From liquid to air: breathing after birth

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 (X RS), forced oscillation technique) and (ii) to compare optimal PAW (P opt) defined by X RS, 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 (P start). PAW was increased stepwise to a maximum pressure (P max) and subsequently sequentially decreased to the closing pressure (Pcl, oxygenation deteriorated) or a minimum of 6 cmH2O, using an oxygenation-based recruitment maneuver. X RS, regional V L (electrical impedance tomography), and V T were measured immediately after (t 0 min) and 2 min after (t 2 min) each PAW decrement. P opt defined by oxygenation, X RS, V L, and V T were determined.

RESULTS

The PAW-X RS and PAW-VT relationships were dome shaped with a maximum at Pcl+6 cmH2O, the same point as P opt defined by VL. Below Pcl+6 cmH2O, X RS became unstable between t 0 min and t 2 min and was associated with derecruitment in the dependent lung. P opt, as defined by oxygenation, was lower than the P opt defined by X RS, V L, or V T.

CONCLUSION

X RS has the potential as a bedside tool for optimizing PAW during HFOV.

Noninvasive measurements of hemodynamic transition directly after birth

BACKGROUND

Cardiac output depends on stroke volume and heart rate (HR). Only HR is used to monitor hemodynamic transition.

METHODS

In 24 term newborns born via cesarean section, HR and preductal blood pressure (BP) were measured. Also, using echocardiography, left ventricular dimensions and (Doppler derived) left ventricular output (LVO) were examined at 2, 5, and 10 min after birth.

RESULTS

Mean (SD) HR and BP did not change with time (mean HR: 157 (21) bpm at 2 min, 154 (17) bpm at 5 min, and 155 (14) bpm at 10 min; mean BP: 51.2 (15.4) mm Hg at 2 min, 50.5 (11.7) mm Hg at 5 min, and 49.6 (9.5) mm Hg at 10 min). Left ventricular end-diastolic diameter increased from 2 to 5 min (14.3 (1.3) vs. 16.3 (1.7) mm; P < 0.001) and stabilized at 10 min (16.7 (1.4) mm). LVO increased between 2 and 5 min (151 (47) vs. 203 (55) ml/kg/min; P < 0.001) and stabilized at 10 min (201 (45) ml/kg/min). LVO increase was associated with rise in left ventricular stroke volume (r = 0.94; P < 0.001), not with rise in HR (r = 0.37; P value not significant).

CONCLUSION

Left ventricular dimensions and LVO significantly increased the first 5 min after birth and stabilized at 10 min, whereas BP remained stable. LVO and left ventricular dimension increase are presumably due to increasing left ventricular preload resulting from pulmonary blood flow and ductal shunting increase.

Ventilation before Umbilical Cord Clamping Improves the Physiological Transition at Birth

The transition from a fetus to a neonate at birth represents a critical phase in our life. Most infants make this transition without complications, but preterm infants usually require some form of assistance due to immature cardiopulmonary systems that predispose them to lifelong sequelae. As the incidence of preterm birth is increasing, there is now an urgent need for the development of management strategies that facilitate this transition, which will likely include improved strategies for the management of the maternal third stage of labor. For instance, recent studies on the physiological transition at birth have led to the discovery that establishing ventilation in the infant before the umbilical cord is clamped greatly stabilizes the cardiovascular transition at birth. While most benefits of delayed clamping previously have been attributed to an increase in placenta to infant blood transfusion, clearly there are other significant benefits for the infant, which are not well understood. Nevertheless, if ventilation can be established before cord clamping in a preterm infant, the large adverse changes in cardiac function that normally accompanies umbilical cord clamping can be avoided. As preterm infants have an immature cerebral vascular bed, large swings in cardiovascular function places them at high risk of cerebral vascular rupture and the associated increased risk of mortality and morbidity. In view of the impact that cord clamping has on the cardiovascular transition at birth, it is also time to re-examine some of the strategies used in the management of the third stage of labor. These include the appropriate timing of uterotonic administration in relation to delivery of the infant and placenta. As there is a lack of evidence on the effects these individual practices have on the infant, there is a necessity to improve our understanding of their impact in order to develop strategies that facilitate the transition to newborn life.

Measuring physiological changes during the transition to life after birth

The transition to life after birth is characterized by major physiological changes in respiratory and hemodynamic function, which are predominantly initiated by breathing at birth and clamping of the umbilical cord. Lung aeration leads to the establishment of functional residual capacity, allowing pulmonary gas exchange to commence. This triggers a significant decrease in pulmonary vascular resistance, consequently increasing pulmonary blood flow and cardiac venous return. Clamping the umbilical cord also contributes to these hemodynamic changes by altering the cardiac preload and increasing peripheral systemic vascular resistance. The resulting changes in systemic and pulmonary circulation influence blood flow through both the oval foramen and ductus arteriosus. This eventually leads to closure of these structures and the separation of the pulmonary and systemic circulations. Most of our knowledge on human neonatal transition is based on human (fetal) data from the 1970s and extrapolation from animal studies. However, there is renewed interest in performing measurements directly at birth. By using less cumbersome techniques (and probably more accurate), our previous understanding of the physiological transition at birth is challenged, as well as the causes and consequences for when this transition fails to progress. This review will provide an overview of physiological measurements of the respiratory and hemodynamic transition at birth. Also, it will give a perspective on some of the upcoming technological advances in physiological measurements of neonatal transition in infants who are unable to make the transition without support.

Establishing functional residual capacity in the non-breathing infant

The transition to newborn life critically depends upon lung aeration and the onset of air-breathing, which triggers major cardiovascular changes required for postnatal life, including increases in pulmonary blood flow. Recent imaging studies indicate that lung aeration and functional residual capacity (FRC) recruitment results from inspiratory efforts, which create transpulmonary pressure gradients. During inspiration, these pressure gradients drive airway liquid movement through the conducting and into the distal airways where it crosses the pulmonary epithelium and enters the surrounding tissue. Although this process can occur rapidly (within 3-5 breaths), liquid clearance from lung tissue is much slower, resulting in oedema and increased interstitial tissue pressures, facilitating liquid re-entry into the airways at FRC. Whereas this liquid may be cleared during the next inspiration, liquid re-entry at FRC can be opposed by Na(+) reabsorption, oncotic pressures and expiratory braking manoeuvres. Recognition that transpulmonary pressure gradients mainly drive airway liquid clearance at birth has provided a clearer understanding of how this process may be facilitated in very preterm infants. In particular, it underpins the rationale for providing respiratory support that initially focuses on moving liquid through tubes (airways) rather than air. As the viscosity of liquid is much greater than air, the resistance to moving liquid is ≈ 100 times greater than air, necessitating the use of higher pressures or longer inflation times. Although it is unclear how this strategy could be safely applied clinically, it is clear that end-expiratory pressures are required to create and maintain FRC in preterm infants.

Mask ventilation of preterm infants in the delivery room

OBJECTIVE

To measure tidal volumes (VT) and describe the interactions between spontaneous breaths and positive pressure ventilation (PPV) inflations during stabilisation of preterm infants in the delivery room (DR). We used a respiratory function monitor (RFM) to evaluate the first 5 min of mask respiratory support provided to preterm infants.

STUDY DESIGN

An observational study of infants <32 weeks gestation, born in a single tertiary perinatal centre receiving mask PPV in the DR. PPV was delivered with a round silicone facemask connected to a T-piece device and RFM. The RFM display was not visible to the resuscitator. Respiratory function parameters in the first 5 min after birth were analysed by breath-type (inflations, assisted inflations, spontaneous breaths between PPV, and breaths during continuous positive airway pressure (CPAP)). Parameters measured included VT, peak inspiratory pressure, peak end expiratory pressure and mask leak.

RESULTS

A total of 2605 inflations and breaths from 29 subjects were analysed. Substantial leak was observed during all four breath types with median leaks ranging from 24% to 59%. Median tidal volumes were greater during inflations (8.3 ml/kg) and assisted inflations (9.3 ml/kg) than spontaneous breaths between PPV (3.2 ml/kg) and breaths during CPAP (3.3 ml/kg).

CONCLUSIONS

Facemask leak is large during resuscitation of preterm infants using round silicone masks. Tidal volumes delivered during PPV inflations are much higher than those generated during spontaneous breathing by an infant on CPAP.

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; term = 32 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.

Establishing lung gas volumes at birth: interaction between positive end-expiratory pressures and tidal volumes in preterm rabbits

BACKGROUND

We investigated the effects of positive end-expiratory pressure (PEEP) and tidal volume (VT) on lung aeration, pulmonary mechanics, and the distribution of ventilation immediately after birth using a preterm rabbit model.

METHODS

Sixty preterm rabbits (27 d) received volume-targeted positive pressure ventilation from birth, with one of the 12 combinations of PEEP (0, 5, 8, or 10 cm H2O) and VT (4, 8, or 12 ml/kg). Outcomes included functional residual capacity (FRC), peak inflating pressure (PIP), dynamic compliance (Cd), and distribution of ventilation.

RESULTS

Increasing PEEP from 0 to 10 cm H2O increased FRC by 4 ml/kg, increased Cd by 0.2 ml/kg/cm H2O, and reduced PIP by 5 cm H2O. Increasing VT from 4 to 12 ml/kg increased FRC by 2 ml/kg, increased Cd by 0.3 ml/kg/cm H2O, and increased PIP by 4 cmH2O. No effect of VT on FRC occurred at 0 or 5 PEEP, and no effect of PEEP occurred at VT = 4 ml/kg. At 0 PEEP, increasing VT increased the proportion of gas entering the smaller apical regions, whereas at 10 PEEP, increasing VT increased the proportion of gas entering basal regions, from 47% to 63%.

CONCLUSION

Both PEEP and VT have independent, additive effects on FRC, lung mechanics, and the distribution of ventilation during the immediate newborn period.

Do we deliver the pressures we intend to when using a T-piece resuscitator?

Background

A T-piece resuscitator (TPR) uses a built-in manometer to set the inflation pressures, but we are not informed what pressures are actually delivered distally. Aim of this study was to measure the proximal and distal pressures under different gas conditions when using a TPR.

Methodology/Findings

A test lung was ventilated using a TPR (PIP 25 cmH₂O, PEEP 5 cmH₂O) with a gas flow rate of 8 L/min. A) Pressure delivered by six different TPRs was tested. To test variability 20 participants were asked to set PEEP and PIP pressures to 25/5 cmH₂O. B) PIP and PEEP were measured proximal and distal of the TPR when using standard tubing or heated tubing with or without a humidifier. In experiment A mean (SD) proximal PIP and PEEP of the TPRs were respectively 20.3 (0.3) cmH₂O (19.9–20.6 cmH₂O) and 4.9 (0.1) cmH₂O. When 20 participants set pressures; PIP 26.7 (0.5) cm H₂O and PEEP 5.9 (0.44) cmH₂O were measured. Experiment B showed that the decrease of PIP between proximal and distal pressures was not clinically significant. However there was a significant decrease of PEEP using the standard tubing (5.1 (0.1) cmH₂O proximally versus 4.8 (0.2) cmH₂O distally; p<0.001) compared to, when using a humidifier with associated tubing and the humidifier turned on, 5.1 (0.1) proximally versus 3.9 (0.2) cmH₂O distally; (p<0.001).

Conclusion/Significance

The accuracy of the built-in manometer of a TPR is acceptable. Most pressures set proximally are comparable to the actual pressures delivered distally. However, when using tubing associated with the humidifier PEEP decreases distally by 1.1–1.2 cmH₂O and users should anticipate on this.

The role of lung inflation and sodium transport in airway liquid clearance during lung aeration in newborn rabbits

BACKGROUND

Recent phase-contrast X-ray imaging studies suggest that inspiration primarily drives lung aeration and airway liquid clearance at birth, which questions the role of adrenaline-induced activation of epithelial sodium channels (ENaCs). We hypothesized that pressures generated by inspiration have a greater role in airway liquid clearance than do ENaCs after birth.

METHODS

Rabbit pups (30 d of gestation) were delivered and sedated, and 0.1 ml of saline (S) or amiloride (Am; an ENaC inhibitor) was instilled into the lungs before mechanical ventilation. Two other groups (30 d of gestation) were treated similarly but were also given adrenaline (S/Ad and Am/Ad) before mechanical ventilation.

RESULTS

Amiloride and adrenaline did not affect functional residual capacity (FRC) recruitment (P > 0.05). Amiloride increased the rate of FRC loss between inflations (Am: -5.2 ± 0.6 ml/kg/s), whereas adrenaline reduced the rate of FRC loss (S/Ad: -1.9 ± 0.3 ml/kg/s) as compared with saline-treated controls (S: -3.5 ± -0.6 ml/kg/s; P < 0.05).

CONCLUSION

These data indicate that inspiration is a major determinant of airway liquid clearance and FRC development during positive pressure ventilation. Although ENaC inhibition and adrenaline administration had no detectable effect on FRC development, ENaC may help to prevent liquid from re-entering the airways during expiration.

Noninvasive Monitoring during Interhospital Transport of Newborn Infants

The main indications for interhospital neonatal transports are radiographic studies (e.g., magnet resonance imaging) and surgical interventions. Specialized neonatal transport teams need to be skilled in patient care, communication, and equipment management and extensively trained in resuscitation, stabilization, and transport of critically ill infants. However, there is increasing evidence that clinical assessment of heart rate, color, or chest wall movements is imprecise and can be misleading even in experienced hands. The aim of the paper was to review the current evidence on clinical monitoring equipment during interhospital neonatal transport.

Antibiotic use in newborns with transient tachypnea of the newborn

BACKGROUND

Initiation of empiric antibiotic treatment for possible early-onset sepsis is recommended for late preterm and term neonates with respiratory distress. There is no evidence base to this approach.

OBJECTIVES

To determine the incidence of adverse infectious events in neonates with transient tachypnea of the newborn (TTN) managed with a risk-factor-based restrictive antibiotic use policy.

METHODS

This is a single institution retrospective cohort study of neonates with primary diagnosis of TTN between 2004 and 2010. The relationship between antibiotic exposure and infectious outcomes during the neonatal hospitalization was evaluated. An infectious outcome was defined as pneumonia, bacteremia, clinical sepsis, or death. Analysis included t test, χ(2) test, and analysis of variance as appropriate.

RESULTS

745 neonates with TTN met inclusion criteria. None of the 494 antibiotic-naive infants, and 212 of the 251 antibiotic-exposed infants had identifiable risk factors for sepsis. No infectious outcomes occurred in infants who did not receive antibiotics. Eight neonates with TTN received full antibiotic treatment for early-onset sepsis. Each was appropriately identified for early receipt of antibiotics based on historical or clinical risk factors for early-onset sepsis.

CONCLUSIONS

This study suggests that empiric postnatal antibiotic treatment may not be warranted for late preterm and term infants with TTN in the absence of specific infectious risk factors.

Influence of the hand squeeze and mask distensibility on tidal volume measurements during neonatal mask ventilation

BACKGROUND

During mask ventilation, the mask volume can vary as it is pressurized or when it is squeezed. The change in volume of the mask may affect tidal volumes delivered and difference in inspired (Vti) and expired tidal volumes (Vte).

OBJECTIVES

To investigate whether hand squeeze and distensibility of the mask during ventilation influences tidal volume measurements.

METHODS

For both experiments, we ventilated a leak-free mask ventilation model using pressures of 25/5 cm H2O through a t-piece. Vti and Vte were measured. (A) Two consultants performed mask ventilation with (1) consistent hand squeeze, (2) release during inflation and squeeze during expiration, (3) squeeze during inflation, release during expiration, and (4) gentle squeeze.

RESULTS

(B) Thirty caregivers performed mask ventilation. Experiment A: Vti was different during consistent hold (1) 8.1 ml (0.4) and loose grip (4) 8.2 ml (0.3), compared to squeezing during inflation (2) 18.9 ml (1.9), or expiration (3) 6.4 ml (3.5). Variance in difference between Vti and Vte occurred only when the mask was squeezed during inflation (-47.4% (101.5)). Experiment B: volumes measured were consistent (intraindividual CV 3-5%, interindividual CV 9-10%). When comparing gas flow rate of 6-10 l/min, volumes increased by approximately 8%, differences in Vti and Vte were small with both flow settings (-0.9% (-3.9-1.4) and -0.6% (-3.3-1.8); n.s.).

CONCLUSION

Variation in mask hold during mask ventilation can influence volume measurement, but this hardly occurs when testing caregivers.

New concepts in neonatal resuscitation

PURPOSE OF REVIEW

There has been a substantial increase in the number of studies of neonatal resuscitation and it is timely to review the accumulating evidence.

RECENT FINDINGS

There have been major changes in the way that newly born infants are managed in the delivery room. Colour is no longer recommended as a useful indicator of oxygenation or effectiveness of resuscitation. Pulse oximetry provides rapid, continuous and accurate information on both oxygenation and heart rate. Resuscitation of term infants should begin with air, with the provision of blended oxygen to maintain oxygen saturations similar to those of term infants requiring no resuscitation. Positive end-expiratory pressure during initial ventilation aids lung aeration and establishment of functional residual capacity. Respiratory function monitoring allows operators to identify factors adversely affecting ventilation, including leak around the face mask and airway obstruction. Clamping of the umbilical cord should be delayed for at least 1 min for infants not requiring resuscitation.

SUMMARY

The International Liaison Committee on Resuscitation guidelines on the management of newborn infants were updated in 2010 and incorporate much of the newly available evidence. The use of intensive care techniques in the delivery room is promising but requires further evaluation. Monitoring techniques and interventions need to be adapted for use in developing countries.

Respiratory function monitor guidance of mask ventilation in the delivery room: a feasibility study

OBJECTIVE

To investigate whether using a respiratory function monitor (RFM) during mask resuscitation of preterm infants reduces face mask leak and improves tidal volume (V(T)).

STUDY DESIGN

Infants receiving mask resuscitation were randomized to have the display of an RFM (airway pressure, flow, and V(T) waves) either visible or masked.

RESULT

Twenty-six infants had the RFM visible, and 23 had the RFM masked. The median mask leak was 37% (IQR, 21%-54%) in the visible RFM group and 54% (IQR, 37%-82%) in the masked RFM group (P = .01). Mask repositioning was done in 19 infants (73%) of the visible group and in 6 infants (26%) of the masked group (P = .001). The median expired V(T) was similar in the 2 groups. Oxygen was provided to 61% of the visible RFM group and 87% of the RFM masked group (P = .044). Continuous positive airway pressure use was greater in the visible RFM group (73% vs 43%; P = .035). Intubation in the delivery room was done in 21% of the visible group and in 57% of the masked group (P = .035).

CONCLUSION

Using an RFM was associated with significantly less mask leak, more mask adjustments, and a lower rate of excessive V(T).

The association of mode of delivery and common childhood illnesses

Participants enrolled in a randomized control trial (RCT) were eligible for this cross-sectional study to determine if children born via cesarean (C)-section had higher rates of common infectious diseases and change in normal daily activities due to illness than children born vaginally. The RCT collected parent-reported health information and mode of delivery was assessed during follow-up calls. Parent-reported rates of infectious sequelae and changes in daily activities were compared between C-section and vaginally delivered children. In total, 72.4% of the 522 children were delivered vaginally. After accounting for age, siblings, breast-feeding as an infant, and clustering within families, C-section delivered children had significantly higher rates of cumulative infectious diseases, lower respiratory tract infections, and cough than vaginally born children. Mode of delivery appears to have some lasting effect on child health 3 to 6 years after birth, specifically respiratory health. Further research is imperative to elucidate the causative effect of mode of delivery on child health.

Cerebral oxygenation in very low birth weight infants supported with sustained lung inflations after birth

Sustained lung inflations (SIs) immediately after birth might decrease the need for subsequent mechanical ventilation in preterm infants. However, effects of SIs on oxygenation and hemodynamics are undetermined. Our aim was to study immediate effects of SIs on heart rate, arterial oxygen saturation, and cerebral tissue oxygen saturation in preterm infants supported with SIs after birth for lung recruitment. Heart rate, arterial oxygen saturation, and cerebral tissue oxygen saturation using near infrared spectroscopy was measured in 24 preterm infants of 28.0 (26.6-29.3) wk GA [median (interquartile range)] during resuscitation using up to three SIs of 20, 25, and 30 cm H2O of 15 s duration each followed by nasal continuous positive airway pressure (CPAP) as first line approach for respiratory support. During positioning and suctioning immediately after delivery infants became progressively hypoxemic and bradycardic before respiratory support was initiated. In 18 infants (75%), more than one SI were applied. During the last SIs, there was a rapid increase in the infants' heart rate and an increase in cerebral tissue oxygen saturation. Arterial saturation increased with slight delay. In conclusion, effective last sustained inflations increase heart rate and cerebral tissue oxygen saturation to be followed by an increase in arterial saturation.

An initial sustained inflation improves the respiratory and cardiovascular transition at birth in preterm lambs

A sustained inflation (SI) facilitates lung aeration after birth but may impair the neonatal cardiovascular transition. We aimed to determine the effect of an initial SI on pulmonary arterial and carotid blood flow (PBF and CBF) after preterm birth. Fetal sheep were instrumented at ∼ 122 d of gestation (d). Lambs were delivered at ∼ 127 d and received either an initial SI (40 cm H2O for 1 min or until a volume of 20 mL/kg was administered) followed by ventilation for 30 min (SI; n = 7) or ventilation for 30 min (non-SI; n = 6). At 10 min after ventilation onset, inspired O2 content increased from 21 to 100% for 10 min. PBF, CBF, pulmonary arterial and carotid pressures, tidal volume, and inspiratory pressures were recorded. PBF was greater during the SI (p < 0.05) but thereafter was similar between groups. Non-SI lambs were hypoxemic and had higher CBF than SI lambs (p < 0.05). Cerebral oxygen delivery was constant in SI lambs but increased ∼ 4-fold in non-SI lambs during ventilation with 100% O2 (p < 0.05). Lung compliance and respiratory status were better in SI than non-SI lambs (p < 0.05). A SI improved lung function without adverse circulatory effects, seemed to stabilize neonatal cerebral O2 delivery, and may protect against cerebral hyperoxia.

Surfactant increases the uniformity of lung aeration at birth in ventilated preterm rabbits

Surfactant deficiency is a major cause of respiratory failure in newborns. We have investigated the roles of surfactant and positive end-expiratory pressure (PEEP) in the development of a functional residual capacity (FRC) and the distribution of ventilation at birth. Preterm rabbit pups (28 d GA) were delivered and received either saline or surfactant and then ventilated with (3PEEP) or without (0PEEP) 3 cm H2O PEEP (groups: saline/0PEEP, surfactant/0PEEP, saline/3PEEP, surfactant/3PEEP). Lung gas volumes were measured using plethysmography, and the uniformity of ventilation was analyzed using phase contrast (PC) x-ray imaging. Surfactant/0PEEP pups had greater FRCs and the lungs were more uniformly ventilated than saline/0PEEP pups; FRC at inflation 19-21 was 2.46 ± 0.52 mL/kg versus 0.91 ± 0.95 mL/kg (p < 0.05). Saline/3PEEP pups developed an FRC of 7.54 ± 1.68 mL/kg at inflation 19-21 (p < 0.05), but the distribution of ventilation was initially nonuniform. Surfactant/3PEEP pups had an FRC of 8.50 ± 0.80 mL/kg (at inflation 19-21), and the distribution of ventilation was more uniform than with saline/3PEEP (p < 0.05). In ventilated preterm newborn rabbits, PEEP has a greater effect on FRC than surfactant, although the two are additive. Surfactant, administered at birth, markedly improved the uniformity of ventilation irrespective of whether PEEP was applied.

Oxygenation with T-piece versus self-inflating bag for ventilation of extremely preterm infants at birth: a randomized controlled trial

OBJECTIVE

To investigate whether infants < 29 weeks gestation who receive positive pressure ventilation (PPV) immediately after birth with a T-piece have higher oxygen saturation (SpO₂) measurements at 5 minutes than infants ventilated with a self inflating bag (SIB).

STUDY DESIGN

Randomized, controlled trial of T-piece or SIB ventilation in which SpO₂ was recorded immediately after birth from the right hand/wrist with a Masimo Radical pulse oximeter, set at 2-second averaging and maximum sensitivity. All resuscitations started with air.

RESULTS

Forty-one infants received PPV with a T-piece and 39 infants received PPV with a SIB. At 5 minutes after birth, there was no significant difference between the median (interquartile range) SpO₂ in the T-piece and SIB groups (61% [13% to 72%] versus 55% [42% to 67%]; P = .27). More infants in the T-piece group received oxygen during delivery room resuscitation (41 [100%] versus 35 [90%], P = .04). There was no difference in the groups in the use of continuous positive airway pressure, endotracheal intubation, or administration of surfactant in the delivery room.

CONCLUSION

There was no significant difference in SpO₂ at 5 minutes after birth in infants < 29 weeks gestation given PPV with a T-piece or a SIB as used in this study.

Transient tachypnea of the newborn: what is new?

An infant born by cesarean delivery is at risk of having excessive pulmonary fluid which makes predisposition to transient tachypnea of the newborn (TTN), because fetal thorax compression during labor leads to the loss of large volumes liquid from the lungs. At birth, the pulmonary epithelium switches from predominantly facilitated Cl⁻ secretion to predominantly active Na+ reabsorption with the increase expression epithelial Na+ -channels (ENaC). Diminished activity or immaturity of this process may contribute to the development of TTN. Familial clustering of some TTN cases shows a genetic predisposition in the developing of this disorder. Antenatal glucocorticoids induce lung Na+ reabsorption by increasing the number and activity of channels even in hypoxia. Since a large release of fetal adrenaline occurs late in labor stimulating ENaC to start reabsorbing lung fluids, aerolized ß-agonists may be used in the treatment. Genetic predisposition for ß-adrenergic hyporesponsiveness may cause TTN in newborn period, and asthma/wheezing in older age groups. Although furosemide accelerates lung fluid resorption and cause pulmonary vasodilatation, oral or aerosolized furosemide cannot be recommended as treatment for TTN unless additional data become available.

Low versus high gas flow rate for respiratory support of infants at birth: a manikin study

BACKGROUND

Neonatal resuscitation guidelines do not specify the gas flow rate during mask ventilation.

AIM

Investigating the effect of gas flow rates on pressures, volumes delivered and mask leak.

METHODS

Flow 5 and 10 liters/min were tested. In study part 1, pressure ranges were measured when ventilating an intubated manikin with a Neopuff®. In study part 2, pediatric staff mask-ventilated a manikin (peak inflation pressure (PIP) 30 cm H(2)O, positive end expiratory pressure (PEEP) 5 cm H(2)O). We measured pressures, expired tidal volume (V(Te)) and mask leak.

RESULTS

Study part 1:an intubated manikin was ventilated with flow 5 versus 10 liters/min: range in PEEP was 0.4-3.6 and 2-14 cm H(2)O, respectively, maximum PIP was 73 cm H(2)O with both flow rates. Study part 2: when mask ventilation was given with flow 5 versus 10 liters/min: leak decreased (24% (8-85) vs. 80% (34- 94); p < 0.0001), V(Te) increased (6.7 (5.1-7.8) vs. 4.7 (2.4-7.0) ml; p < 0.001), PEEP decreased (3.1 (0.8) vs. 3.7 (0.7) cm H(2)O; p < 0.001), PIP was similar (28.1 (2.7) vs. 28.0 (2.3) cm H(2)O; NS). Large leaks decreased V(Te) and PEEP during both flow rates, PIP only with flow 5 liters/min.

CONCLUSION

A low flow rate during neonatal mask ventilation may be a good alternative approach in reducing mask leak, provided that inflation time and flow rate warrants set pressures. Only large leaks seem to influence delivered pressures and volumes. Before resuscitation guidelines are advised, more studies on gas flow rates are needed.

Assessment of flow waves and colorimetric CO2 detector for endotracheal tube placement during neonatal resuscitation

AIM

Clinical assessment and end-tidal CO(2) (ETCO(2)) detectors are routinely used to verify endotracheal tube (ETT) placement. However, ETCO(2) detectors may mislead clinicians by failing to identify correct placement under a variety of conditions. A flow sensor measures gas flow in and out of an ETT. We reviewed video recordings of neonatal resuscitations to compare a colorimetric CO(2) detector (Pedi-Cap®) with flow sensor recordings for assessing ETT placement.

METHODS

We reviewed recordings of infants <32 weeks gestation born between February 2007 and January 2010. Airway pressures and gas flow were recorded with a respiratory function monitor. Video recording were used (i) to identify infants who were intubated in the delivery room and (ii) to observe colour change of the ETCO(2) detector. Flow sensor recordings were used to confirm whether the tube was in the trachea or not.

RESULTS

Of the 210 infants recorded, 44 infants were intubated in the delivery room. Data from 77 intubation attempts were analysed. In 35 intubations of 20 infants both a PediCap® and flow sensor were available for analysis. In 21 (60%) intubations, both methods correctly identified successful ETT placement and in 3 (9%) both indicated the ETT was not in the trachea. In the remaining 11 (31%) intubations the PediCap® failed to change colour despite the flow wave indicating correct ETT placement.

CONCLUSION

Colorimetric CO(2) detectors may mislead clinicians intubating very preterm infants in the delivery room. They may fail to change colour in spite of correct tube placement in up to one third of the cases.

Assessment of chest rise during mask ventilation of preterm infants in the delivery room

BACKGROUND

Current neonatal resuscitation guidelines recommend using visual assessment of chest wall movements to guide the choice of inflating pressure during positive pressure ventilation (PPV) in the delivery room. The accuracy of this assessment has not been tested. We compared the assessment of chest rise made by observers standing at the infants' head and at the infants' side with measurements of tidal volume.

METHODS

Airway pressures and expiratory tidal volume (V(Te)) were measured during neonatal resuscitation using a respiratory function monitor. After 60s of PPV, resuscitators standing at the infants' head (head view) and at the side of the infant (side view) were asked to assess chest rise and estimate V(Te). These estimates were compared with V(Te) measurements taken during the previous 30s.

RESULT

We studied 20 infants who received a mean (SD) of 23 (4) inflations during the 30s. Some observer felt unable to assess chest rise both from the head view (6/20) and from the side view (3/20). Observers from both head and side tended to underestimate tidal volume by 3.5mL and 3.3mL respectively. Agreement between clinical assessment and measured V(Te) was generally poor.

CONCLUSION

During mask ventilation, resuscitators were unable to accurately assess chest wall movement visually from either head or side view.

Regulation of the Pulmonary Circulation in the Fetus and Newborn

During the development of the pulmonary vasculature in the fetus, many structural and functional changes occur to prepare the lung for the transition to air breathing. The development of the pulmonary circulation is genetically controlled by an array of mitogenic factors in a temporo-spatial order. With advancing gestation, pulmonary vessels acquire increased vasoreactivity. The fetal pulmonary vasculature is exposed to a low oxygen tension environment that promotes high intrinsic myogenic tone and high vasocontractility. At birth, a dramatic reduction in pulmonary arterial pressure and resistance occurs with an increase in oxygen tension and blood flow. The striking hemodynamic differences in the pulmonary circulation of the fetus and newborn are regulated by various factors and vasoactive agents. Among them, nitric oxide, endothelin-1, and prostaglandin I2 are mainly derived from endothelial cells and exert their effects via cGMP, cAMP, and Rho kinase signaling pathways. Alterations in these signaling pathways may lead to vascular remodeling, high vasocontractility, and persistent pulmonary hypertension of the newborn.

Respiratory function monitoring to reduce mortality and morbidity in newborn infants receiving resuscitation

BACKGROUND

A respiratory function monitor is routinely used in neonatal intensive care units to continuously measure and display airway pressures, tidal volume and leak during ventilation. During positive pressure ventilation in the delivery room, clinical signs are used to monitor the effectiveness of ventilation. The additional use of a respiratory function monitor during positive pressure ventilation in the delivery room might help to improve the effectiveness of ventilation.

OBJECTIVES

To determine whether the use of a respiratory function monitor in addition to clinical assessment compared to clinical assessment alone in newborn infants resuscitated with positive pressure ventilation reduces mortality and morbidity.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 3, 2010), MEDLINE (January 1996 to March 2010), EMBASE (January 1980 to March 2010) and CINAHL (January 1982 to March 2010). Clinical trials registers and the abstracts of the Society for Pediatric Research and the European Society for Pediatric Research were searched from 2004 to 2009. No language restrictions were applied.

SELECTION CRITERIA

We planned to include randomised and quasi-randomised controlled trials and cluster trials that compared the use of a respiratory function monitor in addition to clinical assessment, compared to clinical assessment alone, in newborn infants resuscitated with positive pressure ventilation.

DATA COLLECTION AND ANALYSIS

Two review authors independently evaluated the search results against the selection criteria. Data extraction and risk of bias assessment were not performed because there were no studies that met our inclusion criteria.

MAIN RESULTS

No studies were found meeting the criteria for inclusion in this review

AUTHORS' CONCLUSIONS

There is insufficient evidence to determine the efficacy and safety of a respiratory function monitor in addition to clinical assessment during positive pressure ventilation at neonatal resuscitation. Randomised clinical trials comparing positive pressure ventilation with and without a respiratory function monitor in addition to clinical assessment at neonatal resuscitation are warranted.

Concomitant ceftriaxone and high-concentration intravenous calcium therapy in adult critical care patients: a matched cohort study

BACKGROUND

Based on case reports in infants, the safety of concomitant use of ceftriaxone and intravenous calcium in all ages has recently come under challenge. Systematic population-based data to guide clinicians with respect to this risk are, however, lacking.

OBJECTIVE

To determine whether concomitant administration of ceftriaxone and intravenous calcium was associated with the occurrence of severe cardiorespiratory events or death in critically ill adults.

METHODS

We performed a matched-cohort study from retrospective data of adults admitted to intensive care units (ICUs) in Calgary, Canada, who were provided continuous high-dose intravenous calcium. Those who received ceftriaxone while on continuous renal replacement therapy were considered exposed. Up to 3 unexposed patients were selected by matching on a number of prognostic factors from the remaining subjects not concurrently exposed to ceftriaxone and calcium. Univariate methods and multivariate conditional logistic regression were used for statistical analysis.

