What are the implications of poorly controlled diabetes on anesthesia care for an older patient with potential comorbidities, such as hypertension or cardiovascular disease, undergoing cataract surgery?

Anesthesia Management for Cataract Surgery in Poorly Controlled Diabetes

For patients with poorly controlled diabetes undergoing cataract surgery, a preoperative medical evaluation by their primary care physician should be considered before proceeding, and local/regional anesthesia is strongly preferred over general anesthesia to maintain better glycemic control and avoid metabolic stress. 1

Preoperative Considerations

Medical Evaluation Requirements

• Poorly controlled diabetes is specifically identified as a condition warranting preoperative medical evaluation by the patient's primary care physician or dedicated preoperative service before cataract surgery, even though routine preoperative testing does not reduce complications in well-controlled patients. 1
• Assess HbA1c and recent capillary blood glucose levels to determine baseline control—target HbA1c <8% for elective procedures when possible. 2
• Screen for diabetic complications that increase perioperative risk:
  • Gastroparesis (present in many diabetics): increases aspiration risk, requiring rapid sequence induction if general anesthesia is necessary 2
  • Cardiac autonomic neuropathy (affects 30-50% of diabetics): increases sudden death risk and hemodynamic instability 2
  • Silent myocardial ischemia (30-50% prevalence): obtain ECG preoperatively 2
  • Diabetic nephropathy: measure GFR as this increases acute renal failure risk perioperatively 1, 2

Critical Preoperative Pitfall

• Screen for recent hypoglycemic episodes (blood glucose <3.9 mmol/L or <70 mg/dL) in the last week, as these predict perioperative risk and require correction before proceeding. 2, 3

Anesthesia Selection: Local vs. General

Strong Preference for Local/Regional Anesthesia

Local anesthesia (retrobulbar block) provides superior metabolic control compared to general anesthesia for cataract surgery in diabetic patients. 4

• Under local anesthesia, blood glucose and cortisol remain stable throughout surgery, whereas general anesthesia causes significant intraoperative hyperglycemia and cortisol elevation. 4
• Local anesthesia maintains glucose homeostasis, prevents the stress hormone response, and allows immediate postoperative oral intake without prolonged fasting. 4
• Regional anesthesia reduces postoperative insulin resistance and provides superior pain control, which is particularly important since poorly controlled pain is a risk factor for hyperglycemia. 1, 2

If General Anesthesia Is Required

• Recognize that general anesthesia triggers a catabolic stress response with increased cortisol, insulin resistance, and hyperglycemia—effects that are magnified in poorly controlled diabetics. 4, 5
• Neither volatile-based nor total intravenous anesthesia shows superiority in diabetic patients; either is acceptable. 3
• Avoid dexamethasone doses >4 mg for antiemetic prophylaxis, as higher doses (8-10 mg) significantly increase hyperglycemia risk for 24 hours postoperatively. 1
• Use 4 mg dexamethasone combined with another antiemetic (droperidol or 5-HT3 antagonist) if needed. 1

Intraoperative Glycemic Management

Target Blood Glucose Range

Maintain blood glucose between 5-10 mmol/L (90-180 mg/dL) intraoperatively to balance infection risk against hypoglycemia. 1, 2

• Hyperglycemia >10 mmol/L (180 mg/dL) increases morbidity and mortality, particularly from infection. 2
• Hyperglycemia >13.5 mmol/L (250 mg/dL) carries a 10-fold higher complication risk. 2
• Do not aim for strict normoglycemia, as this increases hypoglycemia frequency without improving outcomes. 2

Monitoring Protocol

• Measure capillary blood glucose every 2 hours if stable, every hour after insulin dose changes. 1
• Prefer whole blood measurement (arterial or venous from opposite side of glucose infusion) over capillary testing when possible. 1
• Do not rely on continuous glucose monitors (CGM) intraoperatively due to lag time and perfusion-dependent inaccuracy. 2

Insulin Management During Surgery

For poorly controlled diabetics or those on insulin:

• Use continuous IV insulin infusion via electronic syringe for optimal control during cataract surgery if the patient cannot maintain oral intake. 1, 2
• Administer ultra-rapid insulin only, diluted to 1 IU/mL concentration. 1
• Always include simultaneous glucose infusion (G10% at 40 mL/h, providing 100-150 g/day) except during hyperglycemia. 1
• Adjust insulin infusion based on hourly glucose measurements according to standardized protocols. 1

Medication Management on Day of Surgery

• Hold metformin on the day of surgery (except for minor/ambulatory procedures with severe renal failure considerations). 1
• Other oral hypoglycemic agents should be held the morning of surgery. 1
• Never stop basal insulin in Type 1 diabetics due to ketoacidosis risk. 1
• For insulin-dependent patients: give NPH at 50% usual dose, long-acting analogs at 75-80% usual dose. 6

Postoperative Management

Immediate Recovery Period

• Resume oral feeding as soon as possible after surgery—this is the priority for diabetic patients. 1, 2
• Continue hourly blood glucose monitoring until the patient is stable and fully conscious. 2
• Maintain glucose infusion (G10% at 40 mL/h) for insulin-dependent patients until eating to prevent recurrent hypoglycemia. 2

Resuming Diabetes Medications

• Resume regular diabetes medications when blood glucose is 5-10 mmol/L (90-180 mg/dL) and the patient is eating. 6, 2
• If blood glucose exceeds 10 mmol/L (180 mg/dL) postoperatively, administer corrective subcutaneous insulin boluses. 6
• If blood glucose exceeds 16.5 mmol/L (300 mg/dL), hospitalization may be required for IV insulin therapy. 6

Special Considerations for Ambulatory Cataract Surgery

Scheduling Strategy

Schedule poorly controlled diabetic patients early on the surgical list to minimize disruption to medication and meal routines. 1

• If surgery allows the patient to leave recovery before 10 AM, serve breakfast immediately and administer morning medications at that time. 1
• If discharge occurs between 10 AM-noon, patient should take usual medication on hospital arrival with glucose infusion (G10% at 40 mL/h) until next meal. 1
• Minimize changes to antidiabetic treatment and resume oral feeding quickly to facilitate same-day discharge. 1

Pain Management

• Standard analgesics (NSAIDs, acetaminophen, opioids) can be used without modification, as they do not affect glycemic control. 1
• Effective pain control is essential because poorly controlled pain increases hyperglycemia risk. 1

Key Pitfalls to Avoid

1. Do not proceed with elective cataract surgery without addressing severe hyperglycemia (>13.5 mmol/L or 250 mg/dL) or recent hypoglycemic episodes. 2, 3
2. Never stop insulin pumps without immediate IV insulin replacement in Type 1 diabetics, as ketoacidosis develops within hours. 2
3. Recognize hypoglycemia unawareness affects 40% of Type 1 and 10% of insulin-treated Type 2 diabetics, requiring more vigilant monitoring. 2, 3
4. Avoid prolonged preoperative fasting—cataract surgery should ideally involve missing only one meal maximum. 1, 7
5. Do not use high-dose dexamethasone (>4 mg) for antiemetic prophylaxis. 1