Louise Owen, Peter Davis, Arjan B. Te Pas and Colin J. Morley Newborn babies who do not spontaneously breathe at birth require support to safely make the transition to extrauterine life. Over the past 20 years guidelines for those providing care to these infants have been developed.58 The evidence available to guide initial respiratory support is limited, reflecting the challenges associated with conducting research in the delivery room. The crucial steps in the adaptation to extrauterine life involve the transition from liquid-filled to air-filled lungs, and the establishment of functional residual capacity (FRC). These changes normally occur in the first minutes after birth28 and are accompanied by an increase in pulmonary blood flow and the onset of regular respiration. Lung aeration and development of an FRC facilitate gas exchange, leading to an increase in heart rate. If a newborn does not quickly establish effective respiration, assistance is immediately required. This is usually brief and limited to respiratory support,39,47 unless there is abnormal anatomy, significant fetal acidemia, or poor application of respiratory support.57 Preterm infants have different requirements at birth; most breathe and cry53 and may only need minimal respiratory support. Preterm lungs are delicate, and lung injury can occur with just a few manual inflations.74 This has led to a shift in emphasis in preterm stabilization to a gentler approach in an effort to avoid lung injury. The liquid filling the infant’s airways has higher resistance to movement than the gas that replaces it. Therefore, large negative pressures are required for initial lung inflation and to drive the air-liquid interface to the distal airways. The negative transpulmonary pressure created by term infants is typically −50 cm H2O, and up to −100 cm H2O.34 Detailed imaging of rabbit lungs during the first breath demonstrates that lung aeration depends on the generation of transpulmonary pressure, created by repeated inspiratory efforts.23 Lung liquid moves to the interstitial tissue compartment and is then gradually cleared.23 In the early 1960s, measurements of respiratory activity in healthy newborn term infants showed that the first breaths are characterized by short deep inspiration, followed by a prolonged expiratory phase with a closed, or partially closed glottis.34 While the glottis is closed, there is no loss of gas from the lungs. Abdominal muscle contraction pressurizes the chest, further pushing back the air-liquid interface; this is called expiratory braking. Crying through a partially closed glottis pressurizes the chest in a similar way (Figure 33-1).87 During initial breaths, more volume is inspired than expired with each breath, so FRC is established.76 Recordings of the first breaths of preterm infants have shown that they also use crying and expiratory braking to facilitate lung recruitment and development of FRC (Figure 33-2).83,87 Some infants do not breathe or have ineffective breathing at birth. Guidelines recommend initial steps of warming, drying, and stimulating the baby, opening, and in some cases clearing the airway.58 They stipulate that positive pressure support should be commenced at about 60 seconds of age if the baby remains apneic, has irregular or gasping respirations, or has a heart rate less than 100 beats/min (bpm).58 However, these recommendations may not be straightforward: • Healthy babies may not take their first breath immediately after birth; there may be a delay of 30 seconds or longer.34 • In practice, initial evaluation often takes longer than 60 seconds.66 • In healthy term and preterm babies the median heart rate at 1 minute is less than 100 bpm,9 rising to approximately 140 bpm by 2 minutes of age. • Clinical assessment of heart rate at birth, either by palpation or auscultation, is intermittent and often inaccurate.32 • Assessment of a newborn’s color is subjective and unreliable.52 Although assessment of color is emphasized less in the most recent resuscitation guidelines, it remains part of the Apgar score. • These factors make assessment at birth and the decision whether to intervene more complex. If decisions are made too early, unnecessary interventions may be applied. If decisions are delayed, there may be further cardiorespiratory compromise. It may be helpful to be aware that: An infant who has good tone is unlikely to be severely hypoxic. When an infant fails to establish spontaneous breathing after birth, the caregiver must commence positive pressure support. Usually this is initially applied using a face mask and pressure-generating device. If the infant is making some respiratory effort but the effort is poor, continuous positive airway pressure (CPAP) may aid inflation of the lungs and establishment of FRC.46 Continuous positive airway pressure helps establish and maintain end expiratory lung volume, reduces alveolar collapse and decreases work of breathing. It aids lung expansion and helps to conserve