What are the initial settings for programming a Tandem IQ (insulin pump) for a patient with diabetes?

Programming the Tandem t:slim X2 with Control-IQ: Initial Settings

To program a Tandem t:slim X2 insulin pump, you must calculate and enter four essential parameters: total daily dose (TDD), basal rate, insulin-to-carbohydrate ratio (ICR), and insulin sensitivity factor (ISF), all derived from the patient's weight and metabolic status. 1

Step 1: Calculate Total Daily Dose (TDD)

For metabolically stable patients with type 1 diabetes, start with 0.5 units/kg/day as the TDD. 1

• Patients in the honeymoon phase require lower doses of 0.2-0.6 units/kg/day 1
• Higher doses (>1.0 units/kg/day) are needed during puberty, pregnancy, or acute illness 1
• For insulin-naive type 2 diabetes patients, use 0.1-0.2 units/kg/day 1

Example calculation: For a 70 kg patient with type 1 diabetes: 70 kg × 0.5 units/kg = 35 units/day TDD 1

Step 2: Program Basal Rate

Calculate the total basal dose as 0.48 × TDD (approximately 40-60% of total daily dose). 1

• The basal rate is programmed as a constant hourly infusion over 24 hours 2
• This rate can be adjusted throughout the day in different time blocks to account for the dawn phenomenon and daily activities 2
• Many patients require more insulin in the morning hours when counter-regulatory hormones are elevated 2

Example: For TDD of 35 units: 35 × 0.48 = 16.8 units basal per day, which equals approximately 0.7 units/hour 1

Step 3: Calculate Insulin-to-Carbohydrate Ratio (ICR)

The ICR defines how many grams of carbohydrate are covered by 1 unit of insulin. 2

• This ratio is calculated from the TDD and reflects the patient's insulin sensitivity 2
• The ratio can vary throughout the day and should be set at different levels for different time blocks 2
• A typical example ratio is 1:10, meaning 1 unit of insulin covers 10 grams of carbohydrate 2

Step 4: Calculate Insulin Sensitivity Factor (ISF)

Use the formula: ISF = 1700/TDD for rapid-acting insulin analogs. 1

• This factor determines how much 1 unit of insulin will decrease blood glucose 2
• For example, with a ratio of 1:3,1 unit of insulin decreases blood sugar by 3 mmol/L 2
• The ISF is used with bolus doses to correct blood sugar above the preset target before meals 2

Example: For TDD of 35 units: 1700/35 = 49 mg/dL drop per unit of insulin 1

Step 5: Load Insulin and Prime the System

Use only rapid-acting insulin analogs (Novolog, Humalog, or Apidra) in the pump. 1

• A 10mL vial contains 1000 units of U-100 insulin 1
• Tubed pumps require cartridges holding 180-300 units 1
• Patch pumps typically hold 200 units 1
• Never dilute or mix rapid-acting insulin analogs with other insulins or solutions 1

For a patient using 35 units/day, one vial provides approximately 28 days of therapy. 1

Step 6: Set Target Glucose Range

The Control-IQ algorithm automatically adjusts insulin delivery to maintain glucose between 112.5 and 160 mg/dL. 3

• The system predicts glucose levels 30 minutes in the future 3
• Automatic correction boluses are delivered when glucose is predicted to rise >180 mg/dL 3
• Overnight, the system intensifies control to achieve glucose levels of 100-120 mg/dL by morning 4

Initial Monitoring Requirements

Check blood glucose every 2-4 hours during the first 24-48 hours of pump therapy. 1

• Adjust basal rates by 10-20% if hypoglycemia occurs 1
• Increase basal rates by 0.1-0.2 units/hour if fasting glucose remains elevated 1
• Reassess pump settings every 3-7 days until glycemic targets are achieved 1

Control-IQ Specific Features

The Control-IQ system automates insulin correction boluses and has a dedicated hypoglycemia safety system. 4

• The system can suspend insulin administration when glucose is low or predicted to drop within 30 minutes 5
• Median percent time in automation is 94.2% in real-world use 6
• Time in range (70-180 mg/dL) improves from baseline 63.6% to 73.6% after 12 months of use 6

Critical Pitfalls to Avoid

Disconnection, occlusion, or cessation of pump therapy renders the user relatively insulin deficient within 1 hour and absolutely insulin deficient within 4 hours, with severe risk of hyperglycemia and ketosis. 2, 5

• Only short-acting insulin is used in the pump, so there is no long-acting insulin reservoir 2
• The cannula must be changed every 2-3 days to prevent occlusion 2, 5
• If blood glucose exceeds 14 mmol/L (252 mg/dL), check the pump and infusion set, and test for ketones 2, 5

Ongoing Adjustments

All pump parameters should be reviewed and adjusted every 3-6 months at specialized pump therapy clinics. 2

• Settings change with physiological factors such as weight, exercise, and menstruation 2
• The carbohydrate-to-insulin ratio and insulin sensitivity factor require periodic recalculation 2
• The pump's on-board calculator prevents "stacking" of insulin doses by tracking active insulin 2