A person exposed to a certain atmospheric concentration of carbon monoxide for a given period of time will develop a concentration of carboxyhemoglobin in the blood, which will correlate with symptoms.
Parameters:
(1) parts per million CO in atmosphere (ppm)
(2) duration of exposure in minutes
(3) percent carboxyhemoglobin
When plotted with time in minutes as the X-axis and parts per million as Y-axis, a series of curves describing a given percent carboxyhemoglobin are generated.
The curves take the general form of an equilateral hyperbola with Y = (1 / X).
parts per million CO (ppm) =
= ((slope) / (time in minutes)) + (intercept)
|
Curve |
Percent COHb |
A (slope) |
B (intercept) |
|
A |
50 |
26666.686 |
211.37 |
|
B |
45 |
23843.823 |
191.51 |
|
C |
40 |
21332.395 |
169.70 |
|
D |
35 |
18275.146 |
150.88 |
|
E |
30 |
15350.912 |
134.64 |
|
F |
25 |
13443.450 |
105.35 |
|
G |
20 |
10654.650 |
88.033 |
|
H |
15 |
7305.913 |
69.23 |
|
I |
10 |
4942.190 |
39.78 |
|
J |
5 |
2313.065 |
23.35 |
slope (as function of percent COHb) =
= (541.085 * (percent CO)) - 467.023
intercept (as a function of percent COHb) =
= (4.21148 * (percent CO)) + 2.5686
Putting this together with the previous equation:
ppm =
= ((slope) / (time in minutes)) + (intercept) =
= (((541.085 * (percent COHb)) - 467.023) / (time in minutes)) + ((4.21148 * (percent COHb)) + 2.5686)
If this is rearranged:
percent COHb =
= (ppm - 2.5686 + (467.023 / (time in minutes))) / ((541.085 / (time in minutes)) + 4.21148)
|
Percent CO |
Symptoms |
|
5 |
none |
|
10 |
none |
|
15 |
slight headache |
|
20 |
headache |
|
25 |
headache and nausea |
|
30 |
drowsy |
|
35 |
vomiting |
|
40 |
collapse |
|
45 |
coma and permanent brain damage |
|
50+ |
permanent brain damage and death |
Limitation:
• I believe that the curves assume that the person is exerting him/herself. A comatose person with shallow breathing may not reach the estimated levels.
Specialty: Toxicology, Emergency Medicine, Critical Care
ICD-10: ,
