📄 DNB Anaesthesiology · June 2025
10 questions · 100 marks · Model answers with cited sources, key points, exam tips & extra-marks content.
Q1
a) Draw a well labelled diagram of the neuromuscular junction. [4] b) Enumerate any four techniques of neuromuscular monitoring. Write briefly about any one technique with special reference to its clinical indication. [2+4]
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Model Answer
Part A
The Neuromuscular Junction (NMJ) — labelled structure
The NMJ is the specialised chemical synapse between the terminal branch of a motor neuron and a skeletal muscle fibre, where the neurotransmitter acetylcholine (ACh) transmits the action potential from nerve to muscle.
Label the following on the diagram (nerve terminal → cleft → muscle)
- Motor nerve terminal (pre-synaptic) — contains mitochondria and ACh-filled synaptic vesicles clustered at 'active zones'.
- Voltage-gated Ca²⁺ channels — on the pre-synaptic membrane; Ca²⁺ influx triggers vesicle fusion and ACh release.
- Synaptic cleft (~20–50 nm) — contains acetylcholinesterase (AChE) in the basement membrane.
- Post-junctional (muscle) membrane — thrown into secondary/junctional folds; nicotinic ACh receptors (nAChR) crowd the shoulders of the folds.
- Nicotinic ACh receptor — pentamer (adult: 2α, β, δ, ε subunits); ACh binds the two α-subunits to open the cation channel.
- Voltage-gated Na⁺ channels — in the depths of the folds, generate the muscle action potential.
- Schwann cell cap over the nerve terminal.
Part B
Techniques of neuromuscular monitoring
Any four patterns of stimulation (using a peripheral nerve stimulator)
- Single twitch (0.1–1 Hz).
- Train-of-Four (TOF) — four supramaximal stimuli at 2 Hz.
- Tetanic stimulation (50 Hz for 5 s) and Post-Tetanic Count (PTC).
- Double Burst Stimulation (DBS).
Train-of-Four (TOF) — technique & clinical indication
- Technique: four supramaximal stimuli at 2 Hz (0.5 s apart); the ratio of the 4th to the 1st twitch amplitude (TOF ratio) and the number of visible/palpable twitches (TOF count) are assessed, usually at the ulnar nerve (adductor pollicis).
- Depolarising block: all four twitches reduced equally, no fade.
- Non-depolarising block: progressive 'fade' (T4 disappears first); TOF count of 1 ≈ 90–95% receptor block (good surgical relaxation).
- Clinical indication — assessing adequacy of RECOVERY/reversal: a TOF ratio ≥0.9 (quantitative, e.g. acceleromyography) confirms adequate reversal and safe extubation; a ratio <0.9 indicates residual paralysis and aspiration risk. TOF also titrates intra-operative relaxation and guides reversal timing (e.g. sugammadex/neostigmine).
✅ Key Points
- Adult nAChR is a pentamer (2α,β,δ,ε); ACh binds both α-subunits to open the channel. The fetal/extrajunctional receptor has a γ instead of ε subunit.
- Four monitoring patterns: single twitch, TOF, tetanus/post-tetanic count, double-burst stimulation.
- A quantitative TOF ratio ≥0.9 is the gold standard for confirming adequate recovery from non-depolarising block before extubation.
🔑 Clinical Pearls
- 'Fade' (TOF and tetanic) occurs with non-depolarising and Phase-II (dual) block, but NOT with a pure depolarising (Phase-I) block — a quick bedside way to tell them apart.
- Post-Tetanic Count (PTC) is used when the block is so deep that there is no TOF response — essential when profound paralysis is needed and no movement can be tolerated (e.g. microsurgery, neurosurgery).
- The diaphragm and larynx are resistant to relaxants and recover FIRST; the adductor pollicis recovers later — so monitoring adductor pollicis gives a 'safe', conservative estimate of recovery.
- Eyebrow (facial nerve/corrugator supercilii) monitoring parallels the laryngeal muscles and is useful for judging intubating conditions.
❌ Common Mistakes to Avoid
- Relying on clinical signs (head lift, grip) instead of a quantitative TOF ratio — clinical tests miss residual block up to a TOF ratio of ~0.9.
- Monitoring the facial nerve for recovery — it overestimates recovery because facial muscles are relatively resistant.
- Forgetting that hypothermia, acidosis, hypermagnesaemia and aminoglycosides potentiate and prolong neuromuscular block.
💡 Examiner Tip
Draw the diagram clearly and label ≥6 structures — the 4 marks are for labels. For part (b), name four patterns, then take TOF and explicitly tie it to its clinical use (confirming recovery, TOF ratio ≥0.9).
📚 Sources & References
- Miller's Anesthesia, 9th Ed — Neuromuscular physiology & monitoring.
- Morgan & Mikhail's Clinical Anesthesiology, 6th Ed — Neuromuscular blocking agents & monitoring.
- Stoelting's Pharmacology & Physiology in Anesthetic Practice — NMJ.
- Naguib M, Brull SJ. Conceptual and technical insights into neuromuscular monitoring. Anaesthesia 2017.
⭐ Extra Marks Content
⭐ Extra Theory Edge
- Up-regulation of extrajunctional (fetal-type, γ-subunit) receptors occurs in burns, immobilisation, denervation and critical illness — causing hyperkalaemia with suxamethonium and resistance to non-depolarisers.
- Acceleromyography (quantitative TOF) at the thumb is now recommended for every case using non-depolarising relaxants, given the high incidence of unrecognised residual block.
- Sugammadex reverses deep rocuronium/vecuronium block (PTC-guided dosing) rapidly by encapsulation — a game-changer versus neostigmine, which cannot reverse profound block.
Q2
a) What are the advantages and disadvantages of the closed breathing circuit? [5] b) Describe the Mapleson D circuit and give its functional analysis. [5]
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Model Answer
Part A
Closed breathing circuit — advantages & disadvantages
A closed (fully rebreathing) circle system uses fresh-gas flow (FGF) equal only to the patient's metabolic uptake of O₂ (≈250 mL/min) plus anaesthetic uptake; the APL valve is closed and all exhaled gas, after CO₂ absorption, is rebreathed.
Advantages
- Economy — minimal use of oxygen and volatile agent (major cost saving).
- Conservation of heat and moisture (humidification) — reduced airway drying and hypothermia.
- Reduced atmospheric/operating-theatre pollution.
- More stable anaesthetic depth once equilibrated; useful monitor of O₂ uptake.
