Quote from JenSICU_CCRN
The shift to the left decreases hemoglobins affinity for O2 and since the o2 sat detects O2 on Hemoglobin and the Hemoglobin is pushing the O2 off of it the sat is lower. Does that make sense? If the opposite would occur, like if a pt. is cold post-op from the cold OR the O2 sat would be high since the Hemoglobin has an affinity for O2....so it is holding on to it and not releasing it to the tissues. That is why the PO2 on a post op gas looks so good. Some of our pts. (SICU Nurse here) that come over from PACU have PO2's in the high 100's due to the shifting.
Actually, it is just the opposite. On the oxyhemoglobin disassociation curve, the curve shifts to the right
with an increase in temperature, and that is a decreased affinity of the hemoglobin for oxygen. The saturation measures what percentage of Hgb is fully saturated. If you have a decreased affinity for oxygen, more oxygen will unload to the tissues, therefore decreasing the amount that is carried by the hemoglobin, so your pulse ox will read lower. Things that decrease hemoglobin affinity for oxygen include fever, acidosis/increased c02, decreased pH, sickle cell anemia, maternal hemoglobin, etc.
When the patient is cold, your tissues need less oxygen, so the hemoglobin has a higher affinity for oxygen, so the curve shifts to the left
. Other things that shift to the left (and increase affinity) include decreased temp, increased pH, decreased Pco2, fetal hemoglobin, carboxyhemoglobin, and methemoglobin.