What is the approach to assessing hyperkalemia?

Approach to Assessment of Hyperkalemia

Definition

Hyperkalemia is defined as serum potassium (K+) >5.0 mEq/L, with severity classified as mild (5.0-5.9 mEq/L), moderate (6.0-6.4 mEq/L), and severe (≥6.5 mEq/L). 1

• Acute hyperkalemia: serum K+ exceeding upper limit of normal that is not known to be chronic 2
• Chronic hyperkalemia: recurrent episodes of elevated serum K+ requiring ongoing maintenance therapy 2
• Plasma K+ concentrations are typically 0.1-0.4 mEq/L lower than serum levels due to platelet K+ release during coagulation 2

Differential Diagnosis

Pseudohyperkalemia (Must Rule Out First)

• Poor phlebotomy technique: excessive fist clenching, prolonged tourniquet time 3
• Hemolysis during sample collection or processing 3
• Delayed specimen processing 3
• Thrombocytosis or leukocytosis causing in vitro K+ release 2

True Hyperkalemia Causes

Decreased Renal Excretion (Most Common):

• Acute or chronic kidney disease (present in 77% of cases) 4
• Medications affecting RAAS: ACE inhibitors, ARBs, aldosterone antagonists, direct renin inhibitors 2
• Hyporeninemic hypoaldosteronism (especially in diabetic nephropathy) 5
• Reduced distal sodium delivery to collecting duct 6, 7

Transcellular Shift:

• Metabolic acidosis 2
• Hyperglycemia and insulin deficiency (present in 49% of cases) 4
• Medications: beta-blockers, digoxin toxicity, succinylcholine 5
• Tissue breakdown: rhabdomyolysis, tumor lysis syndrome, hemolysis 8

Increased Intake (Usually with Impaired Renal Function):

• High-potassium diet 7
• Salt substitutes containing potassium 2
• Potassium supplements or nutraceuticals 2

History

Key Characteristics to Elicit

• Symptoms are often nonspecific or absent, especially in chronic hyperkalemia 2
• Muscle weakness or paralysis (when present, indicates severe hyperkalemia) 2, 8
• Paresthesias 3
• Palpitations or syncope (cardiac manifestations) 8

Red Flags

• Rapid onset of symptoms suggesting acute hyperkalemia 2
• Severe muscle weakness or ascending paralysis 2
• Cardiac symptoms: palpitations, chest pain, syncope 8
• K+ ≥6.5 mEq/L (medical emergency) 1, 8
• Any ECG changes consistent with hyperkalemia 1

Risk Factors to Assess

• Chronic kidney disease or acute kidney injury 4, 6
• Diabetes mellitus (especially with nephropathy) 5
• Heart failure 2
• Current medications: RAAS inhibitors, NSAIDs, potassium-sparing diuretics, trimethoprim, heparin 2
• Recent medication changes or dose escalations 2
• Dietary history: high-potassium foods, salt substitutes 2
• Dehydration or acute illness 5
• History of previous hyperkalemia episodes 2

Physical Examination (Focused)

Cardiovascular

• Heart rate and rhythm (bradycardia or arrhythmias) 8
• Blood pressure (assess for hypertension or hypotension) 6
• Signs of heart failure: elevated JVP, peripheral edema, pulmonary crackles 2

Neuromuscular

• Muscle strength testing (proximal and distal) 2, 8
• Deep tendon reflexes (may be diminished) 8
• Sensory examination for paresthesias 3

Volume Status

• Signs of dehydration: dry mucous membranes, decreased skin turgor 5
• Signs of fluid overload: edema, ascites 2

Other

• Signs of chronic kidney disease: uremic frost, pallor 6
• Evidence of tissue breakdown: muscle tenderness (rhabdomyolysis) 8

Investigations

Immediate Laboratory Tests

• Repeat serum K+ immediately to confirm and rule out pseudohyperkalemia 3
• Serum creatinine and estimated GFR (assess renal function) 2, 6
• Blood glucose (assess for hyperglycemia) 4
• Arterial blood gas or venous bicarbonate (assess for metabolic acidosis) 2
• Complete blood count (assess for thrombocytosis/leukocytosis if pseudohyperkalemia suspected) 2

Urine Studies (To Determine Etiology)

• Urine potassium, creatinine, and osmolarity 5
• Transtubular potassium gradient (TTKG) or urine K+/creatinine ratio (assess renal K+ excretion) 7

Electrocardiogram (ECG)

• Obtain ECG immediately in all patients with K+ >5.5 mEq/L 2
• Expected findings in order of severity: 1
  • Peaked, narrow T waves (earliest change)
  • Flattened or absent P waves
  • Prolonged PR interval
  • Widened QRS complex
  • Sine wave pattern (pre-arrest rhythm)
• Important: ECG changes are highly variable and not sensitive; only 14% of hyperkalemia cases show typical ECG abnormalities 2, 4

Additional Tests

• Medication review (identify contributing drugs) 2, 6
• Plasma renin and aldosterone levels (if hyporeninemic hypoaldosteronism suspected) 5