Disadvantages
- Risk of delivering a hypoxic mixture — inspired gas concentrations differ from the flowmeter settings; mandatory inspired O₂ (FiO₂) monitoring.
- Slow response — changing depth is sluggish (low FGF means slow wash-in/wash-out); need higher flows to alter concentration quickly.
- Accumulation of unwanted gases — nitrogen (denitrogenation needed), carbon monoxide, acetone, methane and compound A.
- Requires precise agent/gas analysers and CO₂ absorbent management (exhaustion, channelling); more complex and needs vigilance.
- Unpredictable volatile concentration unless an agent analyser is used.
Part B
Mapleson D circuit & functional analysis
The Mapleson D is a T-piece system: fresh gas enters at the patient end (near the mask/tube), the corrugated tubing and reservoir bag are on the expiratory side, and the APL (expiratory) valve is at the machine end near the bag. The Bain circuit is a coaxial modification of the Mapleson D (fresh gas runs inside the outer expiratory tube).
Functional analysis (efficiency for CO₂ removal)
- Controlled ventilation: the Mapleson D is the MOST efficient Mapleson system — during the expiratory pause fresh gas flushes alveolar (CO₂-rich) gas down the tubing toward the valve; a FGF of ~70 mL/kg/min (≈ 1–1.5× minute ventilation) prevents rebreathing.
- Spontaneous ventilation: it is the LEAST efficient (opposite of Mapleson A) — needs a high FGF of ~2–3× minute ventilation (150–250 mL/kg/min) to avoid rebreathing.
- Mnemonic — for the Mapleson family efficiency: 'A' is best for Spontaneous, 'D' (and Bain) is best for controlled/Ventilation ('Dog Bites Can Ache' — D,B,C,A order of efficiency for controlled ventilation).
- Advantages: lightweight, valve away from the patient (good for head/neck surgery), scavenging is easy; the Bain coaxial version warms inspired gas from the surrounding expired gas.
- Hazard (Bain): kinking or disconnection of the inner fresh-gas tube causes massive dead space and rebreathing — check with the Pethick test.
✅ Key Points
- Closed circuit: maximal economy, heat/moisture conservation and low pollution, but risk of hypoxic mixture, slow depth changes and accumulation of unwanted gases — mandates FiO₂ and agent monitoring.
- Mapleson D (and its coaxial Bain version): fresh gas at the patient end; MOST efficient for CONTROLLED ventilation, LEAST efficient for spontaneous ventilation.
- Controlled-ventilation FGF for Mapleson D ≈ 70 mL/kg/min; spontaneous ≈ 150–250 mL/kg/min.
🔑 Clinical Pearls
- In a Bain circuit, always do the Pethick test before use: occlude the patient end, fill the bag via O₂ flush, release — the Venturi effect at the elbow should collapse the bag, confirming inner-tube integrity.
- The Mapleson D is favoured for head-and-neck / ENT and transport because the bulky valve and bag sit away from the surgical field.
- 'Low-flow' or 'closed-circuit' anaesthesia needs an adequate initial high-flow phase to denitrogenate and wash in the agent, then flows are reduced — never start closed.
- Compound A (from sevoflurane + desiccated baralyme) and carbon monoxide (from desiccated absorbent) are the reasons to avoid very low flows with dried-out absorbent.
❌ Common Mistakes to Avoid
- Confusing Mapleson A and D efficiency — A is best for spontaneous, D is best for controlled ventilation (they are functional opposites).
- Running a closed/low-flow circuit without an inspired oxygen analyser — the leading safety hazard is an unrecognised hypoxic mixture.
- Forgetting to denitrogenate before going to low flows, leading to nitrogen accumulation and a falling FiO₂.
💡 Examiner Tip
Tabulate advantages vs disadvantages for the closed circuit. For the Mapleson D, state where fresh gas enters, then give the two FGF requirements (spontaneous vs controlled) and the efficiency ranking — that comparative analysis earns the marks.
📚 Sources & References
- Dorsch & Dorsch — Understanding Anesthesia Equipment.
- Miller's Anesthesia, 9th Ed — Breathing systems.
- Ward's Anaesthetic Equipment.
- Al-Shaikh & Stacey — Essentials of Anaesthetic Equipment.
⭐ Extra Marks Content
⭐ Extra Theory Edge
- Mapleson classification (A–F): A = Magill (best spontaneous), B and C, D = T-piece/Bain (best controlled), E = Ayre's T-piece, F = Jackson-Rees modification (paediatrics).
- The circle system with a CO₂ absorber is the modern practical way to achieve low-flow/closed anaesthesia while allowing rapid depth change by transiently raising flows.
- Environmental angle: volatile agents are greenhouse gases (desflurane the worst); low-flow/closed techniques and TIVA reduce the carbon footprint of anaesthesia — an increasingly examined topic.
Q3
a) What are the anesthetic concerns of intra-operative hypothermia? [3] b) What are the mechanisms that lead to hypothermia during anesthesia? [4] c) Discuss the strategies for preventing intraoperative hypothermia. [3]
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Model Answer
Part A
Anaesthetic concerns of intra-operative hypothermia (core temp <36 °C)
- Cardiac: increased myocardial O₂ demand from shivering, arrhythmias, myocardial ischaemia and adverse cardiac events (a major cause of morbidity).
- Coagulation: impaired platelet function and clotting-enzyme kinetics → increased blood loss and transfusion.
- Wound: vasoconstriction reduces tissue oxygenation → increased surgical-site infection and impaired healing.
- Pharmacology: prolonged action of anaesthetic agents and muscle relaxants (delayed metabolism/recovery, prolonged block).
- Other: prolonged PACU stay, patient discomfort/shivering, and impaired immune function.
Part B
Mechanisms of hypothermia during anaesthesia
- Redistribution (the major early mechanism): anaesthesia-induced vasodilation shifts heat from the warm core to the cool periphery in the first hour — accounts for most of the initial 1–1.5 °C fall.
- Radiation: the largest route of ongoing heat loss to the cold theatre environment.
- Convection: heat loss to moving air (laminar-flow theatres increase this).
- Conduction: to cold operating table, cold IV/irrigation fluids and skin-prep solutions.
- Evaporation: from exposed viscera, skin-prep, and respiratory tract (dry cold gases).
- Impaired thermoregulation: anaesthetics lower the vasoconstriction/shivering threshold and abolish behavioural responses; cold environment and body-cavity exposure add to loss.
