Simple Formula for pH/Impedance Probe Positioning in Children-Time to Update Standard Practice?

To develop a novel formula for pH probe placement with adequate accuracy.

Children (3-18 y) undergoing pH-metry were prospectively evaluated. Their height and corrected pH probe position under X-ray (2 vertebrae above the diaphragm) was recorded and the linear-regression analysis was performed to derive a novel formula. Its accuracy was checked on an additional group of prospectively included children. The success rate of a newly developed formula was estimated and compared to the performance of previously used formulae. The difference in the suggested placement of the probe (cm from nostrils) was calculated.

Based on 670 children with pH probe placed under X-ray, the following formula was developed using the linear-regression analysis: L = 0.184x + 4.4 (cm) (L = probe placement depth, x = body height). Its accuracy was confirmed on additional 111 children resulting in almost 85% success rate. The formula showed significant difference in the suggested placement from formulae used previously: +4.9 ± 0.8 cm, +2.4 ± 0.1 cm, +0.7 ± 0.6 cm, +1.1 ± 0.4 cm, +1.8 ± 0.3 cm, +2.2 ± 0.5 cm from the one by the Strobel, Moreau, Wilson, Nowak, Staiano-Clouse formulae, and the GOSH table with the calculated success rates of 1.8%, 43.2%, 65.8%, 77.5%, 65.8% and 54.1%, respectively. A table suggesting placement depth based on the body height was developed.

The present formula provides 85% success of pH probe placement in children ≥ 3 y suggesting its use in routine practice. More data are needed to confirm that probe adjustment under X-ray is unnecessary.