Continuous non-invasive monitoring of tidal volumes by measurement of tidal impedance in neonatal piglets.
Continuous non-invasive monitoring of tidal volumes by measurement of tidal impedance in neonatal piglets.
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BACKGROUND: Electrical Impedance measurements can be used to estimate the content of intra-thoracic air and thereby give information on pulmonary ventilation.Conventional Impedance measurements mainly indicate relative changes, but no information concerning air-volume is given.The study was performed to test whether a 3-point-calibration with known tidal volumes (VT) during conventional mechanical ventilation (CMV) allows subsequent calculation of VT from total Tidal-Impedance (tTI) measurements using Quadrant Impedance Measurement (QIM).In addition the distribution of TI in different regions of the thorax was examined.
METHODOLOGY AND PRINCIPAL FINDINGS: QIM was performed in five neonatal piglets during volume-controlled CMV.tTI values at three different VT (4, 6, 8 ml/kg) were used to establish individual calibration curves.Subsequently, each animal was ventilated with different patterns of varying VT (2-10 ml/kg) at different PEEP levels (0, 3, 6, 9, 12 cmH(2)O).VT variation was 15-eg2373cl repeated after surfactant depletion by bronchoalveolar lavage.
VT was calculated from tTI values (VT(calc)) and compared to the VT delivered by the ventilator (VT(PNT)).Bland-Altman analysis revealed good agreement between VT(calc) and VT(PNT) before (bias -0.08 ml; limits of agreement -1.18 to 1.
02 ml at PEEP = 3 cmH(2)O) and after surfactant depletion (bias -0.17 ml; limits of agreement -1.57 to 1.22 ml read more at PEEP = 3 cmH(2)O).
At higher PEEP levels VT(calc) was lower than VT(PNT), when only one fixed calibration curve (at PEEP 3 cmH(2)O) was used.With a new calibration curve at each PEEP level the method showed similar accuracy at each PEEP level.TI showed a homogeneous distribution over the four assessed quadrants with a shift toward caudal regions of the thorax with increasing VT.CONCLUSION: Tidal Impedance values could be used for precise and accurate calculation of VT during CMV in this animal study, when calibrated at each PEEP level.