Critical Care Obstetrics part 13 pdf

Neonatal Resuscitation 109 an increase in pulmonary vascular resistance. For the neonate, without connection to the placenta after the cord is clamped, maintenance of the fetal circulation shunts blood away from the lungs, the only available organ of gas exchange. In the circumstances of progressive asphyxia, the fetus or newborn responds with an increase in systemic vascular resistance or vasoconstriction. This decreases blood fl ow to the mus- culature and the intestines, while attempting to increase blood fl ow to the head and heart. Thus, blood fl ow to the cardiac and cerebral vessels is maximized at the expense of “ non - vital ” organs. This pattern of blood fl ow, if prolonged, results in an increasing acidosis [4,5] . The increasing acidosis along with the hypoxia further increases the pulmonary vascular resistance, exacerbating the problem (Figure 8.2 ). For both fetus and newborn, cardiac output and blood pressure are maintained to the vital organs initially, but will, in the face of increased hypoxia and acidosis fail, as the myocardium fails [6] . Primary and s econdary a pnea Superimposed on these circulatory and hemodynamic changes is a characteristic respiratory pattern response to asphyxia. The fetus or neonate will initiate gasping respirations (which may occur in utero ) and, should the asphyxia persist, enter an apneic phase known as primary apnea. If the asphyxia continues, the primary apnea will be followed by a period of irregular gasping respirations. Continued asphyxia will lead to a period of unremit- ting apnea known as secondary apnea. Figure 8.3 illustrates the respiratory and cardiovascular effects of asphyxia. If an infant is in primary apnea and exposed to oxygen when gasping respirations ensue, exposure to oxygen may be suffi cient fetal, may occur at the time of delivery or signifi cantly before the events of parturition. It is important to note that intrauterine ischemic events, even those quite remote from the delivery of the infant, may extend into the newborn period resulting in a com- promised infant. Response to h ypoxia In the normal fetal circulation, blood returning to the heart from the body and placenta is primarily shunted through the foramen ovale to the left side of the heart facilitating oxygenated blood to going to the head and the heart. Blood that reaches the right ventricle is shunted through the ductus arteriosus to the aorta, bypassing the lungs as a result of a high pulmonary vascular resistance [3] . This serves the fetus well as the major organ of gas exchange is the placenta (Figure 8.1 ). However, if the fetus or newborn is subjected to “ hypoxic ” conditions the physiologic response is to exacerbate or maintain Figure 8.1 Fetal circulation. (Reproduced by permission from Faranoff AA, Martin RJ, eds. Neonatal - Perinatal Medicine: Diseases of the Fetus and Newborn , 7th edn. St Louis: Mosby, 2002: 417.) Figure 8.2 Pulmonary vascular resistance (PVR) in the calf. (From [3] .) Chapter 8 110 It is very important to understand that asphyxia may begin in utero . The infant may go through primary apnea in utero and be born in secondary apnea. Thus, it is extremely diffi cult to assess the degree of asphyxia at the time of birth. For this reason, the resuscitative efforts should begin immediately for all infants born with any degree of depression. To wait may only subject the infant to a potentially prolonged resuscitation and an increased risk of neonatal brain damage. Use of the Apgar s core The Apgar score, which is not routinely given until 1 minute of age, should not be used to guide decisions regarding resuscitation interventions. If an infant is born in secondary apnea interven- tion should be initiated immediately rather than waiting until 1 minute. The Apgar score is intended to provide a “ snapshot ” look at the condition of the infant at any one moment in time – it is not to be used as a guide for initiating resuscitation. Elements of a r esuscitation Overview (Figure 8.5 ) The ability to provide for a prompt and effective resuscitation should be available for all infants regardless of the relative risk for resuscitation as estimated by prenatal complications, fetal heart tracings or complications of labor. For infants who are known to be at high risk of being born depressed, based upon the clinical circumstances, the need for resuscitation should be anticipated and prepared for before the moment of delivery. After delivery, a quick assessment allows for appropriate triag- ing of the infant. If the infant is term, breathing or crying, with good muscle tone and clear amniotic fl uid there is no further need for resuscitation and the infant may be handed to an eager mother. The infant who is preterm, and who has any diffi culty with breathing, reduced muscle tone or stained amniotic fl uid should be placed on a preheated radiant warmer for further evaluation. If the neonate is placed on a radiant warmer, the initial steps include drying and warming, correct airway positioning, clearing the airway by suctioning of the mouth and nose, and assessment of respiratory effort, heart rate and color. This should occur within the fi rst few seconds of life and is independent of the 1 - minute Apgar score. Subsequent efforts are dictated by assessment of respiratory effort, heart rate and color. Gasping or apnea, or a heart rate below 100, should prompt initiation of assisted ventilation. Most infants will respond to assisted ventilation alone. In an infant with persistent central cyanosis but adequate spontaneous respirations and a heart rate greater than 100 beats per minute, free - fl ow oxygen may be all that is necessary. While the long - term effects of asphyxia are sometimes unavoid- able, a prompt and effective resuscitation will in most cases, restore spontaneous respiratory effort and reverse the hypoxia, to reverse the process. However, once the infant reaches secondary apnea, positive - pressure ventilation is required to initiate spontaneous ventilation. Furthermore, the longer the duration of secondary apnea, the longer it will take for spontaneous respiratory effort to return following the administration of positive - pressure ventilation (Figure 8.4 ) [7,8] . Figure 8.3 Heart rate and blood pressure changes during apnea. (Reproduced by permission from Textbook of Neonatal Resuscitation , 4th edn. Elk Grove, IL: American Academy of Pediatrics/American Heart Association, 2000: 1 – 7.) 