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Labour Analgesia — 30-Mark Model Answer (Anaesthesia MD Examination)

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Introduction

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1. Physiology and Pathways of Labour Pain (5 marks)

First Stage of Labour

• Pain is visceral in origin - from uterine contractions, cervical dilation, and lower uterine segment distension.
• Afferent impulses travel via the uterine and cervical plexuses through sympathetic nerves, entering the spinal cord at T10-L1.
• Character: crampy, poorly localised, referred to the umbilicus, lower abdomen, and lumbar region.

Second Stage of Labour

• Pain becomes somatic as the presenting part descends and distends the vagina, perineum, and pelvic floor.
• Afferent impulses travel via the pudendal nerve (S2-S4) and posterior cutaneous nerve of the thigh.
• Sensory block must extend from T10 to S4 to cover both stages.

Physiological Consequences of Untreated Labour Pain

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2. Non-Pharmacological Methods (3 marks)

• Breathing techniques - Lamaze, Bradley method, LeBoyer technique
• Continuous labour support - doula or partner presence; Cochrane review of 26 trials (n=15,858) showed shorter labour, more spontaneous vaginal deliveries, less pharmacological analgesia
• Hydrotherapy (water immersion / warm bath)
• TENS (Transcutaneous Electrical Nerve Stimulation) - stimulates Aβ fibres, activates gate control mechanism
• Acupuncture/acupressure - Cochrane review of 28 RCTs (n=3,960): acupuncture minimally reduces labour pain and increases maternal satisfaction; acupressure showed no clear benefit over sham
• Massage - Cochrane review of 10 RCTs: reduces pain in first stage; increases sense of control
• Hypnosis - Cochrane review of 9 trials (n=2,954): reduced systemic analgesia use; no clear difference in neuraxial use
• Intradermal sterile water injections, aromatherapy, biofeedback

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3. Pharmacological Methods

3a. Systemic Analgesics (4 marks)

Opioids

Non-opioid Systemic Agents

• Nitrous oxide (Entonox - 50% N2O + 50% O2) - self-administered via facemask at onset of contraction; rapid onset/offset; minimal uterine effects; provides mild-moderate analgesia; safe for fetus; widely used in the UK
• Low-dose ketamine (10–15 mg IV) - excellent analgesia in 2–5 min without loss of consciousness; most useful just prior to delivery or as adjuvant to regional; doses >1 mg/kg cause hypertonic uterine contractions
• Midazolam (≤2 mg IV) - anxiolytic adjunct to neuraxial blockade; chronic diazepam use associated with fetal depression
• NSAIDs - avoid in labour (premature closure of ductus arteriosus)

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3b. Regional (Neuraxial) Techniques (12 marks)

"Using a local anaesthetic-opioid mixture for lumbar epidural analgesia during labor significantly reduces drug requirements when compared with using either agent alone." - Morgan & Mikhail, 7e

I. Epidural Analgesia

1. Patient positioned sitting or left lateral; sterile technique
2. Identify L3-L4 or L2-L3 interspace; loss of resistance technique (saline or air) for epidural space identification
3. Test dose - 3 mL of 1.5% lidocaine + epinephrine 1:200,000; wait 5 minutes
   • Tachycardia (+20-30 bpm) = intravascular placement
   • Rapid dense motor/sensory block = intrathecal placement
4. If test dose negative: administer 10-15 mL of LA-opioid mixture in 5 mL increments
5. Place supine with left uterine displacement; monitor BP every 1-2 min for 15 min

• Bupivacaine 0.0625–0.1% + fentanyl 2 mcg/mL
• Ropivacaine 0.1% + fentanyl 2 mcg/mL (less motor block, safer cardiac profile than bupivacaine)
• Bupivacaine 0.125% + sufentanil 0.5–1 mcg/mL

• First stage: T10–L1
• Second stage: T10–S4

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II. Combined Spinal-Epidural (CSE) Analgesia

1. Epidural needle placed in epidural space as standard
2. Spinal needle (25G Whitacre or Sprotte pencil-point) passed through epidural needle until dural puncture confirmed by CSF
3. Intrathecal injection of opioid ± low-dose LA
4. Spinal needle withdrawn; epidural catheter threaded and secured

• Fentanyl 15–25 mcg (opioid alone - no motor block; "walking epidural")
• Sufentanil 5–7.5 mcg
• Bupivacaine 2.5 mg + fentanyl 15 mcg (excellent initial analgesia)

• Faster onset (2–5 minutes vs 20 min for epidural)
• Dense analgesia; particularly useful for advanced labour
• Low-dose intrathecal component preserves ambulation ("walking epidural")
• Epidural catheter allows top-up for prolonged labour or operative delivery

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III. Spinal (Intrathecal) Analgesia

• Single-shot intrathecal opioid ± LA
• Provides rapid but time-limited analgesia (1.5–3 hours)
• "Saddle block" - hyperbaric tetracaine 3–4 mg or bupivacaine 2.5–5 mg + fentanyl 12.5–25 mcg for second stage/operative vaginal delivery
• Continuous spinal analgesia via intrathecal catheter: used after accidental dural puncture; provides excellent analgesia and utilises the wet tap

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IV. Other Regional Techniques

• Blocks S2-S4 (pudendal nerve), covering perineum/vaginal outlet
• Technique: transvaginal injection beneath ischial spine through sacrospinous ligament, using Koback needle/Iowa trumpet guide; 10 mL of 1% lidocaine or 2% chloroprocaine per side
• Useful for second stage and perineal repair
• Complications: intravascular injection, retroperitoneal haematoma, retropsoas/subgluteal abscess

