Anaesthesia technology basics

In short

Anaesthesia technology is the applied science of preparing, running and monitoring the equipment and drugs that keep a patient unconscious, pain-free and physiologically stable during surgery. The anaesthesia technologist assembles and checks the anaesthesia machine, prepares airway and vascular equipment, draws up drugs, assists intubation and spinal blocks, watches monitors and manages gas supplies, recovery and sterilisation. It is examined in B.Sc Operation Theatre / Anaesthesia Technology papers (anaesthesia equipment, pharmacology, monitoring, medical gases) and tested in placement rounds at Apollo, Fortis, Manipal, Narayana Health, Max, Medanta, AIIMS and state medical colleges, plus NHM and ESIC technician recruitment. Indian practice follows NABH and NABL standards, the Drugs and Cosmetics Act/Rules for drug and device handling, the NDPS Act for opioids, and the National Commission for Allied and Healthcare Professions Act, 2021, which now registers anaesthesia and OT technologists.

Explained

Types of anaesthesia and the stages of general anaesthesia

• General anaesthesia (GA): reversible loss of consciousness, analgesia, amnesia, areflexia and muscle relaxation; given by inhalation, intravenously (TIVA) or both.
• Regional anaesthesia: nerve conduction is blocked while the patient stays awake — spinal (subarachnoid), epidural, combined spinal-epidural, brachial plexus and other peripheral nerve blocks.
• Local anaesthesia: infiltration or topical, for small procedures. Sedation / monitored anaesthesia care (MAC): anxiolysis to deep sedation with a monitored airway.
• Triad of anaesthesia: hypnosis (unconsciousness) + analgesia + muscle relaxation; modern practice uses a separate drug for each, so doses of each are smaller ("balanced anaesthesia").
• Guedel's stages (described for ether, still examined): I analgesia, II excitement/delirium (avoid — risk of laryngospasm, vomiting), III surgical anaesthesia (four planes, judged by pupil, eye movement, respiration), IV medullary paralysis (overdose — apnoea, dilated fixed pupils, cardiovascular collapse).
• Phases of a GA: premedication → pre-oxygenation → induction → airway placement → maintenance → reversal → emergence → recovery (PACU) handover.
• ASA physical status: I normal healthy; II mild systemic disease; III severe systemic disease; IV severe disease that is a constant threat to life; V moribund, not expected to survive without surgery; VI brain-dead organ donor; suffix E for emergency.
• Fasting (NPO) rule of thumb before elective surgery: 2 h clear fluids, 4 h breast milk, 6 h light meal / formula, 8 h fatty or heavy meal — hospital protocols vary slightly.

The anaesthesia machine (Boyle's apparatus) — gas path, component by component

Follow the gas in the order it travels; exams and interviews both ask it this way.

1. Supply: pipeline gas at about 4 bar (400 kPa) from a central manifold through colour-coded NIST/DISS wall outlets, plus back-up cylinders on the machine yoke. Cylinder pressure is reduced by a pressure regulator to roughly the same working pressure, so the machine draws from the pipeline while cylinders stay in reserve.
2. Indian cylinder colours (IS marking): oxygen black body, white shoulder; nitrous oxide blue; medical air grey body, white-and-black shoulder; carbon dioxide grey; entonox blue with white-and-blue quarters. Many hospitals also use the all-white ISO oxygen cylinder — read the label, never the paint alone.
3. Pin Index Safety System (PISS) for small cylinders, non-interchangeable screw threads (NIST) for pipelines, and colour coding — three independent safeguards against connecting the wrong gas.
4. Flowmeters (rotameters): tapered glass tubes with a rotating bobbin; one per gas, reading in L/min. Oxygen rotameter is placed downstream (nearest the common outlet) so a leak in another tube cannot rob the mixture of oxygen.
5. Safety interlocks: oxygen failure (Ritchie/Bosun) alarm sounds below ~200 kPa; oxygen-nitrous oxide ratio device (hypoxic guard) limits N₂O so FiO₂ cannot fall below about 25%; fail-safe valve cuts N₂O when oxygen pressure falls; non-return valve prevents backflow into the pipeline.
6. Vaporiser: adds a measured percentage of volatile agent. Modern agent-specific, temperature- and flow-compensated, variable-bypass, out-of-circuit (VOC) vaporisers — Tec series for halothane, isoflurane, sevoflurane; desflurane needs an electrically heated, pressurised vaporiser (boiling point about 23 °C). Selectatec back-bar mounting with interlock so only one vaporiser can be switched on.
7. Common gas outlet → breathing system. Oxygen flush bypasses the vaporiser and delivers 35-75 L/min of pure oxygen — never press it during spontaneous ventilation on a Bain circuit or with a patient connected to a ventilator (barotrauma risk, and it dilutes the agent).
8. Scavenging system: active (vacuum) or passive, to remove waste anaesthetic gases from theatre air.
9. Ventilator and bellows: ascending (standing) bellows are preferred — they collapse visibly on a disconnection. Modes: volume-controlled, pressure-controlled, SIMV, pressure support.

