A method of measuring total circulating blood volume (TBV) using indocyanine green (ICG) dye was investigated iii 7 dogs and 16 patients. Since concentration of injected ICG decreases exponentially from the circulating system after recirculation, concentration of the dye at the time of appearance (Cta) can be extrapolated by extending the slope of the dye dilution curve transcribed to a semi-logarithmic graph. TBV was calculated using the following formula : TBV=I/Cta, where I is the amount (mg) of ICG injected. Repeat measurements of TBV using ICG demonstrated good reproducibility (average coefficient of variation, 2.0%) and when compared to measurements made with Evans blue dye resulted in a correlation coefficient of 0.98 or more. We conclude that assessment of TBV using ICG is reliable and experimentally and clinically feasible. total circulating blood volume ; indocyanine green ; dye dilution method Total circulating blood volume (TBV) is one of the most important determinants in the understanding of circulatory physiology. At present, radio-isotopes such as 125I 131I, 51Cr, ssmTc and Evans blue dye (T-1824) are used for estimating blood volume. However, certain disadvantages are inherent to the use of these agents including: radiation contamination, long-term retention or temporary discoloration of the skin. Consequently, and although measurement of TBV is particularly important as a diagnostic tool, it is not routinely employed because of these methodological deficiencies. The development of a safe and reliable technique which could be easily performed is therefore needed.In 1968, Bradley and Barr reported a technique to measure TBV using indocyanine green (ICG), but its application has not been widely accepted. We modified Bradley's method and compared experimental and clinical TBV measurements made with ICG to results obtained usidg Evans blue (EB) dye.

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Biopsy or necropsy specimens of lung from 28 patients with congenital heart disease and Down's syndrome were studied to establish the cause of the postoperative respiratory failure often seen in such cases. Changes in lungs seen after operation included interstitial emphysema and overdistension of peripheral air spaces, associated with hypoplastic alveoli and deficient elastic fibres in the alveolar wall. In specimens taken before operation alveolar hypoplasia was common but interstitial emphysema or overdistension of lower airways was found only rarely. Findings suggest that alveolar hypoplasia is characteristic of Down's syndrome and that distension of peripheral air spaces or interstitial emphysema was due to artificial inflation of the lung during surgery. The severity of the lesions correlated significantly with the duration of artificial respiration and with the severity of the respiratory failure. Hypoplastic lung tissue in patients with Down's syndrome appears to be more susceptible to mechanical stress, and this is likely to be the cause of postoperative respiratory failure.