Part C
Strategies for preventing intra-operative hypothermia
- Pre-warming: active forced-air warming for 20–30 min BEFORE induction reduces the redistribution drop (most effective single measure).
- Active warming intra-op: forced-air warming blankets, warming mattress; warm all IV fluids and irrigation fluids (fluid warmers).
- Raise ambient theatre temperature (≥21 °C, higher for neonates); minimise body exposure; cover the head and limbs.
- Airway: heat-and-moisture exchanger (HME) and warmed humidified gases; low-flow anaesthesia conserves heat.
- Monitor core temperature continuously (nasopharyngeal/oesophageal) and maintain ≥36 °C (NICE/AAGBI).
✅ Key Points
- Redistribution of heat from core to periphery is the dominant early mechanism, causing most of the first-hour temperature drop.
- Perioperative hypothermia increases cardiac events, bleeding/transfusion, wound infection and drug duration.
- Pre-warming plus intra-operative forced-air warming and warmed fluids are the cornerstone of prevention; keep core ≥36 °C.
🔑 Clinical Pearls
- Because the early fall is due to REDISTRIBUTION (not loss to the environment), warming the patient AFTER induction is far less effective than PRE-warming for 20–30 minutes before induction.
- Even 'mild' hypothermia (1–2 °C below normal) triples wound-infection risk and significantly increases blood loss — it is never trivial.
- Shivering can raise oxygen consumption by up to 400–500%, dangerous in patients with limited cardiac/respiratory reserve; treat with warming ± IV pethidine/clonidine.
- Neuraxial anaesthesia also causes hypothermia (blocks vasoconstriction and shivering below the block) and the patient may not feel cold — actively monitor and warm these patients too.
❌ Common Mistakes to Avoid
- Only starting warming after the temperature has already dropped, instead of pre-warming to blunt redistribution.
- Not monitoring core temperature under regional anaesthesia, wrongly assuming the awake patient will report feeling cold.
- Forgetting to warm irrigation fluids (e.g. in TURP, arthroscopy) — a large, often-missed source of heat loss.
💡 Examiner Tip
Respect the 3-4-3 mark split: 3 concise concerns, the 5 physical mechanisms (lead with redistribution), and practical prevention grouped as pre-warm/active warming/environment/airway/monitor.
📚 Sources & References
- Miller's Anesthesia, 9th Ed — Perioperative temperature regulation.
- Sessler DI. Perioperative thermoregulation and heat balance. Lancet 2016.
- NICE CG65 — Inadvertent perioperative hypothermia.
- Barash, Clinical Anesthesia, 8th Ed — Temperature monitoring.
⭐ Extra Marks Content
⭐ Extra Theory Edge
- Thermoregulatory phases under GA: (1) rapid redistribution fall (~1 h), (2) slow linear loss (heat loss > production), (3) plateau (re-established vasoconstriction balances loss).
- Forced-air warming is more effective than circulating-water mattresses because most heat is lost from the anterior body surface by radiation/convection, which forced air addresses.
- Therapeutic (targeted) hypothermia is deliberately used post-cardiac-arrest and in some neuro/cardiac surgery — the same physiology, harnessed for neuroprotection.
Q4
a) Explain the physiology of ventilation-perfusion (V/Q) matching in the various zones of the lungs. [5] b) What happens to V/Q ratio during one lung anesthesia? [2] c) Discuss the effect of changes in functional residual capacity and dead space ventilation on ventilation perfusion matching. [3]
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Model Answer
Part A
V/Q matching and West's lung zones
The overall alveolar ventilation/perfusion (V/Q) ratio is ~0.8 (alveolar ventilation ~4 L/min ÷ cardiac output ~5 L/min). Both ventilation and perfusion increase from apex to base (gravity-dependent), but perfusion increases MORE, so the V/Q ratio is high at the apex and low at the base.
West's zones (upright lung), based on alveolar (PA), arterial (Pa) and venous (Pv) pressures
- Zone 1 (apex): PA > Pa > Pv — alveolar pressure exceeds capillary pressure, so capillaries are compressed → alveolar dead space (ventilation but no perfusion). Not normally present; appears with hypotension or high PEEP/IPPV. V/Q very high.
- Zone 2 (mid): Pa > PA > Pv — flow depends on the arterial–alveolar pressure difference ('Starling resistor'/waterfall effect). V/Q ~1.
- Zone 3 (base): Pa > Pv > PA — continuous flow; perfusion exceeds ventilation → low V/Q ratio. This is where most gas exchange occurs.
- (Zone 4, at the extreme base): interstitial pressure compresses vessels → reduced flow.
- Hypoxic pulmonary vasoconstriction (HPV) actively diverts flow away from poorly ventilated (low-V/Q) alveoli to optimise matching.
Part B
V/Q ratio during one-lung anaesthesia
- The non-ventilated (non-dependent, operative) lung continues to be perfused but is not ventilated → a large intrapulmonary SHUNT (V/Q approaching 0) → hypoxaemia.
- HPV in the collapsed lung, plus gravity and surgical retraction, reduce its blood flow and partially limit the shunt; the ventilated dependent lung takes most of the perfusion. Volatile agents blunt HPV and worsen the shunt.
Part C
Effect of FRC and dead-space changes on V/Q matching
- ↓ FRC (supine position, obesity, GA, atelectasis): airway/alveolar closure below closing capacity → low-V/Q areas and shunt → hypoxaemia. PEEP/recruitment restores FRC and improves matching.
- ↑ Dead space (PE, hypotension → zone 1, excessive PEEP, hypovolaemia): ventilation to non-perfused alveoli (high V/Q) → wasted ventilation and increased PaCO₂–EtCO₂ gradient.
- Both extremes impair gas exchange: low V/Q → hypoxaemia (shunt), high V/Q → hypercarbia/wasted ventilation (dead space). Optimal matching requires adequate FRC (above closing capacity) and adequate perfusion.
✅ Key Points
- Ventilation and perfusion both rise apex→base, but perfusion rises more — so V/Q is high at the apex (Zone 1, dead space) and low at the base (Zone 3, shunt-like).
- West's zones are defined by the relationship of alveolar, arterial and venous pressures; Zone 1 = dead space, Zone 3 = main gas exchange.
- One-lung anaesthesia creates a large shunt (V/Q→0) through the collapsed lung; low FRC causes shunt (hypoxaemia) and increased dead space causes wasted ventilation (hypercarbia).
