Choice of anaesthetic regimen influences haemodynamic response to cemented arthroplasty

Noise-enhanced clustering and competitive learning algorithms

Noise can provably speed up convergence in many centroid-based clustering algorithms. This includes the popular k-means clustering algorithm. The clustering noise benefit follows from the general noise benefit for the expectation-maximization algorithm because many clustering algorithms are special cases of the expectation-maximization algorithm. Simulations show that noise also speeds up convergence in stochastic unsupervised competitive learning, supervised competitive learning, and differential competitive learning.

Bone cement implantation syndrome

Bone cement implantation syndrome (BCIS) is poorly understood. It is an important cause of intraoperative mortality and morbidity in patients undergoing cemented hip arthroplasty and may also be seen in the postoperative period in a milder form causing hypoxia and confusion. Hip arthroplasty is becoming more common in an ageing population. The older patient may have co-existing pathologies which can increase the likelihood of developing BCIS. This article reviews the definition, incidence, clinical features, risk factors, aetiology, pathophysiology, risk reduction, and management of BCIS. It is possible to identify high risk groups of patients in which avoidable morbidity and mortality may be minimized by surgical selection for uncemented arthroplasty. Invasive anaesthetic monitoring should be considered during cemented arthroplasty in high risk patients.

Monitoring for suspected pulmonary embolism

It is fortunate that serious embolic phenomena are uncommon because, with the exception of neurosurgery in the sitting position and cardiac surgery, thoracic echocardiography and the precordial Doppler device, the most sensitive indicators of embolism, are seldom used. Vigilance is required of the anesthesiologist to recognize the rapid fall in end-tidal PCO2, the usual first indicator of a clinically significant PE. Any sudden deterioration in the patient's vital signs should include embolism in the differential diagnosis, particularly during procedures that carry a high risk of the complication.

Relationship of fat embolism to haemodynamic and echocardiographic changes during cemented arthroplasty

PURPOSE

Pressurisation of the medullary cavity during cemented arthroplasty causes "intravasation" of marrow fat. The purpose of this study was to examine the relationship between the amount of pulmonary intravascular fat and the haemodynamic and echocardiographic changes.

METHODS

Anaesthetised mongrel dogs (n = 16) underwent bilateral cemented arthroplasty (BCA) to create a large embolic load. Haemodynamic measurements included blood pressure (BP), pulmonary artery pressure (PAP), right atrial pressure and cardiac output as well as transoesophageal echocardiographic (TEE) assessment of right ventricular (RV) and left ventricular (LV) areas. Using quantitative morphometry on postmortem lung specimens, the proportion of lung tissue occluded by fat was measured.

RESULTS

Mean BP decreased within one minute of BCA, coinciding with the appearance of echogenic material in the RV. The RV area increased by 56% (P < 0.05) and LV area decreased by 34% (P < 0.05) while PAP increased from 15 +/- 3 mmHg to 39 +/- 10 mmHg within one minute (P < 0.001). The PAP remained elevated throughout the study (30 min). Stroke volume decreased in 14/15 dogs, yet cardiac output was maintained by increased heart rate. There was a curvilinear relationship (r = 0.87) between the maximum increase in PAP and the proportion of lung occupied by fat.

CONCLUSION

In this model, stroke volume decreased within one minute of BCA when fat embolism accompanied prosthesis insertion. The TEE detected an increased RV area and reduced LV area associated with decreased stroke volume. The maintenance of cardiac output after intraoperative fat embolism depends primarily on the ability to increase heart rate.

Cardiovascular collapse after femoral prosthesis surgery for acute hip fracture

PURPOSE

Prosthetic revision of hip fractures may result in embolization of tissue products leading to death. In this report, from cases reported to the Anaesthesia Advisory Committee to the Chief Coroner of Ontario, emphasis is placed on the immediate resuscitative procedures which may offset a fatal outcome.

CLINICAL FEATURES

Two elderly patients are reported in whom hip fractures necessitated primary prosthetic hip repair. The first patient, with a history of limited cardiac reserve and syncope, suffered a subcapital hip fracture. Under general anaesthesia, a Moore's prosthesis was inserted. The anaesthetic period remained relatively stable until surgical reaming of the femoral canal. Bradycardia, hypotension and cyanosis developed and quickly proceeded to a fatal cardiac arrest. Autopsy demonstrated diffuse pulmonary embolism of fat and thrombus. The second patient suffered a fracture around the stem of a previously inserted femoral prosthesis. Under general anaesthesia, a new cemented hip prosthesis was inserted, following which hypotension occurred. This was supported with small doses of ephedrine, ventilation was controlled with oxygen and the procedure was quickly terminated. Despite addition of a dopamine infusion, cardiac arrest and death followed. Autopsy disclosed massive fat and bone marrow embolization.

CONCLUSION

The combination of hip fracture, activated clotting factors and borderline cardiopulmonary function presents a risk of death from embolization of tissue products released during the placement of a cemented hip prosthesis. While the outcome of this catastrophe is generally poor, all practitioners should be prepared to immediately institute resuscitative procedures to manage the accompanying cardiovascular collapse.