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Question 5#

B. 0.76 L/min

C. 1.3 L/min

D. D. 20 L/min

Correct Answer is A

Comment:

Question 5#

As part of a clinical study, you are measuring oxygen consumption using indirect calorimetry in a ventilated patient in the ICU and want to compare your measurements to a calculated value. Radial artery and pulmonary artery catheters are placed, and the following measurements are obtained:

- Hb = 11.7 g/dL
- SaO
_{2}= 97% - SvO
_{2}= 72% - CO (thermodilution): 5.1 L/min

Assuming minimal contribution from dissolved oxygen, what is the patient’s calculated oxygen consumption?

A. 0.2 L/minB. 0.76 L/min

C. 1.3 L/min

D. D. 20 L/min

Correct Answer is A

Comment:

Correct Answer: A

The Fick equation relates CO, oxygen consumption, and the arteriovenous oxygen content difference as follows:

CO = VO_{2} / (CaO_{2} - CvO_{2})

Rearrange to solve for oxygen consumption yields:

VO_{2} = CO x (CaO_{2} - CvO_{2})

Oxygen content of arterial or venous blood is given by the equation:

C_{a/v}O_{2} = 1.34 x Hb x S_{a/v}O_{2 } + 0.003 x P_{a/v}O_{2}

Excluding the dissolved oxygen term, CaO_{2} and CvO_{2} can be calculated from the information given:

CaO_{2} = 1.34 x 11.7 x 0.97 = 15.2 ml O_{2} / 100 mL blood

CvO_{2} = 1.34 x 11.7 x 0.72 = 11.3 ml O_{2} / 100 mL blood

Therefore:

VO_{2} = 5100 mL blood / min x (15.2 - 11.3 ml O_{2} / 100 mL blood) = 199 mL O_{2} / min , or approximately 0.2 L/min (A).

References:

- Bizouarn P, Blanloeil Y, Pinaud M. Comparison between oxygen consumption calculated by Fick’s principle using a continuous thermodilution technique and measured by indirect calorimetry. Br J Anaesth. 1995;75:719-723 .
- Miller RD. Miller’s Anesthesia. 8th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2015.