a. Physiologic effects

Continuous positive airway pressure (CPAP) and positive end-expiratory pressure (PEEP) increase the patient’s functional residual capacity (FRC). In neonates, the most common cause of a decreased FRC is infant respiratory distress syndrome (RDS). This condition is caused by the lack of surfactant in the lungs of the premature neonate. The neonate with RDS has relatively airless lungs that are prone to atelectasis. This results in hypoxemia. In addition, each tidal volume breath requires a greater than normal inspiratory effort (Figure 16-1). The restoration of FRC in the neonate increases its Pao₂, decreases the percentage of shunt, narrows the alveolar to arterial difference in oxygen, and reduces its work of tidal volume breathing. CPAP must be used with caution in neonates with persistent pulmonary hypertension (PPHN) of the newborn. An excessive amount of pressure in the alveoli compresses the capillary bed. This decreases pulmonary blood flow, which in turn increases blood flow through the patent ductus arteriosus and worsens the problem.

Figure 16-1 Pressure-volume curves for normal neonate and for one with infant respiratory distress syndrome (RDS). Normal neonate’s lungs inhale a relatively large tidal volume at low pressure. Note how when the same pressure is placed against the lungs of an infant with RDS, the tidal volume is much smaller. To get a normal tidal volume, the RDS infant must generate a much greater negative pressure.

(From Carlo WA, Martin RJ: Pediatr Clin North Am 33:221, 1986.)

b. Indications, contraindications, and hazards

CPAP is indicated for any condition that results in an unacceptably low Pao₂ secondary to a decreased FRC. Some neonates respond so well to CPAP that mechanical ventilation is not needed. In addition, CPAP has been used to keep open the airways of infants with tracheal malacia or other conditions in which the airways collapse abnormally. In general, contraindications include any CPAP-related condition that results in a worsening of the patient’s original status. Some neonates cannot tolerate CPAP and progressively hypoventilate as the pressure level is increased. Clinical judgment is needed to decide how high the PaCO₂ should be allowed to rise before discontinuing the CPAP and beginning mechanical ventilation. In general, the PaCO₂ should not be greater than 50 torr as long as the pH is at least 7.25. An absolute contraindication is apnea resulting in hypoxemia and hypotension. These infants should be mechanically ventilated. Box 16-1 gives a complete listing of indications, contraindications, and hazards.

c. Initiation

Before starting CPAP, a set of baseline arterial blood gases should be taken. Transcutaneous oxygen monitoring or pulse oximetry may be substituted in some clinical situations if oxygenation is the only parameter that must be measured. The neonate’s vital signs should also be recorded. Assemble the CPAP circuit and pressure device. The decision must be made whether to apply the CPAP above the epiglottis (Figures 16-2 and 16-3) or to intubate the infant and apply the CPAP within the trachea. Nasal CPAP (NCPAP) or nasopharyngeal tube CPAP (NP-CPAP) are both widely used to apply pressure from above the epiglottis. The neonate or infant must have an endotracheal tube placed to apply CPAP within the trachea. Among the factors to be considered are the neonate’s gestational age and weight, the amount of secretions that need to be suctioned, the pulmonary problem, and the likelihood of mechanical ventilation eventually becoming necessary. More mature and larger infants with few secretions and relatively stable pulmonary conditions will most likely have CPAP applied above the epiglottis by nasal prongs or nasopharyngeal tube. In contrast, less mature and smaller infants (less than 1000 to 1200 g) who need suctioning and have relatively unstable pulmonary conditions will probably be intubated. Mechanical ventilation can then be easily started if needed.

Figure 16-2 A, Nasal CPAP is delivered through a set of prongs and placement system. Shown is a Kendall Health Argyle CPAP prong and headgear set. B, Nasopharyngeal CPAP is delivered through a shortened endotracheal tube. Shown are 2.5, 3.0, and 3.5 mm ID endotracheal tubes that have been cut off at the proximal end and attached to the ventilator adapter. Always select the prongs or tube that are the proper size to fit the neonate’s airway.

(From Cario J, Pilbeam S: Mosby’s Respiratory Therapy Equipment, ed 8, St Louis, 2010, Mosby.)

Figure 16-3 An assembly for supporting nasal CPAP prongs in an infant.

(Modified from advertisement of Stayflex tubing system from Ackrad.) (From Sills JR: Respiratory care registry guide, ed 1, St Louis, 1994, Mosby.)

CPAP is usually started at about 4 to 5 cm water pressure whether the pressure is applied above or below the epiglottis. The inspired oxygen percentage is usually kept at the previously set level. It is important to make only one change at a time so that each adjustment in care can be evaluated for its own effect. For example, if you simultaneously increased the oxygen percentage by 10% and started 5 cm water of CPAP, it would not be known whether the increase in Pao₂ was from the additional oxygen, the CPAP, or both. Usually the long-term inspired oxygen is limited to 40% to 50% because of concern of the possibility of pulmonary oxygen toxicity.

d. Monitor and adjust alarm settings (ELE Code: IIIG3g) [Difficulty: ELE: R, Ap, An]

Depending on the clinical situation, CPAP can be administered through a freestanding, improvised system or through a mechanical ventilator set on the CPAP mode. A variety of alarms and monitoring systems should be used to ensure the patient’s safety. Patient monitors should have visual and audible alarms and include the following:

e. CPAP adjustment

Blood gases and vital signs must be evaluated at the starting CPAP level. The heart rate, blood pressure, and respiratory rate should be stable or improved. Wait at least 10 minutes after a change in CPAP before getting an arterial blood gases sample. See Table 16-1 for the recommended blood gas limits. In general, the Pao₂ should be kept between 60 and 70 torr, PaCO₂ less than 50 to 55 torr, and pH at least 7.25. If the Pao₂ is too low and the patient’s vital signs are acceptable, the CPAP may be increased in a step of 1 to 2 cm water. The vital signs and blood gases should then be reevaluated. In addition, the neonate’s work of breathing can be indirectly assessed. Improved lung function will be demonstrated by seeing decreased respiratory rate, retractions, expiratory grunting, and nasal flaring. If necessary, the process of adding CPAP and reassessing the patient can be continued. The maximum CPAP level in a neonate is generally held to be 10 cm water; the maximum CPAP level in an infant is generally held to be 15 cm water.

TABLE 16-1 Commonly Recommended Blood Gas Goals for CPAP and Mechanical Ventilator Therapy

NOTE: Keep the Pao₂ no greater than 80 torr in the premature neonate to reduce the risk of retinopathy of prematurity.

* Ptco₂ values may be used after they have been shown to correlate within 15% of the Pao₂ from an arterial blood gas.

† With CPAP, this value may be increased to 50 to 55 torr as long as the pH is at least 7.25.

Mechanical ventilation is usually indicated if more than these maximum CPAP pressures are needed to correct hypoxemia. Depending on the patient, even levels less than these maximum CPAP pressures may not be well tolerated. The infant may become exhausted from exhaling against the back pressure of the CPAP system. That is seen clinically as decreased chest movement from the smaller tidal volume. The PaCO₂ will probably increase. It may be necessary to place the infant on mechanical ventilation to decrease the work of breathing and then add PEEP to maintain the FRC. When nasal prongs or a nasopharyngeal tube are used, CPAP pressures of greater than 8 cm water may cause the infant’s mouth to open. This results in the loss of CPAP. A crying infant also opens its mouth and loses the CPAP. In either case, the CPAP pressure gauge drops to zero or fluctuates below the set pressure.

f. Independently initiate weaning from CPAP (Code: IIIF2i12) [Difficulty: ELE: R, Ap; WRE: An]

As the patient improves, it is necessary to reduce the CPAP level so as not to cause pulmonary barotrauma. The pressure level can be reduced in steps of about 2 cm water. The vital signs and blood gases should be reassessed after each step. The apparatus is usually removed when the CPAP level is down to 2 to 4 cm water. The infant is then placed into an oxyhood at the same oxygen percentage as before or 5% to 15% higher. If the infant has an endotracheal tube that is needed for suctioning or a secure airway, the pressure is usually left at 2 to 4 cm water. After extubation, the infant is placed into an oxyhood as before. Alternatively, the neonate may be weaned to a high flow nasal cannula and then to a traditional, low-flow nasal cannula. See Chapter 6 for more discussion on the high-flow nasal cannula.

If the infant was breathing more than 50% oxygen while on the CPAP, it may be more important to lower the oxygen before decreasing the CPAP level. The following guidelines may prove helpful when deciding whether to first lower the oxygen percentage or the CPAP level:

a. Recommend changing the type of ventilator to be used on the patient (Code: IIIG3i) [Difficulty: ELE: R, Ap; WRE: An]

b. Independently change the type of ventilator to be used on the patient (Code: IIIF2i9) [Difficulty: ELE: R, Ap; WRE: An]

Historically, most neonatal patients requiring life sup-port receive time-triggered, pressure-limited, time-cycled mechanical ventilation (TPTV). These ventilators are pneumatically powered with electrical controls and alarm systems. They are used in the IMV mode and feature a continuous flow of gas from which the neonate can breathe spontaneously. TPTV units are pressure limited to prevent an excessive peak airway pressure and can have therapeutic PEEP added. Furthermore, they are capable of reaching the Food and Drug Administration (FDA) limited rate of 150 breaths/min. The majority of neonatal and small pediatric patients can be effectively ventilated on these types of units.

High-frequency ventilation (HFV) with a small tidal volume has been approved by the FDA for use in the rescue of neonates with RDS and a bronchopulmonary fistula or pulmonary interstitial emphysema (PIE) who fail under conventional TPTV ventilation. HFV has also been used in the short-term support of neonates with a congenital diaphragmatic hernia until corrective surgery can be performed.

Volume-cycled ventilators are commonly used on infants who weigh more than 10 kg (22 lb). The most recent generation of conventional volume-cycled ventilators can be used to deliver a tidal volume as small as 2 to 3 mL. They often have chest wall sensor systems that note movement and match that breathing effort with a machine delivered breath. Volume-oriented ventilation can also be performed with a neonatal TPTV-type ventilator if the patient is apneic. This technique is discussed later.

When selecting a ventilator, it is important to choose one that offers the features needed to ventilate the patient. For example, if real-time graphics are needed to evaluate the patient’s response to a ventilator adjustment, the proper unit will be needed. Any selected ventilator must be able to meet the typical tidal volume goal for a neonatal of 4 to 6 mL/Kg or small pediatric patient of 6 to 8 mL/Kg. A patient receiving HFV for an FDA-approved pulmonary problem has a smaller tidal volume goal.

a. Initiate and adjust continuous mechanical ventilator settings (Code: IIID2b) [Difficulty: ELE: R, Ap; WRE: An]

b. Recommend changes in mechanical ventilation to modify ventilator techniques (Code: IIIG3e) [Difficulty: ELE: R, Ap; WRE: An]

c. Independently modify ventilator techniques (Code: IIIF2i5) [Difficulty: ELE: R, Ap; WRE: An]

With traditional neonatal TPTV, a set tidal volume is not ordered and cannot be measured. With volume-cycled ventilation of a pediatric patient, the tidal volume is ordered just as it is with an adult patient. Typically the therapist is expected to set the following ventilator controls based on a protocol or the patient’s condition and response to the ventilator: sensitivity, flow, I : E ratio, alarms, and humidified gas temperature. Specific examples of ventilator settings, based on pathological problem, will be presented next.

d. Sensitivity

e. Flow

Flow is adjusted to set the inspiratory time, the I : E ratio, or to meet the patient’s needs to better synchronize breathing efforts with the ventilator. The flow should be increased if the patient appears to be attempting to inhale faster than the ventilator is delivering the tidal volume.

f. I : E ratio

g. Alarms

Alarm systems are different for each type of ventilator. Generally speaking, they are set with a safety margin of ±10% from the patient’s normal ventilator settings. A variation of greater than 10% results in an audible or visual alarm condition.

h. Humidified gas temperature

The goal for most patients is to minimize their humidity deficit by giving gas that is humidified and warmed to near body temperature. It is common to have the gas warmed to 90° to 95° F (about 35° C). It should be measured in the inspiratory limb of the circuit as close to the patient as possible.

A review of the literature dealing with neonatal critical care shows that there are few universally accepted strategies for the use and modification of CPAP/PEEP and mechanical ventilation. The discussion presented here is an attempt to describe what are widely accepted approaches to neonatal TPTV and related therapy. The approach used in this discussion focuses on adjusting the ventilator and treating a neonate based on its pathologic problem.

a. Patients with normal cardiopulmonary function

Patients with normal cardiopulmonary function may need mechanical ventilation because of apnea from anesthesia, paralysis, or a neurologic condition. The initial TPTV ventilator parameters for this type of patient are listed in Box 16-3. Once mechanical ventilation is established, it is important to evaluate the patient’s blood gases, vital signs, breath sounds, and any other pertinent clinical information before changing any ventilator parameters.

As the patient recovers and begins to breathe spontaneously, it will probably be necessary to reduce the ventilator-delivered minute volume. This encourages the child to breathe more because the final goal is to completely wean and extubate the patient. The most accepted way to reduce the ventilator-delivered minute volume is to reduce the ventilator rate. A reduction of about 10% is a good starting place but must be tailored to meet the patient’s needs. The tidal volume is maintained as originally set. Obtain a set of blood gases in 10 to 20 minutes (or follow the transcutaneous or pulse oximetry values), and check the patient’s vital signs to see how well the adjustment is tolerated.

If the blood gases show an elevated PaCO₂, the ventilator-delivered minute volume must be raised. Do this by increasing either the alveolar ventilation or respiratory rate. Alveolar ventilation can be increased by increasing either the inspiratory flow or the pressure limit (if it has been reached) to increase the tidal volume. The ventilator rate may be increased if the flow and pressure limit cannot be increased. An increase of about 10% is a good starting place but must be tailored to meet the patient’s needs. As before, blood gases and vital signs should be monitored after every change to see if the increase is well tolerated and accomplishing what was intended.

If the blood gases show that the PaCO₂ is lower than desired, the ventilator-delivered minute volume must be decreased. The first parameter to adjust is usually the rate. Try decreasing the rate by about 10% and check another set of blood gas values. If other parameters need to be reduced, try decreasing the peak inspiratory pressure, inspiratory flow, or inspiratory time about 10% to decrease the tidal volume. Again, check the blood gas values after every adjustment.

If the blood gases show that the Pao₂ is higher or lower than necessary, the oxygen percentage must be adjusted. An increase or decrease of about 5% is a good starting place but must be adjusted as needed. If the patient does not respond to the increased oxygen as expected, the patient should be reevaluated. It may be necessary to reclassify him or her into one of the following categories.

Math Review

CALCULATION OF ESTIMATED TIDAL VOLUME DURING TPTV MECHANICAL VENTILATION

The NBRC examination content outline does not specifically list estimated tidal volume calculations. However, the information may be useful in understanding concepts presented later in the text.

If the neonatal patient receiving TPTV is apneic and neither assisting nor fighting against the ventilator-delivered breath, it is possible to calculate an approximate tidal volume. This is referred to as volume-oriented ventilation. The following formula is used:

In which

T_I = inspiratory time

(It is important that either the pressure limit is not reached or the pressure limit is reached at the same time inspiratory time is completed. If the pressure limit is reached before the inspiratory time limit is reached, part of the inspiratory time is spent as an inflation hold, and no additional tidal volume is delivered.)

= inspiratory flow rate on the ventilator in mL/sec

Vc = volume compressed in the circuit and ventilator

(This is found by multiplying the peak inspiratory pressure by the manufacturer’s stated compliance factors for the circuit and ventilator.)

For example, estimate the delivered tidal volume for an apneic 5 kg infant. The ventilator parameters are inspiratory flow of 5.5 l/min, frequency of 20/min, I : E ratio of 1 : 3, inspiratory time of 0.75 seconds, and expiratory time of 2.25 seconds. Peak inspiratory pressure (PIP) is 15 cm water. The internal compliance of the ventilator is 0.4 mL/cm water, and the circuit compliance factor is 1.6 mL/cm water.

In which:

T_I = .75 seconds

= 5.5 L/min. This is converted to mL/sec by dividing the flow in L/min by 60 seconds. So 5.5 L/min = .092 L/sec or 92 mL/sec:

Vc = 0.4 + 1.6 mL/cm water = 2 mL/cm water = 2 mL/cm water × 15 cm water PIP = 30 mL

Therefore,

It must be emphasized that this is only a calculated tidal volume. Leaks in the system, a decrease in the patient’s compliance, or an increase in the patient’s resistance decreases the true tidal volume. Conversely, an increase in the patient’s compliance or a decrease in the patient’s resistance increases the true tidal volume. Also, if the pressure limit is reached before the inspiratory time is completed, less volume than expected will be delivered. This is because part of the inspiratory time is spent as an inflation hold and no additional tidal volume is delivered (Figure 16-5). Finally, the infant must be completely passive during the delivery of the breath.

