A BIS-guided study of sevoflurane requirements for adequate depth of anaesthesia in Caesarean section

The use of processed electroencephalography (pEEG) in obstetric anaesthesia: a narrative review

Accidental awareness under general anaesthesia (AAGA) remains a major complication of anaesthesia. The incidence of AAGA during obstetric anaesthesia is high relative to other specialities. The use of processed electroencephalography (pEEG) in the form of "depth of anaesthesia" monitoring has been shown to reduce the incidence of AAGA in the non-obstetric population. The evidence for using pEEG to prevent AAGA in the obstetric population is poor and requires further exploration. Furthermore, pregnancy and disease states affecting the central nervous system, such as pre-eclampsia, may alter the interpretation of pEEG waveforms although this has not been fully characterised. National guidelines exist for pEEG monitoring with total intravenous anaesthesia and for "high-risk" cases regardless of technique, including the obstetric population. However, none of the currently available guidelines relates specifically to obstetric anaesthesia. Using pEEG monitoring for obstetric anaesthesia may also provide additional benefits beyond a reduction in risk of AAGA. These potential benefits include reduced postoperative nausea and vomiting, reduced anaesthetic agent use, a shorter post-anaesthetic recovery stay. In addition, pEEG acts as a surrogate marker of cerebral perfusion, and thus as an additional monitor for impending cardiovascular collapse, as seen in amniotic fluid embolism. The subtle physiological and pathological changes in EEG activity that may occur during pregnancy are an unexplored research area in the context of anaesthetic pEEG monitors. We believe that the direction of clinical practice is moving towards greater use of pEEG monitoring and individualisation of anaesthesia.

Awareness and Aortocaval Obstruction in Obstetric Anesthesia

Awareness during general anesthesia for cesarean delivery continues to be a major problem. The key to preventing awareness is strict attention to anesthetic technique. The prevalence and implications of aortocaval compression have been firmly established. Compression of the vena cava is a real occurrence when assuming the supine position. Relief of this compression most likely does not occur until the patient is turned 30°, which is not feasible for performing cesarean delivery. Although it is still wise to tilt the patient, the benefit of this tilt may not be as great as once thought.

Pre-delivery remifentanil infusion for placenta accreta cesarean delivery under general anesthesia: an observational study

OBJECTIVE

General anesthesia may be required for placenta accreta cesarean delivery. Intrauterine fetal anesthetic exposure should be minimized to avoid neonatal respiratory depression; opioids are often delayed until post-delivery.

METHODS

In this observational study, we compared neonatal outcome using pre-delivery remifentanil versus post-delivery (deferred) opioids for placenta accreta cesarean delivery. Choice of anesthesia was discretionary. The primary outcome was Apgar score at 5 min comparing women who received pre-delivery remifentanil versus deferred opioid administration. We recorded maternal/obstetric characteristics, surgical characteristics, maternal hemodynamic data, neonatal outcomes: Apgar scores, umbilical vein pH and respiratory interventions at birth.

RESULTS

Between February 2007 and April 2014 we identified 40 general anesthesia placenta accreta cesarean deliveries. The remifentanil dose rate ranged from 0.06 to 0.46 mcg kg(-1 )min(-1). Obstetric and maternal characteristics were similar. Neonatal Apgar, umbilical pH and respiratory intervention outcomes were similar in both groups; Apgar scores median (interquartile range IQR [range]) at 5 min were 9 (8-10) for pre-delivery remifentanil versus 9 (9-10) for deferred opioid administration, p = 0.18.

CONCLUSIONS

We did not observe a significant effect on neonatal Apgar scores at 1 and 5 min, or respiratory interventions at birth when remifentanil infusion was administered pre-delivery.

Neonatal effect of remifentanil in general anaesthesia for caesarean section: a randomized trial

Background

Remifentanil has been suggested for its short duration of action to replace standard opioids for induction of general anaesthesia in caesarean section. While the stabilizing effect of remifentanil on maternal circulation has been confirmed, its effect on postnatal adaptation remains unclear, as currently published studies are not powered sufficiently to detect any clinical effect of remifentanil on the newborn.

