14.2 Postoperative Complications & Fluid Therapy

Postoperative Complications & Fluid Therapy

Postoperative care requires vigilant clinical monitoring to detect and treat physiological decompensation and surgical complications early. Managing the postoperative surgical patient demands a rigorous, timeline-based diagnostic approach to pyrexia, structured assessment of organ hypoperfusion (notably oliguria), rapid intervention for wound breakdown, and guideline-adherent intravenous fluid prescribing under NICE CG174.

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The Timeline Approach to Postoperative Fever: The "5 Ws"

Postoperative pyrexia (temperature ≥38.0°C) is a frequent clinical challenge. Establishing the time elapsed since the operation provides the single most reliable diagnostic discriminator for identifying the underlying etiology.

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Surgical Wound Complications & Abdominal Evisceration

Surgical wounds heal via complex overlapping phases (haemostasis, inflammation, proliferation, remodelling). Wound complications range from minor superficial infections to catastrophic mechanical disruptions.

Classification of Surgical Site Infections (SSIs)

• Superficial Incisional SSI: Involves only skin and subcutaneous tissue of the incision; diagnosed within 30 days of surgery. Characterised by localized erythema, tenderness, and purulent discharge without fascial involvement.
• Deep Incisional SSI: Involves deep soft tissues (fascia and muscle layers) of the incision. Manifests with systemic pyrexia, fluctuance, deep fascial breakdown, and purulent drainage from the deep layers.
• Organ/Space SSI: Involves any anatomical space deeper than the fascial layers opened or manipulated during surgery (e.g., intra-abdominal abscess, anastomotic leak peritonitis, pelvic collection, subphrenic abscess). Requires urgent contrast-enhanced CT scanning, IV broad-spectrum antimicrobials, and percutaneous or open surgical drainage.

Wound Dehiscence & Burst Abdomen (Evisceration)

Wound dehiscence represents the mechanical separation of previously approximated surgical incision edges. Risk factors include systemic factors (malnutrition, hypoalbuminaemia, active smoking, obesity, chronic corticosteroid therapy, advanced malignancy) and mechanical local factors (wound infection, excessive intra-abdominal pressure from coughing, vomiting, urinary retention, poor suture technique).

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Postoperative Oliguria: Systematic Approach

Acute postoperative oliguria is defined as a urinary output <0.5 mL/kg/h for more than 2 consecutive hours in an adult. In surgical patients, it must be evaluated systematically to differentiate between mechanical obstruction, intravascular hypovolaemia, and established renal parenchymal injury.

                    [ Postoperative Oliguria: <0.5 mL/kg/h ]
                                      │
                     Step 1: Check Catheter Patency
                                      │
        ┌─────────────────────────────┴─────────────────────────────┐
        ▼                                                           ▼
[ Catheter Blocked / Kinked ]                              [ Catheter Patent ]
Flush with 20-50 mL sterile saline                  Assess Volume Status: CRT, JVP, BP, HR
Urine drains freely -> Solved                                      │
                                      ┌─────────────────────────────┴─────────────────────────────┐
                                      ▼                                                           ▼
                             [ Hypovolaemic / Pre-Renal ]                                [ Euvolaemic / Hypervolaemic ]
                             Tachycardia, low BP, dry mucosae                            Elevated JVP, lung crackles, edema
                                      │                                                           │
                             Fluid Challenge:                                            Hold fluids; check U&Es;
                             500 mL balanced crystalloid <15 min                         Evaluate for Acute Tubular Necrosis (ATN)
                             Reassess urine output & hemodynamics                        Consider nephrotoxic drug withdrawal

Stepwise Management of Postoperative Oliguria

1. Step 1: Mechanical Catheter Patency Check (Rule Out Post-Renal):
   • Examine the entire length of the urinary catheter tubing for kinks, dependent loops, or disconnection.
   • Perform a gentle manual flush with 20–50 mL of sterile 0.9% sodium chloride using an aseptic bladder syringe to dislodge intra-luminal blood clots, mucous plugs, or prostatic debris. If fluid cannot be flushed or fails to return, replace the catheter immediately.
2. Step 2: Hemodynamic & Volume Status Assessment (Pre-Renal Differentiation):
   • Review the fluid balance chart: intraoperative blood loss, fluid resuscitation, third-space sequestration, stoma/drain output, and insensible losses.
   • Physical examination: heart rate, blood pressure, capillary refill time (CRT), postural hypotension, jugular venous pressure (JVP), and mucosal hydration.
   • Pre-Renal Hypovolaemia (#1 Cause): If hypovolaemia is identified, immediately administer a fluid challenge of 500 mL balanced crystalloid (e.g. Hartmann's solution or Plasma-Lyte) over <15 minutes.
   • Re-evaluate the clinical response: an increase in blood pressure, deceleration of heart rate, and restoration of urine output to >0.5 mL/kg/h confirms pre-renal hypovolaemia.
3. Step 3: Renal Parenchymal Injury (Intrinsic Renal Cause):
   • If oliguria persists despite adequate intravascular volume restoration, suspect Acute Tubular Necrosis (ATN) secondary to prolonged renal hypoperfusion or nephrotoxic insults (e.g., aminoglycosides, NSAIDs, ACE inhibitors, IV iodinated radiocontrast).
   • Stop all nephrotoxic drugs, monitor electrolytes (hyperkalaemia, metabolic acidosis), review baseline serum creatinine, avoid fluid overloading the anuric patient, and seek urgent nephrology or intensive care guidance.

