Principles of Safe General Anaesthesia

1. The Four Components of General Anaesthesia

2. Preoperative Assessment & Preparation

• History & physical: Identify comorbidities (cardiovascular, respiratory, renal, hepatic disease), prior anaesthetic problems, allergies, current medications
• Airway assessment: Predict difficult airway (Mallampati scoring, thyromental distance, mouth opening, neck mobility) — anticipation is the cornerstone of airway safety
• Fasting (NPO) status: Reduce aspiration risk — typically 6 h for solids, 2 h for clear fluids
• Premedication: Anxiolytics, antacids, antiemetics, continuation or cessation of medications as appropriate
• Informed consent: Including explicit discussion of risks — awareness, aspiration, cardiovascular events, postoperative nausea/vomiting

3. Standard Monitoring (ASA Standards)

4. Airway Management

1. Assess likelihood of difficult ventilation, difficult intubation, difficulty with patient cooperation, and difficult tracheostomy
2. Actively deliver supplemental oxygen throughout airway management
3. Plan primary AND backup strategies before induction
4. If the airway is anticipated to be difficult → preserve spontaneous ventilation (awake fibreoptic intubation, high-flow nasal oxygen, topical anaesthesia)
5. If unexpected difficulty arises after induction → call for help, use video laryngoscope, LMA, bougie, or surgical airway if needed

"Cannot intubate, cannot oxygenate" (CICO) is a life-threatening emergency — front-of-neck access (emergency cricothyroidotomy) must not be delayed.

5. Phases of General Anaesthesia

A. Induction

• Goals: Smooth, rapid loss of consciousness while maintaining cardiovascular stability and protecting the airway
• Agents: Propofol (most common), etomidate (haemodynamically unstable patients), ketamine (trauma, bronchospasm), thiopental (historical)
• Intubation: Facilitated by non-depolarising NMBAs (rocuronium 1.2 mg/kg, vecuronium 0.1 mg/kg) or succinylcholine for rapid sequence intubation (RSI)
• Preoxygenation: 3 minutes tidal breathing or 8 vital capacity breaths of 100% O₂ to denitrogenate (maximise safe apnoea time)
• RSI is mandatory for full-stomach/aspiration-risk patients: rapid induction + cricoid pressure + intubation without bag-mask ventilation

B. Maintenance

• Aims: Adequate depth (prevent awareness and autonomic responses), haemodynamic stability, optimal ventilation
• Inhalational maintenance: Sevoflurane, isoflurane, desflurane ± nitrous oxide
• Total intravenous anaesthesia (TIVA): Propofol infusion ± remifentanil — preferred when inhalational agents are contraindicated (malignant hyperthermia risk, PONV-prone patients, neuromonitoring)
• Ventilation: Lung-protective strategy (tidal volume 6–8 mL/kg IBW, PEEP 5 cmH₂O, FiO₂ titrated to maintain SpO₂ >95%), EtCO₂ maintained in normal range (35–45 mmHg)
• Fluid management: Balanced crystalloids; goal-directed therapy in major surgery; avoid hyperglycaemia
• Temperature: Active warming (forced-air blanket, fluid warmers)

C. Emergence & Extubation

• Criteria for extubation: Awake, following commands, adequate spontaneous ventilation (RR >8, tidal volume >5 mL/kg), SpO₂ >95% on FiO₂ 0.4, reversal of neuromuscular blockade confirmed (train-of-four ratio ≥0.9), normothermic, haemodynamically stable
• Reversal of NMB: Neostigmine + glycopyrrolate (acetylcholinesterase inhibitors), or sugammadex (for rocuronium/vecuronium — preferred for deep block)
• Smooth emergence: Avoid bucking/hypertension — use lidocaine IV, remifentanil, or dexmedetomidine
• Post-extubation: Supplemental O₂, lateral recovery position, monitor for laryngospasm and re-obstruction

