EDAIC key terms

The volume of oxygen reaching the tissues each minute, calculated as cardiac output multiplied by arterial oxygen content. Falling below a critical threshold leads to anaerobic metabolism and tissue hypoxia.

The total oxygen carried in arterial blood per unit volume, the sum of oxygen bound to haemoglobin and oxygen dissolved in plasma. Usually about 200 mL per litre.

The fraction of delivered oxygen consumed by tissues, computed as oxygen consumption divided by oxygen delivery. Normally around 0.25 and rising when delivery falls.

The sigmoid relationship between partial pressure of oxygen and haemoglobin saturation. Shifts right with acidosis, hypercapnia, pyrexia and raised 2,3-DPG, reducing affinity and aiding tissue unloading.

The partial pressure of oxygen at which haemoglobin is 50% saturated, normally about 3.5 kPa (26 mmHg). A useful single number for describing curve position and affinity.

Oxygen saturation sampled from the pulmonary artery, reflecting the balance between whole-body oxygen delivery and consumption. A falling value suggests inadequate delivery or increased demand.

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

The lung volume at which small airways begin to close during expiration. When it exceeds functional residual capacity, airway closure occurs during tidal breathing, causing shunt and hypoxaemia.

Collapse or loss of aeration of lung tissue, producing shunt and reduced compliance. Common after induction of anaesthesia, upper abdominal surgery and in obesity because functional residual capacity falls below closing capacity.

The proportion of cardiac output passing through the lungs without taking part in gas exchange. True shunt is not corrected by increasing inspired oxygen, unlike ventilation-perfusion mismatch.

Active constriction of pulmonary arterioles in poorly ventilated lung regions, diverting blood to better-ventilated areas and limiting shunt. Inhibited by volatile anaesthetics, vasodilators and acidosis.

A positive pressure maintained in the airway at end-expiration, which recruits collapsed alveoli, raises functional residual capacity and reduces shunt, at the cost of raised intrathoracic pressure and reduced venous return.

Continued oxygen uptake during apnoea from a static column of gas in the airway, driven by mass flow and cardiogenic mixing. Extends safe apnoea time when a patent airway is maintained with high-flow oxygen.

Describes fluid movement across a capillary membrane as the net balance of hydrostatic and oncotic pressures, modified by reflection and filtration coefficients. It underpins understanding of oedema formation.

A carbohydrate-rich layer lining the luminal surface of endothelial cells that limits protein and fluid leakage. Shedding during inflammation, ischaemia or fluid overload increases capillary permeability and oedema.

The osmotic pressure exerted by large molecules, chiefly albumin, across a semipermeable membrane. It opposes capillary filtration and is a component of the Starling equation.

The volume of plasma completely cleared of a substance per unit time, equal to elimination rate divided by plasma concentration. It quantifies eliminating capacity independently of plasma level.

The apparent volume in which the total amount of drug in the body would need to be distributed to give the observed plasma concentration. Large values indicate extensive tissue uptake.

The time for plasma concentration to fall by half after stopping an infusion, determined by how long the infusion has run. It reflects redistribution and accumulation in peripheral compartments.

Presystemic elimination of an orally absorbed drug during passage through gut wall and liver before reaching the systemic circulation. It reduces oral bioavailability and is bypassed by intravenous dosing.

The fraction of an administered dose reaching the systemic circulation unchanged, taken as 1 for the intravenous route. It depends on absorption and first-pass metabolism for other routes.

The effect of a drug or physiological factor on heart rate. Positive chronotropes increase rate, for example atropine or adrenaline; negative chronotropes slow it, for example beta-blockers.

The intrinsic contractile strength of the myocardium independent of loading conditions. Positive inotropes such as dobutamine increase force, while volatile anaesthetics and beta-blockers reduce it.

The active relaxation of ventricular muscle during diastole, governing filling. Impaired lusitropy causes diastolic dysfunction with raised filling pressures and is worsened by tachycardia.

The ventricular wall stress at end-diastole, most simply represented by end-diastolic volume. It is a major determinant of stroke volume according to the Frank-Starling relationship.

The load the ventricle must overcome to eject blood, determined by systemic vascular resistance, arterial compliance and outflow obstruction. It is a key target for vasodilator therapy.

The principle that increasing ventricular filling raises stroke volume up to a physiological limit. It explains how the heart matches output to venous return.

Objective assessment of neuromuscular block using nerve stimulation and evoked responses such as train-of-four ratio. A ratio above 0.9 is required to exclude clinically significant residual block.

The ratio of the fourth to the first evoked twitch in response to four supramaximal stimuli delivered at 2 Hz. A ratio below 0.9 indicates residual paralysis.

Persisting weakness after general anaesthesia with neuromuscular blocking drugs, defined by a train-of-four ratio below 0.9. It increases aspiration, airway obstruction and respiratory complications postoperatively.

A modified gamma-cyclodextrin that encapsulates and inactivates rocuronium and vecuronium, reversing even deep block within minutes. It has no effect on benzylisoquinolinium agents such as atracurium.

A pharmacogenetic hypermetabolic reaction to volatile anaesthetics and succinylcholine, caused by uncontrolled calcium release from skeletal muscle via a mutated ryanodine receptor. Treated with dantrolene.

The specific treatment for malignant hyperthermia, which inhibits calcium release from the sarcoplasmic reticulum. It must be given early and in large repeated doses alongside supportive measures.

Prolonged paralysis after succinylcholine in patients with inherited pseudocholinesterase deficiency or low enzyme activity. Management is continued sedation and ventilation until recovery.

A clinical situation in which trained personnel experience difficulty with face-mask ventilation, supraglottic device placement, laryngoscopy, tracheal intubation or front-of-neck access. It should be anticipated from assessment.

Pressure applied to the cricoid cartilage to compress the oesophagus and reduce aspiration risk during rapid sequence induction. Its effectiveness is debated and it can worsen laryngoscopic view.

Nausea or vomiting occurring within 24 hours of surgery, driven by patient, anaesthetic and surgical risk factors. Prophylaxis combines agents with different mechanisms in higher-risk patients.

A 5-HT3 receptor antagonist used to prevent and treat postoperative nausea and vomiting. It can prolong the QT interval and should be used cautiously with other QT-prolonging drugs.