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Postoperative Paralytic Ileus

Postoperative paralytic ileus is a temporary, functional arrest of gastrointestinal peristalsis occurring in the absence of mechanical luminal obstruction. It is an anticipated physiological response following abdominal surgery, typically resolving within 3 to 5 days.

• Pathophysiology: Caused by surgical handling and mechanical manipulation of bowel loops, local peritoneal inflammation, sympathetic hyperactivation, electrolyte disturbances (particularly hypokalaemia and hypomagnesaemia), and systemic opioid analgesia.
• Clinical Presentation: Persistent nausea, copious bilious vomiting, progressive painless abdominal distension, failure to pass flatus or stool, and absent or sparse hypoactive bowel sounds on auscultation (in contrast to the high-pitched, tinkling, hyperactive 'borborygmi' of mechanical small bowel obstruction).
• Diagnostic Distinction: Plain abdominal radiographs or CT scanning reveal diffuse, uniform gaseous distension involving both small and large bowel loops with air in the rectum, without an identifiable discrete mechanical transition point.
• Management: The "Drip and Suck" Protocol:
  • Drip: Intravenous crystalloid fluid replacement tailored to replace nasogastric and third-space losses, with diligent correction of hypokalaemia (maintain K+ >4.0 mmol/L) and hypomagnesaemia.
  • Suck: Insertion of a wide-bore nasogastric (NG) tube on free drainage with regular 4-hourly aspiration to decompress the stomach, relieve vomiting, and prevent pulmonary aspiration.
  • Conservative Measures: Keep nil-by-mouth; mobilize the patient; discontinue or minimize opioid analgesics (switch to paracetamol, regional epidural/transversus abdominis plane blocks, or low-dose adjuncts); encourage chewing gum (sham feeding stimulates cephalic-vagal gastrointestinal motility).

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Malignant Hyperthermia: Pharmacogenetic Emergency

Malignant Hyperthermia (MH) is a rare, life-threatening pharmacogenetic disorder of skeletal muscle calcium homeostasis inherited in an autosomal dominant pattern with variable penetrance. In >70% of cases, it results from gain-of-function mutations in the ryanodine receptor gene (RYR1) on chromosome 19, which encodes the principal calcium release channel of the sarcoplasmic reticulum.

• Pharmacological Triggers: Triggered by exposure to:
  1. Volatile Inhalational Anaesthetic Agents: Sevoflurane, isoflurane, desflurane, halothane.
  2. Depolarising Neuromuscular Blocking Drugs: Suxamethonium (succinylcholine).
• Pathogenesis: Uncontrolled, massive efflux of intracellular calcium from the sarcoplasmic reticulum into the myoplasm overrides normal sarcoplasmic reticular reuptake mechanisms, producing sustained, intense skeletal muscle contraction, catastrophic aerobic and anaerobic hypermetabolism, rapid depletion of ATP, excessive heat generation, severe lactic acidosis, and massive rhabdomyolysis.
• Clinical Features & Timeline:
  • Earliest & Most Sensitive Sign: Unexplained, rapidly rising end-tidal CO₂ (hypercapnia) that is refractory to massive increases in mechanical minute ventilation.
  • Early Signs: Unexplained sinus tachycardia, tachypnoea, labile blood pressure, and masseter muscle spasm (jaw rigidity) following suxamethonium administration.
  • Hypermetabolic Progression: Severe mixed respiratory and high-anion-gap metabolic (lactic) acidosis, hyperkalaemia, generalized board-like muscle rigidity, cyanosis, skin mottling, and cardiac arrhythmias.
  • Rhabdomyolysis: Massive elevation in serum creatine kinase (CK >20,000 U/L), myoglobinuria (dark red-brown 'tea-coloured' urine), and acute renal failure.
  • Hyperthermia (Late Sign): A dramatic, exponential rise in core body temperature (rising by 1–2°C every 5 minutes, frequently exceeding 41–42°C); hyperthermia is a late, confirmatory manifestation of advanced hypermetabolism.

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Intravenous Fluid Therapy in Adults (NICE CG174 Guidelines)

Prescribing intravenous fluids in surgical inpatients must be treated with the same pharmacological precision as any therapeutic drug. Over-prescription of 0.9% normal saline induces hyperchloraemic metabolic acidosis and tissue edema; under-prescription triggers prerenal hypovolaemia and AKI.

The 4 "Rs" of Fluid Management

1. Resuscitation: Urgent restoration of circulating intravascular volume in patients with shock or severe hypoperfusion.
2. Routine Maintenance: Daily baseline requirements for stable patients unable to meet needs enterally.
3. Replacement: Offsetting ongoing abnormal fluid and electrolyte losses (vomiting, diarrhea, stoma, fistulae, surgical drains, polyuria).
4. Redistribution: Compensating for third-space fluid shifts, gross edema, or hypoalbuminaemia.

Fluid Resuscitation Protocol

If a patient exhibits clinical signs of shock (systolic BP <90 mmHg, HR >100 bpm, CRT >2 seconds, respiratory rate >20, oliguria):

• Immediately administer a 500 mL bolus of crystalloid containing sodium in the range 130–154 mmol/L (e.g., Hartmann's solution, Plasma-Lyte, or 0.9% sodium chloride) over less than 15 minutes.
• Reassess following the ABCDE approach. If the patient remains hypoperfused, repeat 250–500 mL boluses up to a cumulative volume of 2000 mL, seeking senior/intensive care assistance.

Routine Maintenance Requirements (Per 24 Hours)

For an adult who is clinically euvolaemic and has no ongoing abnormal fluid losses: