Glossary

Accessory muscles of respiration

The principle muscles of respiration are the diaphragm, external and internal intercostal muscles. During periods of increased respiratory activity (exercise or laboured breathing) it is necessary for the accessory muscles of respiration to become active. These include the sternocleidomastoid and scalene muscles.

Acidosis

Arterial pH < 7.35. This occurs due to an increase in the hydrogen ion concentration and can be the result of either a primary respiratory, or metabolic problem.

Air bronchogram

An air bronchogram is an air-filled bronchus, which has become visible on an X-ray due to consolidation and opacification of surrounding tissue.

Alveolus

Terminal part of the respiratory tree and the site of gas exchange.

Amiodarone

Class III anti-arrhythmic agent used for treating supraventricular and ventricular arrhythmias.

Anaphylaxis

Type 1 immune reaction, resulting from an antigen-antibody reaction on the surface of mast cells. Degranulation of the mast cells causes histamine release, which is responsible for the clinical features seen (rash, urticaria, swelling, wheeze, hypotension etc.). Previous exposure to the antigen is necessary to cause the sensitization.

Angina

Chest pain due to ischaemia of the heart muscle. This occurs when myocardial oxygen demand exceeds supply, commonly due to an obstruction to blood flow through atherosclerotic coronary arteries.

Angioedema

Rapid tissue swelling resulting from an allergic reaction. Life threatening airway obstruction can occur due to the subcutaneous swelling of the lips, tongue and oropharynx.

Angiotensin converting enzyme inhibitors (ACEi)

A class of drugs that inhibit the conversion of angiotensin I to angiotensin II by angiotensin converting enzyme. Angiotensin II is a vasoconstrictor and has sodium-retaining effects. ACE inhibitors therefore cause vasodilation and are used to treat hypertension and cardiac failure.

Antigen

A substance that provokes the production of one or more antibodies in an immune response.

Aphasic

An impairment of language – a spectrum from word-finding difficulty to being completely unable to speak.

Apnoea

The absence of respiration.

Arrhythmia

Abnormal heart rhythm due to abnormal electrical activity within the heart.

Ascites

Excessive free fluid within the abdominal cavity.

Asystole

The absence of cardiac electrical activity.

Atelectasis

Absence of gas from part of the lung due to inadequate aeration of alveoli with subsequent gas absorption. This commonly occurs in dependent areas of the lung and can cause hypoxaemia. Post operative patients are particularly at risk.

Atherosclerosis

Cholesterol deposits in arteries, combined with endothelial disorder, which results in thickening of the arterial walls.

Atrioventricular node (AV)

A collection of cells that lie in the atrial septum just above the coronary sinus opening and is normally the only conducting path between the atria and the ventricles.

Atropine

Anticholinergic drug which blocks the effect of acetylcholine at muscarinic receptors. The drug is used to treat bradycardia.

Base excess

The amount of acid or base (in mmol) required to restore 1 litre of blood to a normal pH (assuming a normal PaCO₂ and temperature). Normal range -2 to +2. By convention a negative number denotes an acidosis and a positive number an alkalosis.

Benzodiazepines

Psychoactive medications with sedative and anxiolytic effects. Examples include lorazepam, chlordiazepoxide and diazepam.

Beta blockers

Drugs that prevent the stimulation of the beta-adrenergic receptors at the nerve endings of the sympathetic nervous system. They reduce the heart rate, contractility and therefore oxygen demand of the myocardium. They are used for a variety of indications including tachyarrhythmias, ischaemic heart disease and hypertension.

Bicarbonate

Anion (HCO₃^-) present in plasma at a normal concentration of 24–33 mmol/L, formed from dissociation with carbonic acid. It is a major buffer of H⁺ ions in the blood and is therefore intimately involved with acid-base balance.

Blood cultures

The collection of blood into specific aerobic and anaerobic blood culture bottles. The bottles contain mediums that aid the growth of microbial organisms in the laboratory.

Blood gas membrane

The alveolar-capillary membrane exists between the alveoli air and pulmonary blood supply. This is where gas exchange occurs.

Brain stem

The most primitive part of the brain containing the midbrain, pons and medulla. Contains basic control centres for breathing, temperature, eye movements and cardiovascular homeostasis.

Bronchial breath sounds

Bronchial breathing is a harsh breath sound. Unlike normal vesicular breathing there is an audible gap between the inspiratory and expiratory phase. If heard in the chest it is abnormal and suggests the presence of consolidation.

Bronchodilators

Drugs given to cause dilation of the bronchioles. Common examples include beta-2-agonists (salbutamol) and anticholinergic agents (ipratropium bromide).

