Estimating plasma volume from red cell volume.

Following the withdrawal of the only licensed supply of 125I-HSA in 1997, most UK centres now simply estimate plasma volume from a knowledge of the red cell volume and venous haematocrit. We compared measured and estimated plasma volume in 107 consecutive patients who had had red cell and plasma volume measured independently in the conventional way. In only 40% of cases was the estimated value accurate to within +/- 5%, and discrepancies of more than +/- 10% were seen in 35%. As there appears to be no simple way of predicting those patients for whom an estimation is inappropriate, it is recommended that plasma volume is measured independently in all patients, using a reputable source of unlicensed 125I-HSA.

An investigation into patient and staff doses from X-ray angiography during coronary interventional procedures.

Radiation doses to patients from interventional coronary X-ray procedures are relatively high when compared with conventional radiographic procedures. These high patient doses can translate into high staff doses owing to scattered radiation. This study investigates patient doses by means of dose-area product (DAP) meters installed in six rooms in two hospitals. DAP measurements in each room ranged from 28.0-39.3 Gy cm2 for coronary angiography and from 61.3-92.8 Gy cm2 for percutaneous transluminal coronary angioplasty, with the mean effective doses calculated to range between 5.1-6.6 mSv and 11.2-17.0 mSv, respectively. These values are comparable with those found in recent literature. DAP measurements were found to correlate strongly (correlation coefficient of 79%) with patient weight. The non-uniform scatter radiation fields surrounding the irradiated area during coronary angiography were also investigated using a tissue equivalent phantom and an ionization chamber. Exposure rates of scattered radiation from digital acquisition were found to be around 16 times higher than those generated from fluoroscopy, and oblique-angled imaging led to greater amounts of scatter owing to the increase in related exposure factors. The distribution of scatter from oblique projections confirms that X-ray photons in the diagnostic energy range are preferentially scattered backwards, toward the X-ray tube. These concepts are a major consideration when training individuals working in the angiography suite in order to keep doses "as low as reasonably practicable".