4 ). The American Society of Anesthesiologists (ASA) task force recommendations 62 are as follows:
- ▪
Continuous positive airway pressure should be initiated in patients with severe OSA preoperatively.
- ▪
There is insufficient literature to offer guidance regarding which patients with OSA can be safely managed on an inpatient versus outpatient basis. It should be a combined decision between the surgeon and anesthesiologist, individualized to the patient.
- ▪
A routine sleep study for all patients with OSA was not recommended.
- ▪
In patients who have had corrective airway surgery, such as uvulopalatopharyngoplasty or surgical mandibular advancement, it should be assumed that they remain at risk of OSA complications unless proven otherwise by a normal sleep study or reversal of symptoms.
| 1. Snoring | Do you snore loudly (louder than talking or loud enough to be heard through closed doors)? | ||||
| 2. Tired | Do you often feel tired, fatigued, or sleepy during daytime? | ||||
| 3. Observed apnea | Has anyone observed you stop breathing during your sleep? | ||||
| 4. Blood pressure | Do you have or are you treated for high blood pressure? | ||||
| 5. BMI | Is it more than a 35 kg/m 2 ? | ||||
| 6. Age | Age over 50 years old? | ||||
| 7. Neck circumference | Neck circumference greater than 40 cm? | ||||
| 8. Gender | Gender male? | ||||
| Score 1 point for each positive outcome. | |||||
| Interpretation: 0–2 = low risk; 3–4 = medium risk; 5–8 = high risk for OSA | |||||
Physical Examination
Physical examination is another essential tool in the preoperative evaluation of the patient’s pulmonary status because it allows the detection of unrecognized pulmonary disease. Although the diagnosis of chronic lung disease is often made by instrumental testing, a combination of data from patient history and from physical exam has reasonable accuracy in predicting the presence of COPD. Lawrence et al. documented that having an abnormal thoracic physical exam result was an independent predictor of PPCs. However, the exact abnormalities detected were not specified, thus decreasing the applicability of their results. The studies by McAlister et al. are more informative because they rigorously evaluated specific physical findings and detected significant correlations between these and the risk of PPCs ( Table 9.5 ). In these studies, multiple physical findings correlated with the incidence of PPCs, and two of them were independent predictors of complications: decreased laryngeal height and positive cough test. The presence of wheezing on standard auscultation is usually considered an important physical sign, but it was not significantly associated with a higher risk of PPCs in these studies. This result is in agreement with a previous study where decreased laryngeal height was an independent predictor of the presence of COPD diagnosed by spirometry, while wheezing was not. These studies suggest that simple findings obtained through a methodical physical exam may help in the prediction of the probability of PPCs. However, none of the physical examination parameters have been added in the current risk prediction models, which were mostly derived from medical record data.
| Finding | Technique | Odds ratio (95% CI) | P value |
|---|---|---|---|
| Positive cough test | Coughing once after deep inspiration triggers recurrent coughing | 4.3 (1.5–12.3) a 3.84 (1.51–9.80) b | 0.01 0.01 |
| Positive wheeze test | Wheezing after five deep inspirations/expirations | 3.4 (1.2–9.4) a 0.94 (0.12–7.08) b | 0.04 1.00 |
| Forced expiratory time ≥ 9 seconds | Duration of forced exhalation after one deep inspiration | 5.7 (2.3–14.2) a 4.28 (1.22–15.02) b | 0.0002 0.04 |
| Maximum laryngeal height ≤ 4 cm | Distance between the sternal notch and the top of the thyroid cartilage at end expiration | 6.9 (2.7–17.4) a 1.17 (0.44–3.12) b | < 0.0001 0.79 |
| Wheezing on standard auscultation | Presence or absence of wheezing on standard thoracic exam | 3.1 (0.9–10.0) a 2.39 (0.54–10.51) b | 0.13 0.23 |
a Data from McAlister FA, Khan NA, Straus SE, et al. Accuracy of the preoperative assessment in predicting pulmonary risk after nonthoracic surgery. Am J Respir Crit Care Med 2003;167(5):741-744.
b Data from McAlister FA, Bertsch K, Man J, et al. Incidence of and risk factors for pulmonary complications after nonthoracic surgery. Am J Respir Crit Care Me d 2005;171(5):514-517.