🔑 Clinical Pearls
- Zone 1 (alveolar dead space) is normally absent but appears with anything that lowers pulmonary artery pressure (haemorrhage, hypotension) or raises alveolar pressure (high PEEP, IPPV) — a reason not to over-PEEP a hypovolaemic patient.
- Positioning matters: in the lateral position, the DEPENDENT lung is better perfused; keeping it ventilated during OLV is what preserves oxygenation.
- HPV is the lung's own V/Q-optimiser — anything that inhibits it (volatile agents in high dose, vasodilators, hypocapnia) worsens shunt and hypoxaemia during OLV.
- The A–a gradient widens with shunt (doesn't correct fully with 100% O₂) but corrects with dead space/V-Q mismatch — a bedside way to distinguish the two.
❌ Common Mistakes to Avoid
- Reversing the zones — remember V/Q is HIGHEST at the apex (Zone 1) and LOWEST at the base (Zone 3).
- Confusing shunt (low V/Q, does not respond to 100% O₂) with dead space/V-Q mismatch (high V/Q, responds to O₂).
- Forgetting that GA itself lowers FRC below closing capacity, which is why atelectasis and hypoxaemia are so common under anaesthesia.
💡 Examiner Tip
Draw the upright lung with the three zones and the pressure relationships (PA/Pa/Pv) — a labelled diagram scores fast. Explicitly link low V/Q → shunt → hypoxaemia and high V/Q → dead space → hypercarbia.
📚 Sources & References
- West's Respiratory Physiology: The Essentials.
- Nunn's Applied Respiratory Physiology.
- Miller's Anesthesia, 9th Ed — Respiratory physiology & one-lung ventilation.
- Lumb — Nunn and Lumb's Applied Respiratory Physiology.
⭐ Extra Marks Content
⭐ Extra Theory Edge
- Closing capacity increases with age, smoking and obesity; when it exceeds FRC, tidal airway closure causes shunt — this is why the elderly and obese desaturate quickly under GA.
- Applying PEEP to the dependent (ventilated) lung and CPAP to the non-dependent (operative) lung is the rational V/Q-based rescue for hypoxaemia in one-lung ventilation.
- The alveolar gas equation and the shunt equation (Qs/Qt) are the quantitative tools behind these concepts — worth quoting the shunt equation for extra marks.
Q5
a) What is power analysis and why is it important when designing a clinical trial? [4] b) What is the significance of P value? [3] c) What is a normal distribution curve? [3]
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Model Answer
Part A
Power analysis
Statistical power is the probability that a study will correctly detect a true effect of a given size when it genuinely exists — i.e. the probability of correctly rejecting a false null hypothesis. Power = 1 − β, where β is the probability of a Type II (false-negative) error. Studies are usually designed for 80–90% power.
Why it is important (and what a power/sample-size calculation needs)
- It determines the required SAMPLE SIZE before the trial begins.
- Inputs: the significance level α (usually 0.05), the desired power (0.8–0.9), the expected effect size (minimal clinically important difference), and the variability (standard deviation) of the outcome.
- An under-powered study risks a Type II error — missing a real, clinically important effect (a 'false-negative' trial).
- An over-powered study wastes resources and needlessly exposes extra participants (ethical concern).
- Thus power analysis makes a trial both scientifically valid and ethically sound.
Part B
Significance of the P value
- The P value is the probability of obtaining the observed result (or one more extreme) IF the null hypothesis were true — i.e. the probability that the finding is due to chance alone.
- Conventionally P <0.05 is 'statistically significant' → the null hypothesis is rejected (the result is unlikely to be due to chance).
- A small P value does NOT indicate the size or clinical importance of an effect, nor the probability that the hypothesis is true.
- It relates to Type I error (α): P <0.05 accepts a 5% chance of a false-positive.
Part C
Normal (Gaussian) distribution curve
- A symmetrical, bell-shaped, continuous probability distribution where mean = median = mode, described fully by its mean (µ) and standard deviation (σ).
- The empirical rule: ~68% of values lie within ±1 SD, ~95% within ±2 SD (1.96 SD), and ~99.7% within ±3 SD of the mean.
- The area under the curve = 1 (100%); the tails are asymptotic.
- It underpins parametric statistical tests (t-test, ANOVA); non-normal data need transformation or non-parametric tests. Skew and kurtosis describe deviations from normality.
✅ Key Points
- Power = 1 − β (probability of avoiding a Type II/false-negative error); designed at 80–90%; drives sample-size calculation.
- P value = probability the result is due to chance if the null hypothesis is true; <0.05 = statistically significant (Type I error rate 5%).
- Normal distribution: symmetrical bell curve, mean=median=mode; 68–95–99.7% within 1–2–3 SD.
🔑 Clinical Pearls
- 'Statistically significant' (small P) is NOT the same as 'clinically important' — a huge trial can make a trivial difference significant. Always look at the effect size and confidence interval, not just the P value.
- A 95% confidence interval is more informative than a P value: if it excludes the 'no-effect' value (0 for differences, 1 for ratios), the result is significant AND you see the precision and magnitude.
- Under-powered 'negative' trials are common in anaesthesia — 'absence of evidence is not evidence of absence'; a non-significant result may just mean too few patients.
- Type I error (α, false-positive) and Type II error (β, false-negative) are the two ways to be wrong — power addresses β, the significance level addresses α.
❌ Common Mistakes to Avoid
- Interpreting P as 'the probability the null hypothesis is true' or 'the probability the result is a fluke for this study' — it is neither.
- Equating a non-significant P with 'no difference' when the study was simply under-powered.
- Applying parametric tests (t-test) to clearly non-normal data without checking the distribution.
💡 Examiner Tip
Define each term precisely and add one clinical implication (effect size vs P, confidence intervals, Type I/II errors). Draw the labelled bell curve with the 68-95-99.7 rule for the last part.
📚 Sources & References
- Petrie & Sabin — Medical Statistics at a Glance.
- Miller's Anesthesia, 9th Ed — Interpreting the medical literature / statistics.
- Bland M — An Introduction to Medical Statistics.
- Altman DG — Practical Statistics for Medical Research.
⭐ Extra Marks Content
⭐ Extra Theory Edge
- Sample-size formula for comparing two means: n per group ≈ 2 × (Zα/2 + Zβ)² × σ² / (difference)². Larger variance or smaller effect → larger sample.
- The 'minimal clinically important difference' (MCID) — not the maximum plausible effect — should drive the effect size in a power calculation.
