# Situation: A 24-year-old woman with type 1 diabetes mellitus uses insulin glargine at bedtime and insulin lispro with meals. Her written plan calls for 1 unit of lispro for every 10 g of carbohydrate in a meal, plus a correction of 1 unit for every 50 mg/dL (2.8 mmol/L) that her premeal glucose is above 150 mg/dL (8.3 mmol/L). One afternoon she plans a 45-minute jog. Her glucose before starting is 92 mg/dL (5.1 mmol/L), and she has no ketones. What should she do?

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> subject: Nursing Practice IV — Care of Clients with Problems in Nutrition and Gastrointestinal, Metabolism and Endocrine, Perception and Coordination

## 문제

Situation: A 24-year-old woman with type 1 diabetes mellitus uses insulin glargine at bedtime and insulin lispro with meals. Her written plan calls for 1 unit of lispro for every 10 g of carbohydrate in a meal, plus a correction of 1 unit for every 50 mg/dL (2.8 mmol/L) that her premeal glucose is above 150 mg/dL (8.3 mmol/L).

One afternoon she plans a 45-minute jog. Her glucose before starting is 92 mg/dL (5.1 mmol/L), and she has no ketones. What should she do?

## 보기

1. Start now, since glucose is above 70 mg/dL (3.9 mmol/L)
2. Take 1 unit of lispro to prevent a rise after the run
3. Eat a carbohydrate snack before she starts to jog **✔ 정답**
4. Delay the jog and recheck her glucose in 15 minutes

**정답: 3**

## 해설

Glucose is checked before exercise; at a value below about 100 mg/dL (5.6 mmol/L), carbohydrate is eaten first because activity increases glucose uptake and can cause hypoglycemia (the international consensus for type 1 diabetes likewise advises about 10 g of carbohydrate before aerobic exercise at 90–124 mg/dL). Exercise is avoided when glucose is above 250 mg/dL (13.9 mmol/L) with ketones. She should also carry a snack during the jog.

## 심화 해설

Clinical reasoning

A pre-exercise glucose of 92 mg/dL (5.1 mmol/L) is technically above the classic hypoglycemia threshold of 70 mg/dL (3.9 mmol/L), but it is still too low to safely begin a 45-minute aerobic session without fuel. During jogging, skeletal muscle contraction increases glucose transporter type 4 (GLUT4) translocation to the cell membrane independently of insulin, which sharply raises glucose uptake into working muscle . At the same time, circulating insulin from the earlier lispro or basal glargine may still be active, and hepatic glucose output does not rise fast enough to match the accelerated peripheral disposal . The result is a predictable downward drift in blood glucose within the first 20–30 minutes of moderate aerobic activity. A pre-exercise glucose below about 100 mg/dL (5.6 mmol/L) means the margin for this exercise-induced drop is too narrow, so carbohydrate should be consumed before starting.

The international consensus approach embedded in the scenario reflects this physiology: for aerobic exercise beginning at 90–124 mg/dL (5.0–6.9 mmol/L), approximately 10 g of fast-acting carbohydrate is recommended before the activity begins. This is not a correction for a high glucose; it is a preventive buffer against the expected fall. Key point! The decision to eat before exercise is based on the starting glucose trend and the expected glucose flux during activity, not simply on whether the number is above the hypoglycemia cutoff.

Taking 1 unit of lispro before the jog would be dangerous. Lispro peaks within roughly 30–90 minutes after injection, overlapping directly with the period of maximal muscle glucose uptake during the run. Adding exogenous insulin on top of contraction-stimulated glucose transport would accelerate the drop and sharply increase the risk of hypoglycemia during or shortly after exercise . Watch out! Insulin should generally be reduced or omitted before unplanned aerobic activity when glucose is at the lower end of the target range, not added.

Delaying the jog and rechecking in 15 minutes without eating would not solve the problem. A stable or slightly changed glucose after a short delay still leaves the same vulnerable starting point, because the issue is the expected glucose consumption during the upcoming 45 minutes of activity, not a transient measurement error. Real-world continuous glucose monitoring data show that hypoglycemia during physical activity is common even in motivated, well-informed adults with type 1 diabetes, and that the risk is strongly influenced by the pre-activity glucose level and the type of activity . A planned aerobic session beginning near 90 mg/dL is precisely the situation where pre-exercise carbohydrate is most protective.

| Pre-exercise glucose | Action before aerobic exercise | Rationale |
| --- | --- | --- |
| Below 90 mg/dL (5.0 mmol/L) | Eat 10–15 g carbohydrate, recheck, then start | Insufficient buffer; high risk of early hypoglycemia |
| 90–124 mg/dL (5.0–6.9 mmol/L) | Eat about 10 g carbohydrate before starting | Expected exercise-induced glucose fall exceeds hepatic compensation |
| 125–180 mg/dL (6.9–10.0 mmol/L) | May start without extra carbohydrate; monitor during activity | Adequate glucose reserve for moderate aerobic work |
| Above 250 mg/dL (13.9 mmol/L) with ketones | Delay exercise; correct insulin and recheck | Exercise can worsen hyperglycemia and ketosis |

The absence of ketones is reassuring and rules out the need to postpone exercise for metabolic safety, but it does not change the hypoglycemia risk calculation. Ketone testing addresses the opposite problem—insulin deficiency and excessive hepatic glucose output—whereas this patient’s concern is insulin-facilitated and contraction-mediated glucose disposal exceeding glucose appearance . Because she has no ketones and her glucose is only mildly low, the correct action is to consume a small carbohydrate snack before the jog and carry additional carbohydrate during the run. The snack should be simple, rapidly absorbed carbohydrate, and she should recheck glucose during or immediately after the activity, since hypoglycemia risk can persist for hours after exercise ends .

## 임상 시나리오

Pre-Exercise Glucose Check in Type 1 DiabetesCarbohydrate first when starting below 100 mg/dL
Before aerobic exercise, check glucose and ketones. If glucose is below 100 mg/dL (5.6 mmol/L), eat 10 g of fast-acting carbohydrate before starting to prevent exercise-induced hypoglycemia.

For glucose 90–124 mg/dL (5.0–6.9 mmol/L), the international consensus recommends about 10 g of carbohydrate before aerobic activity. This is a preventive buffer, not a correction for high glucose.

CautionDo not give lispro for a low-normal glucose; it will worsen the drop. Avoid exercise if glucose is above 250 mg/dL (13.9 mmol/L) with ketones. Carry a snack during activity.

## 핵심 개념

- **GLUT4 translocation** — Insulin-independent movement of glucose transporters to cell membrane during muscle contraction, increasing glucose uptake
- **Pre-exercise glucose threshold** — Below 100 mg/dL indicates need for carbohydrate before aerobic activity to prevent hypoglycemia
- **Correction dose** — Insulin given to lower elevated glucose; not indicated when glucose is below target or low-normal
- **Aerobic exercise** — Sustained activity like jogging that increases glucose utilization and can cause delayed hypoglycemia
- **Ketones** — Checked before exercise; exercise avoided if glucose above 250 mg/dL with ketones present

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