Question 27.1

Pass rate: 26%

Highest mark: ?

A 56 year old female with septic shock and multiple organ failure is admitted  to intensive  care.   She is endotracheally  intubated and  ventilated.  A central venous catheter is inserted into her right subclavian  vein, a Vas Cath  is inserted into her right  femoral   vein  and   a  pulmonary artery  catheter  is  inserted  via  her  left subclavian vein.

a) Blood gas samples are simultaneously  taken  from all three catheters. The oxygen saturations are as follows:




State  which  site  each  of the  blood  gas  samples  is taken  from and  justify  your answer:

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College Answer

60% = pulmonary artery catheter       - pooled blood from SVC and IVC

67% = subclavian vein (superior vena cava) - in sepsis, cerebral blood flow relatively maintained initially

50% = femoral vein (inferior vena cava) - in sepsis, regional O2 consumption and extraction in gut/splanchnic circulation increases


Central venous saturation measurements are discussed in greater detail elsewhere. These measurements are a means of assessment of the adequacy of oxygen delivery.

In brief summary, the further up you move away from the pulmonary artery, the greater your SvO2becomes; whereas if you go further down, the very hypoxic splanchnic venous blood will decrease the SvO2.

a comparison of venous saturation measurments


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Chawla, Lakhmir S., et al. "Lack of equivalence between central and mixed venous oxygen saturation." CHEST Journal 126.6 (2004): 1891-1896.