Pressure measurements during injection of corticosteroids: in vivo studies

Intralesional injection of corticosteroids is an effective treatment for ca pillary hemangiomas, Complications include embolisation of corticosteroid p articles into the ocular circulation resulting in permanent loss of vision; This research is aimed at developing an injection cannula and monitoring s ystem to prevent such inadvertent embolisation. A cannula has been designed to simultaneously estimate the pressure at its tip and the flow rate durin g injection. The estimation technique has previously been validated using a n in vitro model. In this study, the cannula was tested in vivo with canine liver at injection flow rates of 2.5 to 21 ml min(-1). The pressure genera ted in the tissue during injection was calculated using the technique devel oped. This was compared with direct in situ pressure measurements made with a coaxial outer cannula. The mean calculated pressure was seen to be linea rly related to the mean measured pressure with a slope of 0.97, correlation coefficient of 0.99 and standard error of 2.74 mmHg. Similar trends were o bserved between the maximum calculated and maximum measured injection press ure: slope = 1.0, r = 0.99 and standard error = 5.54 mmHg. The estimation o f the mean and maximum pressure from the cannula and monitoring system was accurate in canine liver. High pressures close to 250 mmHg were generated i n tissues during injection.