Figure 16-5 Pressure-time curve seen with pressure limit set at 25 cm water and inspiratory time being increased from 0.5 to 1 second. Pressure limit is reached when inspiratory time is about 0.5 second. As inspiratory time is increased to 1 second (or greater), the pressure limit is held at 25 cm water resulting in a “square wave” pressure curve.

(From Betis P, Thompson JF, Benjamin PK: Mechanical ventilation. In: Koff PB, Eitzman DV, Neu J: Neonatal and pediatric respiratory care, ed 2, St Louis, 1993, Mosby.)

b. Patients with decreased lung compliance and normal airway resistance such as infant respiratory distress syndrome (RDS)

Although RDS in infants weighing less than 1000 g is the most common cause of decreased lung compliance with normal airway resistance, stiff lungs are also found in patients with other lung conditions such as pneumonia and pulmonary edema (Figure 16-6). The greatest challenge presented in the care of these infants is to oxygenate them without causing oxygen toxicity or pulmonary barotrauma. Common recommendations for the initial ventilator settings are listed in Box 16-4. As discussed earlier, blood gases, vital signs, and so forth must be monitored after the infant is placed on the ventilator. Any further adjustments can then be determined and evaluated by another set of blood gases and vital signs.

Figure 16-6 Comparison of the lung volumes and capacities of a 6-year-old child, normal infant, and an infant with IRDS. Note relatively high compliance and low resistance of a normal child compared with an infant, and infant with RDS compared with normal infant.

(From Chatburn RL, Lough MD. Mechanical ventilation. In: Lough MD, Doershuk CF, Stern RC, editors: Pediatric respiratory therapy, ed 3, St Louis, 1985, Mosby.)

The issue of time constants of ventilation helps to better explain the various options available for adjusting the ventilator. As presented earlier, the time constant of ventilation (T_c or time constant of the respiratory system T_RS) is calculated as the product of compliance and resistance. For example, using the following values for a mechanically ventilated neonate with RDS, its time constant is calculated as

Neonates with RDS have a relatively short time constant; therefore the tidal volume and ventilating pressure are delivered rather quickly to the lungs. However, because the lungs are so stiff, there is usually no problem with the tidal volume being fully exhaled as long as five time constants are allowed. An expiratory time of at least 0.5 seconds is usually set initially. The various options available for increasing oxygenation are discussed on the following pages.

2. Increased inspiratory flow

a. Recommend changes in mechanical ventilation to improve alveolar ventilation (Code: IIIG3c) [Difficulty: ELE: R, Ap; WRE: An]

b. Independently modify mechanical ventilation to improve alveolar ventilation (Code: IIIF2i3) [Difficulty: ELE: R, Ap; WRE: An]. With TPTV-type ventilators, increasing the flow increases the tidal volume until the pressure limit is reached.

Increasing the tidal volume should result in an increased Pao₂ and is likely to reduce the PaCO₂. If the pressure limit is reached, the delivered tidal volume is held in the lungs for the duration of the inspiratory time. This acts as an inflation hold and should also increase the Pao₂. The mean airway pressure is raised by holding the tidal volume in the lungs. (See Figure 16-7 for the pressure waveforms seen during low-flow and high-flow conditions.) Under high-flow conditions, the pressure waveform takes on a characteristic square shape (square wave) because the pressure limit is reached. This pattern of ventilation is currently widely used with these types of patients.

Figure 16-7 Comparison of pressure-time curves showing influence of inspiratory flow when the pressure limit is set at 25 cm water pressure. A, Curve at high flow rate. Pressure limit is reached very early in the inspiratory time with resulting “square wave” flow pattern. B, Curve at low flow rate. Pressure limit is not reached until inspiratory time is almost 1 second.

(From Chatburn RL, Lough MD. Mechanical ventilation. In: Lough MD, Doershuk CF, Stern RC, editors: Pediatric respiratory therapy, ed 3, St Louis, 1985, Mosby.)

5. Increased pressure limit

To deliver a larger tidal volume, it may become necessary to increase the pressure limit when it is reached by the peak inspiratory pressure (PIP). It may also be necessary to raise the pressure limit to restore the original tidal volume after the addition of PEEP. This is because the original tidal volume is reduced when PEEP is added and the PIP reaches the pressure limit. This is shown in Figure 16-8. To restore the original tidal volume, the pressure limit (and PIP) must be increased by the same amount as the added PEEP. It is important to remember that as PEEP is reduced, the pressure limit must also be reduced by the same amount. This maintains the original tidal volume.

Figure 16-8 Pressure-time curve showing effect of addition of PEEP on tidal volume. Initially, tidal volume is delivered by pressure difference of 30 cm water (difference between 0 and 30 cm water pressure). With addition of 5 cm water PEEP, pressure difference is reduced to 25 cm water (difference between 5 and 30 cm water pressure). This results in less tidal volume being delivered.

(From Burgess WR, Chernik V: Respiratory therapy in newborn infants and children, ed 2, New York, 1986, Thieme.)

7. Initiate and select appropriate settings for high-frequency ventilation (HFV) (Code: IIID4) [Difficulty: ELE: R, Ap; WRE: An]

High-frequency ventilation (HFV) involves the use of a ventilator respiratory rate that is much greater than commonly needed. The FDA defines HFV as a rate of more than 150/min. Because of this FDA definition of HFV, conventional neonatal TPTV ventilators are not considered high-frequency ventilators. Several manufacturers have developed ventilators capable of rates significantly greater than 150/min. One of these must be used when HFV is indicated. The FDA has also set some guidelines for the appropriate use of HFV. See Box 16-5 for the clinical indications for HFV. The most commonly encountered problem is with a premature neonate with infant respiratory distress syndrome (RDS), a homogenous lung disease causing low compliance. If the RDS patient is failing despite optimal conventional mechanical ventilation and has a mean airway pressure of greater than 15 cm water, high-frequency ventilation is indicated.

