|
Just found this interesting article, sorry it is so lengthy
DISCUSSION
Meconium first appears in the fetal ileum between 10 and 16 weeks of gestation as a viscous, green liquid composed of gastrointestinal secretions, cellular debris, bile and panrcreatic fluid, mucous, blood, lanugo, and vernix. Meconium is approximately 72% to 80% water. MSAF rarely occurs before 38 weeks of gestation. The increased incidence of MSAF with advancing gestational age probably reflects the maturation of peristalsis in the fetal intestine. Intestinal parasympathetic innervention and myelination also increase throughout gestation and may play a role in the amplified passage of meconium in late gestation. Most infants with MSAF do not have lower Apgar scores, more acidosis or clinical illness than infants born with clear amniotic fluid. Perinatal morbidity is increased in newborns with abnormal fetal heart rate patterns in the intrapartum period.
Before the late 1970�s it was thought that aspiration of amniotic fluid and meconium occurred during the first few breaths after delivery. Meconium aspiration syndrome continues to occur in those who are adequately suctioned in the delivery room indicating that in some infants, especially those with asphyxia, in-utero aspiration takes place. Clinically fetal lung fluid flows outward from the lungs into the amniotic sac. However studies with radioopaque contrast and Cr labelled erythrocytes injected into the amniotic sac demonstrated that occasionally some amniotic fluid enters the fetal lung in the non-asphyxiated human fetus. Gasping associated with inhalation of amniotic fluid or meconium occurs in fetal lambs, rhesus monkeys, and humans in response to fetal asphyxia induced by compression of the umbilical cord or aorta.
It goes on to say....
PRACTICAL POINTS :
1. Passage of meconium is physiological in breech deliveries and postdated babies, but would be considered pathological any time if the fetal heart rate monitoring is associated with non reassuring fetal heart rate pattern.
2. Passage of meconium is extremely rare in preterms and its presence should consider diagnosis of listeria sepsis.
3. Majority of MSAF babies have uneventful course unless complicated by abnormal fetal heart rate patterns.
4. Yellow meconium is usually old, while green meconium suggests a more recent insult.
5. The indication for intubation in MSAF babies is only for those who are depressed at birth irrespective of the consistency of meconium.
6. For infants requiring endotracheal suctioning, vigorous stimulation and drying maneuvers are delayed until intubation is performed to avoid initiation of respiration. After clearance of the airway usual steps of resuscitation are performed.
7. Bag and mask ventilation is contraindicated in MSAF babies who are depressed at birth and intubation for intra tracheal suctioning takes precedence for airway clearance.
8. To date there are no data verifying the efficacy of chest physiotherapy either in preventing MAS or in treating the disorder.
9. To date there have been no prospective randomized controlled trials assessing the potential benefits of cesarean versus vaginal delivery in preventing MAS.
10. Negative pressure during suctioning of airway should not exceed - 120mm of Hg. It should be applied continously and not intermittently for optimal retrieval.
11. An intriguing therapy is that of dilute surfactant lavage which has been found to be beneficial in human infants with established MAS.
All this info and more at http://www.neoclinic.net/Artcl/msaf.htm
-------Original Message-------
Date: Thursday, 29 May 2003 7:47:21 PM
Subject: Re: [ozmidwifery] Interesting..
Thanks for your question and the quote Mary,
There are several different ideas within this posting.
Regardless of the mode of delivery and the intrapartum course, if there is mec.stained liquor, the baby is at risk of MAS and it's complications, regardless again of whether it is old or new meconium. Who's to say the mec didn't get there from the first breath after emergence from the uterus at c/s. Would love to find somewhere that perhaps quantifies how much meconium will cause MAS. It would be interesting also to find information on how long it takes to affect the whole lung fields. A chest Xray done soon after birth only shows the damage and effects of the inhaled mec, and a CRP on the baby is only an indicator of tissue damage or inflammation, and not all that useful. The chemical pneumonitis caused from MAS is only one part of the cascade.
Regarding the poor CTG, as we all know, there could be any numbers of reasons for a poor one, not necessarily old meconium. This could be the effect of an insult as opposed to the cause. Would be handy to know more of the ante and intrapartum history first.
As I have already posted, the glottis is usually closed until the stimulation to gasp, be it the squeeze or perhaps environmental factors and exposure to air. I would also be interested to hear any other explanation from others in the know.
