NU2ICU Definitions


For when the staff around you start dropping anachronisms, abbreviations and buzz words …

Starting in ICU you will hear many terms that are foreign to most people outside of that environment, prepare yourself if you have time by trying to commit some of the definitions below to your memory, but only if you want to!

ABSOLUTE HUMIDITY (AH)  –  the amount of water vapour contained in air.  Absolute Humidity saturation (AHs) is the maximum water vapour that air can contain at a given temperature. See relative humidity.

ACIDOSIS   –  abnormal increase in hydrogen ion concentration in the body resulting from an accumulation of an acid or the loss of a base, may be Respiratory and / or Metabolic, indicated by pH < 7.35 in blood.

AFTERLOAD   –  load on the muscle after the commencement of contraction. Determinants – increase = ­Systemic Vascular Resistance (SVR), ­ aortic impedance, negative intrathoracic pressure, ­ ventricular radius  decreases = ¯ SVR, ¯ aortic impedance, positive intrathoracic pressure, ­ ventricular wall thickness.

AIRWAY RESISTANCE  –  the relationship between pressure and flow, how easily gas flows through the conducting pathways to the lungs, conscious 0.6 – 3.2 cmH2O/l per second, sedated and ventilated (includes resistance of endotracheal tube and catheter mount):  5 – 10 H2O/l per second

AIRWAY STATIC COMPLIANCE  –  expired Vt divided by (Pause Pressure – PEEP)  (normal ventilated Pt. 50 – 100 ml/cmH2O or effective dynamic compliance for ICU pt ~ 40 – 50ml/cmH2O)

ALBUMIN  –  regulate blood volume by maintaining the osmotic pressure (also known as colloid osmotic pressure) of the blood compartment. Serves as carriers for molecules of low water solubility isolating their hydrophobic nature, includes lipid soluble hormones like thyroxine, bile salts, unconjugated bilirubin, free fatty acids, calcium, ions and some drugs like warfarin & phenytoin.

ALVEOLAR – ARTERIAL OXYGEN GRADIENT –   5 – 20 mmHg (0.7 – 2.7 kPa) breathing air,  25–65 mmHg (3.3 – 8.6 kPa) breathing 100% oxygen.

ANATOMICAL DEAD SPACE –  the volume of gas filling the conducting airways not lung.

ARDS (Acute or Adult Respiratory Distress Syndrome).  Defined by the “Berlin criteria” of 2012 by the European Society of Intensive Care Medicine and the Society of Critical Care Medicine as:

AUTOMATICITY  –  the ability of cells to generate an action potential or impulse in the absence of  an external stimulus.

AVOGADRO’S HYPOTHESIS – equal volumes of gases, at the same temperature and pressure contain equal numbers of molecules.

BERNOULLI EFFECT  –  the greater the velocity of flow the less the lateral pressure is placed on the vessel, the narrower the tube the greater the velocity the less pressure exerted on the vessel walls.

BOYLE’S LAW  –  pressure of a gas in a closed container is inversely proportional to the volume of the container, or PV = k1

BRAIN DEATH   –  irreversible cessation of all brain function, also as displayed but reversibly by most nurses after night number 4!

CaO2  –  (oxygen content) = 1.36 X Hb X SaO2 + (dissolved O2 = 0.0031 X PO2) (norm @ 20.1 ml / 100 ml blood.

CARBON MONOXIDE –  (CO) has an affinity to haemoglobin 210 times that of O2.

CARDIAC INDEX  –   cardiac output divided by body surface area (norm. 2.5 – 3.5 L/min/M2)

CARDIAC OUTPUT  –  CO = Stroke Volume  X Heart Rate (norm 4 – 6 L/min)

CARDIOGENIC SHOCK   –  inadequate cardiac pumping, characterised by sustained hypotension (systolic <90 mmHg) in the absence of pain, arrhythmias and pharmacological agents.

CEREBRAL PERFUSION PRESSURE   –  CPP = MAP – ICP (Intra Cranial Pressure – norm > 60 mmHg)

CHARLES’S LAW – at a constant pressure, the volume of a given mass of gas varies proportionately to it’s absolute temperature, or V/T = k2.

CHRONOTROPIC EFFECT  –  relates to time / heart rate, examples = positive – Isoprel, negative – Digoxin, Beta Blockers.

COLLOID –  a solution where the particles during the disperse phase are larger than crystalloid molecules but not large enough to settle due to gravity.

CONTRACTILITY  –  the inotropic state of the myocardium, specifically the velocity of fiber shortening during systole.

CORONARY PERFUSION PRESSURE –  ADP (Aortic Diastolic Pressure) minus LVEDP (Left Ventricular End Diastolic Pressure or PAW – Pulmonary Wedge Pressure).

