The sliding scale is one way of working out how much insulin to take before each meal. Most doctors advise against the sliding scale approach. In fact, the American Diabetes Association have pushed for this treatment method to no longer be used.
How the sliding scale works
The "sliding scale" is actually a chart of insulin dosages. A doctor creates this chart based on how the patient's body responds to insulin, their daily activity, and an agreed-upon carbohydrate intake.
Sliding scale insulin therapy involves a doctor creating an individualized chart for their patient.
As one moves along the chart, insulin dosage changes depending on two factors:
Pre-meal blood glucose level
This is usually plotted from low to high, down the chart's left-most column. As one slides from top to bottom, insulin dosage increases. This is because more insulin is needed to manage greater amounts of blood glucose.
This is usually plotted along the chart's top row. As one moves from breakfast to lunch to dinner within the same blood glucose level, dosage may vary.
This is because insulin sensitivity, the way the body responds to insulin, can change throughout the day. The fat content of meals can also change through the day, and the doctor may have taken that into consideration.
To work out the right dosage using a sliding scale, people should:
- test their blood glucose level
- find the matching blood glucose value along the chart's left-hand column
- slide horizontally along that value's row, until the current meal is reached
- take a dosage that matches the number where the two values meet
The blood glucose level test should be carried out about before mealtimes depending on the insulin type being used. People may be instructed to take insulin 15 to 30 minutes before a meal or even after eating if using a rapid-acting insulin.
Along with these mealtime rapid-acting doses, people often take a long-acting insulin dose once or twice a day. This is meant to set a stable baseline blood glucose level for the body to work around.
Benefits and disadvantages
The sliding scale method requires very few daily calculations. People with diabetes may feel more comfortable by following a pre-determined plan. However, these factors also make sliding scale treatment very inflexible.
The major disadvantages of sliding scale therapy are:
All meals must contain a the same amount of carbs, and people must not change their level of physical activity from day to day - something not feasible for many people.
- The same amount of carbs must be eaten with each meal, because a single carb value was used to calculate the chart. This number should not change from day to day.
- Meals need to be eaten around the same time each day. If not, the person's insulin sensitivity may not match up with what was used to work out a specific meal's dosage.
- People should not vary the amount that they exercise much from day to day. Changes in activity and stress also affect blood glucose levels in a way that the sliding scale cannot account for.
Unfortunately, it is nearly impossible for most people to stick completely to these meal and activity restrictions.
Adjustments cannot be made for variations in the amount of carbs eaten, the time meals are eaten, and daily exercise. As a result, they can lead to large changes in blood glucose levels throughout the day.
Medical professionals also worry about the risk of continuous high blood glucose levels that the sliding scale approach poses. An article in Today's Geriatric Medicine explains that instead of preventing elevated blood glucose levels, the sliding scale model only treats these levels after they have already occurred.
The doses that a sliding scale chart requires might also be excessive if a person skips meals or is more sensitive to insulin on a given day. As these doses build up throughout the day, they could lead to a dangerous drop in blood glucose levels.
The American Diabetes Association note that sliding scale therapy can be dangerous both in the long term and short term. Uncontrolled blood glucose levels place stress on the organs, and this puts people at greater risk of complications over time.
In the short-term, if blood glucose becomes extremely high or low, it can lead to diabetic coma.
In place of the sliding scale model, the American Diabetes Association suggest two alternative methods:
Conventional insulin therapy
This method is also called fixed-dose therapy. While this approach can lead to elevated blood glucose levels, it provides more stable insulin coverage than the sliding scale.
The major parts of this treatment are:
- Strict meal timing. Meals must be eaten at the same time each day.
- Two or three pre-dosed insulin injections are taken per day. Meals are coordinated with the injections' peak activity times.
- A long-acting insulin taken once or twice a day.
The short-acting insulin dosages are the same each day, and do not depend on pre-meal blood glucose levels.
Intensive insulin therapy
This method is also called basal-bolus therapy, or tight control. It requires the most daily calculations. However, it is also more flexible and proactive than any other method.
Intensive insulin therapy compensates in real-time for factors that may affect blood glucose levels and insulin sensitivity.
There are three main parts to an intensive insulin plan:
- Basal insulin: This is a long-acting insulin that is taken once or twice a day.
- Nutritional insulin: This is a mealtime dose, which is calculated according to the number of carbohydrates the meal will contain.
- Correctional insulin: The correctional insulin value is combined with the nutritional insulin value to form a complete mealtime dose. It is usually used to account for high blood glucose levels before meals.
To calculate nutritional insulin, divide the grams of carbs in the meal by the grams of carbs that one unit of insulin breaks down.
A correction can also be worked out and taken away from the nutritional dose to account for extra exercise, or any other factors that might increase insulin sensitivity.
To calculate a correction for high blood glucose, target blood glucose is taken away from current blood glucose. The difference is then divided by the number of points the person believes that 1 unit of insulin will drop their blood glucose by.
Small children with diabetes should always stick to conventional insulin therapy because low blood glucose levels can impede brain development.
If intensive insulin therapy is followed carefully, it can mimic the natural function of the pancreas better than any other treatment method.
A study in Diabetes Care compared the sliding scale and intensive methods in 211 hospital patients with type 2 diabetes. Patients treated with intensive therapy showed significantly better blood glucose control, as well as fewer incidences of severe infection and organ failure.
A total of 13 out of the 107 sliding scale patients became caught in a state of consistent high blood glucose, which was only relieved when they were switched to intensive therapy.
However, because its target blood glucose levels are lower than those of the conventional method, intensive therapy does pose a higher risk of hypoglycemia, which is low blood glucose. The benefits of tight control have typically only been shown in patients being treated in an intensive care unit.
The American Diabetes Association advise that young children stick to conventional insulin therapy, because low blood glucose levels can be dangerous to brain development.
They also suggest that older adults and those who already have diabetes complications should not try intensive therapy. Hypoglycemia can put too much stress on their vital organs and lead to strokes and heart attacks.
Intensive therapy can definitely be worth the work for a younger, relatively healthy person, however.
Good blood sugar control can prevent complications from developing, and can help people to live a healthier and longer life.