How to prevent venous thrombosis?

Epidemiological studies show that venous thromboembolism (VTE) is one of the main causes of death and disability in hospitalized patients. PE is the most common and preventable cause of hospital death, and preventing PE is also the most important strategy to reduce the mortality rate of inpatients. There is usually no warning before the occurrence of massive PE, so the success rate of cardiopulmonary resuscitation in such patients is extremely low. Among the patients who died of PE during hospitalization, 70-80% did not consider the possibility of PE before their death.

Most inpatients have one or more VTE risk factors, which are usually mixed. For example, patients with hip fracture usually have risk factors such as older age, lower limb injury, surgical repair and immobilization for several weeks after operation, so these patients are high-risk groups of VTE. The risk of VTE is higher if there are tumors at the same time. For hospitalized patients, VTE risk factors should be routinely evaluated and corresponding preventive measures should be taken. The risk factors of VTE are shown in the table below.

Danger stratification

To prevent VTE, we should first stratify patients and adopt the strategy of grouping prevention. The criteria of stratification mainly include age, disease nature and patients' own factors.

Surgical inpatients

The factors that affect the occurrence of VTE in surgical patients mainly include the type of operation, the operation time and the patient's own factors. According to the above factors, patients are divided into risk categories and corresponding preventive measures are taken. See table 2.

Risk factors: history of VTE, tumor and hypercoagulable state of coagulation factors.

Combined with the following risk factors, such as old age, malignant tumor, neurological dysfunction, previous VTE history or anterior surgery.

Inpatients in internal medicine

VTE is not only related to surgery or trauma. In fact, 50-70% of symptomatic thromboembolism events and 70-80% of fatal PE occur in non-surgical patients. If not prevented, the risk of VTE in general inpatients of internal medicine is low to moderate. The incidence of asymptomatic DVT is 5-7%, and it is mostly confined to the distal veins of lower limbs. However, the risk of VTE is obviously increased in patients with some serious medical diseases, including: patients hospitalized due to congestive heart failure (new york cardiac function classification III and IV) or severe respiratory diseases (exacerbation of chronic obstructive pulmonary disease), patients bedridden due to one or more other risk factors: active cancer, history of venous thromboembolism, sepsis, acute nervous system diseases (stroke accompanied by lower limb mobility inconvenience) and inflammatory bowel diseases. Many medical patients often have multiple risks.

In addition to hospitalized patients, other special circumstances, such as long-distance travel, will also increase the risk of VTE, and the flight time will exceed 6 hours. Regardless of the risk of VTE, we should pay attention to avoid wearing tight clothes on lower limbs and waist, avoid dehydration, and often stretch gastrocnemius; Those at risk of VTE should consider grading compression socks or applying a dose of LMWH or fondaparinux before traveling.

Drug prevention

One of the main obstacles to the strategy of preventing thrombosis is the fear of bleeding complications. However, a large number of meta-analyses and placebo-controlled, double-blind, randomized clinical studies have confirmed that low-dose unfractionated heparin (LDUH), low-molecular-weight heparin (LMWH) or vitamin K antagonist (VKA) hardly increase the risk of clinically significant bleeding complications, and there is increasing evidence that new anticoagulants such as pentose. There is sufficient evidence to show that taking correct preventive strategies can achieve ideal risks/benefits and costs/benefits. Thrombosis prevention strategy can not only improve the prognosis of patients, but also reduce the total hospitalization expenses.

First, antiplatelet drugs

Antiplatelet drugs such as aspirin are very effective in reducing major vascular events in atherosclerosis or high-risk groups. There is evidence that antiplatelet drugs can protect hospitalized patients at risk of VTE, but aspirin alone is not recommended to prevent VTE. The main reason is that the clinical research supporting antiplatelet drugs is small in scale, flawed in design, inconsistent in results, and the curative effect is not as good as other preventive methods, such as heparin.

Second, anticoagulant therapy.

