Randomised trial of volume-targeted ventilation versus pressure-limited ventilation in acute respiratory failure in prematurely born infants.

BACKGROUND: During volume-targeted ventilation (VTV), a constant volume is delivered with each ventilator inflation. OBJECTIVES: To determine whether VTV compared to pressure-limited ventilation (PLV) reduced the time to reach weaning criteria in prematurely born infants with acute respiratory distress, and if any difference was explained by better respiratory muscle strength and/or a lower work of breathing (WOB). METHODS: Infants of <34 weeks of gestational age ventilated for <24 h in the first week after birth were randomised to receive either VTV or PLV. The primary outcome was the time to achieve pre-specified weaning criteria. Respiratory muscle strength was assessed by the measurement of the maximum inflation and expiratory pressures, and the WOB assessed by the transdiaphragmatic pressure time product. Other outcomes reported are the duration of ventilation, occurrence of patent ductus arteriosus, pneumothorax, intraventricular haemorrhage, periventricular leukomalacia and episodes of hypocarbia. RESULTS: Forty infants, median gestational age 27 (range 23-33) weeks, were recruited. The time taken to achieve weaning criteria was similar in the two groups [median 14 h (VTV) vs. 23 h (PLV)]. There were no significant differences between the groups with regard to respiratory muscle strength, WOB or other outcomes, except that fewer of the VTV compared to the PLV group had episodes of hypocarbia (8 vs. 19; p < 0.001). CONCLUSION: In prematurely born infants with acute respiratory failure, use of VTV did not reduce the time to reach weaning criteria, but was associated with a reduction in episodes of hypocarbia.

Persistent unilateral white-out in preterm infant.

We would like to present a case of persistent right sided collapse in a preterm baby with an unexpected diagnosis. Baby X was born floppy requiring resuscitation and was intubated, ventilated and was transferred to NICU. There was decreased air entry on auscultation of right side of the chest, while the rest of the examination was normal. The chest X-ray showed right side white-out suggestive of collapse consolidation. She required significantly high ventilatory pressures to maintain saturations and chest X-ray performed on day 4 remained unchanged with persistent right sided white-out. The CT scan of the chest showed no definable right lung, right pulmonary artery or right main bronchus. The diagnosis of right lung agenesis with single pulmonary artery was made and baby was found to have more congenital malformations on further investigations, and later developed complications leading to palliative care.

Respiratory support practices in infants born at term in the United Kingdom.

Infants born at term requiring mechanical ventilation suffer significant mortality and morbidity, yet few studies have tried to identify the optimum respiratory support for such infants. We, therefore, hypothesised that practice would vary, particularly between different levels of neonatal care provision. The lead clinicians of all 212 UK neonatal units were asked to complete an electronic web-based survey regarding respiratory support practices for term-born infants. Survey questions included the level of neonatal care provided, number of term-born infants ventilated per annum, initial and rescue ventilation modes and whether surfactant or inhaled nitric oxide (NO) were used. The overall response rate was 82 %. A greater proportion of neonatal intensive care units (NICUs) compared to local neonatal units (LNUs) stated that they used volume-targeting, particularly for infants with RDS (p = 0.0006) or congenital pneumonia (p = 0.0005). High-frequency oscillatory ventilation was stated as initial mode by a greater proportion of NICUs compared to LNUs and special care units (SCUs), particularly for respiratory distress syndrome (p < 0.0001) or persistent pulmonary hypertension of the newborn (p < 0.001). Continuous mandatory ventilation was stated to be the rescue mode by a greater proportion of LNUs/SCUs compared to NICUs (p < 0.0001). Surfactant was stated to be most commonly given for respiratory distress syndrome (79 % of units) and MAS (61 % of units); surfactant use was lowest in SCUs (p < 0.0001); inhaled NO was infrequently used by LNUs and SCUs. Conclusions There was considerable variation in respiratory support practices for term-born infants, particularly between different levels of neonatal care provision.

Randomised weaning trial comparing assist control to pressure support ventilation.

