Falling asleep or passing out?

Wednesday, June 16, 2010

The CBS headline was a little misleading. ”Patraeus Falls Ill During Senate Hearing”. In a sports reference, upon further review, General Patraeus briefly lost consciousness while sitting at a table. Words do make a difference. Being unconscious is not normal and though the General’s explanation may be correct that he had missed breakfast and was dehydrated, other potential diagnoses should be considered.

Being awake requires a few things. One cortex or half of the brain needs to be functioning plus the reticular activating system (the on/off switch in the brain stem) needs to be turned on. The heart has to be able to pump blood to the brain, there needs to be enough blood pressure to push the blood uphill to the head, the blood needs to contain oxygen and glucose and toxins that affect the brain can’t be present. When a person goes from fully awake to unresponsive, each requirement needs to be researched to decide the potential cause.

Sometimes it is easy. Medical students who pass out watching their first operation are the victims of a vasovagal episode where the noxious visual stimulus triggers the vagus nerve causing the heart rate to slow and blood vessels to dilate. Blood rushes to the feet instead of the head and the student passes out. The situation resolves spontaneously and the student wakens quickly and more than a little embarrassed. The same situation exists when an older person strains to urinate or have a bowel movement; the vagus kicks in and the person faints on the commode. Examples of other easy things to rule out are low blood sugar (the level can be measured at the patient’s side with a quick finger stick blood test) and dehydration, which should be evident on physical examination and changes in blood pressure and pulse rate. But easy does not equal not dangerous. Loss of blood can drop blood pressure, causing fainting and unconsciousness and patients with bleeding from their stomach or intestine can become gravely ill.

Sometimes it is harder. A patient is sitting at the breakfast table eating and suddenly they are slumped in their cereal for a minute or two and then recover. This is more like the General’s situation. The big question to answer is whether there was a heart rhythm abnormality that caused the heart to slow or stop beating for a few seconds causing syncope or loss of consciousness. It’s hard to sort out because most patients aren’t wearing a heart monitor and it may take detective work over days or months to try to find a cause and sometimes the search his fruitless. The second big question is whether it is a stroke involving blood flow to the brain stem where the on/off switch resides.

It’s the history that gives clues whether to follow the easy or hard pathway. The history leads to a few tests and all may be well…or not. The attention is placed on heart rate and rhythm because the danger lies there. A patient taking a diuretic or water pill for blood pressure control may have low potassium; a kidney dialysis patient may have too much. A patient taking medications that affect the heart rate may have too much medication on board and too slow of a heart rate to supply the brain with blood flow. Or the heart may be beating too quickly resulting in the same lack of blood flow to the brain.

The key to the diagnosis is allowing one to be made. Being unconscious even for a few seconds is not normal and deserves an evaluation. General Petraeus may be correct that he missed breakfast and passed out. Fortunately it happened at a senate hearing and not on the battlefield where missing a meal is routine.

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