A novel approach to measuring circulating blood volume: the use of a hemoglobin-based oxygen carrier in a rabbit model

A novel method for blood volume estimation using trivalent chromium in rabbit models

Background:

Blood volume measurement though important in management of critically ill-patients is not routinely estimated in clinical practice owing to labour intensive, intricate and time consuming nature of existing methods.

Aims:

The aim was to compare blood volume estimations using trivalent chromium [⁵¹Cr(III)] and standard Evans blue dye (EBD) method in New Zealand white rabbit models and establish correction-factor (CF).

Materials and Methods:

Blood volume estimation in 33 rabbits was carried out using EBD method and concentration determined using spectrophotometric assay followed by blood volume estimation using direct injection of ⁵¹Cr(III). Twenty out of 33 rabbits were used to find CF by dividing blood volume estimation using EBD with blood volume estimation using ⁵¹Cr(III). CF is validated in 13 rabbits by multiplying it with blood volume estimation values obtained using ⁵¹Cr(III).

Results:

The mean circulating blood volume of 33 rabbits using EBD was 142.02 ± 22.77 ml or 65.76 ± 9.31 ml/kg and using ⁵¹Cr(III) was estimated to be 195.66 ± 47.30 ml or 89.81 ± 17.88 ml/kg. The CF was found to be 0.77. The mean blood volume of 13 rabbits measured using EBD was 139.54 ± 27.19 ml or 66.33 ± 8.26 ml/kg and using ⁵¹Cr(III) with CF was 152.73 ± 46.25 ml or 71.87 ± 13.81 ml/kg (P = 0.11).

Conclusions:

The estimation of blood volume using ⁵¹Cr(III) was comparable to standard EBD method using CF. With further research in this direction, we envisage human blood volume estimation using ⁵¹Cr(III) to find its application in acute clinical settings.

Preserving enhancement in freeze-dried contrast agent ST68: Examination of excipients

The perfluorcarbon (perfluorobutane) ultrasound contrast agent ST68, composed of sonicated mixtures of non-ionic surfactants, is stable in solution for only a few weeks at 4 degrees C. Freeze-drying critically diminished ST68's ability to reflect ultrasound (its echogenicity). A method of incorporating specific lyoprotectants before lyophilization was investigated. Reintroduction of perfluorobutane to the protected freeze-dried sample, followed by reconstituting with water preserved echogenicity. Glucose, trehalose, sucrose, and mannitol were tested at 100mM and in vitro echogenicity data was collected from samples with dose concentrations of 50-300microl/l. Glucose was found to be the best lyoprotectant providing an average (n=3) maximum peak enhancement of 23.2+/-1.2dB in vitro, measured at 5MHz, 684kPa, and a pulse repetition frequency (PRF) of 100Hz (p<0.05 over freeze-dried ST68 control) and 20.8+/-0.8dB in vivo in New Zealand white rabbits at 5MHz and a PRF of 6.7kHz. Pulse inversion harmonic US images of a rabbit kidney, pre- and post-contrast injection (0.1ml/kg), showed excellent enhancement and clear vascular delineation, similar to that of the original agent. For the first time this contrast agent can be successfully freeze-dried yielding a longer self-life without the need for refrigeration.