Bronchospasm

Narrowing of the bronchi by muscular contraction in response to a stimulus. Can be caused by disease processes (asthma, anaphylaxis, COPD exacerbations) or medications (adenosine, beta-blockers). Often treated with bronchodilators.

Calcium channel antagonists

Block voltage-gated calcium channels in the heart and blood vessels, reducing muscle contraction – reducing myocardial contractility and relaxing peripheral blood vessel smooth muscle tone.

Cardiac arrest

The cessation of effective pumping of the heart. This causes an absence of signs of life (pulse, breathing), and is often caused by a dysfunctional cardiac rhythm (ventricular tachycardia, ventricular fibrillation, pulseless electrical activity or asystole).

Cardiac tamponade

Compression of the heart by fluid (e.g. blood) within the pericardium.

Cardiomegaly

Hypertrophy and enlargement of the heart.

Cardioversion

Restoration of a normal heart rhythm by either drugs (e.g. Amiodarone) or electricity (DC cardioversion).

Carina

The point at which the trachea bifurcates into the right and left main bronchi.

Catecholamines

Hormones acting within the central nervous system including adrenaline, noradrenaline and dopamine.

Cellulitis

Infection of the skin resulting in local inflammation, often with a fever and leucocytosis.

Chest tube

An intercostal drain is a small tube inserted into the pleural space to drain fluid (effusion/haemothorax/empyema) or air (pneumothorax).

Chlordiazepoxide

A benzodiazepine, often used to treat or prevent alcohol withdrawal.

Cholecystectomy

Surgical removal of the gallbladder.

Chronic bronchitis

Chronic inflammation of the bronchioles, often related to smoking. In combination with emphysema, now termed chronic obstructive pulmonary disease.

Colloid

A substance unable to pass through a semipermeable membrane. A suspension of particles rather than a true solution (i.e. crystalloid). The term is used to describe intravenous fluids containing proteins such as starch or gelatin in suspension. Blood and human albumin solution are also examples of colloids.

Consolidation

Radiological appearance caused by fluid instead of air within the alveoli. This is often due to pneumonia. The appearance is an area of white lung rather than black on a CXR.

Continuous positive airway pressure (CPAP)

Positive pressure applied through all phases of the respiratory cycle. This is usually achieved by giving high flow pressurised gas to the patient via a tight fitting mask or hood. The effect is to open collapsed alveoli and improve oxygenation. It is useful in type 1 respiratory failure and in particular, pulmonary oedema.

Crepitations

Crackles, may be inspiratory, expiratory, fine or coarse.

Crystalloids

A substance which, in solution can pass through a semipermeable membrane. Common examples of crystalloid fluids are 0.9% saline and Hartmann's solution.

Computed tomography pulmonary angiogram

Intravenous contrast is injected into the pulmonary arteries and then CT imaging is performed. It is the preferred choice for diagnosing a pulmonary embolism.

Cyanosis

Blue discoloration of the tissues due to increased amounts of non-oxygenated haemoglobin in the blood. Peripheral cyanosis (e.g. finger tips) may be a result of reduced peripheral circulation. Central cyanosis (typically affecting the tongue) is usually due to actual hypoxia.

Deep vein thrombosis

Thrombosis formation in the deep veins, usually of the leg or pelvis.

Diastole

The period between contractions of the heart, when the myocardium relaxes and allows the chambers to fill with blood.

Digoxin

Cardiac glycoside drug, which is used to slow atrioventicular conduction and increase myocardial contractility. Often used for rate control in atrial fibrillation.

Dyspnoea

The subjective feeling of breathlessness or difficulty breathing.

Electrocardiogram (ECG)

A tracing of the electrical activity of the heart against time.

Echocardiogram

An ultrasound scan of the heart, which can show structural cardiac pathology, valvular disorder, assess the function of the heart as a pump and assess wall motion abnormalities.

Electroencephalogram (EEG)

A tracing of brain activity by the placing of electrodes on the scalp. It can be used to record specific patterns and diagnose disorders such as epilepsy.

Embolus (pl. emboli)

Material, such as a thrombus, fat or air that is carried by the blood from one point in the circulation to another where it becomes lodged in a vessel of smaller diameter.

Emphysema

A disease of the alveoli in which decreased elasticity causes alveolar collapse and air trapping.

Encephalitis

Inflammation of the brain (cerebral hemispheres), often caused infection (viruses or bacteria). May cause headache, fever, confusion, drowsiness, hallucinations and convulsions.

Exudate

Fluid with a high content of protein which has escaped from blood vessels into the surrounding tissues, usually as a result of inflammation. 

Haemoptysis

Coughing up blood.

Haemothorax

Blood in the pleural cavity.

Hartmann's solution

A crystalloid solution containing a more physiological combination of dissolved solutes than 0.9% saline.

Hemiplegic

Paralysis of one side of the body. More severe than hemiparesis, which is weakness of one side of the body.

Hypercapnoea/hypercarbia

Increased levels of arterial carbon dioxide. PaCO₂ > 6 kPa.

Hypernatraemia/hyponatraemia

High or low serum sodium levels.

Hypotension

Low blood pressure.

Hypothyroidism

Underactive thyroid gland leading to low T4 levels. Clinical manifestations include cold insensitivity, depression, lethargy, weight gain and constipation.

Hypoventilation

A reduction in alveolar ventilation. It may result from a reduction in respiratory rate and/or tidal volume.

Hypoxaemia

Low oxygen content of the arterial blood. PaO₂ < 12 kPa.

Hypoxia

Low oxygen content in the tissues.

Infarction

Necrosis (death) of tissue secondary to lack of blood supply.

Inflammatory mediators

Chemicals released from damaged tissues, which initiate and propagate the inflammatory process. They consist of enzymes, chemokines and cytokines. Histamine, TNF-alpha and prostaglandins are examples.

Invasive ventilation

Mechanical ventilation via an endotracheal tube, nasotracheal tube or tracheostomy.

Jaundice

A high bilirubin level will lead to a yellow discolouration of tissues. Normally clinically apparent when levels exceed 35 µmols/L. Causes include haemolytic disease, hepatocellular disease and cholestasis (e.g. gall stones, pancreatic carcinoma).

Jugular venous pulsation (JVP)

A clinical measure of central venous pressure. The height of maximal right internal jugular vein (IJV) pulsation is used. Surface markings for the IJV are from the medial end of the clavicle to the earlobe. A double pulsation will be seen which alters with respiration. The patient must be sat at 45 degrees.

Lactic acidosis

A product of anaerobic metabolism. Used as a biochemical measure of tissue hypoxia and will increase in states of inadequate tissue perfusion. Decreased metabolism of lactate by the liver (e.g. in liver failure) will also produce a lactic acidosis.

Laryngospasm

Reflex spasm and closure of the vocal cords in response to a stimulus. May cause complete or partial airway obstruction.

Lumbar puncture

A procedure to obtain a sample of cerebrospinal fluid and/or measure intracranial pressure (opening pressure). Used in the diagnosis of meningitis and subarachnoid haemorrhage (after CT head).

Mean arterial pressure (MAP)

Average arterial blood pressure throughout the cardiac cycle. It represents the mean pressure available to perfuse the tissues and is sometimes preferred to measures of systolic or diastolic pressure as it is less liable to errors of measurement. During a normal cardiac cycle, twice as long is spent in diastole than systole so the MAP can be estimated from the following equation: MAP = diastolic pressure + 1/3 (systolic-diastolic pressure)

Mediastinum

Central structures of the thorax including heart, larynx, oesophagus, vessels of the heart and nerves surrounded by connective tissue.

Melaena

Altered blood from bleeding in the upper GI tract. Commonly from gastric or duodenal ulcers or oesophageal varices. The blood has passed through the digestive system and so is black, has a tarry consistency and has an offensive smell.

Metabolic acidosis

Acidosis due to a metabolic cause. It can be caused by increased acid production by the body, failure to excrete hydrogen ions, loss of bicarbonate or acid ingestion.

Multi organ dysfunction

Also known as multiple organ failure. Syndrome of organ disorder affecting two or more organs, and occurring in organs remote from the site of the primary injury or infection. This can be a consequence of sepsis which is inadequately treated.

Nasogastric aspirate

Aspirate obtained from the stomach through a nasogastric tube. This should have a low pH (stomach acid) and if unable to aspirate a CXR must be used to check the tube passes into the stomach.

Nebuliser

A device used to provide an aerosol of drug that can be inhaled. Used commonly to give inhaled bronchodilators in the acutely unwell patient with bronchospasm.

Non invasive ventilation (NIV)

Non invasive positive pressure ventilation is a form of ventilation through a tightly sealed face mask. A patient's breathing is assisted by essentially blowing gas into the lungs under pressure. BiPAP (bilevel positive airway pressure) is an example of NIV. Type 2 respiratory failure is one indication.

Oedema

Accumulation of fluid in the tissues. Can occur in all tissues as a result of increased hydrostatic forces, reduced oncotic forces and inflammation causing "leaky" capillaries. Examples include cerebral oedema, pulmonary oedema and peripheral oedema.

Oliguria

A low urine output defined as less than 0.5 ml/kg/hr.

Orthopnoea

Shortness of breath in the supine position.

Oxygen saturations

The percentage of haemoglobin fully saturated with oxygen. SpO₂ refers to peripheral oxygen saturation as measured by a pulse oximeter.

Pa (partial pressure) e.g. PaO₂ PaCO₂

A measure of the quantity of dissolved gas (O₂/CO₂) in the blood.

Parietal pleura

The outer lining of the lung which lines the thoracic cavity.

Peak expiratory flow rate (PEFR)

The maximum rate of air flow from the lungs in one forced expiration. Measured using a peak flow meter. It is used to quantify exacerbations of asthma and to monitor response to treatment.

Pleural rub

A rubbing sound heard on auscultation of the chest, which implies inflammation of the pleura.

Pleuritic chest pain

Pain in the chest which is exacerbated by inspiration or coughing. Caused when there is inflammation of the parietal pleura (pulmonary embolism, pericarditis, pneumonia, pneumothorax). It can also be caused by musculoskeletal chest pain.

Polycythaemia

Haemoglobin concentration above 160-170 mg/dL.

Pulmonary embolism

An embolus within the pulmonary vasculature. Emboli often arise from deep vein thromboses in the legs or pelvis.

Pyrexia

A raised core body temperature.

Respiratory acidosis

Acidosis due to an increase in the PaCO₂ caused by alveolar hypoventilation.

Respiratory arrest

Absence of respiration. Bag and mask ventilation is required and the crash team called. Usually quickly followed by cardiac arrest if the oxygenation and ventilation isn't restored.

Rhabdomyolysis

A raised blood level of myoglobin as a consequence of muscle breakdown. Causes include trauma (commonly crush injuries), hyperthermia, drug abuse, extreme physical exertion and prolonged immobility.

Sino-atrial node (SA node)

The pacemaker of the heart located in the right atrium. Normally releases impulses at 60-70 beats/minute. Impulses travel to the AV (atrioventricular node) and then to the ventricles via the bundle of His.

Starling's law

Increasing stretch of myocardial fibres leads to increased contractile force. I.e. myocardial contraction is proportional to the initial length of the myocardial fibre. Also known as the Frank-Starling law of the heart, and not to be confused with the Starling equation which refers to movement of fluid across capillary membranes.

Sympathetic nervous system

The part of the autonomic nervous system concerned with the "fight or flight" response. Activation causes tachycardia, hypertension, peripheral vasoconstriction, bronchodilation and pupil dilatation.

Syncope

Loss of consciousness due to a drop in cerebral perfusion pressure.

Systole

The period of the cardiac cycle during which cardiac contraction occurs.

Tachycardia

Raised heart rate (usually > 100).

Tachypnoea

Raised respiratory rate (usually > 20).

Thoracocentesis

The draining of air or fluid from the pleural space for diagnostic or therapeutic purposes.

Thrombolysis

The dissolution (lysis) of clot by drugs such as analogues of tissue plasminogen activator (tPA).

Thrombophilia

A pathological tendency to form thromboses.

Thromboprophylaxis

Measures taken to prevent venous thromboembolism in hospital patients. Often includes low molecular weight heparin (LMWH) and thromboembolic deterrent (TED) stockings.

Thyroid function tests

Blood test to determine thyroid function. Usually measures thyroid stimulating hormone, free T3 and T4. Not accurate during episodes of acute illness.

Transudate

Fluid with a low content of protein which has passed through a membrane or has been extruded from a tissue. 

Troponin

Troponin I and troponin T are cardiac-specific enzymes released by myocardial cells when damaged. Causes of raised troponin include myocardial infarction, heart failure, cardiac arrhythmias, cardiomyopathies, acute renal failure, sepsis and pulmonary emboli.

Urticaria

Red, hot, itchy rash resulting from the release of histamine from mast cells. Often associated with allergy or hypersensitivity.

Vagal manoeuvres

Actions which increase vagal tone. Include forced expiration against a closed glottis (blowing into a syringe) or carotid sinus massage. May be used in attempts to terminate supraventricular tachycardias before medical therapy is used.

Vasodilation

Relaxation and dilatation of blood vessels. This usually causes a drop in blood pressure.

Vasovagal

A reflex involving stimulation of the vagal nerve and subsequent bradycardia often leading to presyncope or syncope.

Venturi mask

A type of oxygen mask, which is able to deliver oxygen at a specific concentration.

Vesicular breath sounds

Normal breath sounds.

Visceral pleura

The pleura adherent to the surface of the lungs.

Vocal resonance

The transmission of an audible stimulus through the lung fields. The patient is often asked to say "ninety-nine" and the transmission of this sound is assessed by auscultation.

Wheeze

Monophonic or polyphonic inspiratory or expiratory sound caused by narrowing of the airways, often by oedema or obstruction.