3 lung zones

Q: Tip of the pulmonary artery catheter (PAC) should be ideally positioned in zone 3, which is? (select one) 

A) above the level of the left atrium 
B) below the level of the left atrium 


 Answer: B

Lung is divided into 3 zones, known as West's Zones since described by Dr. West 55 years ago. This physiologic division is according to three different pressures in the lungs 

•  mean arterial pressure(PA) 
• mean alveolar pressure(Pa)
• mean pulmonary capillary pressure(Pc) 

Zone 1 has PA>Pa>Pc

 Zone 2 has Pa>PA>Pc

 Zone 3 has Pa>Pc>PA

Tip of the PAC should be ideally positioned in zone 3 which is below the level of the left atrium and gives the appropriate Pulmonary Artery Occlusion Pressure (PAOP).


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Reference: 

West J, Dollery C, Naimark A (1964). "Distribution of blood flow in isolated lung; relation to vascular and alveolar pressures". J Appl Physiol. 19: 713–24.