18.3 Perioperative Anticoagulation, Bridging & Postoperative Complications

Anticoagulation & Heparin Bridging Protocols

Direct Oral Anticoagulants (DOACs: Apixaban, Rivaroxaban, Dabigatran, Edoxaban)

• Rapid Onset & Offset: DOACs have predictable half-lives (8–14 hours). Routine heparin bridging is NOT indicated for DOACs (bridging provides no thrombotic protection and dramatically increases major bleeding complications).
• Discontinuation Timing:
  • Low/Moderate Bleeding Risk & Normal Renal Function: Hold 24 hours prior to surgery (skip 2 doses of Apixaban/Dabigatran, skip 1 dose of Rivaroxaban).
  • High Bleeding Risk OR Renal Impairment (CrCl 30–50 mL/min, particularly Dabigatran): Hold 48 to 72 hours prior to surgery (skip 4–6 doses).
  • Severe Renal Impairment (CrCl < 30 mL/min on Dabigatran): Hold >= 72 to 96 hours.
• Postoperative Resumption: Resume DOAC at full dose 24 hours postoperatively for low bleeding-risk procedures, or 48 to 72 hours postoperatively for high bleeding-risk surgeries once definitive surgical hemostasis is established.

Warfarin Management & Heparin Bridging Guidelines

• Preoperative Warfarin Management: Discontinue Warfarin 5 days prior to surgery to allow the INR to normalize to < 1.5 on the day of surgery. If the INR remains >= 1.5 on the day prior to surgery, administer low-dose oral Vitamin K (1 to 2.5 mg).

1. Postoperative Complications

The 5 Ws of Postoperative Fever

Postoperative fever is a common clinical challenge. Systematic evaluation follows the classic "5 Ws" chronologic framework:

1. Wind (Postoperative Days 1–2):
   • Etiology: Atelectasis is the most common cause of fever in the first 48 hours, caused by shallow breathing, diaphragmatic splinting, and alveolar collapse. Early aspiration pneumonia can also manifest in this window.
   • Management: Aggressive pulmonary toilet, incentive spirometry, early ambulation, and effective pain control. (Routine antibiotics are NOT indicated for uncomplicated atelectasis).
2. Water (Postoperative Day 3):
   • Etiology: Urinary Tract Infection (UTI), strongly associated with prolonged indwelling urethral (Foley) catheterization.
   • Management: Prompt catheter removal, urinalysis, urine culture, and targeted antimicrobial therapy.
3. Wound (Postoperative Days 5–7):
   • Etiology: Surgical Site Infection (SSI), ranging from superficial incisional cellulitis to deep fascial necrosis or intra-abdominal/organ-space abscesses.
   • Clinical Signs: Erythema, warmth, localized induration, purulent wound drainage, wound dehiscence, fluctuance, and focal tenderness.
   • Management: Open surgical incision, evacuate purulence, debride necrotic tissue, pack wound with moist sterile gauze, obtain wound cultures, and initiate systemic antibiotics if surrounding cellulitis or systemic toxicity is present.
4. Walking (Postoperative Days 7–10+):
   • Etiology: Deep Vein Thrombosis (DVT) and Pulmonary Embolism (PE) resulting from perioperative immobilization, endothelial injury, and surgical hypercoagulability.
   • Clinical Signs: Unilateral lower extremity swelling, calf tenderness; acute pleuritic chest pain, tachypnea, tachycardia, and hypoxemia.
   • Management: Diagnostic lower extremity venous duplex ultrasound or CT Pulmonary Angiography (CTPA); immediate therapeutic anticoagulation (LMWH, DOAC, or IV heparin).
5. Wonder Drugs (Anytime / POD > 7):
   • Etiology: Drug-induced fever (antibiotics [beta-lactams, sulfonamides], Heparin-Induced Thrombocytopenia [HIT], anticonvulsants), blood product transfusion reactions, or Malignant Hyperthermia (immediate intraoperative).

