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Results: Anesthesia & Analgesia
(C) 2002 by International Anesthesia Research Society.
Volume 94(2), February 2002, pp 404-408
An Evaluation of Isotonic "Sport Drinks" During Labor [TECHNOLOGY,
COMPUTING, AND SIMULATION: OBSTETRIC ANESTHESIA]
Kubli, Mark FRCA(UK)*,; Scrutton, Mark J. FRCA(UK)+,; Seed, Paul T. MSc,
Cstat++,; O' Sullivan, Geraldine PhD, FRCA(UK)*
*Department of Anaesthesia, St. Thomas' Hospital, London, United Kingdom;
+Department of Anaesthesia, St. Michael's Hospital, Bristol, United
+Kingdom; and
++Maternal & Fetal Research Unit, Department of Obstetrics &
++Gynaecology, Guy's
Kings and St. Thomas' School of Medicine, King's College, London, United
Kingdom Supported by a grant from the Obstetric Anaesthetists' Association,
United Kingdom. September 14, 2001. Address correspondence and reprint
requests to M. Kubli, FRCA, Department of Anaesthesia, St. Thomas' Hospital,
Lambeth Palace Road, London SE1 7EH, United Kingdom. Address e-mail to
[EMAIL PROTECTED]
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Outline
Abstract
Methods
Results
Discussion
References
Graphics
Table 1
Table 2
Table 3
Table 4
Abstract
We compared the metabolic effects of allowing women isotonic "sport drinks"
rather than water to drink during labor. The effect of these drinks on
gastric residual volume was also evaluated. Sixty women in early labor
(cervical dilation P = 0.000) and nonesterified fatty acids (P = 0.000) had
increased and plasma glucose (P = 0.007) had decreased significantly in the
Water-Only group. Gastric antral cross-sectional area after delivery was
similar in the two groups. The incidence of vomiting and the volume vomited
during labor and within the hour of delivery were also similar. There was no
difference between the groups in any maternal or neonatal outcome of labor.
In conclusion, isotonic drinks reduce maternal ketosis in labor without
increasing gastric volume.
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In recent years, maternal mortality from acid pulmonary aspiration
(Mendelson's
syndrome) (1) has dramatically declined. In the Report on the Confidential
Enquiries into Maternal Deaths in England and Wales (1991-1996), only one
mother died from aspiration (2). There are several factors that may be
associated with this audited improvement. These include the increased use of
regional anesthesia for cesarean delivery, improved training of
anesthesiologists, and, possibly, the introduction of nonparticulate
antacids and H2-receptor antagonists. The role of nothing by mouth during
labor, as recommended in the first Report on the Confidential Enquiries into
Maternal Deaths (1952-1954), is less clear (2).
Women in labor exhibit a state of "accelerated starvation," with rapid
increases in the blood levels of [beta]-hydroxybutyrate, acetoacetic acid,
and the nonesterified fatty acids (NEFAs) from which they are derived and
with a concomitant decrease in blood glucose (3). It has been suggested,
although never scientifically proven, that these changes may have
detrimental effects on uterine activity and the progress of labor (4).
A previous study demonstrated that allowing laboring women to eat a light
diet prevented the increase of plasma ketones and NEFAs (5). However, not
surprisingly, feeding resulted in a significant increase in residual gastric
volume, which could predispose to pulmonary aspiration should a complication
of neuroaxial anesthesia occur or should general anesthesia be required
unexpectedly. Isotonic drinks are rapidly emptied from the stomach and
absorbed by the gastrointestinal tract (6,7) and therefore may theoretically
provide a safer alternative to solid food. The aim of this study was to
evaluate whether isotonic drinks would prevent ketosis without increasing
the risk of potential aspiration.
Methods
St. Thomas' Hospital Ethics Committee granted approval for this project.
After informed written consent, 60 women presenting in early labor (cervical
dilation
(R) (still), with the choice of either orange or lemon flavor. Lucozade
Sport
(still) contains a mixed carbohydrate profile (dextrose, maltodextrin, and
glucose) of 64 g/L, a sodium of 24 mmol/L, potassium of 2.6 mmol/L, and
calcium of 1.2 mmol/L and has a tonicity of 300 mOsm/kg.
Women in the Sport Drinks group were encouraged to consume up to 500 mL (one
bottle) in the first hour and then a further 500 mL every 3 to 4 h.
Additionally, they were allowed to take small quantities of water as
desired. Women randomized to the Water-Only group could consume as little or
as much water as they wanted.
For metabolic assessment, plasma [beta]-hydroxybutyrate, NEFAs, and glucose
were measured in early labor and again at the end of the first stage by
using blood samples. Real-time ultrasonography was used to compare residual
gastric volumes between the two groups (9,10). Examinations were performed
with a high-resolution scanner (SSD 620; Aloka, Tokyo, Japan), by use of a
5-MHz curvilinear transducer in the midline of the epigastrium with the
mother sitting up at 45[degrees]. All the ultrasound scans were performed
within 45 min after delivery and by one investigator (MK). The incidence and
volume of vomiting that occurred during labor and within the hour of
delivery were recorded.