Methods

Using a double-blinded randomized design, a total of 151 parturients undergoing caesarean delivery under general anaesthesia were randomized into two groups – 76 patients received a bolus of remifentanil prior to induction, while 75 patients were assigned to the control group. Remifentanil 1 μg/kg was administered 30 seconds before the standard induction of general anaesthesia. The primary outcome measure was an assessment of neonatal adaptation using the Apgar score, while secondary outcomes included the need for respiratory support after delivery and differences in umbilical blood gas analysis (Astrup).

Results

The incidence of lower Apgar scores between 0 and 7 was significantly higher in the remifentanil group at one minute (25% vs. 9.3% of newborns, p = 0.017); whilst at five minutes and later no Apgar score differences were observed. There was no difference in the need for moderate (nasal CPAP) or intensive (intubation) respiratory support, but significantly more neonates in the remifentanil group required tactile stimulation for breathing support (21% vs. 7% of newborns, p = 0.017). There was no difference in the parameters from umbilical cord blood gas analysis between the groups.

Conclusion

At a dose of 1 μg/kg, remifentanil prior to induction of general anaesthesia increases the risk of neonatal respiratory depression during first minutes after caesarean delivery but duration of clinical symptoms is short.

Trial registration

ClinicalTrials.gov: NCT01550640.

Awareness and apgar score in elective Cesarean section under general anesthesia with propofol or Isoflurane: A prospective, randomized, double-blinded clinical trial study

Background:

Awareness is a postoperative recall of events experienced under general anesthesia. In this study, we compared the incidence of awareness between two routine methods used, inhalation (Isoflurane) and intravenous protocol (Propofol), in elective Cesarean section, and also evaluated the effect of these two different methods on the apgar score of newborns.

Materials and Methods:

In this prospective, clinical trial study, 90 pregnant women candidates for elective Cesarean section were randomly enrolled, after taking written consent. Induction of anesthesia in both groups was provided by propofol and succinylcholine in the same manner, and maintenance of anesthesia in Group 1 was provided by propofol 100 μg/kg/minute and in Group 2 with isoflurane 1 MAC, to maintain the bispectral index (BIS) between 45 and 60. Blood pressure, heart rate, electrocardiography (ECG), and also Etco2 and o2sat were recorded throughout the surgery and finally analyzed and compared.

Results:

From 90 patients, four cases of confirmed awareness were found in the propofol group and three cases in the Isoflurane group (8/9% vs. 6/7%), but the apgar scores were comparable between the two groups. Meanwhile there were no significant differences between the two groups in basic information, neonatal apgar scores, hemodynamic changes, and BIS, Electromyography (EMG), and signal quality index (SQI) values.

Conclusion:

According to the patient's state, diagnosis of the anesthesiologist, and other criteria like price and its availability, we could use these drugs in general anesthesia during Cesarean section, although it is recommended that more studies be done to compare the effect of these two drugs in larger groups.

Management of posterior reversible syndrome in preeclamptic women

Posterior reversible encephalopathy syndrome (PRES) is a neurological syndrome associated with a number of conditions including preeclampsia. It is characterized by seizures, alteration of consciousness, visual disturbances, and symmetric white matter abnormalities, typically in the posterior parietooccipital regions of the cerebral hemispheres, at computed tomography (CT) and magnetic resonance (MRI). We report three new cases of PRES in preeclamptic patients and describe the management of these patients. We present a brief review of other cases in the literature, with particular attention to the anesthetic management.

Pulse perfusion value predicts eye opening after sevoflurane anaesthesia: an explorative study

