Hypoglycaemia

Click here for our unit protocol on managing hypoglycaemia in ICU

Why Hypoglycaemia in Critical Care Is Very Dangerous

Hypoglycaemia is associated with a significantly elevated risk of mortality in critically ill patients.

In the worst case scenario a patient having a severe hypo that isn't treated quickly can rapidly develop irreversible brain damage and there have been many cases of catastrophic brain injury resulting in patients dying or ending up in a persistent vegetative state, all as a result of insulin therapy given to try to make the glucose "normal".

Whilst cases like this are rare, they still occur and we should do all that we can to prevent them.

Even those hypo's that don't result in an obvious neurological injury may have serious consequences on a patient's recovery from critical illness. Each hypoglycaemic episode has measurable effects on hormones like cortisol, growth hormone and adrenaline.

If you've ever looked after or know a person with type 1 diabetes where hypo's are a fact of life, they'll tell you how awful they feel for many hours after a severe hypo. Now imagine that person mounting a response to sepsis, major trauma or surgery, it's not surpising studies have shown a correlation between hypoglycaemic episodes and the risk of mortality from critical illness.

Avoidance of Hypoglycaemia

Low blood sugar occurs for many reasons on ICU. When we audit hypo's we see the same risk factors everytime:

• not monitoring blood glucose frequently enough
• feed or IV glucose interruptions
• fasting
• reestablishing or starting long acting (or mixed) insulins
• recent hypoglycaemia episodes
• large doses of IV or subcutaneous insulin

Fasting due to illness or being nil by mouth

We see a lot of hypo's in non-diabetics who are fasting for other reasons. Always consider a glucose contraining IV fluid (Hartmanns does not contain glucose!).

Iatrogenic hypoglycaemia

We are most concerned though with hypoglycaemia caused by insulin.

The main way to avoid this is follow the guidelines on monitoring:

On IV insulin blood glucose must be checked every 1 hour (2 hourly only when stable)

On subcutaneous insulin blood glucose must be checked every 3-4 hours

Looming Hypoglycaemia

This is where the blood glucose is still in the normal range but is falling and a hypo is very likely. For this reason we should stop all IV insulin when blood glucose is below 6mmol/l and check again in the next 30 minutes. It would be entirely reasonable to treat with glucose to avoid it falling further. Recoginising it is key.

A patient on subcutaneous insulin who's blood glucose has been below 6mmol/l should have their long acting doses reviewed immediately. Prevent a hypo by adjusting the dose.

No Feed No Need!

• Most of our patients on IV insulin will be on enteral feed or TPN. If this is stopped, for example when nil by mouth for surgery or unexpectedly because the tube is displaced or a check XR requested, the safest thing to do is to stop the insulin and keep checking blood glucose frequently. The risk of a hypo continues for many hours after the infusion is stopped. It is reasonable to

How Should We Treat Hypoglycaemia on ICU?

Quickly & with the most effective drug - we use IV glucose as first line in Critical Care

A patient on a medical ward on long-acting insulin who becomes hypoglycaemic will often develop symptoms that will alert us to a hypo. They're able to take glucose tablets and don't have IV access, the quickest and safest way to treat the hypo may be orange juice, glucose tablets or glucogel. If they're unconscious then we often use IM glucagon, see below why this might be a waste of time in the critically ill.

A patient on ICU who is sedated on a ventilator will show no signs of hypoglycaemia and so the diagnosis may only be made on regular checks. It requires rapid treatment. They will almost certainly have a central or peripheral line and therefore the quickest and safest way to treat them will be with IV glucose.

How much glucose?

• 50ml of 50% glucose
• 250ml of 10% glucose

Both of these doses contain 25g of glucose which is equal 5 teaspoons of sugar, or 2/3 of a can of coke.

An average adult only has about 5-7.5g of glucose dissolved in their entire blood volume. This means that in your blood there is only 1-2 teaspoons of dissolved sugar. A non diabetic drinking that can of coke will keep their blood sugar pretty constant.

We use 25g which may well spike the blood glucose but this will be transient and will come down quickly, hence the importance of checking again in 15, 30 and 60 minutes.

Why Glucagon Is Almost Aways the Wrong Drug for Treating Hypo's on ICU

We occasionally see our doctors, nurses and ACCP's using glucagon to treat hypo's in critical care. This is likely because they're used to using this on the ward or community, where it's a lifesaving and essential medications for patients who are hypoglycaemic and who cant take oral sugar.

It's rarely the best option in ICU.

What is glucagon?

Glucagon is the hormone produced in the pancreas that acts in the opposite way to insulin. It has a few key actions:

• it stops insulin being produced by the beta cells (glucagon is made in the alpha cells just next door)
• it goes straight to the liver and causes glycogen to break down to glucose raising blood glucose
• it causes flushing, tachycardia and high blood pressure (great for beta blocker overdose, not if you're awake)

How is it given?

Unlike insulin that comes as a ready made injection, glucagon must be reconstituted from powder and injected intramuscularly. This takes time to prepare and it's actions take a few minutes to kick in, even when the liver responds to it.

Why is it not great in critical care?

Whilst it may work in some patients, I really feel it is a drug of last resort for treating hypoglycaemia in critical care. This is because

• it takes time to prepare and administer and it will never be as quick to act as IV glucose
• most of our patients have IV access so IV glucose is quicker and more effective
• 6 glucose tablets down the NG will probably work just as well if there is no IV access
• critically ill patients often have very limited glycogen stores due to fasting and the stress response to illness means they may have used up all of their reserves. Glycogen break down will have been maxed out by their critical illness so glucagon will simply not work as effectively or quickly as in healthy individuals.

So what should we use instead?

Whilst it very reasonable to use this drug in some situations, please see our QRG below and always prescribe a form of IV glucose as a PRN medication when prescribing IV or subcutaneous insulin. When an enteral route is available these can be considered and in those patients recovering and getting better this would be very reasonable.

See the link here for our hypoglycaemia QRG - you'll see that glucagon is the last resort when treating a hypo on ICU.

4 is the Floor!

For hypoglycaemia (or looming hypoglycaemia) give IV glucose as quickly as possible, when no IV route is available go for tablets or orange juice (orally or down the feeding tube).

If neither of those is possible immediately then go for glucagon and/or glucose gel.

Check blood glucose again after 15, 30 and 60 minutes