Duration of the stages of labor, oxytocin requirements, mode of delivery,
Apgar scores, and umbilical artery and venous blood gases were recorded.
Previous metabolic studies in pregnancy suggested that a change in
[beta]-hydroxybutyrate of 0.15 mmol/L (mean, 0.24 mmol/L; sd, 0.20 mmol/L),
in NEFAs of 0.2 mmol/L (mean, 0.85 mmol/L; sd, 0.2 mmol/L), and in glucose
of 0.7 mmol/L (mean, 5.2 mmol/L; sd, 0.7 mmol/L) would be both plausible and
medically important (11). Power calculations indicated that 30 women in each
group would be needed to detect such a difference in [beta]-hydroxybutyrate
with 80% power and at a 5% level of significance. Much smaller numbers would
be needed for the other measures. Metabolic, gastric volume, and vomiting
data were analyzed by parametric methods by using linear regression
analysis, adjusting for baseline as appropriate (12). The standard errors
were corrected for nonnormality and unequal variances by use of the
Huber-White sandwich estimator (13). Demographic data and maternal and fetal
outcomes were analyzed with Student's t-test and [chi]2 analysis as
appropriate. All data were analyzed by the intent-to-treat principle by
using the commercially available statistics software package
Stata(R) version 6.0 (Stata Corp., College Station, TX).
Results
Sixty women were recruited to the study: 30 to the Isotonic Sport Drink
group and 30 to the Water-Only (Control) group. Ninety-one women were asked
to join the study; 31 declined consent. No woman withdrew from the study.
Women in the two groups were similar with respect to age, parity, induction,
and cervical dilation at the time of randomization (Table 1). There was no
difference between the two groups in the duration of labor, use of oxytocin,
mode of delivery, or use of epidural analgesia (Table 2). The babies had
similar Apgar scores and umbilical artery and venous gases (Table 2).
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Table 1. Maternal Characteristics and Use of AnalgesiaData are
presented as n, n (%), or mean (sd).
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Table 2. Labor OutcomesData are presented as mean (sd) or n (%).All
results are nonsignificant.
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The isotonic sport drinks were acceptable to most mothers in the Sport Drink
group, with only one woman refusing to consume more than 200 mL for the
study. There was a progressive decrease in the desire to drink the sport
drink toward the end of the labor and after consuming 750-1000 mL. The two
groups were similar in all of the baseline metabolic indices measured on
entry to the study in early labor (Table 3). However, by the end of labor,
plasma [beta]-hydroxybutyrate and NEFAs were significantly increased and
plasma glucose significantly decreased in the Water-Only group (Table 3). In
one patient in the Isotonic Sport Drink group, a result was not obtained
from an entry sample for [beta]-hydroxybutyrate, and this result was
therefore excluded from the metabolic analysis. Gastric antral
cross-sectional area measured within 45 min of delivery was not
significantly different between the groups (Table 4). There was no
difference between the groups in the volume vomited or number of vomiting
episodes within 1 h of delivery or throughout labor (Table 4). The total
quantity of liquid consumed was significantly more (95% confidence interval,
193-701;P = 0.001) in the Sport Drink group (mean, 925 mL; sd, 384) compared
with the Water-Only group (mean, 478 mL; sd, 579). The mean calorific intake
in the Sport Drink group was 47 (sd, 16) kcal/h and was none in the
Water-Only group.
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Table 3. Plasma Values of Metabolites Measured on Entry into the Study
in Early Labor (mean [sd]) and at the End of Stage 1 of Labora (mean [SE])a
Estimates adjusted for baseline and confidence intervals use robust standard
errors.
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Table 4. Gastric Antral Cross-Sectional Area and Incidence and Volume
of Vomitinga Confidence intervals calculated with robust standard errors.b
Chi-square test.
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Discussion
It has previously been shown that consuming a light diet during labor
prevents the increase in ketone production, but this happens at the expense
of increasing the residual gastric volume (5). In this study, isotonic sport
drinks significantly reduced the increase in ketone production (Table 3) but
did not increase the residual gastric volume when compared with the
Water-Only group. This suggests that isotonic sport drinks may be a safer
alternative to solids in labor. Ketosis occurs when the body metabolizes
fats because carbohydrates are not available in sufficient quantity for use
as a source. In labor, [beta]-hydroxybutyrate is the principle ketone
produced as a result of starvation (14), and in our study the sport drinks
significantly reduced the production of this metabolite (Table 3). Plasma
NEFAs, from which [beta]-hydroxybutyrate is derived, are mobilized from the
liver in response to starvation (14), and, once again, the increase was
significantly reduced in the Isotonic Sport Drink group (Table 3). Indeed,
the mean [beta]-hydroxybutyrate was decreased and the mean plasma NEFA level
remained unchanged throughout the first stage of labor in the Isotonic Sport
Drink group. Mean plasma glucose remained unchanged in the Isotonic Sport
Drink group, demonstrating that sufficient calories were being absorbed and
used compared with the Water-Only group, in which the level decreased
significantly (Table 3).
