dyshemoglobin

dyshemoglobin

(dĭs-hĕm″ō-glō′bĭn),

dysHb

A hemoglobin derivative that is incapable of reversibly associating with oxygen, and so is unable to carry oxygen from the lungs to the cells. The primary defect in dyshemoglobins is a chemical (or stereochemical) alteration of the heme prosthetic group. Two common dyshemoglobins are carboxyhemoglobin (COHb) in which carbon monoxide is covalently bonded to the hemoglobin molecule, and methemoglobin (metHb) in which the ferrous iron is oxidized to the ferric form. Other, indeterminate dyshemoglobins exist in minute amounts in circulating blood.
References in periodicals archive ?
(1998): "Using pulse oximetry when dyshemoglobin levels are high".
These dyshemoglobin forms are subtracted from the oxyhemoglobin value, and this value is referred to as the fractional Sa[O.sub.2] of the ABG.
The pulse oximeter measures the dyshemoglobins as oxyhemoglobin.
Oxygen capacity may be diminished in patients by an increased fraction of inactive hemoglobin, later called dyshemoglobin (5).
S[O.sub.2], and dyshemoglobin fractions would be displayed, but in vain.
If the CO-oximeter had been programmed to display the dyshemoglobin fractions instead of fractional saturation, the diagnosis would have been obvious after analysis of the first arterial blood sample.
It may be convenient that a normal F[O.sub2]Hb signals in a single figure that S[O.sub.2] is not too low and that no significant amount of dyshemoglobin is present.
The purpose of this case conference is to present the limitations and distinctions of the methods used to assess oxygenation status, particularly in cases of increased dyshemoglobin fractions such as methemoglobinemias.
In the presence of substantial dyshemoglobin fractions, F[O.sub.2]Hb values will be considerably lower than the saturation determined by pulse oximetry.
In the absence of a dyshemoglobin, an absorbance ratio of 1.0 corresponds to an oxygen saturation of ~85% (7).
If a substantial proportion of dyshemoglobins are present, the [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] Hb will be lower than the S[O.sub.2] because the latter analyzes only the fully functional hemoglobins and intentionally excludes the nonfunctional dyshemoglobins.
Analysis is based upon an assumption that no dyshemoglobins are present.