Glossary

GLOSSARY OF HAEMODYNAMIC TERMS AND OTHER REFERENCE INFORMATION

Accuracy. The proximity of measurement results to the true value.

Afterload. The force or load against which the heart must contract to eject blood.

Base Excess. Base excess is defined as the amount of strong acid that must be added to each litre of fully oxygenated blood to return the pH to 7.40 at a temperature of 37°C and a pCO2 of 40 mmHg (5.3 kPa). A base deficit (i.e., a negative base excess) can be correspondingly defined in terms of the amount of strong base that must be added. Refer to www.acid-base.com.

BP: Blood Pressure. Arterial blood pressure is the pressure exerted by circulating blood upon the walls of the blood vessels.

BMI: Body Mass Index. A measure of relative weight based on an individual’s mass and height. Refer to apps.who.int

Bradycardia. In an adult, it can be defined as the resting heart rate below 60 beats per minute (BPM), but depends on an individual’s resting HR. It is seldom symptomatic until the rate drops below 50 BPM. Refer to emedicine.medscape.com

BSA: Body Surface Area. The calculated surface of the body. It is used in the ODM+ to calculate indexed parameters. Reference; Du Bois D, Du Bois EF 1916. A formula to estimate the approximate surface area if height and weight be known” Archives of Internal Medicine 17 (6): 863–71.

Chronotrope. A pharmacological agent affecting the heart rate. Positive chronotropes (eg. dopamine) increase the rate while negative chronotropes (e.g. beta blockers) decrease the rate.

CI: Cardiac Index. CI normalises the CO from the left ventricle in one minute to BSA. CI = CO/BSA. The unit of measurement is L/min/m.

CO: Cardiac Output. The volume of blood being pumped by the heart, in particular by a left or right ventricle in one minute measured as L/min.

Conscious Level. A measure of a patient’s arousability and responsiveness to stimuli from the environment. Book reference; Porth C (2007). Essentials of Pathophysiology: Concepts of Altered Health States. Hagerstown, MD: Lippincott Williams & Wilkins. p. 835.

Contractility. The intrinsic strength of the cardiac muscle fibres. Also referred to as inotropy. Poor left ventricular function results in low contractility.

Colloid. Colloids are often based on crystalloid solutions which contain water and electrolytes but have the added larger molecules that do not freely diffuse across a semipermeable membrane. Refer to medscape.org.

CPI: Cardiac Power Index. CPO normalised for BSA.

CPO: Cardiac Power Output. A measure of the pumping ability of the heart, and is calculated as CPO = MAP x CO/451. The parameter was identified by the SHOCK trial as the strongest independent haemodynamic correlate of in-hospital mortality in patients with cardiogenic shock. The study identified the CPO threshold of 0.53 W [a value ≤0.53 was associated with a 58% chance of mortality (positive predictive value), whereas those patients whose CPO was >0.53 had a 71% probability of survival (negative predictive value)]. Reference; Fincke, R., et al., Cardiac power is the strongest hemodynamic correlate of mortality in cardiogenic shock: a report from the SHOCK trial registry. J Am Coll Cardiol, 2004. 44(2): p. 340-8.

Crystalloid. Crystalloids are predominately based on a solution of sterile water with added electrolytes. Refer to medscape.org.

CVP: Central Venous Pressure. The pressure within the superior vena cava and is an approximation of right atrial pressure. Measured in mmHg.

Diuresis. Urine production. Forced diuresis refers to an increased urine formation by drugs or fluid.

DO2: Delivered Oxygen. A measurement of the amount of oxygen delivered to the cells.

EDV: End Diastolic Volume. The volume in the left and right ventricles at the end of diastole (filling).

EF: Ejection Fraction. The percentage of blood volume within the left and right ventricles at the end of diastole (EDV) which is ejected into the vasculature as the SV with each beat. EF = 100 (SV/EDV). ODM+ does not measure EF, however Monnet showed that PV (as Vpeak) correlated very well with EF and suggest “low values of Vpeak should alert the clinician that LVEF is probably low and should prompt an echocardiographic examination in order to confirm the presence of LV systolic dysfunction. The relatively good trending ability of Vpeak suggests that if inotropic therapy is initiated, then the relative changes in Vpeak could allow monitoring of its effects in an easier way than by repeating echocardiography.” Reference; Monnet et al 2013. Assessment of changes in left ventricular systolic function with oesophageal Doppler. BJA 111(5):743-9.

ERP: Enhanced Recovery Programme. ERP is about improving patient outcomes and speeding up a patient’s recovery after surgery. Patients participate in their own recovery process and also ensures that evidence based care is used. Refer to institute.nhs.uk.

ERAS: Enhanced Recovery after Surgery. See ERP.

ESV: End Systolic Volume. The volume of blood in the left and right ventricles after systole (ejection).

Fluid Challenge. A small amount of intravenous fluid is given in a short amount of time to assess whether the patient has a preload reserve that can be used to increase SV with further fluids.

Fluid Responsive. Largely synonymous with ‘preload responsive’. The ability of the ventricles to increase output following a rapid fluid challenge.

