Decreased thiopental requirements in early pregnancy

Anatomical and physiological alterations of pregnancy

The extensive metabolic demands of pregnancy require specific physiological and anatomical changes. These changes affect almost all organ systems, including the cardiovascular, respiratory, renal, gastrointestinal, and hematologic system. The placenta adds another layer of complexity. These changes make it challenging for clinicians to understand presenting signs and symptoms, or to interpret laboratory and radiological tests. Furthermore, these physiological alterations can affect the pharmacokinetics and pharmacodynamics of drugs. Drug safety in lactation is only supported by limited evidence. In addition, the teratogenic effects of medications are often extrapolated from animals, which further adds uncertainties. Unfortunately, pregnant women are only rarely included in clinical drug trials, while doses, regimens, and side effects are often extrapolated from studies conducted in non-pregnant populations. In this comprehensive review, we present the changes occurring in each system with its effects on the pharmacokinetic variables. Understanding these physiological changes throughout normal pregnancy helps clinicians to optimize the health of pregnant women and their fetuses. Furthermore, the information on pregnancy-related physiology is also critical to guide study design in this vulnerable 'orphan' population, and provides a framework to explore pregnancy-related pathophysiology such as pre-eclampsia.

Dose Comparison of Dexmedetomidine Sedation following Spinal Anesthesia: Parturient versus Nonpregnant Women-A Randomized Trial

Background

This study was designed to investigate and compare the effective doses of dexmedetomidine for sedation in parturient patients who underwent Cesarean section (CS) and nonpregnant women who underwent elective gynecologic surgery.

Methods

The study comprised 60 females aged between 25 and 35. They were divided into two groups. The parturient group received a bolus dose of dexmedetomidine over 15 min after the delivery of the fetus and placenta. In the nonpregnant women group, a bolus of dexmedetomidine was administered intravenously upon the completion of spinal anesthesia. The subsequent dose required by patients in each group was then determined through a modified two-stage Dixon up-and-down sequential method. Probit analysis was used to calculate the ED50 and the ED95 of dexmedetomidine for adequate sedation.

Results

The ED50 of dexmedetomidine for adequate sedation in parturient patients was 1.58 μg/kg (1.51–1.66 μg/kg); in nonpregnant women, it was 0.96 μg/kg (0.91–1.01 μg/kg) (95% CI). The ED95 of dexmedetomidine in parturients was 1.80 μg/kg (1.70–2.16) μg/kg and that of nonpregnant women was 1.10 μg/kg (1.04–1.30 μg/kg) (95% CI). The ED50 in parturients was significantly higher than that in nonpregnant women (P < 0.05).

Conclusion

The ED50 of dexmedetomidine for target sedation in parturients who received spinal anesthesia for CS is greater than 1.5 times that in nonpregnant women who received spinal anesthesia for lower abdominal gynecologic surgery. This study postulates that the dose of dexmedetomidine required to achieve optimal sedation following spinal anesthesia is much higher in parturients than in nonpregnant women undergoing gynecologic surgeries. This trial is registered with NCT02111421.

Effect of pre-exposure to sevoflurane on the bispectral index in women undergoing Caesarean delivery under general anaesthesia

BACKGROUND

Patients undergoing Caesarean delivery under inhalation anaesthesia are at a high risk of awareness, especially in the period before delivery. We assessed the effects of pre-exposure to sevoflurane on the bispectral index (BIS) in the interval before delivery.

METHODS

Sixty-four patients undergoing elective Caesarean delivery were randomly assigned to receive 1.0-1.1 vol% (control 1) or 1.2-1.3 vol% (control 2) end-tidal sevoflurane, or the same concentrations of end-tidal sevoflurane combined with pre-exposure to 1 vol% sevoflurane for the last 1 min of the preoxygenation period (the preSevo 1 and preSevo 2 groups, respectively). We assessed BIS values, arterial pressure, and heart rate at the time of induction; before intubation; and upon skin incision, uterine incision, and delivery. We also determined the maternal incidence of intraoperative awareness and the neonatal Apgar scores, and conducted umbilical blood gas analysis.

