Update From the Medical Journals: August 2010
August 31, 2010
By Mary Pickett, M.D.
What's the latest news in the medical journals this month? Find out what your doctor is reading.
In 2007, studies from Japan and Sweden showed that chest compressions can improve a person's chance of surviving a heart attack outside of the hospital, with or without rescue breathing (mouth-to-mouth resuscitation). These were observational studies. They were not designed to compare one type of rescue with the other.
Two randomized studies published by the New England Journal of Medicine on July 29 did just that. In the largest study, cardiopulmonary resuscitation (CPR) instructions were provided over the phone by emergency dispatchers. Half of the callers who needed to start CPR were told to use chest compressions and rescue breathing. The others were told to do chest compressions only. People did just as well with either method. In fact, results were slightly better without rescue breathing when heart-related problems such as an abnormal rhythm caused the heart to stop.
In a cardiac arrest, the most critical time for chest compressions is the first few minutes after the heart stops pumping. That's when there is plenty of oxygen in the blood, but the blood is not moving. Chest compressions by a bystander can be lifesaving because rapid and forceful pushes on the chest can squeeze the blood forward out of the heart. This keeps oxygen flowing to the brain. It can also refresh the blood that is flowing into the coronary arteries on the surface of the heart. If the heart is receiving oxygen because a bystander is doing chest compressions, it is much more likely that the heart can restart its previously normal rhythm.
In situations involving choking or drowning, however, rescue breaths are necessary as a part of CPR. Suffocation causes the blood oxygen to drop low first, and the heart stops as a side effect of too little oxygen. There is no oxygen "reserve" remaining in the blood. Rescue breaths are needed for a successful rescue.
For adults who have a sudden heart attack, it's likely that CPR recommendations for rescue workers, as well as bystanders, will change so rescuers can focus on giving fast and forceful chest compressions.
A blood clot in a leg vein (deep venous thrombosis or "DVT") can be life-threatening. The clot can break away from its starting place and block circulation in the lungs. To prevent this, most patients with a DVT take a blood-thinning medicine (anticoagulant). An anticoagulant causes the clot to stop growing. This makes it less likely to break apart and travel throughout the body. Some patients can't safely take a blood thinning medicine. For these patients doctors recommend inserting a filter in the vena cava, your largest vein. This device works like a strainer to filter out clot fragments as blood passes through. Doctors place it inside the vein using a catheter. Once it's inside the vein, it opens like an umbrella.
On August 9, the Archives of Internal Medicine published a report about safety concerns involving these devices. The study focused on 80 patients at one hospital. About 16% of the filters broke or drifted forwards within the bloodstream. In some cases, this caused injury to the heart. The break rate was 25% among people who had an older model. The older filters had been implanted an average of four years. The U.S. Food and Drug Administration (FDA) issued warnings about vein filters on August 9, stating that it has recorded 900 reports of problems or complications during the past five years.
Although a vein filter can cause a serious complication, so can a DVT. For some patients, it is a challenge to know which is greater the risks or the benefits from using a filter. So far, the FDA has not placed limits on their use or removed them from the market. Recent versions of the filters can be removed from the vein after the immediate danger from the clot has passed. However, this requires an additional procedure and can only occur safely if it is done within the first several months after the filter has been placed.
It is standard to test cholesterol after an overnight fast, because cholesterol numbers vary after a meal. But factors other than food can affect cholesterol, including the amount of estrogen that is circulating in the bloodstream.
Researchers decided to see if women's cholesterol levels varied with their menstrual cycles, as estrogen levels shift within each cycle. They found that the total cholesterol shifted by almost 20% in a typical cycle. The LDL and triglycerides were lowest (best) immediately prior to the start of menstruation. Cholesterol levels were worst during the two weeks that followed the start of menstrual bleeding. The study included 259 women who had cholesterol measured every several days for two months.
It is possible that this understanding will lead to new recommendations to test cholesterol during the third or fourth week of the menstrual cycle, especially before making treatment decisions. The Journal of Clinical Endocrinology and Metabolism reported these findings August 10.
Mary Pickett, M.D. is an Associate professor at Oregon Health & Science University where she is a primary care doctor for adults. She supervises and educates residents in the field of Internal Medicine, for outpatient and hospital care. She is a Lecturer for Harvard Medical School and a Senior Medical Editor for Harvard Health Publications.