January 1997
Perioperative respiratory complications in patients with asthma.
Warner DO, Warner MA, Barnes RD, Offord KP, Schroeder DR, Gray DT, Yunginger JW. Anesthesiology 1996; 85:254-9.

The development of intraoperative bronchospasm has the potential to become an anesthetic disaster, with major morbidity and even death. Asthma occurs in more than 10 million Americans. Because general anesthesia implies airway manipulation, there is a high level of concern for perioperative complications such as laryngospasm, bronchospasm, pulmonary barotrauma and postoperative acute respiratory failure which may be very difficult to treat. Indeed the management of patients with acute asthma by mechanical ventilation is fraught with hazards and has a high morbidity.

Surprisingly, in a retrospective review of 706 patients diagnosed as having "definite asthma" who presented to the Mayo Clinic for general or spinal/epidural anesthesia, Warner et al. found that the risk of perioperative bronchospasm was extremely low (1.7%). Laryngospasm and postoperative respiratory failure developed in only three patients. The incidence of pulmonary barotrauma, unanticipated mechanical ventilation or death was zero. There were two main predictors of these complications: recent acute asthma (symptoms, use of medications or treatment in a medical facility) and older age. There was no difference in the incidence of bronchospasm between regional and general anesthesia, but in the latter the risk was significantly decreased if the trachea was not intubated. The incidence of bronchospasm was low whether or not perioperative corticosteroids were administered.

An important consideration in interpreting the results of this review is that the authors took pains to very carefully define asthma as a symptomatic, variable condition (i.e. with complete remissions) with atopy. They specifically excluded patients with known hyperreactive airways, chronic obstructive lung disease, cystic fibrosis or other major lung diseases. Although they observe that several other studies, both retrospective and prospective, report a low incidence of complications in asthmatic patients, the incidence of bronchospasm appears to depend on how carefully it is sought.

For example, in a prospective study by Pizov et al (1) which found an incidence of wheezing of 25% after intravenous anesthetic induction, an observer carefully auscultated the chest. In contrast, Warner et al. were dependent on notations made in the anesthetic chart, a limitation of all retrospective studies. The authors do point out that even if bronchospasm is rare in their practice, it may lead to severe outcomes.

In an accompanying editorial (2), Bishop and Cheney state their opinion in the title: "Anesthesia for patients with asthma - low risk but not no risk". They point out that for a complication with a low incidence even a study sample of 706 patients may be much too small to define the risk of adverse outcomes precisely. Furthermore, results from a large quality-assurance database suggest that only 10% of patients with perioperative bronchospasm may even have a history of asthma. The wide variation of the incidence of perioperative bronchospasm in patients with asthma cited in the literature (0.8-30%) may depend entirely on the activity of the asthma. For example, Bishop and Cheney point out that in the Mayo Clinic data bronchospasm occurred in only 1.7% of all patients, but in 4.5% of those who had symptoms within 30 days and in 50% (two out of four) of patients with active symptoms at the time of surgery.

In conclusion, this review suggests that patients with asthma who are asymptomatic have a low (but increased) risk of severe morbidity. It does not address the direct relationship between a history of asthma and specific anesthetic techniques designed to decrease the risk of bronchospasm - with the important exception of the use of general anesthesia without tracheal intubation. It does suggest that the risk is dramatically increased when symptoms are current or have occurred within 30 days. Finally, it should be kept in mind that in the majority of cases, perioperative bronchospasm occurs without any history of asthma at all.

References:
(1) Pizov R, Brown RH, Weiss YS, Baranov D, Hennes H, Baker S, Hirshman CA. Wheezing during induction of general anesthesia in patients with and without asthma. Anesthesiology 1995; 82:1111-6.

(2) Bishop MJ, Cheney FW. Anesthesia for patients with asthma - low risk but not no risk. Anesthesiology 1996; 85:455-6