I’m writing this article feeling dizzy, hot, and sick, plus I’m shaking, sweating and feeling a bit confused. The cause of these unpleasant but temporary symptoms is rebound hypoglycaemia. I doubt many people have heard of that term, so despite my confusion I’m going to try to explain it, and how someone who can’t eat food manages to get it.
Rebound hypoglycaemia is the term for developing dangerously low blood sugar levels after eating a meal. It’s also known as post prandial hypoglycaemia and reactive hypoglycaemia. It’s caused by the pancreas making too much insulin after a large, often carbohydrate heavy, meal. It is unknown why it happens, but it can occur regularly in some individuals.
My digestive system barely works so I am fed by parenteral nutrition, which is the process of pumping liquid food straight into the bloodstream. Parenteral nutrition fluid is pushed into my body through a tube by an electronic intravenous (IV) pump. The bags of parenteral nutrition I receive contain 3.4 litres of fluid, which should be pumped into my body over 12 hours, which works out as 283mls per hour. Parenteral nutrition contains a high amount of glucose (sugar) which is processed in the body by insulin. Insulin production can’t move from 0% to 100% in an instant. It builds up and tails off gradually as required.
If I stopped my IV pump working suddenly, moving from 283mls per hour to zero, then the sugar entering my blood would stop while my insulin levels are high as my body had been processing a lot of sugar. My pancreas would continue to produce insulin at a high level for a few minutes despite sugar no longer entering my body, causing my blood sugar levels to get very low. If my sugar levels fell low enough I’d experience symptoms such as shaking, confusion and dizziness, known as rebound hypoglycaemia.
To avoid this problem IV pumps can be programmed to start pumping slowly, building up to full speed, and then reduce output slowly 12 hours later. This is know as ‘ramping up’ and ‘ramping down’. I usually ramp up over 30 minutes and ramp down over 45 minutes which avoids any symptoms.
The process generally works very well, but there are two weak points in the system:
1, The IV pump. – These aren’t as accurate as their manufacturers claim and need to be regularly calibrated. If you program a pump to infuse 3.4 litres, there’s almost always some fluid left at the end of the process, so you have to program the pump again to infuse the remaining fluid. It’s usually too small an amount of fluid to ramp up and ramp down again. I normally set it at full speed and then at a low speed for 10 minutes at the end.
2, The person programming the pump. – In my case I often get engrossed watching TV or reading a book and forget to reduce the pump speed, or sometimes have an unscheduled nap and the fluid runs out at full speed while I’m asleep. On this occasion I was watching Spurs vs Wolfsberger and forgot to ramp down for the second time, so the fluid ran out with the pump running at 283 mls per hour. Oops.
When I was in hospital to be started on parenteral nutrition about 8 years ago, one of the tests they did was to stop the IV pump at full speed to monitor my blood sugar levels and make me aware of the risk of rebound hypoglycaemia. On that occasion I felt fine, however I’ve experienced hypoglycaemia many times since. Symptoms last from 30 minutes to 2 hours and can make me feel really awful.
I’m a huge fan or parenteral nutrition. It’s given me 8 extra years of life, but rebound hypoglycaemia is one of the few flaws with it. If you’re also fed by parenteral nutrition my only advice for trying to avoid the problem is to make sure your IV pump gets regularly calibrated, and try to stay alert towards then end of an infusion instead of watching football, however well Spurs are playing!
Thanks for reading, Ceri.