Pressure measurements during injection of corticosteroids

Corticosteroid injection into the orbit, eyelid and larynx is a common trea tment for inflammation and neoplasm. Complications include embolisation int o the ocular circulation resulting in permanent loss of vision. The overall aim of the reported research is to develop an injection cannula and monito ring system which can prevent inadvertent embolisation into the ocular circ ulation during injection of corticosteroids. To that end, a special cannula was designed that allows simultaneous estimation of pressure at the tip of the cannula and flow rate during injection. The cannula was tested with ba ckpressures corresponding to physiological ranges of 0 to 125mmHg and injec tion flow rates of 3 to II cm(3) min(-1). The estimated pressure at the tip of the cannula during injection of corticosteroids was compared with direc t pressure measurements. The results show that the mean estimated pressure is linearly related to the mean measured pressure with a slope of 0.99 and correlation coefficient of 0.99. Statistical analyses show that with standa rd error of estimate (SEE) of 2.14mmHg, the estimated pressure is well with in the 95% prediction interval limits of the measured values. The estimatio n of pressure from the cannula and monitoring system was accurate and warra nts further testing in animal models.