Small bowel tonometry: a possible technique for monitoring jejunal free flaps

Abstract

Tonometry is a method for measuring intramural pH (pHi) in enteric mucosa. The value of the pHi has been shown to be related to the blood supply of the mucosa.1 It has not been explored as a method for monitoring free flaps. Over the course of 18 months four patients had their jejunal free flaps monitored using tonometry. All patients had an exteriorized monitoring segment of jejunum with the vascular pedicle in common with the reconstructive segment. This is conventional practice in our unit, and was used as a control. A Tonometrics sigmoid catheter (intestinal tonometer) was used to measure the intra luminal pCO2 of the jejunal flap. Simultaneous arterial bicarbonate measurements were taken from an indwelling arterial line. The pHi was then calculated using the Henderson Hasselbach equation: pHi = 6.1+log10[HCO3]art/k×0.03×PCO2(ton) The pHi was determined: (1) in the isolated segment with the pedicle intact, this was the baseline reading; (2) after clamping of the vascular pedicle; (3) following microvascular anastomosis; and (4) 8 hourly for the next 72 h. All flaps survived. The pHi readings were significantly different from the baseline values post clamping and up to 30 min post-revascularisation (P 0.1 Mann-Whitney U-test). Small bowel tonometry may be a potential method for monitoring jejunal free flaps. It provides an objective measure of flap vascularity, it is inexpensive and non-invasive. It can be performed anywhere providing there is easy access to a blood gas analyser. We recognise the need for controlled experiments to validate the technique.