Mechanisms Of Cement Reaction

Pulmonary embolisation Marrow

Cement Air

Methylmethacrylate absorption

Pressurisation of femoral cavity

Heat from cement reaction within femoral cavity

Figure SI.1

which have been used to reduce the likelihood of cement reaction include: distal bone plug in the shaft to limit the spread of cement, venting of the shaft to reduce pressure and air trapping, and waiting for the mixture to be relatively non viscous before insertion to reduce the likelihood of monomer absorption. Although less common a similar reaction may be seen after cemented humeral prostheses.

Anaesthesia for total knee arthroplasty is broadly similar but does not show the same picture of cement reaction unless extra long femoral components are used after extensive reaming. Femoral and sciatic blockade may be used for analgesia or operation and in general techniques of anaesthesia are as for hip arthroplasty. The use of tourniquet restricts blood loss intra-operatively but post operative losses may be brisk. After release of the tourniquet metabolic products are released into the circulation representing an acid load which may cause temporary acidosis and a rise in end tidal carbon dioxide. Bilateral joint replacements are severe surgical insults that should not be undertaken lightly.

Laminectomy

The primary requirement of back surgery is the prone position. Adequate eye care is important and there is no substitute for endotracheal intubation (possibly with an armoured tube) and IPPV using individual drugs of choice. The patient's arms must be carefully and symmetrically moved when turning into the prone position to avoid shoulder dislocation and pressure points should be padded. A suitable support should be employed to avoid abdominal compression, which will both embarrass ventilation and cause venous congestion in the epidural plexus. The Montreal mattress and Toronto frame are frequently used (Figure SI.2).

Fractured Neck of Femur

There are several operations for the treatment of fractured neck of femur (dynamic hip screw, cannulated screws, etc.) depending on the precise site of the break. The majority of patients presenting for this procedure are elderly and frail, and maybe the victims of severe polypharmacy. A picture of dehydration and cardiac decompensation is frequently seen. As the operation is urgent rather than emergency attention should be paid to the correction of those features which can be improved (uncontrolled atrial fibrillation and electrolyte imbalance, to name but two).

Monli ad maHrais

Figure SI.2 Supports for patients in the prone position

Spinal anaesthesia is the most commonly employed technique for this procedure although care must be taken to ensure adequate fluid resuscitation otherwise severe hypotension may result from sympathetic blockade of the lower limbs. Turning the patient for spinal insertion may necessitate analgesia (particularly in the case of heavy solutions when the injured leg will be underneath) and small incremental doses of IV ketamine with or without midazolam are frequently used. Epidural and general anaesthesia may also be used and although the mortality from general anaesthesia is higher in the short term, there is very little difference after three months or so have elapsed when death rates from all techniques approximate.

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