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Correspondence |

Oxyhemoglobin Dissociation Curve Clarification FREE TO VIEW

Troy E. Dominguez, MD, FCCP
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Department of Anesthesiology and Critical Care Medicine, The Children’s Hospital of Philadelphia, Philadelphia, PA

Correspondence to: Troy E. Dominguez, MD, FCCP, Department of Anesthesiology and Critical Care Medicine, The Children’s Hospital of Philadelphia, 34th St and Civic Center Blvd, Philadelphia, PA 19104; e-mail: dominguez@email.chop.edu



Chest. 2007;132(6):2053-2054. doi:10.1378/chest.07-1293
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To the Editor:

I read with interest the report by Das et al1on hemoglobin Bassett producing low pulse oximeter and co-oximeter readings. Since I practice intensive care medicine, two things struck me about this report. One is the implication that the low oximetry readings were related to a rightward shift of the oxyhemoglobin dissociation curve. From the data the authors presented, the measured Po2 at 50% saturation (p50) was normal and the oximetry was low. This suggests the dissociation curve was not shifted and the low oximetry seen in their patient was due to the fraction of the abnormal hemoglobin not binding oxygen. Secondly, the authors state that a rightward shift in the dissociation curve results in a higher p50. However, they incorrectly state that a rightward shift in the oxyhemoglobin dissociation curve occurs with blood transfusion, reduced levels of 2,3-diphosphoglycerate (DPG), hypophosphatemia, and hypothyroidism. Reduced levels of 2,3-DPG result in a leftward shift of the curve and increased affinity of oxygen binding to hemoglobin (lower p50).2 Reduced levels of 2,3-DPG are known to occur with hypothyroidism and hypophosphatemia.3As well, stored blood has reduced levels of 2,3-DPG, potentially resulting in a leftward shift of the curve after transfusion.4

The author has no conflict of interest to disclose.

Das, A, Sinha, S, Hoyer, JD, et al (2007) Hemoglobin Bassett produces low pulse oximeter and co-oximeter readings.Chest131,1242-1244. [PubMed] [CrossRef]
 
Riggs, TE, Shafer, AW, Guenter, CA, et al Acute changes in oxyhemoglobin affinity: effects on oxygen transport and utilization.J Clin Invest1973;52,2660-2663. [PubMed]
 
Zaroulis, CG, Kourides, IA, Valeri, CR, et al Red cell 2,3-diphosphoglycerate and oxygen affinity of hemoglobin in patients with thyroid disorders.Blood1978;52,181-185. [PubMed]
 
Ibrahim, ED, McLellan, SA, Walsh, TS, et al Red blood cell 2,3-diphosphoglycerate concentration andin vivoP50 during early critical illness.Crit Care Med2005;33,2247-2252. [PubMed]
 

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References

Das, A, Sinha, S, Hoyer, JD, et al (2007) Hemoglobin Bassett produces low pulse oximeter and co-oximeter readings.Chest131,1242-1244. [PubMed] [CrossRef]
 
Riggs, TE, Shafer, AW, Guenter, CA, et al Acute changes in oxyhemoglobin affinity: effects on oxygen transport and utilization.J Clin Invest1973;52,2660-2663. [PubMed]
 
Zaroulis, CG, Kourides, IA, Valeri, CR, et al Red cell 2,3-diphosphoglycerate and oxygen affinity of hemoglobin in patients with thyroid disorders.Blood1978;52,181-185. [PubMed]
 
Ibrahim, ED, McLellan, SA, Walsh, TS, et al Red blood cell 2,3-diphosphoglycerate concentration andin vivoP50 during early critical illness.Crit Care Med2005;33,2247-2252. [PubMed]
 
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