- Central Limit Theorem: the distribution of sample MEANS approaches normal as sample size increases, even if the underlying data are not normal — the basis for many parametric tests.
Q6
a) The importance of accurate and detailed anaesthesia documentation. [5] b) Role of audit and feedback in anaesthesia practice. [5]
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Model Answer
Part A
Importance of accurate anaesthesia documentation
- Continuity & safety of care: a complete record (pre-op assessment, consent, drugs/doses/times, vitals, airway grade, fluids, events) lets any subsequent clinician understand and continue care safely.
- Communication & handover: essential for PACU/ICU handover and for future anaesthetics (e.g. difficult-airway alerts, drug reactions).
- Medico-legal protection: a contemporaneous, legible, signed record is the primary defence in any complaint or litigation — 'not documented = not done'.
- Quality, audit & research: structured data enable audit, morbidity/mortality review and research.
- Billing, administration and clinical governance; and documentation of INFORMED CONSENT.
- Trigger for critical-incident reporting and future patient safety (e.g. flagging suxamethonium apnoea, malignant hyperthermia, anaphylaxis).
Part B
Role of audit and feedback in anaesthesia practice
Clinical audit is a quality-improvement process that systematically reviews care against explicit standards and implements change to improve it — the classic 'audit cycle'.
The audit cycle & role of feedback
- Steps: (1) identify a problem/set a standard, (2) measure current practice, (3) compare against the standard, (4) implement change, (5) re-audit to 'close the loop'.
- Feedback: presenting audit results (and individual/departmental performance data) to clinicians changes behaviour and improves compliance — most effective when specific, timely, from a credible source, and paired with clear targets and an action plan.
- Benefits: improves patient safety and outcomes, reduces variation, supports clinical governance, revalidation and CPD, and identifies training needs.
- Examples in anaesthesia: audit of PONV rates, regional-block success/complications, antibiotic prophylaxis timing, normothermia compliance, critical-incident reporting.
- Distinguish from research: audit asks 'are we following best practice?' (no new knowledge, no randomisation), research asks 'what is best practice?'.
✅ Key Points
- Documentation ensures continuity/safety, communication, medico-legal protection, consent, audit/research and future anaesthetic safety — 'not documented = not done'.
- Clinical audit is a cyclical QI process measuring practice against a standard and re-auditing to 'close the loop'.
- Feedback drives behaviour change when it is specific, timely, credible and linked to actionable targets.
🔑 Clinical Pearls
- The single commonest medico-legal failing is an incomplete or illegible record — a contemporaneous, timed, signed anaesthetic chart is your best defence.
- Audit ≠ research: audit compares practice to an existing standard and needs no ethics-committee approval; research generates new knowledge and does.
- An audit is worthless unless the loop is CLOSED — the re-audit after implementing change is what proves improvement; a one-off measurement is just a survey.
- Automated anaesthesia information management systems (electronic records) improve data completeness and enable real-time decision support and effortless audit.
❌ Common Mistakes to Avoid
- Describing audit as a one-off data-collection exercise and omitting the re-audit step that closes the loop.
- Confusing audit with research (and therefore over- or under-stating the need for ethics approval and randomisation).
- Listing documentation uses without mentioning consent and medico-legal defence, which are high-yield points.
💡 Examiner Tip
For part (a), give ≥5 distinct headed reasons. For part (b), draw/describe the audit cycle explicitly and add the features that make feedback effective — and clearly separate audit from research.
📚 Sources & References
- Royal College of Anaesthetists — Raising the Standard: audit recipe book.
- AAGBI/Association of Anaesthetists — Standards of monitoring & record keeping.
- Miller's Anesthesia, 9th Ed — Quality improvement & patient safety.
- NICE / HQIP — Principles of best-practice clinical audit.
⭐ Extra Marks Content
⭐ Extra Theory Edge
- The minimum anaesthetic record (AAGBI) includes pre-op assessment, monitoring used, drugs/doses/routes/times, fluids/blood, airway management and grade, ventilation, position, events and a legible signature.
- Cochrane evidence shows audit & feedback produces small-to-moderate but worthwhile improvements in professional practice, greatest when baseline performance is low and feedback is repeated.
- National audit projects (e.g. NAP series — NAP4 airway, NAP5 awareness, NAP6 anaphylaxis, NAP7 cardiac arrest) are landmark examples of audit shaping anaesthetic practice.
Q7
a) Write briefly about the oxygen cascade with the help of a well labelled diagram. [3] b) What are the various techniques/devices used for oxygenation? [4] c) Apneic oxygenation. [3]
×
Model Answer
Part A
The oxygen cascade
The oxygen cascade describes the stepwise fall in the partial pressure of oxygen (PO₂) from dry atmospheric air to the mitochondria, where it is consumed. Plot PO₂ (kPa/mmHg) on the y-axis against each step on the x-axis — a descending 'cascade'.
Steps (with approximate PO₂ at sea level, room air)
- Dry atmospheric air: PO₂ ≈ 21.2 kPa (159 mmHg) = 0.21 × 101 kPa.
- Humidified tracheal gas: falls to ≈ 19.9 kPa (149 mmHg) after saturation with water vapour (SVP 6.3 kPa at 37 °C).
- Alveolar gas (PAO₂): ≈ 13.3 kPa (100 mmHg) — from the alveolar gas equation, reduced by added CO₂ (PACO₂/R).
- Arterial blood (PaO₂): ≈ 13.0 kPa (~95–100 mmHg) — a small A–a gradient from shunt/V-Q mismatch.
- Capillary/tissue: PO₂ falls further to the mitochondria (~1–3 kPa; 'critical mitochondrial PO₂' ~0.2 kPa).
Part B
Techniques/devices used for oxygenation
- Variable-performance (low-flow) devices — FiO₂ varies with the patient's breathing: nasal cannulae, simple (Hudson) face mask, non-rebreathing mask with reservoir bag.
- Fixed-performance (high-flow) devices — deliver a set FiO₂ regardless of breathing pattern: Venturi masks (entrainment/Bernoulli principle), anaesthetic circuits with a good seal.
- High-Flow Nasal Oxygen (HFNO/THRIVE) — heated, humidified O₂ 30–70 L/min; provides high FiO₂, some PEEP and apnoeic oxygenation.
- Non-invasive ventilation (CPAP/BiPAP) via mask.
- Invasive: tracheal intubation with mechanical ventilation; and, for refractory hypoxaemia, ECMO. Hyperbaric oxygen for specific indications.
