Immediate Management of Elevated BUN and Glucose with Nausea, Vomiting, and Diarrhea
This presentation suggests a hyperglycemic crisis (DKA or HHS) with severe dehydration requiring immediate aggressive intravenous fluid resuscitation with isotonic saline at 15-20 mL/kg/hour, followed by insulin therapy once hypokalemia is excluded. 1, 2
Initial Diagnostic Workup
Obtain STAT laboratory studies including arterial blood gases, complete blood count with differential, urinalysis, plasma glucose, BUN, electrolytes, chemistry profile, and creatinine levels, plus an electrocardiogram. 1 Obtain chest X-ray and cultures as clinically indicated for potential infectious precipitants. 1
Calculate effective serum osmolality using the formula: 2[measured Na (mEq/L)] + glucose (mg/dL)/18 to determine if this meets criteria for hyperosmolar hyperglycemic state (>320 mOsm/kg H₂O). 1
Correct serum sodium for hyperglycemia by adding 1.6 mEq to the measured sodium value for each 100 mg/dL glucose above 100 mg/dL to assess true sodium status. 1
Fluid Resuscitation Protocol
Adults
Begin with isotonic saline (0.9% NaCl) at 15-20 mL/kg body weight per hour during the first hour (approximately 1-1.5 L in average adults). 1, 2 This aggressive initial resuscitation is critical because the elevated BUN reflects true hypovolemia from osmotic diuresis, not intrinsic renal disease. 3, 2
After the first hour, adjust fluid choice based on corrected serum sodium:
- If corrected sodium is normal or elevated: use 0.45% NaCl at 4-14 mL/kg/hour 1
- If corrected sodium is low: continue 0.9% NaCl at 4-14 mL/kg/hour 1
Monitor serum osmolality changes carefully - the induced change should not exceed 3 mOsm/kg H₂O per hour to prevent cerebral edema. 1, 2
Once renal function is assured and serum potassium is known, add 20-30 mEq/L potassium (2/3 KCl and 1/3 KPO₄) to the infusion until the patient is stable. 1
When serum glucose reaches 250 mg/dL, switch to 5% dextrose with 0.45-0.75% NaCl with potassium supplementation as above. 1
Pediatric Patients (<20 years)
Start with isotonic saline (0.9% NaCl) at 10-20 mL/kg/hour for the first hour. 1 In severely dehydrated children, this may be repeated, but initial reexpansion should not exceed 50 mL/kg over the first 4 hours to minimize cerebral edema risk. 1
Continue with 0.45-0.9% NaCl (depending on serum sodium) at 1.5 times the 24-hour maintenance requirements (approximately 5 mL/kg/hour) to achieve smooth rehydration over 48 hours. 1
Insulin Therapy
Do NOT start insulin until hypokalemia (K⁺ <3.3 mEq/L) is excluded - this is a critical safety step. 1
Adults
Administer an intravenous bolus of regular insulin at 0.15 units/kg body weight, followed by continuous infusion at 0.1 unit/kg/hour (5-7 units/hour in adults). 1
If plasma glucose does not fall by 50 mg/dL in the first hour, verify adequate hydration status and double the insulin infusion hourly until achieving a steady glucose decline of 50-75 mg/hour. 1
Pediatric Patients
Do NOT give an initial insulin bolus in children - start directly with continuous infusion of regular insulin at 0.1 unit/kg/hour. 1
Symptomatic Management
For nausea and vomiting in children >4 years and adolescents, consider ondansetron to facilitate oral rehydration tolerance once initial stabilization is achieved. 1 However, note that ondansetron may increase stool volume. 1
Avoid antimotility agents (loperamide) in children <18 years and in any patient with suspected inflammatory diarrhea or fever due to risk of toxic megacolon. 1
In adults with watery diarrhea, loperamide may be considered once adequate hydration is achieved, but only if inflammatory causes are excluded. 1
Monitoring Strategy
Monitor BUN and creatinine every 6-12 hours initially, then daily once stable to assess adequacy of volume replacement. 3, 2 Persistent or worsening BUN despite appropriate fluid therapy should trigger investigation for intrinsic renal injury or ongoing infection. 2
Check serum electrolytes every 2-4 hours during active resuscitation, then every 6-8 hours once stable. 3, 4
Assess mental status frequently to rapidly identify changes indicating iatrogenic complications such as cerebral edema or worsening metabolic derangement. 1
Monitor hemodynamic parameters including blood pressure, heart rate, urine output, and clinical examination findings to judge successful fluid replacement. 1
Critical Pitfalls to Avoid
Do not delay fluid resuscitation while waiting for laboratory results - begin isotonic saline immediately based on clinical assessment. 1
In patients with cardiac or renal compromise, perform frequent assessment during fluid resuscitation to avoid iatrogenic fluid overload. 1
Do not assume the elevated BUN indicates intrinsic renal disease - in the setting of hyperglycemia with gastrointestinal losses, this represents prerenal azotemia from true volume depletion requiring aggressive fluid replacement. 3, 2
Correct fluid deficits within 24 hours but avoid excessively rapid correction of osmolality (>3 mOsm/kg/hour) to prevent cerebral complications. 1, 2