[Intraoperative posture in the surgery of lumbar disk hernia]

[Controversies in neuroanaesthesia: positioning in neurosurgery]

Positioning of the neurosurgical patient has several features such as the existence of specific positions (i.e: sitting, prone hyperlordotic, crouching ou kneeling positions) or the range of facilities for the same surgical indications. The last point, a source of controversy, is the subject of this review. Current indications for the sitting position, positioning for lumbar spine surgery and prevention of eye injuries are successively addressed.

[Air embolism during lumbar discal hernia repair. Retroperioneal vessels lesions have to be suspected]

Occurrence of deep PETCO(2) drop during surgical lumbar disk repair is rare but dramatic. This case report leads to the diagnosis of retroperitoneal vessels lesions. We review the different diagnosis related to the drop of the PETCO(2) during surgery in the genupectoral position. We recommend that the diagnosis of retroperitoneal vessels lesion have to be suspected early if air embolism occurs during lumbar disk surgery.

Cardiac arrest during surgery and ventilation in the prone position: a case report and systematic review

We present a case report of successful resuscitation following cardiac arrest in a patient undergoing surgery in the prone position. A systematic review of the literature identified 22 further cases. Risk factors for intra-operative cardiac arrest in patients in the prone position include: cardiac abnormalities in patients undergoing major spinal surgery, hypovolaemia, air embolism, wound irrigation with hydrogen peroxide, poor positioning and occluded venous return. Cardiac arrest is also a risk in the increasing number of patients with acute respiratory distress syndrome ventilated in the prone position. Management of prone cardiac arrest may be improved by identification of high-risk patients, careful patient positioning, use of invasive monitoring and placement of self-adhesive defibrillator paddles. Suitable techniques for cardiopulmonary resuscitation including methods for chest compression, defibrillation and the management of air embolism are discussed.

[Blood volume changes caused by position under general anesthesia]

The cardiovascular changes in response to general anaesthesia are related to several interacting mechanisms. In addition to the intrinsic effects of anaesthetic agents on the heart and vessels which depress the physiological mechanisms of adaptation, the additive independent effects of posture and mechanical ventilation on intravascular blood volume have to be considered. Physiopathologic studies show that the ultimate related mechanism is the decrease of venous return to the heart. The major effect of posture is the change in the distribution of the blood volume, as the posture modifies the influence of gravity in addition to direct vascular compression and stretching. The deterioration of the cardiac venous return results in dramatic or insidious clinical consequences which lead finally to a low cardiac output. As cardiac function is not a limiting factor of output, any decrease of blood pressure in a patient with a healthy heart must be considered as an hypovolaemic state due to an abnormal contents to container ratio, and must be managed as such.