A 52-year-old female with a history of nonischemic cardiomyopathy and reduced ejection fraction undergoes emergent spine surgery after being involved in a motor vehicle collision. There is significant blood loss during the case requiring transfusion of blood products. The patient arrives to the ICU intubated, sedated, and requiring vasopressor support.
A pulmonary artery catheter is placed to guide management and the mixed venous oxygen saturation is noted to be low.
Which of the following is not a potential cause of decreased oxygen delivery in this patient?A. Acute blood loss anemia
Correct Answer: C
The mixed venous oxygen saturation is the oxygen saturation of blood sampled at the proximal pulmonary artery and reflects the balance between global delivery and global uptake of oxygen. Oxygen delivery is the product of arterial oxygen content and CO: DO2 = CaO2 x CO
In blood, oxygen is carried in two forms: the majority bound to hemoglobin and the remainder dissolved in plasma. Therefore, the arterial content of oxygen is expressed by the following equation representing both components:
CaO2 = 1.34x Hb x SaO2 + 0.003 x PaO2
CaO2 = mL of O2 per 100 mL blood
Oxygen-combining capacity: 1.34 mL of O2 per gram of hemoglobin Hb = grams of hemoglobin per 100 mL blood
SaO2 = fraction of Hb saturated with O2
PaO2 = oxygen tension
Solubility: 0.003 mL of O2 per 100 mL plasma for each mm Hg PaO2 Factors that will decrease oxygen delivery include decreased hemoglobin (A), decreased CO due to heart failure or hypovolemia (B), hypoxia (D), and abnormalities such as carbon monoxide poisoning or methemoglobinemia that affect the oxygen-carrying capacity of hemoglobin. Shivering (C) could potentially decrease mixed venous oxygen saturation through increased metabolic demand and oxygen uptake but should not affect oxygen delivery.