John B. Craft

Uterine blood flow and plasma norepinephrine changes during maternal stress in the pregnant ewe.

Because maternal stress may adversely affect the fetus, the authors tested the effects of brief episodes (15-60 sec) of maternal stress in 18 awake pregnant ewes. Maternal agitation and stuggling occurred either following non-painful stimuli such as loud noises or sudden movements of personnel (ten animals) or following the brief application to the ewes skin of a uniform electrical stimulus of 30 volts with a frequency of 167 Hz for 30-60 sec (eight animals). Stimulation of either type produced a 45-50 per cent increase in mean maternal arterial blood pressure and a concomitant 32-52 per cent decrease in uterine blood flow (P<0.05). The decreases in uterine blood flow were brief, lasting less than 3 min, and were not associated with fetal asphyxia. Maternal plasma norepinephrine levels were measured following electrically induced maternal stress and were increased 25 per cent. The authors conclude that maternal stress may decrease uterine blood flow secondary to release of endogenous norepinephrine.

Placental passage and uterine effects of fentanyl.

Using the chronic maternal–fetal sheep preparation, 27 pregnant ewes were studied to determine the effects of intravenous fentanyl on maternal and fetal physiology, with particular reference to its placental passage, and its effects on uterine blood flow and uterine tone. Three doses of fentanyl were studied-50, 75, and 100 μg. Maternal and fetal arterial blood was collected for determination of fentanyl levels. All blood levels, both maternal and fetal, were normalized to the 50-μg dose. The maternal normalized blood levels were found to fit a biexponential equation describing a two-compartment open model. The half-life of the maternal elimination phase was 42 ± 7.0 min with an overall elimination constant (K) of 0.21 min−1. Maternal plasma fentanyl levels decreased very rapidly in the first 10 min after injection, at which time only 9% of the peak value remained. Fentanyl was detectable in fetal blood as early as 1 min and levels peaked at 5 min. Once equilibrium was established between maternal and fetal blood, the maternal levels remained 2.5 times those of the fetal level from 5 min to 60 min after drug injection. Both maternal and fetal drug levels declined in an approximately parallel fashion. No significant deleterious changes were seen in any maternal or fetal cardiovascular or acid-base parameters, and uterine blood flow and uterine tone were also unaffected (P > 0.05).

Enflurane analgesia in obstetrics.

: The effects of enflurane analgesia (approximately 0.5%) were studied in 55 patients during the second stage of normal vaginal delivery and were compared with effects of nitrous oxide (approximately 40%) in 50 similar patients. The enflurane and oxygen mixture was rated satisfactory by 89% of the mothers and 80% of the anesthesiologists. These ratings did not differ significantly from those for nitrous oxide. Obstetricians, however, rated the enflurane and oxygen mixture superior. The newborns of mothers receiving both agents wee vigorous and comparable when assessed by Apgar scores and cord blood gas tensions. The estimate of blood loss was similar in both groups. Serum inorganic fluoride concentrations in the mother after anesthesia were not significantly increased from preanesthetic levels with either agent. There was no biochemical evidence of renal toxicity. In neonates of mothers given enflurane, the mean umbilical cord concentration of serum inorganic fluoride ions was 2.4 +/- 0.2 micromoles/L, a value well below that associated with nephrotoxicity.

Ketamine, catecholamines, and uterine tone in pregnant ewes

Blood levels of ketamine, measured in both mother (1,230 ng/ml at 1 minute) and fetus (470 ng/ml at 1 minute) illustrate not only rapidly decreasing levels of the drug after its intravenous administration but also its transplacental passage. Concentrations of norepinephrine, epinephrine, and dopamine did not change in the mother or fetus after ketamine, with the exception of maternal levels of epinephrine, which were significantly higher at 45 minutes than control values (p less than 0.05). Maternal effects of ketamine consisted of increases in mean arterial pressure (7% p less than 0.05), cardiac output (16% p less than 0.01), and respiratory acidosis, all of which were slight and transitory. Although resting uterine tone increased (39% p less than 0.01), the uterine blood flow remained constant. None of the physiologic alterations could be correlated with changes in catecholamine levels. Therefore, the cardiovascular and uterine stimulating properties of ketamine at a dose of 0.7 mg/kg are small and are not the result of increased catecholamine levels in plasma. Further studies are necessary to elucidate the mechanism.