• Injections at 4 o'clock and 10 o'clock lateral to cervix
• Controls first-stage pain only
• No longer used for viable fetuses - high rate of transient fetal bradycardia (uterine artery proximity, direct fetal drug absorption); risk of injecting into fetal head
• Still used for intrauterine fetal demise, D&C, D&E procedures

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4. Complications of Neuraxial Analgesia (4 marks)

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5. Effect on Labour and the Neonate (2 marks)

• Labour progress: Dilute LA-opioid combinations do NOT prolong labour or increase operative (caesarean or instrumental) delivery rates - this is a Class A evidence finding (Morgan & Mikhail, 7e)
• Fetus/Neonate: Neuraxial analgesia is vastly superior to systemic opioids for fetal safety; systemic opioids (especially meperidine/morphine) cross placenta and cause neonatal respiratory depression, lower Apgar scores, and neurobehavioural depression; neuraxial drugs - being highly dilute - have minimal neonatal effects
• Maternal catecholamines: Effective analgesia reduces catecholamines, improving uteroplacental perfusion

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6. Contraindications to Neuraxial Analgesia

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Summary Table

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Conclusion

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• Miller's Anesthesia, 2-Volume Set, 10th Edition (Elsevier, 2023)
• Morgan & Mikhail's Clinical Anesthesiology, 7th Edition (McGraw Hill, 2022)
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9th Edition

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Anaesthesia for Awake Craniotomy — Comprehensive MD Exam Answer

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1. Introduction and Rationale

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2. Indications

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3. Presurgical Evaluation

Preoperative Neurological Workup

• Wada test (intracarotid sodium amobarbital test) - selective hemisphere anaesthesia to lateralise speech dominance and test bilateral memory representation
• Video-telemetry with EEG electrode placement - for epilepsy surgery, to record and localise ictal events
• Functional MRI (fMRI) / PET scan - non-invasive cortical mapping
• Neuropsychological baseline assessment - establishes cognitive/language function for intraoperative comparison

Patient Selection Criteria

• Motivated, cooperative, psychologically prepared patient
• Able to follow commands and communicate during testing
• No severe anxiety, claustrophobia, or panic disorder
• No obstructive sleep apnoea (high sedation risk with prone/lateral positions)
• No significant language barrier
• No uncontrolled cough, nausea, or movement disorders

• Severe anxiety or inability to cooperate (relative)
• Morbid obesity (airway management challenges with inaccessible airway)
• Obstructive sleep apnoea
• Uncontrolled cough or movement disorder
• Severe nausea or GERD
• Raised intracranial pressure with risk of herniation
• Children (generally not suitable; poor cooperation)
• Patients unable to understand the procedure

• Detailed explanation of all phases (most important - reduces anxiety and intraoperative failure)
• Psychological rehearsal ("walk-through") of the awake testing phase
• Consider anxiolytic premedication carefully - avoid benzodiazepines if ECoG-based seizure focus localisation is planned (anticonvulsant effect masks EEG activity)
• Anti-emetics (ondansetron, dexamethasone) - routine, especially if opioids are planned
• Anticonvulsants: continue or reduce by half depending on whether intraoperative EEG activation is needed
• NPO as per standard guidelines; IV access, arterial line

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4. Anaesthetic Techniques

Technique 1: Monitored Anaesthesia Care (MAC) / Sedation Throughout ("Awake-Awake-Awake")

• Patient is sedated at a light-to-moderate level throughout
• Spontaneous ventilation maintained with unprotected airway
• Titrated sedation reduced during mapping phase
• Best for cooperative patients with good tolerance

Technique 2: Asleep-Awake-Asleep (AAA) with Supraglottic Airway (LMA)

• Most widely practiced technique
• Three distinct phases:

• During the awake phase, the patient communicates with the neuropsychologist/surgeon
• LMA is preferred over ETT for easier removal and less stimulation

Technique 3: Asleep-Awake-Asleep with Endotracheal Tube (ETT)

• Customised ETTs with local anaesthetic installation in glottis/trachea allow awake extubation without cough
• Used when airway concerns preclude LMA
• More stimulating; technically demanding
• Reported but less commonly used than LMA technique

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5. Scalp Nerve Block - The Cornerstone

• Unilateral (ipsilateral to craniotomy) or bilateral depending on incision
• Local anaesthetic: ropivacaine 0.5-0.75% or bupivacaine 0.25-0.5% with or without adrenaline
• Maximum dose calculations mandatory - volumes can be substantial when combined with surgeon's pin-site infiltration and dural infiltration
• Surgeon supplements with local infiltration of pin sites, skin incision, and dura (especially subtemporal dura - most painful area)
• The anesthesiologist must track cumulative LA dose to prevent toxicity

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6. Sedation and Drug Regimens

1. Minimise patient discomfort during painful phases (positioning, pinning, craniotomy)
2. Ensure patient responsiveness and cooperation during mapping
3. Minimal respiratory depression - airway inaccessible in pin fixation
4. Minimal suppression of EEG activity (if ECoG planned)
5. Rapid offset to allow prompt awakening for testing

Drug Options

A. Propofol-Based Regimens

• Propofol infusion (50-150 mcg/kg/min) - most widely used; rapid offset; excellent titrability
• Often combined with remifentanil (0.02-0.05 mcg/kg/min) for analgesia during painful phases
• Or combined with dexmedetomidine (0.2 mcg/kg/h)
• Critical limitation: Propofol must be discontinued at least 15 minutes before EEG/ECoG recording - it leaves a residual high-frequency, high-amplitude beta activity footprint that can obscure seizure activity
• Propofol + remifentanil: synergistic respiratory depression - great caution in pin-fixed patient