RESULTS

At skin incision, BIS values were significantly lower in the preSevo 1 group than in the control 1 group [50 (13) vs 72 (8), P<0.001] and in the preSevo 2 group than in the control 2 group [44 (11) vs 67 (10), P<0.001]. The mean BIS values in the preSevo 1 and 2 groups were maintained below 60 in the period before delivery. No other parameter differed among groups, and no patient exhibited intraoperative awareness.

CONCLUSIONS

Pre-exposure to low concentrations of sevoflurane reduced BIS values in the interval before delivery, suggesting that this approach may reduce the risk of maternal awareness. Clinical Research Information Service (code KCT0000069, http://cris.cdc.go.kr).

Fetal endoscopic surgery: indications and anaesthetic management

Fetal intervention for certain life-threatening conditions has progressed from being primarily experimental in nature to the standard of care in certain circumstances. While surgical techniques have advanced over the past few years, the anaesthetic goals for these interventions have remained the same; namely, minimizing maternal and fetal risk as well as maximizing the chances of a successful fetal intervention and optimize the conditions necessary to carry the fetus to term gestation. Fetal endoscopic techniques allow access to the fetus without the need for a hysterotomy incision, thus improving the chances of controlled post-operative tocolysis and term gestation after fetal intervention. This procedure, however, is not without associated risks to both fetus and mother. This chapter will address the fetal diseases that may benefit from fetoscopic intervention, the rationale behind why maternal and fetal anaesthesia is required, the various anaesthetics used for these cases and specific considerations of both maternal and fetal physiology that aid in the determination of the best anaesthetic technique for individual cases. Methods of intra-operative fetal monitoring and fetal resuscitation will also be discussed.

Anesthesia for nonobstetric surgery in the pregnant patient

Each year over 75,000 pregnant women in the United States undergo nonobstetric surgery. The operations include those directly related to pregnancy, such as cerclage, those indirectly related to pregnancy, such as ovarian cystectomy, and those unrelated to gestation, such as appendectomy. When a pregnant woman presents for surgery, it is a stressful event for everyone involved. Issues about the surgical problem itself often seem secondary to maternal (and physician) concerns about the effect of surgery and anesthesia on the developing fetus, or the potential to trigger preterm labor. This article reviews the physiologic and anatomic changes that affect anesthetic care during pregnancy. The author also reviews the effects of anesthetic drugs and perioperative events on the fetus and on the pregnancy outcome. The relatively small number of published series are reviewed as well as the controversial recommendations regarding fetal and maternal monitoring during surgery.

Bispectral index in assessment of adequacy of general anaesthesia for lower segment caesarean section

Awareness among parturients during general anaesthesia for caesarean section, though now uncommon, remains a concern for obstetric anaesthetists. We examined the adequacy of our general anaesthetic technique for avoiding explicit awareness by determining the depth of anaesthesia using Bispectral Index (BIS) monitoring. Twenty ASA1 parturients having general anaesthesia for lower segment caesarean section were studied. The drugs and doses used for each anaesthetic were similar Intraoperative Bispectral Index, haemodynamic parameters, end-tidal isoflurane concentration and inspired nitrous oxide fraction were measured and the postoperative incidence of explicit awareness was assessed. All anaesthetists were blinded to the Bispectral Index value throughout the operation. The depth of anaesthesia at various stages of the operation was evaluated by recording the Bispectral Index. Patients were interviewed for any intraoperative recall or awareness at the end of operation. A median BIS of 70 or below was recorded on most occasions during surgery. The range was 52 to 70, with values reaching 60 and below at intubation, uterine incision and delivery. Haemodynamic stability was satisfactory and there was no case of uterine atony, fetal compromise or postpartum haemorrhage. No patient experienced intraoperative dreams, recall or awareness. Our current general anaesthetic technique appeared inadequate to reliably produce BIS values of less than 60 that are associated with a low risk of awareness. However, no patients experienced explicit awareness.

