Respiratory Management of the Newborn

 

I.      FiO2

Fraction of inspired oxygen (range: 0.2 to  1.0)

  • Desirable arterial PO2 is 60-80 mmHg.  Choose the FiO2 necessary to achieve this range. Generally, changes in FiO2 are made in 5% increments or decrements.

  • Inadequate oxygen administration may result in neuronal injury, pulmonary hypertension, and damage to organs including liver, kidney, and gut.  In VLBW infants, excessive oxygen administration may result in chronic lung injury and retinopathy of prematurity. 

  • Best way to monitor administering oxygen is by serial arterial blood gas measurements.  An alternative, continuous, noninvasive technique for monitoring administration of oxygen is pulse oximetry.  Desirable oxygen saturation  for all babies is 84-96%.  
    (Note:  In neonates with ductus-dependent cyanotic congenital heart disease, the desirable range of oxygen saturations may be specified by the cardiologists).

 

II.     IMV

Intermittent mandatory ventilation (ventilator rate)

  • Ventilator rate, expressed in breaths per minute, influences minute ventilation.  A higher rate increases CO2 excretion, whereas a lower rate decreases CO2 excretion.

  • Desirable arterial PCO2 is 35-45 mmHg.  In a strategy called permissive hypercapnea, the accepted arterial PCO2 range is 45-60 mmHg.

  • Initial ventilator rate is 30 breaths per minute.  An adjustment in the ventilator rate needs to be made based on the arterial PCO2.  Generally, changes in ventilator rate are made by increments or decrements of 5 breaths per minute.

  • Inadequate ventilator rate may result in hypercapnea and respiratory acidosis.  Excessive ventilator rate may result in hypocapnea and respiratory alkalosis with associated decrease in cerebral blood flow.

  • Caution is necessary in setting the ventilator rate in a neonate with no spontaneous respiratory effort, as in asphyxia or sedation.

 

III.      PIP

 Peak inspiratory pressure (cmH20)

  • PIP influences tidal volume.  A high PIP increases CO2 excretion by increasing minute ventilation through tidal volume.  A low PIP decreases CO2 excretion.

  • Desirable PIP varies depending on the reason for ventilation.  A high PIP is necessary to ventilate a neonate with lung disease and poor lung compliance.  A low PIP is necessary to ventilate a neonate with apnea from neurologic cause, prematurity, or sedation in the absence of lung disease.

  • Desirable initial PIP is 20 cmH2O.  An adjustment in the PIP needs to be made based on clinical examination, including chest excursion and breath sounds. 

  • Inadequate PIP may result in hypoventilation, respiratory acidosis, and atelectasis.  Excessive PIP may result in hyperventilation, respiratory alkalosis, volutrauma from stretching of lung tissue, and air dissection, including pneumothorax and pulmonary interstitial emphysema.

  • As compliance of the lung changes, delivery tidal volume will change.

  • Determination of PIP is subjective and is based on chest wall excursion; however, tidal volume can be used as a guide.

IV.     PEEP

 Positive end-expiratory pressure (cmH2O)

  • PEEP influences thoracic lung volume at end-expiration.  A high PEEP increases residual lung volume, improves ventilation-perfusion matching and facilitates oxygenation as well as gas exchange.  Excessive PEEP, however, may decrease lung compliance and compromise cardiac function.  A low PEEP decreases residual lung volume and worsens lung compliance. 

  • Desirable initial PEEP is 4-5 cmH2O.  An adjustment in the PEEP needs to be made based on evaluation of oxygenation, gas exchange, and chest radiographic findings.  Generally, changes in PEEP are made by increments or decrements of 1 cmH2O.  PEEP exceeding 8 cmH2O is rarely used in the nursery.  A low PEEP  may be used in neonates with significant pulmonary air dissection.

  • PEEP administered by nasal prongs or mask is called CPAP (continuous positive airway pressure).  Generally, the PEEP generated within the lung is approximately half of the CPAP generated within the nasal passages.

 

V.     IT

Inspiratory time (fraction of second)

  • IT determines the length of inspiration in each ventilated breath and influences the inspiratory/expiratory ratio (I:E ratio)

  • Desirable initial IT is 0.3 - 0.4 seconds.  The IT needs to be shortened as the ventilator rate is increased.  The IT may be lengthened as the ventilator rate is decreased.   Generally the IT is adjusted to allow the expiratory phase to be at least twice as long as the inspiratory phase, (I:E ratio 1:2 - 1:4).

 

VI.  PAW

Mean airway pressure (cmH2O)

  • PAW is equal to the area under the pressure curve of a single respiratory cycle divided by the duration of the cycle.

  • PAW is influenced by PIP, PEEP, I:E ratio, and waveform.  High PIP, high PEEP, prolonged I:E ratio, and square-wave form of ventilation increase PAW.  Low PIP, low PEEP, shortened I:E ratio, and sine-wave form of ventilation decrease PAW.

  • PAW is computed and displayed on the ventilator.  Measurement of PAW incorporates PIP, PEEP, and IT.

