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Arch Dis Child Fetal Neonatal Ed 2000;82:F237-F242 doi:10.1136/fn.82.3.F237
  • Original article

Effect of changes in oscillatory amplitude on Paco2 and Pao2 during high frequency oscillatory ventilation

  1. C Morgan,
  2. P R F Dear,
  3. S J Newell
  1. Neonatal Intensive Care Unit, St James' University Hospital, Beckett Street, Leeds LS9 7TF, UK
  1. Dr Morgan, Neonatal Intensive Care Unit, Royal Free Hospital, Pond Street, Hampstead, London NW3 2QG, UK email:newells{at}sjuhnnu.demon.co.uk
  • Accepted 10 December 1999

Abstract

AIMS To describe the relation between oscillatory amplitude changes and arterial blood gas (ABG) changes in preterm infants receiving high frequency oscillatory ventilation, using a multiparameter intra-arterial sensor (MPIAS).

METHODS Continuous MPIAS ABG data were collected after amplitude changes and stratified according to Fio 2: high (> 0.4) or low (< 0.3). For each amplitude change, the maximum change (from baseline) in Paco 2 and Pao 2 over the following 30 minutes was determined. In total, 64 oscillatory amplitude changes were measured in 21 infants (median birth weight 1040 g; gestation 27 weeks).

RESULTS All amplitude increases produced Paco 2 falls (median −0.98 and −1.13 kPa for high and low Fio 2 groups respectively). All amplitude decreases produced Paco 2 rises (median +0.94 and +1.24 kPa for high and low Fio 2 groups respectively). About 95% of the change in Paco 2 was completed in 30 minutes. Amplitude changes did not affect Pao 2when Fio 2 > 0.4. When Fio 2 < 0.3, amplitude increases produced a Pao 2 rise (median = +1.1 kPa; P < 0.001) and amplitude decreases a fall (median = −1.2 kPa; P < 0.001).

CONCLUSIONS After oscillatory amplitude changes, the speed but not the magnitude of the Paco 2 change is predictable, and a rapid Pao 2 change accompanies the Paco 2 change in infants with mild lung disease and a low Fio 2.

  • A 3 cm H2O change in oscillatory amplitude results in a median change in Paco 2 of about 1.0 kPa (but the range of effect is wide)

  • Following changes in oscillatory amplitude:

  • the speed and direction of change in Paco 2 is predictable;

  • about 95% of the change in Paco 2 is completed within 30 minutes;

  • Pao 2 is unaffected if lung disease is severe;

  • if lung disease is mild/improving, rapid changes in Pao 2 occur (up to 4.7 kPa)

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