Maternal Factors

Maternal risk factors include many medical, physical, and social conditions. Maternal health and individual physiology, pregnancy complications, and maternal behaviors affect the health of the fetus. Any condition that causes an interference with placental blood flow or the transfer of oxygen (O₂) to the fetus can result in an adverse outcome. The clinician must be prepared for the possibility of resuscitation at delivery. This possibility is best anticipated by identifying risk factors that relate to neonatal compromise. Table 48-1 lists maternal risks and related outcomes of which the team preparing to receive the infant should be aware when the infant is delivered.

Fetal Assessment

Fetal assessment is performed with ultrasonography, amniocentesis, fetal heart rate monitoring, and fetal blood gas analysis. Ultrasonography uses high-frequency sound waves to obtain an image of the infant in utero. This image allows the physician to view the position of the fetus and placenta, measure fetal growth, identify possible anatomic anomalies, and assess the amniotic fluid qualitatively.

Amniocentesis involves direct sampling and quantitative assessment of amniotic fluid. Amniotic fluid may be inspected for meconium (fetal bowel contents) or blood. In addition, sloughed fetal cells can be analyzed for genetic normality. Lung maturation can be assessed with amniocentesis. The lecithin-to-sphingomyelin ratio (L : S ratio) involves measurement of two phospholipids, lethicin and sphingomyelin, synthesized by the fetus in utero. As shown in Figure 48-1, the L : S ratio increases with increasing gestational age. At approximately 34 to 35 weeks’ gestation, this ratio abruptly increases to greater than 2 : 1. An L : S ratio greater than 2 : 1 indicates stable surfactant production and mature lungs. Phosphatidylglycerol is another lipid found in the amniotic fluid that is used to assess fetal lung maturity. Phosphatidylglycerol first appears at approximately 35 to 36 weeks’ gestation. If phosphatidylglycerol is more than 1% of the total phospholipids, the risk of respiratory distress syndrome is less than 1%.

Fetal heart rate monitoring is the measurement of fetal heart rate and uterine contractions during labor. Examination of fetal heart rate changes related to uterine contractions identifies a fetus in distress. Fetal well-being is obtained by examining the variability and reactivity of the fetal heart rate. A normal fetal heart rate ranges from 120 to 160 beats/min. Fetal tachycardia can be a sign of fetal hypoxemia or could be related to other factors, such as prematurity or maternal fever. Temporary declines in fetal heart rate are called decelerations and can be mild (<15 beats/min), moderate (15 to 45 beats/min), or severe (>45 beats/min). Decelerations are classified by their occurrence in the uterine contraction cycle.

Figure 48-2 illustrates the three common patterns of early decelerations, late decelerations, and variable decelerations. Early decelerations occur when the fetal heart rate decreases in the beginning of a contraction. This type of deceleration is benign and in most cases is caused by a vagal response related to compression of the fetal head in the birth canal. A late deceleration occurs when the heart rate decreases 10 to 30 seconds after the onset of contractions. A late deceleration pattern indicates impaired maternal-placental blood flow, or uteroplacental insufficiency. With variable decelerations, there is no clear relationship between contractions and heart rate. This pattern is the most common of the three and probably related to umbilical cord compression. Short periods of cord compression are generally benign, but prolonged periods of compression result in impaired umbilical blood flow and can lead to fetal distress. Fetal heart rate variability is the beat-to-beat variation in rate that occurs because of normal sympathetic or parasympathetic influences. A completely monotonous heart rate tracing may be indicative of fetal asphyxia. Fetal heart rate reactivity is the ability of the fetal heart rate to increase in response to movement or external stimuli. A healthy fetus has two accelerations within a 20-minute period.

In utero, the fetus receives its blood supply from the placenta. Only a small portion of the blood that enters the fetal right heart flows through the lungs. This is a result of fetal pulmonary blood vessels being constricted with a high resistance to blood flow. There are two openings in the fetal heart through which most fetal blood flows. These normal anatomic shunts in the fetus are called patent foramen ovale and patent ductus arteriosus (PDA). Blood flows through these openings and into the umbilical vessels before returning to the mother. Pressure in the umbilical vessels is low. During the transition from fetal life to newborn life, the umbilical cord is clamped, and the infant’s systemic blood pressure is increased. The infant begins to breathe, and O₂ enters the infant’s blood. Oxygenated blood entering the pulmonary vessels causes the vessels to dilate and decreases pulmonary resistance. With higher systemic resistance and lower pulmonary resistance, less blood flows through the anatomic openings, and these openings begin to close. Evidence of normal transitional circulation is noted as the infant’s skin turns from a bluish hue to pink over the first several minutes of life.

Evaluation of the Newborn

All newborns should be assessed immediately on delivery. Most newborns (>90%) do not need intervention when transitioning from intrauterine to extrauterine life. The two categories of newborns most likely to need intervention are infants born with evidence of meconium in their airway and premature infants. The need for intervention is determined by assessing for the presence of meconium, breathing or crying, muscle tone, color, and gestational age.

Meconium is the medical term for the infant’s first stools. It is a sticky green-black substance that if inhaled by the infant can cause significant respiratory problems. It is most likely present in a term or postterm newborn. Term infants delivered without evidence of meconium who are crying or breathing and have good tone should not routinely be separated from the mother. They should be dried, covered, and given to the mother and observed for breathing, activity, and color. If meconium is present and the infant is vigorous, pharyngeal suctioning with a bulb suction is appropriate. Simultaneously the infant should be dried and placed under a warmer and assessed for signs of respiratory distress. See later section on Respiratory Assessment of the Infant. If meconium is present in a nonvigorous infant, stimulation should be avoided.