B. Dexmedetomidine-Based Regimens

• Dexmedetomidine (α2-adrenergic agonist): loading dose 0.5-1 mcg/kg over 10-20 min, then infusion 0.2-0.7 mcg/kg/h
• Key advantages:
  • Sedation AND analgesia with minimal respiratory depression - safest agent for spontaneous ventilation
  • Cooperative, arousable sedation - patients respond to verbal commands
  • Does not suppress EEG - can be maintained during ECoG recording (0.1-0.5 mcg/kg/h during testing)
  • Anxiolytic without full amnesia - patients remain cooperative
• Disadvantage: Bradycardia, hypotension; slower onset; occasional delays in arousal; less analgesic than opioid combinations
• Comparative study (Barash, 9e): propofol-remifentanil vs dexmedetomidine - similar sedation and mapping efficacy but lower rates of respiratory depression with dexmedetomidine
• Functional testing has been successfully performed with dexmedetomidine 0.1-0.2 mcg/kg/h during neurocognitive testing

C. Remifentanil Alone or Combinations

• Remifentanil infusion: excellent analgesia with rapid offset (context-sensitive half-life ~3 min); risk of respiratory depression and chest wall rigidity; requires vigilant monitoring
• Combination options:
  • Propofol + remifentanil (most commonly used for MAC)
  • Dexmedetomidine + remifentanil (excellent; minimal respiratory depression)
  • Propofol + fentanyl + dexmedetomidine

D. Drugs to Avoid

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7. Monitoring

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8. Intraoperative Phases and Management

Phase 1: Positioning and Pin Fixation

• Most painful phase (pericranium)
• Adequate scalp block before pin application
• Bolus sedation/analgesia at time of pinning
• Patient positioning critical: maximise neck extension and atlanto-occipital positioning before final head holder lockdown - this widens the airway and allows more latitude for sedation
• Visual access to patient's face must be maintained throughout - for speech testing (naming objects) and detecting motor responses during mapping
• Temperature management, pressure-area padding

Phase 2: Skin Incision and Craniotomy

• Moderately to deeply sedated
• Scalp block analgesia covering the incision
• Surgeon infiltrates incision line additionally
• Monitoring SpO2 and ETCO2 continuously

Phase 3: Dural Opening

• Subtemporal dura traction is particularly painful - ensure adequate dural infiltration with LA
• Commence reducing sedation in preparation for awake phase
• If LMA-based AAA: commence waking patient; remove LMA when responsive

Phase 4: Awake Cortical Mapping (Critical Phase)

• Patient fully awake and cooperative
• Electrocorticography (ECoG): cortical surface EEG to localise seizure foci
  • If no spontaneous activity: provocative agents used
  • Methohexital 0.3 mg/kg - safe, effective seizure activation agent
  • Etomidate 0.05-0.1 mg/kg - alternative
  • Alfentanil bolus 30-50 mcg/kg; Remifentanil 2.5 mcg/kg - under GA
  • Hyperventilation - helps activate foci
• Direct cortical stimulation mapping: bipolar stimulator applied to brain surface
  • Motor mapping: observe for movement in contralateral limbs/face
  • Speech mapping: naming task (patient asked to name images) - speech arrest or errors indicate language cortex
  • Sensory mapping: patient reports tingling/paraesthesia
• Dexmedetomidine can be maintained at low rates (0.1-0.2 mcg/kg/h) during mapping without interfering with testing

Phase 5: Tumour Resection and Closure

• Sedation resumed; LMA reinserted if AAA technique
• Anaesthesia for closure

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9. Complications and Management

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10. Postoperative Management

• PACU or ICU observation (neurological observations every 15-30 min initially)
• Multimodal analgesia: paracetamol, NSAIDs (cautiously), scalp infiltration of long-acting LA
• Nausea prophylaxis continued
• Anticonvulsant medication maintained/resumed
• Monitoring for: delayed seizures, neurological deterioration, haematoma (headache, reduced GCS), raised ICP, pneumocephalus
• Steroids (dexamethasone) to reduce cerebral oedema
• VTE prophylaxis when appropriate

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11. Summary Comparison - Anaesthetic Approaches

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Key Examination Points

1. The essential element is the scalp nerve block - sedation cannot compensate for inadequate local anaesthesia
2. Six nerves of the scalp must be blocked: supratrochlear, supraorbital, zygomaticotemporal, auriculotemporal, lesser occipital, greater occipital
3. Propofol must be stopped ≥15 min before ECoG - residual beta activity obscures seizure focus
4. Dexmedetomidine advantage: sedation + analgesia with minimal respiratory depression; can be maintained during mapping at 0.1-0.2 mcg/kg/h
5. Capnography is essential - airway is all but inaccessible with head in pin fixation
6. Avoid benzodiazepines as premedication if ECoG is planned
7. Seizures during mapping - cold saline first; then propofol 0.5-1 mg/kg; wait before giving propofol in case self-limiting
8. Conversion to GA is pre-planned - video laryngoscope must be immediately available

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• Miller's Anesthesia, 2-Volume Set, 10th Edition (Chapter 53: Awake Craniotomy and Seizure Surgery)
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9th Edition (Chapter: Awake Craniotomy)
• Morgan & Mikhail's Clinical Anesthesiology, 7th Edition

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Brain Death and Organ Harvesting — 30-Mark Model Answer (Anaesthesia MD Examination)

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1. Definition and Historical Context

• First codified by the Harvard Ad Hoc Committee in 1968, following the world's first cardiac transplant by Dr Christiaan Barnard in 1967
• Incorporated into the Uniform Determination of Death Act (USA) and legally recognised in most countries
• The legal time of death is the moment the apnoea test confirms PaCO2 criteria are met in the absence of any respiratory effort
• Equivalent terms: death by neurological criteria (DNC), brain stem death (BSD - UK terminology)

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2. Causes of Brain Death

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3. Prerequisites Before Brain Death Testing (5 marks)

