By Nicole Stevens Overview Meconium is the first substance discharged from the GI tract in the perinatal period Rarely found in amniotic fluid before 34wks gestation likely because its passage may require neural stimulation of a mature GI tract ID: 1006797
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1. Meconium Aspiration Syndrome (MAS)By: Nicole Stevens
2. OverviewMeconium is the first substance discharged from the GI tract in the perinatal period.Rarely found in amniotic fluid before 34wks gestation, likely because its passage may require neural stimulation of a mature GI tract.Meconium aspiration syndrome (MAS), where the newborn aspirates the meconium containing liquor, therefore, mainly affects term or post term newborns.
3. OverviewIn MAS, the meconium is aspirated through the trachea into the bronchial tree, and sometimes into the alveoli. Sequence of events that may follow: Obstruction of airwaysGas trappingChemical pneumonitis (possibly caused by the bile and liver enzymes in the mec)PPHN
4. Risk factorsHypoxia is thought to be the catalyst that leads to passage of meconium into amniotic fluid. Hypoxic episodes may be due to:Head or cord compressionMaternal risk factors leading to uteroplacental insufficiency (such as, maternal HT, PE, chronic respiratory disease, chronic cardiovascular disease, maternal diabetes, post term, heavy smoking)MAS is seen most frequently in the term, post term and growth restricted infant.
5. Perinatal events leading to MASPhysiological passage of meconium, or a stress induced passage (hypoxic event)This meconium stained liquor can be aspirated during gasping inutero, or by aspiration after birth (in mouth/nose)Downwards in the respiratory system you can get proximal airway obstruction, peripheral airway obstruction, alveolitis and epithelial damage, then disruption of alveolo-capillary barrier
6. Events after birth with MASAirway obstruction can cause air-trapping, and atelectasis, and decreased lung complianceMeconium in the lung and the increase in exudate from alveolar that it causes can inhibit surfactant productionAn hypoxic incident causing the passage of meconium may be ongoing, leading to perinatal asphyxia, increasing likelihood of PPHN and HIE
7. Main effects of MASThere are 3 main effects of MASChemical pnuemonitisSurfactant dysfunctionAirway obstruction
8. Chemical pnuemonitisAn inflammatory response that occurs when enzymes, bile salts, and fats in meconium irritate the airways and lung parenchymaCreates a diffuse pneumonia shortly after deliveryAlso creates a cascade of events that leads to vascular leakage and injury
9. Surfactant dysfunctionOccurs when free fatty acids in the meconium strip surfactant from the alveolar surface and produce diffuse atelectasisThe role of surfactant is to reduce the surface tension in the alveoli, without it the alveoli walls will collapse in and want to stick together.Surfactant has a dispersing and spreading effect (like a drop of detergent in oil)
10. Airway obstructionCan be partial or complete, results from the meconium being aspirated into small airways, can result in atelectasis or overdistention of the alveoliOverdistention occurs when there is gas trapping behind meconium particles (ball valve effect); causes uneven ventilation with hyperinflation in some areas and atelectasis in othersLeads to ventilation/perfusion mismatch which contributes to hypoxaemia, hypercapnea and acidosis; which in turn leads to pulmonary arteriolar vasoconstriction and pulmonary hypertenison
11. Differential diagnosisTTNSurfactant deficiencySepsis/pnuemoniaPneumothoraxCDHBirth asphyxia with PPHN and/or haemorrhagic pulmonary oedema
12. Characteristics of MASEarly onset of respiratory distress and hypoxaemiaMost babies with MAS will only need some oxygen therapy and general supportive careVentilator support should be commenced if there is ongoing hypoxaemia or respiratory acidosisLocal incidence is around 1.5 per 1000 births.
