Maternal glucose loading in the management of fetal distress

Glucose and insulin requirements during labor and delivery: the case for normoglycemia in pregnancies complicated by diabetes

OBJECTIVE

To present protocols for maintaining normoglycemia during labor and delivery in order to achieve optimal outcomes of pregnancy in women with diabetes.

RESULTS

Labor has a glucose-lowering effect. In the case of women with insulin-requiring gestational diabetes, no additional insulin is needed with the onset of labor; sufficient glucose should be infused to keep such women from becoming ketotic from the pronged period of starvation. Likewise, protocols derived from glucose-controlled insulin infusion studies reveal that women with type 1 diabetes require no more subcutaneously administered insulin on the morning of an induction of labor or at the onset of spontaneous labor. The intravenously administered solutions should be started with isotonic saline or electrolyte solutions. As soon as active labor is achieved, the solutions should be switched to a glucose-containing fluid and administered at a rate of 2.55 mg/kg per minute.

CONCLUSION

Labor is a form of exercise and thus obviates the insulin requirement in women with all types of diabetes, but it also necessitates an eightfold increase in glucose substrate in order to prevent maternal hypoglycemia and ketosis. The literature presents clear evidence that neonatal hypoglycemia is directly related to maternal hyperglycemia during labor and delivery. Thus, protocols for maintaining normoglycemia during labor and delivery are necessary to achieve optimal results.

NPO during labor. Is there any scientific validation?

Maternal death from pulmonary aspiration of gastric contents has virtually disappeared in the United Kingdom. The one case documented in the most recent triennial report was a woman with multiorgan failure in intensive care and is probably not relevant to the current debate [1]. Although not so well documented, other Western countries seem to be experiencing the same decline in maternal death from this cause. At the same time, the burden of proof is falling increasingly on obstetric anesthesiologists as obstetricians and midwives demand that NPO policies should be rejected, unless anesthesiologists can prove that they are necessary. Without any proof of benefit, many midwives actively encourage eating in women who do not really want to eat. A hospital manager who wants to divert money to other areas of health care might make the same argument about employing less experienced--and therefore cheaper--anesthesiologists or nurse anesthetists on the labor floor. Although no self-respecting obstetric anesthesiologist would accept such a situation, there is still no randomized controlled trial that proves that experienced anesthesiologists reduce maternal mortality. Similarly it is difficult for a mother to comprehend the negligible risk of pulmonary aspiration during labor while her care providers insist that it would be more dangerous for her to cross a busy road! Against a background of conflicting advice from midwives and medical practitioners, the mother is likely to eat if she feels so inclined. Pulmonary aspiration is a rare complication, so even if a light diet in labor became acceptable, it is likely that it would take many years for a subsequent increase in maternal mortality to become apparent. It would be disappointing if mistakes made by a previous generation had to be relearned in the twenty-first century. Increasingly, media-controlled pressure groups dictate health fashions, and the physicians frequently can only stand on the sidelines and advise. Most obstetric anesthesiologists agree that a rigid NPO policy in labor is no longer appropriate and that at least water or ice chips should be allowed. Current evidence suggests that solids and semi-solids should be avoided once a woman is in active labor or requests analgesia. The appropriate advice is to allow a carefully audited introduction of isotonic drinks. These drinks seem to be an effective medium for providing calories while minimizing any increase in gastric volume, and such a policy would be unlikely to reverse the reduction in aspiration that has been achieved over the past 50 years.

Fetal and maternal energy metabolism during labor in relation to the available caloric substrate

AIM

To discuss maternal and fetal metabolic events during labor and the possible role of glucose administration.

RESULTS

The oxidative pathway covers the largest part of the energy demand of labor, although in the second stage or, in polysystolic labor, the non-oxidative pathway becomes important as well. Glucose is the main maternal energy source, but the rise in ketobodies, even during normal labor, suggests a relative shortage. In the first stage of labor, a combination of a respiratory alkalosis, and to a lesser extent, a metabolic acidosis, result in a rise in the maternal pH. In the second stage of labor, the maternal pH decreases due to an increasing metabolic acidosis. Glucose is also the main fetal energetic fuel. In fetal hypoxia, lactate is produced, which in most cases is transferred to the maternal circulation. High maternal lactate concentrations, however, may interfere with this process. Furthermore, fetal hyperglycemia may lead to an increased fetal lactate production.

