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Ann Thorac Surg 1995;60:603-608
© 1995 The Society of Thoracic Surgeons

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Original Articles: General Thoracic

Exercise Oximetry Versus Spirometry in the Assessment of Risk Prior to Lung Resection

Division of Thoracic Surgery and Department of Physiotherapy, The Toronto Hospital, University of Toronto, Toronto, Ontario, Canada

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. Spirometry remains a standard method of assessing patient risk prior to lung resection despite its poor sensitivity and specificity. This study compares the relative ability of standardized exercise oximetry and spirometry-forced expiratory volume in the first second-to predict morbidity and mortality after lung resection.

Methods. The study comprised a retrospective review of 396 consecutive patients of whom 299 underwent both oximetry and spirometry. Oximetry was undertaken during standard exercise under the supervision of a single physical therapist. Spirometry identified 46 patients with a forced expiratory volume in the first second of less than 1.5 L who were considered to be high risk. Exercise oximetry was used to identify patients with arterial oxygen desaturation at rest, while walking on level ground, or while climbing two flights of stairs (n = 65).

Results. Compared with spirometry, exercise oximetry more reliably predicted home oxygen requirements (p < 0.001), need of admission to the intensive care unit (p < 0.05), prolonged hospital stay (p < 0.001), and respiratory failure (p < 0.05). Oximetry identified 50% of the patients who died, all of whom had a forced expiratory volume in the first second of greater than 1.5 L. Despite its superior predictive value, the sensitivity of oximetry remained low.

Conclusions. We conclude that standardized exercise oximetry is a superior screen of the high-risk patient than spirometry (forced expiratory volume in the first second) prior to pulmonary resection when there are no other risk factors noted on initial history and physical examination. A prospective, randomized trial is required to substantiate this conclusion.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
See also page 609.

Since the initial efforts to perform pulmonary resection, surgeons have attempted to develop a means of predicting postoperative morbidity and mortality. Pulmonary function studies have become a routine assessment in many centers even though their ability to predict postoperative complications has been questioned [13]. In an effort to increase the sensitivity of preoperative assessment, more sophisticated studies of cardiopulmonary reserve have been developed. These involve an increasingly complex assessment and an increased cost. Although these tests appear to have a role in the investigation of the high-risk patient, a sensitive screening test to identify that patient is lacking. Ideally such a screening test should be simple to perform, be reproducible, possess reasonable sensitivity for the event or events, and be cost-effective. The current demand for financial accountability for medical services has led us to question the routine use of studies that provide no measurable prediction of outcome. This is particularly the case if there is a satisfactory or equivalent alternative.

In our attempt to develop a randomized clinical trial to assess the efficacy of standardized oximetry versus routine spirometry, we first reviewed our experience with these two modalities. Pulmonary function studies have been part of our routine assessment prior to pulmonary resection for many years. In addition, we have used a standardized form of exercise oximetry in the majority of patients since 1986. The relative efficacy of these two methods of preoperative assessment is the subject of this report.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Patient Population
The charts of 396 consecutive patients undergoing pulmonary resection for any pathologic condition other than trauma between January 1987 and December 1990 were retrospectively reviewed. This specific period was selected to coincide with the standardization of oximetric assessment on the thoracic service. To be included in the study, patients must have undergone routine preoperative spirometry as well as exercise oximetry. It was predetermined before the review that high-risk groups would consist of patients demonstrating a forced expiratory volume in the first second (FEV₁) less than 1.5 L or arterial oxygen saturation less than 90% on exercise. Further subgroup analysis was undertaken after compilation of the data in an effort to evaluate sensitivity and specificity at various levels of desaturation.

Postoperative Outcomes
Given the fact that both measurements reflected respiratory reserve, we determined that the outcomes should largely include respiratory complications. Seven objective outcomes were examined. Analysis of postoperative complications included length of hospital stay, days of oxygen dependency, requirement of home oxygen, admission to the intensive care unit (ICU), respiratory failure, and mortality. The definition of end points for each of these variables was determined before the chart review was undertaken.

