As you know, the risk for DVT and PE in the ICU are high. How high? Depends on how you count them.

Asymptomatic, ultrasound-surveillance-detected DVTs have an incidence of 5-10% during the ICU stay (from the PROTECT trial and a 2005 series), even when patients receive proper thromboprophylaxis. The incidence is even higher (up to 80%) in trauma and burn patients.
But, you might say, asymptomatic DVTs are a different, understudied entity that may not carry the historical risks of clinically detected DVT (many asymptomatic DVTs regress spontaneously, and the subsequent PE risk is not well known. Many orthopedists feel strongly about this).
What about clinically significant PEs? They probably occur in ~1-2% of ICU patients who get appropriate thromboprophylaxis (also from PROTECT). I'm not aware if anyone knows the incidence of asymptomatic PEs, or what they might mean clinically (although there is evidence that some small PEs might be harmless and overdiagnosed generally).

The American College of Physicians recently contradicted the Joint Commission's edict that all hospitalized patients should receive thromboprophylaxis, based on compelling data showing excess harm from bleeding in low-risk patients. However, the data above should be fairly convincing that most critically ill patients are at significantly elevated risk for DVT/PE, and should receive thromboprophylaxis if there's no contraindication. Kwok Ho (of Australia's Royal Perth Hospital), Shaila Chavan and David Pilcher asked: What happens if critically ill patients don't get that thromboprophylaxis in the first 24 hours? They analyzed the ANZICS CORE database's records of 175,000 patients in 134 ICUs in Australia/New Zealand 2006-2010. About half of these were surgical admissions, most of those elective; no single ICU diagnosis dominated (~8% had septic shock, for example). The database has standard fields for thromboprophylaxis in the first 24 hours: "Yes," "No," "Contraindicated," or "Not Indicated." It's unclear to me after reading it how this was entered (did investigators read the charts and code it themselves, doubtful on 175,000 records, or did a data entry person or the treating physician do it during/after the hospitalization?) Results:

16% of patients had thromboprophylaxis omitted during the first 24 hours in the ICU, without any good reason. This was higher in rural (21%) and private (26%) hospitals.
Those who had prophylaxis omitted had higher ICU mortality (7.6% vs. 6.3%) and hospital mortality (11.2% vs. 10.6%). After adjusting for confounders & covariates, the odds ratio of death remained high at 1.22 in the no-prophylaxis group.
No data on the rates of DVT and PE among either group, and no mention of why, which is interesting to me since I would think this database would have that in it (it had abundant other data on diagnoses which they analyzed).

What could explain this? They suggest:

The lack of prophylaxis led to preventable death from PEs.
Omission of prophylaxis was a surrogate for lower quality of care generally, which led to excess deaths.
The patients with prophylaxis omitted were sicker -- but their APACHE scores were actually lower than those who got prophylaxis, so this seems less likely.
I would also suggest, data entry error by the private and rural hospitals, who could have provided proper prophylaxis and good care, but not documented it properly (either the provision of prophylaxis or the presence of contraindications), due to lower resources and less vested interest in academic studies. (I can't tell from the manuscript how likely this was.)

Clinical Takeaway: Pulmonary embolism remains a major preventable cause of death in hospitals. DVT and PE occur at high rates in critically ill patients, even when appropriate thromboprophylaxis is given. Previous studies have shown that omitting VTE prophylaxis for only 1-3 days significantly increases DVT risk in orthopedic/trauma patients. This very large observational study in a mixed medical-surgical population of critically ill patients suggests that omitting thromboprophylaxis for 24 hours in those without a contraindication may increase the risk for in-hospital death. This provides one more argument for checklists and care standardization measures, on this important clinical issue at least.

Ho K et al. Omission of Early Thromboprophylaxis and Mortality in Critically Ill Patients. A Multicenter Registry Study. CHEST 2011;140:1436-1446.

Omitting heparin prophylaxis in first 24 ICU…

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