Early pregnancy does not reduce the C(50) of propofol for loss of consciousness

Requirements for inhaled anesthetics decrease during pregnancy. There are no published data, however, regarding propofol requirements in these patients. Because propofol is often used for induction of general anesthesia when surgery is necessary in early pregnancy, we investigated whether early pregnancy reduces the requirement of propofol for loss of consciousness using a computer-assisted target-controlled infusion (TCI). Propofol was administered using TCI to provide stable concentrations and to allow equilibration between blood and effect-site (central compartment) concentrations. Randomly selected target concentrations of propofol (1.5-4.5 microg/mL) were administered to both pregnant women (n = 36) who were scheduled for pregnancy termination and nonpregnant women (n = 36) who were scheduled for elective orthopedic or otorhinolaryngologic surgery. The median gestation of the pregnant women was 8 wk (range, 6-12 wk). Venous blood samples for analysis of the serum propofol concentration were taken at 3 min and 8 min after equilibration of the propofol concentration. After a 10-min equilibration period of the predetermined propofol blood concentration, a verbal command to open their eyes was given to the patients twice, accompanied by rubbing of their shoulders. Serum propofol concentrations at which 50% of the patients did not respond to verbal commands (C(50) for loss of consciousness) were determined by logistic regression. There was no significant difference in C(50) +/- SE of propofol for loss of consciousness between the Nonpregnant (2.1 +/- 0.2 microg/mL) and Pregnant (2.0 +/- 0.2 microg/mL) groups. These results indicate that early pregnancy does not decrease the concentration of propofol required for loss of consciousness.

IMPLICATIONS

The C(50) of propofol for loss of consciousness in early pregnancy did not differ from that in nonpregnant women, indicating that there is no need to decrease the propofol concentration for loss of consciousness when inducing general anesthesia for termination of pregnancy.

Epidural anaesthesia for caesarean delivery in triple and quadruple pregnancies

BACKGROUND

Mechanical and/or hormonal factors may increase the spread of epidural anaesthesia in pregnancy, and hormonal changes are more pronounced in high-order pregnancies. However, no previous study has evaluated the dose requirements and haemodynamic effects of epidural anaesthesia for caesarean delivery in this latter situation.

METHODS

The anaesthetic requirements to obtain a T4 upper sensory level were retrospectively compared in triple (n = 19) or quadruple (n = 2) pregnancies to 31 singleton pregnancies who received epidural anaesthesia for elective caesarean delivery using 2% lidocaine with 1/200,000 adrenaline.

RESULTS

In high-order pregnancies, the gestational age at delivery was lower than in singleton pregnancies (34.9 +/- 1.9 weeks vs 38.2 +/- 1.1 weeks; P = 0.0001) whereas maternal body weight (76.5 +/- 8.7 kg vs 73.4 +/- 14.8 kg; NS) and lidocaine requirements (428 +/- 95 mg vs 426 +/- 98 mg; NS) were similar. Moreover, although the overall incidence of hypotension was not different (multiple pregnancy; 65% vs 58% in singletons), ephedrine (5.4 +/- 5.3 mg vs 10.7 +/- 13.8 mg; P < 0.05) and additional fluid requirements during onset of the block (4.3 +/- 1.7 mL/kg vs 5.3 +/- 2.6 mL/kg; P = 0.03) were less than in singletons.

CONCLUSION

We found surprisingly similar anaesthetic requirements for epidural anaesthesia in high-order and singleton pregnancies. Mechanical factors may have played an important role. Moreover, the need for ephedrine and fluids was less in high-order pregnancies. This could be related to more pronounced physiological changes or to different physician attitudes.