For length of hospital stay, we examined only the postoperative days, and defined prolonged length of stay as 10 days or longer. Oxygen requirements are assessed every 2 days on the thoracic ward, and the administered amount is titrated to the individual requirement at rest and at exercise. A prolonged requirement of oxygen was defined as 6 days or longer. In our institution, patients undergoing pulmonary resection are initially managed in an intermediate care unit located on the thoracic ward within which arterial lines and a nurse to patient ratio of 1:3 are provided. For the purposes of this review, this is not defined as an ICU; admission to the latter was deemed to occur at any point in the postoperative course if the patient was transferred to the full-scale unit that is capable of mechanical ventilatory support and provides 1:1 nursing care. Respiratory failure was defined as reintubation for a noncardiac-related cause or postoperative ventilation for 24 hours or longer. Mortality was recorded as all-cause mortality during the operative admission.

Pulmonary Function Testing
The Toronto Hospital has a tertiary-level independent pulmonary function laboratory that is capable of performing the full range of spirometric assessment. For the purpose of this review, we focused on the FEV₁. This value has received the greatest interest and debate as a predictor of postoperative function and morbidity. In our laboratory, the reported value is the average of the three best attempts; suboptimal efforts are discarded.

Oximetry
Oximetry was performed with a Nelcor N-10 portable pulse oximeter by or under the direction of the same physical therapist in a standardized manner. This instrument provides continuous analysis of pulse rate and capillary oxygen saturation through a finger probe. A hard copy was obtained for analysis and fixed to the patient's chart. The assessment was performed preoperatively in the following manner: Oxygen saturation and pulse rate were recorded at rest and then during 150-m walk around the ward. Patients were instructed to walk at a moderate to brisk pace with account taken of the patient's age, musculoskeletal abnormalities, and cardiac status. If the patient did not demonstrate oxygen desaturation at rest or with exercise on level ground, he or she was immediately requested to climb two flights of stairs (36 steps) while pulse rate and oxygen saturation were continuously recorded. The distances used were an attempt to correlate exercise with the patient's functional requirement for the activities of daily living. A patient who had desaturation during the walk or on the stairs repeated the test to ensure that the abnormalities recorded were not artifactual. The study was deemed satisfactory if all three phases of the test were performed (ie, rest, walking, and climbing stairs) or if desaturation occurred at any point.

High-Risk Subgroups
The prespecified cutoff for poor spirometry was an FEV₁ of less than 1.5 L. There were 23 patients with an FEV₁ of less than 1.3 L who were analyzed as a high-risk subgroup. Our prespecified cutoff for poor oximetry was a desaturation lower than 90% during any phase of the test. After consideration of the distribution of the data, we analyzed two separate high-risk subgroups to evaluate the sensitivity and the specificity of oximetry. A 4% fall from baseline corresponded roughly to the 70% percentile (ie, 70% of patients had desaturation of less than 4% from baseline), and an absolute decrease of 5 points represented a midpoint between the two previous values. Our original prespecified clinically relevant cutoffs for each test (FEV₁ < 1.5 L for spirometry and desaturation < 90% for oximetry) were compared for their ability to predict postoperative outcomes.

Statistical Analysis
Statistical analysis was performed with the SAS program (SAS Institute, Cary, NC). Categoric data were analyzed using a ² or two-tailed Fisher's exact test where appropriate. Continuous data were analyzed using a two-tailed t test and reported as the mean ± the standard deviation. The cutoffs for oximetry and spirometry were compared on the basis of sensitivity, specificity, and positive and negative predictive values. Significance was assumed at a p value of less than 0.05.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
The patient population consisted of 396 patients, 278 men and 118 women, with an average age of 63.7 ± 9.7 years. Of this total, 299 had undergone both standardized oximetry and reproducible spirometry and form the basis for the statistical analysis. The remaining 97 patients had either one or both measurements omitted or the results were not reproducible on repeated assessment. The 299 evaluable patients underwent the following surgical procedures: pneumonectomy, 44 (15%), lobectomy, 205 (69%); and wedge or segmental resection, 50 (17%). No differences were found between patients undergoing pneumonectomy versus lobectomy, and thus the data reported here are pooled.

