Should We Care About The Calories?

Posted by Jeremy Windsor on Feb 24, 2019

A very senior critical care physician once told me that in sick patients, "appetite is the first thing to vanish and the last thing to return". This approach often led to some very short consultations. After introducing himself he would ask the patient if they wanted anything to eat or drink. If the answer was "yes" to either question the consultation was abruptly terminated and the patient was quickly transferred to the ward. This all came back to me this week after reading the recently published TARGET trial.

For several years critical care physicians have devoted a lot of time and resources to feeding patients. The commonly held belief is that patients in ITU and HDU lose large quantities of weight and this contributes to their demise. The solution has been to insert all manner of feeding tubes and intravenous lines and ply them with lots of calories. The results of the TARGET trial brings this assumption into question.

Researchers recruited 3957 critically ill patients undergoing mechanical ventilation. Two forms of enteral nutrition were compared. Those who were given "routine" enteral nutrition had 1262kcal per day, whilst the rest received "energy dense" enteral nutrition and received 1863kcal per day. 

At Day 90 the mortality rate did not differ between the two groups. A total of 523 of 1948 patients (26.8%) in the "energy dense" group and 505 of 1966 patients (25.7%) in the "routine" group had died. The consumption of more calories did not improve any of the parameters that were measured. Survival time, receipt of organ support, incidence of infective complications and rates of adverse events did not differ between the two groups.

Meanwhile those who received the "energy dense" feed had greater gastric residual volumes, required more pro kinetic drugs and experienced more regurgitation and vomiting.

Of course the message to take away from this study is not to stop feeding critically ill patients. Rather, it is to recognise that large numbers of calories are not needed and make little difference to patient outcomes. Whilst waiting for a patient's appetite to recover there seems to be little gained in giving patients any more than a modest amount of enteral nutrition.

Perhaps there's a lesson here for the mountain medicine community? Whilst appetite is often suppressed at high altitude every effort is made to encourage trekkers and mountaineers to eat as much as possible. But is this right? Are our bodies trying to tell us something? Why would the body waste precious oxygen and nutrients processing large volumes of food and expelling generous quantities of waste? It may be that all the body really needs is a combination of good hydration and a modest amount of calories.

Could too many calories impair performance or even trigger high altitude illnesses such as AMS, HAPE or HACE?

Now there's food for thought!

A detailed review of the TARGET trial can be found here.

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