In a 69-year-old woman with atrial fibrillation on a direct oral anticoagulant who fell and required operative fixation of a hip fracture, what medication regimen and which laboratory and imaging studies are indicated?

Management of Hip Fracture in a 69-Year-Old Woman on DOAC

Resume the DOAC within 24-72 hours postoperatively once surgical hemostasis is achieved, using prophylactic LMWH or fondaparinux starting at least 6 hours after surgery until therapeutic anticoagulation is restarted. 1

Immediate Postoperative Anticoagulation Strategy

The patient has already undergone hip fracture surgery, so the focus shifts to postoperative thromboprophylaxis and resumption of anticoagulation for atrial fibrillation:

VTE Prophylaxis Protocol

• Start prophylactic anticoagulation ≥6 hours post-surgery with either LMWH, UFH, or fondaparinux 1
• Continue prophylactic dosing until therapeutic DOAC is resumed
• No bridging with therapeutic-dose heparin is needed unless the patient has very high thrombotic risk 1

DOAC Resumption Timeline

The therapeutic DOAC should be restarted 24-72 hours postoperatively when surgical hemostasis is confirmed 1. The specific timing depends on:

• Bleeding risk assessment at the surgical site
• Absence of ongoing bleeding
• Stable hemoglobin (though her Hb has dropped from 9.8 to 7.0 g/L, requiring transfusion first)

Critical timing detail: Administer the first therapeutic DOAC dose 12 hours after the last prophylactic LMWH dose to avoid overlap and excessive anticoagulation 1

Urgent Laboratory and Clinical Issues

1. Severe Hyponatremia (Sodium 124-133 mEq/L)

This is the most pressing metabolic abnormality requiring immediate attention:

• Assess volume status clinically (orthostatic vitals, skin turgor, mucous membranes)
• The urine sodium of 34 mEq/L with low serum osmolality (274 mOsm/kg) and low urine osmolality (210 mOsm/kg) suggests euvolemic hyponatremia, possibly SIADH from pain, surgery, or medications
• Fluid restriction is first-line if SIADH confirmed
• Monitor sodium q6-12h initially; correct slowly (≤8-10 mEq/L per 24 hours) to avoid osmotic demyelination
• Consider hypertonic saline only if symptomatic (confusion, seizures)

2. Progressive Anemia (Hb 9.8 → 7.0 g/L)

• Transfuse packed RBCs to maintain Hb >8 g/dL in this elderly patient with cardiovascular comorbidities (atrial fibrillation)
• The drop from 9.8 to 7.0 g/dL represents significant perioperative blood loss
• Recent evidence shows DOAC patients may have 15% greater blood loss and transfusion rates up to 40% 2
• Recheck CBC daily until stable

3. Elevated INR (2.2) and PT (25.7)

• This elevation is likely residual DOAC effect, not warfarin-related
• No reversal needed at this point post-surgery unless active bleeding
• Will normalize as DOAC clears; recheck before resuming therapeutic anticoagulation

4. Renal Function Monitoring

• Creatinine has varied (1.06 → 0.94 → 0.77 mg/dL), with eGFR 76-97 mL/min
• Monitor creatinine postoperatively as renal function affects DOAC dosing 1
• Calculate CrCl using Cockcroft-Gault formula for DOAC dose adjustment

Medication Regimen

Immediate (Days 1-3 Post-Op):

1. Prophylactic anticoagulation (choose one):

   • Enoxaparin 40 mg SC daily (if CrCl >30 mL/min)
   • Fondaparinux 2.5 mg SC daily
   • UFH 5000 units SC q8-12h

2. Pain management (multimodal approach)

3. Fluid restriction for hyponatremia (likely 1000-1500 mL/day)

4. Transfuse PRBCs to Hb >8 g/dL

Days 2-3 Post-Op (Once Hemostasis Confirmed):

Resume therapeutic DOAC for atrial fibrillation 3:

• If on apixaban: 5 mg BID (or 2.5 mg BID if ≥2 of: age ≥80, weight ≤60 kg, Cr ≥1.5 mg/dL) 1
• If on rivaroxaban: 20 mg daily (15 mg if CrCl 30-49 mL/min) 1
• If on dabigatran: 150 mg BID (110 mg BID if age ≥80 or on verapamil) 1
• Give 12 hours after last prophylactic LMWH dose 1

Extended Prophylaxis:

For hip fracture surgery, extended thromboprophylaxis for 28-35 days total is indicated 1. Since she's resuming therapeutic anticoagulation for atrial fibrillation, this provides adequate VTE coverage.

Required Tests

Daily Monitoring (Until Stable):

• Sodium (q6-12h initially, then daily until >135 mEq/L)
• CBC (daily until Hb stable)
• Creatinine/eGFR (every 2-3 days)

Before DOAC Resumption:

• PT/INR, aPTT (ensure normalizing)
• Hemoglobin (ensure >8 g/dL and stable)
• Creatinine (for dose adjustment)

Additional Monitoring:

• Calcium, magnesium, phosphorus (all low; replete as needed)
• Serum osmolality and urine osmolality (already done; confirms hyponatremia etiology)

Common Pitfalls to Avoid

1. Don't delay DOAC resumption excessively: While older protocols suggested 48-72 hour delays, recent evidence shows early surgery (12-24 hours after last DOAC dose) is safe 4, and therapeutic resumption at 24-48 hours doesn't increase mortality 4, 5

2. Don't overlap prophylactic and therapeutic anticoagulation: Wait 12 hours between last LMWH and first therapeutic DOAC dose 1

3. Don't correct sodium too rapidly: Risk of osmotic demyelination syndrome with correction >10-12 mEq/L in 24 hours

4. Don't use neuraxial anesthesia with residual DOAC: This patient has already had surgery, but for future reference, avoid spinal/epidural with any DOAC on board 1

5. Don't forget osteoporosis evaluation: This patient needs bone health assessment and treatment to prevent future fractures 3

Evidence Considerations

The most recent high-quality evidence 4 from 2023 shows that early surgery within 48 hours is safe for DOAC patients without increased transfusion or mortality risk. A 2026 study 5 found higher mortality in DOAC patients but similar transfusion rates with levels <80 ng/mL, suggesting the mortality difference relates to patient comorbidities rather than bleeding. The guideline-based approach 1 of resuming therapeutic anticoagulation at 24-72 hours with prophylactic bridging remains the standard of care and balances stroke prevention against bleeding risk.