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Ann Thorac Surg 1999;67:1444-1447
© 1999 The Society of Thoracic Surgeons

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Original Articles

Assessment of pulmonary complications after lung resection

^a Section of Thoracic Surgery, Department of Surgery, The University of Chicago, Chicago, Illinois, USA

Accepted for publication November 13, 1998.

Address reprint requests to Dr Ferguson, Department of Surgery, The University of Chicago, 5841 S. Maryland Ave, MC 5035, Chicago, IL 60637
e-mail: mferguso{at}surgery.bsd.uchicago.edu

	Abstract

Top Abstract Introduction Patients and methods Results Comment References

 
Background. We assessed the utility of maximum oxygen consumption during exercise (MVO₂) and diffusing capacity for carbon monoxide (DL_CO) in the prediction of postoperative pulmonary complications, and the effect of such complications on postoperative length of hospital stay and the cost of hospitalization.

Methods. Candidates for lung resection were prospectively studied by preoperative measurement of DL_CO (expressed as a percentage of predicted [DL_CO%]) and MVO₂. Postoperative pulmonary complications, duration of postoperative hospitalization, and the cost of hospitalization were assessed.

Results. Forty patients had lung resection with no operative mortality. The postoperative length of hospitalization was longer for the 13 patients who developed pulmonary complications compared with the 27 patients who did not (7.7 ± 0.8 vs 5.0 ± 0.4 days, respectively; p = 0.007), and the cost of hospitalization in the former group was higher ($11,530 ± $1,959 vs $6,578 ± $406, respectively; p = 0.031). Diffusing capacity was higher in patients without than in patients with pulmonary complications (DL_CO% 90.1 ± 5.0 vs 65.3 ± 5.9; p = 0.0034). The mean MVO₂ did not differ between the groups (17.8 ± 0.9 vs 16.3 ± 1.2). DL_CO% predicted pulmonary complications (p = 0.006).

Conclusions. DL_CO% predicts the likelihood of pulmonary complications after major lung resection, which are associated with increased length of hospital stay and cost.

	Introduction

Top Abstract Introduction Patients and methods Results Comment References

 
Resection is the lung cancer patient’s best chance for cure, but many patients with lung carcinoma have coexistent lung and other diseases, and the risk of resection must be carefully assessed before operation. Postoperative complications, especially pulmonary complications, are likely to prolong hospitalization and increase the cost of hospital care, and are associated with an increased risk of mortality. Optimal methods to predict postthoracotomy complications have not been identified, and accurate prediction of the risk of lung resection remains a challenge. In an attempt to improve the preoperative assessment of patients who are candidates for lung resection, many parameters have been proposed to evaluate these risks [1–5]. Among these, maximum oxygen consumption during exercise (MVO₂) [1, 2] and diffusing capacity for carbon monoxide (expressed as a percentage of predicted [DL_CO%]) [3, 6] both have been reported to be independent predictors of postoperative morbidity and mortality after lung resection. We hypothesized that the measurement of MVO₂ would improve the ability to predict complications over that provided by spirometry and DL_CO%.

	Patients and methods

Top Abstract Introduction Patients and methods Results Comment References

 
A prospective study was performed on patients operated on from May 1994 to August 1996. This protocol was approved by our institutional review board, and patients signed a separate informed consent form before entry into this study. Patients were eligible for entry if they had a predicted postoperative forced expiratory volume in 1 sec (FEV₁) > 800 mL. This was calculated using the fraction of functional lung segments remaining after resection [7] or by radioisotope ventilation perfusion studies when available [8, 9]. Patients also had to be considered to have a resectable tumor or other pulmonary disease on the basis of preoperative clinical and radiologic evaluation.

Pulmonary function tests were performed as previously described [3, 6]. With the patient at rest in a seated upright position, spirometric measurements were obtained with a spirometer with analog output to a microcomputer. The FEV₁ was generated in real time by computerized on-line differentiation of the analog spirometric signal. Diffusing capacity for carbon monoxide was measured with the use of automated, computerized solenoid systems by the single breath helium dilution method during a 10-sec breath-holding maneuver. Normal values for lung volumes were taken from regression equations of Morris and associates [10] (men) and Goldman and Becklake [11] (women). Prediction equations for DL_CO were those of Gaensler and Wright [12]. Diffusing capacity was corrected for hematocrit, and results were corrected further for lung volume by the equation of Gelb and associates [13].

