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Half-Life of Carbon Monoxide and the Impact of Oxygen Therapy

Purpose: To use the kinetics of carbon monoxide excretion to estimate blood levels at different times after intoxication.

Description

Carboxyhemoglobin formed following exposure to carbon monoxide decreases at a rate affected by oxygen exposure. Hyperbaric oxygen therapy can reduce the half life of carboxyhemoglobin by over 90% as compared to breathing room air. Increasing oxygen exposure can significantly reduce the time to elimination with reduced morbidity and mortality.


Oxygen Therapy

Half-life for Carboxyhemoglobin (approximate)

none

4 hours (240 minutes, after Clark, 1981)

by face mask (by squad)

3 hours (180 minutes, after Clark, 1981)

100% oxygen

varies with PaO2, see equation below, with mean 74 minutes +/- 25 (Figure 1, page 804,  Weaver et al, 2000)

hyperbaric therapy

24 minutes at 3 atmospheres, may be as low as 15 minutes

 

estimated carboxyhemoglobin half-life in minutes (Weaver, 2000) =

= 106.6 – (0.1 * (PaO2 in mm Hg))

 

Assuming a first order kinetic model:

 

concentration of carboxyhemoglobin at time t =

= (concentration of carboxyhemoglobin at start of period) * EXP((-1) * k * (time in minutes))

 

Parameter

Variable

estimated carboxyhemoglobin at removal from fire

Ci

carboxyhemoglobin at presentation in percent

Cp

carboxyhemoglobin at end of therapy in percent

Cf

elimination constant during transport

k1

elimination constant during definitive therapy

k2

 

 

Oxygen Therapy

Elimination Constant

none

0.693 / 240 = 0.00289

by face mask (by squad)

0.693 / 180 = 0.00385

100% oxygen

0.693 / (106.6 – (0.1 * (PaO2 in mm Hg)))

hyperbaric therapy

0.693 / 24 = 0.0289

 

estimated Ci =

= (Cp) * EXP(k1 * (time in minutes between removal and arrival to hospital))

 

time to target concentration =

= (LN(Cp / Cf)) / k2


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Specialty

Objective

ICD-10