To compare the accuracy of an integrated fiberoptic monitoring system in measuring blood volume (BV) with standard method using chromium-51-tagged erythrocytes in septic shock.
Prospective animal laboratory study.
Measurement and main results
Twenty anaesthetised, and mechanically ventilated pigs (20.9 ± 1.9 kg) were investigated over a period of 8 h. Septic shock was induced with faecal peritonitis (1 g/kg body weight autologous faeces). A central venous catheter was used for the injection of the indicator dyes. BV was measured by detecting indocyanin green by reflection densitrometry using a fiberoptic thermistor tipped catheter inserted into right carotid artery (4F PV 2024, Pulsion Medical Systems). Haemodynamic treatment scheme was aimed at maintenance of a central venous pressure of 12 mmHg. Data were analysed using Bland-Altman analyses, linear regression and correlation. Forty data pairs of simultaneous BV-measurements were yielded during haemodynamic consistency with a mean BV measured by integrated fiberoptic monitoring system of 66.6 ± 20.3 ml/kg (range: 24.5–122.6 ml/kg). Mean BV measured by chromium-51-tagged erythrocytes was 76.1 ± 17.9 ml/kg (range: 49.7–121.6 ml/kg). Linear regression equation was: BV by integrated fiberoptic monitoring system = 0.65 × BV: chromium-51-tagged erythrocytes + 17.6; r = 0.57, P < 0.01. The mean bias was 9.6 ml/kg (95% confidence interval: 3.7–15.4 ml/kg), with limits of agreement of –26.5 to 45.6 ml/kg and a precision of 16.8 ml/kg.
In this model of porcine septic shock we could show a significant correlation in blood volume measurement between fiberoptic monitoring system and chromium-51-tagged erythrocytes. The relatively wide limits of agreement might be due to pronounced circulatory alterations including slow mixing compartments, prolonged equilibration and sequestration in septic shock.