Figure 1 demonstrates the distribution of abnormal results for spirometry and exercise desaturation. There were 46 patients with an FEV₁ lower than 1.5 L, our predetermined level of impaired pulmonary function. Of these 46, 23 patients had an FEV₁ of less than 1.3 L. Desaturation to values lower than 90% occurred in 65 patients, 87 patients had an absolute decrease in saturation of 5 or more from rest, and 115 underwent a 4% relative decrease during the test. Twenty-three patients demonstrated both abnormalities (FEV₁ < 1.5 and desaturation < 90%). Table 1 presents the sensitivity, specificity, and positive and negative predictive values for all postoperative outcomes within each group.

View larger version (18K): [in this window] [in a new window]   Fig 1. . High-risk patients as determined by spirometry (forced expiratory volume in the first second [FEV1] < 1.5 L and < 1.3 L) and by oximetry (desaturation < 90%, > 5, or > 4% from baseline).

View larger version (25K): [in this window] [in a new window]   Fig 2. . Prediction of prolonged oxygen requirement. (FEV1 = forced expiratory volume in the first second; NS = not significant.)

View larger version (21K): [in this window] [in a new window]   Fig 3. . Prediction of supplemental home oxygen requirement. (FEV1 = forced expiratory volume in the first second.)

View larger version (22K): [in this window] [in a new window]   Fig 4. . Prediction of intensive care unit admission. (FEV1 = forced expiratory volume in the first second.)

View larger version (25K): [in this window] [in a new window]   Fig 5. . Prediction of prolonged hospital stay. (FEV1 = forced expiratory volume in the first second.)

View larger version (23K): [in this window] [in a new window]   Fig 6. . (A) Prediction of postoperative respiratory failure and (B) prediction of operative mortality. (FEV1 = forced expiratory volume in the first second; NS = not significant.)

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
In 1955, Gaensler and associates [4] reported that the most important determinant of postoperative morbidity and mortality was preexisting pulmonary function. In the published discussion of that study, Dr Basinger noted that oximetry might be of use in the evaluation of patients prior to pulmonary resection. In the intervening 40 years, many reports that attempted to define the role of various means of predicting postoperative complications have been published. More sophisticated studies of cardiopulmonary performance have produced some meaningful results, which will be discussed. However, there are only three studies [57] that either directly or indirectly evaluate exercise oximetry as a preoperative screen of the high-risk patient.

The results of the present report suggest that exercise oximetry undertaken in a standardized fashion appears to be as accurate as FEV₁ in the prediction of pulmonary-specific complications. As demonstrated in Figures 3 through 6A, oximetry was significantly more predictive of the requirement of home oxygen, need of ICU admission, length of hospital stay, and respiratory failure. Kearney and colleagues [5] in a recent study reported on a similar group of patients with comparable morbidity and mortality but failed to demonstrate any predictive value of FEV₁ less than 1.0 L. Rather, they suggested that the calculation of postoperative FEV₁ was the most reliable predictor of postoperative complications.

We agree with this conclusion, which has also been demonstrated by several other groups [6–10]. However, their conclusions concerning oximetry were apparently made by assessing its value in predicting the total number of complications, the majority of which were atelectasis, cardiac failure, and renal failure. Although oximetry may represent a measure of cardiopulmonary reserve, we would not expect it to predict any of these complications. In a small prospective study, Holden and co-workers [7] evaluated a number of preoperative assessments of risk in patients with an FEV₁ of less than 1.6 L, one of which involved exercise testing with pulse oximetry. Although they concluded that exercise was a useful predictor of mortality, they did not provide the oximetry data in their report.

Markos and associates [6] in a study comprising 52 patients noted that exercise-induced desaturation did predict morbidity and mortality. They also measured maximum oxygen consumption, a determination considerably more sophisticated and associated with a high sensitivity in the prediction of postoperative events in select patients. Of 19 patients with a maximum oxygen consumption of less than 15 mL • kg^-1 • min^-1, 12 (63%) also demonstrated arterial oxygen desaturation with exercise. This suggests that exercise oximetry has reasonable correlation with the more sophisticated tests of cardiopulmonary reserve.

