Hart et al developed a series of curves to describe the probability of survival after acute paraquat intoxication based on the plasma level during the first 28 hours after ingestion. This can help triage patients according the likelihood of survival and to identify those patients who may require early aggressive management. The authors are the ICI Plant Protection Division (Surrey), ICI Central Medical Group (Cheshire), and National Poisons Information Service in England.
Parameters:
(1) time from ingestion in hours (0 to 28)
(2) plasma paraquat concentration in µg/mL (same as mg/L)
If the curves in Figure 2 are examined, the following data is derived. The interpretation may be limited for the first 2-4 hours after the ingestion, with later samples being more representative of the final prognosis.
|
Hours |
90% |
70% |
50% |
30% |
20% |
10% |
|---|---|---|---|---|---|---|
|
0 |
2.00 |
|
|
|
|
|
|
1 |
1.01 |
3.11 |
|
|
|
|
|
2 |
0.58 |
1.52 |
2.88 |
5.25 |
|
|
|
4 |
0.25 |
0.70 |
1.11 |
1.94 |
3.15 |
|
|
6 |
0.13 |
0.43 |
0.70 |
1.21 |
1.85 |
3.27 |
|
8 |
0.10 |
0.31 |
0.54 |
0.89 |
1.41 |
2.49 |
|
10 |
0.08 |
0.27 |
0.45 |
0.73 |
1.09 |
1.94 |
|
12 |
0.06 |
0.23 |
0.39 |
0.61 |
0.89 |
1.52 |
|
14 |
0.04 |
0.22 |
0.35 |
0.49 |
0.76 |
1.31 |
|
16 |
0.04 |
0.21 |
0.33 |
0.47 |
0.67 |
1.13 |
|
18 |
|
0.20 |
0.31 |
0.43 |
0.62 |
1.03 |
|
20 |
|
0.19 |
0.29 |
0.39 |
0.55 |
0.93 |
|
22 |
|
0.18 |
0.26 |
0.35 |
0.52 |
0.87 |
|
24 |
|
0.17 |
0.24 |
0.32 |
0.47 |
0.82 |
|
26 |
|
0.16 |
0.22 |
0.30 |
0.41 |
0.78 |
|
28 |
|
0.15 |
0.19 |
0.26 |
0.39 |
0.73 |
Approximating equations can be formed based on:
(1) each probability curve, creating zones of probability
(2) at each time (done only for 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, and 28 hours)
First Approach
plasma concentration along percentage curve over time interval =
= (A * (hours since ingestion)^2)) + (B * (hours since ingestion) + C
|
Percent |
Interval |
(hour)^2 |
(hour) |
constant C |
|---|---|---|---|---|
|
90% |
0 - 2 |
0.28 |
-1.27 |
2 |
|
90% |
2 - 6 |
0.02625 |
-0.3225 |
1.12 |
|
90% |
6 - 10 |
0.00125 |
-0.0325 |
0.28 |
|
90% |
10 - 14 |
0 |
-0.01 |
0.18 |
|
90% |
14 - 28 |
* |
* |
* |
|
70% |
1 - 2 |
0 |
-1.59 |
4.7 |
|
70% |
2 - 6 |
0.06875 |
-0.8225 |
2.89 |
|
70% |
6 - 12 |
0.005 |
-0.122 |
0.978 |
|
70% |
12 - 28 |
0 |
-0.005 |
0.29 |
|
50% |
2 - 4 |
0 |
-0.885 |
4.65 |
|
50% |
4 - 8 |
0.03125 |
-0.5175 |
2.68 |
|
50% |
8 - 14 |
0.003125 |
-0.10025 |
1.1415 |
|
50% |
14 - 28 |
0 |
-0.011369 |
0.5125 |
|
30% |
2 - 4 |
0 |
-1.655 |
8.56 |
|
30% |
4 - 8 |
0.05125 |
-0.8775 |
4.63 |
|
30% |
8 - 14 |
0.0025 |
-0.121 |
1.696 |
|
30% |
14 - 28 |
0 |
-0.016845 |
0.73 |
|
20% |
4 - 8 |
0.1075 |
-1.725 |
8.33 |
|
20% |
8 - 16 |
0.00946 |
-0.31764 |
3.33714 |
|
20% |
16 - 28 |
0 |
-0.023929 |
1.045 |
|
10% |
6 - 12 |
0.0225 |
-0.695 |
6.625 |
|
10% |
12 - 20 |
0.005357 |
-0.24443 |
3.68057 |
|
10% |
20 - 28 |
0 |
-0.0245 |
1.414 |
where:
• The 90% curve after 14 hours was listed as < 0.03.
Second Approach
The general form of the equation is:
1 / (probability) =
= (A * (concentration)^2)) + (B * (concentration) + C
probability =
= 1 / ((A * (concentration)^2)) + (B * (concentration) + C)
|
Hour |
(concentration)^2 |
(concentration) |
constant C |
|---|---|---|---|
|
6 |
0.386192 |
1.553503 |
0.798846 |
|
8 |
0.641399 |
2.0973255 |
0.802386 |
|
10 |
1.114759 |
2.6166058 |
0.751355 |
|
12 |
2.293851 |
2.5733636 |
0.816308 |
|
14 |
2.920209 |
3.2350395 |
0.784994 |
|
16 |
4.714920 |
2.8613241 |
0.800961 |
|
18 |
4.077696 |
5.3964720 |
0.115741 |
|
20 |
4.150628 |
7.0920715 |
-0.176805 |
|
22 |
4.519083 |
7.7100458 |
-0.139570 |
|
24 |
0 |
13.332812 |
-1.034856 |
|
26 |
0 |
14.017867 |
-0.891082 |
|
28 |
0 |
14.692274 |
-0.702542 |
Limitations:
• Uncertainty may be affected by the patient's sensitivity to paraquat, uncertainty as to the time interval since ingestion, and variation in analytical methods.
Specialty: Toxicology, Emergency Medicine, Critical Care
ICD-10: ,
