Editing Cardiac output (section)

===Doppler ultrasound===
[[File:VTI LVOT.png|thumb|Doppler signal in the left ventricular outflow tract: Velocity Time Integral (VTI)]]

This method uses [[ultrasound]] and the [[Doppler effect]] to measure cardiac output. The blood velocity through the heart causes a Doppler shift in the frequency of the returning ultrasound waves. This shift can then be used to calculate flow velocity and volume, and effectively cardiac output, using the following equations:{{citation needed|date=March 2021}}
* <math>Q = SV \times HR</math>
* <math>SV = VTI \times CSA</math>
* <math>CSA =  \pi r^2</math>
where:
* CSA is the valve orifice cross sectional area,
* r is the valve radius, and,
* VTI is the velocity time integral of the trace of the Doppler flow profile.

Being non-invasive, accurate and inexpensive, Doppler ultrasound is a routine part of clinical ultrasound; it has high levels of reliability and reproducibility, and has been in clinical use since the 1960s.{{citation needed|date=March 2021}}

====Echocardiography====
[[Echocardiography]] is a non-invasive method of quantifying cardiac output using ultrasound. Two-dimensional (2D) ultrasound and Doppler measurements are used together to calculate cardiac output. 2D measurement of the diameter (d) of the aortic annulus allows calculation of the flow cross-sectional area (CSA), which is then multiplied by the VTI of the Doppler flow profile across the aortic valve to determine the flow volume per beat ([[Stroke Volume|stroke volume]], SV). The result is then multiplied by the heart rate (HR) to obtain cardiac output. Although used in clinical medicine, it has a wide test-retest variability.<ref>{{cite journal | vauthors = Finegold JA, Manisty CH, Cecaro F, Sutaria N, Mayet J, Francis DP | title = Choosing between velocity-time-integral ratio and peak velocity ratio for calculation of the dimensionless index (or aortic valve area) in serial follow-up of aortic stenosis | journal = International Journal of Cardiology | volume = 167 | issue = 4 | pages = 1524–31 | date = August 2013 | pmid = 22575631 | doi = 10.1016/j.ijcard.2012.04.105 }}</ref> It is said to require extensive training and skill, but the exact steps needed to achieve clinically adequate precision have never been disclosed. 2D measurement of the aortic valve diameter is one source of noise; others are beat-to-beat variation in stroke volume and subtle differences in probe position. An alternative that is not necessarily more reproducible is the measurement of the pulmonary valve to calculate right-sided CO. Although it is in wide general use, the technique is time-consuming and is limited by the reproducibility of its component elements. In the manner used in clinical practice, precision of SV and CO is of the order of ±20%.{{citation needed|date=October 2014}}