A. Establish Irreversible Cause of Coma

• Known, structural, irreversible catastrophic neurological injury
• Neuroimaging (CT/MRI) explains the coma
• Patient has received aggressive treatment (osmotherapy, ICP management, surgery) and further treatment is futile

B. Exclude Confounding Conditions

C. Qualified Examiners

• Two independent doctors (in most countries) - neither involved in transplant team
• Senior physicians (consultant/attending) qualified in neurology, neurosurgery, or intensive care
• Two separate examinations, separated by an appropriate observation period (institution-dependent)

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4. Clinical Examination for Brain Death (8 marks)

A. Level of Consciousness

• Unresponsive to all stimuli
• No purposeful motor response to painful stimulation (deep pressure on condyles of TMJ, supraorbital notch, nail beds, sternal rub)
• Motor responses from spinally-mediated reflexes (Lazarus sign - arms rising and meeting midline) may still occur and are not incompatible with brain death, but require explanation
• Decerebrate or decorticate posturing IS incompatible with brain death

B. Brainstem Reflexes - All Must Be Absent Bilaterally

• Nystagmus or spontaneous eye movements
• Conjugate eye deviation
• Pinpoint pupils (suggests opioid effect)
• Decerebrate/decorticate posturing
• Grimacing to pain

C. Apnoea Test

• Systolic BP ≥100 mmHg (vasopressors if needed)
• PaO2 ≥200 mmHg (pre-oxygenate with 100% O2 for 10 minutes)
• Normalise PaCO2 to baseline (35-45 mmHg) by adjusting ventilator

1. Obtain baseline ABG confirming normocapnia and adequate oxygenation
2. Disconnect from ventilator
3. Deliver 100% O2 via catheter at carina level (6 L/min) - apnoeic oxygenation maintains SpO2
4. Observe for any respiratory effort (chest/abdominal excursion, gasping) for 8-10 minutes
5. Obtain ABG at end of observation period

• No respiratory effort is observed AND
• PaCO2 ≥60 mmHg OR a rise of ≥20 mmHg from a normal baseline PaCO2

• SpO2 falls below 85-90% (despite apnoeic oxygenation)
• Severe haemodynamic instability (hypotension, severe arrhythmia)
• In these cases, proceed to ancillary/confirmatory tests

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5. Ancillary (Confirmatory) Tests

• Clinical exam cannot be completed (e.g., severe facial trauma, severe lung disease preventing apnoea test)
• Confounders cannot be fully excluded
• Legal or institutional requirements
• Religious/cultural objections to clinical criteria alone

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6. Communication with Family

• Family should not be surprised by brain death - they should have been counselled about the prognosis from the time of severe brain injury
• Announcement: "Your loved one has died but is being supported by machines"
• Organ donation discussion occurs separately from the brain death declaration - by organ procurement organisation (OPO) personnel, not the treating team
• In the USA: federal law requires physician to contact the OPO
• Cultural/religious sensitivity mandatory - some faiths (Orthodox Jewish, Japanese tradition) may not accept brain death criteria
• Family refusal remains a major cause of lost donor potential

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7. Types of Organ Donation

A. Donation After Brain Death (DBD)

• Heart-beating donor
• Optimal organ quality (warm ischaemia avoided)
• Allows time for full evaluation and multiple organ procurement
• Accounts for ~70% of deceased donors (USA)

B. Donation After Circulatory (Cardiac) Death (DCD)

• Non-heart-beating donor
• Maastricht Classification:

• Controlled DCD (Cat III) most common: life support withdrawn in OT; organ procurement begins after 5-minute "no-touch" period of confirmed cardiac arrest
• Warm ischaemia time is longer in uncontrolled DCD - reduces organ quality
• DCD accounted for 30.2% of deceased donors in USA in 2021 (Miller's Anesthesia, 10e)

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8. Pathophysiology Following Brain Death - "The Catecholamine Storm" (4 marks)

Phase 1: Autonomic Storm (Cushing Response/Catecholamine Surge)

• As intracranial pressure rises and herniation occurs, brainstem ischaemia triggers an intense sympathetic discharge
• Plasma catecholamines rise 10-100x above baseline
• Cardiovascular effects: severe hypertension, tachycardia, arrhythmias, myocardial ischaemia, reversible left ventricular dysfunction (catecholamine cardiomyopathy)

Phase 2: Post-Herniation Cardiovascular Collapse

• Loss of sympathetic tone → systemic vasodilation, increased venous capacitance, relative hypovolaemia
• Exacerbated by prior osmotherapy (mannitol), diuresis, and inadequate fluid resuscitation
• Progressive hypotension requiring vasopressors

Phase 3: Hypothalamic-Pituitary Axis Disruption

Phase 4: Systemic Consequences

• Hypothermia - loss of hypothalamic temperature regulation
• Coagulopathy - DIC from thromboplastin release from injured brain
• Pulmonary oedema - neurogenic (sympathetic storm) + aspiration risk
• Anaemia - from haemorrhage, haemodilution
• Infection - ICU-acquired, aspiration pneumonia

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9. ICU Management of the Brain-Dead Organ Donor (5 marks)

The "Rule of 100s" (Trauma Surgery guideline)

• Systolic BP >100 mmHg
• Urine output >100 mL/h
• PaO2 >100 mmHg

A. Haemodynamic Goals

• Vasopressors: Noradrenaline (norepinephrine) first choice; vasopressin has dual benefit (vasopressor + treats DI); avoid high-dose dopamine
• Fluid resuscitation: balanced crystalloids; albumin; avoid synthetic starches
• Inotropes (dopamine, dobutamine) if cardiogenic dysfunction

B. Respiratory Goals (Critical for Lung Donation)

• Frequent suctioning; HOB 30-45°; avoid ventilator-associated pneumonia
• Lung-protective ventilation critical for lung procurement

C. T4 Hormonal Resuscitation Protocol

D. Specific Organ Targets

E. Diabetes Insipidus Management

• Urine output >3-4 mL/kg/h + rising serum Na+ + low urine osmolality (hypotonic)
• Vasopressin (desmopressin DDAVP 0.5-2 mcg IV q6h, or vasopressin infusion)
• Replace fluid losses with 0.45% NaCl or 5% dextrose
• Target sodium: 130-155 mmol/L

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10. Anaesthesia for Organ Procurement (Harvesting) in the Operating Theatre (6 marks)

Role of the Anaesthesiologist

1. Verify the brain death certificates
2. Confirm family consent is in order
3. Confirm no absolute contraindications to donation (e.g., active HIV, active malignancy)
4. Continue ICU-level haemodynamic support
5. Manage spinal reflexes and haemodynamic responses to surgical stimulation

Why Anaesthesia is Required Despite Brain Death?

• Spinal cord reflexes remain intact and may cause gross movements (Lazarus reflex, limb movements) during surgical stimulation, which is distressing to the surgical team
• Haemodynamic reflexes - surgical stimulation can cause spinal-sympathetic reflex responses: hypertension and tachycardia (without pain perception), which can worsen catecholamine-mediated organ injury
• Volatile agents may provide ischaemic preconditioning - theoretical benefit for organ protection
• Muscle relaxants provide optimal surgical conditions

"Neuromuscular blockade required to inhibit spinal motor reflexes... volatile anaesthetics due to theoretical advantage of ischaemic preconditioning... brain death may cause haemodynamic response to noxious stimuli; hypertension should be avoided." (BC Transplant Anaesthesia Guidelines, 2024)

Monitoring in OT

Anaesthetic Technique

• Neuromuscular blockade (NMB): suxamethonium/rocuronium; maintain throughout
• Volatile anaesthetic (isoflurane/sevoflurane): 0.5-1 MAC - suppresses spinal motor reflexes; ischaemic preconditioning
• Opioids (fentanyl): to attenuate haemodynamic responses to incision - not for analgesia (brain dead) but to reduce reflex hypertension
• Continue vasopressors and inotropes as per ICU management
• Ventilation: lung-protective strategy as per ICU

• Continue vasopressin infusion for DI
• Insulin to maintain glucose 6-10 mmol/L
• Methylprednisolone if not already given
• NAC (N-acetylcysteine) 30 mg/kg 1 hour before procurement; 300 mg via portal vein before cross-clamp - shown to improve graft survival
• Prophylactic broad-spectrum antibiotics (cephalosporin)
• Heparin IV bolus (300-400 units/kg) before aortic cross-clamping - to prevent vascular thrombosis during cold flush

Surgical Sequence (Multi-organ Procurement)

1. Midline incision - suprasternal notch to pubis
2. Thoracic dissection - heart, lungs mobilised
3. Abdominal dissection - liver, pancreas, kidneys, bowel
4. Heparin given before cross-clamping
5. Aortic cross-clamp (supradiaphragmatic) + cold perfusion with preservation solution begins
   • At cross-clamp: all vasopressors ceased; ventilator stopped
   • Cardioplegia for heart
6. Sequential organ removal in order of ischaemia tolerance:
   • Heart (most sensitive - 4h cold ischaemia)
   • Lungs (6h cold ischaemia)
   • Liver (12-24h)
   • Pancreas (12-24h)
   • Kidneys (24-36h)
   • Intestines (8-12h)
7. Corneas, skin, bones - post-cardiac death

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11. Donation After Circulatory Death (DCD) - Anaesthetic Implications

• Life support withdrawn in OT (Maastricht III) - comfort care drugs (morphine, midazolam) given to relieve any distress
• No-touch period of 2-5 minutes after cardiac arrest (permanent cardiac arrest confirmed)
• Rapid organ retrieval begins immediately after no-touch period
• Warm ischaemia time is the critical variable - shorter warm ischaemia = better organ outcomes
• Ex-vivo machine perfusion (normothermic or hypothermic) increasingly used to recondition DCD organs

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12. Ethical and Legal Considerations

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13. Summary - Key Examination Points

1. Harvard criteria 1968 - first formalised brain death; 25 assessments required
2. Three absolute requirements for brain death: deep coma (known irreversible cause) + all brainstem reflexes absent + apnoea test positive (PaCO2 ≥60 mmHg or rise ≥20 mmHg, no respiratory effort)
3. Five confounders to exclude before testing: hypothermia, drugs, NMB, metabolic, hypotension
4. Ancillary tests (EEG, CTA, SPECT, TCD) - not routinely required; used when clinical exam incomplete
5. Catecholamine storm → haemodynamic collapse → hypothalamic-pituitary failure → DI, hypothyroidism, adrenal failure
6. T4 protocol: methylprednisolone + T3/T4 + vasopressin + insulin
7. Anaesthesia in OT: NMB + volatile agent + opioids = suppress spinal reflexes + haemodynamic responses; NOT for consciousness (brain dead)
8. CVP strategy: low (4-8) during heart/lung harvesting; raise (10-12) for kidney procurement
9. Dead donor rule and separation of teams are non-negotiable ethical principles
10. DCD donors now account for 30% of deceased donors in the USA; Maastricht classification

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• Miller's Anesthesia, 2-Volume Set, 10th Edition
• Bradley & Daroff's Neurology in Clinical Practice, 8th Edition
• Plum & Posner's Diagnosis and Treatment of Stupor and Coma, 5th Edition
• Mulholland & Greenfield's Surgery: Scientific Principles and Practice, 7th Edition
• BC Transplant - Anesthesia for Donors following Death by Neurological Criteria (2024)
• NOTTO (National Organ & Tissue Transplant Organisation) India - OT Guidelines

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Shivering in Anaesthesia — 10-Mark Model Answer (Anaesthesia MD Examination)

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1. Definition

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2. Physiology of Normal Thermoregulation

• Peripheral thermoreceptors (skin - warm and cold receptors)
• Central thermoreceptors (hypothalamus, spinal cord, deep abdominal structures)

1. Behavioural thermoregulation (moving, dressing, seeking warmth)
2. Peripheral vasoconstriction (reduces heat loss by ~25%)
3. Shivering (increases heat production by 2-5 times above basal metabolic rate)
4. Non-shivering thermogenesis (brown fat activation - mainly in neonates)

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3. Causes of Perioperative Shivering

A. Thermoregulatory (Primary) - Most Common

• Cold operating room environment (standard OT: 20-22°C)
• Cold IV fluids and blood products
• Exposed body cavities (laparotomy, thoracotomy)
• Cold anaesthetic gases (unhumidified)
• Regional anaesthesia (sympathetic block → vasodilation, impaired thermosensation in blocked area)
• Extremes of age (elderly, neonates - impaired thermoregulation)
• Prolonged surgery
• Thin body habitus / low BMI

B. Non-Thermoregulatory (Secondary) Mechanisms

• Cortical disinhibition - anaesthetic agents suppress spinal cord interneurons that normally inhibit reflex muscular activity; on emergence, these reflexes are briefly disinhibited
• Altered pain modulation - especially relevant to epidural/spinal analgesia
• Pyrogen-mediated - inflammatory cytokines (fever shivering)
• Reduced serotonin, noradrenaline, and opioid neurotransmission during anaesthetic recovery - explains why drugs acting on these pathways (meperidine, clonidine, tramadol) are effective
• Neuraxial anaesthesia-specific: cold LA solutions injected into epidural/subarachnoid space → thermoreceptors in spinal cord stimulated; false signal of peripheral cooling despite normal core temperature

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4. Grading / Classification of Shivering

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5. Consequences of Shivering

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6. Prevention of Perioperative Shivering

A. Passive Warming

• Warm blankets; cotton or thermal covers
• Increase ambient OT temperature (especially in paediatrics and burns)
• Minimise exposed surface area

B. Active Warming (Most Effective)

• Forced-air warming blankets (Bair Hugger) - gold standard; most effective convective warming; 30 min pre-warming before induction ("pre-warming") significantly reduces redistribution hypothermia
• Underbody water mattresses - convection heating; highly effective
• Warmed IV fluids - fluid warmers for all large-volume IV fluids and blood products
• Warm humidified anaesthetic gases - reduces respiratory heat loss
• Warm skin preparation solutions - avoid cold antiseptic pooling on skin

C. Pharmacological Prevention

• Meperidine (Pethidine) 0.5-1 mg/kg IV - most studied; highly effective
• Dexmedetomidine - α2-agonist; pre-operative infusion reduces shivering
• Ondansetron 8 mg IV - via 5-HT3 blockade
• Intrathecal/epidural additives - sufentanil, clonidine added to neuraxial solutions reduce post-spinal shivering

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7. Treatment of Established Shivering

A. Non-Pharmacological

• Supplemental oxygen (high-flow face mask) - counteract increased O2 demand
• Active external warming: warm blankets, forced-air warmer
• Temperature monitoring; treat underlying hypothermia

B. Pharmacological Treatment

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8. Special Situations

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9. Summary Algorithm

Shivering detected in PACU
        ↓
Supplemental O2 → Warm blankets/forced-air warming
        ↓
Core temperature <36°C?
   YES → Aggressive active rewarming + Meperidine 25 mg IV
   NO  → Non-thermoregulatory cause → Meperidine 25 mg IV / Clonidine 75 mcg IV
        ↓
Monitor: SpO2, BP, HR, Temperature
        ↓
If refractory: repeat dose or switch agent (tramadol/clonidine/dexmedetomidine)

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Key Examination Points (10 marks)

1. Definition - involuntary oscillatory muscle contractions; primary (thermoregulatory) + secondary (non-thermoregulatory) mechanisms
2. Incidence - 40-65% after GA; 30-55% after neuraxial anaesthesia
3. Three phases of intraoperative heat loss - redistribution (most rapid), linear, plateau
4. Consequences - O2 consumption up to 500%; raised ICP/IOP; cardiovascular stress; worsens coagulopathy
5. Grading - 0-4 (Crossley scale) or BSAS 0-3
6. Prevention - pre-warming + forced-air warming + warmed IV fluids = most effective
7. Meperidine 25-50 mg IV = gold standard treatment; works via κ-opioid receptors
8. Clonidine, tramadol, dexmedetomidine, ketamine - effective alternatives
9. Non-thermoregulatory shivering occurs even in normothermic patients - explains epidural shivering
10. Supplemental O2 mandatory during shivering to compensate 200-500% increase in O2 consumption

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• Morgan & Mikhail's Clinical Anesthesiology, 7th Edition
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9th Edition
• Miller's Anesthesia, 2-Volume Set, 10th Edition

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Cerebral Blood Flow (CBF) — 10-Mark Model Answer (Anaesthesia MD Examination)

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1. Normal Values and Basic Physiology

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2. CBF = CPP / CVR (Cerebrovascular Resistance)

CPP = MAP − ICP (or MAP − CVP if CVP > ICP)

• Normal CPP: 80-100 mmHg
• CPP <50 mmHg → EEG slowing
• CPP 25-40 mmHg → flat EEG
• CPP <25 mmHg → irreversible damage

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3. Regulation of Cerebral Blood Flow

A. Cerebral Autoregulation (Pressure Autoregulation) ★★★

• Normal autoregulatory range: MAP 60-160 mmHg
• Outside this range, CBF becomes pressure-passive (directly proportional to MAP)
• Below 60 mmHg: vasodilation maxed out → CBF falls → ischaemia
• Above 160 mmHg: vasoconstriction maxed out → CBF rises → cerebral oedema, haemorrhage, BBB disruption
• Onset: rapid (10-60 seconds)

• Myogenic - vascular smooth muscle contracts in response to stretch (Bayliss effect)
• Metabolic - metabolites (CO2, H+, adenosine, K+) from active neurons cause local vasodilation
• Neurogenic - sympathetic/parasympathetic innervation modulates tone

• Chronic hypertension shifts the entire curve to the RIGHT (both upper and lower limits shift right) - protective at high pressures but vulnerable to ischaemia at "normal" MAP
• Long-term antihypertensive therapy can partially restore the curve to normal

• Severe head injury/TBI
• Stroke/ischaemia
• Volatile anaesthetics (dose-dependent impairment)
• Severe hypercapnia, hypoxia, sustained seizures
• Prematurity (absent autoregulation in preterm neonates)

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B. CO2 Reactivity (Chemical Regulation) ★★★

CBF is directly proportional to PaCO2 between 20 and 80 mmHg

• Acute metabolic acidosis has little effect on CBF (H+ cannot cross BBB)
• After 24-48h, CSF HCO3- adapts to compensate → the effect of chronic hypocapnia/hypercapnia is diminished (tachyphylaxis to hyperventilation)

• Hyperventilation (PaCO2 to 30-35 mmHg) → reduces CBF by ~25-30% → reduces ICP acutely (used in herniation as temporising measure; NOT for prolonged use)
• Permissive normocapnia preferred in elective neurosurgery

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C. Oxygen Tension (PaO2)

• Hyperoxia: minimal decrease in CBF (~10%)
• Normoxia (PaO2 >60 mmHg): CBF essentially unchanged
• Moderate hypoxia (PaO2 50-60 mmHg): mild ↑ in CBF begins
• Severe hypoxia (PaO2 <50 mmHg): marked ↑↑ in CBF (see graph above - steep rise at low PaO2)

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D. Metabolic Coupling / Neurovascular Coupling

• Local metabolites accumulate (CO2, H+, K+, adenosine, nitric oxide)
• Local cerebrovascular resistance falls
• Regional CBF increases to match demand

• Regional CBF increases during motor/visual/cognitive activity (basis of fMRI)
• Grey matter (metabolically active) has 4x higher CBF than white matter

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E. Temperature

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F. Other Factors

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4. Effects of Anaesthetic Agents on CBF

A. Volatile Anaesthetics

1. Direct cerebral vasodilation (↑ CBF)
2. Decrease CMRO2 → via flow-metabolism coupling → ↓ CBF (indirect)

B. IV Anaesthetic Agents

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5. Clinical Applications in Anaesthesia

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6. Monitoring of CBF

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7. Blood-Brain Barrier (BBB)

• Tight junctions between cerebral endothelial cells; minimal pores
• Allows: lipid-soluble substances (O2, CO2, most anaesthetics, glucose via transport)
• Blocks: ions, proteins, large molecules (mannitol, antibiotics)
• Water moves freely (osmotic gradient exploited by mannitol)
• BBB disruption by: severe hypertension (MAP >150-160 mmHg), trauma, ischaemia, tumours, infection, marked hypercapnia, hypoxia, seizures

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Summary Table - Key CBF Numbers

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• Morgan & Mikhail's Clinical Anesthesiology, 7th Edition (Chapter 26)
• Miller's Anesthesia, 2-Volume Set, 10th Edition (Chapters 53, 80)
• Barash, Cullen & Stoelting's Clinical Anesthesia, 9th Edition (Chapter 18)
• Plum & Posner's Diagnosis and Treatment of Stupor and Coma, 5th Edition

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Massive Blood Transfusion and Blood Components — 30-Mark Model Answer (Anaesthesia MD Examination)

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1. Definitions

Massive Blood Transfusion (MBT)

• Transfusion of ≥10 units of packed red blood cells (PRBCs) within 24 hours (most widely used)
• Transfusion of ≥4 units PRBCs in 1 hour with ongoing haemorrhage requiring continuation
• Replacement of the entire blood volume within 24 hours (adult ~5L = ~10 units PRBCs)
• Some definitions: ≥20 units PRBCs/24h; or ≥50% total blood volume in 3 hours

Haemorrhagic Shock Classification (Basis for MBT Decision)

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2. Indications for Activating a Massive Transfusion Protocol (MTP)

• Penetrating mechanism: 1 point
• SBP ≤90 mmHg on arrival: 1 point
• HR ≥120/min on arrival: 1 point
• FAST positive: 1 point

• ABC score ≥2
• Persistent haemodynamic instability despite initial resuscitation
• Active bleeding requiring urgent surgery or angioembolisation
• Blood transfusion already begun in emergency department
• Estimated blood loss >1500 mL or ongoing surgical bleeding not controlled

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3. Blood Components - Composition and Properties (10 marks)

A. Packed Red Blood Cells (PRBCs)

• ↓ 2,3-DPG → left shift of O2-Hb dissociation curve → reduced O2 delivery
• ↑ K+ (haemolysis) → risk of hyperkalaemia with MBT
• ↑ Hydrogen ions (metabolic acidosis)
• ↓ Platelet and coagulation factor activity
• Microaggregate formation
• ↓ ATP → impaired RBC deformability
• ↑ Free haemoglobin (pro-inflammatory)