Immediate endotracheal intubation before positive pressure ventilation (PPV) is indicated as a means to clear meconium from the airway. The endotracheal tube should be attached to a meconium aspirator, and a suction device should be regulated for −70 to −100 mm Hg. As soon as the endotracheal tube is inserted, suction should be applied to the tube, and then the endotracheal tube is withdrawn. Reintubation and repeat suctioning may be necessary if meconium is still visible in the airway. Frequent assessment of the heart rate is indicated during this process, and if bradycardia is present, bag-mask ventilation should be considered. Intubation of the trachea is not recommended in a vigorous infant with meconium. Preterm infants frequently need intervention. The more preterm the infant, the more likely the infant will need some level of resuscitation. If an infant is preterm, is not breathing, is not vigorous, or does not have good tone, resuscitation efforts should be initiated. Efforts are directed at warming the infant because cold stress may increase O₂ consumption and impair all subsequent resuscitation efforts.

After the infant is dried and warmed, the infant is positioned supine, with the head in a neutral position or slightly extended. A bulb syringe or 8F to 10F suction catheter may be used for secretion removal; however, in the absence of blood or meconium, catheter suctioning should be limited because aggressive pharyngeal suctioning may cause laryngospasm or bradycardia. Suction pressure should not exceed −100 mm Hg. Once the infant is suctioned, dried, and warmed, if apnea or inadequate respirations are present, tactile stimulation may be used to encourage spontaneous breathing. Many infants respond to stimulation and need no further resuscitative efforts. If after 30 seconds the infant has a heart rate of less than 100 beats/min or is apneic, bag-mask ventilation at a rate of 40 to 60 beats/min should be initiated.

The most important and effective action in neonatal resuscitation is effective ventilation. Recommendations from the American Academy of Pediatrics are to attach a pulse oximeter to the infant, begin resuscitation efforts using room air, and assess carefully the amount of O₂ needed.¹ Effective PPV usually results in rapid improvement of heart rate. Initial ventilating pressures of 30 to 40 cm H₂O may be necessary to achieve noticeable chest movement, particularly in a preterm newborn with surfactant deficiency. Continuous assessment of the lowest pressure needed to observe the chest rise is essential throughout the resuscitation. After application of PPV for 30 seconds, the heart rate is reassessed. If the heart rate is less than 60 beats/min, chest compressions are begun, and PPV is maintained. If the heart rate remains less than 60 beats/min after adequate ventilation with 100% O₂ and chest compressions for 30 seconds, appropriate medications are given. As soon as the heart rate is noted to be greater than 100 beats/min, compressions are discontinued. If spontaneous breathing is present, PPV may be gradually reduced and then discontinued. If spontaneous breathing remains inadequate or if heart rate remains less than 100 beats/min, assisted ventilation is continued via bag-mask or endotracheal tube. Figure 48-3 outlines a newborn resuscitation algorithm and includes the targeted saturation levels for the first 10 minutes of life.

Assessment of Gestational Age

Gestational age assessment and assessment of relationship of weight to gestational age are performed shortly after delivery. Determination of gestational age involves assessment of multiple physical characteristics and neurologic signs. Two common systems are used to determine gestational age: the Dubowitz scales and the Ballard scales. The Dubowitz scales involve assessment of 11 physical and 10 neurologic signs.² Physical criteria include assessment of skin texture, skin color, and genitalia. Neurologic criteria include posture and arm and leg recoil. The Ballard scales are a simplified version of the Dubowitz scales and include six physical and six neurologic signs as illustrated in Figure 48-4. Soon after delivery, the newborn is stabilized and weighed, followed by determination of gestational age. Infants born between 38 weeks and 42 weeks are considered term gestation. Infants born before 38 weeks are preterm. Infants born after 42 weeks are postterm.

All newborns weighing less than 2500 g are considered low birth weight. Newborns weighing less than 1500 g are considered very low birth weight (VLBW). Newborns weighing less than 1000 g are considered extremely low birth weight (ELBW). A newborn with a weight that is either too large or too small or who has been born preterm or postterm has a higher risk of morbidity and mortality. As shown in Figure 48-5, by plotting the infant’s gestational age against weight, the newborn’s relative developmental status can be classified. Infants whose weight falls between the 10th and 90th percentiles are appropriate for gestational age (AGA). Infants whose weight is above the 90th percentile are large for gestational age (LGA). Infants whose weight is below the 10th percentile are small for gestational age (SGA).

 Rule of Thumb

Infants weighing less than 2500 g are normally considered low birth weight neonates. Infants weighing less than 1500 g are considered VLBW neonates, and neonates weighing less than 1000 g are considered ELBW neonates.

By classifying infants into one of the combined categories, such as “preterm, AGA,” the clinician can help identify infants at highest risk and predict the nature of the risks involved and the likely mortality rate. Small, preterm infants are at highest risk. Compared with term infants, the lungs of these infants are not yet fully prepared for gas exchange. In addition, their digestive tracts cannot normally absorb fat, and their immune systems are not yet capable of warding off infection. Small, preterm infants also have a very large surface area-to-body weight ratio; this increases heat loss and impairs thermoregulation. Finally, the vasculature of these small infants is less well developed, increasing the likelihood of hemorrhage (especially in the ventricles of the brain).

 Rule of Thumb

Infants born before 38 weeks’ gestation are considered preterm.

Respiratory Assessment of the Infant

Not all respiratory problems occur at birth; many respiratory disorders develop after birth and may develop slowly or suddenly. RTs are commonly called on to help assess and treat infants who develop respiratory distress after birth.

Physical Assessment

Physical assessment of the infant begins with measurement of vital signs. A normal newborn respiratory rate is 40 to 60 breaths/min. The lower the gestational age, the higher the normal respiratory rate will be. A 28-week gestational age infant may normally breathe 60 times a minute, whereas the rate more typical of a term newborn is 40 breaths/min. Tachypnea (>60 breaths/min) can occur because of hypoxemia, acidosis, anxiety, or pain. Respiratory rates less than 40 breaths/min should be interpreted with previous trends of the newborn’s respiratory rate. A baseline respiratory rate of 36 breaths/min in a term newborn is within normal limits; however, a respiratory rate of 36 breaths/min in a preterm newborn previously breathing at 70 breaths/min may indicate compromise. Causes of slow respiratory rates include medications, hypothermia, or neurologic impairment.

