A study of epidural pressures in infants

The pressures exerted on fragile structures in the infant during epidural injections have never been studied previously.

We measured the pressure changes in the epidural space of 20 infants during injection of local anaesthetic solutions. The pressures developed during passage of the epidural needle through the ligaments of spine and in the epidural space during the injection of 1 ml at two rates of injection, over 1 and 2 min and the residual pressure 1 and 2 min after each injection were studied.

The mean pressure while the needle was being advanced through the ligamentum flavum was 69.14 +/- 36.95 mmHg. The epidural pressure after needle had just penetrated the ligament without eliciting the loss of resistance was 1 +/- 9.759 mmHg. A distinct pulsatile waveform identical to the pulse waveform was observed as soon as the epidural space was entered. The pressure rise varied according to the rate of injection. The pressures were 27.79 mmHg when the rate of injection was 1 ml.min(-1), with a residual pressure after 1 min of 12 +/- 5.53 mmHg and 10.14 +/- 5.53 mmHg after 2 min of injection. When the rate of injection was 1 ml.2 min(-1), the pressures were 15.66 +/- 9.48 mmHg with a residual pressure after 1 min of 14.79 +/- 5.15 mmHg and 12.93 +/- 5.46 mmHg after 2 min of injection.

The residual pressures seem to vary more with the volume injected than the rate of injection or the pressures developed during the injection. The relationship between the rate of injection and pressures is significant when compared with adults where the pressures have been measured after an injection rate of 1 ml.s(-1) and 1 ml.5 s(-1). This is a very fast rate compared with our rates of injection of 1 ml over 1 and 2 min. Based on the findings of this study, we recommend a rate of 1 ml.2 min(-1) in infants. In neonates, a slower rate of injection would be preferable.