Insulin sliding scale

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An insulin sliding scale involves intravenous administration of a standard insulin to tightly regulate blood glucose levels. Blood glucose levels are monitored using bedside, finger-prick capillary glucose monitoring machines. The rate of infusion of insulin is titrated according to the glucose level, which is ideally monitored every 1-2 hours. Insulin given intravenously has a short half-life of a few minutes.

A variation of the insulin sliding scale is the Alberti regime, also known as a GKI infusion (glucose, potassium and insulin). This emphasizes that potassium follows glucose into cells under insulin stimulation and patients need such issues to be addressed. Often such regimes will have trigger points based on blood glucose after initial loss of control, where a transition is made from one supplementary intravenous fluid such as 0.9% saline (with potassium added as indicated) to 5% glucose (with potassium added as indicated).

Contents

Indications

LogoKeyPointsBox.pngThere are safer and better s/c insulin regimes in most situations where patients are not nil by mouth and these regimes do not tend to use short acting insulins as are used in iv sliding scales
  • Peri-operative glycaemic control in fasting patients or those with unpredictable food intake.
  • A form of sliding scale is sometimes used for diabetic ketoacidosis. The 'standard' sliding scale should not be used for initial treatment.
  • Hyperkalaemia (glucose infusion simultaneously)
  • Post MI (DIGAMI trials)[1][2]

Criticisms

The principle of adjusting insulin dosage to a rapidly changing glycaemic state is sound in that it attempts to mimic the body's homeostatic mechanisms. The difficulty is that an intravenous sliding scale may fail on the two essential components to a negative feedback system: detection and feedback adjustment.

Firstly, accurate monitoring can be difficult. The success of the scale depends on frequent, usually hourly, monitoring. This is uncomfortable for the patient and disruptive to sleep. In areas with less favourable nursing staff ratios, there is a risk that monitoring is performed infrequently or omitted.

Secondly, the scale needs to be adjusted to the individual. It stands to reason that the patient admitted with a concurrent illness who takes >100 units of subcutaneous insulin in health will require much more than a healthy patient who takes half the amount. Failure to adjust the standard values, as set out below, may result in poorly-controlled glucose levels with frequent fluctuations as the sugar levels swing from high to low.

Thirdly, intravenous access is required. While this may not be a total disaster in type 2 diabetics, in type 1 diabetics who are completely insulin dependent, loss of intravenous access can result in rapid development of diabetic ketoacidosis.

Fourthly, fluid and electrolyte balance requirements depend upon many factors including the presentation. Initial regimes need adjustment based on monitoring of glucose, electrolytes and fluid balance and it is all too easy to concentrate on the first with the additional risk that this additional less frequent monitoring is performed too infrequently or omitted.

Alternatives

In type 1 diabetics who are not eating, one option is to continue the subcutaneous long-acting basal insulin, but omit the short-acting boluses given with meals. There is an evidence base for the safe use of subcutaneous insulin in some specific indications where patients are nil by mouth and acutely ill.

Practicalities

Preparing the Syringe

For simplicity, most hospitals use a concentration of 1 unit of insulin per millilitre. Use an insulin syringe to draw up 50 units of a short-acting insulin like Actrapid. Add it to a 50ml syringe containing 50ml of 0.9% saline.

Prescribing

Example of Insulin Sliding Scale
Blood Sugar Number of units/hour Increased scale
0.0 - 3.9 0.5 1.0
4.0 - 6.9 1.0 2.0
7.0 - 10.9 2.0 3.0
11.0 - 14.9 3.0 4.0
15.0 - 19.9 4.0 6.0
>20.0 6.0 8.0

It is advisable to use your own hospital's protocol(s) - as that is what people will be used to, and errors will be avoided. The important level is the amount of insulin at low blood sugars. If this is for DKA, continue insulin at all times (to switch off ketone production, and so reduce acidosis). If for other reasons (e.g. control peri-operatively) <4mmol should stop insulin. Hypoglycaemia should be treated as usual.