The variables measured in modern pulse oximetry apparatuses include a graphical pulse curve and a specified perfusion value (PV) that could be a sensitive marker for detecting differences in sympathetic activity. We hypothesized that there is a correlation between a reduction of PV and the time to eye opening after general anaesthesia. The objective was to investigate whether PV can predict eye opening after sevoflurane anaesthesia. Prospective, explorative clinical study included 20 patients, ASA physical status 1 or 2, at Skåne University Hospital, Lund, Sweden, from November 2012 to January 2013 scheduled for elective breast tumour surgery. A general anaesthesia was delivered with inhalation of oxygen, nitrous oxide and sevoflurane anaesthesia to a depth of 1.2 minimal alveolar concentration. Sevoflurane inspiratory and expiratory concentrations were measured. Bispectral index monitoring, PV as measured by pulse oximeter, heart rate and carbon dioxide were registered at before anaesthesia, 15 min after induction (at 1.2 minimal alveolar concentration), at end of surgery and at eye opening at the end of anaesthesia. PV values were lower before anaesthesia and at eye opening compared to at 15 min after induction and at end of surgery (P < 0.05). The reduction of PV between end of surgery and eye opening was 0.76. We conclude that the pulse oximeter PV could be a useful variable to assess the timing of recovery, in terms of eye opening after a general anaesthesia.

Effect of decreased fetal perfusion on placental clearance of volatile anesthetics in a dual perfused human placental cotyledon model

Placental transfer of volatile anesthetics is a critical issue in managing fetal distress during cesarean section under general anesthesia. Using dual perfused human placental cotyledons obtained from parturients undergoing elective cesarean section (n = 5), we investigated the effect of decreased fetal perfusion on placental clearance of sevoflurane and isoflurane. Keeping the maternal flow rate fixed, fetal flow rate was consecutively decreased from 3 ml/min (control perfusion) to 2 ml/min (intermediate perfusion) and to 1 ml/min (hypoperfusion). Placental transfer was assessed by the clearance of anesthetics by the placenta, defined by the ratio of anesthetic concentration in fetal vein and maternal artery, multiplied by fetal flow rate. Placental clearance was compared between different fetal perfusion states and anesthetics. Hypoperfusion resulted in a lower clearance of sevoflurane and isoflurane compared with control (P = 0.002, P < 0.001) and intermediate (P = 0.04, P = 0.018) perfusion. Clearances of sevoflurane and isoflurane were comparable during control perfusion (P = 0.93), intermediate perfusion (P = 1.00), and hypoperfusion (P = 0.88). Thus, maintenance of volatile anesthetics at a marginally low concentration may not be necessary when fetal distress is observed during emergency cesarean delivery because placental transfer of volatile anesthetics decreases with decreasing fetal perfusion.

Bispectral index and cerebral oximetry in low-flow and high-flow rate anaesthesia during laparoscopic cholecystectomy - a randomized controlled trial

Introduction

The need to reduce pollution emissions in the operating room and to reduce treatment costs motivates more frequent use of general anaesthesia with a small or minimal fresh gas flow rate. Nevertheless, the reduction of the delivery of fresh gases should not influence the quality and safety of the anaesthesia.

Material and methods

A total of 105 elective laparoscopic cholecystectomy patients were included in the study. There were 72 female (68.6%) and 33 male (31.4%) patients. Patients were randomized by a ‘closed envelope’ method into two groups. Group I included patients with low-flow anaesthesia and group II included patients with high-flow anaesthesia. In all patients the cerebral oximetry was measured separately for each cerebral hemisphere; the bispectral index (BIS), heart rate, blood pressure, end-tidal carbon dioxide concentration and haemoglobin oxygen saturation were monitored.

Results

Heart rate, blood pressure, end-tidal carbon dioxide concentration and saturation were similar in both groups and the differences between them were statistically insignificant. The BIS values were similar in both groups and indicated that patients who underwent low-flow anaesthesia were not exposed to a higher risk of awakening during the procedure than the high-flow anaesthesia patients. The changes in brain oximetry values were similar in both low-flow and high-flow anaesthesia.

Conclusions

Use of both low-flow and high-flow rate general anaesthesia provided patients undergoing laparoscopic cholecystectomy proper oxygenation of the central nervous system, adequate sleep depth and haemodynamic stability.

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).

Role of potassium and calcium channels in sevoflurane-mediated vasodilation in the foeto-placental circulation

Background

Sevoflurane has been demonstrated to vasodilate the foeto-placental vasculature. We aimed to determine the contribution of modulation of potassium and calcium channel function to the vasodilatory effect of sevoflurane in isolated human chorionic plate arterial rings.

