Cement implantation syndrome: a time limited embolic phenomenon.

C EMENTED arthroplasty is among the most common and effective surgical procedures performed for elderly patients. The cement implantation syndrome is a well-recognized complication of this procedure, characterized by systemic hypotension, pulmonary hypertension and oxygen desaturation at the time of cement and prosthesis insertion. ~ This syndrome is now thought to be caused by the haemodynamic effects of emboli and not by the toxic properties of methyl methacrylate monomer. Embolization results from high intramedullary pressures. The cement acts as a seal, preventing decompression during prosthesis insertion and the resultant high intramedullary pressure forces medullary contents into the vasculature. 2 As well as the physical effects of mechanical pulmonary vascular obstruction, the embolized material may contain vasoactive substances that initiate mediator release or create reflex changes that increase pulmonary vascular tone. Non-cemented arthroplasty is associated with fewer emboli, lower intramedullary pressures and considerably less haemodynamic disturbance) Life-threatening hypotension during cemented arthroplasty is rare, yet sudden tmexplained intra-operafive cardiac arrests continue to be reported. 4-6 In this issue of the journal the Anaesthesia Advisory Committee to Ontario's Chief Coroner (Pietak et al.) report on four deaths that appear to be examples of the cement implantation syndrome. 7 They correctly emphasize the need for clinical awareness of such potential complications and an immediate resuscitation protocol. They suggest that the protocol be based on the pathophysiology of acute fight ventricular (RV) failure. Also in this issue of the journal, Lafont et al. using transoesophageal echocardiography (TEE) report that 47 of 48 patients undergoing elective cemented hip arthroplasty had detectable emboli, s Lafont et al., however, have not studied the cement implantation syndrome as no patients in the study developed hypotension or desaturation. Clinical reports and laboratory studies of the cement implantation syndrome all point to RV failure secondary to increased pulmonary artery pressure (PAP) as the underlying cause of systemic hypotension and sudden cardiac arrest. 9,1~ With acute increases in pulmonary vascular resistance (PVR), the thin-walled, compliant RV rapidly dilates with a shift of the interventricular septum to the left within the restrictions imposed by the pericardial cavity. These changes cause an immediate decrease in left ventricular (LV) compliance, reduced LV filling and cardiac output. Coronary perfusion pressure is decreased by the hypotension and right coronary flow is reduced as RV end-diastolic pressure (RVEDP) increases, creating ischaemia. In a recent report, Urban et al. described four patients with a mean increase in PAP of 10 mmHg and considerably decreased RV ejection fractions from 53% to 36%. 9 These changes can occur within seconds of prosthesis insertion and can be complicated by systemic paradoxical emboli. Pietak et al. suggest that some high risk groups can be identified. 7 Patients with limited pre-operative cardiopulmonary reserve due to pre-e~sting pulmonary hypertension, RV dysfunction or coronary artery disease, are susceptible to ischaemia and infarction. They may be particularly at risk if the surgical procedure is chosen that results in a large embolic load. Haemodynamic instability at the time of cement and prosthesis insertion is a surgical complication. Technical factors can increase the embolic load. Some prostheses, such as the Guepar long-stemmed bipolar knee arthroplasty, are clearly associated with an extraordinarily increased risk) 1 Urban's report suggests that revision arthroplasty patients also have a high incidence of increased PAP with reduced ejection fractions. 9 Several patients (4 /14) required increased inotropic support with one death. Arthroplasty for pathological fractures may be a risk factor, perhaps related to pressurization of abnormal vessels in cancerous bone. However, some preventative methods (eg. drilling a venting hole in the cortical bone to