9.2 Insulin Regimens, Type 1 Diabetes, Hypoglycemia & Diabetic Emergencies (DKA/HHS)

9.2 Insulin Regimens, Type 1 Diabetes, Hypoglycemia & Diabetic Emergencies (DKA/HHS)

Exogenous insulin replacement is the mandatory, life-preserving therapy for all patients with type 1 diabetes mellitus (T1D) and represents a vital therapeutic modality for patients with type 2 diabetes who experience progressive β-cell exhaustion, severe symptomatic hyperglycemia, or acute metabolic decompensation. Mastering insulin pharmacokinetics, dose adjustment calculations, acute hypoglycemia rescue protocols, and the emergency management of diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS) is foundational for Canadian pharmacy practice.

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Insulin Pharmacology & Pharmacokinetic Classification

Therapeutic insulins are classified based on their onset, peak effect, and duration of action. Modern recombinant human insulin analogs have largely superseded regular human insulin and NPH for daily maintenance regimens because their modified amino acid sequences prevent hexamer stabilization or promote controlled depot precipitation, better mimicking physiological pancreatic secretion.

                                  INSULIN TIME-ACTION PROFILES
                                  
 [Plasma Insulin]
       │
       │   Rapid-acting (Aspart, Lispro, Glulisine)
       │    Onset 10-15m, Peak 1-2h, Duration 3-5h
       │    ┌───┐
       │   ╱     ╲      Regular Human (Toronto)
       │  ╱       ╲      Onset 30m, Peak 2-3h, Duration 5-8h
       │ ╱         ╲      ┌───────┐
       │╱           ╲    ╱         ╲        NPH (Cloudy)
       │             ╲  ╱           ╲        Onset 1-3h, Peak 4-10h, Duration 12-18h
       │              ╲╱             ╲        ┌─────────────┐
       │                              ╲      ╱               ╲
       │  Long-acting Basal (Glargine, Degludec) ─────────────────────────── Duration 24 - 42+ hours (Flat/Peakless)
       └───────────────────────────────────────────────────────────────────
       0    1    2    3    4    5    6    7    8    9   10   12   16   20   24   Hours

Comprehensive Pharmacokinetic Comparison

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Insulin Regimen Architecture in Type 1 Diabetes

Because individuals with type 1 diabetes experience absolute autoimmune destruction of pancreatic β-cells, exogenous therapy must replicate physiological insulin secretion: a continuous, low-level basal component (suppressing hepatic gluconeogenesis overnight and between meals) and sharp, episodic prandial (bolus) components (disposing of mealtime carbohydrate absorption).

Basal-Bolus Architecture

• Starting Total Daily Dose (TDD): Typically 0.5 units/kg/day in metabolically stable patients without ketoacidosis (range: 0.2–0.4 units/kg/day during the transient "honeymoon phase"; 0.6–1.0+ units/kg/day during acute illness, stress, or adolescent puberty).
• Dose Allocation:
  • Basal Component: ≈ 50% of the TDD administered as a long-acting basal analog once daily (or split BID).
  • Prandial Component: ≈ 50% of the TDD divided approximately equally across three meals as a rapid-acting analog injected immediately before eating.

EXAMPLE: 70 kg Patient Newly Diagnosed with Type 1 Diabetes
1. Calculate TDD:         70 kg * 0.5 units/kg/day = 35 units/day
2. Basal Component (50%): 35 units * 0.50 = 17.5 units -> Round to 17 or 18 units of Glargine or Degludec at bedtime
3. Prandial Pool (50%):   35 units * 0.50 = 17.5 units rapid-acting analog across 3 meals
4. Meal Allocation:       ~6 units of Aspart or Lispro immediately before Breakfast, Lunch, and Dinner

Continuous Subcutaneous Insulin Infusion (CSII / Insulin Pumps)

Insulin pump therapy delivers an uninterrupted subcutaneous micro-infusion of rapid-acting insulin analog only (no basal insulin is ever loaded into an insulin pump). The pump delivers programmed basal rates (varying by hour to match physiological diurnal needs and counter the early morning "dawn phenomenon") plus patient-activated boluses for meals and hyperglycemic corrections.

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Clinical Insulin Calculations: The 500 Rule & The 100 Rule

Patients practicing advanced carbohydrate counting calculate mealtime boluses based on their precise carbohydrate intake and pre-meal blood glucose.

