Pulmonary Embolism and DVT in Trauma

We have long assumed that pulmonary emboli start as clots in the deep veins of the legs (or pelvis), then break off and float into the branches of the pulmonary artery in the lungs. A huge industry has developed around how best to deal with or prevent this problem, including mechanical devices (sequential compression devices), chemical prophylaxis (heparin products), and physical devices (IVC filters).

The really interesting thing is that less than half of patients who are diagnosed with a pulmonary embolism have identifiable clots in their leg veins. In one study, 26 of 200 patients developed DVT and 4 had a PE. However, none of the DVT patients developed an embolism, and none of the embolism patients had a DVT! How can this kind of disparity be explained?

Researchers at the Massachusetts General Hospital retrospectively looked at the correlation between DVT and PE in trauma patients over a 3 year period. DVT was screened for on a weekly basis by duplex venous ultrsonagraphy. PE was diagnoses exclusively using CT scan of the chest, but also included the pelvic and leg veins to look for a source. A total of 247 patients underwent the CT study for PE and were included in the study.

Forty six patients had PE (39% central, 61% peripheral pulmonary arterial branches) and 18 had DVT (16 seen on the PE CT and 2 found by duplex). Of the 46 patients with PE, only 15% had DVT. All patient groups were similar with respect to injuries, injury severity, sex, anticoagulation and lengths of stay. Interestingly, 71% of PE patients with DVT had a central PE, but only 33% of patients without DVT had a central PE.

The authors propose 4 possible explanations for their findings:

1. The diagnostics tools for detecting DVT are not very good. FALSE: CT evaluation is probably the “gold standard”, since venography has long since been abandoned
2. Many clots originate in the upper extremities. FALSE: most centers do not detect many DVTs in the arms
3. Leg clots do not break off to throw a PE, they dislodge cleanly and completely. FALSE: cadaver studies have not show this to be true
4. Some clots may form on their own in the pulmonary artery due to endothelial inflammation or other unknown mechanisms. POSSIBLE

An invited critique scrutinizes the study’s use of diagnostics and the lack of hard evidence of clot formation in the lungs.

The bottom line: this is a very intriguing study that questions our assumptions about deep venous thrombosis and pulmonary embolism. More work will be done on this question, and I think the result will be a radical change in our use of anticoagulation and IVC filters over the next 3-5 years.

Velmahos, Spaniolas, Tabbara et al. Arch Surg. 2009; 144(10):928-932.

Personal Decisions are the Leading Cause of Death

A relatively obscure research paper published last December by Ralph Keeney at Duke University makes this startling claim: over half of the people who died in this country in the year 2000 did so because of their own personal decisions! If you look at current mortality statistics, the top four causes of death from year to year are heart disease, cancer, stroke and injury. We naturally look at this and think that these people had a heart attack or discovered a cancer or crashed their car. What these statistics fail to show is how the people really ended up with these conditions.

Keeney's paper looked beyond what was written on the death certificate and looked at how frequently personal choices caused these conditions. For example, smoking leads to heart disease, cancer, stroke, and high blood pressure, to name a few. Being overweight leads to heart disease, diabetes, high blood pressure, and many others. Inappropriate use of alcohol can lead to cancer, liver disease and a tendency to get into accidents.

The top causes of death were analyzed, looking at the percentage that could be caused by personal decisions such as smoking, diet, exercise, and use of alcohol or other drugs. A personal decision was defined as a situation where the individual could make a choice between two or more readily available alternatives (for example, smoking and not smoking) and that they had control over this choice. These choices are not necessarily easy to make because habits, social pressure, or genetic predisposition can make some alternatives hard to select.

Keeney found that about 55% of deaths in 2000 were caused by personal decisions. This compares to about 5% in the year 1900. This is due to the fact that the majority of the causes of death in 1900 were due to infectious diseases, and there were no antibiotics at the time to treat them.

What this paper shows us is that the need for high quality prevention activities is even greater that we thought, and that we may not be focusing on the right areas. Trauma centers habitually direct their prevention programs toward car seats, diving injuries, red light running, falls prevention and others. What we really need to focus on is personal choice, and teaching people how to make the right decisions. For trauma prevention, alcohol-related programs will probably give the greatest result since it is involved in so many of the top causes of death, even causes not related to trauma.

Trauma centers need to scrutinize their own prevention programs, and look critically at ways they can teach wise choices. It may be necessary to chage the focus of existing programs, or move to new programs that find ways to influence personal decision making. That way, trauma centers can have a hand not only in preventing certain types of injuries, but in directly decreasing the overall death rate as well.

Reference: Keeney RL. Operations Research 56:6, 1335-1347, 2008.

Do Trauma Patients Need A Rectal Exam?

It has long been standard operating procedure to perform a digital rectal exam in all major trauma patients. The belief has always been that valuable information about blood in the GI tract, the status of the urethra, and the neuro exam (rectal tone) could be gleaned from the exam.

Unfortunately, the exam also serves to antagonize or even further traumatize some patients, especially those who may be intoxicated to some degree. On a number of occasions I have seen calm patients become so agitated by the rectal that they required intubation for control.

So is it really necessary? A study in 2001 conducted over a 6 month period (1) showed that the rectal exam influenced management in only 1.2% of cases. The authors felt that there was some utility in 3 special cases:

• Spinal cord injury – looking for sacral sparing
• Pelvic fracture – looking for bone shards protruding into the rectum
• Penetrating abdominal trauma – looking for gross blood

A more recent 2005 study (2) was also critical of the rectal exam and found that using “other clinical indicators” (physical exam and other diagnostic study information) was at least equivalent, changing management only 4% of the time. They concurred with the first two indications above as well.

The Bottom Line: For most major trauma patients, the rectal exam is not worth the patient aggravation it causes. I still recommend it for the 3 special cases listed above, however, as there are no equivalent exams for these potentially serious patient problems.

References:
1. Porter, Urcic. Am Surg. 2001 May;67(5):438-41.
2. Esposito et al. J Trauma. 2005 Dec;59(6):1314-9.

What Percent Pneumothorax Is It?

Frequently, radiologists and trauma professionals are coerced into describing the size of a pneumothorax seen on chest xray in percentage terms. They may something like “the patient has a 30% pneumothorax.”

The truth is that one cannot estimate a 3D volume based on a 2D study like a conventional chest xray. Everyone has seen the patient who has no or a minimal pneumothorax on a supine chest xray, only to discover one of significant size with CT scan.

Very few centers have the software that can determine the percentage of chest volume taken up with air. There are only two percentages that can be determined by viewing a regular chest xray: 0% and 100%. Obviously, 0% means no visible pneumothorax, and 100% means complete collapse. Even 100% doesn’t really look like 100% because the completely collapsed lung takes up some space. See the xray at the top for a 100% pneumothorax.

If you line up 10 trauma professionals and show them a chest xray with a pneumothorax, you will get 10 different estimates of their size. And there aren’t any guidelines as to what size demands chest tube insertion and what size can be watched.

The solution is to be as quantitative as possible. Describe the pneumothorax in terms of the maximum distance the edge of the lung is from the inside of the chest wall, and which intercostal space the pneumothorax extends to. So instead of saying “the patient has a 25% pneumo,” say “the pneumothorax is 1 cm wide and extends from the apex to the fifth intercostal space on an upright film.”