PGIM MD Anaesthesiology key terms

The volume of gas left in the lungs at the end of a normal passive expiration. It is the sum of expiratory reserve volume and residual volume, and it acts as the main oxygen reservoir during apnoea.

The lung volume at which small airways begin to close during expiration. When it exceeds functional residual capacity, as in supine patients, obesity, or infants, airway closure occurs during tidal breathing and causes shunt and hypoxaemia.

The fraction of cardiac output that passes through unventilated lung and therefore returns to the left heart without taking up oxygen. It causes hypoxaemia that responds poorly to increasing inspired oxygen.

The difference between calculated alveolar oxygen tension and measured arterial oxygen tension. It widens with ventilation-perfusion mismatch, shunt, and diffusion impairment, and helps distinguish hypoxaemia from hypoventilation alone.

The total amount of oxygen reaching the tissues each minute, calculated as cardiac output multiplied by arterial oxygen content. Content depends mainly on haemoglobin concentration and saturation, so anaemia and low output both reduce delivery.

The sigmoid relationship between oxygen partial pressure and haemoglobin saturation. A rightward shift, caused by raised carbon dioxide, acidosis, temperature, or 2,3-DPG, releases oxygen more readily to tissues.

Non-invasive estimation of arterial haemoglobin saturation using differential light absorption of red and infrared wavelengths across a pulsatile vascular bed. It is unreliable with poor perfusion, motion, dyshaemoglobinaemia, and very low saturation.

Continuous display of the carbon dioxide concentration in respired gas against time. The waveform confirms tracheal tube placement, detects disconnection and obstruction, and its end-tidal value reflects cardiac output and dead space.

The portion of each breath that does not take part in gas exchange, comprising anatomical airway volume and alveoli that are ventilated but not perfused. It is increased by hypotension, pulmonary embolism, and overdistension of the lungs.

Continued oxygen uptake during apnoea from the mass flow of oxygen into the alveoli as carbon dioxide is absorbed into blood. It prolongs the safe apnoea time during intubation and is delivered by nasal cannulae or a face mask.

A technique for inducing anaesthesia in a patient at risk of aspiration, using a predetermined dose of induction agent followed promptly by a neuromuscular blocker, with avoidance of positive-pressure ventilation before the airway is secured.

Pressure applied to the cricoid cartilage to compress the oesophagus against the cervical spine, intended to reduce passive regurgitation during induction. Its effectiveness is debated and it can worsen laryngoscopic view.

A clinical situation in which trained anaesthetists experience difficulty with face-mask ventilation, supraglottic device placement, laryngoscopy, tracheal intubation, or an invasive airway. Management follows a predefined stepwise algorithm.

Creation of an emergency airway through the cricothyroid membrane, usually with a cannula or scalpel-bougie technique. It is the final rescue step in a cannot-intubate, cannot-oxygenate situation.

Indirect laryngoscopy using a camera-bearing blade that displays the glottis on a screen. It improves glottic visualisation in difficult airways and reduces the force applied to the oropharynx compared with direct laryngoscopy.

A four-point classification of the view obtained at direct laryngoscopy, from full visibility of the vocal cords to visibility of only the epiglottis or soft palate. Higher grades predict difficulty with intubation.

The alveolar concentration of an inhaled anaesthetic at which half of patients do not move in response to a standard surgical stimulus at one atmosphere. It allows comparison of potency between volatile agents.

The time taken for the plasma concentration of a drug to fall by half after an infusion is stopped, measured from the moment of stopping. It lengthens with infusion duration for drugs with slow redistribution, such as thiopentone.

A pump system that uses a population pharmacokinetic model to adjust infusion rate so that a chosen predicted plasma or effect-site concentration is achieved and maintained. It does not measure actual drug concentration.

The combined effect of two drugs acting on the same physiological system, which may be additive, synergistic, or antagonistic. Opioids and volatile agents, for example, interact synergistically to reduce MAC and cause respiratory depression.