1. Insulin-to-Carbohydrate Ratio (ICR): The 500 Rule

The Insulin-to-Carbohydrate Ratio (ICR) quantifies the number of grams of carbohydrate covered by 1 unit of rapid-acting insulin analog:

$\text{ICR (grams of carbohydrate / unit of insulin)} = \frac{500}{\text{Total Daily Dose (TDD)}}$

$\text{Carbohydrate Bolus Dose (units)} = \frac{\text{Grams of Carbohydrate Ingested}}{\text{ICR}}$

2. Insulin Sensitivity Factor (ISF / Correction Factor): The 100 Rule

The Insulin Sensitivity Factor (ISF) represents the expected reduction in blood glucose (in mmol/L) produced by 1 unit of rapid-acting insulin analog. In Canada, where blood glucose is measured in mmol/L, the 100 Rule is utilized (derived from the US 1800 Rule divided by 18):

$\text{ISF (mmol/L drop per unit of insulin)} = \frac{100}{\text{Total Daily Dose (TDD)}}$

$\text{Correction Bolus Dose (units)} = \frac{\text{Actual Blood Glucose} - \text{Target Blood Glucose}}{\text{ISF}}$

Step-by-Step Integrated Bolus Calculation

Clinical Scenario: A 60 kg adult with T1D has an established TDD of 50 units. The patient is preparing to eat a meal containing 60 g of carbohydrate. The pre-meal fingerstick blood glucose is 11.0 mmol/L, and the target preprandial blood glucose is 6.0 mmol/L.

1. Calculate the ICR: $\text{ICR} = \frac{500}{50} = 10\text{ g/unit}$

2. Calculate the Carbohydrate Bolus: $\text{Carb Bolus} = \frac{60\text{ g}}{10\text{ g/unit}} = 6.0\text{ units}$

3. Calculate the ISF: $\text{ISF} = \frac{100}{50} = 2.0\text{ mmol/L per unit}$

4. Calculate the Correction Bolus: $\text{Correction Bolus} = \frac{11.0\text{ mmol/L} - 6.0\text{ mmol/L}}{2.0\text{ mmol/L/unit}} = \frac{5.0}{2.0} = 2.5\text{ units}$

5. Calculate Total Pre-Meal Bolus: $\text{Total Meal Dose} = 6.0\text{ units (Carb)} + 2.5\text{ units (Correction)} = 8.5\text{ units of rapid-acting insulin}$

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Hypoglycemia Pathophysiology, Staging & Clinical Protocols

Hypoglycemia is the most frequent acute complication of insulin and secretagogue therapy, representing the primary limiting barrier to achieving optimal glycemic control.

Definition and Severity Staging

In individuals treated with insulin or sulfonylureas, hypoglycemia is defined as a plasma glucose concentration < 4.0 mmol/L, regardless of whether symptoms are recognized.

                                 HYPOGLYCEMIA SEVERITY SPECTRUM
                                 
 ┌───────────────────────────────┬───────────────────────────────┬───────────────────────────────┐
 │ MILD                          │ MODERATE                      │ SEVERE                        │
 ├───────────────────────────────┼───────────────────────────────┼───────────────────────────────┤
 │ Autonomic symptoms present:   │ Autonomic + Neuroglycopenic:  │ Involves severe cognitive     │
 │ Trembling, sweating, anxiety, │ Headache, confusion, mood     │ impairment, unconsciousness,  │
 │ palpitations, hunger, nausea. │ changes, dizziness, weakness. │ or seizures. Patient REQUIRES │
 │ Patient is conscious and ABLE │ Patient is conscious and ABLE │ ASSISTANCE OF ANOTHER PERSON  │
 │ to self-treat.                │ to self-treat.                │ to recover. (BG usually < 2.8)│
 └───────────────────────────────┴───────────────────────────────┴───────────────────────────────┘

Management of Conscious Hypoglycemia: The Rule of 15

For any conscious patient with confirmed or suspected blood glucose < 4.0 mmol/L:

                                      THE RULE OF 15 FLOWCHART
                                      
                           Blood Glucose Confirmed < 4.0 mmol/L (or symptomatic)
                                                     │
                                                     ▼
                                INGEST 15 GRAMS FAST-ACTING CARBOHYDRATE
                                • 4 chewable glucose tablets (4 g each = 16 g)
                                • 175 mL (3/4 cup) fruit juice or regular soft drink
                                • 6 Life Savers candies (chewed)
                                • 3 teaspoons (15 mL) sugar or honey dissolved in water
                                                     │
                                                     ▼
                                   REST AND WAIT EXACTLY 15 MINUTES
                                                     │
                                                     ▼
                                            RE-TEST BLOOD GLUCOSE
                                                     │
                             ┌───────────────────────┴───────────────────────┐
                             ▼                                               ▼
                     STILL < 4.0 mmol/L?                             BG ≥ 4.0 mmol/L (RECOVERED)
                             │                                               │
                             ▼                                               ▼
                 Repeat 15 g fast-acting carb                 Is next meal > 1 hour away?
                 Wait 15 min & recheck blood glucose                         │
                                                     ┌───────────────────────┴───────────────────────┐
                                                     ▼                                               ▼
                                                    YES                                              NO
                                                     │                                               │
                                                     ▼                                               ▼
                                         Provide a snack with complex                    Proceed to scheduled meal
                                         carbs + protein (e.g., bread &                   at regular time
                                         peanut butter, or cheese & crackers)