Gayle
Meconium Aspiration Syndrome
This is the commonest cause if respiratory distress. It is a condition which may affect both preterm and term infants, particularly if delivered by caesarian section. It is attributed to delayed clearing of the fetal lung fluid into the vessels and lymphatics after birth. The condition is not due to surfactant deficiency and the shake test is usually positive.
MECONIUM ASPIRATION
This is due to the inhalation of meconium during or immediately after delivery. It usually follows on fetal distress during labour. It is limited to mature or wasted infants since preterm infants rarely pass meconium in utero. The inhaled meconium produces areas of emphysema and atelectasis throughout the lungs. There is considerable risk of pneumothorax and pneumomediastinum. A pneumonitis may be caused by chemical irritation or secondary bacterial infection. Many infants with severe meconium aspiraton die or suffer severe lung damage.
http://web.uct.ac.za/depts/ich/teaching/undergrad/6th_year/nnh/nnh_cp16.htm
-------Original Message-------
Date: Thursday, 29 May 2003 6:54:02 PM
Subject: Re: [ozmidwifery] Interesting..
Thanks Gayle for your explanation. What then causes a Term baby to have lungs with tissue choked with old meconium when birthed by elective caesarean because of poor CTG's? MM
----- Original Message -----
Sent: Thursday, May 29, 2003 3:53 PM
Subject: Re: [ozmidwifery] Interesting..
|
Babies lungs are filled with a special fluid that is quite separate to amniotic fluid. It is called Fetal Lung Fluid (FLF). This is what is expelled as the baby is squeezed through the birth canal. The baby occasionally 'spits' a little of this into the amniotic fluid, as a result of fetal breathing. The FLF contains surfactant and lecithin/sphyngomyelin which is what is, or rather used to be measured when an amniocentisis is done to assess gestation and lung maturity. Remember L:S Ratios? Thank heavens for newer technology and the use of ultrasound scanning and telemetry in cases of need. It is retained fetal lung fluid that is responsible for most of the respiratory distress named TTN or transient tachypnoea of the neonate.
Also, a baby can quite easily recover from an distressing episode in utero, and, as outlined above, the mec does not necessarily go into the lungs causing MAS at birth. It is the first gasp in an extrauterine environment that may lead to inhalation of mec passed the originally closed glottis.
Gayle
-------Original Message-------
Date: Thursday, 29 May 2003 2:37:49 PM
Subject: Re: [ozmidwifery] Interesting..
And just to add something more, it is interesting to know that it (the inutero pooing) happens so early in gestation. We have also all been told (at least I have) that the more mature a baby is (ie post dates) then the more likely it is that there will be mec in the liquor. I'd like to read the whole article but from memory the abstract said that passing of meconium had been observed as early as 28 weeks.
Something I've often wondered about is those breathing actions by the baby. When a biophysical profile is done that is one of the items scored so it is obviously expected in all term babies. Yet most babies with mec liquor don't present with MAS. And some (a very few) babies with very normal uncomplicated labours and births do develop MAS. Is it the gasp of a baby in distress (which may happen at any time and be undetected) or just a random gasp that carries the mec deep into the lungs ? Just curious.
I just had a really weird glimpse into the future of all pregnant women past 24 weeks wearing telemetry monitors just in case something untoward happens. Am I paranoid?? I hope so. As Mary said it is all in the interpretation.
marilyn
----- Original Message -----
Sent: Wednesday, May 21, 2003 4:18 PM
Subject: Re: [ozmidwifery] Interesting..
Debbie wrote: "It is well known that babies 'wee' in utero - so why not 'the other'?"
Deb, it is not so much that they do it, but how we interpret it. We have for years been told that meconium in the liqour is a sign of "Fetal Distress" There have been many unnecessary operative procedures carried out on women and babies because it was concluded that slowed Fetal Heart Rate (mostly normal head compression dips) and meconium stained liqour meant distressed baby. Then Voila! Apgars of 9 & 10 at birth or C/S. Midwives, women and doctors too have taken the blame for all sorts of things that happen to babies. (Not denying some negligence claims are true.) It has been known by midwives gor generations that women past their "due date" frequently have meconioum stained liqour. If is present...panic! Now we also know that the symptoms of meconium pneumonia and "meconium aspiration" are mostly present in the lungs before birth because babies do these marvelous "breathing actions" that we didn't know about before U.S studies told us so. It is very complicated. So, this piece of research is a very helpful piece of the jig-saw. cheers, MM
|
| 