OBJECTIVES: To determine if the work of breathing was lower, respiratory muscle strength greater, but the degree of asynchrony higher during weaning by assist control ventilation (ACV) rather than pressure support ventilation (PSV) and if any differences were associated with a shorter duration of weaning. DESIGN: Randomised trial SETTING: Tertiary neonatal unit PATIENTS: Thirty-six infants, median gestational age 29 (range 24 to 39) weeks INTERVENTION: Weaning by either ACV or PSV. MAIN OUTCOME MEASURES: At baseline, 24 hours after entering the study and immediately prior to extubation, the work of breathing (PTPdi), thoracoabdominal asynchrony (TAA) and respiratory muscle strength (Pimax) were assessed and weaning duration recorded. RESULTS: There were no significant differences in the median PTPdi, TAA and Pimax results at any time point. The inflation times during ACV and PSV were similar. The median duration of weaning was 34 (range 7-100) hours in the ACV group and 27 (range 10-169) hours in the PSV group (p=0.88). CONCLUSION: No significant differences were found between weaning by PSV and ACV when similar inflation times were used.

Volume-targeted ventilation in infants born at or near term.

OBJECTIVES: To determine the impact of different volume-targeted (VT) levels during volume-targeted ventilation (VTV) on the work of breathing (WOB) of infants born at or near term and to investigate whether a level of VT reduced the WOB below that experienced on respiratory support without VT. DESIGN: Prospective crossover study. PATIENTS: Sixteen infants, median gestational age of 38 (range 34-41) weeks, birth weight of 3.1 (range 1.5-4.1) kg and postnatal age of 5 (range 2-17) days were studied. The infants were receiving time-cycled, pressure-limited ventilation in a continuous mandatory or in a triggered mode. INTERVENTIONS: The infants were studied first without VT (baseline) and then at VT levels of 4, 5 and 6 ml/kg delivered in a random order. After each VT level, the infants were returned to baseline. MAIN OUTCOME MEASURE: The WOB was assessed by measuring the transdiaphragmatic pressure-time product (PTPdi). RESULTS: One infant became apnoeic at VT of 6 ml/kg. At a VT level of 4 ml/kg, four infants were making such vigorous respiratory efforts that no inflations were delivered. The median PTPdi was higher at a VT level of 4 ml/kg than at 5 ml/kg (p<0.01) or 6 ml/kg (p<0.001). Only at a VT level of 6 ml/kg was the median PTPdi lower than that at baseline (p<0.01). CONCLUSION: Low VT levels (4 ml/kg) during VTV increase the WOB in ventilated infants born at term or near term. The results suggest that a VT level of 6 ml/kg could be used to reduce the WOB.

Work of breathing and volume targeted ventilation in respiratory distress.

OBJECTIVE: To determine the level of volume targeting (VT) associated with the lowest work of breathing (WOB) for prematurely born infants being ventilated with acute respiratory distress. DESIGN: Prospective study. SETTING: Tertiary neonatal intensive care unit. PATIENTS: 18 infants, median gestational age 29 (range 25-34) weeks, being ventilated for acute respiratory distress. INTERVENTIONS: Infants were studied first without VT (baseline). Volume targeted levels of 4 ml/kg, 5 ml/kg and 6 ml/kg were then delivered in random order. After each VT level, the infants were returned to baseline. Each step was maintained for 20 minutes. MAIN OUTCOME MEASURE: The transdiaphragmatic pressure time product (PTPdi) as an estimate of the WOB. RESULTS: The mean PTPdi was higher at a VT level of 4 ml/kg (median 154 cm H(2)O·s/min) compared to baseline (median 112 cm H(2)O·s/min) (p<0.001) and a VT level of 6 ml/kg (median 89 cm H(2)O·s/min) (p<0.001). CONCLUSION: A low level of VT increased the WOB in infants with acute respiratory distress syndrome. The authors' results suggest that, during acute respiratory distress, a VT level of at least 5 ml/kg rather than a lower level might avoid an increased WOB. The most appropriate level of VT needs to be determined in a randomised controlled trial with long-term outcomes.

In vitro assessment of proportional assist ventilation.

OBJECTIVE: During proportional assist ventilation (PAV) the timing and frequency of inflations are controlled by the patient and the patient's work of breathing may be relieved by elastic and/or resistive unloading. It is important and the authors' objective to determine whether ventilators delivering PAV function well in situations mimicking neonatal respiratory conditions. DESIGN: In vitro laboratory study. SETTING: Tertiary neonatal ICU. INTERVENTIONS: Dynamic lung models were developed which mimicked respiratory distress syndrome, bronchopulmonary dysplasia and meconium aspiration syndrome to assess the performance of the Stephanie neonatal ventilator. MAIN OUTCOME MEASURES: The effects of elastic and resistive unloading on inflation pressures and airway pressure wave forms and whether increasing unloading was matched by an 'inspiratory' load reduction. RESULTS: During unloading, delivered pressures were between 1 and 4 cm H(2)O above those expected. Oscillations appeared in the airway pressure wave form when the elastic unloading was greater than 0.5 cm H(2)O/ml with a low resistance model and 1.5 cm H(2)O/ml with a high resistance model and when the resistive unloading was greater than 100 cm H(2)O/l/s. There was a time lag in the delivery of airway pressure of at least 60 ms, but increasing unloading was matched by an inspiratory load reduction. CONCLUSIONS: During PAV, unloading does reduce inspiratory load, but there are wave form abnormalities and a time lag in delivery of the inflation pressure. The impact of these problems needs careful evaluation in the clinical setting.

