ACEM Primary key terms

The process of sorting patients by urgency so that limited resources are directed first to those with immediately life-threatening conditions, using physiological and presenting-complaint criteria rather than diagnosis.

A structured rapid assessment of airway, breathing, circulation, disability and exposure performed on any critically ill or injured patient to identify and treat threats to life before detailed history taking.

Accumulation of air in the pleural space under positive pressure that collapses the lung and obstructs venous return, producing hypoxia, hypotension and tracheal deviation, and requiring immediate needle decompression.

Blood accumulating in the pleural cavity, usually from injury to intercostal or internal mammary vessels or lung parenchyma, causing reduced breath sounds, dullness to percussion and hypovolaemic shock.

A rapid bedside ultrasound protocol examining pericardial, pleural, peritoneal and pelvic windows to detect free fluid or blood in an unstable trauma patient.

The ratio of heart rate to systolic blood pressure; a value above roughly 0.9 suggests occult hypoperfusion and impending haemodynamic decompensation even when blood pressure appears normal.

A scored assessment of eye opening, verbal response and motor response, giving a total from 3 to 15 that grades level of consciousness and predicts severity of brain injury.

The physiological triad of hypertension, bradycardia and irregular respiration occurring when intracranial pressure rises, indicating impending brainstem herniation.

The difference between measured serum sodium and the sum of chloride and bicarbonate, used to classify metabolic acidosis into high-gap causes such as ketones, lactate, urate or toxins and normal-gap causes such as diarrhoea.

The difference between measured and calculated serum osmolality; an elevated gap suggests the presence of unmeasured osmotically active substances such as methanol, ethylene glycol or isopropanol.

The amount of strong acid or base required to restore a blood sample to normal pH at standard conditions; a negative value quantifies the metabolic component of an acidosis.

The principle that the skull is a rigid container holding brain, blood and cerebrospinal fluid, so an increase in one compartment must be offset by a decrease in another or intracranial pressure rises.

Downward displacement of the medial temporal lobe through the tentorial opening, compressing the oculomotor nerve and brainstem to cause a fixed dilated pupil and rapid deterioration in consciousness.

Blood collecting between the skull and dura, classically from tearing of the middle meningeal artery, producing a brief lucid interval followed by deteriorating consciousness and a lens-shaped collection on imaging.

Blood accumulating between the dura and arachnoid, usually from tearing of bridging veins, forming a crescent-shaped collection that may present acutely or chronically with fluctuating consciousness.

Death of heart muscle caused by prolonged ischaemia, typically from acute coronary artery occlusion, producing chest pain, troponin release and characteristic electrocardiographic changes.

A chronic arterial disease in which lipid-rich plaques form within the intima, narrowing the lumen and predisposing to thrombosis, rupture and downstream ischaemic injury.

Tissue damage that occurs when blood flow is restored to previously ischaemic tissue, driven by reactive oxygen species, calcium overload and inflammatory cell influx, sometimes exceeding the original injury.

Programmed cell death in which cells shrink, condense their chromatin and fragment into membrane-bound bodies that are cleared without provoking inflammation, in contrast to necrosis.

A pattern of cell death in which tissue architecture is preserved for a time while nuclei are lost, typical of ischaemic injury to heart, kidney and spleen.

Uncontrolled cell death from severe injury, characterised by swelling, membrane rupture and leakage of cellular contents that triggers an inflammatory response in surrounding tissue.

The volume of blood ejected by the heart per minute, equal to heart rate multiplied by stroke volume, and a principal determinant of tissue oxygen delivery.

The volume of blood ejected by a ventricle in a single contraction, determined by preload, afterload and contractility.

The observation that increasing ventricular filling (preload) stretches cardiac muscle and increases the force of contraction, raising stroke volume up to a physiological optimum.

The average pressure in the arterial circulation over the cardiac cycle, approximated as diastolic pressure plus one third of the pulse pressure, and the pressure that drives organ perfusion.

The summed resistance of the systemic circulation to blood flow, chiefly set by arteriolar tone and a major determinant of diastolic pressure and afterload.

The change in volume of a lung or vessel for a given change in pressure; low compliance means greater pressure is needed to achieve the same expansion.

A mixture of phospholipids secreted by type II alveolar cells that lowers alveolar surface tension, reduces the work of breathing and prevents small alveoli from collapsing.

The volume of gas remaining in the lungs at the end of a normal passive expiration, representing the balance point between lung elastic recoil and chest wall outward recoil.

A network formed by the anterior rami of spinal nerves C5 to T1 that supplies the upper limb, giving rise to the musculocutaneous, axillary, radial, median and ulnar nerves.

A terminal branch of the posterior cord of the brachial plexus that winds around the surgical neck of the humerus to supply the deltoid and teres minor, and is vulnerable in shoulder dislocation.

A large branch of the posterior cord running in the spiral groove of the humerus, supplying the triceps and extensors of the forearm and hand; injury causes wrist drop.

A fibro-osseous passage at the wrist bounded by carpal bones and the flexor retinaculum, transmitting the median nerve and flexor tendons and a common site of nerve compression.

Clear fluid produced mainly by the choroid plexus within the ventricles that cushions the brain and spinal cord and circulates in the subarachnoid space before absorption into venous sinuses.

The apparent volume in which a drug dose would need to be dissolved to achieve the observed plasma concentration; a large value indicates extensive tissue distribution.

The volume of plasma from which a drug is completely removed per unit time by metabolism and excretion, determining the maintenance dose needed to sustain a target concentration.

The time taken for the plasma concentration of a drug to fall by half during elimination; it determines the time to reach steady state and the dosing interval.

Metabolism of an orally absorbed drug by gut wall and liver before it reaches the systemic circulation, reducing its oral bioavailability and favouring alternative routes when the effect is large.

The fraction of an administered drug dose that reaches the systemic circulation unchanged; it is complete by the intravenous route and reduced by first-pass metabolism and poor absorption.

A drug that binds reversibly to a receptor at the same site as the agonist and can be overcome by raising agonist concentration, shifting the dose-response curve rightward without lowering the maximum response.

A ligand that binds and activates a receptor but produces a smaller maximal response than a full agonist, so it can act as an antagonist when full agonist is present.

The ratio of the dose producing toxicity to the dose producing the desired effect; a narrow index means small dose changes can cause harm and monitoring is required.