0 51015 10 20 30 Duration of asphyxia (min) gasp Last To first gasp Time to breathing Time from ventilation (min) Figure 8.4 Time from ventilation to fi rst gasp and to rhythmic breathing in newborn monkeys asphyxiated for 10, 12.5, and 15 minutes at 30 ° C. (From Adamsons K et al. Resuscitation by positive - pressure ventilation and tris - hydroxymethyl - aminomethane of rhesus monkeys asphixiated at birth. J Pediatr 1964; 65: 807.) Neonatal Resuscitation 111 fact that in those infants with persistent neonatal depression, 75% were believed to be due to ineffective or improper ventilatory support. Thus, if adequate ventilation is established, in less than one - tenth of 1% is there any need to progress onto chest compression or medications. Preparation for a r esuscitation Anticipation It must be assumed that the infant delivered of a mother requiring critical care to support and maintain a pregnancy may require resuscitation. Thus, preparation is the fi rst step to assure neonatal resuscitation. A careful review of the antepartum and peripartum maternal history, as well as careful assessment of the infant ’ s response to labor, will frequently identify the potential for the delivery of a depressed infant (Box 8.2 ). This review will help assure that the resuscitative team is less likely to be caught unpre- pared or surprised by an infant born in a high - risk situation who requires immediate resuscitation. If the infant is vigorous and ischemia, hypercapnia and acidosis and minimize the long - term consequences to the child (Box 8.1 ). In those very few infants who do not respond to ventilation, chest compressions and, possibly, medications may be needed. However, before chest compressions or medications are given, it must be assured that the infant is being provided with appropriate positive - pressure ventilation. The resuscitative steps for infants with special circumstances such as thick meconium - stained amniotic fl uid, pneumothorax, congenital diaphragmatic hernia or erythroblastosis/hydrops will be discussed later in this chapter. Importance of e stablishing v entilation In the vast majority of resuscitations, the initiation of effective positive - pressure ventilation alone will restore spontaneous respirations and heart rate. In an exceedingly important and often overlooked paper, Pearlman et al. reported on a large series of over 30 000 deliveries [9] . In their experience only 0.12% of infants required chest compressions or medication. Of note is the Eval HR Eval HR Birth Clear amniotic fluid? breathing or crying? Good muscle tone? Term gestation? Routine Care • Warmth • Clear airway • Dry • Assess color (may go to mother) Place under radiant heater (Suction trachea - if meconium guidelines anpply) Dry thoroughly Remove wet linen Position Suction mouth, then nose Provide tactile stimulation (optional) Below 60 Continue PPV Initiate chest compressions Provide oxygen Above 60 Continue PPV Watch for spontaneous ventilation Then, discontinue PPV if HR above 100 Initiate medication if HR below 60 after 30 seconds of PPV with 100% oxygen and chest compressions Observe and monitor Provide oxygen Evaluate color No PPV ? with oxygen None or gasping Pink or peripheral cyanosis Spontaneous Above 100 Cyanotic 15-30 sec Below 100 Ye s Evaluate respirations Figure 8.5 Overview of resuscitation in the delivery room. HR, heart rate; PPV, positive - pressure ventilation. (Modifi ed from Textbook of Neonatal Resuscitation , 4th edn; Elk Grove, IL; American Academy of Pediatrics/American Heart Association, 2000. Originally published in Faranoff AA, Martin RJ, eds. Neonatal - Perinatal Medicine: Diseases of the Fetus and Newborn , 7th edn. St Louis: Mosby, 2002: 434.) Chapter 8 112 Adequate p ersonnel Individuals vested with the responsibility of resuscitating infants should be adequately trained, readily available and capable of working together as a team. Adequate training involves more than simple completion of a certifi cation course on the resuscitation of the newborn infant. The Neonatal Resuscitation Program of the American Heart Association/American Academy of Pediatrics and similar courses serve simply as starting points. They do not qualify one to assume independent responsibility in the delivery room. Those having completed a course, but still lacking the expertise gained through experience must be adequately supervised and supported by experienced personnel. Ultimately, the ability to resuscitate neonates is not determined by professional designation or course completion, but by experience and expertise. Finally, those responsible for resuscitating an infant must be capable of working together as a team. If individuals are aware of and able to fulfi ll their respective responsibilities as well as antici- pate the needs of other team members, the tension inherent in a diffi cult resuscitation will be reduced. In those institutions where resuscitations are uncommon events, frequent mock code drills will help to maintain skills and develop