Cardiovascular Effects and Placental Passage of Dantrolene in the Maternal-fetal Sheep Model

Using the chronic maternal-fetal sheep preparation, nine pregnant ewes were studied to determine the effects of intravenous dantrolene sodium on maternal and fetal physiology, with particular reference to its placental passage, and its effects on uterine blood flow and uterine tone. Two doses of dantrolene sodium were studied: 1.2 mg/kg and 2.4 mg/kg. After 2.4 mg/kg, maternal cardiac output increased 29% (P < 0.05) after 1 min and returned to normal after 30 min. Maternal mean arterial pressure increased 13% after 1 min and remained significantly elevated (P < 0.05) were observed in maternal heart rate, uterine artery blood flow, or central venous pressure. Maternal arterial pH declined from 7.42 to 7.39 (P < 0.01) after 1 min and returned to baseline values after 10 min. Fetal heart rate decreased 24% (P < 0.01) after 3 min and returned to normal after 10 min; the mean fetal arterial pressure remained unchanged (P > 0.05). Fetal arterial pH declined from 7.29 to 7.27 (P < 0.05) after 1 min and remained significantly decreased for 120 min. Similar changes of lesser magnitude and shorter duration were seen following the 1.2 mg/kg dose. Maternal levels of dantrolene were less than 3 μg/ml. Although an equilibrium between maternal and fetal plasma dantrolene concentrations was apparent at 5 min, the fetal levels of dantrolene were approximately 10% of the mothers. The results indicate that the administration of intravenous dantrolene at 1.2 mg/kg or 2.4 mg/kg has no clinically significant adverse effect on mother or fetus in the sheep model.

Anaesthetic considerations in caesarean section for quadruplets

SummaryA case of a caesarean delivery with epidural analgesia of a term parturient with quadruplets is presented. Maternal considerations of hypotension, respiratory embarrassment and aspiration of gastric content and foetal considerations of prematurity and impaired placental function are discussed relative to the use of general anaesthesia or epidural analgesia.RésuméOn a publié récemment1 une discussion des considérations anesthésiques pour les accouchements de quadruplets par voie vaginale. Nous rapportons ici notre expérience ďun cas de césarienne sous anesthésie péridurale pour un accouchement de quadruplets. Dans une telle situation, il faut considérer les points suivants:(a)Les risques ďhypotension sont grands, les effets de compression aorto-cave étant augmentés par un volume utérin considérable. Si ľon ajoute la vasodilatation avec “pooling” sanguin secondaire au bloc sympathique produit par la péridurale, on peut observer une chute du débit cardiaque avec hypotension et diminution du débit sanguin utérin.3 De plus, ľon a rapporté que ľincidence ďhémorragie post-partum par atonie utérine est deux à trois fois plus fréquente dans les grossesses multiples que dans les accouchements ordinaires.6(b)Le volume utérin très élevé implique un plus grand risque de détresse respiratoire chez la mère.(c)La possibilité de régurgitation et ďaspiration de liquide gastrique est également augmentée. Aussi devrait-on administrer des antacides per os aux patientes avant ľinduction.(d)Les bébés naissent en général de façon prématurée et souffrent fréquemment ďun retard de croissance intra-utérine à cause ďun débit sanguin placentaire diminué. Leur état de prématurés les rend plus susceptibles à la dépression par les anesthésiques généraux et diminue également leur capacité ďadaptation à la vie extra-utérine.(e)Chacun des fœtus restant aura proportion-nellement moins de tissu placentaire fonctionnel que ceux nés avant lui. Si ľon utilise une anesthésie générale, chacun des fœtus successifs recevra également plus ďagent anesthésique que ceux qui sont déjà nés. Avec une anesthésie régionale, un épisode ďhypotension maternel aura des conséquences croissantes sur chacun des fœtus successifs.(f)Le personnel obstétrical, anesthésique et pédiatrique doit être compétent et suffisant pour fournir des soins optima à la mère et aux bébés. Chacun des nouveau-nés devrait avoir sa propre équipe de réanimateurs.

Enflurane Analgesia in Obstetrics

The effects of enflurane analgesia (approximately 0.5%) were studied in 55 patients during the second stage of normal vaginal delivery and were compared with effects of nitrous oxide (approximately 40%) in 50 similar patients. The enflurane and oxygen mixture was rated satisfactory by 89% of the mothers and 80% of the anesthesiologists. These ratings did not differ significantly from those for nitrous oxide. Obstetricians, however, rated the enflurane and oxygen mixture superior. The newborns of mothers receiving both agents were vigorous and comparable when assessed by Apgar scores and cord blood gas tensions. The estimate of blood loss was similar in both groups. Serum inorganic fluoride concentrations in the mother after anesthesia were not significantly increased from preanesthetic levels with either agent. There was no biochemical evidence of renal toxicity. In neonates of mothers given enflurane, the mean umbilical cord concentration of serum inorganic fluoride ions was 2.4 ± 0.2 μmUmoles/L, a value well below that associated with nephrotoxicity.