Part C
Apnoeic oxygenation
- Definition: maintenance of arterial oxygenation during apnoea WITHOUT tidal ventilation, by delivering high-FiO₂ gas to a patent upper airway.
- Mechanism ('aventilatory mass flow'): oxygen is absorbed from the alveoli (~250 mL/min) faster than CO₂ is added (~10 mL/min into the alveolus, most is buffered), creating a sub-atmospheric alveolar pressure that draws oxygen down from the pharynx. Requires a PATENT airway and prior denitrogenation (pre-oxygenation).
- Limitation: CO₂ rises ~0.4–0.8 kPa (3–6 mmHg)/min, so it buys time (oxygenation) but is not ventilation — hypercapnia/acidosis limit its duration.
- Clinical use: extends safe apnoea time during difficult intubation, RSI, and airway/ENT procedures; delivered via nasal cannulae, or high-flow nasal oxygen (THRIVE) which slows the CO₂ rise.
✅ Key Points
- The oxygen cascade: PO₂ falls stepwise from ~159 mmHg (dry air) → ~149 (humidified) → ~100 (alveolar) → ~95 (arterial) → mitochondria (~1–3 kPa).
- Oxygen devices are variable-performance (nasal cannula, Hudson, NRB), fixed-performance (Venturi), HFNO, NIV, or invasive (ETT/ventilation, ECMO).
- Apnoeic oxygenation oxygenates without ventilation via aventilatory mass flow, needs a patent airway and pre-oxygenation, but CO₂ still rises ~3–6 mmHg/min.
🔑 Clinical Pearls
- Pre-oxygenation to an end-tidal O₂ (EtO₂) ≥0.9 (denitrogenation) is what fills the FRC 'oxygen reservoir' and makes apnoeic oxygenation possible — check EtO₂, not just SpO₂ 100%.
- Adding nasal cannula O₂ at 15 L/min during RSI (apnoeic oxygenation) meaningfully prolongs safe apnoea time and reduces desaturation — a cheap, high-yield safety measure.
- The oxyhaemoglobin dissociation curve means SpO₂ stays ~100% until PaO₂ falls below ~13 kPa, then desaturation is precipitous — SpO₂ is a late warning, so watch the reservoir (pre-oxygenation) not just the saturation.
- A Venturi mask's FiO₂ is fixed because gas flow exceeds peak inspiratory flow — ideal for CO₂-retaining COPD patients where a controlled, low FiO₂ is needed.
❌ Common Mistakes to Avoid
- Calling apnoeic oxygenation a form of ventilation — it does not clear CO₂; hypercapnia limits its duration.
- Omitting the humidification step of the cascade (the drop from 159 to 149 mmHg) — a favourite examiner point.
- Assuming a simple face mask delivers a reliable high FiO₂ — it is variable-performance and dilutes with entrained air.
💡 Examiner Tip
Draw the cascade as a descending step graph with PO₂ values labelled at each step. Classify oxygen devices as variable vs fixed performance. For apnoeic oxygenation, give the mechanism AND its CO₂ limitation.
📚 Sources & References
- Nunn's Applied Respiratory Physiology.
- West's Respiratory Physiology: The Essentials.
- Miller's Anesthesia, 9th Ed — Oxygen therapy & apnoeic oxygenation.
- Patel A, Nouraei SAR. THRIVE. Anaesthesia 2015;70:323–329.
⭐ Extra Marks Content
⭐ Extra Theory Edge
- Alveolar gas equation: PAO₂ = FiO₂ (Patm − PH₂O) − PaCO₂/R. Every step of the cascade can be quantified — quoting this equation earns extra marks.
- At altitude the whole cascade shifts down (lower atmospheric PO₂); supplemental O₂ raises the top of the cascade to compensate.
- Diffusion hypoxia (Fink effect) at the end of N₂O anaesthesia is a cascade phenomenon — give 100% O₂ on emergence to prevent alveolar O₂ dilution by out-gassing N₂O.
Q8
a) What are the complications of massive blood transfusion? [6] b) Briefly discuss fibrinogen replacement therapy. [4]
×
Model Answer
Part A
Complications of massive blood transfusion
Massive transfusion = replacement of ≥1 blood volume in 24 h (≈10 units in an adult), or ≥4 units in 1 h, or >50% blood volume in 3 h. Complications are metabolic, haematological, and those common to all transfusion.
Metabolic
- Hypocalcaemia (and hypomagnesaemia): citrate anticoagulant chelates ionised calcium → hypotension, prolonged QT, coagulopathy.
- Hyperkalaemia: potassium leaks from stored red cells (worse with old/irradiated units) → arrhythmias.
- Metabolic acidosis then late metabolic alkalosis (citrate → bicarbonate metabolism).
- Hypothermia: infusion of cold products → part of the lethal triad.
Haematological (dilutional) & the lethal triad
- Dilutional coagulopathy: stored red cells lack platelets and clotting factors → thrombocytopenia and factor deficiency (especially fibrinogen and factors V, VIII).
- Hypothermia + acidosis + coagulopathy = the 'lethal triad' that perpetuates bleeding.
- DIC in the context of shock/tissue injury.
Other transfusion-related complications
- TACO (transfusion-associated circulatory overload) and TRALI (transfusion-related acute lung injury).
- Acute haemolytic (ABO-incompatibility) and febrile/allergic reactions.
- Infection transmission and immunomodulation (TRIM).
- Impaired oxygen delivery from low 2,3-DPG in stored blood (left-shifted curve).
Part B
Fibrinogen replacement therapy
- Fibrinogen (Factor I) is the FIRST coagulation factor to fall to a critical level in major haemorrhage — it is the substrate for clot formation.
- Target: maintain fibrinogen >1.5–2.0 g/L in major/obstetric haemorrhage (higher, >2 g/L, in obstetrics).
- Sources: cryoprecipitate (rich in fibrinogen, FVIII, vWF, FXIII) or fibrinogen concentrate (pathogen-reduced, standardised dose, no thawing, small volume).
- Guidance: use point-of-care viscoelastic testing (ROTEM FIBTEM / TEG functional fibrinogen) to detect and target-treat fibrinogen deficiency early.
- Advantages of concentrate: rapid, standardised, low volume (avoids TACO), no cross-matching; cryoprecipitate is cheaper but needs thawing and carries a larger transfusion-reaction/volume load.
