Volume 12, No. 4 • Winter 1997

Silent Obstruction in Asthma Is Unrecognized Problem

Florence W. Watts, M.D.; Timothy J. Sullivan, M.D.

The prevalence of asthma has doubled over the last 20 years in the United States. Approximately 14 million people in this country have experienced symptoms of asthma in the last year. The causes of this increase are unclear. With this rise in prevalence of asthma, there are more patients with severe disease in the perioperative period. Therefore, anesthesiologists will be managing more asthmatics with more severe disease in the perioperative period. Kabalin et al. Have shown that asthmatics under good control have minimal perioperative ocmplications.1 However, the asthmatic who is not under good control does have an increased rate of respiratory complications in the perioperative period.2 Caramico et al., in preliminary study, showed that among asthmatic children, the incidence of respiratory complications was 4 to 20 times higher than a control population with no history of respiratory disease.3 Perioperative asthmatic deaths in this country tragically continue to occur even following elective procedures. The key to preventing perioperative complications in the asthmatic is to optimize the asthmatic’s lung function prior to surgery.

A significant obstacle preventing clinicians from ensuring that asthmatics are optimized prior to surgery is the phenomenon of “Silent Obstruction.” The anesthesia community is largely unaware of this problem. The term silent obstruction is derived from the cardiac term, silent ischemia. In silent ischemia the cardiac patient ahs ischemia with no symptoms, and no physical signs that can be detected by the clinician. Only with an ECG can the clinician identify this cardiac patient who is having ongoing ischemia. This same scenario holds true for the pulmonary patient as well. Approximately 15 to 25% of the asthma population can not tell when their lung function is worsening when they are obstructed.4,5 This group of asthmatics is referred to as “poor perceivers.” So we have a group of asthmatics who are without symptoms.

No Wheezing!

What about clinical signs to detect airway obstruction? Don’t most asthmatics wheeze when they are obstructed? No!! Most asthmatics do not wheeze when they are obstructed. In a study performed at Grady Memorial hospital in Atlanta, GA, two-thirds of the asthmatics with airway obstruction had no wheezing on auscultation.5 No wheezing, rhonchi, rales, or other abnormalities were detected on expert physical exam. The reason for this is that in asthma the bronchoconstriction is concentric constriction, therefore you frequently do not get the turbulent flow that causes the wheeze sound unless secretions are present to cause turbulent flow. Many studies have shown that the history and physical exam are poor predictors for the level of airway obstruction I the asthmatic patient.6 This subgroup of asthmatics, the poor perceivers, are at a much higher risk for death from asthma than the asthmatics who can tell when their lung function is worsening.

So how do we make sure that asthmatics are optimized for surgery? Just as the cardiac patient with silent ischemia requires an EEG to determine ischemia, we need objective measurement of airway assessment to assess lung function in the asthmatic. The gold standard for measuring lung function is the FEV1 measured by a spirometer. There are inexpensive portable spirometers, costing under $500, that are coming on the market. Ideally, spirometers should be available in all anesthesia preoperative clinics. The maneuver to perform the FEV1 is not difficult to teach. It is operator dependent, so the person giving the test should exhort the patient to maximal effort. Most asthmatics are very proficient with the spirometer, since they should have performed this test as part of their ongoing management. If there is no access to spirometry, then a peak flow meter is the next best choice to assess level of airway obstruction. The clinician wishes to verify that the patient’s measurement on that day is at least 80% of that predicted for normals or close to the “best ever” FEV1 or peak flow reading for that particular patient. If the patient shows that his lung function is not optimized, then a course of steroids should be carefully considered prior to surgery. The amount of steroids given depends on the severity of the disease. Mild asthmatics respond to smaller doses of steroids than the more severe asthmatic, who requires larger and longer duration of steroids to depress the inflammatory response in the lung. One must remember that asthma is a chronic inflammatory disease. The primary drug used to control and optimize the asthmatic prior to surgery is a glucocorticosteroid. Although chronic steroids are fraught with a multitude of complications, a short course of 3 to 7 days of steroids does not carry the same complications. Some groups have advocated giving all asthmatics 3 to 7 days of steroids prior to surgery in lieu of objective airway assessment.1 However, detection of the patient with poorly controlled asthma is crucial.. Steroids may not have normalized lung function in the prescribed time allowed. The NIH’s 1997 expert panel on asthma advocated measuring FEV1 or peak flow and giving steroids as indicated by the masurement.7 As a specialty, we have been using clinical assessment to determine the need for steroids in the asthmatic. This is clearly a dangerous method to use to assure optimization of lung function. If we do not follow the NIH guidelines, we will be faced with more unnecessary perioperative asthmatic deaths. With objective assessment and steroids when needed, we should have minimal complications from our asthmatics undergoing elective procedures.

Understanding Crucial

The problem of silent obstruction in the asthmatic population needs to be made known to all anesthesiologists. By understanding this clinical problem we can have better optimization of the asthmatic prior to surgery. With this knowledge we should have minimal complications, and more importantly no more deaths from asthma in our elective surgical procedures.

Dr. Watts is Director of the Atlanta Lung Research Center, and staff anesthesiologist, Kennestone Hospital, Atlanta. Dr. Sullivan is Chief, Division of Allergy and Immunology, and Professor of Medicine, Emory University, Atlanta.


  1. Kabalin CS, Yarnold PR, Grammer LC: Low complication rate of corticosteroid-treated asthmatics undergoing surgical procedures. Arch Intern Med 1995;155:1379-84.
  2. Warner Do, Warner MA, Barnes RD, Offord KP, Schroeder DR, Gray DT, Yunginger JW: Perioperative respiratory complications in patients with asthma. Anesthesiology 1996;85:459-67.
  3. Caramico L, Bell C, Wang S, Kain Z: Anesthetic risk factors in children with asthma: preliminary findings. Anesth & Analg 1997;84:S183.
  4. Rubinfeld AF, Pain MCF: Perception of asthma. Lancet 1976;1:882-4.
  5. Watts FL, Meyer L, Sullivan TJ. History and physical exam do not accurately reflect severity of airway obstruction in the asthmatic patient. Anesthesiology 1996;85:154a.
  6. Li JTC, O’Connell EJ. Clinical evaluation of asthma. Ann of Allergy Asthma and Immunology 1996;76:1-14.
  7. Expert Panel Report 2: Guidelines for diagnosis and management of asthma. NIH Publication NO. 974051, April 1997.56.

[Editor’s Note: Responses to and comments on all “In My Opinion” articles are always welcome and will be actively considered for publication.]