13. Clinical features of MASEarly onset of respiratory distress in a baby born through meconium stained liquorTachypnoea, cyanosis, variable hyperinflationAuscultation reveals widespread ‘wet’ inspiratory crackles, occasionally with expiratory noises suggesting ball-valve airway obstructionBlood gases: hypoxaemia and hypercarbiaRadiologically: typically starts with global atelectasis in early X-rays to widespread patchy opacification accompanied by areas of hyperinflation and/or actelectasis
14. Management of MASAdministration of O2 is critically important, and in many neonates is all that will be needed for respiratory therapy. The target saturation range is 91 – 95%. The target PaO2 is 60 – 90mmHg.Consider CPAP if there is moderate respiratory distress and hypoxaemiaIntubate if there is persistent hypoxaemia in 100% oxygen; of if there is respiratory acidosis with pH <7.20
15. VentilationIf requiring intubation in the birth room it is usually done without drugsIf done after transfer to a nursery, preferable to sedate and muscle relax prior to intubationMay require high PIPs to achieve gas exchange (30 -35cm H2O)Should be aiming for ↑oxygenation whilst minimizing barotrauma that can lead to air leaks
16. Ventilation cont…Most evidence favours the use of high PEEP (6-8cm H2O) and a long expiratory timeVentilation rates of 40 – 60 breaths/min (the lower the rate, the longer the expiratory time)Inspiratory times of 0.5 – 0.6 secsIf gas trapping occurs, expiratory time can be increased and PEEP decreasedParticularly if there is also PPHN, sedation and muscle relaxation should be maintained if the disease is severe
17. Ventilation cont…Mode of ventilation will be case dependent; could range from conventional ventilation, to HFOV, to HFJV and in infants with severe MAS, if available, ECMO may be used.In Melbourne ECMO and HFJV only available at RCHMAS has been the leading diagnosis for neonates requiring ECMOUse has decreased with the advent of new therapiesSurvival rate 95%, risk of severe disability low, risk of any disability about 17% in survivors (treated with ECMO)
18. Surfactant therapyCurrent evidence not showing a consistent benefit, some babies acutely deteriorate when administeredLung lavage with surfactant is currently being investigated, but not yet able to be recommendedMight be used as a supportive therapy for PPHN
19. Suctioning (birth room and beyond)Routine intrapartum suction not recommended anymoreNewborns with depressed respiratory effort, poor muscle tone and HR <100 born through mec-liquor are recommended to have direct ET suctioning prior to stimulationStomach contents should be evacuated, and a gastric tube should be inserted In intubated infants the large airways can be lavaged with a small amount of normal saline and suctioned PRN.
20. General careCardiovascular support – need IV fluids for volume/hydration, +/- inotropic supportFluid restrictionAntibiotic therapy until primary bacterial infection can be excludedIV therapy (10% dextrose, then 10% dextrose with additives, then parenteral nutrition if unable to feed by 2 - 3 days) and NBM until the respiratory distress is resolving
21. ComplicationsPPHNAir leak (pneumomediastinum, pneumothorax, Cystic lung disease)Pulmonary haemorrhageComplications of asphyxia (seizures, oliguria, coagulopathy, thrombocytopenia)
22. If there is PPHNCorrect potentiating factors: hypoglycaemia, hypocalcaemia, hypomagnesaemia, polycythaemia, hypothermia, painIncrease systemic blood pressure to reduce right to left ductal shunt (by the use of volume expansion and pressor agents)Improve right ventricular function (by the use of inotropes)Use of pulmonary vasodilators (inhaled nitric)
23. MAS (day 1)
24. MAS (2 days later)
25. MAS (more severe case)
26. MAS (same baby)
27. ECMO
28. ManagementBest defense is good offenseAmnioinfusion??? (infusion of warmed normal saline to relieve oligohydramnios and fetal distress, and to decrease meconium staining)Birth room management. Have personnel available who have intubation capabilities; suction with size 12F catheter, or through and ET tube/mec aspiratorAssessment for respiratory distress and/or hypoxia after birth and escalate care as required.
29. Nursing careObservations and documentationBlood taking as requiredAssistance with procedures as requiredCluster cares to reduce handlingMinimise noxious stimulus (lights, noise, voices)Parent support, educationPreparation for transfer if requiring tertiary care (consider accommodation needs of parents, handover to transport nurse, paperwork for transfer)Clean up and preparation for next admission!
30. Interesting factsMeconium staining of the cord can appear with as little as 1 – 3 hours of exposureStaining of the fingers and nails occurs within 4 – 6 hours of exposureStaining of the vernix occurs within 12 – 14 hours
31. REFERENCEShttp://emedicine.medscape.com/article/410756-overviewhttp://www.health.vic.gov.au/neonatalhandbook/conditions/meconium-aspiration-syndrome.htmInternational Journal of PediatricsVolume 2012 (2012), Respiratory Support in Meconium Aspiration Syndrome: A Practical Guide. Peter A. Dargaville