  • High PAW (~10 cmH2O) may be required during acute phase of neonatal lung disease, when compliance is low.  High PAW may cause impairment of venous return by over expanded lungs during recovery phase of neonatal lung disease, when compliance is improving.

 

VII.   VT

  • Tidal volume (ml).  5 ml/kg initial calculation.

  • Certain ventilators deliver a preset VT. All have the ability to set a peak pressure safety valve.

  • VT influences minute ventilation, which can be calculated as follows:

Minute ventilation (ml) = Tidal volume (ml) x ventilator rate (bpm)  (remember the baby may contribute significant minute ventilation with spontaneous breathing).

 

VIII.    PTV (Assist Control)

 Patient triggered ventilation

  • Patient triggered ventilation

  • PTV is a ventilator mode in which the patientís inspiratory effort triggers a controlled positive pressure inflation.  During PTV, all of the infantís respiratory efforts can trigger a positive pressure inflation.

  • Devices developed to detect the patientís inspiratory effort include those that detect a change in abdominal expansion, esophageal pressure, airflow, airway pressure, and impedance.  Each of these devices needs to be sensitive and fast in response.

  • PTV cannot be used in infants with no spontaneous respiratory effort.

 

IX.    SIMV

  • Synchronized intermittent mandatory ventilation

  • SIMV is a ventilator mode in which the maximum number of breaths that can be triggered is determined by a preset SIMV rate.  For example, if the SIMV rate is set at 20 bpm and the infant is breathing at 60 bpm, 20 breaths will be triggered with a positive pressure inflation, whereas the remaining 40 breaths will be of a variable pressure, each dependent on the inspiratory effort of the infant.

  • SIMV may improve ventilation by decreasing discordance between breaths initiated by the infant and those that are initiated by the ventilator.

 

X.        MMV

  • Mandatory Minute Ventilation.

  • MMV is a ventilator mode in which a minimum minute volume (VT x Rate) is set.

  • The maximum number of breaths that can be delivered is determined by a preset MMV rate.  In MMV, if the patient is apneic, they will receive the set number of breaths at the set tidal volume.

  • As the patient breathes and generates some part of the set minute volume, the ventilator will wean away some or all of the set breaths and allow the patient to breathe on their own.

  • The high respiratory rate needs to be properly set in this mode.

 

XI.   Pressure Support (CPAP)

  • Used on spontaneous breaths only to augment the patientís tidal volume.

  • Should be set for patient comfort but not to generate > 5 mL/kg. 

 

XII.     HFOV

High frequency oscillation Ventilation

  • HFOV involves oscillation at a tidal volume of 50-100% of anatomic respiratory dead space and a frequency of 180-900 breaths per minute (3-15 Hz).  Please note: 1 Hz = 60 bpm.

  • HFOV may be used in infants with refractory respiratory failure (e.g. pulmonary hypoplasia, congenital diaphragmatic hernia, severe hyaline membrane disease), air dissection (e.g. pulmonary intestinal emphysema, recurrent pneumothorax), and refractory hypoxemia (e.g. persistent pulmonary hypertension).

  • When using HFOV, the following variables need to be set: frequency (Hz), oscillatory amplitude (∆-P), and mean airway pressure (PAW)

 

Guideline for frequency:

Body Weight(g)     Frequency (Hz)

                   <1000 g                12-15 Hz

                   1001-2500 g           10-12 Hz

                   >2500 g                 8-10 Hz

  • Guidelines for oscillatory amplitudes: Start with 20, increase gradually until chest wall vibration is apparent.  Increase ∆-P to increase CO2 excretion, decrease ∆-P to decrease CO2 excretion.

  • Guidelines for mean airway pressure:  Start with +-2 cmH2O higher than the PAW required during conventional mechanical ventilation.  High PAW promotes alveolar expansion and is indicated in conditions in which the lung volumes are low.  Low PAW may be useful in infants with high lung volumes, cardiac compromise from over expanded lungs, and pulmonary air dissection.

  •  HFOV increases the risk of periventricular-intraventricular hemorrhage in VLBW infants.

 

X.      a/A Ratio

   a     =                PaO2         

   A             (713 X FiO2) - PaCo2

a =  arterial oxygen

A=  alveolar oxygen

713 = atmosphere pressure 760 mmHg minus water vapor pressure 47 mmHg

FiO2 =Fraction of inspired oxygen

PaO2 = partial pressure of arterial oxygen

PaCO2 = partial pressure of arterial carbon dioxide

 

  • a/A ratio decreases with increasing sickness. 

  • a/A  ratio  < 0.2 is one of the indications for  surfactant administration

  • a/A ratio is useful in assessing the ventilatory progress.

 

XI.     OI

Oxygenation index

OI= FiO2 X PAW     X 100

            PaO2

FiO2 =  fraction of inspired oxygen

PAW = mean airway pressure

PaO2 =  partial pressure of arterial oxygen

 

        OI increases with increasing respiratory illness

        OI values may be interpreted as follows:

OI 

<10 

10-20

20-30

>25 

30-40

>40

Indication

 Mild disease

Mild to moderate

Moderate to severe

iNO

Severe

Evaluate for ECMO (Extracorporeal Membrane Oxygenation)