Risha Bhatia

Effect of sustained inflation vs. stepwise PEEP strategy at birth on gas exchange and lung mechanics in preterm lambs.

Background:Sustained inflation (SI) at birth facilitates establishment of functional residual capacity (FRC) in the preterm lung, but the ideal lung recruitment strategy is unclear. We have compared the effect of SI and a stepwise positive end-expiratory pressure (PEEP; SEP) strategy in a preterm model.Methods:127 d gestation lambs received either 20-s SI (n = 9) or 2 cmH2O stepwise PEEP increases to 20 cmH2O every 10 inflations, and then decreases to 6 cmH2O (n = 10). Ventilation continued for 70 min, with surfactant administered at 10 min. Alveolar–arterial oxygen gradient (AaDO2), compliance (Cdyn), end-expiratory thoracic volume (EEVRIP; respiratory inductive plethysmography), and EEV and Cdyn in the gravity-dependent and nondependent hemithoraces (electrical impedance tomography) were measured throughout. Early mRNA markers of lung injury were analyzed using quantitative real-time PCR.Results:From 15 min of life, AaDO2 was lower in SEP group (P < 0.005; two-way ANOVA). SEP resulted in higher and more homogeneous Cdyn (P < 0.0001). Mean (SD) EEVRIP at 5 min was 18 (9) ml/kg and 6 (5) ml/kg following SEP and SI, respectively (P = 0.021; Bonferroni posttest); this difference was due to a greater nondependent hemithorax EEV. There was no difference in markers of lung injury.Conclusion:An SEP at birth improved gas exchange, lung mechanics, and EEV, without increasing lung injury, compared to the SI strategy used.

Surfactant before the first inflation at birth improves spatial distribution of ventilation and reduces lung injury in preterm lambs

The interrelationship between the role of surfactant and a sustained inflation (SI) to aid ex utero transition of the preterm lung is unknown. We compared the effect of surfactant administered before and after an initial SI on gas exchange, lung mechanics, spatial distribution of ventilation, and lung injury in preterm lambs. Gestational-age lambs (127 days; 9 per group) received 100 mg/kg of a surfactant (Curosurf) either prior (Surf+SI) or 10 min after birth (SI+Surf). At birth, a 20-s, 35 cmH2O SI was applied, followed by 70 min of positive pressure ventilation. Oxygenation, carbon dioxide removal, respiratory system compliance, end-expiratory thoracic volume (via respiratory inductive plethysmography), and distribution of end-expiratory volume and ventilation (via electrical impedance tomography) were measured throughout. Early markers of lung injury were analyzed using quantitative RT-PCR. During the first 15 min, oxygenation, carbon dioxide removal, and compliance were better in the Surf+SI group (all P < 0.05). End-expiratory volume on completion of the sustained inflation was higher in the Surf+SI group than the SI+Surf group; 11 ± 1 ml/kg vs. 7 ± 1 ml/kg (mean ± SE) (P = 0.043; t-test), but was not different at later time points. Although neither achieved homogenous aeration, spatial ventilation was more uniform in the Surf+SI group throughout; 50.1 ± 10.9% of total ventilation in the left hemithorax at 70 min vs. 42.6 ± 11.1% in the SI+Surf group. Surf+SI resulted in lower mRNA levels of CYR61 and EGR1 compared with SI+Surf (P < 0.001, one-way ANOVA). Surfactant status of the fetal preterm lung at birth influences the mechanical and injury response to a sustained inflation and ventilation by changing surface tension of the air/fluid interface.