Breathing systems and the circle absorber

• Open: open drop ether on a Schimmelbusch mask (historic). Semi-open / semi-closed: Mapleson systems. Closed: circle with total rebreathing and very low fresh gas flow.
• Mapleson classification A-F: A (Magill) most efficient for spontaneous ventilation (needs ≈ minute volume); D and its coaxial version the Bain circuit most efficient for controlled ventilation (needs ≈ 1.5-2 × minute volume); E Ayre's T-piece and F Jackson-Rees modification for children under about 20 kg (low resistance, no valves).
• Circle absorber system components: fresh gas inlet, two unidirectional (one-way) valves, inspiratory and expiratory limbs, Y-piece, reservoir bag, APL (adjustable pressure-limiting) / pop-off valve, and the CO₂ absorber canister.
• Soda lime: about 80% calcium hydroxide, 4% sodium hydroxide, water and a silica binder, with an indicator dye (white → violet, or pink → white depending on dye) showing exhaustion. Granule size 4-8 mesh. 100 g absorbs roughly 23 L of CO₂. Reaction: CO₂ + H₂O → H₂CO₃; H₂CO₃ + 2NaOH → Na₂CO₃ + 2H₂O + heat; Na₂CO₃ + Ca(OH)₂ → CaCO₃ + 2NaOH. Baralyme is obsolete.
• Channelling (gas tunnelling through settled granules) and a hot, exhausted canister are the two classic absorber faults; sevoflurane with dry soda lime can form Compound A, and desflurane/isoflurane with desiccated absorbent can generate carbon monoxide.
• Advantages of a circle: conserves heat and humidity, saves agent and oxygen, reduces theatre pollution. Limitations: bulky, resistance, risk of absorber exhaustion, and inspired concentration differs from the dial setting at low flows.

Airway equipment and intubation

• Face masks and oral/nasal airways (Guedel airway sized ear-lobe to angle of mouth); bag-valve-mask (Ambu) for ventilation without a machine.
• Supraglottic airways: classic LMA, ProSeal, i-gel, LMA Supreme; sizes by weight — 1 (<5 kg), 1.5, 2 (10-20 kg), 2.5, 3 (30-50 kg), 4 (50-70 kg), 5 (70-100 kg). Do not protect fully against aspiration.
• Endotracheal tubes: cuffed (adults) or uncuffed (small children); internal diameter in mm. Usual adult sizes 7.0-7.5 mm for women, 8.0-8.5 mm for men; paediatric uncuffed ID ≈ (age/4) + 4. Oral depth ≈ 3 × tube ID, roughly 21 cm in women and 23 cm in men at the incisors. Special tubes: armoured/flexometallic, RAE, double-lumen (thoracic), microlaryngeal.
• Laryngoscopes: Macintosh (curved, adult), Miller (straight, infants), McCoy (levering tip); video laryngoscopes (C-MAC, King Vision), flexible fibreoptic scope, bougie, stylet, Magill forceps.
• Cuff pressure should be kept at 20-30 cm H₂O measured with a manometer — higher pressure causes tracheal mucosal ischaemia.
• Confirming correct placement: sustained capnography waveform (the gold standard), chest rise, bilateral equal air entry, no epigastric sounds, misting, SpO₂ maintained.
• Rapid sequence induction (RSI): pre-oxygenation, pre-calculated dose of induction agent plus fast-acting relaxant (succinylcholine or high-dose rocuronium), no manual ventilation, cricoid pressure (debated), immediate intubation — used for a full stomach, trauma, pregnancy.
• Difficult airway: predicted by Mallampati class III-IV, thyromental distance <6 cm, mouth opening <3 cm, restricted neck movement, short thick neck. Keep a difficult airway trolley ready; the fallback ladder ends in supraglottic rescue and front-of-neck access (cricothyroidotomy).