surfactant.46 Continuous positive airway pressure also improves oxygenation, lung compliance, and ventilation-perfusion mismatch.46 A newborn who has no respiratory effort or who is bradycardic will require intermittent positive pressure ventilation (IPPV). Ideally, IPPV should be given with positive end expiratory pressure (PEEP), although not all resuscitation devices are capable of delivering PEEP (Table 33-1). Studies in intubated preterm animals have demonstrated that the addition of PEEP to IPPV results in more rapid acquisition of FRC, improved oxygenation and lung compliance, and decreased lung injury.75 Two studies in preterm infants have failed to show a difference in the proportion of infants requiring intubation in the delivery room14 or any difference in Spo2 at 5 minutes of age10 when PEEP was used, compared with IPPV delivered without PEEP. However, international guidelines state that PEEP is likely to be beneficial in the stabilization of preterm neonates and should be used if equipment is available.58 Adoption of this approach has been high; 76% of units reported using PEEP in the stabilization of newborns in the United States.41 TABLE 33-1 Comparison of Attributes Across the Range of Positive Pressure–Generating Devices Endotracheal intubation should be considered for neonates who have an ongoing need for IPPV and for those who remain bradycardic and/or hypoxic in spite of adequate mask IPPV. The management of preterm neonates who require ongoing respiratory support remains controversial. Both immediate intubation and surfactant, and CPAP alone with rescue intubation and surfactant treatment if certain criteria are met, are widely practiced. A review of several recent studies7 and international guidelines58 suggest that both options are appropriate, and recommend that the decision to be guided by local expertise. As a gentler approach to early respiratory support has become more popular, more preterm infants are likely to be supported by CPAP in the delivery room. Various devices are available for generating positive pressure support in the delivery room. The choice of device may be made based on availability of a gas supply, the skills of the resuscitator, and the desire to deliver sustained inflations, PEEP and CPAP. An international survey in 200451 found that individual centers typically used more than one device, with self-inflating bags (SIBs) being most commonly used (83%). Self-inflating bags (Figure 33-3, A) re-expand after compression. They are the only devices that can be used without a gas supply and have been shown to be the most effective method for reducing mortality from birth asphyxia in resource-poor areas.49 Several types and sizes of SIBs exist. The smallest size, approximately 240 mL, is most appropriate for newborns. The peak pressure delivered by an SIB depends on how hard the bag is squeezed. Self-inflating bags usually incorporate a valve that limits the maximum pressure that can be delivered. The valve can be manually overridden to deliver higher pressures, and can be inadvertently overridden if the SIB is squeezed very hard or very fast. Pressures greater than 100 cm H2O have been reported, resulting in very high delivered volumes, greater than 20 mL/kg.3 Lung model studies have shown that the more fingers used to squeeze the bag, the more pressure is generated.2 For most resuscitations, a gentle squeeze with a finger and thumb is all that is required. Several studies have shown that it is difficult to give consistent peak pressures when using a SIB,8 particularly if an operator is inexperienced.64 If a PEEP valve is attached to an SIB, some PEEP can be delivered. It is difficult to maintain the desired PEEP37 and the level is rate dependent.37 Very little PEEP is generated at inflation rates less than 60/minute because the PEEP decreases quickly.48 This means that an SIB cannot deliver CPAP, and therefore, it may not be the optimal device for stabilizing preterm infants. It is difficult to give sustained inflations with an SIB.38 A flow-inflating bag (FIB) (see Figure 33-3, B) needs a continuous gas supply. Many operators find the flow inflating bag more difficult to use than the SIB. The delivered pressure and tidal volume depend on how hard the bag is squeezed. A pressure-limiting valve can be attached to prevent high pressure being inadvertently delivered. It is recommended that a manometer is used with an FIB50 to deliver consistent peak pressure.26 Positive end-expiratory pressure can be delivered with an FIB by controlling the rate of gas escaping from the back of the bag during expiration. This technique requires experience as it can easily lead to dangerously high PEEP.15 A sustained inflation can be delivered by a skilled operator, but the pressure achieved is more variable than that delivered using a T-piece device.38 It is very difficult to deliver CPAP with an FIB. A T-piece device (see Figure 33-3, C) requires a continuous gas supply to generate a set peak pressure and