coordination among team members. Initial s teps and e valuation To i ts m other or n ot? Most infants are vigorous, cry upon birth and breathe easily thereafter. The decision to bypass resuscitative efforts should, however, be based on data collected during a brief triage of the infant. The infant born at term without obvious deformity or the passage of meconium in utero , who immediately after birth is vigorous, is breathing easily and who exhibits good tone, may be triaged to its mother if those are the wishes of the parents. A light blanket and some drying of the infant by the mother and delivery room staff will help to establish an appropriate thermal environment but should not hinder frequent and adequate assessments of the neonate ’ s condition. If, however, the infant is premature, has passed meconium in utero or exhibits any degree of respiratory distress, hypotonia, or obvious malformations, the infant should be placed onto a radiant warmer for the initial steps of resuscitation. There a more thorough assessment can be performed and possible further resuscitative interventions begun. Initial s teps Thermal m anagement Temperatures in delivery rooms are typically lower than the neutral thermal environment for neonates. This can leave the newly delivered, wet infant at risk for cold stress. Immediately after birth, the infant with any degree of compromise, or for whom there is any concern, should be placed in the microenvi- ronment of a preheated radiant warmer. The infant should be thoroughly dried with all wet blankets removed to reduce evaporative heat loss. These simple measures can minimize the signifi - Box 8.1 Consequences of asphyxia Central nervous system Cerebral hemorrhage Cerebral edema Hypoxic - ischemic encephalopathy Seizures Lung Delayed onset of respiration Respiratory distress syndrome Meconium aspiration syndrome Cardiovascular system Myocardial failure Papillary muscle necrosis Persistent fetal circulation Renal system Cortico/tubular/medullary necrosis Gastrointestinal tract Necrotizing enterocolitis B l o o d Disseminated intravascular coagulation (From Faranoff AA, Martin, RJ, eds. Neonatal - Perinatal Medicine: Diseases of the Fetus and Newborn , 7th edn. St Louis: Mosby, 2002: 420.) pink despite its high - risk situation, it will be only a pleasant sur- prise to those preparing for resuscitation. Traditionally, a cesarean delivery of any type has been considered high risk. Enough information is now available to state that the uncomplicated repeat cesarean section carries no greater risk for the infant than a vaginal delivery [10] . Anticipation of the potential need for resuscitation has been made easier by technologic advances allowing better prenatal assessment of the fetus. But, not all events compromising an infant ’ s response to labor may be predicted. For this reason, equipment and personnel must be immediately available to inter- vene on behalf of the infant requiring an unanticipated resuscitation. Equipment Whenever an infant is delivered, appropriate equipment must be close at hand and in good working order. Having the correct equipment and skilled individuals to establish adequate ventilation is imperative. It is unacceptable for a team member to have to leave the delivery room in order to retrieve an essential piece of equipment. Neonatal Resuscitation 113 cant drop in infant core body temperature experienced immediately after birth [11] . This is particularly important for the infant with any degree of compromise. Hypoxia reduces the infant ’ s homeostatic response to cold stress, and without inter- vention, the hypoxic infant will undergo a greater than normal drop in core body temperature [12] . Hypothermia also reduces the clearance of metabolic acidosis and thus prolongs the recov- ery from perinatal asphyxia [13] . The premature and/or small infant represents an especially diffi cult problem from the aspect of temperature control. As a result of the lack of subcutaneous tissue and thin skin they tend to have greater evaporative water loss across the skin than a term infant. In addition, the large surface area to body mass ratio also facilitates heat loss and a decrease in body temperature. There are three things that can be done to help diminish heat loss in the preterm/small infant. The fi rst two should be done before the anticipated delivery: (i) increase the temperature of the Box 8.2 Factors associated with neonatal depression and asphyxia Antepartum risk factors Intrapartum risk factors Maternal diabetes Emergency cesarean section Pregnancy - induced hypertension Forceps or vacuum - assisted delivery Chronic hypertension Breech or other abnormal presentation Chronic maternal illness Premature labor Cardiovascular Precipitous labor Thyroid Chorioamnionitis Neurologic Prolonged rupture of membranes ( > 18 hours before delivery) Pulmonary Prolonged labor ( > 24 hours) Renal Prolonged second stage of labor ( > 2 hours) Fetal anemia or isoimmunization Persistent fetal bradycardia Previous fetal or neonatal death Non - reassuring fetal heart rate patterns Bleeding in second or third trimester Use of general anesthesia Maternal infection Uterine hyperstimulation Polyhydramnios Narcotics given to mother within 4 hours of delivery Oligohydramnios Meconium - stained amniotic fl uid Premature rupture of membranes Prolapsed cord Post - term gestation Abruptio placentae Multiple gestation Placenta previa Size – dates discrepancy Signifi cant intrapartum bleeding Fetal hydrops Drug therapy, e.g. magnesium adrenergic - blocking drugs Maternal substance abuse Fetal malformation Diminished fetal activity No prenatal care Age < 16 or > 35 years (Modifi ed from Textbook of Neonatal Resuscitation , 4th edn; Elk Grove, IL; American