Georg M. Schmölzer

Assessment of tidal volume and gas leak during mask ventilation of preterm infants in the delivery room

Aim The aim was to compare resuscitators estimates of tidal volume (VT) and face mask leak with measured values during positive pressure ventilation (PPV) of newborn infants in the delivery room. Patients and methods The authors measured inflating pressures and VT delivered using a respiratory function monitor, and calculated face mask leak. After 60 s of PPV, resuscitators were asked to estimate VT and face mask leak. These estimates were compared with measurements taken during the previous 30 s. Results The authors studied 20 infants who received a mean (SD) of 21 (6) inflations during the 30 s. The median (IQR) expired tidal volume (VTe) delivered was 8.7 ml/kg (5.3–11.3). VTe varied widely during each resuscitation and between resuscitators. Five resuscitators could not estimate VTe, one overestimated and 14 underestimated their median delivered VTe. The median (IQR) face mask leak was 29% (16–63%). Leak also varied widely during each resuscitation and between resuscitators. One resuscitator could not estimate mask leak, four overestimated leak and 15 underestimated leak. Conclusion During face mask ventilation in the delivery room, VT and face mask leak were large and variable. The resuscitators were unable to accurately assess their face mask leak or delivered VT.

Reducing lung injury during neonatal resuscitation of preterm infants.

Neonatologists are familiar with the concept of ventilator-induced lung injury (VILI) 1,2 and are increasingly careful in the neonatal intensive care unit (NICU) to apply positive-pressure ventilation (PPV) strategies that are gentle to the lungs. 3 Although PPV also is commonly used in the delivery room (DR), clinicians appear less aware that the same gentle approach should be applied to reduce lung injury during the first few minutes of life. To achieve adequate gas exchange after delivery, lung fluid is cleared and replaced with air, and functional residual capacity (FRC) is established. Mechanical ventilation requires an appropriate minute volume to achieve adequate gas exchange. Clinical signs are used to evaluate the response to ventilation during neonatal resuscitation. The tidal volume (V T ) delivered is rarely measured; thus, airway pressure is not adjusted to optimize V T and reduce volutrauma or underventilation. 4,6 The use of end-expiratory pressure, considered essential to avoid lung injury in the NICU, is still not uniformly applied in the DR. PPV may cause lung injury through various mechanisms, including high airway pressure (barotrauma), high V T and overdistention (volutrauma), repeated alveolar collapse and reexpansion (atelectrauma), and infection and inflammation (bio-trauma).1 These injuries cause leakage of proteinaceous fluid and blood into the airways, alveoli, and lung interstitium, inhibiting surfactant function, interfering with lung mechanics, and contributing to lung injury.1 In this review, we describe what is known about the causes of neonatal lung injury, based on animal and human research. Although human data are scanty, and randomized control trials are needed, we suggest ways in which current practice might be changed to help minimize lung injury during neonatal resuscitation.

Airway obstruction and gas leak during mask ventilation of preterm infants in the delivery room

Introduction Preterm infants with inadequate breathing receive positive pressure ventilation (PPV) by mask with variable success. The authors examined recordings of PPV given to preterm infants in the delivery room for prevalence of mask leak and airway obstruction. Methods and patients The authors reviewed recordings of infants at <32 weeks gestation born between February 2006 and March 2009. PPV was delivered with a T-piece or self-inflating bag and a round silicone face mask. Airway pressures and gas flow were recorded with a respiratory function monitor (RFM). Videos recorded from a web camera were used to review the resuscitation. The first 2 min of PPV were analysed for each infant. Obstruction was arbitrarily defined as a 75% reduction in delivered expired tidal volume (VTe) and significant face-mask leak as >75%. Results The authors analysed recordings of 56 preterm infants. Obstruction occurred in 14 (26%) recordings and leaks in 27 (51%). Both obstruction and mask leaks were seen in eight (14%) recordings, and neither was seen in 15 (27%). Obstruction occurred at a median (IQR) of 48 (24–60) s after the start of PPV. A median (range) of 22 (3–83) consecutive obstructed inflations were delivered. Face-mask leaks occurred from the first inflation in 19/27 (70%) and in the remaining eight at a median (IQR) of 30 (24–46) s after the start of PPV. A median (range) of 10 (3–117) consecutive inflations with a leak >75% were delivered. Conclusion Airway obstruction and face-mask leak are common during the first 2 min of PPV. An RFM enables detection of important airway obstruction and mask leak.

Respiratory monitoring of neonatal resuscitation

Video observations and recordings of respiratory signals from mannequin studies and delivery room (DR) resuscitations are described. This article discusses the uses of a respiratory function monitor (RFM) during training and resuscitations along with potential pitfalls and limitations. It adds objectivity to the clinical assessment. A respiratory function monitor provides real-time quantitative information including tidal volume and leak. It may be used to teach correct mask hold and positioning techniques during simulation-based mannequin. Examples demonstrating its potential usefulness during resuscitations are provided. However, further studies are needed to investigate whether it can help improve short-term and long-term outcomes.