CONCLUSIONS

Maternal hyperglycemia, may lead to an increase in maternal and fetal lactate production resulting in metabolic acidosis. Unlike high dosage intravenous glucose administration, it is not likely that oral intake of carbohydrates leads to maternal and fetal hyperglycemia and subsequently to metabolic acidosis, but studies are rare.

The effect of maternal oxygen administration during the second stage of labor on umbilical cord blood gas values: a randomized controlled prospective trial

OBJECTIVE

Our aim was to determine whether supplemental oxygen during the second stage of normal labor affects cord blood gas and cooximetry values.

STUDY DESIGN

Patients at term pregnancy were prospectively randomized to the control or treatment group at the onset of the second stage of labor. The treatment group received 10 L/min oxygen by face mask, which result in a mean fractional inspired oxygen concentration of 0.81.

RESULTS

There were 86 patients randomized into the study. In the oxygen group there were significantly more cord arterial pH values < 7.20 (9/41 vs 2/44, p < 0.05). The control group was compared with two subgroups of patients receiving oxygen: those receiving oxygen therapy for < or = 10 minutes and those receiving oxygen for > 10 minutes. Analysis of variance demonstrated significant differences (7.285 +/- 0.058, 7.312 +/- 0.056, 7.237 +/- 0.064; F test 8.3, p = 0.0005). Among several independent variables, regression analysis demonstrated that only duration of oxygen therapy had a significant inverse relation to cord arterial pH (F test = 15.6, p = 0.0002).

CONCLUSIONS

Prolonged oxygen treatment during the second stage of normal labor resulted in a deterioration of cord blood gas values at birth.

Haemodynamic changes in IUGR fetus with chronic hypoxia evaluated by fetal heart-rate monitoring and Doppler measurement of blood flow velocity

The measurement of fetal blood flow velocity and 24 h monitoring of fetal heart-rate (FHR) using a computer were performed to clarify the haemodynamics of growth-retarded fetuses with chronic hypoxia. One hundred normal-growth and 18 growth-retarded fetuses were analysed. All the growth-retarded fetuses with chronic hypoxia were characterised by abnormal blood flow velocity waveforms (with the pulsatility index in the descending aorta below the -1.0 SD and in the middle cerebral artery above the +1.0 SD for our reference range, from 100 normal-growth fetuses). In the latter, the incidence of accelerations of defined size and variability in FHR patterns showed a diurnal variation after 30 weeks' gestation. The initial change in FHR patterns during hypoxia in 11 growth-retarded fetuses, resulting in fetal distress, was a derangement of diurnal variations in FHR patterns, followed by a decrease in variability. A rapid increase in blood flow velocity in the middle cerebral artery with the advance of hypoxia was observed before the onset of distress. Maternal low-dose oxygen inhalation elicited a temporary increase in FHR variability in the growth-retarded but not in normal fetuses. Re-inhalation after 1 h elicited a similar change, suggesting that intermittent rather than continuous, oxygen inhalation may be more effective.

A comparison of the effects of four intravenous solutions for the treatment of ketonuria during labour