FTc: Flow Time Corrected. The duration of flow down the thoracic descending aorta during systole, measured in ms by the ODM+ and corrected to a heart rate of 60bpm.

HR: Heart rate. The number of heart beats in one minute.

Hb: Haemoglobin. The iron containing protein in the red blood cell used to carry oxygen from the lungs to the cells. It is measured in either g/dL or mmol/L. In the ODM+, it is used to calculate DO2.

Hyperdynamic. An abnormally increased cardiac output associated with vasodilation and a decreased afterload.

Hypertension. High BP.

Hypervolaemia. Excessive level of circulating blood volume.

Hypoperfusion. Circulatory shock due to inadequate levels of oxygen to the tissues.

​Hypotension. Low BP.

Hypovolaemia. Inadequate level of blood volume, which can be absolute (due to loss of fluid) or relative (lack of volume to fill dilated vessels).

Hypoxaemia. Inadequate levels of oxygen in the blood where cell dysfunction and ultimately cell death can occur.

Inotropy. Related to a level of pharmacologic agents (inotropes) within blood, affecting the rate of contraction of myocardial fibres. Positive inotropes increase and negative inotropes decrease the myocardial contractility.

Intravascular Volume. Volume of blood in the circulation.

Insufflation. The act of blowing a gas, powder, or vapour into a body cavity.

IOFM: Intraoperative Fluid Management. The promotion of optimal fluid balance and the prevention of complications resulting from abnormal or undesired fluid levels (hypovolaemia or hypervolaemia) in the operating theatre and critical care areas. See SVO and Improved Outcomes.

Lactate. A byproduct of anaerobic metabolism. Plasma concentrations represent a balance between lactate production and lactate metabolism.The normal concentration is 0.3-1.3 mmol/L. A high and/or rising lactate suggests inadequate blood flow, either regionally or globally. An elevated lactate is associated with increased mortality. Gut hypoxia causes anaerobic metabolism. The liver receives more lactate from the portal vein. Initially, this is oxidised or converted to glucose by the periportal hepatocytes. Bacterial translocation and profound fluid shifts contribute to circulatory collapse. Global oxygen delivery falls. Endogenous catecholamine release attempts to support the circulation but will also increase glycolysis and lactate formation. As shock develops hepatic blood flow falls and intracellular acidosis inhibits gluconeogenesis from lactate. The liver produces rather than clears lactate. Intestinal bacteria metabolise glucose and carbohydrate to D-lactate. This is only slowly metabolised by human LDH and contributes to the escalating lactic acidosis. Reference; Phypers and Pierce 2006. Lactate physiology in health and disease. Cont Ed in Anaesthesia, Critical Care & pain. 6:128-130.

MAP: Mean Arterial Pressure. Is the value of pressure which would exist at the output node of the heart if there would be no arterial pulsations.

Morbidity. A disease state or symptom.

Mortality. Death.

NIBP: Noninvasive Blood Pressure. The measurement of BP without using an invasive arterial catheter.

Noninvasive. A technique which does not require a penetration of skin to perform a physiologic measurement.

Normotension. MAP within a normal range for the individual. Measured in mmHg.

Normovolaemia. Normal level of circulating blood volume (does not count the additional blood retained in reservoirs, such as in spleen)

Oliguria. Low urine output. If < 500 mL in 24 hours in an adult, it is usually reflective of inadequate renal perfusion unless chronic kidney disease was present previously.

Outcome. A consequence. With regard to the Decision Tree, outcomes are reported in terms of morbidity and mortality.

PEEP: Positive End Expiratory Pressure. Commonly known as the pressure applied to a ventilated breath at the end of expiration in order to prevent alveolar collapse.

Perfusion. Continuous supply of oxygen to the cells through adequate blood flow to the cells.

Peripheral Shutdown. Peripheral circulatory collapse (can be due to shock) involves outlying arteries and veins in the body and can result in organ failure or other serious complications.

PLR: Passive Leg Raise. A bedside test to evaluate the need for fluid.

Pneumoperitoneum. The presence of air or gas in the abdominal (peritoneal) cavity. Changes to intrathoracic pressure may occur which can affect haemodynamics. Limitations exist when using SVV or PPV during abdominal insufflation in any CO technology.

PV: Peak Velocity. The fastest velocity of red cells moving down the thoracic descending aorta as measured by the ODM+ at the top of the waveform. It gives an indication of contractility of the left ventricle and is affected by load. It is also age related and an approximate guide would be 140 minus age.

PPV: Pulse Pressure Variation. The variation in pulse pressure across the respiratory cycle.

Precision. The precision of a measurement system, related to reproducibility and repeatability. It is the degree to which repeated measurements under unchanged conditions show the same results.

Preload. The initial stretching of the cardiomyocytes (cardiac muscle cells) prior to contraction and is affected by filling. If the fibres are more stretched (increased preload), the contraction during systole will generate a higher force (increase in contractility) known as the Frank-Starling Law.