BOX 16-5 Common Clinical Indications for the Use of High-Frequency Ventilation in Infants and Children

Severe hypoxemia and hypercarbia unresponsive to conventional ventilation techniques

Infant respiratory distress syndrome (RDS)

Acute respiratory distress syndrome (ARDS)

Pneumonia

Aspiration syndromes

Pulmonary hemorrhage

Conventional ventilation with a persistent pulmonary air leak

Pneumothorax

Bronchopleural fistula

Pulmonary interstitial emphysema (PIE)

Pneumomediastinum

Pneumoperitoneum

Persistent pulmonary hypertension of the newborn (PPHN)

Pulmonary hypoplasia

Bronchoscopy, laryngoscopy, or tracheal surgery

Despite the FDA guidelines, many respiratory therapists consider a rate of greater than 40/min on a neonatal patient to be HFV. When a conventional TPTV ventilator is used to deliver a respiratory rate of up to 150/min, the term high-frequency positive pressure ventilation (HFPPV) is used. Experience has shown that many RDS infants can be successfully managed with conventional TPTV ventilator set to deliver a small tidal volume at a rate between 40 and 150/min. However, when these methods fail, true HFV is needed.

Ventilator manufacturers have developed two different technologies for delivering FDA-defined HFV. The first is called high-frequency jet ventilation (HFJV). With HFJV, small jets of gas are directed down the patient’s endotracheal tube. These gas jets entrain additional gas into the tube. The two combined volumes of gas make up the patient’s tidal volume. The patient exhales passively because of normal lung recoil. The second method is called high-frequency oscillation (HFO) or high-frequency oscillatory ventilation (HFOV). With HFO, a pumping device (piston, diaphragm, or sound speaker) actively pushes a small tidal volume into the patient from a continuous flow of gas (called bias flow) passing through the circuit and by the endotracheal tube. HFO technology can deliver very high rates because the patient actively exhales the delivered tidal volume. This active exhalation is created by the back stroke of the pumping device that pulls the tidal volume out of the patient’s airways and lungs. See Table 16-2 for a comparison of HFV methods and characteristics.

TABLE 16-2 High-Frequency Ventilation Features and Characteristics

Initial HFV settings depend on the patient’s diagnosis, clinical situation, current conventional ventilator settings, and the type of high-frequency ventilator to be used. Generally speaking, the initial HFV settings include a tidal volume large enough to see chest movement and a continuation of the patient’s original mean airway pressure, PEEP level, and oxygen percentage. The I : E ratio should be set at 1 : 2 and the high-frequency rate should be between 10 and 15 Hertz (Hz) depending on the infant’s body weight. (A Hz is defined as 1 respiratory cycle/sec; 60 respiratory cycles/min. For example, a rate of 600/min is 10/sec or 10 Hz.) After the patient is stabilized on HFV, arterial blood gases should be drawn and analyzed, vital signs assessed, and a chest radiograph obtained. In a patient without a pulmonary air leak, a chest radiograph finding of lung expansion to T8 to T9 on the right hemidiaphragm, without intercostal bulging, is believed to show the best lung volume. Once established, the HFV rate is seldom changed. Adjustments in tidal volume are made by increasing or decreasing what is referred to as either drive pressure (with HFJV) or amplitude (with HFO). Increasing drive pressure/amplitude increases the tidal volume and decreases the carbon dioxide level. The patient’s oxygenation should also improve as the mean airway pressure is increased. Decreasing drive pressure/amplitude decreases the tidal volume and increases the carbon dioxide level. If the patient’s oxygenation should decrease too much, additional therapeutic PEEP may be needed. See Table 15-1 for high-frequency ventilation guidelines with infant and adult patients. See Figure 16-9 for a protocol on initiation and adjustment of HFO. Figure 16-10 shows a protocol for weaning from HFO.

Figure 16-9 Optimum lung volume HFOV strategy flowchart.

(From Minton S, Gerstmann D, Stoddard R: Cardiopul Rev, Yorba Linda, Calif, 1995, Sensormedics Corp. PN 770118-001.)

Figure 16-10 HFOV flowchart for weaning from optimum lung volume strategy.

(From Minton S, Gerstmann D, Stoddard R: Cardiopul Rev, Yorba Linda, Calif, 1995, Sensormedics Corp. PN 770118-001.)

Exam Hint 16-4 (WRE)

If a patient with RDS is failing with conventional mechanical ventilation, high-frequency ventilation is indicated.

c. Patients with increased airway resistance and normal lung compliance such as meconium aspiration syndrome (MAS)

Although meconium aspiration is a commonly seen cause of increased airway resistance, it is also seen in infants with excessive airway secretions or bronchospasm. These neonates usually have normal lung compliance and their clinical problem is getting enough air into and out of the lungs. The meconium or other obstruction causes uneven airflow and results in hypoxemia, air trapping, auto-PEEP, and an increased risk of barotrauma or volutrauma. Because of these issues, there are two key clinical goals. The first is to minimize turbulence during inspiration by reducing the inspiratory flow rate as much as possible. The second is to give a long enough expiratory time to prevent air trapping. Common recommendations for the ventilator settings are listed in Box 16-6. As discussed earlier, blood gases, vital signs, and so forth must be monitored after the infant is placed on the ventilator. Listen to the breath sounds to detect the end of exhalation and a pause before the start of the next inspiration. This is to ensure that the exhalation has been complete and there is no air trapping that would lead to auto-PEEP. Any further adjustments can then be determined and evaluated by another set of blood gases and vital signs.

