Editing Cardiac output (section)

===Pulmonary artery thermodilution (trans-right-heart thermodilution)===
[[File:Pulmonary artery catheter english.JPG|alt=Diagram of Pulmonary artery catheter (PAC)|thumb|Diagram of Pulmonary artery catheter (PAC)]]

The indicator method was further developed by replacing the indicator dye with heated or cooled fluid. Temperature changes rather than dye concentration are measured at sites in the circulation; this method is known as thermodilution. The [[pulmonary artery catheter]] (PAC) introduced to clinical practice in 1970, also known as the [[Swan-Ganz catheter]], provides direct access to the right heart for thermodilution measurements. Continuous, invasive, cardiac monitoring in intensive care units has been mostly phased out. The PAC remains useful in right-heart study done in cardiac catheterisation laboratories.{{citation needed|date=June 2015}}

The PAC is balloon tipped and is inflated, which helps "sail" the catheter balloon through the right ventricle to occlude a small branch of the pulmonary artery system. The balloon is then deflated. The PAC thermodilution method involves the injection of a small amount (10 mL) of cold glucose at a known temperature into the pulmonary artery and measuring the temperature a known distance away {{Convert|6–10|cm|inch|abbr=on}} using the same catheter with temperature sensors set apart at a known distance.{{citation needed|date=June 2015}}

The historically significant Swan-Ganz multi-lumen catheter allows reproducible calculation of cardiac output from a measured time-temperature curve, also known as the thermodilution curve. [[Thermistor]] technology enabled the observations that low CO registers temperature change slowly and high CO registers temperature change rapidly. The degree of temperature change is directly proportional to the cardiac output. In this unique method, three or four repeated measurements or passes are usually averaged to improve accuracy.<ref>{{cite journal | vauthors = Iberti TJ, Fischer EP, Leibowitz AB, Panacek EA, Silverstein JH, Albertson TE | title = A multicenter study of physicians' knowledge of the pulmonary artery catheter. Pulmonary Artery Catheter Study Group | journal = JAMA | volume = 264 | issue = 22 | pages = 2928–32 | date = December 1990 | pmid = 2232089 | doi = 10.1001/jama.264.22.2928 }}</ref><ref>{{cite journal | vauthors = Johnston IG, Jane R, Fraser JF, Kruger P, Hickling K | title = Survey of intensive care nurses' knowledge relating to the pulmonary artery catheter | journal = Anaesthesia and Intensive Care | volume = 32 | issue = 4 | pages = 564–68 | date = August 2004 | pmid = 15675218 | doi = 10.1177/0310057X0403200415 | doi-access = free }}</ref> Modern catheters are fitted with heating filaments that intermittently heat up and measure the thermodilution curve, providing serial ''Q'' measurements. These instruments average measurements over 2–9 minutes depending on the stability of the circulation, and thus do not provide continuous monitoring.

PAC use can be complicated by arrhythmias, infection, pulmonary artery rupture and damage to the right heart valve. Recent studies in patients with critical illnesses, sepsis, acute respiratory failure and heart failure suggest that use of the PAC does not improve patient outcomes.<ref name="Stevenson"/><ref name="Shah"/><ref name="Hall"/> This clinical ineffectiveness may relate to its poor accuracy and sensitivity, which have been demonstrated by comparison with flow probes across a sixfold range of ''Q'' values.<ref name="Phillips et. al. 2">{{cite journal | vauthors = Phillips RA, Hood SG, Jacobson BM, West MJ, Wan L, May CN | title = Pulmonary Artery Catheter (PAC) Accuracy and Efficacy Compared with Flow Probe and Transcutaneous Doppler (USCOM): An Ovine Cardiac Output Validation | journal = Critical Care Research and Practice | volume = 2012 | pages = 1–9 | year = 2012 | pmid = 22649718 | pmc = 3357512 | doi = 10.1155/2012/621496 | doi-access = free }}</ref> Use of PAC is in decline as clinicians move to less invasive and more accurate technologies for monitoring hæmodynamics.<ref>{{cite journal | vauthors = Alhashemi JA, Cecconi M, Hofer CK | title = Cardiac output monitoring: an integrative perspective | journal = Critical Care | volume = 15 | issue = 2 | pages = 214 | year = 2011 | pmid = 21457508 | pmc = 3219410 | doi = 10.1186/cc9996 | doi-access = free }}</ref>