Drugs the technologist must know and prepare

• IV induction: propofol 1.5-2.5 mg/kg (smooth, antiemetic, causes hypotension and pain on injection); thiopentone 3-5 mg/kg; ketamine 1-2 mg/kg IV (dissociative, maintains blood pressure, raises secretions, emergence delirium); etomidate 0.3 mg/kg (cardiostable, adrenal suppression); midazolam for sedation/amnesia.
• Inhalational agents: sevoflurane (pleasant, used for inhalational induction in children), isoflurane (cheap, workhorse in India), desflurane (fast on/off, special vaporiser), nitrous oxide (analgesic carrier gas), halothane (still used in some centres; hepatitis and arrhythmia risk).
• MAC (minimum alveolar concentration) — the concentration that prevents movement in 50% of patients at 1 atm: halothane ≈ 0.75%, isoflurane ≈ 1.15%, sevoflurane ≈ 2%, desflurane ≈ 6%, nitrous oxide ≈ 104%. MAC falls with age, opioids, sedatives, hypothermia and pregnancy; rises in infants and chronic alcohol use. MACs of agents are additive.
• Muscle relaxants: depolarising succinylcholine 1-1.5 mg/kg (onset 30-60 s, lasts 5-10 min; causes fasciculation, raises serum potassium, trigger for malignant hyperthermia, contraindicated in burns, spinal injury, hyperkalaemia); non-depolarising vecuronium, rocuronium, atracurium, cisatracurium (atracurium is the choice in renal/hepatic failure — Hofmann elimination). Reversal: neostigmine 0.05 mg/kg with glycopyrrolate/atropine, or sugammadex for rocuronium/vecuronium.
• Opioids: fentanyl 1-2 µg/kg, morphine, pethidine; all NDPS Act, 1985 controlled items needing a locked cupboard, a register with running balance and witnessed wastage.
• Local anaesthetics: lignocaine 2% (max ≈ 4.5 mg/kg plain, 7 mg/kg with adrenaline), bupivacaine 0.5% heavy for spinal (max ≈ 2 mg/kg), ropivacaine. LAST (local anaesthetic systemic toxicity) — tinnitus, perioral numbness, seizures, cardiac arrest — treated with 20% lipid emulsion.
• Emergency drugs on every trolley: adrenaline, atropine, ephedrine/mephentermine, noradrenaline, hydrocortisone, calcium gluconate, sodium bicarbonate, dextrose 25%, labetalol, nitroglycerine, naloxone, flumazenil, dantrolene (for malignant hyperthermia, often not stocked in smaller Indian hospitals — check), 20% lipid emulsion.

Monitoring, safety checks and medical gas systems

• Minimum monitoring in every anaesthetic: continuous presence of a trained person, pulse oximetry (SpO₂), NIBP, ECG, capnography (EtCO₂), airway pressure and disconnection alarm, FiO₂ analyser, temperature, and a nerve stimulator when relaxants are used (train-of-four).
• Pulse oximeter: two LEDs at 660 nm (red) and 940 nm (infrared) measure the pulsatile absorbance ratio to give functional SpO₂. Misleads in carboxyhaemoglobin (falsely high), methaemoglobinaemia (reads ≈ 85%), poor perfusion, motion, nail polish, bright ambient light; it does not detect hypoventilation early if oxygen is being given.
• Capnography: infrared absorbance at 4.26 µm, mainstream or sidestream. Normal EtCO₂ 35-45 mmHg. A flat trace = disconnection, oesophageal intubation, cardiac arrest; a sloping plateau = obstruction/bronchospasm; a raised baseline = rebreathing (exhausted soda lime or stuck valve); a sudden fall = embolism, hypotension or low cardiac output; a rising EtCO₂ with tachycardia and rigidity = suspect malignant hyperthermia.
• Invasive monitoring: arterial line (beat-to-beat BP, blood gases), CVP, cardiac output monitors, BIS/entropy for depth of anaesthesia.
• Machine check before every list: pipeline and cylinder pressures, no leaks (occlude the common outlet and squeeze — the "two-bag" and low-pressure leak tests), rotameters free, vaporiser filled and seated with the filler cap tight, soda lime colour, one-way valves moving, APL valve working, ventilator and bellows, suction working, scavenging connected, breathing circuit and reservoir bag intact, monitors calibrated, emergency drugs and difficult-airway trolley, self-inflating bag as a back-up.
• WHO Surgical Safety Checklist (sign-in, time-out, sign-out) — mandatory in NABH-accredited hospitals; the technologist contributes the equipment and monitoring items.
• Medical gas pipeline system (MGPS): central oxygen manifold or liquid medical oxygen (LMO) tank with a vaporiser, nitrous oxide manifold, medical air plant (4 bar) and separate surgical air (7 bar), vacuum plant; area valve service units, pressure alarms, and annual testing. Oxygen purity for medical use is 99.5% (IP, "Oxygen 93%" is a separate monograph for concentrators). India's National Building Code and NABH require MGPS design to recognised standards (HTM/ISO 7396-1-based); quote the hospital's own commissioning document rather than a remembered IS number.
• Theatre environment: 20-25 air changes per hour with HEPA filtration, positive pressure, temperature 20-24 °C, humidity 50-60%, and anaesthetic gas scavenging to limit staff exposure.
• Sterilisation of anaesthesia equipment: single-use ETTs and circuits where possible; autoclave 121 °C/15 psi/15-20 min or 134 °C/3.5 min for heat-stable items; ETO or plasma (H₂O₂) sterilisation for laryngoscope blades, LMAs and fibreoptic scopes; 2% glutaraldehyde / OPA high-level disinfection for scopes; bacterial-viral filter at the patient end of the circuit. Biomedical waste is segregated under the Bio-Medical Waste Management Rules, 2016 (as amended) — yellow, red, white (translucent, sharps) and blue bags.