✅ Key Points
- Massive transfusion complications: metabolic (hypocalcaemia from citrate, hyperkalaemia, acidosis, hypothermia), dilutional coagulopathy (low platelets & fibrinogen → lethal triad), and TACO/TRALI/haemolytic reactions.
- Fibrinogen is the first factor to become critically low in major bleeding; keep >1.5–2 g/L (>2 in obstetrics).
- Replace fibrinogen with cryoprecipitate or fibrinogen concentrate, ideally guided by ROTEM/TEG (FIBTEM).
🔑 Clinical Pearls
- Ionised hypocalcaemia from citrate is common and dangerous in massive transfusion — give IV calcium (chloride/gluconate) and monitor ionised Ca²⁺; it also impairs clotting and myocardial contractility.
- 'Old blood' (near expiry) has more potassium and less 2,3-DPG — prefer fresher units and use blood warmers to avoid hyperkalaemic arrest and hypothermia.
- Fibrinogen is the FIRST to fall and the FIRST to replace — a FIBTEM A5 on ROTEM gives an answer in minutes, far faster than a laboratory Clauss fibrinogen.
- Balanced 1:1:1 (RBC:FFP:platelets) resuscitation plus early TXA and calcium is the modern damage-control transfusion strategy that prevents many of these complications.
❌ Common Mistakes to Avoid
- Forgetting to replace/monitor calcium during rapid transfusion (citrate toxicity is under-treated).
- Waiting for laboratory coagulation results instead of using point-of-care viscoelastic testing to guide early, targeted fibrinogen/product therapy.
- Confusing TACO (volume overload, hypertension) with TRALI (immune lung injury, normal/low filling pressures) — they are managed differently.
💡 Examiner Tip
Classify massive-transfusion complications as metabolic / haematological / other-reactions for a structured 6 marks. For fibrinogen, give the target level, the two products, and mention ROTEM-guided therapy.
📚 Sources & References
- Miller's Anesthesia, 9th Ed — Transfusion therapy & massive transfusion.
- AAGBI / NICE — Blood transfusion and management of major haemorrhage.
- Barash, Clinical Anesthesia, 8th Ed — Blood therapy.
- European guideline on management of major bleeding and coagulopathy following trauma (2023).
⭐ Extra Marks Content
⭐ Extra Theory Edge
- Citrate is normally metabolised by the liver; hypocalcaemia is worse with rapid transfusion, hypothermia and hepatic dysfunction (e.g. liver transplant).
- Fibrinogen concentrate is increasingly first-line in postpartum haemorrhage (FIB-PPH concept) because low fibrinogen strongly predicts progression of PPH.
- Major-haemorrhage protocols with fixed-ratio packs and early cryoprecipitate/fibrinogen and TXA improve survival compared with reactive, laboratory-led replacement.
Q9
a) Buffer systems in the body. [5] b) Mechanism of action of local anaesthetics. [5]
×
Model Answer
Part A
Buffer systems in the body
A buffer resists change in pH on addition of acid or base; a physiological buffer is a mixture of a weak acid and its conjugate base. Buffers are the first, immediate line of defence in acid–base homeostasis (before respiratory and renal compensation).
The major buffer systems
- Bicarbonate/carbonic acid (HCO₃⁻/H₂CO₃) — the most important EXTRACELLULAR buffer; an 'open' system because CO₂ is removed by the lungs and HCO₃⁻ regulated by the kidney (Henderson–Hasselbalch: pH = 6.1 + log[HCO₃⁻/(0.03 × PCO₂)]).
- Haemoglobin — the major buffer in blood for carbonic acid; deoxyhaemoglobin is a better buffer (Haldane effect); histidine residues do the buffering.
- Phosphate buffer (H₂PO₄⁻/HPO₄²⁻) — important intracellularly and in renal tubular fluid (titratable acid).
- Plasma proteins — buffer via their histidine imidazole and other side chains (intracellular proteins too).
- Bone — carbonate/phosphate stores buffer chronic acid loads.
Part B
Mechanism of action of local anaesthetics (LA)
Local anaesthetics are weak bases (a lipophilic aromatic ring + intermediate ester/amide link + hydrophilic amine) that reversibly block nerve conduction by inhibiting voltage-gated sodium channels.
Mechanism
- The unionised (base, B) form is lipid-soluble and DIFFUSES across the axolemma into the axoplasm.
- Inside the more acidic axoplasm it re-equilibrates to the ionised (cationic, BH⁺) form, which is the ACTIVE moiety.
- BH⁺ enters and binds the α-subunit of the voltage-gated Na⁺ channel from the INSIDE, preferentially when the channel is OPEN/inactivated ('use-dependent' or phasic block).
- This blocks Na⁺ influx → prevents the rising phase of the action potential → the threshold for depolarisation is not reached → conduction blockade.
- Order of blockade: small myelinated (B, then Aδ/C pain, temperature) fibres are blocked before large motor (Aα) fibres — 'differential block' (autonomic → sensory → motor).
- Potency ∝ lipid solubility; onset ∝ pKa (lower pKa = more unionised = faster onset); duration ∝ protein binding.
✅ Key Points
- Buffers (immediate defence): bicarbonate (main extracellular, 'open' system), haemoglobin, phosphate, proteins and bone.
- The bicarbonate system is quantitatively most important because the lungs (CO₂) and kidneys (HCO₃⁻) independently regulate its two components.
- LAs are weak bases: the unionised form penetrates the membrane, the ionised (BH⁺) form blocks the intracellular voltage-gated Na⁺ channel in a use-dependent manner.
🔑 Clinical Pearls
- LAs work poorly in infected/acidic tissue because the low pH keeps more drug ionised (BH⁺), so less unionised base crosses the membrane — hence 'the abscess that won't freeze'.
- pKa determines onset (lidocaine pKa 7.9 → fast; bupivacaine 8.1 → slower); lipid solubility determines potency; protein binding determines duration — a neat structure–activity summary examiners love.
- Adding bicarbonate to an LA raises the unionised fraction and speeds onset; adding adrenaline prolongs duration by vasoconstriction and reduces systemic absorption/toxicity.
- Differential block explains why a patient under spinal can feel touch/pressure but no pain, and why sympathetic block (hypotension) extends a few dermatomes above the sensory level.
❌ Common Mistakes to Avoid
- Saying the unionised form blocks the channel — it is the IONISED (BH⁺) form that binds the channel from inside; the unionised form only gets it there.
- Forgetting the bicarbonate system is an 'open' buffer (its power comes from lung/kidney regulation of CO₂ and HCO₃⁻), not just its pKa.
