Persistant Pulmonary Hypertension of the Newborn
aka persistent foetal circulation
Occurs in 1:1000 term and post term newborns
?related to defect in NO production (L-arginine > NO using nitric oxide synthase enzyme)
Failure of reduction of pulmonary vascular resistance and thus persisting R>L shunt through PDA
Leads to failure of oxygenation
Risk factors:
birth asphyxia
MAS
early-onset sepsis
RDS
hypoglycemia
polycythemia
maternal use of NSAIDs (with in utero constriction of the ductus arteriosus)
maternal late trimester use of SSRIs
pulmonary hypoplasia (due to diaphragmatic hernia, amniotic fluid leak, oligohydramnios, or pleural effusions)
Ex
Cyanosis
Holosystolic murmur (TR)
Ix
Pre and post ductal sats (difference of >5% = R>L shunt i.e. R arm (oxygenated) high, foot/Umb (mixed) lower
CXR: ?diaphagmatic hernia
ECHO: TR, R>L shunt at PFO/PDA
Rx
Gentle ventilation with permissive hypercarbia
Sedation
Nitric Oxide (NO as opposed to N2O i.e. nitrous oxide aka laughing gas)
Sildenafil (still under investigation)
Inotropes? dopamine, dobutamine, adrenaline, milrinone
ECMO
Occurs in 1:1000 term and post term newborns
?related to defect in NO production (L-arginine > NO using nitric oxide synthase enzyme)
Failure of reduction of pulmonary vascular resistance and thus persisting R>L shunt through PDA
Leads to failure of oxygenation
Risk factors:
birth asphyxia
MAS
early-onset sepsis
RDS
hypoglycemia
polycythemia
maternal use of NSAIDs (with in utero constriction of the ductus arteriosus)
maternal late trimester use of SSRIs
pulmonary hypoplasia (due to diaphragmatic hernia, amniotic fluid leak, oligohydramnios, or pleural effusions)
Ex
Cyanosis
Holosystolic murmur (TR)
Ix
Pre and post ductal sats (difference of >5% = R>L shunt i.e. R arm (oxygenated) high, foot/Umb (mixed) lower
CXR: ?diaphagmatic hernia
ECHO: TR, R>L shunt at PFO/PDA
Rx
Gentle ventilation with permissive hypercarbia
Sedation
Nitric Oxide (NO as opposed to N2O i.e. nitrous oxide aka laughing gas)
- Start at 20ppm (if no response ?ECMO), if good wean as below
- wean by 5ppm every 4 hours until stable on 5ppm
- wean by 1ppm every 4 hours (prevent rebound PHTN), usually off after 5 days
- if deteriorates go back to last tolerated dose or start again and wean more slowly
- Supply as close to ET as possible to prevent conversion to NO2 i.e. nitrogen dioxide (pulm injury)
- Mechanism: binds and activates guanylate cyclase, increasing intracellular levels of cGMP (cyclic guanosine 3',5'-monophosphate), which leads to vasodilation
- Metabolism: half life 3-6 seconds, combines with oxyhaemaglobin to create methaemaglobin and nitrate > excreted in urine
Sildenafil (still under investigation)
Inotropes? dopamine, dobutamine, adrenaline, milrinone
ECMO
- Alveolar-arterial gradient >620 for 8-12 hr and an OI >40 that is unresponsive to iNO predict a high mortality rate (>80%) and are indications for ECMO
- start at 80% of the estimated cardiac output: 150-200 mL/kg/min
- requires heparin in circuit so contraindicated in high risk for IVH (weight <2 kg, gestational age <34 wk)