Neonatal abstinence syndrome--postnatal ward versus neonatal unit management.

AIM: The aim of this cohort study was to test the hypothesis that caring for infants with neonatal abstinence syndrome (NAS) with their mothers on the postnatal ward rather than admit them to the neonatal unit would reduce treatment duration and length of hospital stay. RESULTS: The outcomes of infants with NAS cared for in 2002-2005 (Group A, n = 42) and 2006-2007 (Group B, n = 18) were compared. Group A infants were admitted to the neonatal unit for assessment and treatment as necessary, but Group B infants remained on the postnatal ward with their mother. Sixty infants (median gestational age 39, range 26-42 weeks) were included in the study. The proportion of infants in Group B compared to Group A requiring treatment for NAS was lower (45% versus 11%, p = 0.012) and the durations of treatment (mean 12.7 versus 7.3 days, p = 0.05) and hospital stay (mean 19.8 versus 15.9 days, p = 0.012) were shorter in Group B. No infant in either group was readmitted within the next 2 months. CONCLUSIONS: These results suggest caring for infants with NAS on the postnatal ward rather than the neonatal unit reduces the need for treatment and duration of hospital stay.

Compliance and resistance levels and unloading in proportional assist ventilation.

During proportional assist ventilation (PAV), resistive and elastic unloading relieve the work of breathing. Excessive unloading, however, results in resonant oscillations and runaway pressures. Our aim was to determine the appropriate levels of unloading that could be applied to clinical practice. A lung model, resistance (50 or 150 cmH(2)O l(-1) s(-1)) and compliance (0.4 or 0.8 ml/cmH(2)O), was used. The volumes and airway pressures delivered by the ventilator at varying levels of resistive and elastic unloading and simulated breaths were recorded. Oscillations in airway pressure only occurred when the level of resistive unloading exceeded the model's resistance. When the level of unloading fully compensated for the model's compliance, peak inflating pressures greater than 40 cmH(2)O were delivered; peak pressure limits of 20 cmH(2)O, however, resulted in very short (0.2 s or less) inflation times. High peak pressures were not delivered if the level of elastic unloading used was limited to that which reduced the model's elastance to that of a 'normal lung'. In conclusion, these results suggest that when using PAV, it is important to assess the compliance and resistance of the infant and endotracheal tube, so that levels of unloading that fully compensate for the resistance and compliance levels can be avoided.

An in vitro assessment of gas trapping during high frequency oscillation.

Our aim was to assess the influence of oscillatory frequency, inspiratory-to-expiratory (I:E) ratio and airway pressure on gas trapping during high frequency oscillatory ventilation (HFOV). A lung model was used, which had a high compliance (4.0 ml (cmH(2)O)(-1)) and resistance (160 cmH(2)O l(-1) s(-1)) resulting in a long time constant (0.64 s). To assess whether gas trapping occurred, the mean pressure within the lung model (equivalent to alveolar pressure) was compared to the mean airway pressure (MAP) measured at the manifold (manifold MAP) of the two oscillators used, the SLE 5000 (I:E ratio 1:1) and the Sensor Medics 3100A (tested at I:E ratios of 1:2 and 1:1). The effects were assessed of raising the MAP from 15 to 35 cmH(2)O, the oscillatory amplitude from 30 to 70 cmH(2)O and the frequency from 5 to 15 Hz (5 to 20 Hz SLE only). There were no significant trends for differences between the pressure within the lung model and the 'manifold' MAP to increase (i.e. no evidence of gas trapping), as MAP, amplitude or frequency was increased, regardless of which oscillator or I:E ratio was used. Increasing the pressure amplitude led to a progressive fall in the pressure within the lung model when an I:E ratio of 1:2 was used (p < 0.05). Our results suggest that significant gas trapping does not occur during HFOV even if there is high compliance and resistance.