Materials and Methods

Patients who underwent hysterectomy for benign disease from January 2010 through December 2012 and were recorded in the American College of Surgeons (ACS) National Surgical Quality Improvement Program (NSQIP) database were included in this study. Current Procedural Terminology ( CPT ) codes were used to identify patients who underwent hysterectomy and to classify patients by route of surgery ( Figure ). CPT codes that include hysterectomy along with other procedures, such as lymphadenectomy, which would indicate the hysterectomy was being performed as treatment for a malignancy, were not included. Additionally, patients were excluded if their preoperative International Classification of Diseases, Ninth Revision code indicated presence of a malignancy. Definition of route of surgery was based on the primary CPT code. There is no CPT code for conversion from laparoscopic or vaginal hysterectomy to an open procedure. Converted cases were likely recorded using an open CPT code and so we are unable to analyze conversion cases separately. Additionally, cases in which patients underwent a mini-laparotomy for specimen removal are likely recorded as laparoscopic and CPT code does not allow us to discern between these patient groups.

Patient selection flowchart

Flowchart detailing patient selection from National Surgical Quality Improvement Program (NSQIP) database for study inclusion.

CPT, Current Procedural Terminology ; ICD-9, International Classification of Diseases, Ninth Revision ; LH , laparoscopic hysterectomy; LSC , laparoscopic; SCH , supracervical hysterectomy; TAH , total abdominal hysterectomy; TLH , total laparoscopic hysterectomy; VH , vaginal hysterectomy.

Barber. MIS hysterectomy decreases VTE risk. Am J Obstet Gynecol 2015 .

The ACS-NSQIP database is a national quality improvement database. Participating institutions employ nurses to prospectively collect variables such as patient demographics, preoperative variables, operative variables, and postoperative variables for 30 days following surgery. These variables are then deidentified of both patient-specific and hospital-specific information and placed into the national database.

Demographic variables abstracted included age, race, and body mass index (BMI). Patient-related preoperative variables abstracted included hypertension requiring medication, diabetes mellitus requiring insulin or oral therapy, smoking in the last year, total pack-years, and preoperative functional status (a standardized assessment of the patient’s ability to perform activities of daily living within the last 30 days). Operative variables abstracted included operative time, year operation was performed, surgical approach, and American Society of Anesthesiologists (ASA) score. Postoperative variables abstracted included time from operation to discharge, presence of pulmonary embolism (PE) or deep-vein thrombosis (DVT) requiring therapy, and time from operation to VTE event.

NSQIP definitions of VTE were used. A PE was defined as “a lodging of a blood clot in a pulmonary artery with subsequent obstructions of blood supply to the lung parenchyma, confirmed by a ventilation perfusion scan interpreted as high probability of PE or a positive computed tomography spiral examination, pulmonary arteriogram, or computed tomography angiogram.” A DVT was defined as “identification of a new blood clot or thrombus within the venous system, confirmed by duplex, venogram, or computed tomography. The patient must be treated with anticoagulation therapy and/or placement of a vena cava filter or clipping of the vena cava.”

Cases of VTE were compared with control patients and routes of surgery were compared to one another. VTE rates were compared for subjects with and without previously validated risk factors for VTE (eg, BMI, age, smoking) using Student t for continuous variables and Pearson χ ² test for categorical variables. Association between VTE and variables of potential clinical significance including route of surgery were analyzed using binomial logistic regression to examine for potential confounding. A P value of < .05 was considered significant for all analyses. SPSS, version 20.0 (IBM Corp, Armonk, NY) was used for all analyses. The institutional review board of Northwestern University approved this study and declared it exempt from formal review.

Results

Demographic variables and known VTE risk factors are presented in Table 1 for both cases and controls. A total of 44,167 patients underwent a hysterectomy from January 2010 through December 2012. Route of surgery was open in 12,733 patients (28.8%), laparoscopic in 22,559 patients (51.1%), and vaginal in 8875 patients (20.1%). Mean age was 47.9 ± 10.7 years and mean BMI was 30.0 ± 7.9 kg/m ² . Of the patients, 7% were diabetic, 26.5% were hypertensive, and 18.5% had smoked within the last year. The majority of patients had an independent functional status (99.4%). Mean total operative time was 129.3 ± 68.1 minutes and mean time from surgery to discharge was 1.82 ± 2.0 days.

