Abstract
Summary: This paper describes a study comparing the impedance cardiac output (ICO) with effective pulmonary capillary blood flow (Qpc eff), measured by rebreathing N2O, in a group of healthy babies during the neonatal period. The calculation of ICO requires a value for the electrical resistivity of blood, p. The resistivity of blood was measured on 40 samples of neonatal blood with hematocrit range of 18–70% and a new relationship was defined between haematocrit and resistivity, whereby p = 67.919 exp (0.02433 Het) (Fig. 2). A total of 109 simultaneous measurements of Qpc eff and ICO, made from 32 different babies studied upon 41 occasions, was considered for correlation purposes (Table 2). The different methods are plotted against each other in the graphs (Fig. 3). It is seen that using any one of the available data for human blood resistivity alone, a good correlation between ICO and Qpc eff is only achieved over a part of the haematocrit range. A hematocrit-related correction factor, S, has been derived to be applied to the stroke volume equation. The corrected ICO compared with Qpc eff results is shown in Figure 5 and the correlation coefficients and percentage differences between the two methods for the different hematocrit groups are shown in Table 2. The mean ICO is 205 ml kg1 min1 SEM 3.5 (range 124–289).
Impedance cardiography is a safe and easy technique to apply to the newborn human infant but even if accurate values for resistivity are used, a further hematocrit-related factor should be applied for optimal results.
Speculation: A technique having been established by which impedance cardiography can be used to make accurate measurements of cardiac output in the healthy newborn infant, it is now possible to use this method to provide noninvasive observations on the normal cardiovascular physiology of the newborn and to assess its potential for making clinically useful measurements on sick infants.
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Costhloe, K., Stocks, J., Godfrey, S. et al. Cardiac Output in the Neonatal Period Using Impedance Cardiography. Pediatr Res 11, 1171–1177 (1977). https://doi.org/10.1203/00006450-197712000-00001
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DOI: https://doi.org/10.1203/00006450-197712000-00001
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