The risk of pneumothorax can be predicted from
(1) the depth of the lesion and
(2) if the patient has an increased total lung capacity (hyperinflation).
Depth of Lesion from Surface
depth factor =
= (0.63 * (depth of lesion from surface in centimeters)) - 2.55
probability of pneumothorax based on depth of the lesion =
= 1 / (1 + EXP((-1) * (depth factor)))
|
Depth from Pleural Surface
|
Probability of Pneumothorax
|
|
1 cm
|
13%
|
|
4 cm
|
49%
|
|
7 cm
|
86%
|
Effect of Total Lung Capacity
Equations of Roberts (1991) to predict normal total lung capacity (TLC)
TLC in liters in males =
= (7.956 * (height in meters)) - 6.948
TLC in liters in females
= (7.107 * (height in meters)) - 6.435
patient's TLC as percent of predicted =
= (patient's TLC in liters) / (predicted TLC) * 100
Interpretation:
• If the person's TLC is > 120% of predicted, then there is an increased risk of pneumothorax.