Academy of Pediatrics/American Heart Association, 2000. Originally published in Faranoff AA, Martin RJ, eds. Neonatal - Perinatal Medicine: Diseases of the Fetus and Newborn , 7th edn. St Louis: Mosby, 2002: 420.) delivery room and (ii) make sure that the radiant warmer is preheated before the birth of the infant. Finally, for infants less than 28 weeks, it is now recommended that consideration be given to placing the infant in a standard, food - quality 1 - gallon polyethyl- ene bag that can easily be obtained from a grocery store. A hole is cut in the closed end of the bag and the bag slipped over the baby with his or her head coming out of the hole. The “ zipper ” end can then be closed (Figure 8.6 ). This allows a resuscitation to proceed with minimal evaporative heat loss and full visualiza- tion of the infant. The infant can be placed in the bag in place of, or after, drying. A preheated transport incubator can be used to help maintain body temperature during transport to the nursery or NICU. Clearing the a irway The airway is normally cleared with the use of a bulb syringe or suction catheter. The mouth is suctioned fi rst and then the nose. Chapter 8 114 It is now clear that at about 1 minute, following an uncomplicated birth, most infants breathing room air will only attain an oxygen saturation of around 60 – 70%. By 5 minutes, most infants have reached ranges in the mid - to high 80% range and, in many infants, it may take 10 minutes to reach oxygen saturations of 90% or higher [15,16] . This matter may be complicated by individual variation in the clinical assessment of color during the transition of a neonate. In the breathing infant with a heart rate of above 100 who appears cyanotic, the use of a pulse oximeter may be of some value. Using the newer pulse oximetry models with placement of the oximeter probe on the right hand (preductal), it should be possible to obtain an S p O 2 reading by a couple of minutes of age in most infants. If the S p O 2 is less than 85% then blended oxygen can be provided to whatever extent is necessary to raise the S p O 2 to between 85% to 90%, or until it is quite clear that additional oxygen makes no difference in the oxygen saturations, in which case the infant is likely to have cyanotic congenital heart disease. Having said this, it is important to understand that we do not know what the optimal oxygen saturation of a transitioning newborn is at any point in time. Thus, the best we can do is to have oxygen blenders and pulse oximeters in delivery units that deal with high - risk infants in order to provide some guidance so that the supplemental oxygen can be provided at the levels which are no higher than necessary. If the infant is in need of supplemental oxygen, it seems prudent to start at about 40% and move up or down as indicated. Free - fl ow oxygen in high concentrations can easily be admin- istered by oxygen mask (with escape holes) or by cupping the hand around the end of the oxygen tubing and holding this close to the infant ’ s nose and mouth. A fl ow - infl ating (anesthesia) bag and mask or a mask on the end of a T - tube device (such as the Neopuff ® ) held lightly over the infant ’ s nose and mouth may also deliver a measured concentration of inspired oxygen. Caution should be used to avoid a seal of the mask to the face so as to avoid providing positive pressure to the lung. A self - infl ating bag is not capable of providing free - fl ow oxygen. Cold, dry oxygen can be given in an emergency; however, a persistent need for free - fl ow oxygen should prompt humidifi cation and heating of the oxygen. Assisted v entilation If an infant is not breathing, is breathing but incapable of sustain- ing a heart rate of above 100, or is in signifi cant respiratory distress and requiring supplemental oxygen, some form of assisted ventilation may be necessary. This may be simply the provision of a continuous positive end - expiratory pressure to a spontaneously breathing infant or intermittent mandatory positive - pressure ventilation with end - expiratory pressure to infants who are not breathing or are in signifi cant respiratory distress. When resuscitating a newborn, one must establish a functional residual capacity (FRC) and provide tidal volumes breaths. In the past when positive - pressure ventilation was used the concerns were to provide a peak inspiratory pressure capable of effecting This is done to fi rst clear secretions in the mouth and potentially prevent their aspiration should deep breaths occur with nasal suctioning. Gentle suctioning of the mouth will avoid the refl ex bradycardia associated with stimulation of the posterior pharynx [14] . The infant exposed to meconium in utero represents a special case and will be discussed later. Tactile s timulation Drying and suctioning are generally suffi cient to stimulate respirations in the newborn infant. Other methods such as fl icking the feet or rubbing the back have been traditionally used to stimulate a more vigorous respiratory response. If there is no immediate response to these supplemental methods, positive - pressure ventilation should be promptly initiated. Continued tactile stimulation in an unresponsive infant will not succeed and may prolong the asphyxial process. If, after suctioning and tactile stimulation an infant exhibits apnea or a heart rate of ≥ 100 beats/min, positive - pressure ventilation should be initiated. Free - fl ow o xygen The use of oxygen has become a topic which has been subject to a great deal of discussion and, in some sense, controversy. This is related to the potentially harmful effects of hyperoxia, especially in an asphyxiated infant. As prolonged hypoxia is to be avoided, it is also necessary to avoid hypoxemia. Most