1. heparin

In the prevention of venous thrombosis, a large number of studies have confirmed the efficacy of subcutaneous injection of heparin, but the bioavailability of subcutaneous injection of heparin is lower than that of intravenous administration. Subcutaneous injection of low-dose ordinary heparin LDVH is suitable for middle and high-risk patients, such as inpatients in general surgery, internal medicine, obstetrics and gynecology and urology. However, for extremely high-risk patients, it is not suitable for single application, such as preventing hip and knee replacement, and patients with various risk factors in other surgical operations.

Dose: According to the different risk levels of patients, two doses are recommended, and APTT does not need to be monitored.

Moderately dangerous dose: 5000U, twice a day, subcutaneous injection.

High risk dose: 5000U, subcutaneous injection three times a day.

Treatment start time:

Internal medicine: medication can be started without anticoagulation contraindications.

Operation: In most preventive studies, LDUH 5000U was injected subcutaneously 0-2 hours before operation.

Starting medication after operation: 12- 24 hours after operation, subcutaneous injection of 5000U Bid or Tid.

2. Low molecular weight heparin

Although the pharmacological characteristics of different low molecular weight heparins are significantly different, and each LMWH should be regarded as an independent drug, the research results show that there is no significant difference in the curative effects of different low molecular weight heparins. At present, there is no study to directly compare the curative effects of different LMWH on surgical patients, and different preparations need to refer to the recommendations in the product manual.

Moderately dangerous dose: LMWH≤3400U once a day.

High risk dose: LMWH & gt；; 3400U/ day, once a day.

Table -3 Preventive Anticoagulant Doses of Different Low Molecular Weight Heparin

Treatment start time:

The starting time of treatment is affected by the patient's surgery and bleeding risk. It is necessary to comprehensively evaluate the efficacy and bleeding risk of anticoagulants to determine the time to start prevention. Anesthesia methods may also have an impact on the selection and start time of preventive drugs.

1. In general surgery, obstetrics and gynecology, and urology, it usually takes 5-7 days or more to inject heparin/kloc-0 subcutaneously for-2 hours before operation and every morning after operation until the patient can move.

2. Trauma: For most patients with moderate and high-risk trauma, once the initial bleeding is controlled, they can start. Contraindications for early LMWH prevention include: intracranial hemorrhage, progressive hemorrhage, uncontrollable hemorrhage, severe coagulation dysfunction that cannot be corrected, incomplete spinal cord injury with suspected or confirmed paraspinal hematoma. No obvious bleeding from head trauma, laceration or contusion of internal organs (such as lung, liver, spleen or kidney), retroperitoneal hematoma after pelvic fracture and complete spinal cord injury are not contraindications for LMWH after the possible progressive bleeding is ruled out. Most patients can start using LMWH for prevention within 36 hours after trauma.

3. Orthopedic surgery: There is little difference between preoperative and postoperative application of LMWH, and both methods can be used. For patients with selective THR, LMWH was given 12 hours before operation or 12-24 hours after operation, or half of the higher preventive dose was given for the first time 4-6 hours after operation, and the higher preventive dose was given the next day.

4. Hip fracture: If HFS is not operated immediately, it is recommended to take preventive measures before operation and give short-acting anticoagulants such as LDUH or LMWH.

5. For patients with high risk factors of bleeding, it is suggested to postpone the first application of LMWH to 12 until 24 hours after operation, until the bleeding at the operation site has basically stopped after examination.

6. Patients with acute spinal cord injury should be prevented from LMWH, and should start using it after successful basic hemostasis. If CT scan or MRI examination shows that patients with incomplete spinal cord injury have paravertebral hematoma, LMWH should be delayed for 1-3 days to start its application.

Treatment time:

● For the vast majority of patients, including surgical and internal medicine inpatients, the optimal course of preventive anticoagulant therapy is still unclear.

● General principle: Moderate-risk and high-risk patients should take medicine until they resume their activities or leave the hospital.

● Very high-risk patients need to continue to use it for 2-4 weeks after discharge, and it may take longer according to the situation.

● The ideal time limit for preventing thrombosis in internal medicine patients is not clear, and the time for administration with evidence is generally 2 weeks.