DVT Prophylaxis
Almost every patient you admit needs a documented decision about venous thromboembolism prophylaxis, and "forgot to address it" is not one of the acceptable answers.
Everyone gets a decision, not everyone gets a drug
Hospital acquired VTE is one of the more preventable ways an admitted patient dies, and it is one of the easiest things in a chart to audit afterward. The standard you are held to is not "did you give enoxaparin." It is "did you consider it, and is your reasoning visible."
There are three acceptable outcomes for every admission, and only three:
- Pharmacologic prophylaxis, with the agent and dose written.
- Mechanical prophylaxis only, with the reason the drug was withheld written.
- No prophylaxis, with the reason written. This one is rare and it had better be good.
What is not acceptable is a blank. Clicking through the order set without reading is how a 78 year old with metastatic colon cancer and three days of bed rest gets nothing.
Risk assessment models, in outline
You are not expected to memorize these. You are expected to know which one applies to your patient and to have actually looked at it.
For acutely ill medical inpatients. Eleven items. The heavy ones, worth 3 points each, are active cancer, previous VTE, reduced mobility, and a known thrombophilia. Recent trauma or surgery carries 2. The lighter items, 1 point each, include age 70 or over, heart or respiratory failure, acute myocardial infarction or ischemic stroke, acute infection or rheumatologic disease, obesity, and ongoing hormonal therapy. A score of 4 or more is the usual threshold for high risk.
For surgical patients. Longer, more granular, weighted for age, procedure type, cancer, prior VTE and thrombophilia. Bands run from very low at 0 to 1, through moderate at 3 to 4, to high at 5 and above. Surgical services usually have a preferred version embedded in their order set. Use theirs.
Two scores from the same registry work, and the trick is to run them together: an IMPROVE VTE score for clot risk and an IMPROVE bleeding risk score for the other side of the ledger. The bleeding score is the one that earns its keep, because it puts numbers on the patient you already suspected you should not anticoagulate: active gastroduodenal ulcer, bleeding in the prior three months, low platelets, advanced age, renal or hepatic failure, ICU status, central venous catheter.
The score is a prompt for thought, not a verdict. A Padua of 3 in a patient with a fresh femur fracture and no mobility is still a patient I anticoagulate.
The pharmacologic options
Illustrative adult dosing for a patient with normal renal function and normal body habitus:
- Enoxaparin 40 mg SC once daily. The default for most medical inpatients. Some surgical protocols use 30 mg SC every 12 hours instead. Predictable, once daily, no routine monitoring.
- Unfractionated heparin 5000 units SC every 8 or every 12 hours. Every 12 hours for lower risk patients, every 8 hours for higher risk and most surgical patients. Short half-life, cleared independently of the kidney, reversible. This is what you use when you might need to stop it in a hurry.
- Fondaparinux 2.5 mg SC once daily. A synthetic factor Xa inhibitor. Its niche is the patient with a history of heparin induced thrombocytopenia, since it does not cross react with HIT antibodies in the way heparin and low molecular weight heparin do. Long half-life and no good reversal agent, so it is a poor choice in anyone you may need to reverse.
Direct oral anticoagulants have a role in extended prophylaxis after certain orthopedic operations and in selected medical patients, but that is a decision made with the primary service and not something to start on your own overnight.
Renal dosing, and when to give up on enoxaparin
Enoxaparin is cleared renally. It accumulates. The patient with a creatinine clearance of 22 who gets 40 mg daily for six days is being quietly overdosed, and you will find out when they bleed.
- CrCl 30 mL/min or above: standard prophylactic dosing.
- CrCl below 30 mL/min: reduce enoxaparin to 30 mg SC daily, or switch to unfractionated heparin.
- Dialysis, acute kidney injury with a moving creatinine, or a clearance you do not trust: use unfractionated heparin 5000 units SC every 8 or 12 hours. It is not renally cleared and the half-life is short.
- Fondaparinux: avoid below a clearance of 30. It has no useful reversal.
Calculate the clearance. Do not eyeball the creatinine. An 82 year old woman weighing 48 kg with a creatinine of 1.1 does not have normal renal function.
Obesity
Standard prophylactic doses were derived in patients who no longer resemble much of the inpatient population. In substantial obesity, a fixed 40 mg daily produces lower anti-Xa levels and there is reasonable evidence of more breakthrough VTE.
Common institutional approaches, and I mean common rather than universally agreed, escalate to enoxaparin 40 mg SC every 12 hours, or weight based dosing around 0.5 mg/kg every 12 hours, above roughly 40 kg/m2 of body mass index or above 100 to 150 kg of actual weight. For unfractionated heparin, 7500 units SC every 8 hours is a frequent escalation. Protocols genuinely differ here, and the pharmacist knows the local answer better than you do. Ask.
Contraindications and the bleeding versus clot judgment
Absolute reasons to withhold the drug are fewer than people think. They include active clinically significant bleeding, a planned procedure within hours, an epidural catheter at the wrong point in its timing, severe thrombocytopenia, and known HIT if you are reaching for a heparin.
Everything else is a weighing exercise. The mistake I see most often is treating a mildly abnormal INR or a platelet count of 90,000 as a hard stop. It is not. A cirrhotic with an INR of 1.8 is not auto-anticoagulated, and cirrhotics get portal and deep vein thrombosis.
