Venography no longer the gold standard. Other diagnostic studies may be more useful. Venography has fallen from favor because it is moderately uncomfortable, requires injection of a contrast material that may trigger an allergic reaction or renal injury, and causes phlebitis in approximately 5% of patients.2 Newer, noninvasive diagnostic tests have been developed, fortunately.
Doppler ultrasound. B-mode duplex Doppler imaging is the most common technique to diagnose symptomatic venous thrombosis, especially when it arises in the proximal lower extremity. With duplex Doppler imaging, the femoral vein can be visualized, and clots may be seen directly. Compression of the vein with the tip of the ultrasound probe makes it possible to assess venous collapsibility, which is diminished when a thrombus is present.
Doppler imaging is less accurate when evaluating the calf and pelvic veins.
Magnetic resonance venography (MRV) sensitivity and specificity are comparable to venography. In addition, MRV may detect thrombi in pelvic veins that are not imaged by venography. The primary drawback is the time required to examine the lower extremity and pelvis. Further, MRV rarely identifies calf thrombi (most often not life-threatening, but potentially symptomatic) and is considerably more expensive than ultrasound.
INTEGRATING EVIDENCE AND EXPERIENCE
Which prevention strategy works best?
We now consider low-molecular-weight heparin and external pneumatic compression the best choices
Because low-dose unfractionated heparin, low-molecular-weight heparin (LMWH), and external pneumatic compression all reduce the incidence of postoperative venous thromboembolism in high-risk gynecologic surgical patients, the question is: Which strategy is best?
We conducted 2 randomized clinical trials to answer this question.
Trial 1 Low-dose heparin vs pneumatic compression
Women were randomized to receive either low-dose heparin (5,000 U subcutaneously preoperatively and every 8 hours after surgery until hospital discharge) or external pneumatic compression of the calf prior to surgery and until hospital discharge.1
The incidence of DVT was identical in both groups, and no patients developed a pulmonary embolus throughout 30 days of follow-up. However, bleeding complications occurred more often in the group randomized to low-dose heparin. Specifically, nearly 25% had APTT levels in the “therapeutic” range, and significantly more patients required blood transfusions. After this trial, our institution decided to use external pneumatic compression because of its more favorable risk profile.1
Trial 2 LMWH vs pneumatic compression
The question of the best therapy arose again with the advent of LMWH, because of the possibility that these drugs carried a lower risk of bleeding complications. We therefore conducted a second trial to compare LMWH with external pneumatic compression.2
Because higher doses of LMWH had already proven to be more effective in cancer patients, we gave women in the trial 5,000 U dalteparin (Fragmin) preoperatively and 5,000 U daily postoperatively until hospital discharge.
In this trial, external pneumatic compression and LMWH produced similar low frequencies of DVT and no pulmonary emboli throughout 30 days of follow-up. We also found no association between LMWH and bleeding complications or transfusion requirements. Compliance and patient satisfaction were similar for both modalities.2
Bottom line
We now consider LMWH and external pneumatic compression the best choices for prophylaxis in gynecologic surgical patients.
REFERENCES
1. Clarke-Pearson DL, Synan IS, Dodge R, Soper JT, Berchuck A, Coleman RE. A randomized trial of low-dose heparin and intermittent pneumatic calf compression for the prevention of deep venous thrombosis after gynecologic oncology surgery. Am J Obstet Gynecol. 1993;168:1146-1154.
2. Maxwell GL, Synan I, Dodge R, Carroll B, Clarke-Pearson DI. Pneumatic compression versus low molecular weight heparin in gynecologic oncology surgery: a randomized trial. Obstet Gynecol. 2001;98:989-995.
Does laparoscopic surgery add risk?
Increasing use of laparoscopic surgery raises an important question: What is the thromboembolic risk of laparoscopy itself? On one hand, many laparoscopic surgeries are prolonged, and intraperitoneal pressure from the pneumoperitoneum reduces venous flow. On the other hand, many patients who have laparoscopy have shorter hospital stays and return sooner to normal activities than those who have open procedures.
Although the risks of venous thromboembolism (VTE) have not been studied as thoroughly as other aspects of laparoscopy, they appear to be low. To date, there are no randomized trials of VTE prophylaxis among women undergoing gynecologic laparoscopy.
The prudent course
Nevertheless, it would seem prudent to consider prophylaxis when women with additional risk factors undergo extensive laparoscopic procedures.
Pulmonary embolism is often stealthy
Many of the typical signs and symptoms of pulmonary embolism are associated with other, more common pulmonary complications following surgery. Classic findings that should alert the physician to the possibility of pulmonary embolism include:
- pleuritic chest pain
- hemoptysis
- shortness of breath
- tachycardia
- tachypnea
Often, however, the signs are subtle and may include only persistent tachycardia or a slight elevation in respiration.