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Re: AROM vs. PitocinFrom: Richard Chudacoff, MD (rchudacoff@mylinuxisp.com)Thu Aug 31 12:09:11 2000
This is great. Can I get CME hours for it? Rick -----Original Message----- From: ob-gyn-l@obgyn.net [mailto:ob-gyn-l@obgyn.net]On Behalf Of Steve Raymond Sent: Thursday, August 31, 2000 11:29 AM To: Multiple recipients of list OB-GYN-L Subject: Re: AROM vs. Pitocin Seems to me that a little seminar on the initiation of labour is needed here with all these different ideas floating around. If a woman at term has her membranes ruptured and nothing else is done then 80% will deliver within the next 24 hours. This has been shown by work done in the late 60's. Several people showed that the use of oxytocin after 24 hours of waiting to see what would happen would ensure delivery of the other 20% (by whatever route was indicated obstetrically), so it became commonplace to do an ARM in the evening and, if not in labour in the morning, to start oxytocin then. With the wide acceptance of active management and the realization that the incidence of amnionitis was proportional to the length of time the membranes were ruptured, people started to realise that it made sense to start oxytocin at the same time as the ARM to shorten the membrane rupture to delivery interval. This way you could avoid the wasted time that inevitably occurred if contractions didn't establish straight away from ARM alone. Prostaglandin metabolism and physiology was extensively studied in the early 70's and its role in the initiation of labour has been shown to be that of increasing oxytocin receptors in the myometrium. So it was obvious that the woman who is approaching term differs from the one in labour by the number of her oxytocin receptors, as oxytocin levels in the serum don't change a great deal. The mechanism by which labour starts is thus a process of gradual increase in the ability of circulating oxytocin to stimulate contractions. While there is also a direct effect of Prostaglandin on softening of the cervix its major action is to raise the sensitivity of the myometrium. The woman who is a long way from the spontaneous onset of labour has low PG levels, low oxytocin receptor numbers and an unripe cervix. If you use exogenous oxytocin you may be able to induce some uterine activity even in the presence of a cervix with a low Bishop's score, but if you increase the sensitivity of the myometrium it will clearly mean that the uterus will contract sooner and at a lower infusion rate. How to do that? Obviously administering a prostaglandin is the first thing that springs to mind, but you can increase endogenous prostaglandin by other means too. One is to stretch the cervix digitally and sweep the membranes - the good old fashioned "stretch & sweep". Another means is to rupture the membranes - also involves a bit of stretching of the cervix. So the answer to the original question "..does pitocin work with intact membranes?" is similar to the answer to the question "How long is a piece of string?" It all depends on where the woman is on the continuum of increasing likelihood of going into labour, which is dependent on her oxytocin receptors, which is dependent on her prostaglandin levels. Of course the woman with the ripe cervix is easy to induce - she's half way there herself, and may need only an ARM, but if you want to be sure of success in getting contractions you need to make sure there is a good bit of PG circulating as well, and there's nothing like "belt and braces" ARM + Oxytocin. Obviously adding some PG wouldn't be a bad idea either, but it's difficult to get the same sort of control as we currently have with oxytocin infusions in concentrated dose passing through an IVAC pump. Thus we tend to use the various forms of Prostaglandin in those patients who are not in the "high receptor" stage, because it allows the exogenous physiological dose of oxytocin to regulate itself and it's difficult (but not impossible) to overdose. If anyone can come up with a reliable method of counting oxytocin receptors we'd be well on the way to ensuring that the method of induction employed is tailored exactly to the individual patient ainsron@msn.com wrote:
> My practice patterns are very similar. I see no benefit using cytotec
> for a patient with a ripe cervix. I'll usually wait 2-4 hours after
> >How many initiate induction w/ ARM vs oxytocin (in the presence of a
> > --
-- Dr. Steve Raymond Head of Department of O & G Empangeni Hospital Empangeni SOUTH AFRICA 3880 Ph:(+27)(035)7721111
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