A hospital acquired pulmonary embolus and a retroperitoneal hematoma will both kill your patient. The point of the risk scores is to stop you from treating one of those outcomes as vivid and the other as theoretical. If you withhold prophylaxis, you have made an active clinical decision and you own it, so write the reason and set a date to reconsider.
Mechanical prophylaxis
Intermittent pneumatic compression is the right answer when the drug is contraindicated, and a reasonable addition to the drug in very high risk surgical patients. The sleeves empty the deep venous system intermittently and, to some degree, increase endogenous fibrinolytic activity.
Two practical points. First, they only work when they are on the patient and plugged in, which on any given morning round is roughly half the time, so look at the legs yourself. Second, they are contraindicated over an acute DVT, over severe peripheral arterial disease, over open wounds, burns, ulcers and fresh skin grafts, and in severe neuropathy where the patient cannot report pain from a badly fitted sleeve.
Graduated compression stockings alone are weak prophylaxis. Use the pumps.
Special populations
Spinal hematoma is rare, catastrophic and largely preventable by timing. Typical guidance holds a prophylactic dose of enoxaparin for around 12 hours before neuraxial puncture or catheter removal, and 24 hours after a treatment dose, with the next dose given no sooner than about 4 hours after the catheter comes out. Numbers vary by agent and by society. Do not improvise this. Anesthesia owns the timing, the anesthesia record documents it, and you call them before you write anything while a catheter is in place.
Mechanical prophylaxis from admission. Pharmacologic prophylaxis is usually started once the surgeon or neurointensivist is satisfied the bleed is stable, often on imaging at around 24 to 72 hours. That timing is not yours to choose. Ask, then chart who said it and when.
A frequently used practice is to withhold pharmacologic prophylaxis below a platelet count of roughly 50,000 per microliter, with some centers going lower in stable hematology patients and some being more cautious in a bleeding patient. The count matters less than the trajectory and the cause. A stable count of 60,000 in chronic liver disease is a different animal from 60,000 falling by half in two days.
No heparin and no low molecular weight heparin, including flushes. Fondaparinux is the usual prophylactic choice. Make sure the allergy field in the chart says HIT and not just "heparin," because the next person to write an order will look there.
Duration and extended prophylaxis
For most medical inpatients, prophylaxis runs for the duration of the hospital stay or until the patient is genuinely walking again, whichever comes first. Routine extension after discharge for general medical patients is not standard practice and has generally traded a small reduction in VTE for an increase in bleeding.
Extended prophylaxis after discharge is standard in a few defined groups: major orthopedic surgery of the lower extremity, where courses in the range of 10 to 35 days are typical and hip replacement sits at the longer end, and major abdominal or pelvic surgery for cancer, where roughly 4 weeks is common. If your patient is going home after either, the discharge medication list needs the drug on it and the discharge summary needs a stop date.
The reason you held prophylaxis on day one usually expires. The platelet count recovers, the procedure happens, the epidural comes out, the bleed stops. Put a line in the daily assessment: "VTE prophylaxis held for thrombocytopenia, platelets 62,000 today and rising, will start enoxaparin when above 50,000 for 24 hours."
Decision table
| Situation | Usual approach | Watch for |
|---|---|---|
| Medical inpatient, Padua 4 or more, no bleeding risk | Enoxaparin 40 mg SC daily | Renal function, weight |
| Medical inpatient, low risk and fully ambulatory | Often no drug, mobilize | Document the reasoning |
| CrCl below 30 or dialysis | Heparin 5000 units SC q8 to q12h | Platelet count, HIT |
| Body mass index above 40 | Escalated dose per local protocol | Ask pharmacy for the local rule |
| Active bleeding or severe thrombocytopenia | Pneumatic compression only | Reassess daily for a restart date |
| Epidural catheter in place | Anesthesia dictates the timing | Spinal hematoma |
| Prior HIT | Fondaparinux 2.5 mg SC daily | Renal clearance, no reversal |
| Hip or knee arthroplasty | Extended course after discharge | Stop date in the discharge summary |
How to document the decision
One sentence in the assessment and plan. It takes ten seconds and it is the entire difference between a defensible chart and an indefensible one. See charting to survive a lawsuit for why the reasoning matters more than the outcome.
What most people write
"DVT ppx: SCDs."
What to write instead
"VTE prophylaxis. Padua score 5, high risk, driven by active malignancy and immobility. Platelets 44,000 today with no active bleeding, so pharmacologic prophylaxis is held for now and intermittent pneumatic compression is in place with the sleeves confirmed on at the bedside. Will start enoxaparin 40 mg SC daily once platelets are above 50,000. Creatinine clearance 62 mL/min so no renal adjustment anticipated. Reassessed daily."
The risk, the reason for the deviation, the alternative you chose, the trigger for changing course, and the fact that you looked again. That is what a documented decision means.
Related: common night calls for the overnight version of these problems, and admit and transfer orders for where the prophylaxis line lives in the order set.
This is not medical advice. It is a teaching outline for clinicians and clinicians in training. Every agent, dose, threshold and interval below is illustrative. Follow your own institution's protocol, verify every drug and dose against a current reference, and use your own clinical judgment.