Look again at the issue of time constants of ventilation to better understand the various options for adjusting the ventilator. Using the following values for a mechanically ventilated neonate with meconium aspiration, its time constant is calculated as follows:

Tc compliance (.005 L/cm water) × resistance(150 cm water/L/second because the infant is intubated and has an obstructive problem.)

Simplify as follows:

(Compare this with a Tc of 0.15 for a normal, spontaneously breathing neonate and a Tc of 0.1 for a ventilated infant with RDS.)

This relatively long time constant means that the tidal volume and peak inspiratory pressure are rather slowly delivered to the alveoli. There is little chance of causing barotrauma or volutrauma from high ventilating pressures; however, it takes a fairly long inspiratory time to deliver an adequate tidal volume. Care must be taken to provide enough expiratory time for the tidal volume to be exhaled completely. Briefly then, the challenge is to deliver an adequate tidal volume to maintain acceptable blood gases at a rate slow enough to prevent air trapping on exhalation.

In general, the inspiratory flow and rate are kept low, inspiratory and expiratory times are kept relatively long, and the I : E ratio should favor a long time for complete exhalation. Furthermore, it is important to frequently suction the airway to remove meconium or secretions. Postural drainage and percussion are also provided to mobilize the secretions so that they can be suctioned out. Usually these procedures and the natural breakdown of meconium result in reduced airway resistance within a few days. Ventilatory support can then be lessened.

d. Patients with persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is also referred to as persistent pulmonary hypertension (PPH), persistent fetal circulation (PFC), or persistence of the fetal circulation. Infants with PPHN present clinically with an elevated pulmonary artery pressure and a right-to-left shunt through a patent ductus arteriosus (PDA) or the foramen ovale. Therefore, their oxygenation fluctuates greatly. The problem may be seen right after birth or up to 24 hours later. PPHN seems to result from fetal hypoxemia and acidosis. These, in turn, are caused by or associated with maternal drug addiction, infection, preeclampsia, abruptio placenta, postterm gestation, oligohydramnios, and meconium staining or aspiration. The following four tests are done to help confirm the diagnosis:

a. Check and adjust alarm systems (ELE Code: IIIE9) [Difficulty: ELE: R, Ap, An]

b. Monitor and adjust alarm systems (ELE Code: IIIG3g) [Difficulty: ELE: R, Ap, An]

All alarm systems must function properly, so test all audible and visual alarms. The respiratory therapist should be familiar with the most widely used neonatal ventilators and those that can be used with pediatric as well as adult patients. It is common practice to set most ventilator alarms at ± 10% from the set value.

If the patient is on a CPAP system, the low-pressure or disconnection alarm should be set to alarm if the pressure drops about 2 cm water below the set level. For example, if the patient is on 8 cm water CPAP, the alarm setting should be set at 6 cm water.

Many types of alarm systems have a timer that can be set to delay when the alarm sounds. For example, if the neonatal patient has a ventilator rate of 30/min, the cycling time between mandatory breaths is 2 seconds. The delay should be set so that the alarm sounds in 1 to 2 seconds after a mandatory breath fails to be delivered. If the patient is on a CPAP system, the timer may be set for no delay or a short delay after the CPAP pressure drops below the set value. Always adjust all alarm systems to fit the clinical situation and the patient’s condition.

a. Select ventilator graphics e.g., waveforms, scales (Code: IIID3) [Difficulty: ELE: R, Ap; WRE: An]

A patient who has been intubated and placed on a modern mechanical ventilator with a microprocessor and graphics software can have ventilator flow, volume, and pressure waveforms visualized on the monitor. Usually these parameters can be individually selected and paired up for comparison (such as pressure versus volume) or compared versus time (such as volume versus time). Select the parameters that best provide the data to help explain the patient’s situation. Some units allow the information to be stored in memory or printed out. Compare current information with any past data.

b. Perform the procedure to measure ventilator graphics (e.g., pressure or volume) (WRE Code: IB9o) [Difficulty: WRE: R, Ap, An]

Because not every ventilator can provide waveform information, the correct unit must be selected for the patient. For example, the Drager Babylog 8000 has the monitor and graphics software built into the unit. Follow the ventilator manufacturer’s guidelines to direct the unit to create the desired flow, volume, or pressure waveforms.

c. Interpret ventilator graphics e.g., pressure/volume (WRE Code: IB10o) [Difficulty: WRE: R, Ap, An]

Ventilator flow, volume, and pressure waveforms offer much clinically useful information. For example, expiratory flow can be monitored to look for air trapping and auto-PEEP. As discussed earlier, this is a concern if the neonate has obstructive airway disease or if a high respiratory rate is being used. Volume can be monitored as an indicator of improving or worsening lung compliance. Pressure can also be monitored as it relates to improving or worsening lung compliance. Less pressure is needed to deliver the desired tidal volume if the patient’s lung compliance is improving. Conversely, more pressure is needed to deliver the desired tidal volume if the patient’s lung compliance is worsening. Chapter 15 and this chapter include examples of waveform tracings.

d. Recommend changes in mechanical ventilation based on ventilator graphics (Code: IIIG3h) [Difficulty: ELE: R, Ap; WRE: An]

e. Independently adjust mechanical ventilation based on ventilator graphics (Code: IIIF2i8) [Difficulty: ELE: R, Ap; WRE: An]

As discussed earlier, be prepared to make adjustments in the ventilator as indicated by graphics. For example, if air trapping and auto-PEEP are observed, be prepared to increase the expiratory time, decrease the inspiratory time, or decrease the tidal volume to ensure that there is a complete exhalation.

