Background: Volume-targeted ventilation is used in neonates to reduce volutrauma and hyperventilation. Little is known about appropriate tidal volume (VT) settings in extremely low birth weight (ELBW) infants who remain intubated for extended periods.
Hypothesis: The VT required to maintain adequate PCO2 changes as the underlying disease evolves in ELBW infants ventilated for prolonged periods.
Objective: Obtain normative data for VT associated with normocapnia in infants ventilated with Volume Guarantee (VG) over the first three weeks of life. Design/Methods: Set and measured VT, peak pressure, respiratory rate and blood gas (BG) values were extracted from records of babies <800 g born January 2003 to August 2005, ventilated with VG during days 1-2, 5-7 and 14-21. Only VT that corresponded to PCO2 values within a defined normal range were included. Descriptive statistics were used to define the patient cohort. Mean VT and PCO2 for each patient during each epoch was calculated and these values were analyzed by repeated measures ANOVA.
Results: Twenty-six infants (615±104g) were included. 828 paired BG and VT sets remained: d1-2=251, d5-7=185, d14-17=216, d18-21=176. PCO2 values rose from 43.98±5.44 mmHg on d1-2 to 46.30±5.12 on d5-7, 53.87±6.8 on d14-17 and 53.90±6.2 mmHg on d18-21. Mean exhaled VT was 5.15±0.62 ml/kg on d1-2, 5.24±0.71 on d5-7, 5.63±1.0 on d14-17 and 6.07±1.4 ml/kg on d18-21 (p<0.05).
Conclusions: Despite permissive hypercapnia, tidal volume requirement rises with advancing post-natal age in ELBW infants. The increase is greatest during the third week of life and is likely due to distention of upper airways (acquired tracheomegaly) and increasing heterogeneity of lung inflation (increased alveolar dead space).
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