of what has been written involves the role of oxygen in infants who are in need of active resuscitation with ventilatory support, which we will discuss later in this chapter. However, in the infant who is breathing spontaneously with no or minimal signifi cant signs of respiratory distress and whose heart rate is above 100, yet who remains cyanotic, there is general agreement that there is a need for supplemental oxygen. However, when to introduce the oxygen and at what levels to start are not well agreed upon. Figure 8.6 Use of plastic bag for reducing evaporative heat loss. (Reproduced from Textbook of Neonatal Resuscitation , 5th edn. Elk Grove, IL: American Academy of Pediatrics/American Heart Association, 2006: 8 – 6.) Neonatal Resuscitation 115 appropriate tidal volume is very limited. We have neither the knowledge nor the tools to assure appropriate tidal volumes in the immediate newborn lung during resuscitation. How then do we approach a positive - pressure infl ation? Where in the past we looked for a “ easy rise and fall of the chest ” or provided enough positive pressure to reach certain pressure values, now it is recommended that just enough pressure be provided to improve the heart rate, color and muscle tone. These signs are considered the best indicators that infl ation pressures are adequate. If these signs are not improving, then one should look for the presence of chest movement and increase the pressure, assuming that one has a good face - mask seal [22] . Keep in mind that in order to establish an FRC, it may be necessary to use higher pressures and longer inspiratory times for the fi rst few breaths than for subsequent breaths. Positive e nd - e xpiratory p ressure ( PEEP ) We are concerned with not only the degree of inspiration but also the expiratory wing of the breath. In surfactant - defi cient animals, ventilation without end - expiratory pressure may result in collapse of the distal units of the lung. Repeated re - expansion of units of the lung that are allowed to become atelectatic at end - expiration leads to shear stresses on the lung that results in similar consequences as those induced by overexpansion of the lung. When surfactant - defi cient rabbit lungs are allowed to attain low end - expiratory volumes they have reduced compliance and greater histologic lung injury than those lungs ventilated at a higher end - expiratory volume maintained with end - expiratory pressures [23] . When rat lungs are ventilated with a low end - expiratory lung volume there is increased cytokine release [24] and increased pulmonary edema [25] . It has also been shown that when saline - lavaged rabbit lungs or preterm lambs are ventilated at low lung volumes there is an impaired response to surfactant. On the other hand, there is also evidence that if preterm lamb lungs are held open at end - expiration with positive end - expiratory pressure, surfactant function is preserved [26,27] . For a very long time we have used end - expiratory pressure with all infants who are on ventilators. Thus, in addition to avoiding overexpansion of the lung, it also may be important to resuscitate infants, especially the premature infant, using an end - expiratory pressure. This may help avoid the potential damage which can result from repeated re - opening of lung units that are allowed to become atelectatic at end - expiration. Now, many neonatologists routinely use an end - expiratory pressure when they resuscitate an infant with positive - pressure ventilation to prevent the lung from collapsing at end - expiration with the induction of shear stress upon the subsequent infl ation. Continuous p ositive a irway p ressure ( CPAP ) End - expiratory pressure, in the form of mask CPAP, is becoming more and more frequently used in the delivery room with infants who are spontaneously breathing yet have some degree of chest movement that resembled an “ easy breath ” . In recent years we have taken into consideration the potential lung damage that can come from over - infl ation that may occur if chest movement is the only indicator of adequate ventilation. We have also begun to recognize that there is a potential for damage when the lungs are allowed to defl ate to an end - expiratory pressure of zero with the induction of shear stresses upon re - infl ation. This has led to the use of a positive end - expiratory pressure, especially when ventilating premature infants, whose immature lungs may well be more susceptible to shear stresses than the term infant [17] . Tidal v olume v entilation In a resuscitation of a newborn, one has to provide tidal volume breaths that are suffi cient to promote adequate gas exchange, but which do not over - distend the lung. The parameter most often used for monitoring adequacy of inspiratory fl ow while bagging is chest wall movement. What is not known is how chest wall movement relates to appropriate expansion of alveoli and true tidal volume in the non - uniformly infl ated lung of the neonate, and especially the premature infant with lung disease. It is quite possible, in fact, even likely, that when chest wall movement is used as a guide for positive - pressure ventilation in the delivery room we are overdistending more compliant portions of the lung in our quest for chest rise. This is especially problematic in the immature, surfactant - defi cient lung which may be subject to non - uniform expansion. In these circumstances positive - pressure inspiratory gas may be forced into those areas that are more compliant, overdistending those areas of the lung. These issues become important to consider as we now realize that overdistention of the alveoli can induce lung damage. There is good evidence that overdistention of the lung (volutrauma) is