Pulmonary Disease and Preoperative Pulmonary Evaluation
GENERAL PRINCIPLES
Clinically significant pulmonary complications include atelectasis, pneumonia, bronchospasm, exacerbation of preexisting chronic lung disease, and respiratory failure.38 Postoperative respiratory failure, defined as ventilator dependency for more than 48 hours or unplanned reintubation, carries a 30day mortality rate as high as 26.5%.39
Risk Factors
• Surgical site is generally considered the greatest determinant of risk of pulmonary complications, with proximity to the diaphragm correlating with increasing risk.40 Neurosurgery and surgeries involving the mouth and palate also impart increased risk.39,41
• Duration of surgery also correlates strongly with risk.42-44
• Regional anesthesia may reduce risk of pneumonia and respiratory failure as compared with general anesthesia.45-47 Prolonged neuromuscular blockade is also strongly associated with postoperative pulmonary complications.48
• COPD is a well-known risk factor, with disease severity associated with risk of serious complications.49
• Interstitial lung disease places patients at elevated risk for surgical lung biopsy and resection of malignancy but is not as well studied in patients undergoing general surgery.50-52
• Pulmonary hypertension is associated with significant morbidity in patients undergoing surgery.53,54
• Conversely, treated asthma and restrictive physiology associated with obesity do not appear to be significant risk factors.55,56
• CHF may increase the risk of pulmonary complications to an even greater degree than that seen with
COPD.57
• Multiple indices of general health status including degree of functional dependence and American Society of Anesthesiologists (ASA) class have been linked to poor pulmonary outcomes.56,57 Odds ratios for postoperative respiratory failure of 2.53 and 2.29 were observed for hypoalbuminemia ( 30 mg/dL), respectively, in a large cohort.41
• Age >50 years has been identified as an independent predictor of postoperative pulmonary complications.
Risk increases linearly with age.• Smoking is a well-established risk factor for both postoperative pulmonary and nonpulmonary complications. As with malignancy, risk appears to be dose-dependent and associated with active use 44,58,59
• Obstructive sleep apnea (OSA) increases the odds of postoperative complications two- to fourfold.60 Unrecognized OSA may pose an even greater risk; it is estimated that over 50% of patients with OSA presenting for surgery are undiagnosed.61-63
Risk Stratification
• Several validated risk indices have been developed for quantitating risk of postoperative pulmonary complications. Of these, the Arozullah respiratory failure index offers both practicality and ease of use. It consists of six factors for which point scores are assigned based on multivariate analysis to stratify patients into five classes of postoperative respiratory failure risk (ranging from 0.5% to 26.6%).41
DIAGNOSIS
Clinical Presentation
HISTORY
Preoperative pulmonary evaluation should focus on the abovementioned patient-dependent risk factors.
• Is there a history of lung disease? If so, what is the patient's baseline (e.g., level of exertional tolerance, degree of hypoxemia)? Is there evidence of recent deterioration (e.g., increased cough, sputum production)? Though not an absolute contraindication to surgery, it may be prudent to postpone an elective procedure until an exacerbation is treated or a superimposed upper respiratory tract infection has resolved.
• A full smoking history should be obtained.
• Screening for OSA should be undertaken. The STOP-Bang questionnaire (see Chapter 10, Obstructive Sleep Apnea) can be implemented to determine risk of OSA.
• As nonpulmonary comorbidities impact the likelihood of pulmonary complications, a review of other organ systems is mandatory.
PHYSICAL EXAMINATION
• Vital signs can be helpful in determining pulmonary risk. Both body mass index (BMI) and BP are components of the STOP-Bang questionnaire.
Oxygen saturation by pulse oximetry may assist in risk stratification.64• High Mallampati score may corroborate clinical suspicion for OSA. A study of 137 adults being evaluated for OSA found that every 1-point increase in Mallampati score increased the odds of OSA by 2.5.65
• Stigmata of chronic lung disease (e.g., increased anteroposterior dimension of the thorax, digital clubbing, adventitious lung sounds) should be actively sought along with signs of de compensated HF (jugular venous distention, rales, pretibial edema).
Diagnostic Testing
• Routine laboratory testing
î As mentioned earlier, underlying chronic kidney disease and hypoalbuminemia portend increased risk of postoperative pulmonary complications. The addition of serum bicarbonate 28 mmol/L or above to a STOP-Bang score of three or above increases the specificity for detecting moderate to severe OSA from 30% to 82%, though sensitivity is accordingly reduced.66
• CXR
î As many findings deemed abnormal on routine CXR are chronic and do not alter management, imaging is recommended only if signs or symptoms (e.g., unexplained dyspnea) warrant investigation.67,68
• Arterial blood gas (ABG) analysis
î No data exist that suggest that ABG results contribute to risk estimation beyond the variables delineated earlier.
• Pulmonary function testing (PFTs)
î The value of preoperative PFTs is at best debatable outside of lung resection surgery, where its role is relatively well defined. However, they may be considered in further evaluation of selected patients with unexplained dyspnea or exertional impairment or for those with known lung disease with unclear baseline.
TREATMENT
• Preoperative treatment should focus on modifiable risk factors.
• The effect of preoperative smoking cessation on pulmonary complications has been largely described in cardiothoracic surgeries, where a benefit to quitting smoking at least 2 months prior to surgery has been shown.69 Though the effect on a general surgical population is less clear, pooled data show a significant reduction in pulmonary complications.70 Maximizing the preoperative smoking cessation period appears to minimize complications.
Though it is unknown whether smoking cessation is beneficial within 2 weeks of surgery, previous concerns about a paradoxical increase in complications appear unfounded.71• COPD and asthma therapy should be optimized (see Chapter 9, Obstructive Lung Disease), and respiratory tract infections should be treated. Indeed, risk of postoperative pulmonary complications is increased in the month following a respiratory tract infection.72 Nonemergent surgery may need postponement to allow recovery of pulmonary function to baseline.
• OSA should be treated prior to elective high-risk surgery when feasible. A cohort study revealed a significant reduction in cardiovascular complications (primarily cardiac arrest and shock) between undiagnosed and diagnosed OSA after prescription of continuous positive airway pressure (CPAP).73 However, a subsequent meta-analysis of 904 patients failed to show a significant difference in postoperative adverse events despite statistically significant reduction in apnea-hypopnea index with postoperative use of CPAP, a finding attributed to overall poor adherence.74 Patients with known OSA should be continued on CPAP perioperatively.75
• Alternative procedures with reduced pulmonary risk should be considered for high-risk patients. Laparoscopic procedures may yield fewer pulmonary complications; regional nerve block appears to be associated with decreased risk as well.76,77 If general anesthesia (particularly with neuromuscular blockade) is absolutely necessary, duration should be minimized to the degree possible.