Normal infant heart rates range from 100 to 160 beats/min. Heart rate can be assessed by auscultation of the apical pulse, normally located at the fifth intercostal space, midclavicular line. Alternatively, the brachial and femoral pulses may be used. Weak pulses indicate hypotension, shock, or vasoconstriction. Bounding peripheral pulses occur with major left-to-right shunting through a patent ductus arteriosus (PDA).³A strong brachial pulse in the presence of a weak femoral pulse suggests either PDA or coarctation of the aorta. Table 48-3 lists normal ranges of blood pressure for neonates of different sizes.

TABLE 48-3

Normal Neonatal Blood Pressures

Weight (g)	Systolic (mm Hg)	Diastolic (mm Hg)
750	35-45	14-34
1000	39-59	16-36
1500	40-61	19-39
3000	51-72	27-46

From Whitaker K: Comprehensive perinatal and pediatric respiratory care, ed 3, Albany, NY, 2001, Delmar.

 Rule of Thumb

The normal respiratory rate for a full-term infant is 40 to 60 breaths/min.

Chest examination in an infant is more difficult to perform and interpret than in an adult because of the small chest size and the ease of sound transmission through the infant chest. Thorough observation of the infant greatly enhances the assessment data obtained. Infants in respiratory distress typically exhibit one or more key physical signs: nasal flaring, cyanosis, expiratory grunting, tachypnea, retractions, and paradoxical breathing. Nasal flaring is seen as dilation of the ala nasi on inspiration. The extent of flaring varies according to facial structure of the infant. Nasal flaring coincides with an increase in work of breathing. In concept, nasal flaring decreases the resistance to airflow. It also may help stabilize the upper airway by minimizing negative pharyngeal pressure during inspiration.⁴ Cyanosis may be absent in infants with anemia, even when arterial partial pressure of oxygen (PaO₂) levels are decreased. In addition, infants with elevated fetal hemoglobin levels may not become cyanotic until PaO₂ decreases to less than 30 mm Hg. Hyperbilirubinemia, common among newborns, may mask cyanosis. Grunting occurs when infants exhale against a partially closed glottis. By increasing airway pressure during expiration, grunting helps prevent airway closure and alveolar collapse. Grunting is most common in infants with respiratory distress syndrome, but it is also seen in other respiratory disorders associated with alveolar collapse. Figure 48-6 illustrates the Silverman score, which is a system of grading severity of lung disease.

Retractions refer to the drawing in of chest wall skin between bony structures. Retractions can occur in the suprasternal, substernal, and intercostal regions. Retractions indicate an increase in work of breathing, especially because of decreased pulmonary compliance. Paradoxical breathing in infants differs from paradoxical breathing normally seen in adults. Instead of drawing the abdomen in during inspiration, an infant with paradoxical breathing tends to draw in the chest wall. This inward movement of the chest wall may range in severity. As with retractions, paradoxical breathing indicates an increase in ventilatory work. Applying continuous positive airway pressure (CPAP) to a newborn exhibiting signs of respiratory distress including grunting, flaring, and retracting may help to increase lung volume and improve gas exchange. The benefits of CPAP in children are discussed in more detail later.

Respiratory Assessment of the Pediatric Patient

Normal breathing in children is evidenced by quiet inspiration and passive expiration at an age-appropriate rate. Respiratory rates are rapid in neonates and decrease in toddlers and older children. Table 48-5 lists normal respiratory rates. The initial assessment of a pediatric patient starts with evaluating airway patency. Normal heart rates are higher in younger children and decrease with age. In assessing a pediatric patient, establishing if the airway is patent or has any obstructive component is essential. Signs that suggest upper airway obstruction include increased inspiratory effort with retractions or inspiratory efforts with no airway or breath sounds.

The clinician observes for movement of the chest or abdomen. The clinician listens for breath sounds focusing on both inspiratory sounds and expiratory sounds. Chest or abdominal movement without breath sounds may indicate total airway obstruction, and basic life support maneuvers are indicated. High-pitched sounds heard on inspiration (stridor) are often indicative of upper airway conditions, whereas expiratory noises are more often associated with lower airway obstruction.

Causes of stridor in children can be infections, such as croup; foreign body aspiration, particularly in a small child; congenital or acquired airway abnormalities; allergic reactions; or edema after a procedure. Inhaled epinephrine via nebulizer and intravenous steroids are commonly used to treat stridor. Common causes of lower airway obstruction are bronchiolitis and asthma. When wheezing is noted, inhaled bronchodilators are indicated. If the patient is able to use a metered dose inhaler (MDI), repeated inhalations can act quickly to improve aeration. When the patient is unable to use the MDI appropriately or when severe symptoms are present, delivering a bronchodilator with a nebulizer can bring relief. More than one nebulizer treatment often is necessary to relieve airway inflammation. A common approach is to deliver three consecutive treatments. If the patient continues to be symptomatic, continuous bronchodilator therapy may be delivered with a nebulizer attached to an infusion pump set to administer a bronchodilator continuously. Tachycardia secondary to the beta-1 effect of inhaled bronchodilators can be seen. Frequent reassessment of any patient receiving continuous bronchodilator therapy is essential. Heliox, an inhaled mixture of helium and O₂ (described in the section on specialty gases), has been shown to be beneficial in cases of some airways conditions in children.