of greater concern than trauma caused by high pressure (baro- trauma) [18] . Wada et al. demonstrated that in preterm lambs ventilated for 30 minutes at high tidal volumes, compared to controls, there was a decrease in compliance, lower ventilatory effi ciencies and a decreased subsequent response to surfactant [19] . Bjorklund et al. showed that only six large breaths delivered with manual ventilation immediately after birth created enough injury in the lung to result in an attenuated response to surfactant, greater diffi culty in ventilating the animal and more widespread lung injury in histologic sections [20] . Overdistention of the lung can induce a series of events that lead to lung injury, e.g. interstitial and alveolar edema, as well as the initiation of an infl ammatory response by attraction and acti- vation of neutrophils and macrophages. Simply stretching the lung opens stretch - activated ion channels and increases epithelial and endothelial permeability. It can also result in conformational changes in the membrane molecules. Studies at both a cell level and of whole lung have shown that overdistention can alter cell metabolism leading to a cascade of cytokines and chemokines which are proinfl ammatory and lead to further lung injury [21] . Thus, there is good evidence that overdistention of the lung promotes lung injury. However, at this point our ability to assure Chapter 8 116 Those who routinely use a fl ow - infl ating bag believe it gives greater responsiveness and greater individual control. Self - infl ating bags, however, require less expertise and experience to use effectively than do fl ow - infl ating bags. They will require a special attachment to provide end - expiratory pressure (PEEP); however, they cannot deliver CPAP. Self - infl ating bags also require an oxygen reservoir to provide variable concentrations of oxygen. To guard against the delivery of excessive pressure to the infant ’ s lungs, all resuscitation bags should be equipped with a pressure gauge, a pressure - relief valve (pop - off valve) or both. Pop - off valves ideally vent pressures of greater than 30 – 40 cmH 2 O, but great variability can exist between individual bags [16] . Should pressures greater than 30 – 40 cmH 2 O be needed to establish adequate chest rise, a fi nger can easily be placed over the pop - off valve. Any bag without a pop - off valve should have a pressure gauge. Pressure gauges with built - in pressure release valves are available. A T - tube device capable of providing both CPAP and PEEP, controlling the peak - inspiratory pressure as well as the inspiratory time, has been developed (Figure 8. 7 ). The most common one on the market today is called the NeoPuff ® . It is important to check any apparatus for defects before every resuscitation. Reusable bags will develop leaks and cracks over time, and bag reassembly after cleaning may not be correct. It is greatly preferable to discover a faulty bag and mask before it is urgently needed. The apparatus can quickly be checked for function by occluding the air outlet and squeezing the bag or occluding the opening in the T - tube. A pressure should be generated and refl ected on the pressure gauge and/or the pop - off valve should vent air above 30 – 40 cmH 2 O. Use of m ask - CPAP As pointed out previously, in infants who are breathing yet exhibit some degree of respiratory distress and/or an oxygen need, the use of CPAP has become increasingly more common. The easiest way to do this is with the NeoPuff ® . After setting the F i O 2 and the desired degree of continuous positive airway pressure, the attached mask can be sealed to the face, permitting the infant to exhale against a continuous pressure. The same effect can be obtained with a fl ow - infl ating bag by use of the fl ow - control valve. Although there are no well - established values at which to start CPAP most neonatologists will begin with at least 5 cmH 2 O pressure and move up, if necessary. It is uncommon to go to pressures in excess of 8 cmH 2 O. Care must be taken to avoid providing excessive end - expiratory pressure to an infant with good lung compliance. Use of p ositive - p ressure v entilation In the infant who is not breathing, has inadequate respirations to keep the heart rate above 100 or who has an excessive work of breathing and a high F i O 2 requirement on CPAP, there is a need for positive - pressure ventilation. Any of the three devices that respiratory distress. The goal is the same as discussed above, namely helping to recruit and maintain alveoli open by prevent- ing collapse of alveoli at end - expiration. In breathing preterm lambs when the use of CPAP was compared with intubation and positive - pressure ventilation, it has been shown that at 2 hours of age, those animals resuscitated and treated only with CPAP have higher lung volumes, as well as less evidence of an infl ammatory response or acute lung injury [28] . In 1987 the incidence of chronic lung disease was examined at eight institutions throughout the United States. Of note was the fact that Columbia University, had the lowest incidence of chronic lung disease and the most frequent use of CPAP as method of resuscitation and ventilatory support in the nursery [29] . This was confi rmed again in 2000 when the incidence of chronic lung disease was examined at two Boston hospitals (22%) and compared to the hospital at Columbia University (4%). The conclu- sion of the paper was that “ … most of the increased risk of CLD among very low birth weight infants hospitalized at 2 Boston NICUs, compared with those at Babies ’ Hospital, was explained simply by the initiation of mechanical ventilation. ” [30] . There are a great number of cohort studies indicating that