Block produced by suxamethonium, which activates the acetylcholine receptor before causing prolonged depolarisation. It has the fastest onset and shortest duration of all muscle relaxants but triggers hyperkalaemia and malignant hyperthermia.

Assessment of neuromuscular block using peripheral nerve stimulation and evoked muscle responses, such as train-of-four or post-tetanic count. It guides reversal and reduces residual paralysis after anaesthesia.

A modified gamma-cyclodextrin that encapsulates rocuronium and vecuronium in the plasma, rapidly reversing even deep block. It does not reverse depolarising block and can cause anaphylaxis and bradycardia.

A pharmacogenetic hypermetabolic crisis triggered by volatile anaesthetics or suxamethonium, caused by uncontrolled calcium release from skeletal muscle. It presents with rising temperature, rigidity, and hypercapnia and is treated with dantrolene.

Adverse effects of excessive local anaesthetic in the circulation, ranging from perioral tingling and tinnitus to seizures, arrhythmias, and cardiac arrest. Intravenous lipid emulsion is a key treatment alongside standard resuscitation.

A lipid preparation given as a bolus and infusion to treat severe local anaesthetic systemic toxicity. It is thought to create a lipid sink that removes drug from cardiac tissue and improves myocardial function.

A device delivering small electrical currents through an insulated needle to identify a peripheral nerve by the muscle twitch it evokes. It allows localisation with lower local anaesthetic volumes than a purely landmark technique.

A peripheral nerve block of the saphenous nerve in the thigh, providing analgesia after knee surgery while largely preserving quadriceps strength. It is preferred over femoral block when early mobilisation matters.

The combination of analgesic drugs and techniques acting at different points in the pain pathway, such as paracetamol, NSAIDs, opioids, and regional blocks. It improves pain relief and reduces opioid requirements and their side effects.

A method in which the patient triggers small intravenous opioid doses from a programmable pump with a set lockout interval. It accommodates individual analgesic requirements but requires monitoring for respiratory depression and sedation.

An acute inflammatory lung injury causing bilateral opacities on imaging and severe hypoxaemia not fully explained by cardiac failure. Management is largely supportive, with lung-protective ventilation and prone positioning in severe cases.

A ventilation strategy using low tidal volumes based on predicted body weight, limited plateau pressure, and appropriate positive end-expiratory pressure. It reduces ventilator-induced lung injury and mortality in acute respiratory distress syndrome.

Airway pressure maintained above atmospheric at the end of expiration. It recruits collapsed alveoli, improves oxygenation, and reduces atelectasis, but can impair venous return and cause barotrauma.

Placing a ventilated patient face down to improve oxygenation, thought to act by recruiting dorsal lung regions and reducing ventilation-perfusion mismatch. Prolonged sessions reduce mortality in moderate to severe acute respiratory distress syndrome.

Life-threatening organ dysfunction caused by a dysregulated host response to infection. It is identified clinically by a rise in the sequential organ failure assessment score and requires prompt antibiotics, fluids, and source control.

Chemical injury to the lungs after inhalation of gastric contents, causing bronchospasm, hypoxaemia, and pulmonary oedema within hours. It is distinct from aspiration pneumonia, which is an infectious process.

A pregnancy-specific disorder defined by new hypertension after 20 weeks with proteinuria or other organ dysfunction. Anaesthetic concerns include difficult airway, pulmonary oedema, thrombocytopenia, and the need to control blood pressure before induction.

Injection of local anaesthetic, usually with an opioid, into the subarachnoid space to provide surgical anaesthesia for delivery. It avoids the airway risks of general anaesthesia but commonly causes hypotension from sympathetic blockade.

A drug, typically phenylephrine or noradrenaline, given to counter the fall in blood pressure caused by sympathetic blockade during spinal anaesthesia. Phenylephrine is preferred in caesarean section to avoid fetal acidosis.

Reflex closure of the vocal cords triggered by irritation of the airway, often during light anaesthesia or on emergence. It is managed with jaw thrust, continuous positive airway pressure, deepening anaesthesia, and, if needed, a small dose of suxamethonium.