Complications, recovery and legal-professional framework

• Airway: failed intubation, oesophageal intubation, laryngospasm, bronchospasm, aspiration, dental damage, cuff leak, kinked tube, endobronchial intubation.
• Cardiovascular: hypotension after induction or spinal, hypertension on laryngoscopy, arrhythmias, cardiac arrest.
• Others: awareness under anaesthesia, hypoxia, hypo/hyperthermia, shivering, PONV, post-dural-puncture headache, nerve injury from positioning, drug error, anaphylaxis, malignant hyperthermia (treat with dantrolene 2.5 mg/kg, stop triggers, cool, treat hyperkalaemia and acidosis).
• Spinal/epidural specifics: sterile technique, L3-L4 or L4-L5 interspace (cord ends at L1-L2 in adults), 25-27 G pencil-point needle for spinal to reduce headache, 16-18 G Tuohy with loss-of-resistance for epidural; watch for hypotension, bradycardia, high block, total spinal.
• Recovery (PACU): oxygen, monitoring, pain and nausea control; modified Aldrete score (activity, respiration, circulation, consciousness, saturation — each 0-2; ≥9 for discharge).
• Professional and legal: anaesthesia is given by a qualified anaesthesiologist; the technologist assists and never independently induces anaesthesia or prescribes. Registration and scope of practice come under the National Commission for Allied and Healthcare Professions Act, 2021 and the state allied-health councils; informed consent, drug registers (NDPS), device handling under the Drugs and Cosmetics Act, 1940/Rules and the Medical Devices Rules, 2017; records retained per hospital and NABH policy.

Key points

• Triad of anaesthesia - hypnosis + analgesia + muscle relaxation, each from a separate drug (balanced anaesthesia).
• Pin Index Safety System - unique pin pattern per gas on small cylinders; NIST threads and colour coding do the same job for pipelines.
• Oxygen rotameter position - always last/downstream so a cracked tube cannot cause a hypoxic mixture.
• Pipeline pressure 4 bar (≈ 400 kPa); oxygen cylinder full pressure ≈ 137 bar (2,000 psi); N₂O cylinder reads ≈ 51 bar until the liquid is gone, so its gauge does not show contents.
• Hypoxic guard - mechanically limits N₂O so delivered oxygen cannot fall below about 25%.
• Oxygen flush - 35-75 L/min of pure oxygen bypassing the vaporiser; barotrauma risk if used carelessly.
• Mapleson A best for spontaneous ventilation, Mapleson D/Bain best for controlled ventilation, E/F for small children.
• Soda lime - 80% Ca(OH)₂ + 4% NaOH + water; colour change and heat show it is working/exhausted; ~23 L CO₂ per 100 g.
• Capnography - the single most useful monitor; sustained waveform confirms the tube is in the trachea.
• Pulse oximetry - 660 nm and 940 nm; falsely high with CO poisoning, ≈85% in methaemoglobinaemia.
• MAC - concentration preventing movement in 50% of patients; isoflurane 1.15%, sevoflurane 2%, desflurane 6%, N₂O 104%; values are additive.
• Succinylcholine 1-1.5 mg/kg - fastest onset and offset; hyperkalaemia and MH risks.
• Neostigmine + glycopyrrolate reverses non-depolarising block; sugammadex reverses rocuronium/vecuronium specifically.
• ETT cuff pressure 20-30 cm H₂O measured with a manometer, not by feel.
• Paediatric uncuffed ETT ID = (age/4) + 4 mm; depth ≈ 3 × ID in cm.
• ASA I-VI with E suffix - the standard pre-operative risk grade.
• Aldrete score ≥ 9 - usual threshold for PACU discharge.
• Ascending bellows collapse on disconnection, which is why they are preferred over descending bellows.

