[Intraoperative posture in the surgery of lumbar disk hernia]

For surgery of the lumbar disc, with a posterior route, the patient is placed either in a prone, or a knee-chest, or a lateral position. They aim at facilitating the surgical access in decreasing local bleeding and collapsing the dural sheath. This benefit, as a result of the maintenance of the pressure in the epidural venous system at a low level, is obtained through the absence of any abdominal compression as well as the posture. In the prone position, the abdominal compression and the increase of the physiologic lordosis impair the systemic venous return and carry the risk of cardiac arrest. In addition to these adverse effects, the conventional knee-chest position increases the haemodynamic repercussions in modifying the distribution of blood volume and increasing the potential risk of mediastinal compression and air embolism. The lateral position generates only minor haemodynamic modifications, except in the obese. However it is difficult to stabilize the patients' position and to maintain the alignment of the spine. Therefore it is used the less one. The postural risks of all three positions are numerous and include mainly the compression of nerves, vessels and skin. Finally the selection of the position depends basically on morphological criteria and the adaptative capacities of the patient. The optimal position is the one offering a low pressure level in the spinal venous system, while maintaining the venous return.