Methods

Quadruplicate ex vivo human chorionic plate arterial rings were used in all studies. Series 1 and 2 examined the role of the K⁺ channel in sevoflurane-mediated vasodilation. Separate experiments examined whether tetraethylammonium, which blocks large conductance calcium activated K⁺ (K_Ca++) channels (Series 1A+B) or glibenclamide, which blocks the ATP sensitive K⁺ (K_ATP) channel (Series 2), modulated sevoflurane-mediated vasodilation. Series 3 – 5 examined the role of the Ca⁺⁺ channel in sevoflurane induced vasodilation. Separate experiments examined whether verapamil, which blocks the sarcolemmal voltage-operated Ca⁺⁺ channel (Series 3), SK&F 96365 an inhibitor of sarcolemmal voltage-independent Ca⁺⁺ channels (Series 4A+B), or ryanodine an inhibitor of the sarcoplasmic reticulum Ca⁺⁺ channel (Series 5A+B), modulated sevoflurane-mediated vasodilation.

Results

Sevoflurane produced dose dependent vasodilatation of chorionic plate arterial rings in all studies. Prior blockade of the K_Ca++ and K_ATP channels augmented the vasodilator effects of sevoflurane. Furthermore, exposure of rings to sevoflurane in advance of TEA occluded the effects of TEA. Taken together, these findings suggest that sevoflurane blocks K⁺ channels. Blockade of the voltage-operated Ca⁺⁺channels inhibited the vasodilator effects of sevoflurane. In contrast, blockade of the voltage-independent and sarcoplasmic reticulum Ca⁺⁺channels did not alter sevoflurane vasodilation.

Conclusion

Sevoflurane appears to block chorionic arterial K_Ca++ and K_ATP channels. Sevoflurane also blocks voltage-operated calcium channels, and exerts a net vasodilatory effect in the in vitro foeto-placental circulation.

The effects of midazolam on the bispectral index after fetal expulsion in caesarean section under general anaesthesia with sevoflurane

The effects of midazolam used with low concentration inhaled anaesthetics on the bispectral index (BIS) was investigated after fetal expulsion during caesarean section. Forty-five patients undergoing caesarean section received either normal saline (control, n = 15), or an intravenous bolus of 0.03 mg/kg (n = 15) or 0.05 mg/kg (n = 15) midazolam. Changes in BIS and maternal haemodynamics were monitored before induction, on intubation, at uterine incision, on delivery, at 3, 5 and 10 min after fetal expulsion, at subcutaneous tissue closure, at skin closure, on eye opening and at extubation. BIS values in the group that received 0.05 mg/kg midazolam were significantly lower than in the other two groups at 3, 5 and 10 min after fetal expulsion, and at subcutaneous tissue closure and skin closure. Values of BIS < 60 could only be maintained with 0.05 mg/kg midazolam and there was no delay in maternal emergence or recovery.

Sevoflurane and the feto-placental vasculature: the role of nitric oxide and vasoactive eicosanoids

BACKGROUND

The effects and mechanisms of action of volatile anesthetics on the feto-placental vasculature are not known. We aimed to quantify the vasoactive effects of sevoflurane and determine the role of nitric oxide (NO) and of vasoactive eicosanoids in mediating these effects in isolated human chorionic plate arterial rings.

METHODS

Quadruplicate ex vivo human chorionic plate arterial rings were used in all studies. Series 1 quantified the vasodilation produced by sevoflurane in rings preconstricted with the thromboxane analog U46619. Series 2A-C examined the role of NO in sevoflurane-mediated vasodilation. In separate experiments, we examined the potential for the nonspecific NO inhibitors, L-NAME, L-nMMA, and the inactive D-NAME, to modulate the vasodilation produced by sevoflurane. Series 2D determined whether sevoflurane altered vascular smooth muscle sensitivity to exogenous NO. Series 3A-D examined the role of vasoactive eicosanoids in sevoflurane-mediated vasodilation. In separate experimental series, we examined whether the nonspecific cyclooxygenase inhibitor, indomethacin, or the 5-lipoxygenase inhibitor, nordihydroguaiaretic acid, modulated sevoflurane-mediated vasodilation.