Effect of sustained inflation duration; resuscitation of near-term asphyxiated lambs

Objective The 2010 ILCOR neonatal resuscitation guidelines do not specify appropriate inflation times for the initial lung inflations in apnoeic newborn infants. The authors compared three ventilation strategies immediately after delivery in asphyxiated newborn lambs. Design Experimental animal study. Setting Facility for animal research. Subjects Eighteen near-term lambs (weight 3.5–3.9 kg) delivered by caesarean section. Interventions Asphyxia was induced by occluding the umbilical cord and delaying ventilation onset (10–11 min) until mean carotid blood pressure (CBP) was ≤22 mm Hg. Animals were divided into three groups (n=6) and ventilation started with: (1) inflation times of 0.5 s at a ventilation rate 60/min, (2) five 3 s inflations or (3) a single 30 s inflation. Subsequent ventilation used inflations at 0.5 s at 60/min for all groups. Main outcome measures Times to reach a heart rate (HR) of 120 bpm and a mean CBP of 40 mm Hg. Secondary outcome was change in lung compliance. Results Median time to reach HR 120 bpm and mean CBP 40 mm Hg was significantly shorter in the single 30 s inflation group (8 s and 74 s) versus the 5×3 s inflation group (38 s and 466 s) and the conventional ventilation group (64 s and 264 s). Lung compliance was significantly better in the single 30 s inflation group. Conclusion A single sustained inflation of 30 s immediately after birth improved speed of circulatory recovery and lung compliance in near-term asphyxiated lambs. This approach for neonatal resuscitation merits further investigation.

Expired CO2 Levels Indicate Degree of Lung Aeration at Birth

As neonatal resuscitation critically depends upon lung aeration at birth, knowledge of the progression of this process is required to guide ongoing care. We investigated whether expired CO2 (ECO2) levels indicate the degree of lung aeration immediately after birth in two animal models and in preterm infants. Lambs were delivered by caesarean section and ventilated from birth. In lambs, ECO2 levels were significantly (p<0.0001) related to tidal volumes and CO2 clearance/breath increased exponentially when tidal volumes were greater than 6 mL/kg. Preterm (28 days of gestation; termu200a=u200a32 days) rabbits were also delivered by caesarean section and lung aeration was measured using phase contrast X-ray imaging. In rabbit kittens, ECO2 levels were closely related (p<0.001) to lung volumes at end-inflation and were first detected when ∼7% of the distal lung regions were aerated. ECO2 levels in preterm infants at birth also correlated with tidal volumes. In each infant, ECO2 levels increased to >10 mmHg 28 (median) (21–36) seconds before the heart rate increased above 100 beats per minute. These data demonstrate that ECO2 levels can indicate the relative degree of lung aeration after birth and can be used to clinically assess ventilation in the immediate newborn period.

Heart rate changes during resuscitation of newly born infants <30 weeks gestation: an observational study

The International Liaison Committee on Resuscitation recommends starting positive pressure ventilation (PPV) in the delivery room when heart rate (HR) <100 beats per min (bpm) and giving cardiac compressions when HR <60 bpm. Objective To describe the effect of PPV on HR in infants <30 weeks gestation with HR <100 bpm in the first minutes after birth. Study design Retrospective observational study of infants, <30 weeks gestation, born between 14 February 2007 and 28 February 2009 with HR <100 bpm soon after birth. Methods Infants with a HR <100 bpm receiving PPV at birth were eligible for the study. Video recordings and respiratory physiological data were obtained during delivery room resuscitation and analysed to determine if the rate of change in HR varied with measures of PPV, for example, expiratory tidal volume. Results It took a median (IQR) 73 (24–165) seconds of PPV for infants HR to rise above 100 bpm and a median (IQR) 243 (191–351) seconds to rise above 120 bpm. There were large fluctuations in HR after reaching 100 bpm and before reaching 120 bpm. In 18/27 (67%) of infants the HR did not remain stable until a threshold of approximately 150 bpm was reached. In 6/27 (20%) of the infants the rise in HR was almost instantaneous. In the remaining 21/27 (80%) HR rise was more gradual. There was a poor correlation between time of HR increase to 120 bpm and tidal volume (p=0.13). Conclusion It takes more than a minute for newly born infants <30 weeks gestation with a HR <100 bpm to achieve a HR above 100 bpm. In these infants HR does not stabilise until it reaches 120 bpm.

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.

Electrical impedance tomography can rapidly detect small pneumothoraces in surfactant-depleted piglets.

PurposeDiagnosis of pneumothorax relies on clinical suspicion and chest X-ray, and is often delayed. We aimed to determine whether electrical impedance tomography (EIT) can accurately identify the presence of surgically created pneumothoraces before significant changes in clinical parameters.MethodsSix anesthetized and muscle-relaxed piglets with surfactant-depleted lungs were studied. Following chest drain insertion into the right ventral chest, 10–20xa0ml aliquots of air were instilled into the pleural space to a maximum volume of 200xa0ml. The pneumothorax was drained by attaching a Heimlich valve to the chest drain. At each instillation and after draining the pneumothorax, global and regional end-expiratory intra-thoracic volumes (EEV) were measured using respiratory inductive plethysmography (RIP) and EIT concurrently with