How should hyponatremia be managed in patients scheduled for elective surgery?

Management of Hyponatremia in Elective Surgery

Elective surgery should be postponed in patients with serum sodium <130 mmol/L until hyponatremia is corrected, as preoperative hyponatremia significantly increases perioperative mortality and major complications. 1

Risk Assessment and Decision to Proceed

Preoperative Sodium Thresholds

• Serum sodium <130 mmol/L represents a critical threshold where elective surgery should be delayed, as this level is associated with a 60-fold increase in hospital mortality (11.2% vs 0.19% in normonatremic patients) 2
• Patients with sodium 130-135 mmol/L (mild hyponatremia) carry increased risk but may proceed with surgery if asymptomatic, though closer perioperative monitoring is essential 2, 1
• Preoperative hyponatremia increases adjusted odds of major complications by 37% (adjusted OR = 1.37; 95% CI, 1.23-1.53) and early mortality hazard by 27% (adjusted HR = 1.27; 95% CI, 1.13-1.43) 1
• Hyponatremia performs as a specific prognosticator with 88% specificity for major complications, making it a valuable clinical indicator 1

High-Risk Surgical Populations

• Women undergoing elective surgery face disproportionate risk, with case series documenting severe postoperative hyponatremia leading to seizures, respiratory arrest, and permanent brain damage in previously healthy women (mean age 41 years) 3
• Hip and knee arthroplasty patients develop hyponatremia in 40% of cases postoperatively, with 7% experiencing moderate-to-severe deficiencies 4
• Risk factors include female sex, older age, lower body weight, preoperative hyponatremia, and use of thiazides or ACE inhibitors 4

Preoperative Evaluation and Correction

Diagnostic Workup

• Obtain serum sodium, serum osmolality, urine osmolality, and urine sodium concentration to determine the underlying etiology and guide treatment 2
• Assess extracellular fluid volume status through physical examination: look for orthostatic hypotension, dry mucous membranes, decreased skin turgor (hypovolemia) versus peripheral edema, ascites, jugular venous distention (hypervolemia) 2
• Check thyroid function (TSH) and morning cortisol to exclude hypothyroidism and adrenal insufficiency 2
• Serum uric acid <4 mg/dL has 73-100% positive predictive value for SIADH 2

Treatment Based on Volume Status

For Hypovolemic Hyponatremia:

• Discontinue diuretics immediately if sodium <125 mmol/L 2
• Administer isotonic saline (0.9% NaCl) for volume repletion at 15-20 mL/kg/h initially, then 4-14 mL/kg/h based on response 2
• Urine sodium <30 mmol/L predicts 71-100% response to saline infusion 2

For Euvolemic Hyponatremia (SIADH):

• Implement fluid restriction to 1 L/day as first-line treatment 5, 2
• Add oral sodium chloride 100 mEq three times daily if fluid restriction fails 2, 6
• Consider urea or demeclocycline for refractory cases 5, 2
• Avoid vaptans (tolvaptan) in the immediate preoperative period due to risk of overly rapid correction and need for hospital monitoring 7, 8

For Hypervolemic Hyponatremia (Heart Failure, Cirrhosis):

• Fluid restriction to 1-1.5 L/day for sodium <125 mmol/L 2
• Temporarily discontinue diuretics if sodium <125 mmol/L 2
• In cirrhotic patients, consider albumin infusion alongside fluid restriction 2
• Never use hypertonic saline unless life-threatening symptoms present, as it worsens ascites and edema 2

Critical Correction Rate Guidelines

Standard Correction Targets

• Maximum correction must not exceed 8 mmol/L in 24 hours to prevent osmotic demyelination syndrome 5, 2, 7
• Target correction rate of 4-6 mmol/L per day for chronic hyponatremia 2
• Monitor serum sodium every 4-6 hours during active correction 2

