Compare and contrast the roles of the pulmonary artery catheter and transoesophageal echocardiography in the management of the critically ill patient with shock.

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College Answer

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.

Discussion

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. 
Average of 3 thermodilution measurements required

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.
Core temperature
Mixed venous blood samples for ScVO2

Anatomical information regarding cardiac structure

Realtime observation of cardiac function

Risks

Haemorrhage/vascular access risks
Pulmonary artery rupture and haemorhage
Right heart valve damage
Right ventricular damage
Knotting inside right ventricle
Arrhythmias

Oesophageal perforation
Oral cavity damage
Risk associated with sedation and anaesthesia

Advantages

Continuous monitoring technique

Able to acquire blood samples

Minimally invasive

Disadvantages

Invasive; significant risks of insertion

Intermittent monitoring technique

No sampling possible

References