Formulas and examples

Example 1 - Ventilator setting. A 70 kg adult for laparotomy, lung-protective setting at 7 mL/kg, RR 12/min.

• V_T = 7 × 70 = 490 mL.
• MV = 490 × 12 = 5,880 mL/min = 5.88 L/min.
• For a Bain (Mapleson D) circuit under controlled ventilation, fresh gas flow needed ≈ 1.5-2 × MV = 8.8 to 11.8 L/min, against only ≈ 0.5-1 L/min once a circle system is in steady state — the reason circles dominate elective Indian theatre practice.

Example 2 - Oxygen cylinder duration. A size-D (water capacity 2.3 L) emergency oxygen cylinder for transport reads 120 bar on the gauge; the patient needs 6 L/min.

• Contents ≈ 120 × 2.3 = 276 L at atmospheric pressure.
• Duration = 276 / 6 = 46 minutes. Keeping a 25% safety reserve, plan for about 34 minutes of transport.
• A size-E cylinder (4.7 L water capacity) at the same 120 bar holds 120 × 4.7 = 564 L → 564/6 = 94 minutes.

Example 3 - Local anaesthetic maximum dose. A 60 kg woman for an axillary block with lignocaine plus adrenaline (7 mg/kg).

• Maximum dose = 7 × 60 = 420 mg.
• Lignocaine 2% = 20 mg/mL → maximum volume = 420 / 20 = 21 mL.
• If 1% (10 mg/mL) is used instead, the maximum volume doubles to 42 mL for the same 420 mg — the dose in mg is the limit, not the volume.

Example 4 - Paediatric airway and tube. An 8-year-old child, 24 kg, elective hernia repair.

• Uncuffed ETT ID = (8/4) + 4 = 6.0 mm; keep 5.5 and 6.5 ready.
• Insertion depth ≈ 3 × 6.0 = 18 cm at the lips.
• LMA size for 24 kg = size 2.5 (20-30 kg).
• Suction catheter size ≈ 2 × ETT ID = 12 Fr.
• Succinylcholine for RSI at 1.5 mg/kg = 1.5 × 24 = 36 mg; from a 50 mg/mL vial that is 0.72 mL — dilute to 10 mg/mL and give 3.6 mL to avoid a dosing error.

Example 5 - MAC arithmetic. Maintenance with 60% nitrous oxide and 0.8% isoflurane in oxygen.

• N₂O contribution = 60 / 104 = 0.58 MAC.
• Isoflurane contribution = 0.8 / 1.15 = 0.70 MAC.
• Total = 0.58 + 0.70 = 1.28 MAC — adequate for surgical anaesthesia in a young adult; in a 75-year-old, MAC requirement falls roughly 6% per decade over 40, so this is a relatively deep plane and hypotension should be expected.

Where it is used

• Hospital operation theatres and day-care surgery centres: Apollo, Fortis, Manipal, Max, Medanta, Narayana Health, AIIMS and state medical colleges employ anaesthesia/OT technologists on every list, with government posts through NHM, ESIC, railways and state PSC technician cadres.
• ICU, emergency and cath lab: ventilator management, intubation assistance, arterial lines, procedural sedation, transport ventilation and code-blue teams.
• Labour rooms and cardiac/neuro theatres: epidural analgesia trolleys, cell savers, cardiopulmonary bypass support roles, neuromonitoring set-ups.
• Medical device industry: application specialists, service and installation engineers for anaesthesia workstations and monitors — Skanray, Allied Medical, BPL Medical Technologies, Philips, GE Healthcare, Dräger, Mindray — and MGPS installation and testing firms.
• Biomedical and quality roles: preventive maintenance of workstations and vaporisers, calibration of flow and gas analysers, NABH/NABL documentation, infection-control audits of anaesthesia equipment.
• Teaching, simulation and overseas practice: skills labs in allied-health colleges, and technologist/OTA roles in the Gulf (DHA, HAAD, MOH licensing exams) and the UK/Ireland for registered Indian graduates.

