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Pulmonary Artery Catheter
| A flow-- directed balloon-tipped pulmonary artery catheter enables catheterization of the right heart for measurement of pressures without requiring the manipulative and radiologic control demanded by other methods of cardiac catheterization. The pulmonary artery occlusion (wedge) pressure reflects left atrial pressure because, at no flow, the pressures can equilibrate between the distal end of the pulmonary artery catheter and the left atrium. The flow-directed pulmonary artery catheter measures cardiac output by the thermodilution technique. Specifically, a thermistor in the distal end of the pulmonary artery catheter sensed the change in blood temperature produced by the rapid injection of iced (or room temperature) solution administered through the proximal (central venous pressure) port of the catheter. Cardiac output is inversely proportional to the area under the time-temperature curve (calculated by the cardiac output computer and expressed as L*min~1) because blood flow is the source of the thermal dilution. The output of only the right ventricle is measured by this technique. Specially designed pulmonary artery catheters are capable of providing cardiac pacing or fiberoptic oximetry with the ability to constantly monitor mixed venous hemoglobin oxygen saturation. When metabolic oxygen requirements are unchanging, the mixed venous hemoglobin oxygen saturation is directly proportional to the cardiac output. Pulmonary artery catheters are often inserted percutaneously via the right internal jugular vein. Insertion of the catheter requires continuous displays of pressures and recognition of characteristic waveforms. The balloon on the distal end of the catheter is inflated with I to 1.5 ml of air only after a right atrial tracing has been confirmed. The inflated balloon facilitates passage (flotation) of the distal end of the catheter with blood flow into the pulmonary artery. A right ventricular tracing should appear after the catheter is inserted 28 to 32 cm, and a pulmonary artery occlusion pressure tracing is evident after insertion of the catheter 45 to 50 cm. The balloon is deflated at this point, and a pulmonary artery pressure tracing should again appear. Re inflation of the balloon with about I Omi of air should result in reappearance of the pulmonary artery occlusion pressure tracing. Strict adherence to these insertion distances will minimize the likelihood of catheter loops or intracardiac knot formation. The balloon should not be left in the inflated position except during actual measurement of pulmonary artery occlusion pressure so as to minimize the likelihood of pulmonary ischemia or infarction. Other risks of pulmonary artery catheter insertion include mechanically induced cardiac dysrhythmias and heart block. A rare but catastrophic complication of the use of pulmonary artery catheters is pulmonary artery perforation. Because the pulmonary artery diastolic pressure agrees well with the pulmonary artery occlusion pressure in the absence of pulmonary hypertension, it is logical to use the end--diastolic pressure as an indirect measurement of left atrial pressure. Indications for use of the pulmonary artery catheter are numerous and often controversial. The need for intravascular fluid volume replacement, the presence of underlying cardiac diseases, and the responses to intravenous fluid infusion are commonly monitored with a pulmonary artery catheter. Oxygen delivery can also be calculated using the VA catheter and may be of value in critically ill patients. Measurement of cardiac filling pressures and cardiac output and calculation of systemic and pulmonary vascular resistance are essential information for evaluating various disorders. |
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