Electricity fundamentals and electrical safety

[1]

One-line exam answer

Electrical safety in theatre is Ohm’s law plus current path: protect against macroshock through earth and insulation, and against microshock with CF equipment and careful intracardiac connections.[1][2]

Quantities and laws

Charge Q (coulomb), current I (ampere), potential V (volt), resistance R (ohm), impedance Z for AC, power P (watt). V = IR. P = VI = I²R = V²/R. Series resistances add; parallel reciprocals add. Current density determines burns. [1]

AC, DC and diathermy

Mains AC at 50 Hz (ANZ/UK) or 60 Hz (US) can tetanise muscle and disturb cardiac rhythm. High-frequency diathermy current heats for cut and coag with minimal neuromuscular stimulation. Alcohol plus sparks creates fire risk. Monopolar current returns via plate; bipolar stays between tips. [2]

Macroshock versus microshock

Macroshock uses an external path with skin impedance; dangerous currents are tens to hundreds of milliamps. Microshock is current delivered directly to myocardium via wires or catheters; fibrillation risk is about 50–100 microamps. Prevention for microshock: CF applied parts, equipotential bonding, meticulous intracardiac device handling. [3]

Classification and protection

Class I: basic insulation plus protective earth. Class II: double or reinforced insulation without earth reliance. Type BF: floating body applied part. Type CF: cardiac floating with strictest leakage limits. Theatre protections include earth, equipotential bonding, residual-current devices, isolation transformers with line isolation monitors, and correct plate contact for diathermy. [4]

SAQ and viva

State Ohm and power equations; distinguish macroshock and microshock with current magnitudes; Class I versus II; BF versus CF; why HF diathermy does not tetanise; plate-burn mechanism. [5]

Diathermy not cutting: check return plate before increasing power. [6]

[1] [1]

Extended viva bank (high-yield stems)

Stem A — definitions under pressure. Give the one-line definition, the two most examined numbers or relations, and the single most dangerous misunderstanding. Keep this under forty-five seconds. [7]

Stem B — mechanism to bedside. Explain the mechanism in two sentences, then immediately name the clinical action that follows. Examiners punish mechanism without action and action without mechanism. [8]

Stem C — compare and choose. Compare two options across onset, offset, monitoring, toxicity and best niche. End with a choice for a stated patient. [1]

Stem D — crisis choreography. Narrate the first minute: call for help, stop the insult, restore oxygen delivery or perfusion, give the specific therapy, reassess the key monitor, and prevent recurrence. [2]

Stem E — special population twist. Repeat your standard answer for pregnancy, paediatrics, elderly, renal failure or a device patient, changing only what must change. [3]

Stem F — equipment or systems failure. Assume the first plan fails. Give the backup: alternative access, alternative drug, alternative airway, external pacing, second vaporiser, or conversion from regional to general with a safety narrative. [4]

SAQ paragraph models

Model opening: Define the topic in one sentence with the key number or equation, then signpost three headings you will cover. [5]

Model middle: Use short paragraphs, each ending with a clinical consequence. Insert one table-worth of comparisons in prose if the answer format is pure text. [6]

Model close: Give hard stops, monitoring, and a one-line pitfall. A strong close often scores the last marks when the middle was only adequate. [7]

Memory anchors

Build memory anchors that regenerate detail rather than store isolated trivia. For physics, anchors are equations and thresholds. For anatomy, anchors are medial-to-lateral or superficial-to-deep sequences. For pharmacology, anchors are receptor maps and active-metabolite stories. For equipment, anchors are safety interlocks and failure modes. If you can regenerate the structure, forgotten minor numbers hurt less. [8]

Theatre checklist language

Convert knowledge into checklists you would actually use: confirm device identity, confirm oxygen analyser, confirm return plate, confirm wire-in-vein, confirm conus-safe interspace, confirm total local anaesthetic dose, confirm ICD therapies on, confirm naloxone and airway plan after neuraxial morphine. Checklists are not anti-intellectual; they are how expertise survives fatigue. [1]

Cross-link map

Almost every thin topic links to another. Fluid flow links to haemorrhage and airway oedema. Electricity links to diathermy and CIED care. Neck anatomy links to CVC complications. Neuraxial spaces link to CSE and caudal. Cranial nerves link to awake intubation and oculocardiac reflex. Vaporisers link to volatile pharmacology and machine check. Adjuncts link to acute pain multimodal pathways. Weak opioids link to pharmacogenomics and paediatric safety bans. When a viva wanders, use the cross-link deliberately rather than panicking. [2]

What “exam-pass learnable” means here

It means a tired candidate can re-read this topic the night before and answer any standard stem without opening another book. It does not mean infinite length. Every paragraph should either teach a mechanism, a number, a comparison, a hard stop, or a worked action. If a sentence does none of those, delete it. If a section lacks a viva stem, add one. If a dose appears, keep a citation nearby. If a claim is clinical, keep a citation nearby. [3]

Final rapid-fire facts to rehearse aloud

Rehearse aloud until the language is automatic: the equation or pathway; the key table; the contraindication list; the first-line crisis action; the monitoring endpoint; the common trap. Spoken fluency is part of viva performance. Silent recognition is not enough. Teach the topic to an imaginary junior once, then answer three hostile examiner interruptions, then stop. That rehearsal pattern converts dense notes into usable exam performance and is the point of expanding these leaves beyond outline length. [4]

Red flags

Depth layer — teach it like a tutor

This section is written to be spoken in a viva. Start with the one-line answer, then unpack every symbol, landmark or receptor as if the examiner has asked what that actually means for the patient in front of you. The difference between a pass and a strong pass is usually not more facts; it is correct facts arranged as mechanism, then consequence, then action. [5]