RESULTS

Sevoflurane produced dose-dependent vasodilation of preconstricted chorionic plate arterial rings, with mean ring vasodilation increasing from 15 +/- 7% at 2% sevoflurane to 67 +/- 17% (mean +/- sd) at 8% sevoflurane. Blockade of NO synthase did not attenuate the vasodilator effects of sevoflurane. Sevoflurane did not alter smooth muscle sensitivity to NO. Indomethacin augmented sevoflurane vasodilation at 10(-5) M, but not at 10(-6) M. Conversely, nordihydroguaiaretic acid attenuated sevoflurane-mediated vasodilation at 3 x 10(-6) M but not at 3 x 10(-7) M.

CONCLUSIONS

Sevoflurane was a vasodilator in the feto-placental vasculature in this in vitro model. Sevoflurane-mediated vasodilation is NO and cyclooxygenase-independent and appears to be mediated in part via a lipoxygenase generated vasodilator eicosanoid.

Using EEG to monitor anesthesia drug effects during surgery

The use of processed electroencephalography (EEG) using a simple frontal lead system has been made available for assessing the impact of anesthetic medications during surgery. This review discusses the basic principles behind these devices. The foundations of anesthesia monitoring rest on the observations of Guedel with ether that the depth of anesthesia relates to the cortical, brainstem and spinal effects of the anesthetic agents. Anesthesiologists strive to have a patient who is immobile, is unconscious, is hemodynamically stable and who has no intraoperative awareness or recall. These anesthetic management principles apply today, despite the absence of ether from the available anesthetic medications. The use of the EEG as a supplement to the usual monitoring techniques rests on the observation that anesthetic medications all alter the synaptic function which produces the EEG. Frontal EEG can be viewed as a surrogate for the drug effects on the entire central nervous system (CNS). Using mathematical processing techniques, commercial EEG devices create an index usually between 0 and 100 to characterize this drug effect. Critical aspects of memory formation occur in the frontal lobes making EEG monitoring in this area a possible method to assess risk of recall. Integration of processed EEG monitoring into anesthetic management is evolving and its ability to characterize all of the anesthetic effects on the CNS (in particular awareness and recall) and improve decision making is under study.

Emergency Caesarean section: best practice*

Good multidisciplinary communication is crucial to the safe management of women requiring non-elective Caesarean section. Anaesthetists should participate actively in resuscitation of the fetus in utero; relief of aortocaval compression is paramount. Epidural top-up with levobupivacaine 0.5% is the anaesthetic of choice for women who have been receiving labour epidural analgesia. If epidural top-up fails to provide bilateral light touch anaesthesia from S5 - T5, a combined spinal-epidural technique with small intrathecal dose of local anaesthetic is a useful approach. Pre-eclampsia is not a contra-indication to single-shot spinal anaesthesia, which is the technique of choice for most women presenting for Caesarean section without an epidural catheter in situ. Induction and maintenance doses of drugs for general anaesthesia should not be reduced in the belief that the baby will be harmed. Early postoperative observations are geared towards the detection of overt or covert haemorrhage.

The Effects of Isoflurane and Desflurane Titrated to a Bispectral Index of 60 on the Cortical Somatosensory Evoked Potential During Pediatric Scoliosis Surgery

In this study, we compared the effect of isoflurane and desflurane on the posterior tibial somatosensory evoked potential recorded by scalp electrodes during correction of idiopathic scoliosis in pediatric patients. Depth of sedation was controlled by maintaining bispectral index (BIS) at 60 throughout the study. Comparison of patients breathing desflurane and isoflurane showed an evoked cortical amplitude (N37-P45) of 0.53 +/- 0.3 microV versus 1.3 +/- 0.8 microV (P = 0.014), respectively. In addition to this comparison, a crossover design was included whereby the desflurane or isoflurane received in the first part of the study was changed to the other anesthetic. Substituting one anesthetic for another confirmed our initial finding that the cortical evoked amplitude is greater with isoflurane than with desflurane. No differential effect was found between desflurane and isoflurane on the evoked subcortical (N31-P34) amplitude or the P37 latency.