Work of Breathing and Different Levels of Volume-Targeted Ventilation

Abstract

Addition of low VT levels to patient-triggered modes increases the WOB during weaning. This can be avoided by using a VT level of 6 mL/kg. ABSTRACTOBJECTIVES. The objectives of this study were to determine the impact of different volume-targeted levels on the work of breathing and to investigate whether a level that reduced the work of breathing below that experienced during ventilatory support without volume targeting could be determined.METHODS. The transdiaphragmatic pressure-time product, as an estimate of the work of breathing, was measured for 20 infants (median gestational age: 28 weeks) who were being weaned from respiratory support by using patient-triggered ventilation (either assist-control ventilation or synchronous intermittent mandatory ventilation). The transdiaphragmatic pressure-time product was measured first without volume targeting (baseline) and then at volume-targeted levels of 4, 5, and 6 mL/kg, delivered in random order. After each volume-targeted level, the infants were returned to baseline. Each step was maintained for 20 minutes.RESULTS. The mean transdiaphragmatic pressure-time product was higher with volume targeting at 4 mL/kg in comparison with baseline, regardless of the patient-triggered mode. The transdiaphragmatic pressure-time product was higher at a volume-targeted level of 4 mL/kg in comparison with 5 mL/kg and at 5 mL/kg in comparison with 6 mL/kg. The mean work of breathing was below that at baseline only at a volume-targeted level of 6 mL/kg. CONCLUSIONS. Low volume-targeted levels increase the work of breathing during volume-targeted ventilation. Our results suggest that, during weaning, a volumetargeted level of 6 mL/kg, rather than a lower level, could be used to avoid an increase in the work of breathing. Pediatrics 2009;123:e679-e684 D URING VOLUME-TARGETED VENTILATION (VTV), a nearly constant tidal volume is delivered. This minimizes excessive tidal volume delivery, reducing volutrauma and the likelihood of hypocarbia. In one study, use of VTV was associated with avoidance of severe hypocarbia or hypercarbia in Ͼ90% of the first 48 hours for infants at Ͻ33 weeks of gestation. 1 VTV may be useful in situations in which there are changes in lung function, such as when infants are recovering from respiratory distress and being weaned from a ventilator. During VTV, compared with pressure-limited ventilation, blood gas values were maintained at lower airway pressures. 2 Those results suggested that infants make a greater contribution to minute ventilation during VTV than during pressure-limited ventilation and hence their work of breathing (WOB) may be higher with VTV, which may affect weaning and extubation adversely. 3 It seems likely, however, that higher volume-targeted (VT) levels would reduce the WOB and, with a sufficiently large targeted volume, the WOB would be lower during ventilatory support with versus without volume targeting. These hypotheses have not been tested, however, and a variety of VT levels have been used in VTV studies. 4-8 The aims of this study w...

Randomised Trial of Volume-Targeted Ventilation versus Pressure-Limited Ventilation in Acute Respiratory Failure in Prematurely Born Infants

“…A wide range of reported tidal volume (VT) levels (4-10 ml/kg) were used in the studies included in the meta-analysis [1]. We have shown that in the short-term, the work of breathing (WOB) is reduced during VTV if higher rather than lower levels of volume targeting are used [2,3,4]. Increasing the level of respiratory support by increasing the level of volume targeting, however, could unfavourably impact on respiratory muscle strength.…”

Lower back-up rates improve ventilator triggering during assist-control ventilation: a randomized crossover trial

“…The mean difference between settings of 30 min À1 and 50 min À1 was 6 min À1 (99% confidence interval [3][4][5][6][7][8][9]. No statistically significant differences were observed in delivered PIP or changes in TcCO 2 , FiO 2 , SpO 2 , HR or BP.…”

“…Synchronized intermittent mandatory ventilation provides a fixed number of triggered inflations per minute. AC has been associated with reduced patient effort 4,5 and reduced variability of tidal volume, 6 particularly when combined with volume guarantee (VG). 4,7 In AC mode, the ventilator rate varies with the breathing pattern of the infant.…”

Randomised weaning trial comparing assist control to pressure support ventilation

“…In addition, we compared methods of weaning which supported all of the infant's breaths. We have previously reported that the work of breathing is increased during weaning when only a proportion of the infant's breaths were supported by mechanical inflations compared with when all the infant's breaths were supported 6. Our study has some limitations.…”

“…The work of breathing was assessed over a 5-min period on each occasion by measurement of the transdiaphragmatic pressure time product (PTPdi, New York, USA) as previously described in detail 6. The mean PTPdi was calculated from 20 consecutive infant's breaths including those that were or were not supported by positive pressure inflations.…”