set PEEP. The peak pressure is achieved by occluding a hole in the top of the device with a finger. When the hole is not occluded, PEEP is delivered. Inflation time depends on the length of time the hole is occluded (but is often >0.5 seconds). T-pieces are easy to use, and are preferred by both experienced and inexperienced operators.26 In manikin studies, the T-piece device delivers peak and PEEP pressures that are more accurate and consistent than other devices, resulting in more stable tidal volume delivery,63 even for inexperienced operators.64 However, recordings in neonates suggest that there is often more mask leak with a T-piece than with SIBs70 and less response to changing lung compliance.35 Additionally, care needs to be taken because alteration of gas flow during T-piece resuscitation changes the delivered pressures, particularly the PEEP.84 Occlusion of the hole on the T-piece allows delivery of a sustained inflation of any duration or pressure.38 The T-piece is capable of delivering CPAP63 and therefore may be the optimal device for providing respiratory support for preterm infants at birth.26 Despite these characteristics, no trials have demonstrated superiority of one device over another.27 A newborn can be stabilized using a ventilator, which provides accurate delivery of peak and PEEP pressures and CPAP. Ventilators allow synchronization and tidal volume measurement.90 In the resource-limited setting, no devices may be available to generate positive pressure support, so mouth-to-mask45 and mouth-to-tube88 ventilation may be used. Both are preferable to mouth-to-mouth resuscitation, but still carry some risk of infection.62 In summary, there are advantages and pitfalls with all the devices used to provide positive pressure during resuscitation (see Table 33-1), and with the possible exception of a ventilator, no device provides information on perhaps the most important parameter—the tidal volume being delivered. Whichever device is used, providers need to be trained in how to set up and use the equipment.81 Pressures may be delivered via several interfaces. Face masks are very commonly used,51 but nasal tubes, laryngeal masks, and endotracheal tubes are also frequently applied. Use of a face mask requires a good seal between the mask and the newborn’s face.94 This is difficult to achieve and maintain,15 leading to reduced pressure and tidal volume delivery. Round, cushion-rimmed masks are used more commonly than anatomically shaped, triangular masks.51 There is conflicting evidence as to whether leak is greater with triangular masks than with round cushion-rimmed masks.50,56 It seems that mask leak is common and frequently large with both mask types.50,70 A face mask should seal around the mouth and nose but not cover the eyes or overlap the chin.61 Several makes and sizes of round face masks are available; however, even smaller masks than those typically used may be better for the most preterm infants.55 Accurate positioning and hold are required to minimize mask leak. The optimal position can be obtained when the correct-sized mask is rolled upward onto the face from a finger placed on the chin tip (Figure 33-4); this technique reduces leak.94 The best hold for a mask varies with the brand of mask being used. For example, with a round Laerdal mask, equal pressure with the thumb and index finger applied to the top flat portion of the mask, where the silicone is thickest, results in the best seal (Figure 33-5, A).94 The fingers should not encroach onto the skirt of the mask because this causes the rim to kink.61 When using the larger sizes of the Fisher & Paykel Healthcare round mask, the thumb and index finger should form a C shape (as in the “OK” hand gesture) placed around the top flat portion of the mask, applying an even distribution of pressure to the outer edge of the mask to provide the best seal (see Figure 33-5, B).94 Initial education and regular retraining are important for the maintenance of this important skill.94
Role of Positive Pressure Ventilation in Neonatal Resuscitation
Normal Transition and Initial Spontaneous Breathing
Delayed Transition and Need for Respiratory Support
Basics of Positive Pressure Support
Device
Self-Inflating Bag
Flow-Inflating Bag
T-Piece
Ventilator
Operates independent of gas supply
X
X
X
Delivers accurate, consistent peak pressure
X
X
Measures delivered peak pressure
X
X
Ability to deliver a sustained inflation
X
May be possible
X
Delivers PEEP
May be possible
May be possible
Delivers CPAP
X
X
Delivered pressures are independent of gas flow
X
Measures delivered tidal volume
X
X
X
May be possible
Application of Noninvasive Positive Pressure Support
How to Generate Positive Pressure
Self-Inflating Bags
Flow-Inflating Bags
T-Piece
Other Options for Providing Positive Pressure
Choosing an Interface to Deliver Positive Pressure
Face Masks
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Role of Positive Pressure Ventilation in Neonatal Resuscitation
, Yes; X, no.