the use of CPAP for ventilatory support in the delivery room reduces the number of infants who need to be ventilated. There are, however, no randomized, controlled clinical trials of suffi cient power that compare the use of CPAP with positive - pressure ventilation in neonatal resuscitation. In spite of the lack of “ gold standard ” trials, the use of CPAP is becoming more and more accepted [31] . The 2006 edition of the American NRP points out that “ Some neonatologists recommend administering CPAP to a spontaneously breathing baby … ” The Australian Neonatal Resuscitation guidelines point out that there are no randomized controlled trials of CPAP and then go on to say: “ However, there is accumulating evidence that it is benefi cial and no evidence of harm when used with babies with stiff lungs. Therefore, CPAP or PEEP (at least 5 cmH 2 O) should now be considered when resuscitating very premature infants. ” [32] . Resuscitation d evices It is now recommended that any device used in assisted ventilation be capable of controlling peak inspiratory pressure and end - expiratory pressure as well as inspiratory time. In addition, the device should be able to deliver a variable amount of oxygen ranging from room air to 100%. There are three devices currently in use that, with various degrees of ease, can meet these requirements. These are the self - infl ating bag, the fl ow - infl ating bag and a T - tube device with CPAP and PEEP capability. Regardless of what device is used, those who participate as part of the neonatal resuscitation team should be trained, comfortable and profi cient in its use. If a self - infl ating or fl ow - infl ating bag is used, the volume must be appropriate for the newborn infant (200 – 750 mL total volume) and capable of delivering high concentrations of oxygen. An infant will only require between 5 and 8 cc/kg with each ventilation. A large bag makes it diffi cult to provide such small volumes. Neonatal Resuscitation 117 Circult Pressure Inspiratery Pressure Control Maximum Pressure Relief Gas Outlet Gas Intlet Figure 8.7 T - tube device capable of providing CPAP and PEEP. (Reproduced from Textbook of Neonatal Resuscitation , 5th edn. Elk Grove, IL: American Academy of Pediatrics/American Heart Association, 2006: 3 – 55.) Table 8.1 Problems associated with inadequate chest expansion. Problem Correction Inadequate face mask seal Reapply mask to face Alter position of hand that holds mask Blocked airway Bag and mask Check infant ’ s position Suction mouth, oropharynx, and nose Insert oral airway if indicated (Pierre – Robin, macroglossia) Bag and endotracheal tube Suction the tube Misplaced endotracheal tube Remove endotracheal tube, ventilate with bag and mask, replace tube Inadequate pressure Increase pressure, taking care not to overexpand the chest; may require adjusting or overriding the pop - off valve (Reproduced by permission from Faranoff AA, Martin, RJ, eds. Neonatal - Perinatal Medicine: Diseases of the Fetus and Newborn , 7th edn. St Louis: Mosby, 2002: 429.) have been discussed are capable of providing positive - pressure ventilation. However, in order to add end - expiratory pressure to prevent alveolar collapse at end - expiration, one needs to add a device to the self - infl ating bag. Initially, positive - pressure ventilation will be provided with a mask. Positive - pressure ventilation, like the fi rst spontaneous breaths in the healthy infant, must establish FRC and an adequate tidal volume to halt the development or progression of the asphyxial process. To prevent overdistention of the lungs, the goal is to use just enough pressure to effect an improvement in heart rate, oxygen saturation/color, muscle tone and spontaneous breathing. The fi rst breaths may require a greater peak inspiratory pressure and a longer inspiratory time than subsequent breaths. It is recommended that the rate of ventilation should be between 40 and 60 breaths per minute. If the infant improves, yet continues to need positive - pressure ventilation, be aware of how much tidal volume you are providing. If the chest movement is enough to make the infant appear to be taking deep breaths, you are probably overinfl ating the lungs. In addition, to increasing the risk of the type of lung damage we previously discussed, you are also at an increased risk for producing a pneumothorax. If no improvement occurs with the fi rst few breaths, it may be necessary to increase the inspiratory pressure. However, before you do this, check to see if there is any chest movement and have someone listen with a stethoscope to assess breath sounds. If these are poor fi rst check to see if there is an adequate seal between the mask and the face and make sure the airway is not blocked. If these are OK, and there is no improvement, increase the pressure. If there continues to be no improvement, it may be necessary to intubate the infant and provide positive pressure through the endotracheal tube. Table 8.1 describes common problems associated with inadequate chest expansion and potential corrective actions easily performed in the delivery room. Endotracheal i ntubation The task of endotracheal intubation is best accomplished by two people. One inserts the tube into the airway, while the other assists and then assesses for correct placement of the tube by listening for equal breath sounds on both sides of the chest. Uncuffed endotracheal tube sizes ranging from 2.0 to 4.0 should be available in the delivery suite. A 2.5 endotracheal tube will be Chapter 8 118 the animal and human work can be gleaned from two recent review articles [33,34] . Multiple animal studies have provided evidence indicating that the generation of oxygen free radicals during the reperfusion phase of