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Epidural Test Dose
As most of us know the question as to the ideal test dose
keeps recurring and although much research has been done there still is
controversy especially around recognition of an intravascular injection.
The recommendation of an epinephrine test dose to detect intravascular
cannulation arose during the 1980s when several women died following
inadvertent intravascular injection of a large bolus of bupivacaine
(0.5% or 0.75%). Since that time the limitations of an epinephrine TD
in parturients have been recognized. There is a recent systematic
review on this subject by Joanne Guay from Montreal (Anesth Analg
2006;102:921-9). As this review points out the answer is not yet
in, particularly when multiorifice epidural catheters are used in
parturients (one orifice may be intravascular while the others are
not). An excellent review for all of us providing obstetrical
anesthesia.
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Risk of Preeclampsia
A report from the Netherlands attempted to predict the risk of
maternal complications or neonatal outcome on admission in women
with early-onset, severe preeclampsia. (Am J Obstet Gynecol
2006;185:495-503). The data came from a randomized trial of
temporizing management of women with HELLP syndrome, severe preeclampsia,
eclampsia or hypertension-related fetal growth restriction with
pregnancies between 24 and 34 completed weeks. Women were randomized
into an attempted prolongation of pregnancy or maternal disease
stabilization and delivery after corticosteroid therapy for fetal lung
maturation.
Their findings are interesting. There was no
difference in major maternal morbidity (pulmonary edema, placental
abruption, liver hematoma, severe infection, thrombotic morbidity,
encephalopathy) between groups but there were more C/S in the
temporizing management group. Not surprisingly adverse neonatal outcome
was dependent on gestational age.
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Does Sodium Citrate make you ill?
Surprise! Surprise! Finally someone has done the study to confirm what
most of us knew or at least felt – namely that sodium citrate causes
nausea in elective C/S patients. (Kjaer et al. Can J Anesth
2006;53:776-80). This study enrolled 123 women having an elective
C/S under spinal anesthesia. They were randomized to have either saline
or famotidine iv 90 mins preop followed by either water or sodium
citrate orally 15 mins preop. Nausea was assessed prior to the oral
solution, 1 min after the spinal was initiated, 5 mins after spinal
initiation, at time of uterine exteriorization, and in the recovery
room. They anticipated an incidence of any nausea of 33% in the control
group and wanted a decrease of 10% (i.e. to 23%) in the non-sodium
citrate group.
The sodium citrate group had more nausea 5 min
after spinal placement with an odds ratio of 3.65 (p=0.006) and the
incidence of any nausea was more common in the sodium citrate group (37%
vs 14%). All subjects had an infusion of ephedrine 5 mg/min and
phenylephrine 20 mg/min started after the woman was placed supine and
hypotension was similar between groups (22%).
Overall you have to omit sodium citrate in 4
patients to avoid one case of nausea in elective C/S patients having
spinal anesthesia. The authors admit that famotidine may have suppressed
nausea in the group that did not receive sodium citrate. Because
elective C/S patients have fasted and have received an H-2 blocker (e.g.
ranitidine or famotidine) many obstetric anesthesiologists no longer
administer sodium citrate to fasted women having elective procedures.
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Meningitis Again!
The August issue of Anesthesiology
(2006;105:381-93) contains a report by Baer of a primigravida who
developed fatal bacterial meningitis following epidural analgesia for
labor along with a review of reported cases (179 from 1952 to 2005).
Two of those cases, both in parturients, resulted in maternal death.
Two involved epidurals with two attempts to place the catheter and one
was a spinal. This report discusses issues surrounding the diagnosis
and management of postdural puncture meningitis. Once again the
controversy about whether we should wear gowns arises. This article is
accompanied by an editorial by David Hepner.
longer administer sodium citrate to fasted women
having elective procedures.
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Incidence of serious complications
The same issue of Anesthesiology contains an article
by Ruppen et al which examined the incidence of epidural hematoma,
infection and neurologic injury in obstetric patients with epidural
analgesia/anesthesia (Anesthesiology 2006;105:394-9). Using
PubMed, EMBASE and MEDLINE they extracted reports of these
complications. The overall rate of epidural hematoma was 1 in 183,000
or 5 per million when cases before 1990 were included and 1:168,000
women or 6 per million from reports after 1990. Rates of “deep epidural
infection” were 1:145,000 women after 1990 or 7 per million and rates of
persistent neurologic injury were 1:237,000 women of 4 per million after
1990.
As always there may be the problem of
underreporting of these complications due to fears of litigation so this
study may under-represent the actual incidence.
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Postdural puncture headache and
gender
The September issue of Anesthesiology contains a
systematic review looking at the influence of gender on PDPH (Anesthesiology
2006;105:613-8). There is nothing new in this report as the authors
found that non-pregnant females had approximately twice the chance of
developing a PDPH compared to males. The authors suggest several
possible mechanisms for this including differences in the way
nociceptive information is processed, differences in degree of central
sensitization and sensitivity to noxious stimuli in addition to
psychosocial factors and differences in cerebral vasodilatory response.
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Influence of volume on epidural
analgesia
Chan et al (Int J Obstet Anesth 2006;15:201-5)
examined the effect of diluent volume on a single epidural dose of
ropivacaine for labor pain. They randomized 60 laboring primips in
early labor to receive 30 mg of ropivacaine in a 5 ml, 10 ml or 20 ml
volume. Pain was measured using a VAS at the peak of a contraction for
30 minutes. They did not find volume to be a factor as analgesia was
similar among the groups, suggesting drug mass is more important.
This contrasts with a study by Christiaens (Reg
Anesth Pain Med 1998;23:134-41) who studied 20 mg of bupivacaine
diluted in 4 ml, 10 ml and 20 ml. The 4 ml did not produce adequate
analgesia and although analgesia was similar in the 10 and 20 ml groups
it lasted longest in the 20 ml group. This result was confirmed by
Lyons (only presented as an abstract) who looked at the minimum local
anesthetic volume. He found that a larger volume resulted in the need
for a lower dose of bupivacaine.
Lee suggested some possible reasons for the
discrepancy between their study and that of Christaens. These included
the smaller size of subjects in their study (Asians vs Europeans),
related to the lowest volume studied (4 ml vs 5 ml) and the fact that
Christiaens used a lidocaine test dose. One other difference is the
drugs used and as many of us know there has been a constant debate about
the relative effectiveness of similar concentrations of bupivacaine and
ropivacaine.
I anticipate that we will see more studies on this subject in the
future.
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Dr. Joanne Douglas
BC Women's Hospital
Vancouver, British Columbia
The views expressed in this newsletter are
strictly those of the author. Information contained in this newsletter does not represent
specific advice to individual patients. Questions about this information or any other
medical condition should be referred to a qualified physician or therapist.
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