The patient’s MVO₂ was determined by a multi-stage incremental test ("ramp workload study") using a cycle ergometer and a metabolic cart retrofitted with standardized exercise Medgraphics software (Medgraphics, St. Paul, MN). The duration of exercise was determined by the physician administering the exercise study, and exercise took place at a standardized work rate (5, 10, 15, or 20 W/min) based on the patient’s mass, height, age, and FEV₁, as described by Wasserman and colleagues [14]. Expired gas was collected by a mouthpiece. Arterial blood gases were obtained at rest and at maximum exercise. Digital oximetry was used to monitor arterial saturation continuously during exercise and recovery periods. The patient’s heart rate and electrocardiogram were monitored during the study. Oxygen consumption was recorded (in L/kg/min) according to the technique of Jones and coworkers [15]. The MVO₂ was defined as the highest oxygen consumption achieved during the exercise test.

Postoperative pulmonary complications were prospectively monitored, and were defined as any pulmonary problem that required special treatment during hospitalization for the operation or within 30 days after operation, and included postoperative ventilation support > 24 h, reintubation for respiratory failure, acute carbon dioxide retention (CO₂ > 45 mm Hg), pneumonia, atelectasis, and the need for supplemental oxygen (O₂) at the time of hospital discharge. Pneumonia was defined as a new pulmonary infiltrate accompanied by fevers that necessitated intravenous antibiotics for treatment. Respiratory failure and atelectasis were defined as previously described [3, 6]. Wound infection, empyema, prolonged air leak (> 7 days), and bronchopleural fistula were considered to be surgical complications and were not defined as pulmonary complications in this study. Length of postoperative hospital stay (LOS) and the direct costs of hospitalization excluding professional fees and normalized to 1998 dollars were determined.

Patients with and without pulmonary complications were evaluated by Student’s t test for continuous variables and by ² analysis for categorical variables. We used ² analysis to compare the utility of spirometry, DL_CO%, and MVO₂ in the prediction of pulmonary complications. We also compared DL_CO%, and MVO₂ using receiver operator characteristic (ROC) curve analysis [16]. A p value < 0.05 was regarded as statistically significant.

	Results

Top Abstract Introduction Patients and methods Results Comment References

 
Forty patients who entered the study had a lung resection by open thoracotomy. There were 29 men and 11 women, with a mean age of 63.5 years (range 43 to 82 years). Thirty-five had non-small cell lung cancer, including 19 stage I, 3 stage II, 9 stage IIIA, 3 stage IIIB, and 1 stage IV, according to the American Joint Committee on Cancer staging system [17]. Five had pulmonary resection for other reasons. The operations performed were 29 lobectomies, 2 bilobectomies, and 9 segmental or wedge resections. There was no operative mortality. Pulmonary complications developed in 13 patients, including pneumonia (11), the need for supplemental O₂ at the time of hospital discharge (6), and respiratory failure (1). The overall pulmonary complication rate was 32.5% (13/40). The pulmonary morbidity rate for lobectomies and bilobectomies was 38.2% (12/31), and for resections of less than one lobe was 11.1% (1/9; p = 0.12 by ² analysis). Nonpulmonary complications included prolonged air leak (4), cardiac arrhythmia (10), and pulmonary embolism (1).

The mean LOS for all patients was 7.9 ± 2.1 days. The range of LOS was 1 to 13 days for 39 of the patients, and 1 patient who developed pulmonary complications (pneumonia associated with respiratory insufficiency requiring reintubation with prolonged ventilatory support) had a LOS of 90 days. Excluding this outlier, the mean LOS for patients without pulmonary complications was 5.0 ± 0.4 days, and for patients with pulmonary complications was 7.7 ± 0.8 days (p = 0.0074) Two patients had surgical complications, including wound infection in the outlier described above and pulmonary embolism and wound infection in a patient who also suffered postoperative pneumonia, and had a LOS of 10 days.

The mean direct cost of hospitalization for all patients was $11,962 ± $3,928. The range of hospital costs was $3,352 to $26,707 for 39 of the patients, and the single outlier who had the 90-day LOS had a hospital cost of $162,514. Excluding this outlier, the mean hospital cost for patients without pulmonary complications was $6,578 ± $406, and for patients with pulmonary complications was $11,530 ± $1,959 (p = 0.031).