As noted in the section describing newborn assessment, use of accessory muscles, grunting, flaring, and retracting all can be signs of respiratory distress. Head bobbing, noted by chin up and neck extended during inspiration with chin falling during expiration, and seesaw respirations, indicated by the chest retracting and the abdomen expanding during inspiration, are signs of impending respiratory failure. Assessing the child’s level of alertness is essential. Levels of alertness range from fully awake, agitated, minimally responsive, to unresponsive. A child’s ability to protect his or her airway should be questioned in a minimally responsive or unresponsive child.

O₂ should be administered as any other drug, using the lowest dose necessary to achieve the intended goal. The goal of O₂ therapy is to provide adequate tissue oxygenation. However, O₂ therapy is most frequently adjusted according to O₂ saturation levels. A clear understanding of the limitation of O₂ saturation is needed to interpret the saturation reading and make appropriate decisions. Infants and children receiving O₂ therapy have variable O₂ saturation target ranges depending on age and underlying condition.

Lower saturation levels are targeted in infants less than 32 weeks’ gestation. There is evidence that exposure to supplemental O₂ in a premature infant is a risk factor for the development of retinopathy of prematurity (ROP). ROP is caused by an abnormal vascularization of the retina, which in the most severe cases leads to retinal detachment. Preterm neonates weighing less than 1500 g are most susceptible. Hyperoxia is not the only factor associated with ROP, but close monitoring and adjusting of O₂ therapy to avoid hyperoxia is crucial to decrease the risk of ROP. Specific saturation goals for this age group should be established, and O₂ should be adjusted to maintain the intended target. Avoiding very high or very low saturation levels is critical. Adjusting the delivered O₂ concentration by small increments avoids large swings in saturation levels.7–11

In a term infant with primary pulmonary hypertension of the newborn (PPHN), a higher targeted saturation level is desired to avoid further pulmonary constriction associated with hypoxemia. The position of the saturation probe needs to be considered when interpreting saturation. Intracardiac shunting can occur in the presence of PPHN. One saturation probe positioned on the upper right extremity represents preductal saturations and is indicative of the saturation of blood being delivered to the brain. O₂ saturation measured on other extremities is considered postductal and represents saturation to other parts of the body.

Newborns with certain cardiac anomalies are dependent on their intracardiac shunt through the ductus arteriosus to survive. An increased saturation in newborns promotes constriction of the ductus arteriosus. Although this constriction is normally a positive response, it may cause premature closure of the ductus arteriosus in infants with ductal-dependent congenital heart defects. An infant born with hypoplastic left heart syndrome, a defect in which the left-sided heart structures are poorly developed, relies on the patency of the ductus arteriosus for systemic blood supply. In addition, hyperoxia can increase aortic pressures and systemic vascular resistance, decreasing the cardiac index and O₂ transport in children with acyanotic congenital heart disease. The emphasis for O₂ therapy for all newborns should be to provide only as much O₂ as indicated by the infant’s condition. O₂ therapy should be administered using a written care plan with specified clinical outcomes (e.g., titrate flow/FiO₂ to maintain SpO₂ 88% to 92%, notify physician if FiO₂ is >0.40).

Secretion Clearance Techniques

Secretion clearance techniques that can be applied to infants and children include chest physiotherapy, positive expiratory pressure therapy, autogenic drainage, flutter therapy, and mechanical insufflation-exsufflation.12,13 Secretion clearance techniques are considered when accumulated secretions impair pulmonary function and an infiltrate is visible on a chest radiograph. Secretion retention is common in children who have pneumonia, bronchopulmonary dysplasia, cystic fibrosis, bronchiectasis, and some neuromuscular diseases. Figure 48-7 shows postural drainage and percussion positions for infants and children.

Humidity and Aerosol Therapy

Key differences in humidity and aerosol therapy in infants and children include assessment of patient response to therapy, age-related physiologic changes, and equipment application.

Airway Management

Airway management methods in infants and children are unique because of the anatomic differences between neonates and adults. Specifically, equipment and technique must be tailored to each child according to his or her size, weight, and postpartum age. Masks, oral airways, suction catheters, laryngoscope blades, and endotracheal tubes in a wide selection of infant and child sizes are needed to account for variations in patient age and weight. Table 48-8 provides recommendations regarding endotracheal tube and suction catheter sizes for infants and children.

Methods of Administration

The application of CPAP is most commonly accomplished noninvasively. In preterm and term neonates, nasal prongs or nasopharyngeal tubes were traditionally used. However, the more recent introduction of improved interface devices has led to more consistent CPAP delivery and better patient comfort (Figure 48-8). These interfaces include nasal masks and soft, pliable nasal cannulas that provide a comfortable interface without applying excessive pressure to maintain a tight fitting seal. The American Association for Respiratory Care (AARC) has published Clinical Practice Guideline: Application of CPAP to Neonates via Nasal Prongs, Nasopharyngeal Tube, or Nasal Mask. Excerpts from this guideline appear in Clinical Practice Guideline 48-1.

For larger children, nasal masks, oronasal masks, nasal pillows, and other interfaces similar to interfaces used in adults may be used. In all patients, it is important to assess the patient-device interface at regular intervals to allow prevention or early detection and intervention in the event of pressure ulcers.

The appliance or interface is connected to either a mechanical ventilator set in the CPAP mode or a stand-alone CPAP device The complexity of stand-alone devices ranges from a simple continuous flow of gas against a fixed resistance or threshold to sophisticated CPAP generators that adjust flow and trigger sensitivity in the presence of a leak or increased patient demand. CPAP levels are selected based on clinical observation. Initial CPAP levels are usually 5 to 6 cm H₂O and are adjusted in increments of 1 to 2 cm H₂O. The patient’s SpO₂, respiratory rate, work of breathing, breath sounds, and blood pressure are monitored. The appropriate CPAP level is achieved when the respiratory rate decreases to near-normal ranges, signs of respiratory distress are lessened, and SpO₂ increases while O₂ requirements are reduced. Arterial and capillary blood gas analysis may provide additional information in determining the effectiveness of CPAP, and chest radiographs are obtained to determine the degree of lung inflation.