====Transcutaneous====
Ultrasonic Cardiac Output Monitor (USCOM) uses [[Continuous wave doppler|continuous wave Doppler]] to measure the Doppler flow profile VTI. It uses [[anthropometry]] to calculate aortic and pulmonary valve diameters and CSAs, allowing right-sided and left-sided ''Q'' measurements. In comparison to the echocardiographic method, USCOM significantly improves reproducibility and increases sensitivity of the detection of changes in flow. Real-time, automatic tracing of the Doppler flow profile allows beat-to-beat right-sided and left-sided ''Q'' measurements, simplifying operation and reducing the time of acquisition compared to conventional echocardiography. USCOM has been validated from 0.12 L/min to 18.7 L/min<ref name="Su">{{cite journal | vauthors = Su BC, Yu HP, Yang MW, Lin CC, Kao MC, Chang CH, Lee WC | title = Reliability of a new ultrasonic cardiac output monitor in recipients of living donor liver transplantation | journal = Liver Transplantation | volume = 14 | issue = 7 | pages = 1029–37 | date = July 2008 | pmid = 18581505 | doi = 10.1002/lt.21461 | s2cid = 37185399 | doi-access = free }}</ref> in new-born babies,<ref name="Phillips et. al. 3">{{cite journal | vauthors = Phillips R, Paradisis M, Evans N, Southwell D, Burstow D, West M | year = 2006 |title=Cardiac output measurement in preterm neonates: validation of USCOM against echocardiography |journal=Critical Care |volume=10 |issue=Suppl 1 |page=343 |doi=10.1186/cc4690|pmc=4092718 | doi-access = free }}</ref> children<ref name="Cattermole">{{cite journal | vauthors = Cattermole GN, Leung PY, Mak PS, Chan SS, Graham CA, Rainer TH | title = The normal ranges of cardiovascular parameters in children measured using the Ultrasonic Cardiac Output Monitor | journal = Critical Care Medicine | volume = 38 | issue = 9 | pages = 1875–81 | date = September 2010 | pmid = 20562697 | doi = 10.1097/CCM.0b013e3181e8adee | s2cid = 24949904 }}</ref> and adults.<ref name="Jain et. al.">{{cite journal | vauthors = Jain S, Allins A, Salim A, Vafa A, Wilson MT, Margulies DR | title = Noninvasive Doppler ultrasonography for assessing cardiac function: can it replace the Swan-Ganz catheter? | journal = American Journal of Surgery | volume = 196 | issue = 6 | pages = 961–67; discussion 967–68 | date = December 2008 | pmid = 19095116 | doi = 10.1016/j.amjsurg.2008.07.039 }}</ref> The method can be applied with equal accuracy to patients of all ages for the development of physiologically rational haemodynamic protocols. USCOM is the only method of cardiac output measurement to have achieved equivalent accuracy to the implantable flow probe.<ref name="Phillips et. al. 2"/> This accuracy has ensured high levels of clinical use in conditions including sepsis, heart failure and hypertension.<ref name="Horster">{{cite journal | vauthors = Horster S, Stemmler HJ, Strecker N, Brettner F, Hausmann A, Cnossen J, Parhofer KG, Nickel T, Geiger S | title = Cardiac Output Measurements in Septic Patients: Comparing the Accuracy of USCOM to PiCCO | journal = Critical Care Research and Practice | volume = 2012 | pages = 1–5 | year = 2012 | pmid = 22191019 | pmc = 3235433 | doi = 10.1155/2012/270631 | doi-access = free }}</ref><ref name="Phillips et. al. 5">{{cite journal | vauthors = Phillips R, Lichtenthal P, Sloniger J, Burstow D, West M, Copeland J | title = Noninvasive cardiac output measurement in heart failure subjects on circulatory support | journal = Anesthesia and Analgesia | volume = 108 | issue = 3 | pages = 881–86 | date = March 2009 | pmid = 19224797 | doi = 10.1213/ane.0b013e318193174b | s2cid = 35618846 }}</ref><ref name="Kager">{{cite journal | vauthors = Kager CC, Dekker GA, Stam MC | title = Measurement of cardiac output in normal pregnancy by a non-invasive two-dimensional independent Doppler device | journal = The Australian & New Zealand Journal of Obstetrics & Gynaecology | volume = 49 | issue = 2 | pages = 142–44 | date = April 2009 | pmid = 19441163 | doi = 10.1111/j.1479-828X.2009.00948.x | s2cid = 25371483 | doi-access = free }}</ref>

====Transoesophageal====
[[File:TEE-Sonde.png|alt=A Transesophageal echocardiogram (BrE: TOE, AmE: TEE) probe.|thumb|A transoesophageal echocardiogram probe.]]