High-Risk Populations Requiring Slower Correction

• Patients with advanced liver disease, alcoholism, malnutrition, or prior encephalopathy require even more cautious correction at 4-6 mmol/L per day (maximum 8 mmol/L in 24 hours) 2, 7
• The FDA label for tolvaptan explicitly warns that "in susceptible patients, including those with severe malnutrition, alcoholism or advanced liver disease, slower rates of correction may be advisable" 7

Perioperative Management

Timing of Surgery

• Allow minimum 48-72 hours for correction of moderate-to-severe hyponatremia before proceeding with elective surgery 2
• For mild hyponatremia (130-135 mmol/L) in asymptomatic patients, surgery may proceed with enhanced monitoring 2
• Emergency surgery in hyponatremic patients requires ICU-level monitoring and nephrology consultation 2

Intraoperative Fluid Management

• Use isotonic fluids (0.9% NaCl or lactated Ringer's) for maintenance during surgery, avoiding hypotonic fluids 2
• Isotonic balanced solutions are preferred maintenance fluid therapy to prevent worsening hyponatremia 2
• Monitor for syndrome of inappropriate antidiuresis (SIAD), which commonly develops postoperatively due to pain, nausea, and stress 2

Postoperative Monitoring

• Check serum sodium at 8 hours and 24 hours postoperatively, as the case series of healthy women showed average time to seizures was 49 hours post-surgery with mean sodium of 108 mmol/L 3
• Monitor for net fluid retention, which averaged 7.5 liters in the catastrophic case series 3
• Watch for early symptoms: nausea, headache, confusion, which may be mistaken for routine postoperative sequelae 4, 3
• Severe symptoms (seizures, altered mental status) require immediate treatment with 3% hypertonic saline targeting 6 mmol/L correction over 6 hours 9

Common Pitfalls to Avoid

• Never proceed with elective surgery in patients with sodium <130 mmol/L without correction, as this dramatically increases mortality and morbidity 2, 1
• Avoid misattributing hyponatremic symptoms (confusion, weakness, nausea) to routine postoperative recovery, leading to delayed diagnosis 4, 3
• Do not use hypotonic IV fluids postoperatively in patients at risk for SIAD (pain, nausea, stress), as this is entirely preventable and affects 15-30% of hospitalized patients 2
• Never correct chronic hyponatremia faster than 8 mmol/L in 24 hours, even if symptoms seem severe, as osmotic demyelination syndrome can cause permanent neurological disability or death 5, 2, 7
• In the catastrophic case series, delayed recognition led to misdiagnosis of acute cerebral vascular disorder, resulting in unnecessary CT scans, angiography, and brain biopsies while hyponatremia went untreated 3
• Avoid fluid restriction in neurosurgical patients with cerebral salt wasting, as this worsens outcomes; these patients require volume and sodium replacement 5, 2

Special Considerations for Specific Surgical Populations

Orthopedic Surgery (Hip/Knee Arthroplasty)

• Hyponatremia occurs in 40% of cases, with identifiable risk factors including female sex, older age, lower body weight, and bilateral procedures 4
• Thiazides and ACE inhibitors are the only medications significantly associated with postoperative hyponatremia 4
• Consider holding thiazide diuretics 48-72 hours preoperatively in high-risk patients 4

Neurosurgical Patients

• Distinguish between SIADH and cerebral salt wasting (CSW), as treatments are opposite: SIADH requires fluid restriction, CSW requires volume and sodium replacement 5, 2
• Fludrocortisone may be considered for hyponatremia in subarachnoid hemorrhage patients at risk of vasospasm 5
• Never use fluid restriction in subarachnoid hemorrhage patients at risk of vasospasm 5

Cirrhotic Patients

• Hyponatremia in cirrhosis increases risk of spontaneous bacterial peritonitis (OR 3.40), hepatorenal syndrome (OR 3.45), and hepatic encephalopathy (OR 2.36) 2
• Correction rates must be even more conservative (4-6 mmol/L per day) due to higher risk of osmotic demyelination 2, 7
• Albumin infusion may improve hyponatremia in hospitalized cirrhotic patients 2