Chemistry:CO-oximeter

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A pulse CO-oximeter is a non-invasive, multi-wavelength instrument that measures the oxygen carrying state of hemoglobin in a blood specimen, including oxygen-carrying hemoglobin (O2Hb), non-oxygen-carrying but normal hemoglobin (HHb) as well as the dyshemoglobins such as carboxyhemoglobin (COHb) and methemoglobin (MetHb). Pulse CO-oximeters use four or more wavelengths whereas the common pulse oxymeter uses only two. Simpler oximeters measure only the ratio of oxyhemoglobin to total 'bindable' hemoglobin (i.e. oxyhemoglobin + deoxyhemoglobin-HHb) and as a result will incorrectly report the true oxygen saturation in patients with significant dyshemoglobin levels.[1] CO-oximetry is useful in defining the causes for hypoxemia, or hypoxia, (oxygen deficiency at the tissue level).

Mechanism

A CO-oximeter measures the absorption of light passing through blood at multiple wavelengths of light to several dozens of wavelengths, in order to distinguish oxyhemoglobin, and deoxyhemoglobin, and thus determine the oxyhemoglobin saturation (the percentage of oxygenated hemoglobin compared to the total amount of available hemoglobin (Hb)). Measurement of greater numbers of wavelengths enables the instrument to distinguish between these and carboxyhemoglobin,-COHb, methemoglobin -metHb, other hemoglobin moieties and 'background' light-absorbing species. Traditionally, measurement is made from arterial blood processed in a specific device designed to be able to measure proportions of multiple components of several hemoglobin moieties using multi-wavelength spectrophotometry and complex, but straightforward internal computations. While these units still are in wide use, blood gas analyzers with integral CO-oximetry modules have also been developed and successfully marketed by several manufacturers.[2][3] More recently, some 'pulse' or more precisely 'peripheral' oximeters have made it possible to estimate carboxyhemoglobin with non-invasive technology similar to a simple (peripheral) pulse oximeter.[4] In contrast, the use of a standard or simple pulse oximeter is not effective in the diagnosis of CO poisoning as patients who have carbon monoxide poisoning may have a normal oxygen saturation reading on a pulse oximeter.[5]

Usage

See also

References

  1. ↑ Luks, Andrew M.; Swenson, Erik R. (2011). "Pulse Oximetry at High Altitude". High Altitude Medicine & Biology 12 (2): 109–119. doi:10.1089/ham.2011.0013. PMID 21718156. 
  2. ↑ "Spectrophotometric measurement of carboxyhemoglobin and methemoglobin in blood". Clinical Chemistry 25 (8): 1388–93. August 1979. doi:10.1093/clinchem/25.8.1388. PMID 455674. http://www.clinchem.org/cgi/pmidlookup?view=long&pmid=455674. Retrieved 2009-07-17. 
  3. ↑ "Evaluation of methods used to estimate inhaled dose of carbon monoxide". Thorax 35 (1): 47–51. January 1980. doi:10.1136/thx.35.1.47. PMID 7361284. 
  4. ↑ "Reliability of new pulse CO-oximeter in victims of carbon monoxide poisoning". Undersea & Hyperbaric Medicine 35 (2): 107–11. 2008. PMID 18500075. http://archive.rubicon-foundation.org/8084. Retrieved 2009-07-17. 
  5. ↑ "Carboxyhaemoglobinaemia and pulse oximetry". British Journal of Anaesthesia 66 (5): 625–6. May 1991. doi:10.1093/bja/66.5.625. PMID 2031826. 

Further reading

  • CLSI, C46-A2- Blood Gas and pH Analysis and Related Measurements; Approved Guideline—Second Edition, Wayne, PA, 2010
  • Zijlstra WJ, Maas AHJ, Moran RF. Definition, significance and measurement of quantities pertaining to the oxygen carrying properties of human blood.. Scand J Clin Lab Invest, 56(Suppl), 224, 27–45, 1996
  • Brunelle JA, Degtiarov AM, Moran RF, Race LA, Simultaneous measurement of total hemoglobin and its derivatives in blood using CO-oximeters: Analytical principles; Their application in selecting analytical wavelengths and reference methods; A comparison of the results of the choices made. Scand J Clin Lab Invest, 56: (Suppl) 224, 47–69, 1996.
  • Brunelle JA, Moran RF, Data processing in CO-oximeters that Use overdetermined systems (Reply). Clin Chem, 43:1, 189–191, 1997
  • Degen BR, Moran RF, Comparison and assessment of blood gas related quantities including base excess, the gas exchange indices and temperature corrected pH/ PO2/PCO2, as defined in approved NCCLS standard C12-A, using a computer simulation of input variables., Scand J Clin Lab Invest , 56:(Suppl) 224, 89-106 1996.
  • Moran R, Hemoglobin F and measurement of oxygen saturation and fractional oxyhemoglobin. Clin Lab Sci, 7:3, 162–164, 1994.
  • Brunnelle JA, Degtiarov AM, Moran RF, Race LA, CO-oximetric measurement of oxyhemoglobin, deoxyhemoglobin, and dyshemoglobins in blood: Effects of analytical wavelength and reference method selection. Lab Hematol. 1:2, 161 - 164, 1995.
  • Moran RF, Implications of Fetal Hemoglobin : Measurement of oxygen saturation, fractional oxyhemoglobin, carboxyhemoglobin and methemoglobin. Crit Care International, April–May 8–9, 1995.
  • Moran RF, The case for standardized terminology: Oxygen "saturation" values can trick the unwary and lead to clinical misjudgement., Crit Care Med, 21:5, 805–807, 1993.
  • Moran RF, Lab Consultant: [High Percentage of zero carboxyhemoglobins due to correction algorithm for small, "impossible", values.] Clin Chem News, 18:12, 18–19, 1992.
  • CLSI document C25A, can provide in-depth information and references.

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