Pressure-limited sustained inflation vs. gradual tidal inflations for resuscitation in preterm lambs

Support of the mechanically complex preterm lung needs to facilitate aeration while avoiding ventilation heterogeneities: whether to achieve this gradually or quickly remains unclear. We compared the effect of gradual vs. constant tidal inflations and a pressure-limited sustained inflation (SI) at birth on gas exchange, lung mechanics, gravity-dependent lung volume distribution, and lung injury in 131-day gestation preterm lambs. Lambs were resuscitated with either 1) a 20-s, 40-cmH2O pressure-limited SI (PressSI), 2) a gradual increase in tidal volume (Vt) over 5-min from 3 ml/kg to 7 ml/kg (IncrVt), or 3) 7 ml/kg Vt from birth. All lambs were subsequently ventilated for 15 min with 7 ml/kg Vt with the same end-expiratory pressure. Lung mechanics, gas exchange and spatial distribution of end-expiratory volume (EEV), and tidal ventilation (electrical impedance tomography) were recorded regularly. At 15 min, early mRNA tissue markers of lung injury were assessed. The IncrVt group resulted in greater tissue hysteresivity at 5 min (P = 0.017; two-way ANOVA), higher alveolar-arterial oxygen difference from 10 min (P < 0.01), and least uniform gravity-dependent distribution of EEV. There were no other differences in lung mechanics between groups, and the PressSI and 7 ml/kg Vt groups behaved similarly throughout. EEV was more uniformly distributed, but Vt least so, in the PressSI group. There were no differences in mRNA markers of lung injury. A gradual increase in Vt from birth resulted in less recruitment of the gravity-dependent lung with worse oxygenation. There was no benefit of a SI at birth over mechanical ventilation with 7 ml/kg Vt.

Oxygen delivery using neonatal self-inflating resuscitation bags without a reservoir

Background Guidelines recommend avoidance of excessive oxygen administration during neonatal resuscitation. Blenders are used in some but not all hospitals. It has been suggested that self-inflating bags without a reservoir deliver around 40% oxygen and could be used to provide an inexpensive and effective technique of avoiding oxygen toxicity. Objective To explore how much oxygen is delivered when using two different brands of neonatal self-inflating resuscitation bags without a reservoir. Methods In a benchtop setting, the smallest non-disposable self-inflating bags from the Laerdal and Ambu ranges were tested. Oxygen concentration delivered by these devices under a variety of conditions was measured. 108 combinations of oxygen flow rates (10; 5 to 1 litre/min), ventilation rates (30, 60, 100 inflations/min) and peak inspiratory pressure ranges (20 to 25 cm H2O, 35 to 40 cm H2O or pop-off valve range, 55 to 60 cm H2O) were tested. Results Delivered oxygen concentration varied depending on three parameters: gas flow rate, ventilatory rate and pressure. At a pressure of 20 to 25 cm H2O, mean oxygen concentration delivered by both bags exceeded 70% at any gas flow rate except for 1 litre/min (where delivered oxygen concentration was 60% to 70%). When the pop-off valve was opened at 35 to 40 cm H20, oxygen concentrations fell to 30% to 45% at gas flow rates ≤2 litres/min. The Ambu bag delivered a lower oxygen concentration than the Laerdal bag but this difference was not clinically important. Conclusion When using the Laerdal and Ambu infant resuscitation self-inflating bags without a reservoir, delivered oxygen concentration is >70% for currently recommended flow and pressure settings.

Optimal mean airway pressure during high-frequency oscillatory ventilation determined by measurement of respiratory system reactance

Background:The aims of the present study were (i) to characterize the relationship between mean airway pressure (PAW) and reactance measured at 5 Hz (reactance of the respiratory system (XRS), forced oscillation technique) and (ii) to compare optimal PAW (Popt) defined by XRS, oxygenation, lung volume (VL), and tidal volume (VT) in preterm lambs receiving high-frequency oscillatory ventilation (HFOV).Methods:Nine 132-d gestation lambs were commenced on HFOV at PAW of 14 cmH2O (Pstart). PAW was increased stepwise to a maximum pressure (Pmax) and subsequently sequentially decreased to the closing pressure (Pcl, oxygenation deteriorated) or a minimum of 6 cmH2O, using an oxygenation-based recruitment maneuver. XRS, regional VL (electrical impedance tomography), and VT were measured immediately after (t0min) and 2 min after (t2min) each PAW decrement. Popt defined by oxygenation, XRS, VL, and VT were determined.Results:The PAW–XRS and PAW–VT relationships were dome shaped with a maximum at Pcl+6 cmH2O, the same point as Popt defined by VL. Below Pcl+6 cmH2O, XRS became unstable between t0min and t2min and was associated with derecruitment in the dependent lung. Popt, as defined by oxygenation, was lower than the Popt defined by XRS, VL, or VT.Conclusion:XRS has the potential as a bedside tool for optimizing PAW during HFOV.

