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Management of a PAC during CPB:
Although not discussed in great detail in standard texts, the management of the PAC during CPB should be specifically addressed by the anaesthetist in order to avoid the rare but potentially lethal complication of pulmonary artery rupture.

When the patient is placed on CPB, there is a tendency for the PAC to migrate distally. In one series, the catheter tip migrated between 2 and 8 cms while on CPB and by the end of bypass about 90% were located in a lobar or segmental vessel and over 60% were permanently wedged 1. This distal migration predisposes to vascular damage occurring either as a result of catheter-tip penetration of the vessel wall, or, by allowing wedging at very low inflation volumes which facilitates inflation-induced rupture. In any event, the risk of pulmonary artery rupture is certainly markedly increased during the period of bypass and it has been stated that about 1/3 of all cases are associated with CPB 2.

The tendency for distal catheter migration has been attributed to:

 1. A reduction in size of the right ventricle when CPB is instituted 3,
2. surgical handling of the heart, and
3. lung deflation 4.

One of the authors (DAP) has the impression that catheter migration is a greater problem if the jugular rather than subclavian route is used. It is possible that sternal retraction itself tends to withdraw catheters placed via the subclavian vein.

Hypothermia hardens PACs which also may increase the risk of vascular damage. Cohen et al 2 tested the hypothesis that hypothermia-induced catheter stiffness was a factor in pulmonary artery rupture. In a pulsating-membrane model exposed to a PA catheter tip, they found that the membrane rupture rate varied significantly with temperature and concluded that perforation of the model pulmonary artery by a PAC was 5 times more likely during hypothermia to temperatures of 25 degrees C when compared to the normothermic model.

At least three PAC management strategies have been used during bypass.

1. Leaving the PAC in the pulmonary artery.
The PAC may be safely left in the pulmonary artery, provided that it is withdrawn a few centimetres from the wedge position and that it is monitored for the duration of bypass 5. The option has the advantage that the catheter can still be used in the assessment of the need for left heart venting during the procedure. If this approach is chosen, the catheter must be withdrawn further if 'overwedging' is observed at any time during the procedure.

2. Withdrawal of the PAC into the right ventricle.
Stone et al 3 reported a series of 200 patients in whom the catheter was withdrawn into the right ventricle during CPB. This option removes the ability to use the catheter in the assessment of need for left heart venting during bypass and exposes the thin-walled right ventricle to the risk of damage from a hypothermic catheter tip. In addition, it also suffers from problems associated with catheter reflotation which are outlined below. Stone subsequently modified his technique so that the catheter tip was positioned in the main pulmonary artery rather than the right ventricle 6.

3. Withdrawal of the PAC into the superior vena cava.
If the clinician wishes to withdraw the PAC from the pulmonary artery, or surgical access necessitates the removal of the PAC, it should be withdrawn to the superior vena cava and not refloated until the venous line is removed 7. This option has the obvious disadvantages that:

1. The PAC is unavailable during weaning from CPB.
2. In a ‘sick’ patient, the immediate post-bypass period is not the ideal time to be attempting catheter flotation. – Cardiac output may be low, the risk of arrhythmias may be high and the immediate post-bypass period is a bad time for clinician distraction.
3. The central venous lumen may be inadvertently positioned outside the circulation.

Reflotation of the catheter should not be attempted while the patient is on complete or partial bypass because of the risk of entrapment of the PAC in the venous cannula.

References:

1. Johnston WE, Royster RL, Choplin RH et al Pulmonary artery catheter migration during cardiac surgery. Anesthesioloy 64; 258-262. (1986)

2. Cohen JA; Blackshear RH; Gravenstein N; Woeste J Increased pulmonary artery perforating potential of pulmonary artery catheters during hypothermia. J Cardiothorac Vasc Anesth, 5:234-6, 1991 Jun

3. Stone JG, Khambatta HJ, McDaniel DD. Catheter induced pulmonary arterial trauma:can it always be averted? J Thorac Cardiovasc Surg 86;146-155,1983.

4. Cokis C, Coombs L Rupture of an Abnormal Pulmonary Artery with a Flow-Directed Pulmonary Artery Catheter Anaesth Intens Care 1997; 25:147-149

5. Gravlee GP, Davis RF, Utley JR. Cardiopulmonary bypass: Principles and Practice. 588-589 Williams and Wilkins 1993.

6. Kopman EA .Pressure monitoring during cardio-pulmonary bypass. J Thorac Cardiovasc Surg 87:319-320,1984.

7. Gilbert TB Scherlis ML Fiocco M Lowinger TA Pulmonary artery catheter migration causing venous cannula obstruction during cardiopulmonary bypass. Anesthesiology 1995 Feb, 82 [2]: 596- 7.

Last edited on: 13/11/2000

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