Weaning and eventually discontinuing CPAP is considered when oxygenation is adequate at FiO₂ less than 0.30 to 0.40, there is a sustained reduction in work of breathing, and chest radiograph and clinical assessment indicate resolution of the underlying disorder. The use of CPAP for prolonged periods in preterm infants helps reduce the work of breathing and prevent intubation. Long-term and intermittent use of CPAP is indicated in children with obstructive airway problems, chronic lung disease, and neuromuscular disorders.

High-Flow Nasal Cannula

Supplemental O₂ administration by nasal cannula is the most comfortable and simplest means of providing O₂ for infants and children. Evidence in preterm and term neonates indicates that using a nasal cannula at flow rates of 2 to 8 L/min may be as effective as and is easier to apply than a nasal CPAP system.30,31

Specially designed humidification systems have been developed and allow the use of nasal cannulas at flow rates of 2 to 30 L/min.³² These devices maximize humidification and minimize condensation accumulating in the small diameter supply tubing. High-flow nasal cannula systems have been used successfully in neonates for the same indications that CPAP has been used. Instead of titrating levels of CPAP, the flow rate is incrementally adjusted. However, the amount of positive pressure that the high-flow nasal cannula potentially produces cannot be measured, and inadvertent high levels may occur, particularly if the nasal cannula fits snugly in the nares.^33–35

High-flow nasal cannula systems have the potential for maximizing supplemental O₂ administration because the O₂ concentration delivered to the patient should approximate the set FiO₂. This approximation occurs because the anatomic reservoir of the upper airway is continuously flushed, greatly reducing the entrainment of room air. High-flow nasal cannula systems may be beneficial in stabilizing acute respiratory failure caused by hypoxemia, which may reduce the need for noninvasive or invasive assisted ventilation, such as in the case of a pulmonary exacerbation in a patient with cystic fibrosis or a patient experiencing congestive heart failure.

Basic Principles

Conventional mechanical ventilation is the delivery of a bulk flow of humidified gas into and out of the lungs. The removal of CO₂, typically measured by PCO₂, is directly related to alveolar ventilation (frequency × V_T). Gas moves from the ventilator across an artificial airway in response to a change in pressure or pressure gradient. The magnitude of pressure required to move a particular amount of volume is derived from the compliance of the pulmonary system and the resistance of the airways.

Compliance is a measure of the distensibility of the lungs and is expressed as the volume change per unit of pressure change (C = ΔV/ΔP). Resistance is the tendency for airflow across the tracheobronchial tree to be impeded at a particular pressure per unit of gas flow (R = ΔP/flow). The product of compliance and resistance is the respiratory time constant, or the measure of time necessary for the equilibration of a change in airway pressure (TC = C × R). A patient with stiff or noncompliant lungs, such as a preterm infant with surfactant deficiency, has short time constants, meaning less time is required for equilibration, and filling and emptying of lungs occur faster, which means shorter inspiratory and expiratory times. A patient with a disease characterized by impaired airflow or high resistance, such as a child with asthma, has longer time constants, in which more time is required for filling and emptying, meaning longer inspiratory and expiratory times are needed.

Goals of Mechanical Ventilation

The basic goals of mechanical ventilation are to improve O₂ delivery to meet metabolic demand and eliminate CO₂, while reducing the work of breathing.38,39 The basic aim of assisted ventilation is to meet the goals while minimizing the associated deleterious effects. One approach to mechanical ventilation begins with the selection of an appropriate breath type, either pressure-controlled or volume-controlled, and a mode that best meets the physiologic needs of the patient’s condition.⁴⁰ Box 48-5 lists the indications for mechanical ventilation in infants and children.

Modes of Ventilation and Breath Delivery Types

Historically, the most common mode of ventilation used in neonates and children was intermittent mandatory ventilation. Because early infant ventilators were unable to respond to the small triggering efforts of these patients, mandatory timed breaths were superimposed over a continuous flow of gas. These asynchronous, mandatory breaths provided most of the ventilation, while the patient was allowed to breathe spontaneously from the continuous gas source. Eventually, technologic improvements resulted in triggering devices that provided synchronization of the mandatory breaths with patient effort (synchronized intermittent mandatory ventilation [SIMV]) followed by the ability to provide assist control (A/C) and pressure support ventilation (PSV). Despite evidence that SIMV is more likely to result in patient-ventilator asynchrony,41,42 most neonatal and pediatric patients are managed by using one of these three modes or a combination (i.e., SIMV + PSV). The most common triggering device for infant ventilators is a pneumotachygraph placed in the ventilator circuit, often proximal to the airway, which in many cases also serves as a monitoring device. The pneumotachygraph allows for the integration of a flow signal, which can be displayed as inhaled and exhaled V_T and minute ventilation. Figure 48-9 displays graphic representations of A/C, SIMV, and PSV.

In almost all cases of neonatal ventilation, the mechanical breaths delivered during SIMV and A/C are time-cycled, pressure-limited breaths.⁴³ Inspiration is initiated by patient effort or as a result of the set respiratory rate (whichever comes first). Based on the available flow—continuous, demand, or both—the set inspiratory pressure is reached early in the inspiratory phase and maintained throughout the remainder of the inspiratory time, after which the ventilator cycles to expiration. Most current-generation ventilators are capable of providing volume-targeted, pressure-limited ventilation, often referred to as pressure-regulated volume control or volume guarantee. In this dual mode of ventilation, the inspiratory V_T is compared with a preset target V_T, and the inspiratory pressure on the next breath is adjusted up or down in an attempt to meet the target volume. True volume-controlled breaths are rarely used for ventilating neonatal patients. (See Chapter 42 for details.)

