Epidural spread of iohexol following the use of air or saline in the ‘loss of resistance’ test

Abstract

ObjectiveTo compare, using CT epidurography, the cranial distribution of contrast after epidural injection when saline or air is used for the loss of resistance (LOR) technique in identifying the epidural space. Study designProspective, randomized, cross-over experimental study. AnimalsNine healthy adult Beagle dogs. MethodsUnder general anaesthesia, a spinal needle (22-gauge, 70 mm) was inserted through the lumbosacral space, and the position in the epidural space confirmed using the LOR technique employing either 0.3 mL per dog of saline or of air. Epidurography using CT was performed before and 5, 10 and 20 minutes after epidural injection of 0.2 mL kg−1 of iohexol. The cranial distribution of iohexol was recorded as the number of vertebral segments reached from the seventh lumbar vertebrae. ResultsThe median values in vertebral segments of the cranial distribution at 5, 10 and 20 minutes after epidural injection were 19.5, 20.5 and 21.0 respectively with the saline treatment, and 12.0, 15.0 and 16.0 respectively in the air treatment. At all time points spread of contrast was significantly less with the air treatment. All dogs after air treatment had some air bubbles in the epidural space, and in seven, the spinal cord was moderately compressed by the air. No neurological complications were observed after recovery. Conclusions and clinical relevanceThe use of air for the LOR technique is associated with significantly less spread, uneven cranial distribution of the contrast medium and compression of the spinal cord. It is recommended that saline, and not air, should be used to identify the epidural space by this method.