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Work of breathing during SIMV with and without pressure support
  1. D-S Patel,
  2. G F Rafferty,
  3. S Lee,
  4. S Hannam,
  5. A Greenough
  1. Division of Asthma, Allergy and Lung Biology, School of Medicine, King’s College London, London, UK
  1. Professor Anne Greenough, Newborn Unit, 4th Floor Golden Jubilee Wing, King’s College Hospital, Denmark Hill, London SE5 9RS, UK; anne.greenough{at}


Objective: In a randomised trial, pressure support with synchronised intermittent mandatory ventilation (SIMV) compared to SIMV alone was associated with a significant reduction in supplementary oxygen duration. The hypothesis that the addition of pressure support to SIMV compared to SIMV alone would reduce the work of breathing was examined.

Design: Prospective study.

Setting: Perinatal service.

Patients: 20 infants, with a mean gestational age of 31 weeks, being weaned from mechanical ventilation were studied.

Interventions: 1 h periods of SIMV and SIMV with pressure support at 50% of the difference between the peak inflating pressure and positive end expiratory pressures.

Main outcome measures: The work of breathing was assessed by measurement of the transdiaphragmatic pressure time product (PTPdi).

Results: The mean PTPdi on SIMV plus pressure support was 112 cm H2O.s/min, approximately 20% lower than that on SIMV alone (141 cm H2O.s/min) (p<0.001).

Conclusion: The addition of pressure support to SIMV reduces the work of breathing in infants being weaned from the ventilator.

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  • Funding: Dr Patel is supported by The Charles Wolfson Charitable Trust.

  • Competing interests: AG has held grants and received honoraria for giving lectures and advising various ventilator manufacturers.

  • Ethics approval: This study was approved by the King’s College Hospital Research Ethics Committee.