Positioning a patient for surgery requires great care and caution. Correct positioning provides the surgeon with good access to the site, minimizes blood loss and reduces the risk of damage to nerves, soft tissue, compartments and the cardio-pulmonary system. Each position has its specific risks. These have to be evalued against the benefits. Extreme positions of the joints should be avoided whenever possible. The ulnar nerve or the plexus brachialis are at highest risk in the positioning of extremities. Good anatomical comprehension makes it possible to take effective counter-measures. In the case of damage to the ulnar nerve in spite of optimal positioning, some authors found pre-existent non-symptomatic dysfunction in up to 30% of the cases. Patients suffering from peripheral vascular disease are usually at higher risk to suffer acute ischaemia, or, in the extreme, rhabdomyolysis with compartment syndrome, when positioned with elevated extremities (as in lithotomy position) or when a tourniquet is applied. Next to other factors, the duration of surgery seems to be of some importance. Operation sites above the heart carry a higher risk of venous air embolism unrelated to the positioning. In these cases adequate monitoring should be generously applied. Loss of visus is a rare but very severe complication most often seen in connection with the prone position. Still, postoperative blindness has occurred in all positions. It is absolutely imperative to avoid all pressure to the bulbus. The same law applies to surgery and positioning: indicated and correctly executed positioning, to which the patient has effectively consented, is legal, even if damage should occur. If the plaintiff demands compensation for damage, the distribution of onus of proof depends essentially on the accuracy of documentation. If documentation is faulty, the plaintiff may be granted relief or even shift of the onus of proof. This does not apply to a criminal lawsuit; in that case, culpable medical fallibility must be proven, since otherwise, the principle of "in dubio pro reo" applies. The interdisciplinary responsibilities concerning the positioning must be clearly defined and it is essential that the documentation of positioning as well as the documentation of positioning control is carried out as accurately as possible. Correct positioning can effectively aid surgery. Slovenly positioning should not be accepted, as there is a high probability of ill effects, possibly of permanent damage.

Specific modes of positioning are essential for successful surgery. These are again critically assessed in this final part of our review. Technically correct execution can minimize the risk of damage caused by positioning, although the possibility of damage still exists. First of all, the position on the fracture table is discussed. Great care must be taken concerning the perineal post and leg holder. In the lateral decubitus position, the correct positioning of head and spine as well as that of the lower arm are of great importance. When using the Trendelenburg and reverse Trendelenburg position, the effect on the cardiopulmonary system and the intracranial pressure must to be taken into consideration. Prone position and its modifications (i.e. tuck position) demand diligent care concerning the positioning of the head. There must be absolutely no bulbus compression and the abdominal wall should not be under pressure. While employing the sitting position, the patient should be adequately monitored so that venous air embolism can be recognized and treated as soon as possible. Because of the increased occurrence of grave complications, the sitting position should be used only if this is absolutely necessary.

Total hip replacement is a frequently practised operation. Depending on age, circumstances and individual assessment, cemented, non-cemented and hybrid forms are used. Apart from general risks, such as vascular and/or neural injuries, thrombosis and infections, there are specific risks, depending on the surgical technique. If cemented systems are used, the anesthesiologist must be on the alert in respect of a possible multi-causal cardiopulmonary depression during the implantation of the prosthesis. Incidents may be reduced or moderated by measures such as reduction of pressure from the femoral cavity or anesthetic measures such as avoidance of N2O during or after cementation, use of anti-histamines, etc., but there is no absolute protection from severe reactions by the cardiopulmonary system. In these cases it is imperative to recognise and treat hypoxic conditions immediately, whatever the cause, such as cardiac or pulmonary depression. If a non-cemented hip replacement is used or a revision is necessary the main problem is usually a higher blood loss. Especially in such cases it is necessary to apply a well-organised sequence of blood-saving methods to protect patients from the general risks of homologous blood transfusion. Even though the main concern of the public is the possibility of contamination of donor blood with the AIDS virus, transmission of hepatitis C virus is a much more common problem. Depending on the diagnostic methods the occurrence of thrombosis after total hip replacement has been reported to be as much as 55%. To minimise this high incidence, sufficient prophylaxis, adequate fluid therapy, suitable anesthetic techniques and cutting down on the duration of the operation should be taken into account. The use of low molecular weight heparins has certain advantages. If deep vein thrombosis has occurred, therapy consists of anticoagulation with intravenous heparin and immobilisation. A rare but severe complication is a deep hip prosthetic infection. More than 50% of infections are caused by coagulase-negative staphylococci and anaerobic bacteria. To avoid sepsis it is imperative to employ adequate high-dosage antibiotics, revisional surgery and, if necessary, even excision arthroplasty. There is no "ideal" anesthesiological method for total hip replacement. Regional techniques as well as general anesthesia have their specific pros and cons which are controversially discussed in respect of their priority. To achieve early diagnosis of embolism, especially in the case of high risk patients, the exigency of extensive haemodynamic monitoring as well as Doppler-ultrasound is discussed.(ABSTRACT TRUNCATED AT 400 WORDS)

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