Correspondence
Preoperative Pulmonary Evaluation
N Engl J Med 1999; 341:613-614August 19, 1999
- Article
To the Editor:
The informative review of preoperative pulmonary evaluation by Dr. Smetana (March 25 issue)1 omitted any reference to sleep apnea and its complications in the postoperative setting. Sleep apnea is associated with an increased risk of acute upper-airway obstruction after extubation,2 more severe postoperative oxygen desaturation than that in normal persons,3 and increased risks of atrial fibrillation4 and cardiorespiratory arrest,2 even if the operation does not involve the upper airway.
A comprehensive preoperative evaluation should include simple questions about symptoms of sleep apnea: the presence of loud, habitual snoring, episodes of apnea witnessed by a bed partner, episodes of nocturnal choking and gasping, and daytime hypersomnolence.5 Obesity (body-mass index [the weight in kilograms divided by the square of the height in meters] ≥30) and orofacial or pharyngeal abnormalities (e.g., tonsillar enlargement and retrognathia) are associated with an increased risk of sleep apnea.
If there is sufficient clinical evidence of sleep apnea, a preoperative polysomnogram should be obtained. Moreover, close postoperative observation and early institution of nasal continuous positive airway pressure may be beneficial in preventing the immediate postoperative complications of sleep apnea.2 Given the high prevalence of this disorder in the general population and the effects of anesthetic agents on upper-airway function,6 physicians should be aware of the potential postoperative risks for patients with sleep apnea.
6 ReferencesJason J. Marx, M.D.
Naresh Punjabi, M.D.
Alan Schwartz, M.D.
Johns Hopkins Sleep Disorders Center, Baltimore, MD 212241
Smetana GW . Preoperative pulmonary evaluation. N Engl J Med 1999;340:937-944
Full Text | Web of Science | Medline2
Rennotte MT ,Baele P ,Aubert G ,Rodenstein DO . Nasal continuous positive airway pressure in the perioperative management of patients with obstructive sleep apnea submitted to surgery. Chest 1995;107:367-374
CrossRef | Web of Science | Medline3
Gentil B ,Lienhart A ,Fleury B . Enhancement of postoperative desaturation in heavy snorers. Anesth Analg 1995;81:389-392
CrossRef | Web of Science | Medline4
Mooe T ,Gullsby S ,Rabben T ,Eriksson P . Sleep-disordered breathing: a novel predictor of atrial fibrillation after coronary artery bypass surgery. Coron Artery Dis 1996;7:475-478
CrossRef | Web of Science | Medline5
Strohl KP ,Redline S . Recognition of obstructive sleep apnea. Am J Respir Crit Care Med 1996;154:279-289
Web of Science | Medline6
Robinson RW ,Zwillich CW . The effect of drugs on breathing during sleep. Clin Chest Med 1985;6:603-614
Web of Science | Medline
To the Editor:
Dr. Smetana has compiled information on important patient-related risk factors that need to be addressed before surgery. However, we disagree with his statement “Obesity is not a significant risk factor for pulmonary complications.”
In obese patients, the total lung capacity, functional residual capacity, and vital capacity are reduced by up to 30 percent.1 The work of breathing is increased because of abnormal chest elasticity, increased chest-wall resistance, increased airway resistance, abnormal diaphragmatic position and upper-airway resistance, and the need to eliminate a higher daily production of carbon dioxide.1 Patients with severe obesity generally have hypoxemia, with a widened alveolar–arterial oxygen gradient due to ventilation–perfusion mismatching.1 Alveolar collapse and airway closure at the bases contribute to this phenomenon. The reduction in functional residual capacity in the supine position increases ventilation–perfusion mismatching. This may result in severe arterial hypoxemia and sudden death in the immediate postoperative period.2
Atelectasis and ventilator-associated pneumonia are more likely to develop in intubated patients who are obese than in those who are not obese, and these conditions prolong the need for mechanical ventilation. In addition, obese patients have a higher volume of gastric fluid, with a lower pH, than nonobese patients; this factor, together with an increased intraabdominal pressure, predisposes them to gastroesophageal reflux and aspiration pneumonitis.3,4 Furthermore, obese patients have a higher incidence of postoperative thromboembolic disease than nonobese patients.3 Rose and coauthors reported that acute postoperative respiratory events were twice as likely to occur in obese as in nonobese patients.4
4 ReferencesJoseph Varon, M.D.
Baylor College of Medicine, Houston, TX 77030Paul Marik, M.D.
