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Preoperative Risk Assessment of Respiratory Failure

Brinson, Erika L. MD*; Thornton, Kevin C. MD*

International Anesthesiology Clinics: January 2018 - Volume 56 - Issue 1 - p 26–46
doi: 10.1097/AIA.0000000000000170
Review Articles

Preoperative risk assessment is a critical step in preparing patients for surgery. The average cost of a hospital stay more than doubles for patients who have even minor postoperative complications,1,2 highlighting the need to identify and optimize those at risk. Cardiac assessment is routine before noncardiac surgery, with well-studied tools and guidelines in place for risk stratification.3 Postoperative pulmonary complications (PPCs) are more common than cardiac complications4,5 and carry a far greater cost.2 Unfortunately preoperative pulmonary risk assessment has historically been a vague task and the impact of PPCs widely underappreciated.

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The heterogenous nature of PPCs makes them more difficult to study than cardiac complications, partly because of inconsistent definitions. Most studies include some combination of atelectasis, pneumonia, bronchitis, bronchospasm, hypoxia, respiratory failure, prolonged mechanical ventilation, and exacerbation of underlying chronic lung disease.6–9 Pulmonary edema and pulmonary embolism are occasionally added, but the pathophysiology is different; hence, they will be omitted from this discussion. In 2015 a joint task force of the European Society of Anaesthesiology and the European Society of Intensive Care Medicine published specific definitions for PPCs with an aim to standardize criteria for future research10 (Table 1).

Table 1

Table 1

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Compared with other postoperative complications, the clinical and financial burden of PPCs is often overlooked.11 PPCs are second only to wound infections as the most common postoperative complications.2 Most large studies show rates of around 2% to 6.8%.4,7,8 PPCs may be more predictive of long-term mortality than cardiac complications.12,13 Older patients who require surgery have increased mortality in the following months, and, for those who suffer postoperative complications, the mortality rate increases sevenfold.12 One study showed that the 30-day mortality rate for patients with postoperative respiratory failure (PRF) was 27% versus 1% in those without.14 Five-year and 10-year mortality among patients who suffered PRF was >50% and >70%, respectively.15 PPCs reduce median long-term survival by 87%,15 and patients report worse physical function and both worse physical and mental health in the following years.16 PPCs are also associated with worse outcomes and increased rates of rehospitalization.8

PPCs are the most expensive group of postoperative complications. They increase the cost of the average hospitalization 12-fold and can nearly quadruple the length of stay.2 This adds up to an estimated cost of over $3.4 billion annually in the United States alone.11 Correctly identifying patients at high risk allows preoperative optimization, improved surgical planning, targeted respiratory interventions, and admission to the appropriate level of care.

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Perioperative Pulmonary Physiology

The combination of major surgery and general anesthesia leads to a series of structural and functional changes that predispose the lungs to complications. Postoperative pulmonary physiology is characterized by restrictive changes causing a decrease in all lung volumes,17–19 particularly following surgery close to the diaphragm.20 After upper abdominal surgery, there is a reduction in vital capacity (VC) by 50% to 60% and functional residual capacity (FRC) by ≥30%,17 often accompanied by a complete absence of abdominal muscle movement for 24 hours.21 There is a shift toward rib cage breathing using accessory muscles, similar to the pattern seen after bilateral diaphragm paralysis.19 The marked reduction in VC and diaphragm excursion persists for at least a week following surgery.21 Diaphragm impairment is not seen with lower abdominal surgery and the return to baseline VC is much more rapid.21

Pulmonary function reaches a nadir, 24 to 72 hours postoperatively, usually returning to baseline over the next 7 days, but can remain depressed for longer than 3 weeks.18,22 The FRC may drop below closing capacity, particularly in elderly patients23 and in those with chronic lung disease, leading to airways that remain closed throughout the respiratory cycle.22 FRC is decreased regardless of the type of anesthesia, mode of ventilation, or absence of paralysis.23