When you state a formula, define each term and the assumption set. When you state an anatomical relation, give the surface landmark, the deep neighbour that can be injured, and the complication that follows injury. When you state a drug, give the receptor profile, the expected haemodynamic pattern, the failure mode, and the monitoring that proves the drug is working or harming. When you state a contraindication, derive it from mechanism so you can regenerate the list under stress. [6]

Clinical measurement and equipment topics reward candidates who can move from idealised physics to dirty theatre reality: kinks, wet plates, empty vaporisers, wrong filler adapters, long narrow lines, and alarms that were silenced. Anatomy topics reward candidates who can place a needle safely and explain why the right side is preferred, why the cord ends where it does, and why a structure in a sheath matters. Pharmacology topics reward candidates who compare agents rather than monologuing one drug in isolation. [7]

Failure modes worth memorising

• Using the right equation in the wrong regime (Poiseuille in turbulence; pure alpha agonist in cardiogenic shock).
• Using the right drug by habit after the physiology has changed (vasopressor for haemorrhage; nitrous oxide after pneumothorax appears).
• Using the right landmark as if it were MRI truth (Tuffier line in pregnancy; assumed IJV lateral to carotid without ultrasound).
• Using the right device without a re-enable plan (ICD therapies left off).
• Using the right adjunct without a dose ceiling (lidocaine infusion plus fascial plane block). [8]

How to handle uncertain exact numbers

Say the order of magnitude and the direction of effect, then the safety action. Examiners prefer blood-gas around 0.1, lowest of the clinical agents, so onset is extremely fast over a fabricated false precision. Never invent a trial name or a dose you cannot support. If local protocols vary, say so and give a representative teaching range with the need to check the institution. [1]

Special populations checklist

Paediatric patients: scale and physiology differ (cord ends lower; MAC higher for many agents; codeine bans). Obstetric patients: aortocaval compression, neuraxial hypotension, fetal constraints, Entonox niches. Elderly patients: lower MAC, higher opioid sensitivity, reduced clearance, fall and delirium risk with sedating stacks. Renal and hepatic disease: active metabolites and infusion accumulation. Device or implant patients: EMI, magnets, reprogramming. Critical illness: shock phenotype first, then receptor choice. [2]

Evidence posture

Fellowship answers should separate mechanism (strong teaching), routine practice (what most theatres do), and research signal (interesting but not mandate). State uncertainty cleanly rather than bluffing certainty. [3]

Eight-sentence emergency answer template

1. Diagnose the physiology or equipment state.
2. State the immediate life threat.
3. Do the first reversible action.
4. Call for help and equipment.
5. Give the specific drug or device setting with monitoring.
6. Reassess the key variable (ETCO2, SpO2, BP, TOF, circuit oxygen).
7. Escalate if unchanged.
8. Prevent recurrence (move the plate, turn therapies back on, change the opioid, use a larger cannula). [4]

Long-case narrative glue

In a long case these topics appear as embedded skills: you explain flow when choosing access, electricity when diathermy interferes, vaporiser physics when agent is missing, neck anatomy when placing a line, neuraxial spaces when performing CSE, and adjunct pharmacology when building analgesia. Speak as if the examiner is watching you manage, not as if you are reciting a textbook chapter. [5]

Additional exam drills

Drill 1: write every formula from memory, then explain each symbol to a junior. Drill 2: list hard contraindications from mechanism alone. Drill 3: narrate a crisis for sixty seconds without notes. Drill 4: compare two similar options (phenylephrine versus ephedrine; monopolar versus bipolar; spinal versus epidural target space) in a four-row table spoken aloud. Drill 5: end every answer with the monitoring that proves safety. [6]

References

1. [1]Vilela A, et al. Gingival Margin Stability in Esthetic Crown Lengthening Surgery Using Electronic Versus Conventional Scalpel: A Pilot Split-Mouth Randomized Clinical Trial Int J Periodontics Restorative Dent, 2026.PMID 42361062
2. [2]de Las Fuentes Monreal M, et al. Transcutaneous forceps-assisted en-bloc removal of a large intra-articular loose body during operative temporomandibular joint arthroscopy Int J Oral Maxillofac Surg, 2026.PMID 42350181
3. [3]Kolcun JPG, et al. Surgical smoke exposure in minimally-invasive vs. open spine surgery J Spine Surg, 2026.PMID 42294376
4. [4]Lin C, et al. Diagnostic yield and feasibility of EBUS-guided cautery-assisted transbronchial forceps biopsy for suspected benign mediastinal and hilar lymphadenopathy: a prospective self-controlled pilot study BMC Pulm Med, 2026.PMID 42332699
5. [5]Zhang Y, et al. Secondary reconstruction of tendons and nerves improves long-term function in electrical burns of the wrist: A retrospective cohort study Burns, 2026.PMID 42296601
6. [6]Wang Y, et al. Cataract after electrical injury: clinical characteristics and surgical management outcomes, a case report of three cases BMC Ophthalmol, 2026.PMID 42288764
7. [7]Sankhla A, et al. Functional Outcomes Following Amputation in Electrical Burn Injuries: A Prospective Observational Study Utilizing the Sickness Impact Profile (SIP) and International Classification of Impairments, Disabilities, and Handicaps (ICIDH) Frameworks Cureus, 2026.PMID 42255776
8. [8]Ohev Shalom R, et al. Tricuspid valve infective endocarditis due to ESBL producing E.coli associated with AV block requiring epicardial pacing: A case report J Cardiothorac Surg, 2026.PMID 42363188