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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Intensive care medicine 12 (1986), S. 71-79 
    ISSN: 1432-1238
    Keywords: Cardiac output ; Flow modulation ; Mechanical ventilation ; Thermodilution method
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The reliability of cardiac output estimation by thermodilution during artificial ventilation was studied in anesthetized pigs at the right side of the heart. The estimates exhibited a cyclic modulation related to the ventilation. The amplitude of the modulation was independent of the level of positive end-expiratory pressure, ventilatory pattern and volemic loading of the animals. However, a non-constant phase relation existed between the ventilatory cycle and the modulation. Single observations at a fixed moment in the ventilatory cycle are therefore not appropriate for estimation of mean cardiac output nor for studying its relative changes. The averaging of estimates spread equally over the ventilatory cycle led to a much larger reduction in the deviation of the averages from the mean cardiac output than an averaging procedure of randomly selected estimates. The accracy of estimation of mean cardiac output by two estimates equally spread in the ventilatory cycle was equal to the accuracy obtained by averaging five randomly selected estimates. Averaging four estimates, equally spread in the cycle, appeared to be the optimal procedure. For 89% of all averages an accuracy of 5% around the mean was obtained and for 99% an accuracy of ±10%.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1238
    Keywords: Cardiac output ; Mechanical ventilation ; Multiple injections ; Thermodilution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The application of the thermodilution method in conditions associated with variations in blood flow implies a misuse of the Stewart Hamilton equation. Therefore, we studied the reliability of the thermodilution method for the estimation of mean cardiac output (CO) during mechanical ventilation in patients (n=9). Variation of the injection moment in the ventilatory cycle elicited a cyclic variation of CO estimates. This variation was not the same for all patients neither in phase nor in amplitude. Therefore, no specific phase in the ventilatory cycle could be selected for an accurate estimation of mean CO. Averaging CO estimates randomly distributed in the ventilatory cycle led to an improvement of accuracy with the square root of the number of observations. The averaging of CO estimates spread equally over the ventilatory cycle led to a much better result, e.g., the variation in the average of two estimates equally spread in the ventilatory cycle was similar to the variation in the average of four random estimates. We conclude that averaging of 3 or 4 estimates spread equally over the ventilatory cycle is an adequate strategy to estimate mean cardiac output in patients reliably.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-2013
    Keywords: Key words Venous return ; Central venous pressure ; Inspiratory pause procedures ; Venous capacity ; Venous resistance ; Mechanical ventilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In eight mechanically ventilated, anaesthetized pigs weighing 10.3 ± 0.8 kg (mean ± SD) we studied the effect of the inflation time of the lung on the estimation of the mean systemic filling pressure (P sf) from the changes in venous return and central venous pressure during inflation of the lung. For this purpose we applied slow inflation procedures (SIP) to the lung with inflation times of 2.4, 4.8, 7.2, 9.6 and 12 s at tidal volumes (V T) of 15 and 30 ml/kg. The data were compared with the values of P sf obtained from inspiratory pause procedures (IPPs). A linear regression between venous return and central venous pressure applied during a SIP underestimated P sf compared with the value obtained with IPPs. An exponential fit through the values of P sf obtained from the different SIPs predicted an inflation time of about 15 s for an estimation of P sf that is not different from the P sf (IPP). The advantage of the SIP method is that the P sf can be determined much faster than with the method based on IPPs. However, due to the rather long inflation time needed, the method may be only applicable under circumstances where neurohumoral control mechanisms are suppressed as during intensive care and anaesthesia.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-2013
    Keywords: Venous return ; Central venous pressure ; Inspiratory pause procedures ; Venous capacity ; Venous resistance ; Mechanical ventilation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In eight mechanically ventilated, anaesthetized pigs weighing 10.3 ± 0.8 kg (mean ± SD) we studied the effect of the inflation time of the lung on the estimation of the mean systemic filling pressure (P sf) from the changes in venous return and central venous pressure during inflation of the lung. For this purpose we applied slow inflation procedures (SIP) to the lung with inflation times of 2.4, 4.8, 7.2, 9.6 and 12 s at tidal volumes (V T) of 15 and 30 ml/kg. The data were compared with the values ofP sf obtained from inspiratory pause procedures (IPPs). A linear regression between venous return and central venous pressure applied during a SIP underestimatedP sf compared with the value obtained with IPPs. An exponential fit through the values ofP sf obtained from the different SIPs predicted an inflation time of about 15 s for an estimation ofP sf that is not different from theP sf (IPP). The advantage of the SIP method is that theP sf can be determined much faster than with the method based on IPPs. However, due to the rather long inflation time needed, the method may be only applicable under circumstances where neurohumoral control mechanisms are suppressed as during intensive care and anaesthesia.
    Type of Medium: Electronic Resource
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