Pulmonary Risk (Anesthesia Text)

5-10% of all surgical patients (and 94% of those undergoing abdominal surgery) will experience post-operative pulmonary complications [Mitchell Arch Surg 133: 194, 1998]. According to Miller, the use of mild or moderate obesity as a risk factor is controversial, however he quotes Flum’s U.Washington data on 16,155 bariatric patients which suggested that all cause mortality rates were higher for men (7.5% vs 3.7% at 1 year), patients older than 65 (11.1% vs 3.9%) and that 90 day odd ratio of death is 1.6 times higher if surgeons have done less than the median number of cases, but did not specifically stratify patients based on actual weight [Flum DR JAMA 294: 1903, 2005]. Obese patients do have a higher incidence of pulmonary thrombotic complications [Gutt Am J Surg 189: 14, 2005]. Most studies have reported a lower risk of pulmonary complications for neuraxial anesthesia, but not all, thus no definitive conclusions can yet be made [Miller]

Postoperative Respiratory Failure[edit]

Defined as inability to extubate a patient within 48 hours of surgery. A “respiratory risk score,” which does not take into account physical exam data or PFTs, can be used to predict the likelihood of this. Importantly, 27% of the patients used in this study died within 30 days, however the population studied was particularly ill (~ 1/3 were emergency thoracic procedures) [Arozullah Ann Surg 232: 242, 2000; Arozullah AIM 135: 847, 2001]

Table. Respiratory Risk Score [Arozullah Ann Surg 232: 242, 2000]
Predictor Points
   AAA 27
   Thoracic Surgery 21
   NSGY, upper abdominal, or peripheral vascular 14
   Neck 11
   Emergency 11
Albumin < 30 g/dL 9
BUN > 30 mg/dL 8
Partially or fully dependent 7
Age >= 70 6
Age 60-69 6

<=10 0.5%
11-9 2.2%
20-27 5.0%
28-40 11.6%
>40 30.5%
  • Note – this data are all based on male patients with a high burden of comorbid conditions, and almost 1/3 of surgeries were thoracic emergencies


Site of surgery also affects risk of postoperative pulmonary complications, with risk increasing as the diaphragm is approached. Upper abdominal and thoracic cases carry the highest risk (10-40%) [Kroenke Chest 104: 1445, 1993]

COPD is clearly a risk [Smetana NEJM 340: 937, 1999] and these patients should be treated aggressively preoperatively if possible. The data on actual treatment are limited but it is possible that bronchodilators, PT, antibiotics, smoking cessation, and corticosteroids may reduce risk in this population. Asthmatics in particular have a higher incidence of bronchospasm [Warner Anesthesiolgoy 85: 460, 1996]

Preoperative Pulmonary Testing

Preoperative Chest Radiographs

A retrospective study which attempted to establish a protocol based on clinical status, medical history, and type of surgery (905 total patients) showed that of these 905, 368 had no risk factors {?abandoning chest radiographs completely did not affect outcome [Rucker JAMA 250: 3209, 1983] – in this study, 504 patients had identifiable risk factors and of these, 114 (22%) were found to have serious abnormalities on preoperative chest roentgenogram. However, according to Miller, only 15% of the X-rays were useful to anesthesiologists and only 5% had an impact on the surgical or anesthetic plan}. The majority of data do not support the broad use of preoperative chest radiographs, and the ASA has stated that chest X-rays are not indicated on the basis of age or preexisting respiratory condition, unless there is a surgical indication [Miller]

Pulmonary Function Testing

There is agreement that all lung resection candidates should undergo PFTs, otherwise such testing should be performed selectively [Pasternak Int Anesth Clin 40: 31, 2002; Mitchell Arch Surg 133: 194, 1998; Fisher Am J Med 112: 219, 2002]. In general, clinical findings are more predictive of pulmonary complications. Additionally, according to Miller, who cites Fisher, patients defined as “high risk” by PFTs can still have surgery with an acceptable risk of complications [Fishman NEJM 348: 2059, 2003 – RCT of medication vs. lung reduction surgery for 1218 patients showing that lung-volume–reduction surgery increases the chance of improved exercise capacity but does not confer a survival advantage over medical therapy. It does yield a survival advantage for patients with both predominantly upper-lobe emphysema and low base-line exercise capacity. Patients previously reported to be at high risk and those with non–upper-lobe emphysema and high base-line exercise capacity are poor candidates for lung-volume–reduction surgery, because of increased mortality and negligible functional gain. “High risk” patients in this study (FEV1 20% or less of predicted value) had a 90 day mortality of 28.5% (20/70), as opposed to 5.2% (28/538)]