a. Manipulate pneumatic ventilators by order or protocol (Code: IIA6a) [Difficulty: ELE: R, Ap; WRE: An]

b. Manipulate fluidic ventilators by order or protocol (Code: IIA6a) [Difficulty: ELE: R, Ap; WRE: An]

c. Manipulate electric ventilators by order or protocol (Code: IIA6a) [Difficulty: ELE: R, Ap; WRE: An]

d. Manipulate a microprocessor ventilator by order or protocol (Code: IIA6a) [Difficulty: ELE: R, Ap; WRE: An]

e. Manipulate high-frequency ventilators by order or protocol (WRE code: IIA6c) [Difficulty: WRE: R, Ap]

a. Get the necessary equipment for the procedure

Conventional neonatal ventilators use a circuit that has all of the standard features of an adult circuit as discussed in Chapter 15. Commonly, disposable single-patient-use corrugated plastic circuits are used. They are inexpensive and meet the needs of most patients. Condensation is drained out into water traps that are placed at low points in the natural draping of the inspiratory and expiratory limbs of the circuit. If excessive moisture is a problem or if the gas temperature must be maintained within a narrow range, a heated-wire circuit may be used. These types of circuits are built with a heated wire either loosely threaded through the lumen or coiled within the tubing itself. They are integrated with the humidification system and a servo unit for automatic temperature regulation. Because of the added wiring, these disposable circuits are considerably more expensive than the simple circuits used with most patients. A heat-moisture exchanger (HME) is usually only used with children because the tidal volume must be greater than the dead space of the HME. If a HME is used for passive humidification, it is added between the patient’s endotracheal tube and the Y of the ventilator circuit.’

Be aware that corrugated circuits have a relatively high internal resistance and compressible volume. The corrugations lead to gas turbulence that increases as the flow is raised. When the tubing is warmed, it becomes more stretchable. This stretch results in more tidal volume lost to the circuit instead of being delivered to the patient.

When high flow rates and ventilating pressures are needed, as in HFV, a smooth bore and low compressible volume circuit is used instead of the standard disposable type. A special circuit made of noncompliant tubing is needed with the SensorMedics 3100A ventilator. In addition, to complete an HFJV circuit, a Hi-Lo Jet endotracheal tube or special endotracheal tube adapter is needed to deliver the jetted gas and add the entrained gas for the tidal volume. These are shown in Chapter 15.

b. Put the equipment together and make sure that it works properly

c. Troubleshoot any problems with the equipment

Conventional neonatal ventilator circuits are basically the same as adult circuits with an inspiratory limb and an expiratory limb. Water traps are usually added. An obvious difference is the smaller diameter so that there is less compressible volume. Some are smooth bore to minimize gas turbulence, and some have a heated wire running through them to keep a constant temperature and eliminate condensation. It is important that a heated-wire circuit be used only with the servo-controlled humidifier for which it is designed. Mixing circuits and humidifiers can lead to either overheating or underheating problems. Furthermore, do not cover a heated-wire circuit with a blanket. The circuit should not be allowed to touch the patient to avoid burns. If the patient is inside an incubator with a radiant warmer, the circuit’s temperature probe must be kept outside.

An added feature is a third small-bore tubing for measuring the proximal airway pressure. The tube runs from the patient Y to the proximal airway pressure nipple on the ventilator. Make sure that all the connections are tight to prevent gas leaks.

d. Recommend a change in the patient breathing circuit (ELE code: IIIG3j) [Difficulty: ELE: R, Ap, An]

As discussed previously, there are situations when a special circuit should be used rather than a standard corrugated plastic circuit. A heated-wire circuit should be used if the patient needs to have the gas temperature and humidity level kept within a narrow range. If the patient is changed to a high-frequency ventilator, a special circuit designed for the ventilator must be used.

Ventilator circuits should not be changed routinely for infection control purposes. Current guidelines recommend that they be changed only when visibly soiled. A heat-moisture exchanger may be used for at least 48 hours. Change it whenever it is visibly soiled or contains sputum or blood.

a. Get the necessary equipment for the procedure

Nasal CPAP devices are widely used with neonates who are born prematurely and have RDS. Their immature lungs lack sufficient surfactant and need the CPAP pressure to keep the alveoli open. Often, nasal CPAP meets the patient’s needs so that endotracheal intubation and mechanical ventilation can be avoided. Nasal CPAP works with neonates because they are obligate nose breathers.

Nasal CPAP is associated with the hazards of gastric distension and reflux aspiration. These occur when the airway pressure forces air into the stomach. A gastric tube is usually inserted to vent the air out. There are two different devices for administering nasal CPAP. A nasopharyngeal tube is actually an endotracheal tube that has been cut shorter (see Figure 16-2, B). Select a tube that is the largest that can be easily inserted into the patient. Nasal prongs come in short and long versions (see Figure 16-2, A); both types involve prongs that fit into both nostrils. The prongs come in different diameters so that the proper size can be found to fit the internal diameter of the infant’s nares.

b. Put the equipment together and make sure that it works properly

Follow the manufacturer’s instructions for assembly of the CPAP device and CPAP circuit. See Figures 16-2 and 16-3 as well as the illustration of the CPAP circuit in Chapter 15 for general assembly guidance.

c. Troubleshoot any problems with the equipment (WRE Code: IIA2) [Difficulty: Ap]

A sudden drop in the CPAP level to zero indicates a disconnection at the patient or somewhere in the breathing circuit. Check all connections and reassemble the break. The patient may need to be manually ventilated while the problem is corrected.

