Two simple-to-use calculation tools, which physicians can use to predict separately the 30-day risk of postoperative venous thromboembolism in hospital and after discharge, have been developed. Researchers based the two nomograms on the results of a retrospective analysis of more than 450,000 thoracic and abdominal surgical patients in the American College of Surgeons National Surgical Quality Improvement Program database.
"Substantial variation exists in the incidence of VTE [venous thromboembolism] and VTEDC [venous thromboembolism after hospital discharge] after abdominal or thoracic surgery, depending on patient and procedural factors," wrote Dr. Robert Canter, Dr. Dhruvil R. Shah, and colleagues at the University of California, Davis. They analyzed these factors to determine statistically significant risks in order to construct the predictive nomograms, according to their report published in the July issue of the Journal of Surgical Research. Dr. Canter is the senior author of the study and associate professor of surgery in the Division of Surgical Oncology at UC Davis.*
The authors used data obtained from the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) to construct a nomogram by which physicians could use a ruler and draw lines from each separate risk factor on a no-yes gridline to a point score for that factor. By adding the point results for all factors, the total number of points could then be used to calculate the 30-day risk of developing a VTE. A separate nomogram using the same process was constructed for calculating the risk of a VTEDC.
The researchers assessed 471,867 patients who underwent inpatient abdominal or thoracic operations between 2005 and 2010. Patients who underwent primary vascular and spine operations were excluded. The overall unadjusted, 30-day incidence of postoperative VT) in these patients was 1.5% and that of VTEDC was 0.5%, and the annual incidence rates remained unchanged over the period studied. The median time to VTE was 9 days and the median time to VTEDC was 17 days, and these also did not change over the study period.
The majority of patients were white (75.5%) and men (59%), with a mean age of 54 years and a mean body mass index of 31 kg/m2; 93% of the patients were functionally independent.
Comorbidities included smoking (19%), history of preoperative infection or sepsis (16.5%), diabetes (15%), and a variety of cardiovascular conditions or procedures (9%). The vast majority of operations were abdominal (98%), with most performed on the gastrointestinal tract (51.5%). Thoracic operations accounted for 2.1%. Minimally invasive (excluding bariatric) surgery was performed in 37% of cases, with 20% of all operations performed for cancer. A total of 11% of patients experienced one or more major postoperative complications within 30 days of the operation, including post discharge.
Multivariate analysis showed that the significant predictors of both VTE and VTEDC were age, body mass index, presence of postoperative infection, operation for cancer, procedure type (primarily splenectomy), multivisceral resection, and nonbariatric laparoscopic surgery. Significant factors predicting VTE but not VTEDC were a history of chronic obstructive pulmonary disease, disseminated cancer, and emergent operation (J. Surg. Res. 2013;183:462-71).
In addition to the nomogram, the researchers used internally developed concordance indices to measure the probability of concordance between the predicted and measured outcomes and found that these were 0.77 for VTE and 0.67 for VTEDC. They acknowledge that the lower value for VTEDC is a probable indicator of unknown and uncaptured risk factors, possibly including socioeconomic status, a change in postoperative functional status,
Limitations of the study included those inherent to using the ACS-NSQUIP database, which meant that they could not identify patients who had a prior history of VTE or central line placement, both of which have been cited as VTE risk factors, according to the researchers. In addition, asymptomatic VTE events and events for which patients did not receive anticoagulation were not captured in the database.
"Although these nomograms require external validation to ensure reproducibility, these tools will aid clinicians, researchers, and administrators in determining which subset of patients undergoing abdominal or general thoracic general surgical operations are at highest risk for postoperative VTE and VTEDC. Our data may allow for more targeted quality improvement interventions to reduce VTE and VTEDC" in these patients, the researchers concluded.
The authors disclosed no conflicts that the editors of the journal determined should be reported in the article.
*UPDATED: This story was updated to include Dr. Canter's information and photo.