Blood Gases – the value of PaCO2

The use of preoperative PaCO2 is controversial but seems to not be helpful – one study of 51 patients undergoing elective major abdominal surgery suggested that abnormalities in FEV1 and PaCO2 values do not identify patients destined to require postoperative ventilation > 24 hours, but that a longer history of cigarette smoking, a lower preoperative PaO2, a larger P(A-a)O2, and a large intraoperative blood loss are predictive [Jayr et al. Chest 103(4): 1231, 1993]. Another study [Fishman NEJM 348: 2059, 2003]

Preventive Strategies

Lung expansion maneuvers (deep-breathing exercises and incentive spirometry have been studied most extensively) and pain control are intended to optimize lung mechanics. Preoperative education appears to be more beneficial in terms of reducing complications as compared to education which begins only postoperatively. In one study of 172 patients, both intermittent positive pressure breathing (15 min x 4/day), incentive spirometry (4x/day), and deep breathing exercises (15 min x 4/day) reduced pulmonary complications from 48% to 21-22% [Celli et al. Am Rev Respir Dis 130: 12, 1984]. However, intermittent positive pressure breathing and CPAP, while effective, are not recommended due to their high cost

Smoking Cessation

The length of time necessary to benefit previous smokers is not exactly clear. 12-24 hours is enough to decrease carboxyhemoglobin levels and shift the dissociation curve rightward (increasing tissue availability). 1-2 weeks may be enough to reduce sputum volume [Moore Clin Chest Med 21: 139, 2000], however recent cessation of smoking may lead to increased airway reactivity, and improvement in mucociliary transport and small airway function may take as long as 12 weeks [Miller]. A study of 410 non-cardiac surgery VA patients showed that smoking cessation within 4 weeks of surgery actually increased pulmonary complications [Bluman et. al. Chest 113: 883, 1998]. In CABG patients, reduced pulmonary complications require 8 weeks of cessation, and in pulmonary surgery patients, at least 4 weeks [Warner et. al. Anesthesiology 60: 380, 1984]. Note that smoking status is not a risk factor for major cardiac events [Warner Anesthesiology 104: 356, 2006], although it does seem to be a univariate and multivariate risk factor for pulmonary complications such as respiratory failure, ICU admission, pneumonia, laryngospasm, and increased use of respiratory therapy services [Warner Anesthesiology 104: 356, 2006].

Obstructive Sleep Apnea

Obstructive Sleep Apnea (OSA) is defined as complete apnea for 10 seconds, five times per hour, associated with a 4% decrease in SaO2 (while sleeping). Hypopnea is a less-severe form of obstruction (50% reduction in airflow, also accompanied by a 4% fall in SaO2). Both OSA and hypopnea require a sleep study for diagnosis. Sleep studies are scored with an apnea/hypopnea index (AHI – mild OSA is 5-15, moderate OSA is 15-30, and severe OSA is > 30 AHI). Moderate/severe OSA is treated with CPAP

OSA can lead to significant comorbidities, including systemic and pulmonary hypertension, LVH, arrhythmias, and cognitive impairment

Obesity is the most important risk factor for OSA, although most patients with OSA are not obese. The STOP and STOP-BANG criteria were developed to assist anesthesiologists in predicting who is at risk for OSA, and both correlated well with polysomnography [Chung F et al. Anesthesiology 108: 812, 2008].

Diagnosis of OSA

  • OSA: complete apnea for 10 seconds, five times per hour, associated with a 4% decrease in SaO2
  • Hypopnea: 50% airflow reduction, 15 times or more per hour, 4% decrease in SaO2
  • Physiologic Effects of OSA: systemic and pulmonic HTN, LVH, arrhythmia, cognitive impairment
  • STOP: Snoring; Tired; Observed Not Breathing; Blood Pressure (2 or more = high risk)
  • STOP-BANG: STOP + BMI > 35, Age > 50, Neck > 40 cm, Male (3 or more = high risk)

In 2014, Memtsoudis et al. analyzed hospital discharge data of 530,089 patients who underwent total hip or knee arthroplasty in approximately 400 U.S. Hospitals between 2006 and 2010. The diagnosis of OSA emerged as an independent risk factor for major postoperative complications (OR 1.47; 95% confidence interval [CI], 1.39–1.55). Pulmonary complications were 1.86 (95% CI, 1.65–2.09) times more likely and cardiac complications 1.59 (95% CI, 1.48–1.71) times more likely to occur in patients with SA. In addition, SA patients were more likely to receive ventilatory support, use more intensive care, stepdown and telemetry services, consume more economic resources, and have longer lengths of hospitalization (Anesth Analg 2014;118:407–18).



Stavros G Memtsoudis, Ottokar Stundner, Rehana Rasul, Ya-Lin Chiu, Xuming Sun, Satya-Krishna Ramachandran, Roop Kaw, Peter Fleischut, Madhu Mazumdar
The impact of sleep apnea on postoperative utilization of resources and adverse outcomes.
Anesth. Analg.: 2014, 118(2);407-18