Pediatric patients may be ventilated with either volume-controlled or pressure-controlled breaths. The choice may be based on health care team or institutional preference, prior experience, and equipment availability or may be evidence-based for specific diseases (e.g., asthma).

Ventilator Settings and Parameters

After the mode of ventilation is selected, the RT begins to adjust the various settings associated with the mode, while keeping in mind the goals of ventilation and the patient’s weight, underlying problem, and reason for mechanical ventilation. The RT often can get a sense of the patient’s compliance by manually ventilating the patient and observing the pressure needed to make the chest rise.

Tidal Volume

When selecting V_T, the clinician must consider a volume that provides adequate lung inflation without overstretching the alveoli. Setting V_T that is too high most likely would result in lung injury. V_T of 6 to 8 ml/kg is generally considered safe in most patients. However, in some patients with extremely low lung compliance, such as patients with severe acute respiratory distress syndrome (ARDS), it may be necessary to reduce V_T to 4 to 5 ml/kg.

If the clinician chooses to deliver volume-controlled breaths, V_T is set as a control variable. Every mechanical breath delivers an identical V_T at either a preset inspiratory time or a preset flow rate. Set V_T, inspiratory time, and flow all are interrelated. If V_T is set at 300 ml, and flow rate is 30 L/min (0.5 L/sec), the inspiratory time is 0.6 second. See formulas in Box 48-6.

Box 48-6   Interrelationship of Tidal Volume, Flow, and Time

< ?xml:namespace prefix = "mml" />VT=Flow in L/sec×Inspiratory time

Inspiratory time=VT/Flow rate

When ventilating patients with pressure-controlled breaths, V_T is not set, but it should be monitored. The clinician must compare the monitored V_T with a predetermined target and adjust the delta P to meet that target.

Regardless of whether the clinician chooses volume-controlled or pressure-controlled breaths, he or she must recognize that some of the V_T is compressed in the circuit and not delivered to the patient; this is referred to as compressible volume loss. Most current-generation ventilators automatically compensate for compressible volume loss and adjust the delivered and displayed (monitored) V_T accordingly. With older ventilators, during volume-controlled breaths, the clinician must calculate the compressible volume loss and increase the set V_T to deliver the desired volume to the patient. During volume-controlled and pressure-controlled breaths, the calculated compressible volume loss must be subtracted from the ventilator displayed exhaled V_T. See Box 48-7 for calculation of compressible volume loss.

Box 48-7   Determining Effective or Corrected Tidal Volume

Effective VT=Delivered VT−Compressible volume

Compressible volume=Compressible factor×(PIP−PEEP)

Example: A 12-year-old child weighing 28 kg requires assisted ventilation. V_T is set at 240 ml, PIP is 25 cm H₂O, and PEEP is 5 cm H₂O. The compressible factor for the ventilator is 2 ml/cm H₂O.

Compressible volume=(2 ml/cm H2O)×(25−5 cm H2O)=40 ml

Effective VT=240 ml−40 ml=200 ml

Effective VT/kg=200 ml÷28 kg=7.1 ml/kg

 Rule of Thumb

Large V_T (>8 ml/kg) is likely to overstretch the lung, resulting in acute lung injury, and should be avoided. Patients with severe ARDS may require even lower V_T (4 to 5 ml/kg).

Mini Clini

Pediatric Ventilation

 Problem

A 10-year-old boy with a complex medical history including history of trisomy 21, intractable infantile spasms, seizure disorder, and developmental delay (nonverbal), is admitted with increased difficulty breathing and found to be positive for respiratory syncytial virus. His home regimen includes nocturnal NIV via nasal mask with an inspiratory pressure of 8 cm H₂O, 3 cm PEEP, and 2 L/min of O₂ added to the breathing circuit. On admission, the patient complains of shortness of breath. His respiratory rate is 40 breaths/min, and SpO₂ is 88% on a nonrebreathing mask. What should the RT suggest?

Solution

• NIV—consider beginning NIV via oronasal mask

• PIP—10 to 12 cm H₂O

• PEEP—3 to 5 cm H₂O

• Set respiratory rate—12 breaths/min

• FiO₂—1.0

Although this patient receives NIV for nocturnal support when stable, he currently has an acute infection superimposed on chronic restrictive lung disease. Beginning NIV now may provide sufficient support to prevent intubation during this acute condition. Initial PIP of 10 to 12 cm H₂O titrated to patient comfort may provide additional support, increasing V_T and allowing respiratory rate to return to baseline. Choosing an oronasal mask may prove to be a more efficient interface than the patient’s usual nasal mask at this time. The set respiratory rate of 12 breaths/min is intended to be a backup rate because this patient is spontaneously breathing and should be allowed to establish his own breathing pattern. FiO₂ should be adjusted to maintain an acceptable SpO₂.

To guide practitioners in providing quality care, the AARC has published Clinical Practice Guideline: Neonatal Time-Triggered, Pressure-Limited, Time-Cycled Mechanical Ventilation. Excerpts from this guideline appear in Clinical Practice Guideline 48-2.

48-2   Neonatal Time-Triggered, Pressure-Limited, Time-Cycled Mechanical Ventilation

AARC Clinical Practice Guideline (Excerpts)*

Indications

• Apnea

• Hypoxemic (PaO₂ < 50 mm Hg) or hypercapnic (pH < 7.20-7.25) respiratory acidosis despite use of CPAP and supplemental O₂ (i.e., FiO₂ ≥ 0.60)

• Abnormalities on physical examination

• Increased work of breathing shown by grunting, nasal flaring, tachypnea, and sternal and intercostal retractions

• Presence of pale or cyanotic skin

• Agitation

• Alterations in neurologic status that compromise the central drive to breathe

• Apnea of prematurity

• Intracranial hemorrhage

• Congenital neuromuscular disorders

• Impaired respiratory function resulting in a compromised FRC owing to decreased lung compliance or increased airways resistance or both, including but not limited to

• Respiratory distress syndrome

• Bronchiolitis

• Meconium aspiration syndrome

• Congenital diaphragmatic hernia

• Pneumonia

• Sepsis

• Bronchopulmonary dysplasia

• Radiographic evidence of decreased lung volume

• Impaired cardiovascular function

• PPHN

• Postresuscitation

• Congenital heart disease

• Shock

• Postoperative state characterized by impaired ventilatory function

Contraindications

There are no specific contraindications when indications are judged to be present.