- Reversing the differential block order — autonomic/sensory fibres are blocked before motor fibres.
💡 Examiner Tip
List the five buffers and single out bicarbonate with the Henderson–Hasselbalch equation. For LAs, describe the ionised/unionised journey and the use-dependent Na-channel block, then relate pKa/lipid solubility/protein binding to onset/potency/duration.
📚 Sources & References
- Guyton & Hall — Textbook of Medical Physiology (acid-base & buffers).
- Stoelting's Pharmacology & Physiology in Anesthetic Practice — Local anaesthetics.
- Miller's Anesthesia, 9th Ed — Local anaesthetics.
- Ganong's Review of Medical Physiology.
⭐ Extra Marks Content
⭐ Extra Theory Edge
- Isohydric principle: all buffer systems in a solution are in equilibrium with the same [H⁺], so measuring one (bicarbonate) reflects the status of all — the basis of interpreting an ABG.
- Local anaesthetic systemic toxicity (LAST): CNS excitation → seizures → coma, and cardiac Na-channel block → arrhythmias/collapse (bupivacaine is the most cardiotoxic). Treatment: stop injection, ABC, and 20% lipid emulsion (Intralipid).
- Liposomal bupivacaine and the chiral single-enantiomers (levobupivacaine, ropivacaine) were developed specifically to reduce this cardiotoxicity.
Q10
a) When does the neonatal pattern of circulation convert to an adult circulation in the pediatric patient? [4] b) What is transitional circulation and what are the intra-operative factors that can affect the conversion of a neonatal circulation to an adult circulation? [2+4]
×
Model Answer
Part A
Conversion of foetal to adult circulation
- At birth, the first breaths expand the lungs → pulmonary vascular resistance (PVR) FALLS sharply and pulmonary blood flow rises; clamping the cord removes the low-resistance placenta → systemic vascular resistance (SVR) RISES.
- These reversed pressure relationships close the foetal shunts.
- Foramen ovale: closes FUNCTIONALLY within minutes–hours as left atrial pressure now exceeds right atrial pressure (anatomical closure over weeks–months; ~25% remain probe-patent as a PFO).
- Ductus arteriosus: closes FUNCTIONALLY within 24–72 h (rising PaO₂ and falling prostaglandins cause constriction); anatomical closure (ligamentum arteriosum) by 2–3 weeks.
- Ductus venosus: closes within 3–7 days (becomes ligamentum venosum).
- Thus the 'adult' pattern is functionally established within days but the neonate remains vulnerable to reversion for the first weeks of life.
Part B
Transitional circulation & intra-operative factors affecting conversion
Transitional circulation is the labile period (first days–weeks of neonatal life) during which the foetal channels (ductus arteriosus, foramen ovale) are only functionally, not anatomically, closed and can RE-OPEN, allowing reversion to a right-to-left shunt ('persistent pulmonary hypertension of the newborn', PPHN).
Intra-operative factors that raise PVR and can reverse the transition (→ right-to-left shunt)
- Hypoxaemia — the most potent pulmonary vasoconstrictor; maintain good oxygenation.
- Hypercarbia and acidosis — both raise PVR; maintain normocapnia and correct acidosis.
- Hypothermia — raises PVR and reopens shunts; keep the neonate warm.
- Pain/stress and light anaesthesia (catecholamine surge), high airway pressures/over-inflation or atelectasis, and hypovolaemia.
- Prevention: adequate oxygenation, normocapnia, normothermia, adequate anaesthetic depth/analgesia, careful ventilation and avoiding acidosis keep PVR low and preserve the adult pattern.
✅ Key Points
- At birth PVR falls and SVR rises, functionally closing the foramen ovale (minutes–hours) and ductus arteriosus (24–72 h); anatomical closure takes weeks.
- Transitional circulation is the labile early-neonatal period when foetal channels can re-open and revert to a right-to-left shunt (PPHN).
- Anything that raises PVR — hypoxia, hypercarbia, acidosis, hypothermia, pain, high airway pressure — can reverse the transition intra-operatively.
🔑 Clinical Pearls
- Remember the pulmonary-hypertension provocateurs as the '4 H's + acidosis': Hypoxia, Hypercarbia, Hypothermia, Hypovolaemia/pain and Acidosis — avoid all in the sick neonate to prevent a right-to-left shunt.
- A neonate who suddenly desaturates under anaesthesia may have reopened the ductus/foramen ovale (PPHN) — treat by reversing the trigger: 100% O₂, hyperventilate to mild hypocapnia, warm, deepen anaesthesia, correct acidosis.
- The probe-patent foramen ovale (present in ~25% of adults) is the same channel — it explains paradoxical air/thrombus embolism, relevant in sitting-position neurosurgery.
- Ductus-dependent congenital lesions rely on the duct staying OPEN — here prostaglandin E1 is given to keep it patent; the opposite of normal transition.
❌ Common Mistakes to Avoid
- Confusing functional with anatomical closure — the shunts close functionally in hours–days but can reopen for weeks (the basis of transitional circulation).
- Forgetting hypothermia and acidosis as PVR-raising triggers, focusing only on hypoxia.
- Not appreciating that the neonate's circulation is labile and reversible, unlike the fixed adult pattern.
💡 Examiner Tip
Give the timeline of shunt closure (foramen ovale, ductus arteriosus, ductus venosus) with functional vs anatomical times. Define transitional circulation, then list the PVR-raising intra-operative triggers as a memorable group.
📚 Sources & References
- Gregory's Pediatric Anesthesia.
- Coté & Lerman — A Practice of Anesthesia for Infants and Children.
- Miller's Anesthesia, 9th Ed — Neonatal physiology & pediatric anesthesia.
- Rudolph AM — Congenital Diseases of the Heart (foetal circulation).
⭐ Extra Marks Content
⭐ Extra Theory Edge
- Foetal shunts: ductus venosus (bypasses liver), foramen ovale (RA→LA), ductus arteriosus (pulmonary artery→aorta) — all bypass the non-functioning foetal lungs.
- Persistent Pulmonary Hypertension of the Newborn (PPHN) is treated with oxygen, mild hyperventilation/alkalosis, inhaled nitric oxide (selective pulmonary vasodilator), and ECMO if refractory.
- Indomethacin/ibuprofen (prostaglandin inhibitors) close a patent ductus arteriosus, while prostaglandin E1 keeps it open in duct-dependent congenital heart disease — a key pharmacological contrast.