Paediatrics: Neonatal respiratory support

2021-03-05 12:00 AM

Excess oxygen is toxic, particularly in preterm infants. All infants receiving supplemental oxygen should have SpO2 monitoring as a minimum.

Neonatal respiratory support

Supplemental oxygen

Excess oxygen is toxic, particularly in preterm infants. All infants receiving supplemental oxygen should have SpO2 monitoring as a minimum. If significant hypoxia, consider an arterial line to directly monitor PaO2. Term infant’s oxygen saturation levels should be >95% in air—usually 97%. The ‘correct’ saturation range for preterm ( 32/40, 1500g) infants has not been determined. Maintaining SpO2 around 90–95% and avoidance of ‘swings’ in either saturation or FiO2 is reasonable whilst evidence from large RCTs is awaited. Supplemental oxygen can be given via:

  • Head box (concentration easily monitored).
  • Nasal cannula <2L/min (cannot monitor effective FiO2—depends on gas flow rate, FiO2,and tidal volume, can’t humidify effectively).
  • High flow nasal cannula >2L/min. Can be effectively humidified. Generates CPAP effect.

CPAP 

Prevents airway collapse and loss of lung volume. Maintenance of functional residual capacity above closing volume reduces work of breathing.

Uses

  • RDS and respiratory support, particularly for preterm infants.
  • Post-extubation.
  • In upper airway obstruction.

Method

  • Nasal mask or binasal prongs, rarely face mask or via ETT.
  • Usual pressure is 5–6cmH2O. Probable safe upper level is 8cmH2O, but ‘rise’risk of pulmonary air leaks as pressure i.
  • Some equipment can deliver bi-level CPAP with or without synchronization to spontaneous breaths.

Complications

  • Pulmonary air leaks, e.g. pneumothorax. (particularly if treating RDS in an infant who has not received surfactant).
  • Nasal trauma.
  • Baby upset leading to hypoxia.
  • rise Airway resistance and effort of breathing.
  • Upper GI distension or perforation (insert gastric tube on free drainage to reduce risk, rarely seen with modern equipment).

Positive pressure ventilation

Intermittent positive pressure ventilation (IPPV).

High frequency oscillatory ventilation (HFOV).

Synchronized ventilation

Nomenclature confusing, but includes the following:

  • Synchronized intermittent positive pressure ventilation (SIPPV)/assist control/patient-triggered ventilation (PTV): every spontaneous patientbreath can trigger time-limited positive pressure inflation.
  • Synchronized intermittent mandatory ventilation (SIMV): rate of triggeredbreaths is preset; any other spontaneous patient breaths are unassisted in case of apnoea the set rate is given.
  • Pressure support: all spontaneous breaths are supported by positivepressure for as long as inspiratory flow continues above a defined threshold. Can be combined with other modes.

Studies in newborn infants show no particular advantage for SIPPV or SIMV compared to conventional IPPV during acute stages of respiratory illnesses such as RDS. May be useful during weaning, or if infant is not synchronizing with ventilator. Smaller infants may not be able to trigger breaths (older ventilators). Autocycling can cause over ventilation in PTV.

Extracorporeal life support (ECLS)

Provided only in a very small number of specialist centres in the UK. Also known as extracorporeal membrane oxygenation (ECMO), ECLS reduces mortality in severe respiratory disease, e.g. meconium aspiration syn-drome, persistent pulmonary hypertension of the newborn.1 Early transfer to an ECLS centre is important as these infants are often critically unwell.

Criteria for eligibility: severe, but reversible cardiac or respiratory disease and oxygenation index persistently >30–40 where:

Oxygenation index = [(mean airway pressure × FiO2)/PaO2 (kPa)] × 100

FiO2 is expressed as a decimal, e.g. 30% O2 = 0.3

Contraindications

  • Weight <1.8kg.
  • Gestation <34wks.
  • Severe congenital malformation.
  • Intracranial haemorrhage or poor CNS prognosis (e.g. severe HIE).
  • Coagulopathy.

Technique

Blood taken from a major cannula is passed through a membrane oxy-genator and then returned to the body. Blood is heparinized (activated clotting time 2–3 × normal) and low level conventional ventilation is maintained. ECMO is maintained until disease recovery. May be:

  • Venous–venous: double lumen cannula in right jugular vein or rightatrium;
  • Venous–arterial: blood drawn from right jugular vein and returned toright carotid artery.

Outcome Survival rates are high for reversible lung pathologies. Up to 10% of ECMO survivors suffer major long-term problems. Complications include brain injury (secondary to neck vessel trauma, thromboembolism, CNS haemorrhage, a complication of pre-ECMO disease/therapy) and peripheral thromboembolic phenomenon, e.g. may cause renal failure.