DETECTION OF EMBOLIC EVENTS BY CAPNOGRAPHY AND TRANSESOPHAGEAL ECHOCARDIOGRAPHY DURING TOTAL HIP-REPLACEMENT

Trans-oesophageal echocardiography and continuous monitoring of the pa rtial pressure of carbon dioxide at end expiration (PETCO2) were perfo rmed in 63 dogs during total hip replacement and in three dogs during femoral stem revision. The PETCO2 usually did not change during insert ion of the acetabular prosthesis, but in 17.5% of the cases, it decrea sed by more than 10 mmHg after insertion of the femoral prosthesis. In all of the cases, transoesophageal echocardiography revealed echogeni c structures in the right side of the heart, immediately after inserti on of the acetabular and of the femoral prostheses. These appeared as either numerous pinpoint echoes, which passed through the right side o f the heart in a ''snow flurry'' like fashion or more echogenic partic les. The embolaemia, seen ultrasonographically, was categorized into o ne of six grades of severity. Statistical analysis showed significant positive correlations between the severity of the embolaemia and the e xtent of the decrease in PETCO2 (rs = 0.405; P = 0.001; n = 60), and b etween the severity of the embolaemia and the duration of the decrease in PETCO2 before it returned to baseline values (rs = 0.345; P = 0.00 7; n = 60). Trans-oesophageal echocardiography demonstrated that embol aemia was induced during cemented prosthesis insertion. It was propose d that an increase in intramedullary pressure, during insertion, force s bone marrow into the venous circulation. Bone marrow itself can cons titute an embolus, but also it may activate intravascular coagulation, thus leading to thromboembolism, in addition to bone marrow embolism. Elongated particulate emboli, up to several centimetres in length, we re seen on ultrasonogrammes and were thought to be, at least in part, products of intravascular coagulation. A significant decrease in the p latelet concentration in peripheral venous blood, after insertion of t he femoral prosthesis, was also indicative of intravascular coagulatio n. The extent of the impairment of gas exchange was documented by mean s of capnography. The significant positive correlation between the emb olaemia, seen via ultrasonography, and the decrease in PETCO2 strongly suggest a causal relationship between the two variables. The rapid re covery, that occurred in most patients, is attributed to the enormous lytic ability of pulmonary tissue. Prophylactic measures include the m aintenance of normovolaemia during the operations, thorough lavage of the intramedullary cavity before prosthesis insertion and steps to pre vent an increase in intramedullary pressure during implantation.