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Tuesday, June 21, 2016

Exercise associated collapse

The term exercise-Associated Collapse (EAC) as used by Dr. Tim Noakes of Cape Town South Africa refers to athletes collapsing after completing a marathon or longer event, though the term more generally could refer to anyone collapsing during or after an endurance event.
Noakes writing specifically about the endurance race event collapse is describing a runner who typically finishes the event and then feels lightheaded, possible nauseated and may indicate that he feels like he will faint. The blood pressure is low in the 100 to 110 range with a mild tachycardia in the 110 range. Noakes emphasizes that the appropriate intervention is to elevate the legs or low the head below leg level. This maneuver, in his vast experience will bring about recovery fairly quickly without the use of IV fluids. This approach received some documented support from a small randomized trial recently published by Noakes and co workers. See here for abstract.

Although the runner will be to varying degrees dehydrated, or volume depleted, Noakes indicates that the faint is not due to the volume status per se. Rather the mechanisms he postulates is as follows:

The post exercise collapse ( as opposed to the collapse that may occur while exercising which brings to mind a number of other more serious possible causes ) is due to postural hypotension related to several factors.

With exercise in the heat there is increased blood flow to vessels near the skin leading to a redistribution of blood to the peripheral veins ,more so as the ambient temperature increases.

Next the action of the calf muscles, while exercise continues, will reduce the volume of blood stored in the lower limbs and maintains an adequate venous return to the heart. When exercise stops, the calf muscle mechanism for venous return decreases and blood accumulates in the dilated venous system leading to decreased venous return and hypotension in the upright position.He also suggests that in the trained athlete there is a blunted compensatory increase in heart rate in response to a lowered blood pressure further increasing the likelihood of faint or near fainting.

So the treatment is the standard treatment for what used to be called vaso-vagal faint namely the Trendellenberg position. He believes that dehydration is not the cause and volume repletion is not the treatment, although obviously volume replacement is appropriate but can be done orally.

Noakes in his book ,Lore of Running, 4th edition, says that approach has worked well in his vast experience in the medical tent after the Comrades ultramarathon in South Africa.

Key information to management of the collapsed athlete is the following;

Location of collapse (i.e. while running versus after the race)
Level of consciousness and cognition (altered states suggest something more ominous that benign post exercise hypotension-particularly exercise associated hyponatremia )
Rectal temperature greater than 40C ( 104 F) means heat stroke.

Noakes and others have emphasized the importance of prompt measurement of serum sodium and blood sugar. Serum sodium less than 120 plus altered mental status should lead to administration of 3 % NaCl.

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