Two parts of a mealtime dose
A mealtime dose of rapid-acting insulin in a basal-bolus plan has two parts. The meal (carbohydrate) dose covers the carbohydrate in the meal, and the correction dose brings a high premeal glucose back toward target. Her plan uses an insulin-to-carbohydrate ratio of 1 unit per 10 g and a correction factor of 1 unit per 50 mg/dL (2.8 mmol/L) above 150 mg/dL (8.3 mmol/L). The total dose is the meal dose plus the correction dose, rounded only at the end.
Step-by-step calculation
Each part is calculated separately and the parts are not rounded, as the question instructs.
| Step | Calculation | Result |
|---|
| Meal dose | 72 g ÷ 10 g per unit | 7.2 units |
| Glucose above target | 262 − 150 mg/dL | 112 mg/dL |
| Correction dose | 112 ÷ 50 mg/dL per unit | 2.24 units |
| Total | 7.2 + 2.24 | 9.44 units, rounded to 9 units |
Where the wrong answers come from
Each distractor reflects a typical calculation error. 7 units is the meal dose alone and omits the correction for a high premeal glucose. 2 units is the correction alone and omits the meal dose. Watch out! 12 units comes from dividing the whole glucose value by 50 (262 ÷ 50 = 5.24) instead of only the amount above the target; adding this to the meal dose gives 12.44, rounded to 12. The correction is always based on the difference from the target, never on the full glucose value.
Insulin lispro and safe administration
Insulin lispro is a rapid-acting insulin with an onset of about 15 minutes, so it is given shortly before the meal, and the client must be ready to eat. Insulin glargine at bedtime provides the long-acting basal insulin and is not adjusted for meals. The nurse teaches her to double-check calculations, to use the same ratio and correction factor written in her plan, to monitor for hypoglycemia (shakiness, sweating, confusion) especially if she eats less than planned, and to treat low glucose promptly with fast-acting carbohydrate.
Exam takeaway
Key point! Total bolus = (carbohydrate grams ÷ ratio) + ((current glucose − target) ÷ correction factor). Calculate each part separately, add them, and round only the total when instructed.