The Transoesophageal Doppler includes two main technologies; [[Transesophageal echocardiogram|transoesophageal echocardiogram]]—which is primarily used for diagnostic purposes, and [[Esophogeal doppler|oesophageal Doppler]] monitoring—which is primarily used for the clinical monitoring of cardiac output. The latter uses continuous wave Doppler to measure blood velocity in the [[descending aorta|descending thoracic aorta]]. An ultrasound probe is inserted either orally or nasally into the oesophagus to mid-thoracic level, at which point the oesophagus lies alongside the descending [[thoracic aorta]]. Because the transducer is close to the blood flow, the signal is clear. The probe may require re-focussing to ensure an optimal signal. This method has good validation, is widely used for fluid management during surgery with evidence for improved patient outcome,<ref>{{cite journal | vauthors = Mythen MG, Webb AR | title = Perioperative plasma volume expansion reduces the incidence of gut mucosal hypoperfusion during cardiac surgery | journal = Archives of Surgery | volume = 130 | issue = 4 | pages = 423–29 | date = April 1995 | pmid = 7535996 | doi = 10.1001/archsurg.1995.01430040085019 }}</ref><ref>{{cite journal | vauthors = Sinclair S, James S, Singer M | title = Intraoperative intravascular volume optimisation and length of hospital stay after repair of proximal femoral fracture: randomised controlled trial | journal = BMJ | volume = 315 | issue = 7113 | pages = 909–12 | date = October 1997 | pmid = 9361539 | pmc = 2127619 | doi = 10.1136/bmj.315.7113.909 }}</ref><ref>{{cite journal | vauthors = Conway DH, Mayall R, Abdul-Latif MS, Gilligan S, Tackaberry C | title = Randomised controlled trial investigating the influence of intravenous fluid titration using oesophageal Doppler monitoring during bowel surgery | journal = Anaesthesia | volume = 57 | issue = 9 | pages = 845–49 | date = September 2002 | pmid = 12190747 | doi = 10.1046/j.1365-2044.2002.02708.x | s2cid = 43755776 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Gan TJ, Soppitt A, Maroof M, el-Moalem H, Robertson KM, Moretti E, Dwane P, Glass PS | title = Goal-directed intraoperative fluid administration reduces length of hospital stay after major surgery | journal = Anesthesiology | volume = 97 | issue = 4 | pages = 820–26 | date = October 2002 | pmid = 12357146 | doi = 10.1097/00000542-200210000-00012 | s2cid = 10471164 }}</ref><ref>{{cite journal | vauthors = Venn R, Steele A, Richardson P, Poloniecki J, Grounds M, Newman P | title = Randomized controlled trial to investigate influence of the fluid challenge on duration of hospital stay and perioperative morbidity in patients with hip fractures | journal = British Journal of Anaesthesia | volume = 88 | issue = 1 | pages = 65–71 | date = January 2002 | pmid = 11881887 | doi = 10.1093/bja/88.1.65 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Wakeling HG, McFall MR, Jenkins CS, Woods WG, Miles WF, Barclay GR, Fleming SC | title = Intraoperative oesophageal Doppler guided fluid management shortens postoperative hospital stay after major bowel surgery | journal = British Journal of Anaesthesia | volume = 95 | issue = 5 | pages = 634–42 | date = November 2005 | pmid = 16155038 | doi = 10.1093/bja/aei223 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Noblett SE, Snowden CP, Shenton BK, Horgan AF | title = Randomized clinical trial assessing the effect of Doppler-optimized fluid management on outcome after elective colorectal resection | journal = The British Journal of Surgery | volume = 93 | issue = 9 | pages = 1069–76 | date = September 2006 | pmid = 16888706 | doi = 10.1002/bjs.5454 | s2cid = 25469534 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Pillai P, McEleavy I, Gaughan M, Snowden C, Nesbitt I, Durkan G, Johnson M, Cosgrove J, Thorpe A | title = A double-blind randomized controlled clinical trial to assess the effect of Doppler optimized intraoperative fluid management on outcome following radical cystectomy | journal = The Journal of Urology | volume = 186 | issue = 6 | pages = 2201–06 | date = December 2011 | pmid = 22014804 | doi = 10.1016/j.juro.2011.07.093 }}</ref> and has been recommended by the UK's National Institute for Health and Clinical Excellence ([[NICE]]).<ref>{{Cite web|url=https://www.nice.org.uk/mtg3|title=CardioQ-ODM oesophageal doppler monitor &#124; Guidance &#124; NICE|date=25 March 2011 |access-date=23 February 2022|archive-date=23 February 2022|archive-url=https://web.archive.org/web/20220223063027/https://www.nice.org.uk/guidance/mtg3|url-status=live}}</ref> Oesophageal Doppler monitoring measures the velocity of blood and not true ''Q'', therefore relies on a nomogram<ref>{{cite web |first1=Graham D. |last1=Lowe |first2=Barry M. |last2=Chamberlain |first3=Eleanor J. |last3=Philpot |first4=Richard J. |last4=Willshire |name-list-style=vanc |year=2010 |title=Oesophageal Doppler Monitor (ODM) guided individualised goal directed fluid management (iGDFM) in surgery – a technical review |work=Deltex Medical Technical Review |url=https://www.deltexmedical.com/downloads/TechnicalReview.pdf |url-status=dead |archive-url=https://web.archive.org/web/20150923213441/https://www.deltexmedical.com/downloads/TechnicalReview.pdf |archive-date=23 September 2015 |access-date=13 October 2014 }}</ref> based on patient age, height and weight to convert the measured velocity into stroke volume and cardiac output. This method generally requires patient sedation and is accepted for use in both adults and children.{{citation needed|date=March 2021}}