The results demonstrated no significant difference in either maternal or
fetal outcomes despite these metabolic improvements. To detect a 10% change
in duration of labor or a 6.6% increase in the spontaneous delivery rate
(power at 90%, 5% significance level), it is estimated that 2400 primiparous
women would need to be studied. Production of ketones from the mobilization
and breakdown of NEFAs is the physiological consequence of starvation, and
in normal pregnancy women are prone to ketosis because of a change in the
maternal hormonal milieu (14). Ketone bodies are not waste products of
metabolism but are readily available alternate energy sources for the
contracting uterus and the brain of both mother and fetus. Although ketones
may increase with the duration of labor in a mother deprived of a calorific
source, no causal relationship with outcome has ever been proven (4).
Indeed, this increase in ketones may prove to be inconsequential to the
progress and outcome of labor. A study evaluating the effect of feeding on
labor outcome is now in progress.
Despite the greater quantity of liquid taken during labor in the Isotonic
Sport Drink group, residual gastric volumes were similar in the two groups,
indicating rapid gastric emptying of the isotonic drinks. Lucozade Sport
(still), the isotonic sport drink used in the study, contains a mixed
carbohydrate profile (dextrose, maltodextrin, and glucose) of 64 g/L and has
a tonicity of 300 mOsm/kg. Mixed carbohydrate solutions empty faster than
glucose-alone solutions (6), as do isotonic carbohydrate solutions, compared
with hypertonic carbohydrate-containing solutions (7). Large concentrations
of carbohydrates in solutions have an increased osmolality and are
associated with a slower rate of gastric emptying (7). The source of
carbohydrate will influence fluid osmolality, and to avoid very high
osmolalities, the quantity of monosaccharides must be smaller than that of
disaccharides or polysaccharides. Indeed, in a study in exercising athletes
(15), an ideal solution to achieve maximal carbohydrate availability without
impairing fluid homeostasis was found in beverages with 60-80 g/L of
carbohydrate and isoosmolar 300 mOsm/kg. The sport drink used in the study
has advantages of being isotonic with faster gastric emptying, but having a
smaller carbohydrate content; therefore, fewer calories are available to the
parturient.
The mean values for the gastric antral cross-sectional area in both the
Isotonic and Water groups were similar to those of a group who drank water
only in a previous study (5). The use of the ultrasound as a two-dimensional
modality to provide an estimate of gastric volume, a three-dimensional
measure, has been validated previously (9,10) and was used in a similar
study evaluating the effect of eating solid food during labor (5). Three of
the participants were excluded from the gastric analysis because of
inability to visualize the
stomach: two in the Sport Drink group and one in the Water group. Volumes
vomited within an hour of delivery and throughout labor were also not
significantly different, again showing that isotonic drinks were being
emptied from the stomach as fast as water. Evidence to date indicates that
pregnancy may not significantly alter gastric emptying of liquids or solids
but that established labor may cause an unpredictable delay in gastric
emptying (16). Opioid drugs given parenterally for pain relief cause a
marked delay in gastric emptying (8,17). Studies of the effect of small-dose
epidural infusions containing fentanyl 2 [mu]g/mL have not demonstrated a
profound delay in gastric emptying (18,19). However, in one study, a slight
delay (not statistically significant) was noted at 4.5 hours after 125 [mu]g
of fentanyl, leading the investigators to suggest that delay in gastric
emptying may occur in a dose-dependent manner (18). The evidence is
conflicting (20,21). The mean total doses of epidural fentanyl in the
Isotonic Sport Drink and Water groups during labor were 181 and 205 [mu]g,
respectively, which equates to 27 and 24 [mu]g/h, of fentanyl. It is
possible that epidural fentanyl in small-dose infusions may have an effect,
but it is likely to be small compared with the delay in gastric emptying
produced by parenteral opioids. The women who required cesarean delivery in
this study had their lumbar epidural analgesia converted to anesthesia for
surgery.
This study demonstrates that only a relatively small calorific intake of 47
kcal/h prevents the development of ketosis and that isotonic drinks are
rapidly emptied from the stomach and absorbed by the gastrointestinal tract
in the laboring mother. Isotonic drinks provide an alternative source of
nutrition to food. To be isotonic, the calorific load of such drinks is
limited to approximately 30 kcal/dL.
It is not known whether the degree of ketosis that occurs in some women
during labor is a harmless physiological state or a pathologic condition
that interferes with uterine activity, but further research in this field is
needed. Our study supports the policy of allowing mothers who have not
received parenteral opioids to consume isotonic drinks once they are in
established labor.
We thank the mothers, midwives, and obstetricians at St. Thomas' Hospital
for their cooperation and support. We would like to acknowledge the guidance
provided by Dr. L. MacDonald, Consultant Radiologist, St. Thomas' Hospital;
G. A. Metcalfe (Dietitian), St. Thomas' Hospital; and Beechams (Ltd.) for
the supply of the Lucozade isotonic sport drinks. We thank the Obstetric
Anesthetists Association for funding the salary of MK and costs of the
laboratory tests.
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Accession Number: 00000539-200202000-00033
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