During assist control ventilation and pressure support ventilation (PSV), the start of ventilator inflation is determined by the start of the infant's inspiratory effort. During PSV, termination of inflation is determined by the level of the infant's inspiratory flow. In a randomized trial, no significant differences were found between assist control and pressure support ventilation with regard to the duration of weaning, time to successful extubation, work of breathing, rate of asynchrony and level of respiratory muscle strength.

Objectives: To test the hypothesis that the duration of weaning would be shorter using assist control ventilation (ACV) rather than pressure support ventilation (PSV). To determine if any differences in the duration of weaning reflected differences in the work of breathing, the rate of asynchrony or the level of respiratory muscle strength.

Patients and methods: Thirty-six infants, median gestational age 29 (range 24 to 39) weeks, were randomized to weaning by either ACV or PSV. The duration of weaning was recorded. At baseline (study entry), 24 hours after entering the study and immediately prior to extubation, the work of breathing was assessed by measuring the transdiaphragmatic pressure time product (PTPdi), thoracoabdominal asynchrony (TAA) was assessed using respiratory inductance plethysmography and respiratory muscle strength measured by recording the maximal inspiratory pressure produced during an airway occlusion during crying (Pimax). Immediately prior to extubation, the level of active expiration was also assessed.

Inclusion Criteria:

• Ventilated neonates less than 14 days of age

Exclusion Criteria:

• Congenital heart disease, hypoxic ischaemic encephalopathy