Malignant Hyperthermia (MH)

• Pathophysiology: A life-threatening, autosomal dominant pharmacogenetic disorder of skeletal muscle excitation-contraction coupling. Most commonly caused by gain-of-function mutations in the ryanodine receptor 1 gene (RYR1) on chromosome 19q13.1 (or the voltage-gated calcium channel alpha-1S subunit gene [CACNA1S]).
• Triggering Agents:
  1. Volatile Halogenated Inhalational Anesthetics: Sevoflurane, Desflurane, Isoflurane, Halothane.
  2. Depolarizing Neuromuscular Blocker: Succinylcholine.
  • (Safe Anesthetics: Propofol, etomidate, ketamine, barbiturates, opioids, local anesthetics, and non-depolarizing neuromuscular blockers like rocuronium and vecuronium are completely safe).
• Pathogenesis: Exposure to triggers leads to uncontrolled, massive efflux of calcium from the sarcoplasmic reticulum into the myoplasm via dysfunctional RYR1 channels. This triggers sustained, hyperactive actin-myosin cross-bridging, causing intense muscle contraction, massive ATP consumption, aerobic/anaerobic hypermetabolism, extreme heat production, metabolic acidosis, rhabdomyolysis, and myocyte lysis.
• Clinical Presentation:
  • Earliest & Most Sensitive Sign: Unexplained, rapid, progressive elevation in End-Tidal CO2 (ETCO2 / hypercarbia) that is refractory to substantial increases in minute ventilation.
  • Muscle Rigidity: Masseter muscle spasm (trismus) following succinylcholine administration; generalized skeletal muscle rigidity ("wooden-chest").
  • Autonomic Instability: Sinus tachycardia, tachypnea, labile blood pressure, and ventricular arrhythmias.
  • Hyperthermia: Rapidly rising core body temperature (frequently exceeding 40.0°C to 42.0°C [104.0°F to 107.6°F], rising up to 1°C every 5 minutes); hyperthermia is a late sign but confirms catastrophic hypermetabolism.
  • Laboratory Findings: Severe mixed respiratory and lactic acidosis, profound hyperkalemia (from myocyte necrosis; can trigger fatal ventricular fibrillation), markedly elevated serum creatine kinase (CK > 10,000 to 100,000 U/L), hyperphosphatemia, and myoglobinuria (cola-colored urine leading to acute tubular necrosis).
• Emergency Resuscitation Protocol:
  1. Immediately Discontinue Triggering Agents: Stop all volatile anesthetics and succinylcholine; shut off vaporizers. Maintain anesthesia with IV propofol/opioids.
  2. Hyperventilate with 100% Oxygen: Deliver 100% high-flow O2 at >= 10 L/min using clean circuit to blow off excess CO2.
  3. Administer IV Dantrolene Sodium (Definitive Antidote): Initial bolus dose of 2.5 mg/kg IV rapidly, repeated every 5 to 10 minutes until hypercarbia, rigidity, and tachycardia resolve (cumulative doses up to 10 to 30 mg/kg may be required). Mechanism: Dantrolene directly binds to the RYR1 channel, inhibiting sarcoplasmic calcium release and halting uncontrolled muscle hypermetabolism.
  4. Active Aggressive Cooling: Infuse cold (4°C) IV normal saline (500–1000 mL); apply ice packs to axillae, groin, and neck; perform cold gastric/bladder lavage. Stop cooling when core temperature reaches < 38.5°C to avoid rebound hypothermia.
  5. Treat Life-Threatening Hyperkalemia: IV Calcium chloride (10 mL of 10% solution) or Calcium gluconate, IV Regular Insulin (10 units) + 50% Dextrose (50 mL), IV Sodium bicarbonate (50 mEq), and nebulized Albuterol.
  6. Maintain Renal Perfusion: Administer IV fluids and IV Furosemide/Mannitol to achieve target urine output > 1 to 2 mL/kg/hour, preventing obstructive myoglobinuric acute renal failure.