EFFECT OF THORACIC AND ABDOMINAL PRESSURE CHANGES ON THE EPIDURAL SPACE PRESSURE

SUMMARY The effect of changes in superior and inferior vena caval pressures on the pressure in the epidural space was studied in fifteen unpremedicated patients and in five dogs. It was found that the epidural space, unlike the subarachnoid compartment had two types of pressure oscillations during spontaneous respiration. A superior vena caval-like pattern was found in the cervico-thoracic region, whereas an inferior vena caval-like pattern was the most frequent finding in the lumbar epidural space. Manoeuvres producing a generalized increase of venous pressure raised the epidural pressure all along the spine. Manoeuvres raising the venous pressure in the superior or in the inferior vena caval system were accompanied by a preferential increase in the pressure of the cervical or in the lumbar epidural space. As a consequence, it is suggested that the epidural space, unlike the subarachnoid compartment, presents some degree of functional compartmentalization into three zones: cervico-thoracic, lumbar and sacral. It is postulated that changes in visceral cavity pressures can be transmitted to the epidural space directly, through the intervertebral foramina and indirectly via both vena cava and the cerebrospinal fluid. It is concluded that factors increasing intrathoracic or intra-abdominal pressures will raise epidural space pressure and, as a consequence, may favour the spread of anaesthetics injected into the epidural space.