Extrapulmonary Factors
A review of the patient’s general history is important to increase the accuracy of the preoperative pulmonary evaluation because several extrapulmonary factors correlate with the probability of PPCs. Advanced age is probably an important risk factor. Early studies did not include multivariate analysis to account for the presence of coexisting diseases in older patients and were probably flawed. Later studies that did account for the other conditions confirmed that an association between age and PPC exists. Li et al. found the association of age as an independent risk factor for postoperative complications in patients undergoing abdominal aortic aneurysm (AAA) repair. Similar results were shown in two studies in patients undergoing nonthoracic surgery. Arozullah et al. detected an independent association of advanced age with both postoperative ventilatory failure and postoperative pneumonia. Patients older than 80 years of age are 5.1 times more likely to have PPCs than patients who are younger than 50 years of age. These studies used multivariate analysis and fulfilled the criteria of a high-quality design for the evaluation of prognostic variables. This aspect is relevant here in the context of increasing rate of surgeries in elderly patients.
Other nonpulmonary factors are associated with the risk of PPCs. Arozullah et al. reported that indexes of a poor nutritional status, such as a low serum albumin concentration and a history of weight loss, and indexes of an altered blood volume status, such as abnormal blood urea nitrogen concentration, were all associated with PRF and with pneumonia. In these same studies, an increased probability of PPCs was also observed in patients who had a history of dependent functional status, recent alcohol use, diabetes, congestive heart failure, and renal failure. Preoperative neurologic impairment and history of stroke have also been reported to be independent predictors of PPCs in more than one study, probably due to an increased occurrence of aspiration of gastric or pharyngeal secretions. Evidence suggests that congestive heart failure is one of the significant risk factor for PPCs (OR, 2.93; CI, 1.02–8.43).
The ASA classification is a reasonable instrument to evaluate the patient’s overall physical condition, and its score is related to the incidence of postoperative complications. Multiple studies have detected a correlation of the ASA score with PPCs. An ASA score higher than 2 was predictive of PPCs after abdominal surgery. In a prospective longitudinal study, the coexistence of advanced age and ASA score > 2 identified the majority (88%) of the patients who developed any PPC. Gupta et al. analyzed NSQIP data and studied the preoperative variables associated with PPCs. After multivariate analysis, patients in the ASA class IV had an OR of 1.28 (CI, 1.04–1.57) for PPCs. Recently, ASA was included as a component of the PRF risk index proposed by Gupta et al.
Other health classification systems that are not specifically focused on the respiratory system may be useful in the pulmonary evaluation. Both the Goldman cardiac risk index and the Charlson comorbidity index have been reported to be associated with the incidence of PPCs. Preoperative functional dependence and altered sensorium were shown to be risk factors. Preoperative anemia as defined by hemoglobin < 10g% was shown to be associated with a threefold higher risk for developing PPC. At the same time, there is no clear evidence to show that preoperative transfusion eliminates the risk.
Other risk factors are supported by equivocal evidence, including gastroesophageal reflux, alcohol abuse, weight loss, diagnosis of cancer or sepsis, and a positive cough test. There is no strong evidence to state whether exercise ability, diabetes, and human immunodeficiency virus infection are independent risk factors for PPCs.
It is common to assume that patients who are obese are at high risk of having PPCs, but this belief has been questioned on the basis of studies that failed to detect correlations between obesity and PPCs. For example, a study on patients undergoing thoracotomy did not find a higher risk of PPCs in obese patients. However, factors related to the type of surgery and to patient selection in these studies might explain these results, because other studies did detect a correlation between obesity and PPCs. In fact, an elevated body mass index (BMI) was an independent predictor of PPCs by multivariate analysis in at least two studies. In the prospective blinded study by McAlister et al., a BMI > 30 kg/m 2 was associated with increased risk for PPCs by univariate analysis, although the correlation was not significant by multivariate analysis. The guidelines of the American College of Physicians (ACP) state that obesity is not a significant risk factor for PPCs and should not affect patient selection for otherwise high-risk procedures. This statement is true even for a morbidly obese patient.
Surgical Factors
Multiple studies reported correlations between surgical factors and incidence of PPCs ( Table 9.6 ), both the type of surgery and the location of the incision are key contributors to this pulmonary risk. In the studies by Arozullah et al., abdominal aortic, thoracic, and upper abdominal surgery were the strongest of all independent predictors of PPC because they had the highest ORs for respiratory failure and pneumonia. Other studies reported increased risk of PPCs during abdominal surgery and particularly after upper abdominal incisions. In fact, the risk of PPCs is higher when the incision is closer to the diaphragm. McAlister et al. detected a correlation between the rate of PPCs and abdominal surgery, although this was not confirmed by univariate analysis. This discrepancy with previous studies may be explained by the fact that only a minority of the study patients underwent upper abdominal surgery in McAlister’s study. Emergent surgery was associated with higher risk of PPC. In the NSQIP studies, both neurologic and neck surgery were associated with increased risk of respiratory failure and pneumonia, suggesting a role of poor airway protection in the genesis of PPC, although the ORs were not as high as for thoracoabdominal surgery.
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