RESULTS

We identified 142 patients exposed to the implicated combination who could be matched to at least one unexposed patient. Hospital mortality was 66% in the exposed versus 63% in unexposed patients (p = 0.442). ICU length of stay, ICU mortality, hospital length of stay, and the frequency of acute oxygenation events were all similar by univariate analysis. Multivariate conditional logistic regression modeling failed to find a significant association between exposure and hospital mortality (adjusted OR 1.15, 95% CI 0.65 to 2.04) or other relevant outcomes.

CONCLUSIONS

In this high-risk group, administration of high concentrations of calcium and concurrent ceftriaxone was not significantly associated with greater mortality or adverse outcomes compared to matched unexposed patients. Although this was an underpowered study and rare adverse effects from the interaction of these 2 compounds cannot be completely excluded, these data provide overall reassurance of the safety of this combination in the majority of critically ill adults.

Cleft palate is caused by CNS dysfunction in Gad1 and Viaat knockout mice

Background

Previous studies have shown that disruption of GABA signaling in mice via mutations in the Gad1, Gabrb3 or Viaat genes leads to the development of non-neural developmental defects such as cleft palate. Studies of the Gabrb3 and Gad1 mutant mice have suggested that GABA function could be required either in the central nervous system or in the palate itself for normal palatogenesis.

Methodology/Principal Findings

To further examine the role of GABA signaling in palatogenesis we used three independent experimental approaches to test whether Gad1 or Viaat function is required in the fetal CNS for normal palate development. We used oral explant cultures to demonstrate that the Gad1 and Viaat mutant palates were able to undergo palatogenesis in culture, suggesting that there is no defect in the palate tissue itself in these mice. In a second series of experiments we found that the GABA_A receptor agonist muscimol could rescue the cleft palate phenotype in Gad1 and Viaat mutant embryos. This suggested that normal multimeric GABA_A receptors in the CNS were necessary for normal palatogenesis. In addition, we showed that CNS-specific inactivation of Gad1 was sufficient to disrupt palate development.

Conclusions/Significance

Our results are consistent with a role for Gad1 and Viaat in the central nervous system for normal development of the palate. We suggest that the alterations in GABA signaling lead to non-neural defects such as cleft palate as a secondary effect due to alterations in or elimination of fetal movements.

Imaging lung aeration and lung liquid clearance at birth using phase contrast X-ray imaging

The transition to extra-uterine life at birth is critically dependent on airway liquid clearance to allow the entry of air and the onset of gaseous ventilation. We have used phase contrast X-ray imaging to identify factors that regulate lung aeration at birth in spontaneously breathing term and mechanically ventilated preterm rabbit pups. Phase contrast X-ray imaging exploits the difference in refractive index between air and water to enhance image contrast, enabling the smallest air-filled structures of the lung (alveoli; < 100 microm) to be resolved. Using this technique, the lungs become visible as they aerate, allowing the air-liquid interface to be observed as it moves distally during lung aeration. Spontaneously breathing term rabbit pups rapidly aerate their lungs, with most fully recruiting their functional residual capacity (FRC) within the first few breaths. The increase in FRC occurs mainly during individual breaths, demonstrating that airway liquid clearance and lung aeration is closely associated with inspiration. We suggest that transpulmonary pressures generated by inspiration provide a hydrostatic pressure gradient for the movement of water out of the airways and into the surrounding lung tissue after birth. In mechanically ventilated preterm pups, lung aeration is closely associated with lung inflation and a positive end-expiratory pressure is required to generate and maintain FRC after birth. In summary, phase contrast X-ray imaging can image the air-filled lung with high temporal and spatial resolution and is ideal for identifying factors that regulate lung aeration at birth in both spontaneously breathing term and mechanically ventilated preterm neonates.

Inspiration regulates the rate and temporal pattern of lung liquid clearance and lung aeration at birth

At birth, the initiation of pulmonary gas exchange is dependent on air entry into the lungs, and recent evidence indicates that pressures generated by inspiration may be involved. We have used simultaneous plethysmography and phase-contrast X-ray imaging to investigate the contribution of inspiration and expiratory braking maneuvers (EBMs) to lung aeration and the formation of a functional residual capacity (FRC) after birth. Near-term rabbit pups (n = 26) were delivered by cesarean section, placed in a water plethysmograph, and imaged during the initiation of spontaneous breathing. Breath-by-breath changes in lung gas volumes were measured using plethysmography and visualized using phase-contrast X-ray imaging. Pups rapidly (1-5 breaths) generate a FRC (16.2 +/- 1.2 ml/kg) by inhaling a greater volume than they expire (by 2.9 +/- 0.4 ml.kg(-1).breath(-1) over the first 5 breaths). As a result, 94.8 +/- 1.4% of lung aeration occurred during inspiration over multiple breaths. The incidence of EBMs was rare early during lung aeration, with most (>80%) occurring after >80% of max FRC was achieved. Although EBMs were associated with an overall increase in FRC, 34.8 +/- 5.3% of EBMs were associated with a decrease in FRC. We conclude that lung aeration is predominantly achieved by inspiratory efforts and that EBMs help to maintain FRC following its formation.