Sometimes the feet of an infant are not available for taking a blood sample. Reiner et al discussed taking blood from the tip of the third (middle) fingers. The authors are from Columbus Children's Hospital in Columbus, Ohio.
The reasons the feet may not be available are discussed in the previous section.
Factors:
(1) The puncture must be deep enough for free blood flow.
(2) The puncture must not be too deep, with injury of the phalangeal bone/cartilage.
(3) Compression during the procedure must be taken into account.
(4) Malnutrition and other factors that may reduce subcutaneous tissue. Obesity (macrosomia) can increase the subcutaneous tissue.
Body Weight in kg
Minimum Depth (95% Limits)
0.66
0.6 mm
2.5
1.4 mm
5
1.9 mm
10
2.3 mm
15
2.6 mm
20
2.7 mm
25
2.9 mm
This can modeled as:
minimum distance between skin surface and underlying bone/cartilage in mm =
= 0.8358 + (0.6308 * LN(body weight in kilograms))
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