Accuracy of blood volume measurement using an integrated fiberoptic monitoring system in septic shock

Objectives

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.

Design

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.

Conclusion

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.