CPAP (PEEP / EPAP)  –  Continuous Positive Airway Pressure (Positive End Expiratory Pressure / Expiratory Positive Airway Pressure), the maintenance of a continuous positive pressure throughout the respiratory cycle, a spontaneous breathing mode.

CREATININE CLEARANCE RATIO –  normal 70 ~ 150:1, varies 10~25% in normal adults,  Clcr ~ 133 – (0.64 x age)   (ml/min/1.73m2).

CRYSTALLOID – a non-colliodal substance which passes readily through biological membranes and is capable of being crystallised.

CRITICAL TEMPERATURE –  is the temperature above which a gas cannot be liquefied by pressure alone, O2 = -119 oC, N2O = 36.5 oC  therefore a gas is a substance in the gaseous phase above it’s critical temp and a vapour is a substance in the gaseous phase below it’s critical temp

DALTON’S LAW –  each gas in a mixture of gases exerts its own pressure as if all the other gases were not present.

DECEREBRATE POSTURING –  the head is arched back, the arms are extended by the sides, and the legs are extended and all limbs rotated internally.

DECORTICATE POSTURING –  the trunk and legs are extended and the arms are flexed on the chest, indicates damage to higher brain areas and has a better prognosis than decerebrate posturing.

DIABETES INSIPIDUS – a syndrome characterised by polyuria, excessive thirst and polydipsia. Neurogenic DI results from a lack of ADH (anti-diuretic hormone) in the circulation in response to osmotic stimuli.  Usually in cases of severe head injury.  Also can be Psychogenic or Nephrogenic.

DIFFUSION –  spontaneous movement of molecules or other particles in solution, owing to their random thermal motion, to reach a uniform concentration throughout the solvent.

DROMOTROPIC EFFECT  –  increased or decreased strength of conduction

EJECTION FRACTION – left ventricle hold approx. 120 mls of blood – due to valves and thick muscular wall maximum blood expelled of systole is approx. 70 – 75 mls or 65-70% this represents a normal EF

ELECTRICAL CARDIOVERSION – restoration of the hearts normal rhythm by delivery of a synchronised DC electric shock through conductive pads on the patients chest.

FICK’S LAW – the rate of diffusion of a substance across a unit area is proportional to the concentration gradient for that substance, further the diffusion of a gas across a membrane, or into or out of a liquid, is proportional to the gas solubility in the liquid.  CO2 being more soluble than O2 diffuses far more rapidly across the alveolar membrane and into the RBC, or N2O being far more soluble than N2 may diffuse into and expand closed cavities during use.

FICK PRINCIPLE – the rate of appearance, or disappearance, of any substance from any organ is given by the Arterio -Venous concentration difference multiplied by the blood flow.

FILTRATION –  the movement of fluid through a membrane due to hydrostatic pressure.

FRANK-STARLING LAW OF THE HEART  –  the greater the initial stretch of the ventricle prior to contraction the greater the strength of contraction, within physiological limits, beyond this limit contraction is no longer enhanced and stroke volume decreases ie Left Ventricular Failure, Congestive Cardiac Failure.

FUNCTIONAL RESIDUAL CAPACITY – the volume of gas remaining in the lungs following normal expiration (the lung volume in which gas exchange is taking place)

HEAT LOSS – there are four routes of thermal loss from the body;

  • radiation        ~ 40%
  • convection    ~ 30%
  • evaporation  ~ 20%
  • respiration     ~ 10%  (humidification 8% + heating of air 2%)

HENRY’S LAW – at a constant temperature, the amount of a given gas dissolved in a given liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

HYPERCAPNOEA  –  increased amount of carbon dioxide in the arterial blood (norm 35 – 45 mmHg)

HYPOCALCAEMIA –  (risk usually caused by Thyroid operations) symptoms include tingling or ‘pins and needles’ sensation in and around the mouth and lips, and in the extremities of the hands and feet. Trousseau sign of latent tetany (eliciting carpal spasm by inflating a blood pressure cuff and maintaining the cuff pressure above systolic) or Chvostek’s sign (tapping of the inferior portion of the zygoma will produce facial spasms) may progress to laryngospasm and cardiac arrhythmias.

HYPOTHERMIA –  core temperature below 350 , mild 320 – 350, mod 280 – 320, severe < 280

HYPOXIA  –  4 types;

  • Hypoxic        –   reduced exposure of oxygen to the body eg plastic bag, altitude, ventilatory failure, pulmonary shunt etc
  • Stagnant      –    oxygen transport failure eg tourniquet, hypovolaemia, pulm embolism etc
  • Anaemic      –     arterial O2 tension normal but circulating Hb is reduced or not functioning eg massive haemorrhage anaemia, carbon monoxide poisoning etc
  • Histotoxic  –     impairment of cellular metabolism of supplied O2 eg cyanide or arsenic poisoning, alcohol intoxication

INOTROPIC EFFECT –  relates to ability to contract / contractility, examples = positive – Adrenaline, Noradrenaline, negative – Beta Blockers.

INTERMITTENT POSITIVE PRESSURE VENTILATION   –  mechanised breathing where gas is pushed into the lungs under positive pressure, as opposed to normal breathing where gas is drawn in by negative pressure.

LaPLACE’S LAW – states that the change in pressure within an air bubble is inversely proportional to its radius or ▲P >2s/r (P = pressure, s = surface tension, R = radius)

MASSIVE BLOOD TRANSFUSION   –  greater than half the patients normal blood volume or more than 10 units – within 24 hours.

MEAN ARTERIAL PRESSURE – MAP = systolic minus diastolic = pulse pressure (PP), divide PP by 3 add result to diastolic for MAP

MECHANICAL VENTILATION FLUID RETENTION – Decreased cardiac output → Decreased renal perfusion → Stimulation of the renin–angiotensin–aldesterone axis →  Decreased atrial stretch results in Decreased secretion of atrial natriuretic peptide (ANP) from atria →  Increased ADH secretion → Increase in plasma norepinephrine = Salt and water retention

NIPPV – or NPPV or NIV is the nomenclature for Non-Invasive Positive Pressure Ventilation or application of ventilator support via a mask or nasal interface

NOSOCOMIAL INFECTION   –  infection acquired at least 48 hours after hospital admission, also known as hospital acquired infection.

NU2ICU – a website for beginners in ICU nursing, you should go there…

O2 EXTRACTION RATIO (O2ER) –  relationship between oxygen delivered and consumption expressed as a ratio (norm 22 – 30%).

OSMOSIS – the movement of solvent across a semipermeable membrane, down a thermodynamic activity gradient for that solvent.

OSMOTIC PRESSURE – the pressure required to prevent the movement of a solvent

  • over 99% of plasma osmolarity is due to electrolytes (plasma proteins contribute ~ 1mosmol/l)
  • normal RBC’s lyse at osmolarities < 200mosmol/l
  • as capillaries are relatively impermeable to protein this generates an osmotic pressure difference between plasma and the interstitial fluid (plasma oncotic pressure ~ 26 mmHg)

OXYGEN ABSORPTION ATELECTASIS – Regions of low-V/Q mismatch are more prone to absorptive atelectasis, since it is in these regions that ventilation is poor, and the oxygen enriched air in the alveoli that is absorbed by alveolar capillaries is not replenished. This results in a loss of volume of the obstructed lung or lobe.

OXYGEN DELIVERY (DO2)  –  the amount of oxygen in arterial blood which is transported to the tissues by the cardiovascular system, DO2 = CaO2 X CO  (norm 500 – 650 ml/min/m2).

OXYGEN DIFFUSE ALVEOLAR DAMAGE – O2 when reduced to reactive oxygen radicals, such as the superoxide anion (O2), the hydrogen peroxide (H2O2), and the hydroxyl radical (OH−), can cause tissue injury. Nitrogen washout can affect the secretion and quality of surfactant exposing the alveoli membrane to injury causing an inflammatory response if unrelieved may lead to fibrosis.

OXYGEN DISSOCIATION CURVE  –  graphic display of relationship between increased and decreased affinity of oxygen binding to haemoglobin, effecting release to the cells

Left Shift = increased affinity                                                                                                                                  Right Shift = decreased affinity

Alkalosis (↑ pH)                                                                                                                                                                       Acidosis (↓ pH)

Hypocapnoea (↓ PaCO2)                                                                                                                                                    Hypercapnia (↑PaCO2)

Decreased temperature                                                                                                                                                     Increased temperature

Decreased 2,3-DPG                                                                                                                                                              Increased 2,3-DPG


Carbon monoxide


PASCAL’S PRINCIPLE  –  a confined liquid transmits pressure applied to it from an external source equally in all directions.

PASSIVE LEG RAISE –  involves raising the legs of a patient (without their active participation), which causes gravity to pull blood from the legs, thus increasing circulatory volume available to the heart (cardiac preload) by around 500 mls (250ml/leg).   The real-time effects of this maneuver on haemodynamic parameters such as blood pressure and heart rate are used to guide the decision whether or not more fluid will be beneficial.

PHLEBOSTATIC AXIS  –  reference point for accurate central venous and pulmonary artery pressures, reflects the level of the right atrium (mid-axilla 4th intercostal space).

PHYSIOLOGICAL SHUNT –  right to left side of heart via lungs = 3% of cardiac output (see shunt).

PRELOAD  –  initial fibre length before contraction. Determinants – Frank-Starling “Law of the Heart”, not directly indicated by pressure, ventricular compliance (­ = GTN, relief of ischaemia ¯ = Catecholamines, hypoxia, ischaemia).

PRINCIPLE EXTRACELLULAR CATION   –  Sodium = 85% (norm 137 – 145 mmol/L).

PRINCIPLE INTRACELLULAR CATION  –  Potassium = 90% (norm 3.5 – 4.9 mmol/L in plasma).

PULSE PRESSURE –  difference between systolic and diastolic pressures, a reflection of stroke volume, ejection velocity and systemic vascular resistance  (norm 30 – 40 mmHg).

PULSUS PARADOXUS –  abnormal decrease in Sysytolic Blood Pressure (SBP) of more than 10 mmHg during inspiration may indicate cardiac tamponade, adhesive pericarditis, severe lung disease or advanced heart disease.

POSITIVE PULSUS PARADOXUS –  abnormal increase in SBP of more than 10 mmHg during mechanical (ventilated) exhalation – usually indicates hypovolaemia, best observed by changing arterial sweep speed to 6.25cm/sec and using cursor to detect baseline..

PRESSURE CONVERSION –   mmHg to kPa = divide by 7.519,  cmH2O to kPa = divide by 0.0980665; therefore 1 mmHg = 1.36 cmH2O = 0.133 kPa = 0.0193 PSI.

RAIN OUT  –  condensation back into water of humidity in saturated gas when temperature loss decreases vapour carrying abilities, the dew point.

RELATIVE HUMIDITY –  the ratio of the mass of water vapour in a given volume of air to the mass required to fully saturate that volume of air at a given temperature (%), fully saturated air @ 20oC contains ~ 17 mg/l,  when @ 37oC contains ~ 44mg/l (maximum possible at sea level).

RENAL FAILURE –  renal function is inadequate to maintain the volume and concentration of the body’s internal environment, usually characterised by an increase in metabolic waste products in the blood

RESIDUAL VOLUME   –  volume of gas remaining in the lungs following forcible expiration, the volume of gas unable to be exhaled

RESPIRATORY FAILURE  –  PaO2 less than 60 mmHg with or without a PaCO2 greater than 50 mmHg breathing room air at sea level at rest without the presence of metabolic alkalosis.

SEPSIS – a bacterial infection in the bloodstream or body tissues. This response may be called systemic inflammatory response syndrome (SIRS).  According to the Society of Critical Care Medicine, there are different levels of sepsis:

SHOCK – severe pathological syndrome associated with inadequate tissue perfusion and abnormal cellular metabolism.

SHUNT – the proportion of cardiac output not participating in gaseous exchange (does not come in contact with ventilated alveoli)

SIRS – systemic inflammatory response syndrome symptoms of 2 or more symptoms including, but are not limited to:

  • Body temperature less than 36°C or greater than 38°C
  • Heart rate greater than 90 beats per minute
  • Tachypnoea greater than 20 breaths per minute; or, an arterial partial pressure of carbon dioxide less than 32 mmHg
  • White blood cell count less than 4000 cells/mm³ (4 x 109 cells/L) or greater than 12,000 cells/mm³ (12 x 109 cells/L); or the presence of greater than 10% immature neutrophils (band forms)

STARLING’S EQUILIBRIUM   – the factors which control the movement of fluids between the capillary and the interstitium – membrane permeability, hydrostatic pressure, osmotic pressure.

SYSTEMIC VASCULAR RESISTANCE (SVR)  –  the resistance against which the left ventricle must eject to force out its stroke volume with each beat, as peripheral vessels constrict SVR increases (norm 900 – 1400 dyne sec/cm5)

TENSION PNEUMOTHORAX  –  accumulating air in the pleural space collapses the lung, accumulation increases intrapleural pressure rises, mediastinum is pushed away from the effected side this movement compresses the trachea, heart and great vessels, a medical emergency.

TISSUE OCCLUSION PRESSURE –  applied pressures to produce, for example, 50% reduction of the unloaded resting value of oxygen – ranges from 22 mmHg (trachea / oesophagus etc) to 92 mmHg (thigh muscle etc) prolonged resulting cellular hypoxia may cause pressure ulcers.

VENTILATOR ASSOCIATED PNEUMONIA (VAP) –  occurs within 48 hours in people who are on mechanical ventilation through an endotracheal or tracheotomy tube for at least 48 hrs.


OK now repeat that back to us…