6. Prevention of Critical Complications

7. Drug Safety Principles

• Never administer NMBAs without confirmed IV access and ability to ventilate — awake paralysis is a medico-legal emergency
• Label all syringes at the time of drawing and before administration
• Verify drug and dose — medication errors are a leading cause of awareness and cardiac arrest
• Maintain anaesthetic continuity — do not allow vaporiser to empty or TIVA infusion to run dry

8. WHO Surgical Safety Checklist

• Sign In (before induction): patient identity, procedure, site marked, anaesthetic machine and medication check, pulse oximetry, allergy/difficult airway/aspiration risk, blood loss risk
• Time Out (before skin incision): team introductions, procedure confirmation, antibiotic prophylaxis, anticipated critical events
• Sign Out (before leaving OR): instrument/sponge counts, specimen labelling, equipment concerns, recovery plan

Summary

"The four components of general anesthesia are usually achieved in modern anesthesia by a combination of IV anesthetics and analgesics, inhalational anesthetics, and, frequently, muscle relaxants. Because the drugs that produce these components cause both desirable and undesirable physiologic changes, the pharmacologic effects of the agents must be matched to the pathophysiology of the patient's comorbidities." — Sabiston Textbook of Surgery, p. 345

• Morgan and Mikhail's Clinical Anesthesiology, 7e
• Sabiston Textbook of Surgery, p. 344–346
• Miller's Anesthesia, 10e

Osteomyelitis

1. Pathogenesis & Routes of Infection

1. Haematogenous spread — bacteria seed bone during bacteraemia; the most common route in children and for vertebral osteomyelitis in adults
2. Contiguous spread — from adjacent infected soft tissue, or after surgery/trauma (open fractures, joint replacement, sternal surgery)
3. Vascular insufficiency / neuropathy — chronic progressive deep soft tissue infection, most commonly diabetic foot

Why the Metaphysis?

2. Microbiology

3. Classification

By Duration

The presence or absence of bone necrosis (sequestrum), not a specific duration, is the critical determinant guiding management. — Harrison's, p. 1106

Cierny-Mader Classification (Long Bone Osteomyelitis)

• Type I — Medullary (endosteal) infection
• Type II — Superficial (cortical surface only)
• Type III — Localized (full-thickness cortex, stable bone)
• Type IV — Diffuse (segmental instability, worst prognosis)

• Class A — Normal immune system and vascularity
• Class B — Locally (BL) or systemically (BS) compromised
• Class C — Treatment worse than disease; suppressive therapy only

4. Pathological Stages & Morphology

Acute Phase

• Bacteria proliferate → neutrophilic infiltration
• Necrosis of bone cells and marrow within 48 hours
• Infection spreads via Haversian canals to periosteum
• Subperiosteal abscess formation (especially in children)
• Periosteal elevation → impairs blood supply → amplifies necrosis
• Pus formation → pus passes through cortical bone; if periosteum is breached → soft tissue abscess → sinus tract to skin

Chronic Phase

• Sequestrum — devascularised dead bone (hallmark of chronic osteomyelitis)
• Involucrum — periosteal new bone formed around the sequestrum; may encase it → "bone-within-a-bone" appearance
• Brodie's abscess — a subacute form; well-defined lytic lesion with sclerotic rim on imaging; typically in young males
• Sinus tracts — pus tracks through gaps in involucrum to the skin surface

5. Clinical Features

Acute Haematogenous Osteomyelitis (Children)

• Fever, malaise, toxaemia
• Localised bone pain, tenderness, erythema, warmth, swelling over the affected metaphysis
• Pseudoparalysis / refusal to bear weight / move limb
• May coexist with sympathetic joint effusion or frank septic arthritis

Vertebral Osteomyelitis (Adults)