There were 154 cases of VTE (0.35%) among all patients who underwent a hysterectomy. Fifty-three patients had DVT alone (34.4%), 85 patients had a PE alone (55.2%), and 16 patients had both a PE and a DVT (11.7%) ( Table 2 ). Mean time to postoperative VTE was 9.1 ± 7.0 days and did not differ dependent on surgical approach. There was also no difference between type of VTE event (PE vs DVT) dependent on route of surgery.

Patients with postoperative VTE were more likely to have a high BMI ( P = .003), be of African American race ( P < .001), have diabetes ( P = .037), and have a higher ASA score ( P = .002), and were less likely to have an independent preoperative functional status ( P < .001). Patients with VTE also had surgeries that were 29 minutes longer than those without VTE ( P < .001) and had operation-to-discharge times that were 2.7 days longer ( P < .001). Patients with VTE did not differ from those without VTE with respect to age, hypertension, smoking status, or year the operation was performed ( Table 1 ).

To identify variables associated with the route of surgery that may have influenced VTE rates, patients who underwent open surgery were compared with those that underwent minimally invasive surgery (MIS) ( Table 3 ). First, surgical approaches within the minimally invasive and open groups were compared to one another and no significant difference was found in VTE rates between vaginal and laparoscopic procedures or abdominal and open supracervical hysterectomies (data not shown). As VTE rates were not different, the groups were then combined into a MIS group and an open hysterectomy group. Patients receiving MIS were thinner ( P < .001) and more likely to be Caucasian ( P < .001), had lower rates of diabetes mellitus ( P < .001) and hypertension ( P < .001), were more likely to have an independent functional status ( P < .001), and fewer were current smokers ( P < .001). They were also slightly older than those receiving open surgery ( P < .001). Patients were more likely to receive MIS as the year of the operation progressed from 2010 through 2012 ( P < .001). MIS patients also had longer operative times ( P < .001), driven by the length of the laparoscopic cases, and shorter operation-to-discharge times ( P < .001).

Table 3

Characteristics of patients in minimally invasive and open approach groups

Variable	MIS (n = 31,434)	Open (n = 12,733)	P value
Age, y	48.1 ± 11.2	47.5 ± 9.6	< .001
BMI	29.8 ± 7.5	31.0 ± 7.7	< .001
Race			< .001
American Indian or Alaska Native	164 (0.5)	64 (0.5)
Asian	839 (2.7)	476 (3.7)
African American	3209 (10.2)	2480 (19.5)
Pacific Islander	94 (0.3)	59 (0.5)
Caucasian	23,908 (76.1)	7621 (59.9)
Unknown	3220 (10.2)	2033 (16.0)
Hypertension	8021 (25.5)	3676 (28.9)	< .001
Diabetes mellitus	2091 (6.7)	1002 (7.9)	< .001
Current smoking	5733 (18.2)	2417 (19.0)	NS
ASA score	2.02 ± 0.57	2.09 ± 0.62	< .001
Preoperative functional status			< .001
Independent	31,273 (99.5)	12,628 (99.2)
Partially dependent	90 (0.3)	76 (0.6)
Totally dependent	11 (0.03)	10 (0.1)
Unknown	60 (0.2)	19 (0.1)
Year operation performed			< .001
2010	5889 (18.7)	3108 (24.4)
2011	10,280 (32.7)	4537 (35.6)
2012	15,265 (48.6)	5088 (40.0)
Total operative time, min	131.9 ± 69.0	123.1 ± 65.4	< .001
Days from operation to discharge	1.3 ± 1.6	2.8 ± 2.4	< .001

All data are presented at n (%) for categorical variables and mean ± SD for continuous variables.

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