Atelectasis develops in the dependent portion of the lung in 90% of anesthetized patients.24 The causes seem to be 3-fold: absorption behind closed airways (an effect worsened by inhaling high concentrations of oxygen),23 external compression of lung tissue,25 and loss of surfactant or surfactant function.26 Increasing atelectasis leads to worsening ventilation/perfusion mismatch and shunt fraction, which in turn decrease the arterial partial pressure of oxygen, an effect that is more pronounced in older patients.24 Even a short general anesthetic can produce lung injury27 from repeated opening and closing of alveoli, causing stress and inflammation.25

Lung compliance is decreased and resistance is increased,23 leading to increased work of breathing.18 An abnormal respiratory pattern develops with rapid, shallow respirations, and the absence of sighs.20 Patients may be unwilling or unable to take deep breaths because of pain, diaphragm dysfunction, and other factors.22 The cough reflex and force are impaired, with an association between the degree of impairment and risk of PPCs.28 Residual anesthetic effects and opioids decrease the response to hypoxia and hypercarbia.20

The risk of aspiration increases postoperatively.29 Impaired defenses may allow aspirated bacteria to proliferate.30 On a microscopic level there is decreased mucociliary clearance,18 reduction in the number and activity of alveolar macrophages, increased alveolar-capillary permeability, inhibition of surfactant function and release, increased activity of nitric oxide synthetase, and enhanced sensitivity of the pulmonary vasculature to neurohumoral mediators.6,30

Age-related pulmonary changes make the lungs less resilient following surgery and general anesthesia. These changes include decreased elastic recoil and chest wall compliance, increased closing capacity, decreased alveolar surface area causing decreased VC, increased residual volume, and increased ventilation/perfusion mismatch.31 Older patients generally have decreased respiratory muscle strength, increased work of breathing, decreased pulmonary reserve, and increased sensitivity to respiratory depressants,31 putting them at high risk for PPCs.

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Preoperative Risk Factors

Identifying the important risk factors for PPCs has been challenging. More than 50 separate variables have been found statistically significant.32 Although many are interesting targets for further investigation, clinicians should focus on recognizing the most significant risk factors. Half of the risk comes from patient-related factors and the other half from surgical ones.32 Unfortunately, many important predictors of PPCs are nonmodifiable. Some, such as nutritional status, chronic obstructive pulmonary disease (COPD), congestive heart failure, and anemia, can potentially be optimized before surgery, but there are no data demonstrating that this improves outcomes. Interestingly, conditions that directly affect the preoperative pulmonary status, such as COPD, smoking, and dyspnea, seem to confer a more modest risk.8 The following risk factors are listed in approximate order of importance (Table 2).

Table 2

Table 2

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Surgical Site

Surgical site is the single most important risk factor for PPCs. Thoracic and upper abdominal procedures are particularly high risk in nature,7,8,14,33–37,46–49,52 presumably because of their proximity to the diaphragm. Lung resection,7 esophageal surgery,8,38,39 and open aortic aneurysm repair7,14,40,41 also have high rates of PPCs. Postoperative pulmonary and diaphragm dysfunction, pain, and tissue injury probably all contribute to the risk.32 Other surgeries, including lower abdominal surgery,42 peripheral vascular surgery,41,50 neurosurgery, and head and neck surgery,53 also increase risk, but to a more moderate degree.7,14,40 The relatively high incidence of PPCs following vascular surgery may be partly attributable to the burden of comorbidities present in many vascular patients.32

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Advanced Age

Advanced age is one of the most significant risk factors across a wide variety of surgical procedures.8,33–39,41–45 The risk begins increasing at 50 years,7 and continues rising with age,14,40 particularly for patients older than 80 years of age.8,36 Advanced age has been associated with increased postoperative morbidity, mortality, and most types of postoperative complications.72 In many studies it may be a surrogate for comorbidity, disability, and frailty,32 the latter of which has emerged as an important concept in preoperative assessment.73 Aspects of frailty, such as impaired cognition, function, and mobility, are associated with worse surgical outcomes.32,54,73