Effect of closed endotracheal tube suction method, catheter size, and post-suction recruitment during high-frequency jet ventilation in an animal model.

High‐frequency jet ventilation (HFJV) is often used to treat infants with pathologies associated with gas trapping and abnormal lung mechanics, who are sensitive to the adverse effects of suction.

A Comparison of Different Bedside Techniques to Determine Endotracheal Tube Position in a Neonatal Piglet Model

Endotracheal tube (ETT) malposition is common and an increasing number of non‐invasive techniques to aid rapid identification of tube position are available. Electrical impedance tomography (EIT) is advocated as a tool to monitor ventilation.

Choice of flow meter determines pressures delivered on a T-piece neonatal resuscitator.

Using a Neopuff Infant Resuscitator (Fisher & Paykel Healthcare, Auckland, New Zealand), Hawkes et al 1 showed that a peak inflating pressure (PIP) >100 cm H2O can be delivered with a flow meter at maximum flow. We tested five flow meters to determine the pressures delivered at different flow rates. Gas flow was analysed using the Timeter RT-200 Flow Analyser (Timeter-Instruments, St Louis, Missouri, USA). Each flow meter was tested connected to a wall oxygen outlet or a low-flow air/oxygen blender (Cardinal Health, Ohio, USA). Positive pressure ventilation was given to a leak-free test lung using a Neopuff. Neopuff set to PIP 20 cm H2O, …

Phototherapy in transport for neonates with unconjugated hyperbilirubinaemia.

In Victoria, neonates with severe unconjugated hyperbilirubinaemia at risk of requiring exchange transfusion are retrieved by the Paediatric Infant Perinatal Emergency Retrieval Service and transferred to a Neonatal Intensive Care Unit where an exchange transfusion can be performed if necessary. Transfer may result in prolonged periods without phototherapy in neonates at risk of developing bilirubin encephalopathy. We aimed to describe our experience of the introduction of phototherapy using a portable phototherapy unit during transport.

Neonatal Resuscitation in Resource-Limited Settings: Titrating Oxygen Delivery without an Oxygen Blender

OBJECTIVE To test whether 4 commonly used self-inflating bags with a reservoir in situ can reliably deliver different oxygen concentrations (21%-100%) using a portable oxygen cylinder with flows of ≤5 L/min. STUDY DESIGN Four self-inflating bags (from Laerdal, Ambu, Parker Healthcare, and Mayo Healthcare) were tested to provide positive pressure ventilation to a manikin at 60 inflations/min by 4 operators. Oxygen delivery was measured for 2 minutes, combining oxygen flows (0.25, 0.5, 1, 5 L/min) and peak inspiratory pressures (PIPs 20-25, 35-40 cmH2O). RESULTS Combinations (n=128) were performed twice. Oxygen delivery depended upon device, oxygen flow, and PIP. All self-inflating bags delivered mean oxygen concentrations of <40% with 0.25 L/min, regardless of PIP. Three self-inflating bags delivered ≤40% with flow 0.5 L/min at PIP 35-40 cmH2O, whereas all delivered >40% at PIP 20-25 cmH2O. With 1 L/min, 3 self-inflating bags delivered 40%-60% at PIP 35-40 cmH2O and all delivered >60% at PIP 20-25 cmH2O. With 5 L/min, all self-inflating bags delivered close to or 100%, regardless of PIP. Differences in oxygen delivery between self-inflating bags were statistically significant (P<.001) even when differences were not clinically important. CONCLUSION Self-inflating bags with a reservoir in situ can deliver a variety of oxygen concentrations without a blender, from <40% with 0.25 L/min oxygen flow to 100% with 5 L/min. The adjustment of oxygen flow may be a useful method of titrating oxygen in settings where air-oxygen blenders are unavailable.