B. Fresh Frozen Plasma (FFP)

C. Platelets

D. Cryoprecipitate

E. Whole Blood

F. Prothrombin Complex Concentrate (PCC)

G. Fibrinogen Concentrate (Haemocomplettan/RiaSTAP)

• Lyophilised fibrinogen; immediate reconstitution; no blood group compatibility
• Dose: 3-4 g to raise fibrinogen by ~1 g/L (based on ROTEM/TEG guidance)
• Increasingly replacing cryoprecipitate in many protocols

H. Recombinant Activated Factor VII (rFVIIa - NovoSeven)

• Rescue agent for refractory life-threatening haemorrhage unresponsive to standard measures
• Mechanism: activates Factor X on platelet surface; bypasses intrinsic pathway
• Requires: pH >7.2, Temperature >35°C, Fibrinogen >0.5 g/L, Platelets >50,000/µL to work
• Dose: 90-120 mcg/kg; expensive; thrombotic risk

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4. Trauma-Induced Coagulopathy (TIC) / Acute Coagulopathy of Trauma (4 marks)

Acidosis + Hypothermia + Coagulopathy = Death

1. Activated Protein C (APC) pathway - tissue hypoperfusion activates endothelial thrombomodulin → thrombin-thrombomodulin complex → activates protein C → inhibits factors Va and VIIIa → reduced thrombin generation
2. Hyperfibrinolysis - APC inhibits PAI-1 → increased tPA activity → clot breakdown
3. Endothelial glycocalyx shedding - shed proteoglycans (syndecan-1) = "auto-heparinisation"
4. Platelet exhaustion - widespread ADP release from injured tissues renders platelets unresponsive to further stimulation
5. Dilution - large-volume crystalloid resuscitation dilutes clotting factors and platelets
6. Hypothermia - reduces enzyme activity of coagulation cascade; impairs platelet function
7. Acidosis - reduces thrombin generation; reduces factor activity

• TEG (Thromboelastography) and ROTEM (Rotational Thromboelastometry) assess global haemostasis:
  • Rate of clot formation (R-time / CT)
  • Clot strength (MA / MCF)
  • Fibrinolysis (LY30 / ML)
• Guide specific factor/platelet/fibrinogen replacement - reduces total blood product use vs empiric 1:1:1 approach

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5. Damage Control Resuscitation (DCR) and MTP (6 marks)

The "Bloody Vicious Cycle"

The 1:1:1 Ratio - Evidence

• 1:1:1 (FFP:Platelets:PRBCs) vs 1:1:2
• 1:1:1 achieved haemostasis more rapidly and fewer deaths from exsanguination at 24 hours
• No difference in 30-day mortality but haemostatic benefit was clear

• Confirmed 1:1:1 beneficial in most massively bleeding patients
• Earlier plasma delivery reduced mortality

Typical MTP Structure (Cooler-Based):

• After every 6-10 units of blood products: ABG + electrolytes + glucose + lactate
• CBC, PT/INR, APTT, fibrinogen level
• TEG/ROTEM at intervals - guides goal-directed therapy

Transfusion Targets During MBT:

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6. Tranexamic Acid (TXA) - Key Evidence

• Mechanism: Competitive inhibitor of plasminogen; antifibrinolytic
• CRASH-2 Trial (Lancet 2010): 20,000+ trauma patients; TXA 1 g IV over 10 min, then 1 g over 8 hours; significantly reduced all-cause mortality (14.5% vs 16.0%; p=0.0035); greatest benefit when given within 1 hour of injury
• Critical time window: Benefit greatest <1h; significant if <3h; mortality INCREASES if given after 3 hours (pro-thrombotic risk)
• Dose: 1 g IV bolus over 10 min within 3 hours of injury/surgery; repeat 1 g if still bleeding
• Now standard of care in MBT for trauma; also used in obstetric haemorrhage (WOMAN Trial), cardiac surgery

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7. Complications of Massive Blood Transfusion (8 marks)

A. Metabolic Complications

B. Haematological Complications

C. Immune-Mediated Complications

D. Infectious Complications

• HIV: 1 in 2 million units
• Hepatitis C: 1 in 1.9 million units
• Hepatitis B: 1 in 300,000 units
• Bacterial contamination (platelets highest risk due to room temperature storage): septic shock
• CMV, malaria, prions (vCJD)

E. Other Complications

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8. Alternatives to Allogenic Blood Transfusion

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9. Summary - Anaesthetist's Checklist for MBT

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Key Examination Points

1. Definition of MBT: ≥10 units PRBCs in 24h (most common definition)
2. Lethal triad: Hypothermia + Acidosis + Coagulopathy
3. 1:1:1 ratio (DCR): FFP : Platelets : PRBCs - PROPPR trial evidence
4. TXA: Within 3 hours; CRASH-2 trial; Class I evidence; do NOT give after 3 hours
5. Blood components: Know composition, storage, volumes, shelf life
6. Hypocalcaemia: Most immediately correctable metabolic complication - calcium for every 4 units
7. Hypothermia: Most dangerous - impairs ALL coagulation enzymes
8. TRALI vs TACO: Permeability vs hydrostatic oedema; both within 6h of transfusion
9. TEG/ROTEM: Goal-directed haemostatic resuscitation; reduces unnecessary blood product use
10. Acute haemolytic reaction: Stop transfusion immediately; ABO incompatibility; potentially fatal

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• Miller's Anesthesia, 2-Volume Set, 10th Edition (Chapters 45, 46, 62)
• Morgan & Mikhail's Clinical Anesthesiology, 7th Edition (Chapter 39)
• Schwartz's Principles of Surgery, 11th Edition (Chapter 4, 5)
• Mulholland & Greenfield's Surgery, 7th Edition (Chapter 19)
• Sabiston Textbook of Surgery, 21st Edition (Chapter 10)
• CRASH-2 Trial Collaborators, Lancet 2010; PROPPR Trial, JAMA 2015