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Procedure Duration

Longer surgeries and anesthetics increase the risk for PPCs.7,8,38,41,42 The incidence begins climbing when procedures exceed 2 hours35,36,44 and may continue to increase with the operative time.44 The risk for PPCs following prolonged surgery may be even higher than with surgery near the diaphragm.32,36,49 Minimizing operative time could be beneficial to high-risk patients.32

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American Society of Anesthesiologist (ASA) Classification

ASA Physical Status classification, despite its high interrater variability,74 is an important predictor for PPCs.37,41,46 Risk begins to increase with each classification >1,7 and most studies show substantial increases with ASA≥3.8,33,38,43–45,51 As ASA class reflects overall severity of illness, this is a logical association, but it does not offer any specifics about which conditions should be intervened upon to minimize risk.32

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Emergency Surgery

Emergency surgery is an independent predictor of PPCs7,14,36,38,40,41,42,45,46,48,49,51 and increased postoperative mortality.75 No studies have shown whether postponing surgery decreases this risk.32

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Preoperative Oxygen Saturation

Preoperative room air pulse oximetry (SpO2) was rarely included in older studies, but the development and validation of a simple method of stratification by Canet et al36,49 makes it a valuable tool. They grouped patients on the basis of room air SpO2≥96%, ≤95%, and ≤90%, and found that low SpO2 was the single most important risk factor for PPCs. It overshadowed COPD, smoking, and heart failure as risk factors on multivariate analysis, possibly because it is a surrogate for the severity of disease for all of these processes.36 Other studies have supported these findings,48,76 but further investigation may improve its utility.57

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Heart Failure

Congestive heart failure has been shown to be a strong predictor of PPCs.7,14,38,41,45,49,50 The risk increases with disease severity.32,49

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Dyspnea and Respiratory Infection

Preoperative dyspnea and respiratory symptoms markedly increase the risk for PPCs,8,38,39,48,50 possibly because they provide evidence of acute exacerbation32 or suboptimal management of underlying lung disease. Chronic sputum production77 and preoperative respiratory infection may also put patients at risk.14,36,49 Active respiratory symptoms may be a bigger risk than a recent infection, but delaying surgery could be reasonable in the presence of other major risk factors (age, ASA, high-risk surgery, etc.).32

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Serum Albumin

When included, low serum albumin has been a consistent risk factor for PPCs.14,38 Unfortunately, it is often excluded, particularly in retrospective studies, because it is not routinely collected.32 Most studies show elevated risk at <3.5 g/dL,7,38 increasing with worsening nutritional status.14 Low albumin is a predictor of postoperative mortality and should be measured routinely to help with risk stratification.75

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Severe COPD

Severe COPD conferred significant risk7,8,35,37–41,43,45,47,50,51 in all except a few older studies that did not account for disease severity.33,34 COPD is often of great concern to the clinician performing the preoperative evaluation, but the weighted risk is lower compared with several other conditions.32 This may be due to variability in the rigor of diagnosis, accuracy of charting, and study design, all of which can fail to accurately stratify patients on the basis of disease severity.32 Properly staging COPD may improve its predictive value.32

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Functional Status/Dependency

Dependent functional status is a strong predictor of PPCs,8 particularly for fully dependent patients.7,14,37,39,40,46 Patients who are nonambulatory41 or admitted from a location other than home48 may also be at high risk. Functional dependence is another indicator of frailty and becomes more prevalent with age. Approximately 30% of patients older than 70 years of age have some degree of disability.32

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Renal Dysfunction

Acute kidney injury, chronic kidney disease,7,14,38,40,41 and renal failure8,14,38,39,41,51 may all increase the risk for PPCs. The presence of multiple comorbidities and perioperative volume overload may account for this risk.32

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Anemia is common in preoperative patients, nearly 40% in 1 study.78 Even mild anemia is associated with both increased 30-day mortality78 and PPCs,38,41 independent of the need for transfusion.32,36 Perioperative blood transfusion7,14,40,42,51 and significant intraoperative blood loss42 have also been correlated with an increased risk for PPCs. It is unclear whether the risk is related to anemia or transfusion. The optimal target hemoglobin is yet to be determined.32

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Preoperative sepsis44,50 and shock8,37,38,46,48 are likely risk factors. Intraperitoneal infection33 and open39 or infected38 surgical wounds may also predispose patients to PPCs.