Forty women in whom ketonuria was detected during the first stage of labour were allocated randomly to intravenous treatment with one litre of either normal saline, Hartmann's solution, 5% dextrose or 10% dextrose. The solutions were administered over 1 h and blood was taken immediately beforehand and thereafter at 30-min intervals for 90 min to assess their effect on intermediary metabolism, plasma osmolality and acid-base status. Although both the 5 and 10% dextrose infusions caused a rapid decline in whole blood D-3-hydroxybutyrate concentrations, they also produced pathological degrees of maternal hyperglycaemia and hyperinsulinaemia and a marked elevation in the mean blood lactate and pyruvate concentrations. Administration of 10% dextrose was also associated with a significant increase in serum osmolality. Hartmann's solution produced significantly higher mean whole blood lactate and pyruvate concentrations than did normal saline. There was a significant increase in the venous base deficit in the group infused with 10% dextrose, indicating that the buffering capacity of the blood had been exceeded. It is concluded that rapid infusions of dextrose or Hartmann's solution should not be administered during labour. Normal saline should be used for rehydration and if dextrose therapy is deemed necessary the dose administered should not exceed physiological requirements.

Feto-maternal consequences of high-dose glucose infusion during labour

The effects on the fetus of high doses of glucose given to the mother in labour to correct maternal ketonuria were investigated. Three groups of patients were compared: one group received 1 litre of 10% (w/v) glucose intravenously over 1 h, the second group received 1 litre of 0.9% sodium chloride solution intravenously over 1 h and the final group had no supplementary infusion. It was observed that whereas glucose administration rapidly corrected maternal ketonaemia, there was a significant fall in pH and a rise in lactate in fetal blood. These effects were not observed in the other two groups. It was concluded that the use of high doses of intravenous glucose in labour should be avoided.

Effect of glucose infusion on the maternal and fetal acid-base equilibrium during labor

The effect of hypertonic glucose infusion on the maternal and fetal acid-base equilibrium was studied in 20 clinically normal parturients and their concepts. Samples of maternal peripheral venous blood and fetal capillary blood were collected before and after intravenous infusion of 25 g of glucose into the mother at 15-minute intervals. No significant alterations in the parameters of the maternal acid-base equilibrium were observed. On the fetal ide, a significant decrease in pO2 at intervals of 30, 45 and 60 minutes after glucose infusion (fig. 1), and an increase of total CO2 after 60 minutes (fig. 2) were observed. These findings did not permit us to state that glucose infusion may be responsible for the alterations found, since it is known that as labor progresses, PO2 tends to decrease while total CO2 tends to increase. On the other hand, an increase in glycemic levels is known to stimulate the rate of glucose consumption at the expense of its aerobic metabolism, by reducing the oxygen level and increasing CO2, the final products of this glucolytic pathway.

Metabolic effects of constant hypertonic glucose infusion in well-oxygenated fetuses

In order to investigate the metabolic effects of a constant hypertonic glucose infusion in well-oxygenated fetuses, ten experiments were carried out in nine long-term experiments in fetal lambs. It appeared that a constant hypertonic glucose infusion did not significantly affect the fetal blood gases, pH, and plasma lactate levels when fetal glucose was kept below 150 mg. per 100 ml. It was also demonstrated that glucose infusions significantly increased the fetal lactate levels and decreased the blood pH when fetal plasma glucose was over 150 mg. per 100 ml. However, there was no decrease in fetal PO2 and pco2 until fetal glucose reached values over 300 mg. per 100 ml. These studies suggest that constant hypertonic glucose infusion does not improve fetal blood gases or pH and that fetal hyperglycemia over 300 mg. per 100 ml. produces severe metabolic acidosis.

Fetal carbohydrate metabolism: its clinical importance

A basic understanding of fetal nutrition and metabolism is essential in the clinical management of the obstetric patient. The fetus depends upon a constant infusion of glucose for energy production and growth. Maternal glucose is the prime source of this nutrient. Alterations in maternal carbohydrate homeostasis will lead to changes in fetal metabolism. In diabetes mellitus, hyperglycemia may produce hyperinsulinemia and macrosomia. The growth-retarded fetus may have a decreased supply of maternal glucose and reduced amounts of hepatic glycogen and adipose tissue. The fetus must depend upon these stores for survival during periods of intrauterine hypoxia. In the newborn period, hypothermia and hypoxia may rapidly deplete energy reserves. With this information, the clinician may more knowledgeably manage dietary demands in the antepartum patient, fetal distress during labor, and the immediate newborn period.