Hazards and Complications

• Air leak syndromes secondary to barotrauma or volume overinflation (i.e., volutrauma) including pneumothorax, pneumomediastinum, pneumopericardium, pneumoperitoneum, subcutaneous emphysema, and pulmonary interstitial emphysema

• Chronic lung disease associated with prolonged PPV and O₂ toxicity (e.g., bronchopulmonary dysplasia)

• Airway complications associated with endotracheal intubation

• Laryngotracheobronchomalacia

• Unplanned extubation

• Damage to upper airway structures

• Air leak around uncuffed endotracheal tube

• Malpositioning of endotracheal tube

• Subglottic stenosis

• Obstruction of endotracheal tube with mucus

• Main stem intubation

• Kinking of endotracheal tube

• Pressure necrosis

• Increased work of breathing (during spontaneous breaths) owing to the high resistance of small endotracheal tubes

• Nosocomial pulmonary infection (e.g., pneumonia)

• Decreased venous return, decreased cardiac output, increased intracranial pressure leading to intraventricular hemorrhage

• Supplemental O₂ may lead to increased risk of ROP

• Complications associated with endotracheal suctioning

• Failure of ventilator, alarms, circuit, humidifier; loss of or inadequate gas supply

• Patient-ventilator asynchrony

• Inappropriate ventilator settings leading to auto-PEEP, hypoventilation or hyperventilation, hypoxemia or hyperoxemia, and increased work of breathing

Assessment of Need

Determination that valid indications are present

Assessment of Outcome

Establishment of neonatal assisted ventilation should result in improvement in the patient’s condition or reversal of indications:

• Reduction in work of breathing as evidenced by decreases in respiratory rate, severity of retractions, nasal flaring, and grunting

• Radiographic evidence of improved lung volume

• Subjective improvement in lung volume as indicated by increased chest excursion and aeration by chest auscultation

• Improved gas exchange

• Ability to maintain a PaO₂ ≥ 50 mm Hg with FiO₂ < 0.60

• Ability to reverse respiratory acidosis and maintain pH > 7.23

• Subjective improvement as indicated by decrease in grunting, nasal flaring, sternal and intercostal retraction, and respiratory rate

Monitoring

Patient-ventilator system assessments should be performed every 2 to 4 hours and should include documentation of ventilator settings and patient assessments as recommended by the AARC clinical practice guideline on patient-ventilator system assessments (see Chapter 46) and AARC clinical practice guideline on humidification during mechanical ventilation (see Chapter 35). Monitoring should include the following:

• O₂ and CO₂ monitoring

• Periodic sampling of blood gas values; keep PaO₂ < 80 mm Hg in preterm infants to avoid ROP

• An unstable infant should be monitored continuously by transcutaneous O₂ monitor or pulse oximeter

• An unstable infant should be monitored continuously by transcutaneous or end-tidal CO₂ monitoring

• Fractional concentration of O₂ delivered by the ventilator should be monitored continuously

• Continuous monitoring of cardiac activity (via electrocardiograph) and respiratory rate

• Monitoring of blood pressure by indwelling arterial line or by periodic cuff measurements

• Continuous monitoring of airway pressures including PIP, PEEP, and mean pressure ()

• Higher Paw may improve oxygenation; however, Paw > 12 cm H₂O may lead to barotrauma

• The difference between PIP and PEEP (ΔP) in conjunction with patient mechanics determines V_T; as ΔP changes, V_T varies

• PIP should be adjusted initially to achieve adequate V_T as reflected by chest excursion and adequate breath sounds or by V_T measurement

• PEEP increases FRC and may improve oxygenation (PEEP is typically adjusted at 4-7 cm H₂O—higher levels may cause hyperinflation, particularly in obstructive airways disease [e.g., meconium aspiration syndrome or bronchiolitis])

• Many neonatal ventilators provide continuous monitoring of ventilator rate, inspiratory time, and inspiratory-to-expiratory (I : E) ratio; if only two of these variables are directly monitored, the third should be calculated

• Lengthening inspiratory time increases Paw and should improve oxygenation

• I : E ratio >1 : 1 may lead to auto-PEEP and hyperinflation

• Rates of 30 to 60/min with shorter inspiratory times (e.g., I : E ratio 1 : 2) are commonly used in patients with respiratory distress syndrome

• Depending on the internal diameter of the ventilator circuit, excessive flows can cause expiratory resistance that leads to increased work of breathing and increased PEEP. Some ventilators have demand-flow systems that permit the use of lower baseline flow rates but provide the patient with additional flow as needed

• Because of the possibility of complete obstruction or kinking of the endotracheal tube and the inadequacy of ventilator alarms in these situations, continuous V_T monitoring via an appropriately designed (minimum dead space) proximal airway flow sensor is recommended

• Periodic physical assessment of chest excursion and breath sounds and for signs of increased work of breathing and cyanosis

• Periodic evaluation of chest radiographs to follow the progress of the disease, identify possible complications, and verify endotracheal tube placement

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^*For complete guideline, see American Association for Respiratory Care: Clinical practice guideline: neonatal time-triggered, pressure-limited, time-cycled mechanical ventilation. Respir Care 39:808, 1994.