ischemic injury is associated with increased damage. After a pilot study demonstrating no difference in outcomes of resuscitation with room air versus 100% oxygen, a seminal and, to date, the only large multicenter controlled study was done [35] . This study enrolled 609 infants to more rigorously test the hypothesis that room air resuscitation of the asphyxiated infant would not increase morbidity and mortality. There were no signifi cant differences in mortality, incidence and severity of hypoxic - ischemic encephalopathy, acid – base status, oxygen saturations or arterial oxygen concentrations. There are human data to indicate that the initial use of 100% oxygen increases the time to the onset of spontaneous respiration, increases the time of resuscitation, results in a lower 5 - minute Apgar score, increases oxidative stress and results in some, at least in the short term, oxidative injury in the kidney and heart. There is also a suggestion that there is an increased neonatal mortality, although this fi nding is debated. There have been a limited number of randomized controlled human studies, which indi- vidually and when looked at in a meta - analysis [36] indicated that starting resuscitation with room air and adding oxygen if needed, does no harm. The American NRP recommends that 100% oxygen should be used when resuscitating term infants with cyanosis or a need for positive pressure ventilation. When resuscitating the pre - term infant one should use a blender and pulse oximeter and begin somewhere between room air and 100% oxygen; increasing or decreasing the F i O 2 upon the response of the infant. On the other hand, the Australian Neonatal Resuscitation Guidelines state that “ However, at present, the best available evidence suggests air should be used initially with supplemental oxygen reserved for infants whose condition does not improve after effective ventilatory support. ” [32] . The Canadian recom- mendations indicate that positive - pressure ventilations should be initiated with room air and supplemental oxygen used at 90 seconds of age if the heart rate is below 100 beats per minute or cyanosis persists [37] . Others have suggested starting with an F i O 2 of 40% and moving up or down as necessary. Chest c ompressions As emphasized above, in all but a fraction of 1% of infants, provision of positive - pressure ventilation will be suffi cient to over- come any bradycardia and lead to spontaneous respirations. If, however, after ventilation with 100% oxygen, the newborn remains bradycardic, chest compressions will be needed to maintain systemic blood fl ow. The American Heart Association/American Academy of Pediatrics currently recommends beginning chest compression for a heart rate of less than 60 beats/min. This can be done with the two - fi nger method, or the thumb method may be used to small enough for all but the 500 – 600 - g, extremely low birth weight infants (Table 8.2 ). If a soft, fl exible wire stylet is used to assist with endotracheal tube placement, it should not extend past the tip of the endotracheal tube, thus ensuring that the stylet does not damage the tracheal wall or carina. A tip to lip distance in cm should be used to estimate depth of placement (Table 8.3 ). When the tube is placed in the airway, whichever resuscitation device one is using should be attached to the endotracheal tube and a series of breaths initiated. Placement should initially be checked both by auscultation of equal breath sounds on both sides of the chest along with a lack of signifi cant auscultated gastric breath sounds or of signifi cant gastric distension. The placement should be confi rmed by the use of a small, portable exhaled CO 2 detector. Complications of endotracheal intubation include hypoxia, bradycardia, infection and contusions or lacerations to the struc- tures of the upper airway, including the vocal cords themselves. Rarely but tragically, the trachea or esophagus will be perforated. The utmost care must be given to placement of the endotracheal tube to avoid such complications. Even more vigilance must be exercised if an endotracheal tube is placed with the use of a stylet. Room a ir v ersus 100% o xygen The use of room air as opposed to 100% oxygen in the resuscitation of an infant is a source of much debate. The references for Table 8.2 Endotracheal tube sizes. Tube size (mm ID) Weight (g) Gestational age (weeks) 2.0 * 500 – 600 or less 25 – 26 or less 2.5 < 1000 < 28 3.0 1000 – 2000 28 – 34 3.5 2000 – 3000 34 – 38 3.5 – 4.0 > 3000 > 38 * May be needed if a size 2.5Fr tube does not fi t. ID, internal diameter. (Reproduced by permission from Faranoff AA, Martin, RJ, eds. Neonatal - Perinatal Medicine: Diseases of the Fetus and Newborn , 7th edn. St Louis: Mosby, 2002: 426.) Table 8.3 Endotracheal tube placement. Weight (kg) Depth of insertion (cm from upper lip) 1 7 * 2 8 3 9 4 10 * Infants weighing less than 750 g may require only 6 cm insertion. (Reproduced by permission from Textbook of Neonatal Resuscitation , 4th edn. Elk Grove, IL: American Academy of Pediatrics/American Heart Association, 2000: 5 – 19.) . requiring critical care to support and maintain a pregnancy may require resuscitation. Thus, preparation is the fi rst step to assure neonatal resuscitation. A careful review of the antepartum. to assure neonatal resuscitation. A careful review of the antepartum and peripartum maternal history, as well as careful assessment of the infant ’ s response to labor, will frequently identify. essential piece of equipment. Neonatal Resuscitation 113 cant drop in infant core body temperature experienced immediately after birth [11] . This is particularly important for the infant with any

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