Arterial blood gases (pO₂, pCO₂), FEV₁, FEV₁%, DL_CO, DL_CO%, and MVO₂ were evaluated comparing patients with and those without pulmonary complications (2 patients did not undergo assessment of DL_CO). All of the tests except MVO₂ and DL_CO were statistically significantly different (Table 1). Using a series of incremental cutoff values for DL_CO% and MVO₂, DL_CO% was demonstrated to predict pulmonary complications (p < 0.01), whereas there was no such predictive relationship at any chosen cutoff point for MVO₂. A similar method used for FEV₁ (FEV₁%) also showed that there was no strong clinical predictive relationship at any cutoff points (Table 2). ROC analysis showed that the curve of DL_CO% was shifted up and to the left, compared with the same MVO₂, indicating that DL_CO% is superior to MVO₂ in the prediction of pulmonary complications (Fig 1).

View larger version (18K): [in this window] [in a new window]   Fig 1. Comparison of maximum oxygen consumption during exercise (MVO2) and diffusing capacity for carbon monoxide expressed as a percent of predicted (DLCO%) using receiver operator characteristic (ROC) analysis.

	Comment

Top Abstract Introduction Patients and methods Results Comment References

DL_CO% has become increasingly popular as an independent predictor of postoperative pulmonary complications after major lung resection. We previously reported that when DL_CO% was < 60, the pulmonary complication rate was 45%, and when DL_CO% was >100, the rate was only 11% [3]. Other reports have also confirmed the role of DL_CO% in predicting postoperative morbidity [9, 24]. In addition, the use of postoperative predicted values of DL_CO% increases its predictive ability [6]. Nevertheless, there is still controversy in its clinical application [22]. This controversy led us to compare MVO₂ and DL_CO% prospectively.

The overall pulmonary complication rate of 32.5% in this series is similar to the rate of 39% reported by Busch and colleagues [25]. The complication rate in a group of patients who have lobectomy is usually greater than in a group of patients who have a lesser resection. We found a similar difference in our study, although the small numbers of patients in our study precluded achieving statistical significance. There was no mortality in this series, which is likely due in part to advances in preoperative patient assessment, anesthetic techniques, postoperative care, and the lack of pneumonectomy operations.

FEV₁ remains a practical spirometric criterion for predicting postoperative morbidity and mortality [5, 9, 26]. The guidelines for operability, such as FEV₁ > 2 L or > 80% predicted for pneumonectomy, are still widely used in clinical evaluation [5, 27]. Our results show that mean FEV₁ and FEV₁% values in the group without complications were significantly greater than those in the group with complications. This supports the fact that FEV₁ and FEV₁% are useful in assessing postoperative pulmonary complications. Our study also confirms that DL_CO% is a useful predictor of postoperative pulmonary complications after lung resection in patients who meet spirometric criteria for resection, supporting findings previously reported from our institution and by others [3, 6, 9, 26].

Some investigators have found MVO₂ to be a valuable prognostic parameter for postoperative complications [1, 2, 22]. However, there was no significant difference in MVO₂ between groups of patients with and without complications in our study. These results are different from those of Bolliger and associates [22]. We excluded surgical complications such as prolonged air leak, bronchopleural fistula, wound infection, and other surgical problems in the determination of pulmonary complications in a manner similar to that of Bolliger and associates [22]. However, the need for supplemental O₂ was included as a pulmonary complication in our study, making our results more representative of postoperative pulmonary complications. Though MVO₂ did not correlate with pulmonary complications in our series, we could not conclude that MVO₂ was of no value in preoperative evaluation, because our group was not large enough.

This study confirms the association between an impaired DL_CO% and an increased risk of pulmonary complications after lung resection, and demonstrates that DL_CO% is superior to MVO₂ in predicting pulmonary complications. MVO₂ provides little additional information in the assessment of pulmonary risk over that provided by DL_CO%, FEV₁, and FEV₁%. We confirm that patients who experience postoperative pulmonary complications after lung resection have an increased length of postoperative hospital stay and a resultant increase in the cost of hospitalization. Our results suggest that evaluation of DL_CO% is a valuable part of the preoperative assessment for most lung resection candidates.

	References

Top Abstract Introduction Patients and methods Results Comment References

 

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This Article Abstract Full Text (PDF) 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): Jun Wang Jemi Olak Mark K. Ferguson Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Wang, J. Articles by Ferguson, M. K. Search for Related Content PubMed PubMed Citation Articles by Wang, J. Articles by Ferguson, M. K.