Physiological deadspace measurements in ventilated preterm infants
Research Project
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01.01.2009
- 30.06.2010
Should ventilator target tidal volumes be adjusted for gestational age? Authors: Roland Neumann, roland.neumann@health.wa.gov.au1, Alexander Larcombe, alexanderl@ichr.uwa.edu.au2, Graham Hall, graham.hall@health.wa.gov.au2,3, J. Jane Pillow, jpillow@meddent.uwa.edu.au4, Sven Schulzke, sven.schulzke@health.wa.gov.au1,4. Author Affiliations: 1King Edward Memorial Hospital and 2Telethon Institute for Child Health Research Perth, Australia; 3School of Paediatrics and Child Health and 4School of Women s and Infants Health, University of Western Australia, Perth, Australia. Background: Preterm infants are susceptible to volutrauma, but lung volumes capacities may vary. The relationship between gestation and the alveolar deadspace and tidal volumes is unknown. Aims: To measure Vd,MM on day 1 of life in ventilated very preterm infants. We hypothesized that after adjusting for set target tidal volume on the ventilator ( volume guarantee ) and respiratory rate, the ratio of alveolar to total tidal volume (Valv/VT) increases with gestational age at birth. Methods: 120 s of tidal breathing was recorded from unsedated, sleeping preterm infants (n=43; gestation 23-31 w, mean (SD) birth weight 1.1 (0.4) kg, postnatal age 14.3 (7.2) h) receiving patient-triggered ventilation (Babylog 8000 plus, Draeger Medical, Luebeck, Germany) using a mainstream ultrasonic flowmeter (Spiroson Exhalyzer D, Ecomedics AG, CH). Airway deadspace was calculated from the molar mass signal (Vd,MM). Alveolar volume (Valv) was calculated as VT Vd,MM. Arterial blood gases were obtained immediately after lung function testing. Multiple linear regression was used to analyse outcomes. Results: Mean (SD) values for Vd,MM, VT, and Valv/VT were 2.51 (0.61) mL/kg, 6.57 (1.54) mL/kg, and 0.62 (0.06) respectively. Mean (SD) arterial PaCO2 was 42.9 (5.8) mmHg. Valv/VT was positively associated with gestational age (R2 = 0.26, p = 0.012) after adjusting for set volume guarantee (range 3.8-5.1 mL/kg) and respiratory rate. Conclusions: In ventilated very preterm infants, Valv/VT on day 1 increases with gestational age. Ventilator target tidal volumes should be adjusted for maturity as well as body size at birth to avoid potential alveolar overdistension.
