Presented at the Neonatal Society 2008 Autumn Meeting.
Patel DS, Walker S, Lee S, Hannam S, Rafferty G, Greenough A.
School of Medicine, Division of Asthma, Allergy and Lung Biology, King’s College London, London, UK
Background: During volume targeted ventilation (VTV) a mean constant tidal volume is delivered. This mode of ventilation may be particularly useful in infants with acute RDS who may have rapid changes in compliance related to surfactant administration. Meta-analysis of VTV studies has shown a reduction in the duration of ventilation but no difference in the rates of bronchopulmonary dysplasia (BPD) (1). A range of different targeted volumes however were used in those studies, reflecting there is no consensus on which level of volume targeting should be used.
Aim: To determine the optimal volume targeted level in, that is the level associated with the lowest work of breathing, in infants with RDS.
Methods: The work of breathing was assessed by measurement of the transdiaphragmatic pressure time product (PTPdi). A dual tipped catheter was used to measure gastric and oesophageal pressure, airflow was measured using a pneumotachograph and airway pressure measured from a side port on the pneumotachograph. Infants were ventilated using the SLE 5000 ventilator. PTPdi was first measured without volume targeting (baseline) and then at volume targeted levels of 4, 5 and 6 ml/kg which were delivered in random order. After each volume targeted level, the infants were returned to baseline. Each step was maintained for 20 minutes. Prospective sample size calculation showed that 20 infants were required to detect a 40% difference in the PTPdi with 80% power at the 5% level.
Patients: Twenty infant (nine male) with a median gestational age 28 weeks were studied. Eighty five percent of their mothers had received antenatal steroids and ninety percent of the infants had received surfactant. Baseline ventilator settings were a median PIP of 16 cmH2O, PEEP of 4cmH2O, ventilator rate of 40 breaths/minute (bpm) and FiO2 of 0.27. The study was approved by the King’s College Hospital Research Ethics Committee and parents gave informed written consent.
Results: The mean PTPdi was higher at a volume target level of 4mls/kg as compared to the mean PTPdi at baseline (i.e. without volume targeting), p = 0.004. PTPdi was higher when 4mls/kg rather than 6mls/kg (p = 0.002) or 5mls/kg (p = 0.04) were used. The minute volume did not differ significantly between the volume targeted levels, but the expiratory volume was significantly higher and the total respiratory rate, significantly lower at the higher volume targeted levels.
Conclusions: A low level of volume targeting increases the work of breathing in infants with RDS. Our results suggest a volume targeted level of at least 5mls/kg should be used in prematurely born infants with acute respiratory distress syndrome.
References
1. McCallion N, Davis P, Morley C. Cochrane Database Syst Rev 2005(3):CD003666.