Compare and contrast the roles of the pulmonary artery catheter and transoesophageal echocardiography in the management of the critically ill patient with shock.
The PA catheter provides access to pulmonary and central venous circulations, at a relatively low incremental cost. The main information obtained is from measurement of pressures (eg. within right atrium or pulmonary arteries), but additional information includes core temperature, pressure waveforms, occlusion pressure, cardiac output (thermodilution or continuous), mixed venous oxygen saturation (intermittent [including from sites other than PA] or continuous). Standard limitations include the variable relationship between pressure and volume, and the risks of using derived variable. Other risks can be categorised into those associated with central venous catheterisation (e.g. arterial puncture, air embolus, infection), floating of the catheter (e.g. arrhythmias), and balloon inflation (e.g. PA rupture). Some information can be continuously monitored (e.g. pulmonary arterial pressures); other is intermittently sampled (e.g. occlusion pressure, thermodilution cardiac output), but without the risks of reinsertion.
Transoesophageal echocardiography requires additional very expensive monitoring equipment, and an expensive (but re-usable) probe. The TOE allows visualisation of cardiac (and surrounding) structures, and measurement/estimation of a number of haemodynamic parameters. A visual estimate is obtained of various parameters: including volume status (pre-load), contractility (left and right sided systolic and diastolic function), regional wall motion, abnormal masses (eg. vegetations) and peri-cardial/pleural/peri-aortic collections. Using Doppler, assessment of valvular function, and estimate of pressures and cardiac output is also possible. This is an intermittent technique (not usually left in situ for more than a few hours), which is highly operator dependent, where most risks associated with insertion and manipulation (eg. gastrointestinal bleeding/rupture). Insertion and manipulation usually requires some degree of sedation.
Indications depend on specific information desired, and the local expertise. The potential information obtained with either technique must be weighed against the risks in any given clinical scenario. If standard precautions are used, mortality or major morbidity with either technique is thankfully rare.
This question lends itself well to a table format.
|
Issues |
PA catheter |
TOE |
|
cost |
Cheap |
Expensive |
|
Skill required |
Minimal expertise |
Skilled operator required |
|
Accuracy of measurements |
Positional; dependent on placement of balloon in Wests Zone 3. |
Operator-dependent |
|
Validity of interpretation |
Dependent on the normality of cardiac anatomy (accuracy diminishes in presence of valvular regurgitation or septal defects) |
Interpreter-dependent |
|
Information derived |
Pressure in chambers and in the PA. |
Anatomical information regarding cardiac structure Realtime observation of cardiac function |
|
Risks |
Haemorrhage/vascular access risks |
Oesophageal perforation |
|
Advantages |
Continuous monitoring technique Able to acquire blood samples |
Minimally invasive |
|
Disadvantages |
Invasive; significant risks of insertion |
Intermittent monitoring technique No sampling possible |
This is an article on how one might measure PAC-style chamber pressures using the TOE and the Bernoulli equation.
Chassot, P. G. "[Hemodynamic surveillance: transesophageal echocardiography or Swan-Ganz catheter?]." Revue medicale de la Suisse romande 121.9 (2001): 667-675.