Sophisticated evaluations of cardiopulmonary reserve are available. Lung diffusion capacity was shown by Ferguson and co-workers [11] to be a better predictor of postoperative events compared with standard spirometry. However, only 70% of the reported patients had assessment of lung diffusion capacity in this retrospective study, a finding suggesting a testing bias. In addition, the cutoff for increased mortality was a lung diffusion capacity of less than 60% with no data available on the distribution below that point. Many patients with bronchogenic carcinoma have a lung diffusion capacity lower than 60%. Other studies [12, 13] have not supported the accuracy of lung diffusion capacity.

The predicted postoperative FEV₁ has traditionally been calculated with the aid of a nuclear quantitative perfusion scan, which has been shown to more accurately predict postoperative complications than standard spirometry [5,8–10]. Measurements of pulmonary vascular resistance [14, 15] have been shown to be sensitive to mortality after pulmonary resection. The greatest attention in preoperative risk prediction has focused on maximum oxygen consumption. Several studies [16–21] have demonstrated the value of this test, but none has accurately determined a lower limit that possesses acceptable sensitivity and specificity. Two recent studies [6, 7] using maximum oxygen consumption failed to show any predictability of postoperative mortality. Despite controversies concerning the relative value and sensitivity of these various tests, none of the authors of these studies recommend that their particular assessment be adopted as a routine method of screening.

As suggested by our present study, the report of Kearney and colleagues [5], and the large multicenter report by Ginsberg and coauthors [22], the mortality after resection is low. As a result, it is impractical and costly to perform sophisticated studies on all patients. Our goal should be to identify a screening test with the maximum sensitivity and reasonable specificity to select those patients who should undergo more intensive assessment. There are several reports [1–3] in the literature that confirm the fact that preoperative spirometry has a low predictability rate.

The performance of spirometry is subject to a technical and professional fee that is specific for each individual test. Exercise oximetry comprises a portion of a trained physical therapist's time (approximately 30 minutes) and thus may potentially have economic benefit.

Spirometry remains an established preoperative screening test. However, the test is static and fails to evaluate cardiorespiratory dynamics at exercise or the conditioning of the patient. To a degree, exercise testing does accomplish this goal. Indeed, several studies [23–28] have attempted to quantify the long-held surgical belief that stair climbing correlates with survival after pulmonary resection. They have shown varying degrees of predictability. The addition of oximetry and the standardization of the exercise attempt to supply objective data to the subjective impression of dyspnea on the stairs.

This study is a retrospective review of our experience with a standardized form of exercise oximetry used as a screening test to identify the high-risk patient. The results suggest that oximetry undertaken in a standardized fashion is as predictive as spirometry (FEV₁) for the occurrence of a number of pulmonary complications. For the complications of home oxygen requirement, ICU admission, postoperative length of stay, and respiratory failure it was significantly more predictive than an FEV₁ of less than 1.5 L. Indeed, the chances of a patient who did not experience desaturation on exercise to avoid these complications were 91% to 99%.

We emphasize that this is a retrospective study and that the sensitivity of the measurement is low. We suggest that in the patient without historical or physical cause for concern, it is a cost-effective screening test. Should desaturation occur, a more detailed assessment using sophisticated tests is recommended. Can oximetry replace spirometry as a routine screen? This question demands a randomized trial and likely should compare exercise oximetry with a predicted FEV₁ as described by Kearney and associates [5], as the latter is derived without the addition of nuclear scanning and thus comes closer to fulfilling the definition of the ideal screening test. Nonetheless, the data of Kearney and co-workers indicates that the sensitivity of the calculated postoperative FEV₁ was overall only 55% (our calculation from their raw data). Until the completion of a randomized trial, we believe that exercise oximetry as readily fulfills the definition of a screening test as does spirometry in the uncomplicated patient who is about to undergo pulmonary resection.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Presented at the Thirty-first Annual Meeting of The Society of Thoracic Surgeons, Palm Springs, CA, Jan 30–Feb 1, 1995.

Address reprint requests to Dr Todd, Division of Thoracic Surgery, The Toronto Hospital, EN 10-230, 200 Elizabeth St, Toronto, Ont, Canada M5G 2C4.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Vivek Rao Thomas R. J. Todd F. Griffith Pearson Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Rao, V. Articles by Pearson, F. G. Search for Related Content PubMed PubMed Citation Articles by Rao, V. Articles by Pearson, F. G. Related Collections Related Article