Pulse Oximetry. Indirect monitoring of SpO2 (as opposed to measuring through a blood gas sample). A plethysmogram (a volumetric measurement of an organ) is produced by illuminating the skin and measuring changes in light absorption. This determines an approximate percentage of erythrocytes (red cells), which contain Hb to carry the oxygen to the cells.

RR: Respiratory Rate. The number of breaths per minute.

SaO2: percentage of oxygenated red blood cells in arterial blood; this parameter is obtained in a blood laboratory from a sample of arterial blood and may be approximated by a continuous measurement of SpO2.

SCVO2: Central Venous Oxygen Saturation. The oxygen saturation of blood in the large veins returning deoxygenated blood to the heart. It is a measure of how much oxygen has been taken out of the arterial blood by the body’s cells. A normal SCVO2 is 70% or above, and when below this level it indicates that the body’s cells are extracting more oxygen than normal from the blood, which in turn indicates that cardiac output may be insufficient. At approximately 55%, anaerobic metabolism may not be apparent as the body is effectively compensating for suboptimal delivery of oxygen by increasing extraction. At an SCVO2 of approximately 30 or 40%, there is likely to be an associated anaerobic metabolism with a concurrent rise in lactate. When a high lactate is seen in conjunction with a high SCVO2, consideration should be given to a focal area of ischaemia or necrosis (e.g. dead gut, ischaemic leg), ineffective cellular utilisation of oxygen (e.g. due to severe vasoconstriction).
Reference; Sqaura P. 2014. Central venous oxygenation: when physiology explains apparent discrepancies. Crit Care 18(6):579.

SD: Stroke Distance. A Doppler measurement also known as the area under the curve or the velocity time integral. A nomogram based mainly on the age of the patient converts SD to SV. It correlates well with SV and can be used if volumetric measurements cannot be displayed e.g. when a patient is outside of the nomogram limits.

​Shock: A circulatory collapse is defined as a general or specific failure of the circulation. This form is sometimes called peripheral vascular failure, shock or peripheral vascular shutdown. Signs: pulse – rapid, weak, thready, respiration – shallow, irregular, laboured, BP – low, falling, mental state – confused, sluggish, anxious, eyes – pupils may be dilated, skin – cold, clammy, sweating. A milder or preliminary form of circulatory collapse is circulatory insufficiency.

SpO2: Peripheral Capillary Oxygen Saturation. An estimation of the oxygen saturation level. Normal levels are approximately 95-100%. Between 90 and 95%, blood oxygen level is considered low and if the level is below 90%, hypoxaemia results.

SV: Stroke Volume. The amount ejected from the ventricles per beat. Measured in mL.

SVI: Stroke Volume Index. SV normalised for BSA.

SVR: Systemic Vascular Resistance. The resistance to flow that must be overcome to push blood through the circulatory system. Measured as dyn·s/cm5

SVRI: Systemic Vascular Resistance Index. The resistance to flow that must be overcome to push blood through the circulatory system indexed for BSA.

SVO: Stroke Volume Optimisation. The achievement of an optimal SV by the use of fluid and vasoactive or inotropic drugs, to ensure best oxygen delivery and perfusion of the cells.

SvO2: Mixed Venous Oxygen Saturation. See SCVO2. Normal value approximately 65%.

SVV: Stroke Volume Variation. The variation of SV across a respiratory cycle.

Tachycardia. An abnormally high heart rate due to many causes. Can affect left ventricular function.

Temperature. A comparative measure of hot and cold.

Thoracic. Relating to the thorax.

Trendelenburg. The patient is flat on the back with the feet higher than the head by 15-30 degrees.

Vasoconstriction. The narrowing of the blood vessels resulting from contraction of the muscular wall of the vessels, in particular the large arteries and small arterioles. Can be due to physiological reactions or due to the use of vasoconstricting drugs where the effect is a primary or secondary one.

Vasoactive. A drug that has the effect of either increasing or decreasing blood pressure and/or heart rate.

Vasodilation. The widening of blood vessels. Can be due to physiological reactions or due to the use of vasodilating drugs where the effect is a primary or secondary one.

Vasopressor. A drug that vasoconstricts the blood vessels to increase total peripheral resistance in order to increase BP.

Volaemia. The status of circulating intravascular volume.

Volume Expansion. Increase of fluid in the blood by the use of crystalloids, colloids or blood products. Refer to medscape.org.

Suggested Reading

British National Formulary. www.bnf.org

​Dvorak G.O., Hemodynamic Monitoring: Invasive and Non Invasive Clinical Application. 2008 ed 4. Saunders.

Grossman S., and Porth C.M., Porth’s Pathophysiology: Concepts of Altered Health States. 2013 ed 9. Lippincott Williams & Wilkins.

Klabunde R.E., Cardiovascular Physiology Concepts. 2005. Lippincott Williams & Wilkins.

Porter R.S., The Merck Manual of Diagnosis and Therapy. 2011 ed 19. Wiley. See also www.merckmanuals.com

Oates C., Cardiovascular Haemodynamics and Doppler Waveforms Explained. 2001. Greenwich Medical Media.