This came up in  Question 19 from the second paper of 2007.

The awesomeness of the PA catheter is discussed in greater detail elsewehere.

Appropriate zone positioning is also discussed.

To maintain a column of blood between the pressure transducer and the left atrium, the balloon has to be below the atrium. This means you have to send the catheter tip into Wests Zone 3 when you are floating it .

• This should happen naturally because Wests Zone 3 normally enjoys higher blood flow.
  • THAT may not be the case in a patient ventilated with positive pressure (blood is pushed around into all zones) or some other reason for a high intrathoracic pressure.
  • To maximize your chance of sending the catheter tip to Zone 3, one may artificially increase the blood flow to that zone by turning the patient on one side.

Tests which suggest appropriate Zone 3 positioning of the PAC

• On lateral CXR, the tip of the catheter is at or below the left atrium
• Respiratory variation of PAOP is < 50% of the static airway pressure (peak – plateau)
• Change the PEEP: PAOP changes by 50% of the change in PEEP
• The PAWP is less than the PA diastolic pressure
• The PAWP contour has recognizable a and v waves; in Zones 1 and 2 it is unnaturally smooth.
• Wedge PO2 minus Arterial PO2 = 19mmHg
• Arterial PCO2 minus Wedge PCO2 = 11mmHg
• Wedge pH minus Arterial pH = 0.008

• On the Xray, the tip should appear 3 -5 cm from the midline, no more than 2cm from the hilum.
• It should be INFERIOR to the LA position.