Functional residual capacity measurement by heptafluoropropane in ventilated newborn lungs
- Publisher: Freie Universität Berlin Universitätsbibliothek, Garystr. 39, 14195 Berlin
610 Medizin und Gesundheit | 610 Medical sciences; Medicine | HFP | gas dilution technique | FRC | Heptafluoropropane | neonate | tracer gas | Functional residual capacity
Objective: Heptafluoropropane is an inert gas commercially used as propellant for inhalers. Since heptafluoropropane can be detected in low concentrations, it could also be used as a tracer gas to measure functional residual capacity. The aim of the present study was to validate functional residual capacity measurements by heptafluoropropane wash-in/wash-out (0.8%) during mechanical ventilation in small, surfactant-depleted lungs using a newborn piglet model.
Design: Prospective laboratory and animal trial.
Setting: Animal laboratory in a university setting.
Subjects: Sixteen newborn piglets (age <12 hrs, median weight 1390 g [705–4200 g]) before and after surfactant depletion by lung lavage.
Interventions: Heptafluoropropane was measured with an infrared mainstream sensor connected with the flow sensor of the Dräger Babylog 8000. Accuracy and precision of the measurement technique were tested in a mechanical lung model with a volume range from 11 to 35 mL. Furthermore changes of functional residual capacity were assessed in vivo by variation of ventilatory variables.
Measurements and Main Results: In vitro the absolute error of functional residual capacity was <1 mL (relative errors <3%) with a coefficient of variation <4%. The coefficient of variation of consecutive in vivo measurements was only slightly higher
After lung lavage, the functional residual capacity decreased despite increased ventilator pressures. In healthy lungs, the increase in peak inflation pressure and positive end-expiratory pressure had only a moderate, non-significant effect on functional residual capacity, whereas in surfactant-depleted lungs an elevated PEEP increased functional residual capacity significantly.
Conclusions: Heptafluoropropane is a suitable tracer gas for precise functional residual capacity measurements tested in vitro and allows for reproducible measurements in ventilated small lungs without any adverse effects on mechanical ventilation. The sensitivity of the method is sufficiently high to demonstrate the effect of changes in ventilatory settings on the functional residual capacity.