Noninvasive Ventilation

Noninvasive ventilation (NIV), also known as noninvasive positive pressure ventilation, has become more popular recently in neonatal patients. In the past, use of NIV was limited by the lack of available interfaces; however, these are becoming more readily available. Figure 48-8 shows various interfaces that may be used for NIV (or CPAP) in neonates. More recent evidence supports the use of both synchronized and nonsynchronized NIV in the neonatal intensive care unit (ICU).⁴⁶ It is hoped that future research will clarify which patients are most likely to benefit from this form of support.

NIV has been used extensively in patients of all ages, including pediatric patients.47–50 Indications may include short-term support of hypoxemic respiratory failure, such as that seen with pulmonary edema associated with left-sided heart failure; prevention of intubation; postextubation support; and long-term support of patients with neuromuscular disease. Some limitation of available interfaces persists, particularly in smaller patients; however, most patients can be fitted without too much difficulty. As with CPAP and other noninvasive interface devices, care must be taken to prevent or minimize patient injury owing to iatrogenic pressure ulcers from a tight or poorly fitted device.

NIV may be provided with simple, single-limb devices such as bilevel positive airway pressure generators, or sophisticated ICU ventilators. Care must be taken whenever a single-limb circuit is employed to provide sufficient PEEP in the system to prevent rebreathing of gases (see Chapter 46).

Monitoring Mechanical Ventilation

The RT should develop a systematic approach to monitoring the effects of mechanical ventilation. Components of a ventilator assessment should include an evaluation of the artificial airway, physical examination, assessment of patient-ventilator interaction,⁵¹ analysis of laboratory and radiographic data, adjunct ventilator monitoring, and a systematic ventilator safety assessment including alarm function and assessment of humidification. Alarms should be connected to a central monitoring system to alert appropriately clinicians away from the bedside of a change the patient’s condition.

A flow sheet is used to prompt the user and guide the clinician through the process of assessing the patient, while serving as documentation of the ventilator settings and outputs. In the past, these flow sheets were paper and were maintained as part of the patient’s medical record. It is becoming more common to have the flow sheet integrated into an electronic medical record that is readily available to the entire patient care team. Although many elements of the patient-ventilator assessment are automatically entered via an electronic interface and require validation only by the clinician, some data must still be entered by hand. It is hoped that as these systems become more sophisticated and standardization improves, all of the data, including ventilator information, laboratory values, and radiographic and other imaging data, will automatically download, eliminating transcription errors, providing a more comprehensive assessment, and allowing the clinician to focus on the patient and patient-ventilator interaction.

Weaning from Mechanical Ventilation

Weaning or, more appropriately, liberation from mechanical ventilation is a topic that until more recently has received little attention in pediatric and neonatal patients. Clear guidelines for “assessment of readiness to extubate” and “spontaneous breathing trials” are standard practice in adults. However, this assessment has not yet become standard practice in pediatric and neonatal patients even though there are resources available to guide the pediatric/neonatal clinician in this area.⁵⁴ Nevertheless, these patients should be assessed daily to determine their readiness for liberation from mechanical ventilation. Some general considerations for extubation are presented in Box 48-8; however, distinct differences exist among these various patients, and it is reasonable to develop an age-specific, multidisciplinary approach to this task. One alternative would be to begin with existing adult guidelines and modify them to meet the needs of pediatric and neonatal patients. Two sets of guidelines, one for pediatric patients and one for neonates, are presented in Boxes 48-9 and 48-10. (See Chapter 47 for details on weaning.)

High-Frequency Ventilation

High-frequency ventilation (HFV) is a form of invasive mechanical ventilation that uses small V_T values (less than dead space) at rapid frequencies, sometimes greater than 900 breaths/min (15 Hz). The primary goal of HFV is to provide adequate ventilation and oxygenation, while limiting the incidence of lung injury. HFV has been used as a primary mode of ventilation and a rescue therapy for patients determined to be failing conventional mechanical ventilation. Although early studies showed a beneficial effect compared with conventional ventilation, there has been no demonstrated improvement in outcome compared with current lung protective strategies.55–61 HFV remains an acceptable mode of ventilation for patients of any age but should be used only by clinicians expert in its clinical application and knowledgeable about its physiologic effects.

There are three basic types of HFV: high-frequency oscillatory ventilation, high-frequency jet ventilation, and high-frequency percussive ventilation. High-frequency oscillatory ventilation is the most common form of HFV. Oxygenation is achieved by inflating the patient’s lungs to a high resting level, or FRC, by establishing a high , similar to CPAP, at levels typically ranging from 16 to 30 cm H₂O. This “recruitment” improves the ratio by opening previously collapsed alveoli. Ventilation is provided by the to-and-fro movement of a large piston in the ventilator circuit that results in high-frequency oscillations in the patient’s airways. Gas exchange results from a combination of six mechanisms: bulk flow of gas, longitudinal dispersion, pendelluft, asymmetric velocity profiles, cardiogenic mixing, and molecular diffusion.

Complications of Mechanical Ventilation

Box 48-11 summarizes the most common complications associated with mechanical ventilation in newborns and other pediatric patients.

Heliox

Heliox is gas mixture of O₂ and helium. Typical concentration of a tank of heliox is 80%/20% or 70%/30%. Helium is less dense than air. Inhaling a less dense gas can reduce airway resistance and result in decreased work of breathing. In patients with a high O₂ requirement, helium is less effective. Heliox has been used in conjunction with other therapies in the treatment of partial airway obstruction and asthma where airway resistance is high. It can be used to help deliver bronchodilators and serve as a temporizing measure while steroids are administered to reduce airway swelling. When high O₂ concentrations are necessary, heliox is not likely to be effective as the amount of inspired helium is diminished. Signs of decreased work of breathing, decreased use of accessory muscles, improved aeration, and decreased respiratory rate after initiating heliox are indications of its effectiveness.