Management of Severe Hypoglycemia (Unconscious or Incapacitated)

When a patient is unconscious, seizing, or aggressive and unable to swallow safely:

1. Community / Pre-Hospital Emergency Interventions:
   • Call 911 / EMS immediately.
   • Place the patient in the lateral recovery position to prevent airway obstruction or aspiration from vomiting.
   • Do NOT attempt to administer oral fluids, glucose gels, or food into the mouth (aspiration hazard).
   • Administer Glucagon without delay:
     • Subcutaneous / Intramuscular Glucagon Injection Kit: 1 mg reconstituted powder injected IM into deltoid or anterior thigh.
     • Nasal Glucagon Powder (Baqsimi): 3 mg single-use intranasal device. Actuated into one nostril; passively absorbed across nasal mucosa. Effective even if the patient is unconscious or has severe nasal congestion.
   • Once the patient regains consciousness and can swallow safely, provide oral fast-acting glucose followed by complex carbohydrates. Anticipate post-awakening nausea and vomiting.
2. Healthcare Setting with Established IV Access:
   • Administer Dextrose 50% in Water (D50W): 20 to 50 mL (10 to 25 g of elemental dextrose) administered via slow IV push over 2 to 3 minutes. Re-check blood glucose within 10 to 15 minutes; follow with continuous 5% or 10% dextrose infusion if prolonged hypoglycemia is anticipated (e.g., sulfonylurea overdose).

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Diabetic Emergencies: DKA versus HHS Comparative Framework

Diabetic Ketoacidosis (DKA) and Hyperosmolar Hyperglycemic State (HHS) represent life-threatening acute metabolic crises resulting from insulin deficiency coupled with counter-regulatory hormone surge (glucagon, catecholamines, cortisol, growth hormone).

                                DKA vs. HHS PATHOPHYSIOLOGICAL DIVERGENCE
                                
             ABSOLUTE INSULIN DEFICIENCY                           RELATIVE INSULIN DEFICIENCY
                     (Classic DKA)                                        (Classic HHS)
                          │                                                     │
             Massive Lipolysis in Adipocytes                       Minimal Residual Insulin Present
                          │                                        (Suppresses Lipolysis & Ketogenesis)
                          ▼                                                     │
             Free Fatty Acids -> Liver Beta-Oxidation                           ▼
                          │                                        Uncontrolled Hepatic Gluconeogenesis
                          ▼                                                     │
             KETONE BODY GENERATION                                             ▼
             (Beta-Hydroxybutyrate & Acetoacetate)                 EXTREME HYPERGLYCEMIA (> 33.3 mmol/L)
                          │                                                     │
                          ▼                                                     ▼
             HIGH ANION GAP METABOLIC ACIDOSIS                     MASSIVE OSMOTIC DIURESIS
             (pH < 7.30, HCO3 < 15, Kussmaul Breathing)            Severe Dehydration (8-12 L Deficit)
                                                                   Hyperosmolality (> 320 mOsm/kg)
                                                                   Altered Mental Status / Coma

Diagnostic Comparison: DKA vs. HHS

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Critical Resuscitation Protocols: Fluids, Potassium Gates, and Insulin Transitions

The acute medical management of DKA and HHS requires a prioritized, multi-step resuscitation algorithm:

                               DKA/HHS EMERGENCY RESUSCITATION GATES
                               
 1. FLUID RESUSCITATION       • Hour 1: 1000 - 1500 mL 0.9% Normal Saline (NS) IV
    (IMMEDIATE FIRST STEP)    • Then 250 - 500 mL/hr of 0.45% or 0.9% NS based on corrected sodium
                                            │
                                            ▼
 2. POTASSIUM SAFETY GATE     • CHECK SERUM POTASSIUM BEFORE STARTING INSULIN!
    (CRITICAL GATE)           • If K+ < 3.3 mmol/L:  HOLD INSULIN! Infuse IV KCl 20-40 mEq/hr
                              • If K+ 3.3 - 5.0 mmol/L: Start insulin + add 20-30 mEq KCl/L fluid
                              • If K+ > 5.0 mmol/L:  Start insulin; do not add potassium; check q1-2h
                                            │
                                            ▼
 3. IV REGULAR INSULIN        • Regular insulin infusion: 0.1 units/kg/hr IV continuous
    (AFTER POTASSIUM SAFE)    • Target blood glucose decline rate: 3.0 to 5.0 mmol/L per hour
                                            │
                                            ▼
 4. GLUCOSE PRESERVATION      • When BG reaches ~14.0 mmol/L (DKA) or ~16.5 mmol/L (HHS):
    (PREVENT BRAIN EDEMA)       ADD 5% DEXTROSE (D5W) TO IV FLUIDS
                              • Keep insulin running to close anion gap and clear ketonemia!
                                            │
                                            ▼
 5. SUBCUTANEOUS OVERLAP      • DKA Resolved: BG < 14, pH > 7.30, HCO3 ≥ 18, Anion Gap normal
    (PREVENT REBOUND)         • INJECT SC BASAL INSULIN 2 TO 4 HOURS BEFORE STOPPING IV INFUSION