If the CPAP level drops more than 2 cm of water pressure during an inspiration, the flow is inadequate and should be increased. Flow is also inadequate if the patient shows an increased use of accessory muscles of respiration or appears to have an increased work of breathing. Too high a flow is seen by an inadvertently high level of CPAP or the appearance that the patient is having a difficult time exhaling. A common problem with small diameter tubes like these is mucous plugging. A plugged tube may result in a backup of gas and can increase CPAP; however, depending on the CPAP system, there may be no change in pressure. Careful patient monitoring is important. Watch for a decrease in a drop in oxygenation, an increase in the respiratory rate, or retractions as signs of airway obstruction. Suction to clear out the mucous plug or remove the tube and place a new one.

a. Get the necessary equipment for the procedure

The general discussion and an illustration related to CPAP systems was presented in Chapter 15. Freestanding neonatal systems are similar to those used with adults. All currently available neonatal ventilators offer a CPAP mode. This allows the practitioner to easily switch the intubated neonate from IMV to CPAP without the need to set up new equipment. Humidification options are similar to those for mechanical ventilation. A heated Cascade-type or wick-type humidifier can be used to provide moisture to the inhaled gas.

b. Put the equipment together and make sure that it works properly

c. Troubleshoot any problems with the equipment (WRE Code: IIA2) [Difficulty: Ap]

The previous discussion about putting together and fixing problems with the CPAP device applies to the CPAP circuit.

d. Recommend a change in the patient breathing circuit (ELE code: IIIG3j) [Difficulty: ELE: R, Ap, An]

CPAP circuits should not be changed routinely for infection control purposes. Current guidelines recommend that they be changed only when visibly soiled (sputum or blood).

a. Get the necessary equipment for the procedure

The general discussion of humidification equipment was presented in Chapters 8 and 15. See the figures there and the general discussion for set-ups in ventilator and CPAP breathing circuits. Both heated humidifiers and heat-moisture exchangers are used with pediatric patients. Heated passover-type humidifiers systems are preferred with neonates.

b. Put the equipment together and make sure that it works properly

c. Troubleshoot any problems with the equipment

Again, see Chapters 8 and 15 for assembly and troubleshooting of humidification systems. With a Cascade-type of passover-type humidifier, the gas temperature is usually maintained close to the neonate’s body temperature to maintain a neutral thermal environment. Make sure that the water level is kept in the recommended range to properly humidify the gas.

a. Recommend changes in the therapeutic plan when indicated (Code: IIIH4) [Difficulty: ELE: R, Ap; WRE: An]

In many cases, time-triggered, pressure-limited, time-cycled (TPTV) mechanical ventilation with the IMV mode is utilized. An infant who is attempting to exhale when the IMV breath is being delivered is said to be “bucking” or “fighting” the ventilator. This problem is almost unavoidable because the IMV breaths are difficult to synchronize on the majority of neonatal ventilators. If the asynchrony between the infant’s efforts and the ventilator is too great, there is an increased risk of hypoxemia and barotrauma or volutrauma. Carefully evaluate the patient to determine if the patient is breathing rapidly because of pain or improper adjustment of the ventilator. Make sure that the flow, rate, pressure limit, and so forth are correctly set for the patient’s condition.

As discussed earlier, the ventilator must be adjusted to maintain desired arterial blood gas goals. It may be necessary to change from CPAP, to conventional ventilation modes, to high-frequency ventilation as the patient’s condition changes.

b. Recommend sedation and/or use of muscle relaxant(s) (Code: IIIG1c) [Difficulty: ELE: R, Ap; WRE: An]

Sedation or paralysis should be considered only after all other causes of asynchrony have been ruled out. In many cases, when the ventilator is appropriately adjusted, the patient breathes in synchrony with it. If this cannot be achieved, sedation or paralysis must be considered.

Antianxiety agents are not typically used with neonates. Morphine sulfate or other opiates are typically used for pain but other less powerful medications may also be tried. If the patient must be paralyzed, pancuronium (Pavulon), atracurium (Tracrium), and vecuronium (Norcuron) are commonly used. Remember that these paralyzing agents have no effect on the patient’s ability to feel pain or to be afraid of what is happening. Pain medications must be given as necessary.

c. Recommend discontinuing treatment or procedure based on the patient’s response (Code: IIIG1i) [Difficulty: ELE: R, Ap; WRE: An]

d. Terminate the treatment or procedure if the patient has an adverse reaction to it (Code: IIIF1) [Difficulty: ELE: R, Ap; WRE: An]

Be prepared to stop a particular treatment or change in ventilator parameter if the patient has an adverse reaction to it. Physical assessment is vitally important because a neonate or small child cannot communicate how he or she feels about the care being provided.

a. Recommend weaning from mechanical ventilation (Code: IIIG1g) [Difficulty: ELE: R, Ap; WRE: An]

As the neonate’s condition improves, weaning must be considered. Indications of improvement include acceptable blood gas results, improved chest radiograph, and stable vital signs.

b. Initiate and modify weaning procedures (Code: IIID7 and IIIF2i12) [Difficulty: ELE: R, Ap; WRE: An]

Specific steps in increasing ventilator support were discussed earlier with each of the types of common pathologic conditions and the various modes of ventilation. In general, ventilator support should be reduced in the opposite manner that it was increased. Remember to evaluate the patient’s arterial blood gas values and vital signs before and after making a change in the ventilator parameters. If the patient’s condition deteriorates, the ventilator setting(s) should be placed as before. General steps in weaning ventilator support in a patient receiving traditional time-triggered, pressure-limited, time-cycled mechanical ventilation (TPTV) include the following:

a. Recommend extubation (Code: IIIG1h) [Difficulty: ELE: R, Ap; WRE: An]

If the patient is stable with low pressure CPAP or a spontaneous breathing trial of 30 to 120 minutes, and the endotracheal tube is not needed for a suctioning route, the endotracheal tube can be removed.

b. Perform extubation (Code: IIIB9) [Difficulty: ELE: R, Ap; WRE: An]

The following additional steps are generally taken to ensure an appropriate, safe extubation: