Isoflurane or halothane for cesarean section: comparative maternal and neonatal effects

Fluoride Metabolism in Pregnant Women: A Narrative Review of the Literature

Epidemiological studies use biomarkers of fluoride exposure in pregnant women as surrogate measures of fetal fluoride exposure; however, there is little understanding of how pregnancy affects fluoride metabolism and its biomarkers. This narrative review summarizes the changes of pregnancy that have the potential to impact fluoride’s absorption, distribution and excretion, and highlights the limited body of evidence on the topic. The physiologic systems that experience pregnancy-associated changes relevant to fluoride’s metabolism are the cardiovascular, renal, metabolic and gastrointestinal, as well bone and calcium metabolism and the body’s acid-base balance. The available evidence indicates that fluoride is found in the maternal plasma and urine, placenta, amniotic fluid and fetus. Although plasma and urinary fluoride vary across gestation, there is insufficient quality evidence to determine the direction or extent of such variation. Furthermore, there is no doubt that fluoride from maternal blood crosses the placenta and is absorbed and excreted by the fetus; however, the biological mechanisms behind this placental passage are unknown. Research on maternal and prenatal biomarkers of fluoride exposure would benefit from studies on how pregnancy-associated changes affect the metabolism of fluoride across gestation, the mechanisms for the intestinal absorption of fluoride in pregnant women, and the placental passage of fluoride.

Anaesthetic interventions for prevention of awareness during surgery

BACKGROUND

General anaesthesia is usually associated with unconsciousness. 'Awareness' is when patients have postoperative recall of events or experiences during surgery. 'Wakefulness' is when patients become conscious during surgery, but have no postoperative recollection of the period of consciousness.

OBJECTIVES

To evaluate the efficacy of two types of anaesthetic interventions in reducing clinically significant awareness:- anaesthetic drug regimens; and- intraoperative anaesthetic depth monitors.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, ISSUE 4 2016); PubMed from 1950 to April 2016; MEDLINE from 1950 to April 2016; and Embase from 1980 to April 2016. We contacted experts to identify additional studies. We performed a handsearch of the citations in the review. We did not search trial registries.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of either anaesthetic regimens or anaesthetic depth monitors. We excluded volunteer studies, studies of patients prior to skin incision, intensive care unit studies, and studies that only randomized different word presentations for memory tests (not anaesthetic interventions).Anaesthetic drug regimens included studies of induction or maintenance, or both. Anaesthetic depth monitors included the Bispectral Index monitor, M-Entropy, Narcotrend monitor, cerebral function monitor, cerebral state monitor, patient state index, and lower oesophageal contractility monitor. The use of anaesthetic depth monitors allows the titration of anaesthetic drugs to maintain unconsciousness.

DATA COLLECTION AND ANALYSIS

At least two authors independently scanned abstracts, extracted data from the studies, and evaluated studies for risk of bias. We made attempts to contact all authors for additional clarification. We performed meta-analysis statistics in packages of the R language.

MAIN RESULTS

We included 160 studies with 54,109 enrolled participants; 53,713 participants started the studies and 50,034 completed the studies or data analysis (or both). We could not use 115 RCTs in meta-analytic comparisons because they had zero awareness events. We did not merge 27 of the remaining 45 studies because they had excessive clinical and methodological heterogeneity. We pooled the remaining 18 eligible RCTs in meta-analysis. There are 10 studies awaiting classification which we will process when we update the review.The meta-analyses included 18 trials with 36,034 participants. In the analysis of anaesthetic depth monitoring (either Bispectral Index or M-entropy) versus standard clinical and electronic monitoring, there were nine trials with 34,744 participants. The overall event rate was 0.5%. The effect favoured neither anaesthetic depth monitoring nor standard clinical and electronic monitoring, with little precision in the odds ratio (OR) estimate (OR 0.98, 95% confidence interval (CI) 0.59 to 1.62).In a five-study subset of Bispectral Index monitoring versus standard clinical and electronic monitoring, with 34,181 participants, 503 participants gave awareness reports to a blinded, expert panel who adjudicated or judged the outcome for each patient after reviewing the questionnaires: no awareness, possible awareness, or definite awareness. Experts judged 351 patient awareness reports to have no awareness, 87 to have possible awareness, and 65 to have definite awareness. The effect size favoured neither Bispectral Index monitoring nor standard clinical and electronic monitoring, with little precision in the OR estimate for the combination of definite and possible awareness (OR 0.96, 95% CI 0.35 to 2.65). The effect size favoured Bispectral Index monitoring for definite awareness, but with little precision in the OR estimate (OR 0.60, 95% CI 0.13 to 2.75).We performed three smaller meta-analyses of anaesthetic drugs. There were nine studies with 1290 participants. Wakefulness was reduced by ketamine and etomidate compared to thiopental. Wakefulness was more frequent than awareness. Benzodiazepines reduces awareness compared to thiopental, ketamine, and placebo., Also, higher doses of inhaled anaesthetics versus lower doses reduced the risk of awareness.We graded the quality of the evidence as low or very low in the 'Summary of findings' tables for the five comparisons.Most of the secondary outcomes in this review were not reported in the included RCTs.

AUTHORS' CONCLUSIONS

Anaesthetic depth monitors may have similar effects to standard clinical and electrical monitoring on the risk of awareness during surgery. In older studies comparing anaesthetics in a smaller portion of the patient sample, wakefulness occurred more frequently than awareness. Use of etomidate and ketamine lowered the risk of wakefulness compared to thiopental. Benzodiazepines compared to thiopental and ketamine, or higher doses of inhaled anaesthetics versus lower doses, reduced the risk of awareness.

Inhibitory effects of desflurane and sevoflurane on oxytocin-induced contractions of isolated pregnant human myometrium

BACKGROUND

In this study, we investigated the inhibitory effects of desflurane and sevoflurane on oxytocin-induced contractions of isolated human myometrium.

METHODS

Following delivery of the infant and placenta, a small segment of myometrium was excised from the upper incisional surface of the lower uterine segment and 20 strips, randomly assigned into two groups (n = 10), were obtained from 20 non-laboring term parturients. The study protocol consisted of a 60-min period of spontaneous contractions, control recording with oxytocin 2 x 10(9) m (10-min period), washout interval of 10 min, volatile administration (three times per 15-min period) of 0.5, 1 and 2 minimum alveolar concentration (MAC), response to oxytocin (10-min period), a further washout interval (10-min period) and subsequent control recording with oxytocin without anesthetics.

RESULTS

After oxytocin administration, the frequency and amplitude of contractions increased (P < 0.05) and the duration decreased (P < 0.05). The frequency and amplitude of contractions induced with oxytocin decreased significantly at 0.5, 1 and 2 MAC of desflurane and sevoflurane (P < 0.05). The amplitude of contractions was significantly different at 1 MAC between the two groups (P < 0.05). The duration of contractions at 2 MAC decreased in both groups (P < 0.05).

CONCLUSIONS

Desflurane and sevoflurane at 0.5, 1 and 2 MAC inhibit the frequency and amplitude of myometrial contractions induced with oxytocin in a dose-dependent manner. However, desflurane inhibits the amplitude less than sevoflurane at 1 MAC. We suggest that 0.5 MAC of both agents and 1 MAC of desflurane may be safely used in the presence of oxytocin following delivery of the infant and placenta during Cesarean section without fear of uterine atony and hemorrhage.

Bispectral Index Values at Sevoflurane Concentrations of 1% and 1.5% in Lower Segment Cesarean Delivery

Inadequate hypnosis in the absence of opioid analgesia may account for the increased incidence of awareness in cesarean delivery. An end-tidal concentration of 0.5 MAC isoflurane in 50% nitrous oxide (N(2)O) during cesarean delivery resulted in bispectral index (BIS) values >60, the threshold below which consciousness is unlikely. Our aim was to determine the BIS values achieved with the equivalent end-tidal concentration of sevoflurane and to determine if a larger concentration would consistently maintain BIS values <60. Twenty ASA physical status I-II parturients were randomized to receive an end-tidal concentration of either 1% sevoflurane or 1.5% sevoflurane delivered in 50% N(2)O throughout surgery. Thiopental 4 mg/kg was used for anesthetic induction. Morphine 0.1-0.15 mg/kg was administered only after delivery. Mean BIS values in the period between skin incision and neonatal delivery were 61 (95% confidence interval, 57-64) in the 1% sevoflurane group, versus 42 (95% confidence interval, 37-47) in the 1.5% sevoflurane group. BIS values were significantly different between groups at skin incision, uterine incision, delivery, and 10 min after delivery, but not thereafter. Indices of maternal and neonatal outcome were similar between groups.

IMPLICATIONS

Bispectral index (BIS) values <60 are consistent with a high probability of unconsciousness. An end-tidal concentration of 1.5% sevoflurane maintained BIS values <60 during cesarean delivery, whereas 1% did not. Adverse effects were not seen with the use of larger concentrations of sevoflurane.

Effects of obstetric analgesics and anesthetics on the neonate : a review

Most anesthetic and analgesic agents in current use traverse the placental barrier in varying degrees, but are well tolerated by the fetus if judiciously administered. For labor analgesia, many options are available. Systemic administration of opioids and sedatives is one such option. Repeated maternal administration of opioids such as pethidine (meperidine) results in significant fetal exposure and neonatal respiratory depression. Patient-controlled analgesia with synthetic opioids such as fentanyl, alfentanil, and the new ultra-short-acting remifentanil may be used for labor analgesia in selected patients. Other options for labor analgesia include epidural and combined spinal-epidural techniques. With such techniques, neonatal exposure to opioids and sedatives can be minimized or totally avoided. While limiting the fetal exposure to the harmful effects of depressant drugs, epidural anesthesia and/or analgesia improves placental perfusion and oxygenation of the fetus, which is beneficial, especially in conditions such as pregnancy-induced hypertension. Regional blocks are also administered for the majority of cesarean deliveries because of the overwhelming and unequivocal evidence of maternal and fetal safety compared with general anesthesia for this indication. However, in some instances, administration of general anesthesia is unavoidable. Neonatal respiratory depression with low Apgar scores, and umbilical arterial and venous pH associated with general anesthesia, is often transient. A properly administered anesthetic, whether regional or general, has no significant adverse fetal or neonatal effects.

Airway management on placental support (AMPS)--the anaesthetic perspective

Neonatal airway obstruction has been reported to have a high mortality. Antenatal diagnosis of this condition is now possible. Anaesthetic and surgical techniques have been developed that allow neonatal airway obstruction to be managed at delivery, while the fetus remains oxygenated via the placental circulation. Three case studies are presented, and the anaesthetic issues for mother and fetus/neonate are discussed with reference to previously published cases of airway management on placental support. In particular, techniques for uterine relaxation and maintenance of placental circulation are explored. The history of these procedures and issues of planning and logistics are also discussed.

The in-vitro effects of sevoflurane and desflurane on the contractility of pregnant human uterine muscle

The effect of desflurane and sevoflurane on the contractility of the uterus was examined in vitro on strips of human myometrium obtained at the time of elective cesarean section. Small strips (1 mm x 2 mm x 10 mm) of muscle were prepared and suspended in an organ bath containing oxygenated physiological saline. Force of contraction was recorded continuously using an isometric tension transducer. Following the onset of regular spontaneous contractions, baseline measurements were obtained and the strips were exposed to varying concentrations of sevoflurane or desflurane corresponding to 0.5, 1.0 and 1.5 minimum alveolar concentration (MAC). Sevoflurane depressed contractility to 72 +/- 18% of control at 0.5 MAC, 37 +/- 15% at 1.0 MAC and 27 +/- 16% at 1.5 MAC compared with 65 +/- 14 of control at 0.5 MAC, 43 +/- 18% at 1.0 MAC and 22 +/- 11% at 1.5 MAC for desflurane. The degree of depression of uterine muscle contractility produced by both these agents was significantly different from control at all concentrations. In conclusion, both sevoflurane and desflurane depress the contractility of isolated pregnant human myometrium at concentrations of 0.5, 1.0 and 1.5 MAC. These agents produce a similar degree of depression of uterine muscle contractility.

Pharmacological considerations during pregnancy

We present a brief overview of recent literature concerning some of the drugs used in pregnancy, labour and delivery. Obstetric anaesthesia continues to evolve through the reuse of old drugs such as magnesium sulphate or the manipulation of current drugs (e.g. propofol for emesis) in order to improve patient outcome. Pregnant women have traditionally been therapeutic orphans. The use of new agents such as levobupivacaine and ropivacaine in obstetric patients lags behind that of their non-pregnant counterparts. However, this gap is decreasing and these new drugs offer benefits to the parturient woman.

Effects of maternal anesthesia in the neonate

All commonly used anesthetic agents and drugs undergo placental transfer. Understanding the placental transfer of anesthetic drugs and their effects on the neonate is essential for optimal administration of both regional and general anesthesia. Regional anesthesia is decidedly safer for the mother and, when properly performed, actually may be beneficial to the stressed neonate. The healthy neonate also benefits from maternal analgesia during labor and delivery. General anesthesia may result in transient neonatal depression, particularly when delivery is of an emergency nature. The skill and knowledge of the anesthesiologist are more important than the type of anesthesia administered. Therefore, when properly performed, both regional and general anesthesia are quite safe in terms of neonatal outcome.

Desflurane: a new volatile anesthetic for cesarean section. Maternal and neonatal effects

Desflurane, a new volatile anesthetic agent with low blood/gas solubility, has recently been studied in clinical and animal trials but its use in obstetrics has not been adequately evaluated. This prospective study was undertaken to evaluate the maternal and neonatal effects of desflurane in obstetrical patients. Seventy-five healthy parturients undergoing primary or repeat cesarean section were randomly assigned to one of three groups of 25 each, end-tidal 3% desflurane, 6% desflurane or 0.6% enflurane, combined with 50% N2O and O2. All patients had rapid sequence induction of anesthesia with thiopentone sodium followed by succinylcholine for tracheal intubation. After delivery, anesthesia was maintained with reduced concentration of desflurane or enflurane with 67% N2O in O2, supplemented by butorphanol tartrate. Maternal hemodynamic parameters, blood loss and maternal awareness during surgery were monitored. Neonatal outcome was evaluated by Apgar scores, neurological and adaptive capacity scores (NACS), cord blood gas and acid-base status, and time to sustained respiration (TSR). Maternal blood loss did not differ significantly between the three groups and none of the patients developed intraoperative awareness. All three groups responded to psychomotor performance equally fast. Patients in all three groups developed transient hypertension and tachycardia during induction of anesthesia which returned to baseline values in approximately 5 min. Neonatal outcome was equally good in the three groups. More neonates in the 6% desflurane group had TSR > 90 s compared to the 3% desflurane group (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Use of sevoflurane during elective cesarean birth: a comparison with isoflurane and spinal anesthesia

This randomized study compared sevoflurane 1% and isoflurane 0.5% in terms of maternal and neonatal outcomes. In addition, neonatal outcome in both groups was compared with a cohort of patients delivered by cesarean birth using spinal anesthesia. Fifty-five patients presenting for elective cesarean birth under general anesthesia were randomly assigned to receive either sevoflurane 1% or isoflurane 0.5% in a 50% nitrous oxide and oxygen mixture for maintenance. Twenty patients requesting regional anesthesia received a subarachnoid block using 1.5 mL bupivacaine 0.75% in 8.25% dextrose with fentanyl 10 micrograms. Intraoperative hemodynamic variables and perioperative adverse events were recorded. Neonatal data included Apgar scores at 1 and 5 min, umbilical artery gas analysis, neurologic adaptive capacity scores (NACS) at 2 and 24 h, and a modified neonatal behavioral assessment scale (NBAS) at 24 h. Sevoflurane and isoflurane at equianesthetic concentrations (0.46 MAC-h [minimum alveolar anesthetic concentration hours]) were associated with similar blood pressure and heart rate changes during the operation. Blood loss, uterine tone, and perioperative complications were not problematic and were similar with the two drugs. No differences were seen in emergence times or in the time to being judged fit for discharge from the recovery room. Similarly, the level of postoperative comfort was the same in both groups. Comparing the general and the spinal anesthetic groups, no differences could be detected in neonatal outcome. Fluoride concentrations were modestly increased above preoperative levels in maternal and umbilical blood samples after sevoflurane administration.(ABSTRACT TRUNCATED AT 250 WORDS)