Washington Hospital Center, Washington, DC 20010-29751
Ray CS ,Sue DY ,Bray G ,Hansen JE ,Wasserman K . Effects of obesity on respiratory function. Am Rev Respir Dis 1983;128:501-506
Web of Science | Medline2
Drenick EJ ,Fisler JS . Sudden cardiac arrest in morbidly obese surgical patients unexplained after autopsy. Am J Surg 1988;155:720-726
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Marik P ,Varon J . The obese patient in the ICU. Chest 1998;113:492-498
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Rose DK ,Cohen MM ,Wigglesworth DF ,DeBoer DP . Critical respiratory events in the postanesthesia care unit: patient, surgical, and anesthetic factors. Anesthesiology 1994;81:410-418
CrossRef | Web of Science | Medline
To the Editor:
In discussing the value of the partial pressure of arterial carbon dioxide (PaCO2) as a predictor of the need for postoperative ventilation, Dr. Smetana failed to mention the follow-up study by Nunn et al.,1 which involved a larger sample than the study by Milledge and Nunn2 that was cited by Smetana. With the larger sample, the authors concluded that the preoperative partial pressure of arterial oxygen (PaO2) and dyspnea at rest were the best predictors of the need for postoperative ventilation.1 They concluded that arterial-blood gas pressures have greater predictive value than the results of spirometric tests. The position paper of the American College of Physicians also recommends measurements of arterial-blood gases, in addition to spirometry, in patients with a history of dyspnea and tobacco use who are undergoing upper abdominal or coronary-artery bypass surgery.3
3 ReferencesMark S. Shulman, M.D.
St. Elizabeth's Medical Center of Boston, Boston, MA 021351
Nunn JF ,Milledge JS ,Chen D ,Dore C . Respiratory criteria of fitness for surgery and anaesthesia. Anaesthesia 1988;43:543-551
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Milledge JS ,Nunn JF . Criteria of fitness for anaesthesia in patients with chronic obstructive lung disease. BMJ 1975;3:670-673
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American College of Physicians
Medline
Author/Editor Response
Dr. Smetana replies:
To the Editor: Dr. Shulman cites the 1990 position paper of the American College of Physicians to support the use of preoperative arterial-blood gas analyses. The authors of that report presented no evidence of the predictive value of PaO2. They based their recommendation that arterial-blood gas analyses be performed on studies of only eight patients with hypercapnia. In studies of patients undergoing lung-reduction surgery1 or lung resection,2 hypercapnia was not a risk factor for postoperative pulmonary complications.
Dr. Shulman suggests that an abnormal PaO2 is an important risk factor, citing a study of patients with severe chronic obstructive pulmonary disease and a forced expiratory volume in one second of less than 1 liter.3 Only 4 of the 25 patients with preoperative hypoxemia required postoperative ventilation. There were no other postoperative pulmonary complications and no deaths among patients undergoing nonemergency surgery. Dyspnea at rest was more predictive of complications than was hypoxemia. Clinicians would have identified the patients with hypoxemia as being at high risk on clinical grounds alone.
Drs. Varon and Marik correctly describe pulmonary-function abnormalities in obese patients. These physiologic changes do not, however, consistently contribute to an increase in clinically significant pulmonary complications. In one of the studies they cite, obese patients had more unanticipated ventilatory problems in the immediate postoperative period, but with no increase in pneumonia, bronchospasm, atelectasis, or respiratory failure.4 If one pools the data from the six studies that I cited, which involved a total of 4526 patients, the risk of pulmonary complications was 21 percent for both obese and nonobese patients. Obesity is a risk factor for postoperative thromboembolism, but that was not the subject of my review.
Marx et al. cite a study in which two untreated patients with sleep apnea required reintubation after surgery.5 Fourteen patients were treated with postoperative continuous positive airway pressure, with no adverse events. One must distinguish difficulties in perioperative airway management from postoperative pulmonary complications. Patients with sleep apnea may be at increased risk for perioperative ventilatory problems, but these problems can be treated without increasing the risk of postoperative pulmonary complications. In my review, previously diagnosed sleep apnea was not a risk factor for pulmonary complications in any study of patient-related factors. The data do not support routine screening before surgery. Whether screening patients for undiagnosed sleep apnea reduces postoperative pulmonary complications deserves further study.
5 ReferencesGerald W. Smetana, M.D.
Beth Israel Deaconess Medical Center, Boston, MA 022151
Wisser W ,Klepetko W ,Senbaklavaci O , et al. Chronic hypercapnia should not exclude patients from lung volume reduction surgery. Eur J Cardiothorac Surg 1998;14:107-112
CrossRef | Web of Science | Medline2
Kearney DJ ,Lee TH ,Reilly JJ ,DeCamp MM ,Sugarbaker DJ . Assessment of operative risk in patients undergoing lung resection: importance of predicted pulmonary function. Chest 1994;105:753-759
CrossRef | Web of Science | Medline3
Nunn JF ,Milledge JS ,Chen D ,Dore C . Respiratory criteria of fitness for surgery and anaesthesia. Anaesthesia 1988;43:543-551
CrossRef | Web of Science | Medline4
Rose DK ,Cohen MM ,Wigglesworth DF ,DeBoer DP . Critical respiratory events in the postanesthesia care unit: patient, surgical, and anesthetic factors. Anesthesiology 1994;81:410-418
CrossRef | Web of Science | Medline5
Rennotte MT ,Baele P ,Aubert G ,Rodenstein DO . Nasal continuous positive airway pressure in the perioperative management of patients with obstructive sleep apnea submitted to surgery. Chest 1995;107:367-374
CrossRef | Web of Science | Medline
- Citing Articles (1)
Citing Articles
1
Andreas Zollinger, Christoph K. Hofer, Thomas Pasch. (2001) Preoperative pulmonary evaluation: facts and myths. Current Opinion in Anaesthesiology 14:1, 59-63
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