Interview questions

• Q: Why is the oxygen flowmeter placed downstream of the other gases? A: So that if another flowmeter tube cracks, gas escapes from it rather than diluting the oxygen already entering the mixture — it protects against a hypoxic mixture.
• Q: A nitrous oxide cylinder gauge still reads 51 bar. How much gas is left? A: You cannot tell. N₂O is stored as liquid, so the pressure stays near 51 bar until all the liquid has evaporated; contents are checked by weighing the cylinder against its tare weight.
• Q: What is the single best way to confirm an endotracheal tube is in the trachea? A: A sustained capnography waveform over several breaths; chest rise and auscultation support it but can mislead.
• Q: What does a raised, non-zero baseline on the capnograph mean? A: Rebreathing of CO₂ — usually exhausted soda lime, a stuck or incompetent one-way valve, or inadequate fresh gas flow.
• Q: Why is succinylcholine avoided in a patient with burns or a spinal cord injury a week old? A: Up-regulated extrajunctional acetylcholine receptors cause a massive potassium release, risking hyperkalaemic cardiac arrest.
• Q: What are the three safety systems that prevent connecting the wrong gas? A: Colour coding, the Pin Index Safety System on small cylinders, and non-interchangeable screw threads/indexed quick connectors on pipelines.
• Q: Why do we prefer ascending bellows on an anaesthesia ventilator? A: They collapse and stop moving if the circuit disconnects, giving an immediate visual sign; descending bellows keep moving under gravity and can hide a disconnection.
• Q: What is MAC and what lowers it? A: The minimum alveolar concentration that prevents movement to a surgical stimulus in 50% of patients; it falls with age, opioids, benzodiazepines, hypothermia, pregnancy, hypotension and severe anaemia.
• Q: Your patient on sevoflurane suddenly shows rising EtCO₂, tachycardia, masseter rigidity and fever. What do you do? A: Suspect malignant hyperthermia — stop the volatile and succinylcholine, call for help, hyperventilate with 100% oxygen on a clean circuit, give dantrolene 2.5 mg/kg, cool actively and treat hyperkalaemia and acidosis.
• Q: Why is a spinal needle inserted below L2? A: The spinal cord normally ends at L1-L2 in adults, so puncture below that level reaches cerebrospinal fluid without risking cord injury.
• Q: Which muscle relaxant would you choose for a patient with renal failure and why? A: Atracurium or cisatracurium — they are broken down by Hofmann elimination and ester hydrolysis in plasma, independent of renal and hepatic clearance.
• Q: How do you handle a fentanyl ampoule left part-used? A: Opioids are NDPS-controlled: record the amount given and the amount wasted in the register, discard the remainder with a witness, and have both signatures — never carry it over or pocket it.

Common mistakes

• Treating SpO₂ as a ventilation monitor — a patient on high FiO₂ can be badly hypercapnic with a normal saturation; only capnography shows it.
• Reading a nitrous oxide gauge as a contents gauge, or trusting cylinder paint colour instead of the label and pin index.
• Tilting, over-filling or filling a vaporiser with the wrong agent — the agent-specific keyed filler exists precisely to stop this; a tipped vaporiser must be flushed before use.
• Forgetting that the dose limit for local anaesthetics is in mg/kg, and calculating volume without converting percentage to mg/mL (1% = 10 mg/mL).
• Inflating the ETT cuff "till it feels firm" instead of measuring 20-30 cm H₂O, and ignoring tube depth so the tip sits in the right main bronchus.
• Pressing the oxygen flush with the patient connected to a ventilator or a Bain circuit, risking barotrauma and simultaneously diluting the anaesthetic agent to awareness levels.
• Skipping the pre-list machine check, the circuit leak test or the back-up self-inflating bag because "the machine was fine in the last case".

Related topics

Operation theatre technology · Human anatomy and physiology (respiratory and cardiovascular) · Medical gas pipeline systems and cylinder handling · Patient monitoring instrumentation · Sterilisation, disinfection and biomedical waste management · Critical care and ventilator basics