The use of low fluid volumes/24 hours in heart failure/renal failure (eg 10% glucose plus insulin infusion instead of 5% glucose plus insulin infusion) and attention to water, sodium and potassium balance by daily review, at least, is emphasized. All too often blood results are looked at, and not the fluid regime charted to supplement the insulin infusion, the patient's actual fluid balance and weight.

A number of recent advances in understanding common indications, doses and alternatives for intravenous insulin have occurred:

References

  1. Malmberg K, Rydén L, Efendic S, Herlitz J, Nicol P, Waldenström A, Wedel H, Welin L. Randomized trial of insulin-glucose infusion followed by subcutaneous insulin treatment in diabetic patients with acute myocardial infarction (DIGAMI study): effects on mortality at 1 year. Journal of the American College of Cardiology. 1995 Jul; 26(1):57-65.
  2. Malmberg K, Rydén L, Hamsten A, Herlitz J, Waldenström A, Wedel H. Effects of insulin treatment on cause-specific one-year mortality and morbidity in diabetic patients with acute myocardial infarction. DIGAMI Study Group. Diabetes Insulin-Glucose in Acute Myocardial Infarction. European heart journal. 1996 Sep; 17(9):1337-44.
  3. Malmberg KA, Efendic S, Rydén LE. Feasibility of insulin-glucose infusion in diabetic patients with acute myocardial infarction. A report from the multicenter trial: DIGAMI. Diabetes care. 1994 Sep; 17(9):1007-14.
  4. Malmberg K, Rydén L, Wedel H, Birkeland K, Bootsma A, Dickstein K, Efendic S, Fisher M, Hamsten A, Herlitz J, Hildebrandt P, MacLeod K, Laakso M, Torp-Pedersen C, Waldenström A. Intense metabolic control by means of insulin in patients with diabetes mellitus and acute myocardial infarction (DIGAMI 2): effects on mortality and morbidity. European heart journal. 2005 Apr; 26(7):650-61.(Link to article – subscription may be required.)
  5. Cheung NW, Wong VW, McLean M. The Hyperglycemia: Intensive Insulin Infusion in Infarction (HI-5) study: a randomized controlled trial of insulin infusion therapy for myocardial infarction. Diabetes care. 2006 Apr; 29(4):765-70.
  6. Gandhi GY, Nuttall GA, Abel MD, Mullany CJ, Schaff HV, O'Brien PC, Johnson MG, Williams AR, Cutshall SM, Mundy LM, Rizza RA, McMahon MM. Intensive intraoperative insulin therapy versus conventional glucose management during cardiac surgery: a randomized trial. Annals of internal medicine. 2007 Feb 20; 146(4):233-43.
  7. van den Berghe G, Wouters P, Weekers F, Verwaest C, Bruyninckx F, Schetz M, Vlasselaers D, Ferdinande P, Lauwers P, Bouillon R. Intensive insulin therapy in the critically ill patients. The New England journal of medicine. 2001 Nov 8; 345(19):1359-67.
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  12. Bradley P, Tobias JD. Serum glucose changes during insulin therapy in pediatric patients with diabetic ketoacidosis. American journal of therapeutics. 2007 May-Jun; 14(3):265-8.(Link to article – subscription may be required.)
  13. Wagner A, Risse A, Brill HL, Wienhausen-Wilke V, Rottmann M, Sondern K, Angelkort B. Therapy of severe diabetic ketoacidosis. Zero-mortality under very-low-dose insulin application. Diabetes care. 1999 May; 22(5):674-7.
  14. Umpierrez GE, Cuervo R, Karabell A, Latif K, Freire AX, Kitabchi AE. Treatment of diabetic ketoacidosis with subcutaneous insulin aspart. Diabetes care. 2004 Aug; 27(8):1873-8.
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  16. Lepercq J, Abbou H, Agostini C, Toubas F, Francoual C, Velho G, Dubois-Laforgue D, Timsit J. A standardized protocol to achieve normoglycaemia during labour and delivery in women with type 1 diabetes. . 2007 Dec 7.(Epub ahead of print) (Link to article – subscription may be required.)
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