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Dr. Kinasewitz is from the Department of Pulmonary and Critical Care Medicine, Physiology, and Biophysics, and Dr. Welch is from the Department of Pulmonary and Critical Care Medicine, University of Oklahoma Health Sciences Center.
Correspondence to: Gary T. Kinasewitz, MD, FCCP, Box 26901, WP 1310 Oklahoma City, OK 73190; e-mail: gary-kinasewitz{at}ouhsc.edu
Major surgery under general anesthesia poses a significant stress to the cardiopulmonary system. Previous investigators have shown that postoperative morbidity and mortality are higher in those patients with limited cardiopulmonary reserves. Patients with pulmonary disease have a higher incidence of postoperative complications, and the frequency of complications increases in proportion to the severity of the pulmonary impairment.1 2 3 Similarly, the presence of increasing numbers of cardiac risk factors increases the risk of postoperative complications in patients with cardiac disease.4
While cardiac performance and respiratory function each can be
evaluated individually, exercise testing offers the advantage of
examining both systems in a single study. Formal exercise testing with
analysis of gas exchange and measurement of maximal oxygen uptake
(
O2max) can provide
information regarding the extent and cause of a patient’s limitation,
whether it be cardiac or pulmonary in origin. However, this form of
exercise testing requires specialized equipment, is expensive, is
time-consuming, and is not readily available at all hospitals. In this
issue of CHEST, the study by Girish and colleagues
(see page 1147) takes us back to a simpler era before this
sophisticated exercise equipment was available and reminds us of
several important points.
Stair climbing is the traditional and time-honored form of
exercise testing that was incorporated into the preoperative evaluation
of many surgeons long before the ability to measure
O2 became available in
clinical practice. Its tradition is so ingrained in surgical lore that
it is unclear who was the first physician to actually observe a patient
climbing stairs. Nonetheless, in a retrospective review of patients
undergoing pneumonectomy at the University of Minnesota from 1947 to
1965, Van Nostrand and colleagues noted an unacceptably high 50%
mortality rate in those patients who were unable to climb two flights
of stairs, whereas the mortality rate was only 10% in patients who
were able to complete this test.5
Thus, patients were
considered to be suitable candidates for pneumonectomy if they could
climb two or more flights of stairs. Subsequent
investigators6
7
have confirmed that stair climbing can be
a valuable adjunct to the preoperative assessment. Holden et
al7
studied 16 patients at high risk for thoracotomy
because they had an FEV1 < 1.6 L. Four of 5
patients who were unable to climb > 44 steps (equivalent to two
flights of stairs in most hospitals), but only 1 of 11 patients who
exceeded 44 steps died in the postoperative period.
Stair climbing is a simple form of exercise that imposes a progressive
burden on the cardiopulmonary system. In healthy individuals,
O2max measured during stair
climbing is comparable to that measured during treadmill
exercise.8
Since the presence of either cardiac or
pulmonary disease can limit exercise capacity, it is not surprising
that patients with underlying cardiopulmonary disorders have difficulty
climbing stairs. The degree of limitation is roughly proportional to
the severity of the impairment in cardiac or pulmonary
function.9
10
Previous studies have shown that
O2max measured in the exercise
laboratory is a good indicator of postoperative risk in patients
undergoing thoracic procedures. A
O2max > 20 mL/kg/min is
associated with a low risk of postoperative
complications,11
12
whereas a
O2max < 10 mL/kg/min or 1
L/min is associated with markedly increased morbidity and
mortality.12
13
The risk of complications is intermediate
in patients with a O2max
between these values.11
14
In patients with chronic
airflow obstruction, climbing two flights of stairs corresponds to a
O2max of about 12 mL/kg/min,
whereas the O2max exceeds 20
mL/kg/min in those patients who are able to climb five flights of
stairs.10
The study by Girish et al extends these observations in several ways. They studied a large group of diverse patients prior to elective thoracotomy or upper abdominal surgery and found a significant inverse relationship between the number of flights of stairs climbed and postoperative morbidity. Only 1 of 20 patients who successfully climbed five flights of stairs had a postoperative complication, thus confirming previous studies that have shown an excellent correlation between cardiopulmonary fitness and postoperative outcome. In contrast, 10 of 15 patients who were unable to climb more than two flights of stairs experienced postoperative complications.
Second, Girish et al found that the inability to climb stairs, irrespective of the reason, was associated with a poor outcome. Eight of nine patients who refused or were unable to climb a single flight of stairs had postoperative complications, including one death. Previous investigators15 have shown that an inability to perform low-level exercise is associated with increased postoperative morbidity and mortality. It has long been recognized that bedrest can produce deconditioning and can impair aerobic performance.16 The results of the study by Girish et al remind us that inactivity due to obesity or other medical conditions that limit mobility can have a similar deconditioning effect and thereby can increase the risk of postoperative morbidity.
Third, Girish et al found no difference in postoperative morbidity between patients undergoing upper abdominal and thoracic operations. It is obvious why a thoracic incision would impair chest wall excursion and would predispose the patient to pulmonary complications. However, it is less readily apparent why surgery that does not directly involve the diaphragm would be associated with increased morbidity. The diaphragm is an integral part of the chest wall apparatus, and upper abdominal surgery clearly is associated with impaired diaphragmatic movement and decreased transdiaphragmatic pressure generation.17 18 The mechanism of this impairment is unclear, but the consequence is increased cardiopulmonary morbidity compared to that in patients undergoing lower abdominal operations.19 20
The ideal screening test should be simple, inexpensive, and widely available. Stair climbing meets these criteria and, even in the new millennium, remains a valid technique to screen for cardiopulmonary fitness. Patients who are able to climb five flights may be deemed suitable candidates for major surgery without further evaluation. Those patients who cannot or will not tolerate this level of exertion should be evaluated by directed techniques such as an echocardiogram or pulmonary function tests to more precisely determine the etiology and extent of their impairment.
References
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