Step 1: Fluid Resuscitation (Priority One)

Intravenous fluid expansion must precede or accompany insulin administration to restore intravascular volume, improve tissue perfusion, and re-establish glomerular filtration. Administer 0.9% Normal Saline (NS) at 1000 to 1500 mL during the first hour. Subsequently, calculate corrected sodium:

$\text{Corrected } [\text{Na}^+] = \text{Measured } [\text{Na}^+] + 0.3 \times (\text{Glucose} - 5.5)$

If corrected sodium is normal or elevated, switch maintenance fluids to 0.45% NS at 250 to 500 mL/hr. If corrected sodium is low, maintain 0.9% NS.

Step 2: The Absolute Potassium Safety Gate

Insulin drives potassium from the extracellular space into intracellular compartments via stimulation of the Na+/K+-ATPase pump. Additionally, rehydration dilutes extracellular potassium and enhances urinary potassium excretion.

• If Serum K+ < 3.3 mmol/L: HOLD INSULIN COMPLETELY. Administer IV potassium chloride at 20 to 40 mEq/hr until serum potassium rises above 3.3 mmol/L. Administering insulin to a severely hypokalemic patient can trigger fatal cardiac arrhythmias (ventricular fibrillation, torsades de pointes) or acute respiratory arrest secondary to diaphragm paralysis.
• If Serum K+ is 3.3 to 5.0 mmol/L: Initiate insulin infusion concurrently with IV fluid containing 20 to 30 mEq KCl per liter to maintain serum potassium safely between 4.0 and 5.0 mmol/L.
• If Serum K+ > 5.0 mmol/L: Start insulin infusion without supplemental potassium; monitor serum potassium every 1 to 2 hours until levels decline below 5.0 mmol/L.

Step 3: Intravenous Regular Insulin Infusion

• Administer continuous intravenous regular human insulin at a fixed rate of 0.1 units/kg/hr (or an initial IV bolus of 0.1 units/kg followed by 0.1 units/kg/hr). Target a steady glucose reduction rate of 3.0 to 5.0 mmol/L per hour.
• If blood glucose fails to decline by at least 3.0 mmol/L in the first 2 to 4 hours despite adequate fluid resuscitation, double the hourly insulin infusion rate.

Step 4: Dextrose Addition and Prevention of Cerebral Edema

When blood glucose drops to ≈ 14.0 mmol/L in DKA (or ≈ 16.5 mmol/L in HHS), add 5% Dextrose to IV replacement fluids (e.g., 5% Dextrose with 0.45% NS) and adjust the insulin infusion rate downward to 0.05 units/kg/hr.

Cerebral Edema Alert: Overly rapid reductions in plasma osmolality cause water to shift into relatively hyperosmolar brain parenchyma, precipitating cerebral edema (manifesting as headache, lethargy, bradycardia, hypertension, or sudden neurological collapse, primarily in children and young adults). Prevent by maintaining plasma glucose drop rates ≤ 5.0 mmol/L/hr and maintaining blood glucose at 11.0–14.0 mmol/L until ketoacidosis resolves. Emergency treatment: IV Mannitol (0.5 to 1.0 g/kg) or 3% hypertonic saline.

Step 5: Transition to Subcutaneous Insulin

Resolution of DKA is defined by:

1. Blood glucose < 14.0 mmol/L;
2. Venous pH > 7.30;
3. Serum bicarbonate ≥ 18 mmol/L; and
4. Normalization of the serum anion gap (≤ 12 mmol/L).

When DKA has resolved and the patient is alert and able to eat, transition to a subcutaneous regimen. The subcutaneous basal insulin must be injected 2 to 4 hours before discontinuing the intravenous insulin infusion. Because intravenous regular insulin has an elimination half-life of only 5 to 9 minutes, stopping the infusion without an active subcutaneous basal depot produces an immediate absolute insulin deficit, precipitating rebound hyperglycemia and recurrent ketoacidosis within hours.