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Recent Weight Loss

Patients with a weight loss of >10% in the 6 months before surgery have an increased rate of PPCs.7,14,38,40,50 Being underweight41,50 or having low muscle mass (low blood urea nitrogen)40 may also be important risk factors, possibly because of poor nutritional status.32

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Impaired Sensorium

Patients with impaired sensorium have a higher risk of many postoperative complications, including PPCs.14,38,40,54 Delirium is associated with increased mortality79 and poses a risk to nonsurgical patients as well. Investigations into the best methods for prevention and treatment are prevalent in the critical care literature, but successful interventions have been limited.80 Impaired sensorium may be another marker of frailty and tends to occur in older patients with multiple comorbidities.54

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As far back as the 1940s, smoking was considered a risk factor for PPCs, and some were advocating preoperative smoking cessation.81 Many studies confirm this risk.8,35,37,38,40,41,43,50,52 However, it may not be as significant as expected,36 possibly because younger smokers have not developed clinical evidence of lung disease, which seems to be an important factor for PPCs.32

The optimal timing for preoperative smoking cessation remains unclear. Several studies showed that short-term cessation, 2 to 8 weeks before surgery, either resulted in a small-risk reduction82 or at least no increased risk.83 Intensive preoperative intervention is advisable, as many patients successfully stop smoking permanently, and smoking cessation may decrease the risk for other serious postoperative complications, such as wound infections.83,84

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Alcohol use >2 drinks per day may be a risk factor for PPCs,14,38,40 but studies that did not quantify the amount used have found a more variable association.36,47,50 Whether eliminating alcohol decreases complications and the optimal timeframe to stop before surgery is unknown.84

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Genetic Variations

Genetic variations of inflammatory mediators, such as vascular endothelial growth factor (VEGF), have been linked to PPCs64 and acute respiratory distress syndrome (ARDS).65,66 The VEGF pathway is an important mediator of the inflammatory response to lung injury67 and seems to protect the pulmonary endothelium and helps moderate capillary permeability in ARDS.66 Large-scale studies are still needed, but this may be an important area for future investigation.

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General Anesthesia

General anesthesia may place patients at an increased risk for PPCs,7,38–40 but this finding is not ubiquitous.8,35 Whether the risk is abated by perioperative neuraxial or regional techniques is questionable,42,56 particularly with the improved safety of general anesthetics.32

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Obstructive Sleep Apnea (OSA)

Many studies have found OSA to be a risk factor for serious complications, such as myocardial infarction, as well as postoperative oxygen desaturation58 and CO2 retention, but have not specifically found an increased risk for PPCs.59 One study did show that severe OSA was a moderate risk factor, but it did not matter whether the OSA was diagnosed or undiagnosed.60 The conflicting evidence7,57 may be due to variability in diagnosis and perioperative management. It is unlikely a significant risk if appropriately managed,57,61 although it still needs further study.32

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Other Significant Factors

Liver disease seems to be a significant risk factor for PPCs8,38,48–50 and is included on several risk indices.39,49 Some studies have found an association between male sex and PPCs,8,38,51 but others have found no link, and sex is not included on most risk indices.14,36,39,44,46

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Possible Risk Factors

Besides COPD, other pulmonary diseases that have been associated with elevated risk include pulmonary hypertension85 and interstitial lung disease.86 Diabetes is a frequently studied variable,7,14,36,40,44,46,47,49–51 but seems to be a less important factor and is not included in final risk indices.32 A current diagnosis of cancer may also confer some degree of risk.34,39,50 Factors identified in a small number of studies include hypertension,50 gastroesophageal reflux disease,47 corticosteroid use,7,39,40 bleeding disorders,38 hypernatremia,38 and cerebrovascular disease.14,38,40 These conditions may contribute to risk, but are probably of much less importance than other variables.

