Drugs administered to mothers have the potential to cross the placenta and reach the fetus. Under particular circumstances, the comparison of the drug concentration in the maternal and fetal plasma may give an idea of the exposure of the fetus to the maternally administered drugs. In this review drugs are classified according to their type of transfer across the placenta. Several drugs rapidly cross the placenta and pharmacologically significant concentrations equilibrate in maternal and fetal plasma. Their transfer is termed ‘complete’. Other drugs cross the placenta incompletely, and their concentrations are lower in the fetal than in maternal plasma. The majority of drugs fit into 1 of these 2 groups. A limited number of drugs reach greater concentrations in fetal than maternal plasma. It is said that these drugs have an ‘exceeding’ transfer. The impression prevails that suxamethonium chloride (succinylcholine chloride) and doxorubicin do not cross the placenta. However, a careful analysis of the literature suggests that this impression is wrong and that all drugs cross the placenta, although the extent transfer varies considerably. The following parameters were considered as possible factors determining the extent of placental transfer: (i) the molecular weight of the drug; (ii) the pKa (pH at which the drug is 50% ionised); and (iii) the extent of drug binding to the plasma protein. Drugs with molecular weights greater than 500D have an incomplete transfer across the human placenta. Strongly dissociated acid drug molecules should have an incomplete transfer, but this does not seem to be an absolute rule. For example, ampicillin and methicillin transfer completely and they are strongly dissociated at physiological pH. The extent of drug binding to plasma protein does not influence the type of drug transfer across the human placenta.

Placental Transfer of Drugs Administered to the Mother

Cataract in the Adult Eye Preferred Practice Pattern

Spinal anaesthesia is generally preferred for Caesarean section. Its superiority for the baby is often assumed. Umbilical artery acid-base status provides a valid index of fetal welfare. Twenty-seven studies reporting neonatal acid-base data with different types of anaesthesia were used to compare umbilical artery or vein pH and base deficit, using random-effect meta-analysis. Cord pH was significantly lower with spinal than with both general (difference: -0.015; 95% CI -0.029 to -0.001; 13 studies, 1272 subjects) and epidural anaesthesia (difference -0.013; 95% CI -0.024 to -0.002; 11 studies, 828 subjects). Larger doses of ephedrine contributed to the latter effect (p = 0.023). Sixteen studies reported a base deficit, which was significantly higher for spinal than for general (difference 1.109; 95% CI 0.434-1.784 mEq.l(-1); seven studies, 695 subject) and epidural anaesthesia (difference 0.910; 95% CI 0.222-1.598 mEq.l(-1); seven studies, 497 subjects). Spinal anaesthesia cannot be considered safer than epidural or general anaesthesia for the fetus.

https://associationofanaesthetists-publications.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2044.2005.04223.x

Anaesthesia for Caesarean section and neonatal acid‐base status: a meta‐analysis*

Background We systematically reviewed evidence addressing the effectiveness of nitrous oxide for the management of labor pain, the influence of nitrous oxide on women's satisfaction with their birth experience and labor pain management, and adverse effects associated with nitrous oxide for labor pain management. Methods We searched the MEDLINE, EMBASE, and Cumulative Index to Nursing and Allied Health Literature (CINAHL) databases for articles published in English. The study population included pregnant women in labor intending a vaginal birth, birth attendees or health care providers who may be exposed to nitrous oxide during labor, and the fetus/neonate. Results We identified a total of 58 publications, representing 59 distinct study populations: 2 studies were of good quality, 11 fair, and 46 poor. Inhalation of nitrous oxide provided less effective pain relief than epidural analgesia, but the quality of studies was predominately poor. The heterogeneous outcomes used to assess women's satisfaction with their birth experience and labor pain management made synthesis of studies difficult. Most maternal adverse effects reported in the literature were unpleasant side effects that affect tolerability, such as nausea, vomiting, dizziness, and drowsiness. Apgar scores in newborns whose mothers used nitrous oxide were not significantly different from those of newborns whose mothers used other labor pain management methods or no analgesia. Evidence about occupational harms and exposure was limited. Conclusions The literature addressing nitrous oxide for the management of labor pain includes few studies of good or fair quality. Further research is needed across all of the areas examined: effectiveness, satisfaction, and adverse effects.

Nitrous Oxide for the Management of Labor Pain: A Systematic Review

Background. Oxygen supplementation is given routinely to parturients undergoing Caesarean section under regional anaesthesia. While the aim is to improve fetal oxygenation, inspiring a high oxygen fraction (FIO2 ) can also increase free radical activity and lipid peroxidation in both the mother and baby. In this prospective, randomized, double-blind study, we investigated the effect of high inspired oxygen fraction (FIO2 ) on maternal and fetal oxygenation and oxygen free radical activity in parturients having Caesarean section under spinal anaesthesia. Methods. Forty-four healthy parturients were randomized to breathe either 21% (air group) or 60% oxygen (oxygen group) intraoperatively via a ventimask. Maternal arterial blood was collected at 5-min intervals from baseline until delivery, and umbilical arterial and venous blood was collected at delivery. We measured blood gases and the products of lipid peroxidation (8-isoprostane, malondialdehyde (MDA), hydroperoxide (OHP)) and purine metabolites. Results. At delivery, the oxygen group had greater maternal arterial PO2 [mean 30.0 (SD 6.3) vs 14.2 (1.9) kPa; mean difference 15.8 kPa, 95% confidence interval 12.9‐18.7 kPa, P<0.001] and greater umbilical venous PO2 [4.8 (1.0) vs 4.0 (1.4) kPa; mean difference 0.8 kPa, 95% confidence interval 0.0‐1.5 kPa, P=0.04] compared with the air group. Maternal and umbilical plasma concentrations of lipid peroxides (8-isoprostane, MDA, OHP) were greater in the oxygen group than in the air group (P<0.05). Conclusions. We conclude that breathing high FIO2 modestly increased fetal oxygenation but caused a concomitant increase in oxygen free radical activity in both mother and fetus. Br J Anaesth 2002; 88: 18‐23

Effects of high inspired oxygen fraction during elective Caesarean section under spinal anaesthesia on maternal and fetal oxygenation and lipid peroxidation

Predictors of desaturation in the postoperative anesthesia care unit: an observational study.

Nous avons etudie trois groupes de 13 malades et nouveaux-nes au cours de cesariennes electives faites sous anesthesie avec N2O, O2 et epidurale. La moitie du groupe fait a l’epidurale a recu de l’oxygene additionnel par masque.

/pdf/acid-base-studies-in-elective-caesarean-sections-during-3psi8h9r0w.pdf

Acid-base studies in elective caesarean sections during epidural and general anaesthesia.

Acid-base studies in elective caesarean sections during epidural and general anaesthesia

Monitored anesthesia care provided by registered respiratory care practitioners during cataract surgery: a report of 1957 cases.

Two per cent lidocaine with 1:200,000 epinephrine was used for lumbar epidural analgesia in nineteen caesarian sections. Maternal and foetal blood lidocaine concentrations were obtained. Maternal uptake, placental transmission, and foetal metabolism of lidocaine are discussed.

/pdf/transmission-of-lidocaine-hydrochloride-across-the-placenta-20jj6j7vvg.pdf

Transmission of lidocaine hydrochloride across the placenta during Caesarian section.

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