Functional residual capacity and ventilation homogeneity in mechanically ventilated small neonates.
A modification of a computerized tracer gas (SF6) washout method was designed for serial measurements of functional residual capacity (FRC) and ventilation homogeneity in mechanically ventilated very-low-birth-weight infants with tidal volumes down to 4 ml. The method, which can be used regardless of the inspired O2 concentration, gave accurate and reproducible results in a lung model and good agreement compared with He dilution in rabbits. FRC was measured during 2-4 cmH2O of positive end-expiratory pressure (PEEP) in 15 neonates (700-1,950 g), most of them with mild-to-moderate respiratory distress syndrome. FRC increased with body weight and decreased (P less than 0.05) with increasing O2 requirement. Change to zero end-expiratory pressure caused an immediate decrease in FRC by 29% (P less than 0.01) and gave FRC (ml) = -1.4 + 17 x weight (kg) (r = 0.83). Five minutes after PEEP was discontinued (n = 12), FRC had decreased by a further 16% (P less than 0.01). The washout curves indicated a near-normal ventilation homogeneity not related to changes in PEEP. This was interpreted as evidence against the presence of large volumes of trapped alveolar gas.
Vilstrup
C T
CT
Department of Anesthesia, University Hospital, Lund, Sweden.
Björklund
L J
LJ
Larsson
A
A
Lachmann
B
B
Werner
O
O
D001835:Body Weight / Q000502:physiology; D005652:Functional Residual Capacity / Q000502:physiology; D005865:Gestational Age; D006371:Helium; D006801:Humans; D007231:Infant, Newborn / Q000502:physiology*; D008954:Models, Biological; D011175:Positive-Pressure Respiration; D012119:Respiration / Q000502:physiology*; D012121:Respiration, Artificial; D012127:Respiratory Distress Syndrome, Newborn / Q000503:physiopathology; D013459:Sulfur Hexafluoride
D006371:Helium; D013459:Sulfur Hexafluoride