The Science Journal of the American Association for Respiratory Care

1995 OPEN FORUM Abstracts

METHEMOGLOBIN PRODUCTION RATES AT THREE LEVELS OF HEMOGLOBIN SATURATION AND 80 PPM NITRIC OXIDE

Daniel Fisher, Robert M. Kacmarek, Warren M. Zapol, C. Alvin Head Department of Anesthesiology and Respiratory Care, Massachusetts General Hospital and Harvard Medical School, Boston, MA

Inhaled nitric oxide (NO) can improve oxygenation and lower pulmonary artery pressure in humans without systemic vascular effects. The selectivity of inhaled NO for the lung is due to its great affinity for the iron moiety of hemoglobin (Hb). However upon binding, the iron is oxidized producing methemoglobin (Mhb) and this reduces the oxygen carrying capacity of Hb. This study was conducted to determine the relationship between oxyhemoglobin saturation (SaO_2), nitric oxide and the production of Mhb.

Methods: Fifteen ml of blood was heparinized and immediately divided into three tubes for tonometry (RNA medical) from each of five healthy volunteers. The blood was tonometered with different gas concentrations of nitrogen, oxygen or both, to produce three different SaO_2 levels of 0, 75 and 100%. While maintaining the same delivered FiO_2, 80 ppm NO was added. The % Mhb of the total Hb in each sample was measured (Ciba-Corning 270 CO-oximeter) before NO and every 10 minutes for 140 minutes during NO exposure.

Results: %Mhb increased in all samples with 100 > 75> 0% SaO_2 (pɘ.05). Mean +/- SD for samples at each SaO_2 is presented below:

Time %Mhb with %Mhb with %Mhb with

(mins) 0% SaO_2 75% SaO_2 100% SaO_2

0 0.12 +/- 0.15 0.13 +/- 0.100.30 +/- 0.00

200.25 +/- 0.15 1.90 +/- 1.312.60 +/- 0.93

400.42 +/- 0.26 3.73 +/- 1.907.28 +/- 2.63

600.68 +/- 0.20 5.67 +/- 1.6916.88 +/- 11.73

801.00 +/- 0.48 7.60 +/- 1.8125.82 +/- 19.91

100 1.40 +/- 0.84 9.78 +/- 2.8027.98 +/- 31.18

120 1.70 +/- 1.02 12.03 +/- 4.73 44.38 +/- 30.55

140 2.35 +/- 1.32 14.88 +/- 7.31 47.73 +/- 27.64



Conclusions: (1) Using whole blood from healthy humans, 80 ppm NO increases %Mhb both as a function of time and SaO_2, in vitro. (2) The clinical significance of these findings, in vivo, have not been established.

OF-95-128

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