Sunday, 24 January 2010

Artificial nutrition support

Bowl of chickpeas with dollop of yogurt and steam rising
Well, a couple of people have asked, "How did it go?" The simple answer is that I really, really don't know. Just two exams and loads of time to revise should be a recipe for confidence, but it didn't work out like that.

I've written before that I didn't really like Health Promotion much, and it was a difficult subject to revise. I like facts that I can remember and connect together to build up a picture - a biological system, or cell functions, or some other physiological process. With research I can make more of the whole than the simplified parts we are given in basic lectures, so in an exam I can usually show some insight or original thought, which I believe is what gets particular credit in that setting. With Health Promotion it didn't to seem to get more sophisticated the more I looked at it. I didn't manage the time in the exam very well, so the last question was very rushed, and I probably only managed one original thought in the whole thing.

The second exam was Diet Therapy. The subject is actually very interesting, and extremely relevant to what I'm hoping to do at the end of the degree. About half of it is about accumulating facts, and the other half is applying those facts to a situation with a patient in it - making deductions, drawing conclusions, appreciating limitations. The main problem was that it was a double module - twice the amount of material to learn, but only two hours for the exam.

I went into the exam fairly confident of my knowledge, but there was absolutely no time to think or consider a question; it was about reading the paper as quickly as possible and then launching straight into an answer. Given that real, qualified, experienced dietitians would probably have more time to consider a situation presented to them, it seems harsh to expect us novices to work so quickly. I was careful to manage the time allowed, but it was almost impossible to put anything other than basic information in there - no time for original thought, and plenty of scope for making mistakes. So maybe I wrote what was wanted, but maybe not. I really can't tell.

I haven't written about the content of the course for a while, so perhaps this is a good opportunity. The Diet Therapy module covered some aspects of professional behaviour: ethics, proficiency and standards of conduct. There was material on trauma, surgery and burns, all of which produce a similar response in the body. We looked at specific conditions including Motor Neurone Disease, Parkinson's Disease, Multiple Sclerosis, dementia, HIV/AIDS, cancer and stroke, all of which have the common consequence of undernutrition at some point. Dysphagia, a problem with swallowing, is also a frequent symptom, sometimes caused by the illness, sometimes a side effect of treatment.

The rest of the material was about undernutrition - how to recognise it, assess the situation, plan a nutritional intervention and monitor results. We learned about nutritional support of various kinds, from food fortification using everyday foods, supplements on prescription or over-the-counter, and artificial nutrition support, via tubes into the stomach or intestines, or intravenous. Palliative and end-of-life care was also included, since one of the issues might be withholding or withdrawal of artificial nutrition and hydration, e.g. for permanent vegetative state or end-stage dementia or cancer.

That's quite a lot, isn't it? It all has to be evidence-based as well, so I know what the National Institute for Health and Clinical Excellence (NICE) says about most of these conditions, as well as Dietary Reference Values suggesting how much of different nutrients ought to meet our requirements. Given that I learned pretty much the whole thing, it would have been nice to be able to show off a bit more in the exam.

[If you're not fond of my treatises on complex dietetic subjects, then you might prefer to stop reading now - see you next time!]

For example. I could tell you the procedure for inserting a fine-bore nasogastric (NG) tube, and what the potential complications are. This is a short-term feeding option (less than 4 weeks), but if the patient is unconscious, it might be better to use a Ryles tube, which has a wider bore but is less well tolerated if the patient is awake - it's often used in critical care and burns. A longer term option is a gastrostomy - a tube that goes directly through the skin and stomach wall into the stomach. It can be put in place using an endoscope down through the nose into the stomach to make sure the incision is in the right place (a PEG), but for someone with MND who needs constant respiratory support, it can be placed radiologically (a RIG). And there are other types.

One of the problems of feeding directly into the stomach is the risk of aspiration, where the stomach contents are regurgitated and enter the lungs, and if this happens (perhaps because of vomiting), then feeding into the upper part of the small intestine (jejunum) past the stomach's pyloric sphincter might be indicated. This can be a short term nasojejunal tube, an extension via a PEG into the jejunum, or directly into the jejunum (a jejunostomy). Another reason for post-pyloric feeding might be gastric stasis, when the stomach isn't doing its job, and food just sits there without being moved on past the pylorus.

This is all very well if the only problem is that for some reason not enough food and fluid can be taken through the mouth to meet requirements - maybe the patient is unconscious, can't swallow safely or has an obstruction in the upper GI tract. If the lower GI tract is accessible and functional, it should always be used - it is thought (but not certain) that the microorganisms in the gut are kept in check somehow by food coming through and being digested and absorbed. If that isn't happening, one hypothesis is that gut bacteria are somehow 'translocated' across the intestinal barrier and cause trouble in the body.

Sometimes it can't be helped, and the gut is simply not working well enough to absorb sufficient food to meet requirements, whether the food is coming orally or through a tube (enteral nutrition). Maybe the blood supply to the gut is insufficient (ischaemia), or there is an obstruction (perhaps from a tumour), or a critical section has been removed (e.g. Crohn's disease), or the absorptive structure of the gut has been destroyed by radiation enteritis as part of cancer treatment, or there is a risk of losing too much fluid through a stoma (ileostomy or colostomy), or the pancreas or liver aren't secreting digestive juices for whatever reason.

Then we have to consider parenteral nutrition, which is intravenous feeding. The difficulty with this is that our bodies are designed to absorb food through the gut. Any absorbed carbohydrate (mostly glucose) goes straight from the gut to the liver via the hepatic portal vein, and the liver only releases a little at a time into the systemic circulation. Arteries and veins other than the hepatic portal vein aren't used to high glucose concentrations, and don't like it - this is the source of some of the problems relating to diabetes.

I suppose that artificially feeding into the hepatic portal vein isn't a viable option, so the best alternative must be the largest vein possible, so that lots of blood flows past and quickly dilutes the intravenous glucose. For long-term parenteral nutrition a 'central line' does this, but it's not a trivial procedure to put one of those in, so often a peripheral vein is used. Nutrients can only go in very slowly, and with lots of fluid to make sure concentrations aren't too high and cause phlebitis, which is inflammation of the vein. Too much fluid can also cause problems, and that's aside from the risk of sepsis (used to be called blood poisoning) because you're putting stuff directly into the bloodstream.

So NICE best practice evidence-based guidance tells us to use the oral route for feeding if at all possible, then enteral feeding, with parenteral nutrition as a last resort.

And I didn't have the opportunity to write any of that in the exam.


aims said...

From everything you've done before - I have confidence that you'll do just as well in these.

Perhaps your teachers need to read your blog at times for the final answers? :0)

aims said...

btw - I found that very interesting!