• Back pain (most common presenting symptom, >85%)
• Lumbar spine 60%, thoracic 30%, cervical 10%
• Fever in only ~50% of patients (analgesic use blunts this)
• Neurological deficit if epidural abscess complicates
• Primary foci: urinary tract, skin/soft tissue, intravascular catheter, endocarditis

Chronic Osteomyelitis

• Persistent or recurrent pain, discharging sinus tracts, systemic malaise
• Intermittent flares after years of quiescence

6. Investigations

Radiographic signs of improvement lag behind clinical recovery even on appropriate therapy. — Grainger & Allison's Diagnostic Radiology, p. 1638

7. Treatment

General Principles

• Obtain microbiological diagnosis before starting antibiotics (blood cultures + bone biopsy) — unless sepsis mandates immediate treatment
• Drain pus whenever present
• Rest and splintage of the affected limb
• Treat underlying conditions (diabetes, malnutrition, sickle cell disease)

Antibiotic Therapy

• Flucloxacillin (or nafcillin) IV for MSSA
• Vancomycin IV for MRSA or unknown organism in high-risk settings
• Adjust based on culture and sensitivity results

• Acute without necrosis: 4–6 weeks total (IV then oral step-down)
• Chronic / with sequestrum: 6+ weeks combined with surgery
• Vertebral osteomyelitis: 6 weeks (RCT evidence — 6 weeks = 12 weeks, cure rate ~91% both groups)
• Implant-associated, early (<30 days): debridement + implant retention + 3 months antibiotics
• Implant-associated, late (>30 days): implant removal + 6 weeks antibiotics

Surgical Treatment

8. Special Forms

Brodie's Abscess

• Subacute haematogenous osteomyelitis, mainly in young males
• Well-defined lytic cavity with sclerotic rim, most common in tibial metaphysis
• Penumbra sign on MRI (peripheral high-signal granulation tissue surrounding low-signal abscess)

Vertebral / Spinal Osteomyelitis (Spondylodiscitis)

• Most common form of haematogenous osteomyelitis in adults
• MRI shows T2 hyperintensity in disc and adjacent vertebrae + gadolinium enhancement
• Complications: epidural abscess, spinal cord compression, vertebral collapse, psoas abscess

Diabetic Foot Osteomyelitis

• Arises from progressive deep soft tissue infection
• Diagnosis: "probe-to-bone" test (positive = bone felt through ulcer), MRI
• Treatment: prolonged antibiotics ± surgical debridement ± amputation

Tuberculous Osteomyelitis (Pott's Disease)

• Haematogenous spread from primary pulmonary focus
• Predilection for thoracolumbar vertebrae; insidious onset
• Gibbus deformity, psoas abscess, cord compression
• Tuberculosis dactylitis — "spina ventosa" (cyst-like cavities with diaphyseal expansion)

9. Complications

10. Summary

"Not the duration of infection, but the presence or absence of bone necrosis is crucial. Acute osteomyelitis without bone necrosis can generally be treated with antibiotics alone. In contrast, for chronic osteomyelitis antibiotic treatment should be combined with debridement surgery." — Harrison's Principles of Internal Medicine 22e, p. 1106

• Always obtain blood cultures and bone biopsy before antibiotics (unless septic)
• MRI is the imaging gold standard
• S. aureus is the cause in ~80–90% of culture-positive cases
• Oral antibiotics are non-inferior to IV when bioavailability is adequate (2025 meta-analysis, PMID 40280255)
• Surgery is required for chronic osteomyelitis with sequestrum, implant-associated infection, and vertebral disease with neurological compromise

• Robbins Pathologic Basis of Disease, p. 989–993
• Harrison's Principles of Internal Medicine 22e, pp. 1104–1109
• Bailey & Love's Short Practice of Surgery, 28e, pp. 655–657
• Grainger & Allison's Diagnostic Radiology, p. 1620–1644
• Rockwood & Green's Fractures in Adults, 10e (Cierny-Mader Classification)
• Schwartz's Principles of Surgery, 11e