In certain circumstances, laparoscopic surgery may decrease the risk versus an open procedure,49,62 but this connection is not well established.63 Nasogastric tubes have also been correlated with PPCs,35 but most recent studies have not borne this out.

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Insignificant Factors

Despite a correlation in some early studies33,34 increasing body mass index alone is not a predictor of PPCs,7,8,36,45 although in certain situations it may confer some degree of risk.43,50 Well-controlled asthma has also not been found to be a significant factor.7 Hip,55 gynecologic, and urologic surgeries all seem to have a low rate of risk for PPCs.7

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Preoperative Assessment

A thorough history and physical examination remains the most important component of the preoperative evaluation.87 History should include information about respiratory symptoms including cough, sputum production, exercise tolerance, and dyspnea, as well as recent pulmonary infections, chronic heart and lung disease, smoking, and alcohol use. Use of the STOP-Bang questionnaire to screen for OSA has been validated88 and is now widely advocated. Although patients with OSA have not been found at uniformly higher risk for PPCs, identification may improve perioperative management.

The physical examination should be thorough and include careful evaluation for signs of COPD, asthma, heart failure, neurological disease, and significant orthopedic abnormalities such as spinal deformities that could impair respiration. Evidence of frailty including memory difficulties, weakness, and poor functional status may also suggest increased risk.

A positive cough test has been found to be a risk factor for PPCs.35,36 The cough test can be easily performed during the examination by having the patient take a deep breath and cough once. If they involuntarily cough again the test is positive. The cough test has not been included in many studies, but it may be worth further investigation, as it is free and easy to perform.32

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Preoperative Testing

According to the 2012 ASA practice advisory on the preanesthesia evaluation, “preoperative tests should not be ordered routinely” and “may be ordered, required, or performed on a selective basis for purposes of guiding or optimizing perioperative management.”87 The clinician must weigh the possible gain against the cost and potentially irrelevant information that may be obtained.89 Routine screening tests have a low predictive value, and the findings are often either ignored or do not affect management.89,90 One review found that just 0% to 3% of abnormalities on preoperative testing influenced management, and only abnormalities in hemoglobin, electrolytes, and kidney function predicted significantly higher complication rates.90 Although certain test results, such as low forced expiratory volume in 1 second1,77 have been associated with PPCs, this information can often be gained from the history and a physical examination.

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Laboratory Testing

A complete blood count should be obtained before surgeries in which significant blood loss is expected or if there is suspicion of infection, leukopenia, severe anemia, or thrombocytopenia based on history and physical examination.90 Renal function tests are indicated for patients undergoing major surgery and those at risk of renal dysfunction,90 as renal insufficiency is a known risk factor for both PPCs8,14,38 and cardiac complications.3

There is a strong association between low albumin and PPCs.14,38 A low albumin level can alert clinicians to increased surgical risk and provide the opportunity to potentially reevaluate the urgency of a procedure. It is reasonable to check an albumin level if one has not been performed recently in patients with serious chronic illness, liver disease, recent major illness, or in whom malnutrition seems likely.90 However, no studies have been conducted to evaluate whether improving nutrition status has a significant effect on the risk for PPCs.

An arterial blood gas (ABG) is only occasionally indicated. A review of seven blinded studies showed that hypercarbia was not independently associated with increased risk.91 ABG results have not been shown to add predictive value for PPCs.52

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Pulmonary Function Testing (PFT) and Chest X-Ray

Preoperative PFTs do not predict PPCs,91,92 even in patients with severe COPD,93 and do not add to the pulmonary examination in identifying patients at elevated risk.7,94 No degree of respiratory impairment is an absolute contraindication to non–lung resection surgery.95 In 2006 the American College of Physicians recommended against the routine use of preoperative chest x-ray or spirometry to help predict the risk of PPCs.93 It is reasonable to order lung function tests in patients with unexplained dyspnea or exercise intolerance to differentiate between cardiac and pulmonary causes if clinical evaluation is equivocal.89,95 PFTs can also be used to determine whether patients with severe lung disease are optimized.95 PFTs are important for planning lung resection surgeries,94,95 but that is outside the scope of this discussion.

Rarely do preoperative chest radiographs reveal an unexpected finding, and, although over 20% are abnormal, <3% will change management.90 Patients who report recent upper respiratory infection, COPD, smoking, cardiac disease, or who are of advanced age have a high likelihood of having an abnormal chest x-ray,87 but, in most cases, these abnormalities have not been associated with PPCs.35 Chest x-ray may be reasonable in select patients, but, even in those patients with the risk factors listed above, it is not a required preoperative test.87

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Exercise Testing

Cardiopulmonary exercise testing, stair climbing, and 6-minute walk distance (6MWD) have all been used to measure preoperative fitness. Cardiopulmonary exercise testing measures the anerobic threshold in response to exercise and the maximal oxygen consumption (VO2Max). Increasing values of either indicate a fitter individual.95 There is an association between reduced peak VO2 and increased rates of PPCs after resection for lung cancer.68

Symptom-limited stair climbing may help predict risk for cardiopulmonary complications following high-risk surgery. One study found that patients unable to climb 1 flight of stairs had an 89% risk of complications, whereas those who could climb 7 flights had no complications.69

A low 6MWD has also been shown to correlate with increased risk for PPCs.70 One study showed that patients who developed PPCs had a shorter 6MWD (average 256 m) compared with those who did not (average 440 m). A 6MWD of ≤325 m was 77% sensitive and 100% specific for predicting PPCs, which was similar to the predictive ability of the forced expiratory volume in 1 second1.71 Although there is an association between reduced exercise capacity and development of PPCs, there are no studies to show that the results impact outcomes.

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Preoperative Pulmonary Risk Indices

A simple tool to predict pulmonary risk that mirrors the preoperative cardiac risk index has proven an elusive goal. The Cardiopulmonary Risk Index68 was one of the first attempts. It combined modified Goldman criteria and a pulmonary index that required both an ABG and PFTs to estimate the risk.68 The Cardiopulmonary Risk Index was initially found to have an excellent positive predictive value for PPCs in patients undergoing pulmonary resection for lung cancer,68 but it was inaccurate for other thoracic surgery patients96 and has been largely abandoned.

In 2000 Arozullah et al14 published a PRF risk index on the basis of a well-designed prospective cohort study of 81,719 primarily male patients undergoing noncardiac surgery and internally validated on an additional 99,390 patients from the National Veterans Affairs Surgical Quality Improvement Program (NSQIP).14 However, the system is cumbersome to use, lacks external validation, and was only designed to predict PRF, not all PPCs. In 2001 similar methods were used to develop the Postoperative Pneumonia Risk Index, which included many more risk factors.42 The widely cited 2006 guidelines from the American College of Physicians were based primarily on the results of the Arozullah trials.7,57,93 This was followed by the 2007 Patient Safety in Surgery (PSS) Study,38 a collaboration between the VA-NSQIP and the American College of Surgeons to explore whether the Arozullah PRF risk index was applicable to the private sector. They identified 28 variables as independent predictors of PRF, many of which required specific laboratory values, making it too complex for routine clinical use.

Following the Arozullah risk index, many scoring systems were developed on the basis of retrospective studies,37,39,44–48,50 several using the NSQIP database.37,39,44,46,50 The Gupta studies stand out because they were used to build online score calculators for both PRF and pneumonia, available at,46 The online calculators have the same limitations as many of the other studies: they are retrospective, are yet to be externally validated, and were based on the NSQIP data set.97 However, they are much easier to use. Some problems with the development of so many new risk indices were that each subsequent attempt added little or no new knowledge, and most were of limited practical utility.97

The Assess Respiratory Risk in Surgical Patients in Catalonia (ARISCAT)36 trial was a prospective, multicenter study that attempted to create a more generalizable scoring system by using a broad surgical population and including all PPCs as a composite outcome. The score correctly discriminated 90% of outcomes.36 In the validation sample, PPC rates were 1.6% for the low-risk group, 13.3% for the intermediate risk group, and 42.1% for the high-risk group. They identified seven variables that put patients at risk for PPCs: age, low preoperative room air oxygen saturation, acute respiratory infection in the month before surgery, preoperative anemia (≤10 g/dL), surgical incision site (upper abdominal or intrathoracic), duration of procedure ≥2 hours, and emergency surgery. This score was the first to highlight the significance of low SpO2, anemia, and recent respiratory infection and was also the first major study to specifically look at preoperative SpO2. Male sex and positive cough test were not included in the final model, but they did confer a moderate risk.57 Alcohol intake, obesity, snoring, and diabetes were all found to be unrelated to PPCs.

The ARISCAT score was recently validated by the Prospective Evaluation of a Risk Score for Postoperative Pulmonary Complications in Europe (PERISCOPE) study.76 This degree of external validation is rare in perioperative medicine and a first for PPC risk indices. It lends credibility97 to this index and supports its implementation in clinical practice.98 The ARISCAT score is probably the most useful risk index developed to date, as it is well validated, widely applicable, accurate, and simple. All required information can be easily collected at the preoperative visit. Patients who fall into the high-risk category have a >1 in 3 chance of having a PPC, a much greater risk than can be predicted with nearly any other assessment tool.

In 2015 Canet et al49 used the PERISCOPE cohort to build a risk score to predict PRF alone. PRF was stratified into 3 levels of severity on the basis of degree of hypoxia and type of respiratory support required. Seven independent predictors of PRF were identified: low preoperative SpO2 on room air, preoperative respiratory symptoms, heart failure, chronic liver disease, open thoracic or abdominal surgery, duration of surgery, and emergency surgery. The PERISCOPE-PRF score identified 82% of patients who would go on to develop PRF and distinguished 3 levels of risk. It has not yet been externally validated.49

There is still no consistent agreement about which are the most important risk factors for PPCs, probably because of the diversity of pulmonary complications and their definitions, population differences, variability in the risk factors examined, and study design.32 A one-size-fits-all predictive tool may never be possible, but validation of the ARISCAT score is a helpful start. It may allow accurate identification of patients at high risk32 to improve resource allocation and target preoperative preventive measures97 (Table 3).

Table 3

Table 3

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Minimizing Preoperative Risk

There are no prospective, randomized, controlled trials demonstrating that identifying high-risk patients improves outcomes. However, several promising strategies are under study to improve perioperative lung protection.99 Currently, recommendations for minimizing preoperative risk are based on expert opinion. Optimizing chronic pulmonary and cardiovascular disease, improving nutritional status, and correcting anemia and volume status are all advisable.14,97,99 The optimal timing of alcohol and smoking cessation is unknown,84 although >4 weeks has been suggested.100 As the long-term benefits of smoking cessation are well documented, it should be recommended regardless of time frame.101 Some recommend delaying surgery for ∼1 month for high-risk patients with a current or recent respiratory infection.32,57

Pulmonary rehabilitation14,100 and “prehabilitation” might improve the strength and functional reserve of older patients.32 A recent meta-analysis found that preoperative inspiratory muscle training could halve the risk of PPCs in patients undergoing high-risk surgery,102 but additional research is still needed. Choosing shorter procedures,98 aggressive perioperative respiratory therapy, and planned admission to units with closer monitoring might all be beneficial for high-risk patients.

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The literature guiding preoperative pulmonary assessment has grown more robust in recent years, and the most important risk factors have been identified. Predictive scores, such as the ARISCAT index, can aid in identifying subsets of high-risk patients who might benefit the most from specific interventions.98 However, there is still a lot to learn. No randomized trials show that identifying high-risk patients helps improve outcomes. Potential preoperative interventions such as prehabilitation may have a role, but the impact on surgical outcomes is yet to be defined.103 Trials showing efficacy of preventive measures are still lacking.49

Familiarity with the common and most significant risk factors, appropriate use of available respiratory risk indices, a thoughtful approach to preoperative testing, optimization whenever possible, and aggressive perioperative preventive measures are currently our best tools for preventing PPCs.

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