Empiric Treatment

For Severe Hyperkalemia (K+ ≥6.5 mEq/L) or Any ECG Changes

Step 1: Cardiac Membrane Stabilization (Immediate, within 1-3 minutes) 2, 1

• Calcium chloride 10%: 5-10 mL (500-1000 mg) IV over 2-5 minutes (preferred) 1
• Alternative: Calcium gluconate 10%: 15-30 mL IV over 2-5 minutes 1
• Onset: 1-3 minutes; Duration: 30-60 minutes 2, 1
• Does NOT lower serum K+, only stabilizes cardiac membranes 1
• Repeat dose if no ECG improvement in 5-10 minutes 2
• Monitor for bradycardia during administration 1

Step 2: Shift K+ Into Cells (Onset 15-30 minutes, Duration 4-6 hours) 1

• Insulin + Glucose: 10 units regular insulin IV with 25g glucose (50 mL D50W) over 15-30 minutes 1
• Nebulized albuterol: 10-20 mg over 15 minutes 1
• Sodium bicarbonate: 50 mEq IV over 5 minutes (only if concurrent metabolic acidosis) 2, 1
• These are temporary measures; rebound hyperkalemia can occur after 2 hours 1

Step 3: Eliminate K+ From Body (Definitive Treatment) 1

• Loop diuretics: Furosemide 40-80 mg IV (only effective with adequate renal function) 1, 5
• Cation exchange resins: Sodium polystyrene sulfonate 15-50g orally or rectally 1, 5
• Newer K+ binders: Patiromer or sodium zirconium cyclosilicate (safer alternatives) 2, 1
• Hemodialysis: most effective method for severe or refractory hyperkalemia, especially with renal failure 1, 8

For Moderate Hyperkalemia (K+ 6.0-6.4 mEq/L) Without ECG Changes

• Initiate Step 2 and Step 3 treatments above 1
• May omit calcium if no ECG changes 2

For Mild Hyperkalemia (K+ 5.0-5.9 mEq/L)

• Discontinue or adjust contributing medications 2, 6
• Dietary potassium restriction 2
• Consider loop or thiazide diuretics (if adequate renal function) 2
• Consider newer K+ binders if on RAAS inhibitors for cardiovascular disease 2, 1

Chronic Hyperkalemia Management

• For patients on RAAS inhibitors with K+ >5.0 mEq/L: initiate approved K+ binder and maintain RAAS inhibitor therapy 2, 1
• For K+ >6.5 mEq/L: discontinue or reduce RAAS inhibitor, initiate K+ binder when levels >5.0 mEq/L 2
• Monitor K+ levels within 7-10 days after starting or increasing RAAS inhibitor doses 2

Indications to Refer

Emergency Department/Hospital Admission

• K+ ≥6.5 mEq/L (medical emergency) 1, 8
• Any ECG changes consistent with hyperkalemia 1
• Symptomatic hyperkalemia: muscle weakness, paralysis, cardiac symptoms 2, 8
• Acute kidney injury requiring urgent intervention 6
• Refractory hyperkalemia despite medical management 8

Nephrology Referral

• Recurrent hyperkalemia episodes despite management 2
• Need for hemodialysis 1, 8
• Chronic kidney disease with difficult-to-manage hyperkalemia 6
• Suspected hyporeninemic hypoaldosteronism 5
• Need for optimization of RAAS inhibitor therapy in CKD patients 2

Cardiology Referral

• Heart failure patients requiring RAAS inhibitor optimization 2
• Cardiovascular disease patients with recurrent hyperkalemia limiting guideline-directed medical therapy 2

Critical Pitfalls

Diagnostic Pitfalls

• Failing to rule out pseudohyperkalemia before initiating aggressive treatment 3, 1
• Relying solely on ECG findings: only 14% of hyperkalemia cases show typical ECG changes 2, 4
• Not repeating K+ measurement to confirm diagnosis 3
• Ignoring proper phlebotomy technique: avoid excessive fist clenching, minimize tourniquet time 3
• Delayed specimen processing leading to falsely elevated results 3

Treatment Pitfalls

• Administering calcium in patients on digoxin without extreme caution (risk of digoxin toxicity) 8
• Giving insulin without glucose or inadequate glucose, causing hypoglycemia 1
• Using sodium bicarbonate in patients without metabolic acidosis (ineffective) 2, 1
• Expecting diuretics to work in patients with severe renal impairment 1, 5
• Not monitoring for rebound hyperkalemia after temporary measures (insulin, albuterol) wear off 1
• Calcium chloride extravasation through peripheral IV causing tissue injury (use central line when possible) 1

Management Pitfalls

• Discontinuing life-saving RAAS inhibitors unnecessarily instead of using K+ binders 2, 1
• Not monitoring K+ levels 7-10 days after starting or escalating RAAS inhibitor doses 2
• Inadequate follow-up leading to recurrent episodes 4
• Not reviewing all medications that may contribute to hyperkalemia: NSAIDs, trimethoprim, heparin 2, 6
• Failing to address dietary potassium intake and salt substitutes 2
• Overcorrection leading to hypokalemia 1
• Lack of standardized treatment protocols leading to suboptimal management 2