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

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.

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.

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.

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.