Major morbidity after lung resection: a comparison between the European Society of Thoracic Surgeons Database system and the Thoracic Morbidity and Mortality system

Introduction

The rate of postoperative complications is often used in our specialty as a parameter for evaluating both the effectiveness of treatment and the quality of care (1,2). However, a standardized grading of complication is lacking.

The Thoracic Morbidity and Mortality (TM&M) classification system of surgical complications has been proposed as a method for classifying the postoperative adverse events, based on the complexity of the therapeutic procedure necessary to treat them (3).

The aim of the present study was to compare the distribution of the severity of complications according to the TM&M system versus the distribution according to the classification proposed by European Society of Thoracic Surgeons (ESTS) Database (4) in a population of patients submitted to lung resection in our unit.

Materials and methods

This is a retrospective study performed on data prospectively collected in an electronic clinical database, approved by the local Institutional Review Board. Informed consent was obtained from all patients to use their personal information and data for clinical and scientific purposes.

The local data manager prospectively performed the data collection. The demographic and clinical information of all patients submitted to pulmonary resection in the previous 30 days were entered into an electronic database on a monthly basis. Table 1 lists the database variables used for the present study and how they were codified. All the included variables had a level of completeness greater than 95%.

Table 1. Variables used for the analysis.
Full Table

We included in the present analysis all patients consecutively submitted to pulmonary resection in our Institution from January 2000 to April 2011. Within this cohort, those patients experiencing at least one postoperative complication were analyzed.

Definition of different types of complications and TM&M classification system

Postoperative adverse events were classified according to the definitions proposed by the ESTS Database Committee (2,4,5). According to these definitions the “major cardiopulmonary morbidity” included any of the followings, regardless the complexity of treatment used to manage them: pneumonia, atelectasis requiring bronchoscopy, adult respiratory distress syndrome, mechanical ventilation longer than 24 h, pulmonary edema, pulmonary embolism, myocardial ischemia, cardiac failure, arrhythmia, stroke, acute renal insufficiency.

The TM&M classification system (3,6) is a method for classifying the complications after thoracic surgery based on the Clavien-Dindo classification schema (7,8). Following this method, each complication is graded from I to V, reflecting an increasing severity and complexity of management regardless the type of complication. Table 2 shows the different grades of complications as defined by the TM&M classification.

Table 2. Grading of complication following the TM&M classification system.
Full Table

For the purpose of this study, we recoded all postoperative complications registered in our database using the TM&M classification system. For patients with multiple complications, we considered only the most severe one, as suggested by Seely and colleagues (3). Two staff surgeons independently reviewed each complicated patient and assigned the correspondent TM&M grade for the reported complication. Disagreements between reviewers were resolved by consensus.

Managements of complications were prospectively collected in the medical records and in the clinical database, which were reviewed for retrieving that information and assigning the score.

We then verified the frequency of distribution of the different grades of complications in our series and in particular among those patients who had been classified as having major cardiopulmonary complications according to ESTS definitions.

A descriptive statistics was used. Results are reported as means and standard deviation for numeric variables or frequency of occurrence for categorical variables. The statistical analysis was performed on Stata 9.0 statistical software (Stata Corp. College Station, TX).

Results

From January 2000 to April 2011, 1,518 consecutive patients were submitted to pulmonary resection in our Unit. Among them, 457 patients experienced at least one complication. The following 290 complications were classified as major cardiopulmonary complications according to the ESTS criteria: 112 arrhythmia, 84 pneumonia, 40 atelectasis requiring bronchoscopy, 16 adult respiratory distress syndrome, 16 pulmonary edema, 14 myocardial ischemia, 4 cardiac failure, 3 stroke, 1 acute renal insufficiency.

Table 3 shows the baseline and surgical characteristics of the entire population and of those patients with and without complications. The majority of patients were submitted to pulmonary lobectomy for primary malignant neoplastic disease. Compared to non-complicated patients, those with complications were older (P<0.001), were more frequently male (P<0.001), underwent more frequently to major anatomic resections for lung cancer (P<0.001). Moreover, the complicated patients had significantly lower values of Forced Expiratory Volume in one second (FEV1) (P<0.001) and Carbon Monoxide Lung Diffusion Capacity (DLCO) (P<0.001) and higher American Society Anesthesiologists (ASA) (P<0.001) and Eastern Cooperative Oncology Group (ECOG) scores (P<0.001).

Table 3. Baseline and surgical characteristics of all patients and comparison between not complicated and complicated patients.
Full Table

Table 4 shows the distribution of postoperative complications by their complexity of management according to the TM&M classification system. More than 65% of complications were graded as minor complication (72% after lobectomy and 30% after pneumonectomy).

Table 4. Distribution of postoperative complications by their complexity of management according to the TM&M classification system.
Full Table

Twenty three percent of total complications were defined as major according to the TM&M classification (including mortality). These complications occurred in approximately 7% of the total population of operated patients.

According to the ESTS definitions, major cardiopulmonary complications occurred in 63% of complicated patients corresponding to 19% of the total population.

As reported in Table 5, ESTS-defined major cardio-pulmonary complications required a major treatment or lead to death (grade III to V according to the TM&M system) in only 38% of cases. Sixty-two percent of major cardiopulmonary complications according to ESTS definitions were therefore recoded as minor complications according to TM&M. On the other hand, 38 complications not defined as major according to the ESTS were recorded as major complications (III or IV) according to the TM&M system due to their complex management. None of them however lead to death-grade V.

Table 5. Distribution of the major cardio-pulmonary ESTS complications following the TM&M system.
Full Table

Discussion

The definition of quality in a health care system is very difficult to obtain. This is because the quality of care could be measured at different levels and from different point of view (9,10).

In our specialty the complication rate following a surgical operation is a parameter very often used to verify the level of quality delivered by health care providers (11,12). Nevertheless a universally accepted definition of what we intend for complication after a surgical procedure is lacking. Moreover different types of complications are weighted the same, even though they may imply different complexities of management and put different burdens on the postoperative course.

The TM&M system is a method for classifying the postoperative adverse events in thoracic surgery developed by Seely and coll (3,6). This system is based on the complications classification model proposed by Dindo and coll. in 2004 (7), which grades the complications according to the effort to treat them. Following this method, each postoperative adverse event is univocally graded assigning a score that reflects an increasing severity and complexity of management.

The objective of the present investigation was to assess whether there was any discrepancy between the incidence of major complications as defined by the TM&M classification and the ESTS criteria.

We found that more than 70% of the complications registered in patients submitted to lobectomy or to wedge-segmentectomy were graded as minor complication according to the TM&M. This means that the majority of the complications experienced by our patients had a minimal impact on their postoperative course and required no treatment or only pharmacologic or minor interventions. These results seem in line with the data reported by Seely and coll. in 2010 (3). Conversely, 70% of complicated patients submitted to pneumonectomy experienced major complications, reflecting a higher severity of morbidity and the consequent need of more complex treatments.

Subsequently, we pointed our attention on a specific group of adverse events, which were considered major cardio-respiratory complications according to the classification proposed by the ESTS. In our specialty this group of postoperative complications is often selected as a primary endpoint for outcome analyses or as an instrument to measure the quality of care (13).

In particular, the risk-adjusted cardiopulmonary morbidity was recently adopted as one of the parameters used to measure the outcome domain of the Composite Performance Score (CPS), a quality indicator proposed by ESTS to evaluate all aspects (preoperative, intraoperative and postoperative domains) of the surgical practice. The CPS is currently used as a pivotal evaluation instrument in the ESTS Quality Certification Program (2,5).

According to the TM&M system, only 38% of those cardiopulmonary complications defined as major by the ESTS criteria were graded III or higher. This finding may question the systematic use of un-weighted cardiopulmonary complications for outcome analyses.

A potential limitation of the present study is represented by its retrospective nature. This implies a lesser accuracy in the definition of the treatment used, especially for those complications that required just a medical treatment.

Moreover the effectiveness of the treatment for an adverse event is dependent both from the characteristics of the patient and from the type of care offered. The standardization of the therapy proposed for each complication is mandatory to obtain reliable information about its results. In relation to this aspect, we should underline that, despite in our unit the postoperative course was managed following specific pathways of care, standardized treatment protocols for postoperative complications were implemented only after January 2008.

In conclusion, we found that only one third of those complications defined as “major” according to the ESTS Database required complex management and were graded as major complications by the TM&M system. For this reason, we think that the TM&M classification system may complement more traditional classification methods in order to reliably weigh morbidity and refine outcome analyses.

Acknowledgements

Disclosure: The authors declare no conflict of interest.

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