Adequacy of Maternal Anesthesia Depth With Two Sodium Thiopental Doses in Elective Caesarean Section

A Randomized Clinical Trial

Golnar Sabetian; Farid Zand; Fatemeh Mirhadi; Mohammad Reza Hadavi; Elham Asadpour; Laleh Dehghanpisheh; Zeinabsadat Fattahi Saravi; Seyed Mostajab Razavi


BMC Anesthesiol. 2021;21(201) 

In This Article

Abstract and Introduction


Background: Administration of an optimal dose of anesthetic agent to ensure adequate depth of hypnosis with the lowest risk of adverse effects to the fetus is highly important in cesarean section. Sodium thiopental (STP) is still the first choice for induction of anesthesia in some countries for this obstetric surgery. We aimed to compare two doses of STP with regarding the depth of anesthesia and the condition of newborn infants.

Methods: In this clinical trial, parturient undergoing elective Caesarian section were randomized into two groups receiving either low-dose (5 mg/kg) or high-dose (7 mg/kg) STP. Muscle relaxation was provided with succinylcholine 2 mg/kg and anesthesia was maintained with O2/N2O and sevoflurane. The depth of anesthesia was evaluated using isolated forearm technique (IFT) and bispectral index (BIS) in various phases. Additionally, infants were assessed using Apgar score and neurobehavioral test.

Results: Forty parturient were evaluated in each group. BIS was significantly lower in high-dose group at skin incision to delivery and subcutaneous and skin closure. Also, significant differences were noticed in IFT over induction to incision and incision to delivery. Apgar score was significantly lower in high-dose group at 1 min after delivery. Newborn infants in low-dose group had significantly better outcomes in all three domains of the neurobehavioral test.

Conclusion: 7 mg/kg STP is superior to 5 mg/kg in creating deeper hypnosis for mothers. However, it negatively impacts Apgar score and neurobehavioral test of neonates. STP seems to has dropped behind as an acceptable anesthetic in Cesarean section.

Trial registration: IRCT No: 2016082819470 N45, 13/03/2019.


Determining the optimal dosage of anesthetic agents is challenging. This fact is particularly a matter of concern in Caesarean section.[1,2] The susceptible fetus can be affected by the administered agents passing through the placenta, resulting in the delivery of anesthetized "sleepy baby".[3] Robust study on appropriate drug regimens to guarantee adequate depth of anesthesia during Caesarean section is surprisingly rare. This may be due to paucity of use of general anesthesia for Caesarean section and its application only in emergency situations when conducting randomized trials is extremely difficult.

Sodium thiopental (STP), a short-acting well known barbiturate, is currently a routine choices for induction of general anesthesia in Cesarean section in some countries.[4] The usual recommended dose of thiopental for induction of general anesthesia for Caesarean section is 4–5 mg/kg, but several studies showed that parturient are at risk of inadequate anesthesia.[5] The incidence of unexpected awareness during Caesarean has been decreased to 0.26–0.4% by using modification of induction technique and larger dose of thiopental, but it is still more prevalent than in general surgical population (0.1–0.2%).[6,7] Obstetric general anesthesia includes many risk factors for accidental awareness during general Anesthesia (AAGA) including use of STP for anesthesia, rapid sequence induction, deep neuromuscular block, obesity, difficult airway management, and emergency surgery.[8] Thiopental in combination with rapid sequence induction is an important risk factor for awareness, possibly because of inappropriate low dose.[8]

The bispectral index (BIS) is a sensitive objective tool which analyses the patient's electroencephalogram (EEG) and represents a 0 (silence) to 100 (complete wakefulness) scale. Values ranging from 40 to 60 indicate appropriate hypnosis for surgery.[9–11] However the isolated forearm technique (IFT) has been proposed as the gold standard test for detecting wakefulness during Caesarean section.[12] It is based on isolation of the forearm from the effects of neuromuscular blocking drug by occlusion of the circulation by a pneumatic tourniquet inflated before injection of neuromuscular blocking agent. Movement of the hand in response to a recorded command played to the patient is then monitored.[12,13] Nevertheless, it has been reported that lower than previously recommended values for BIS are needed to avoid IFT test responses during laryngoscopy, intubation and skin incision.[14] Some investigators have reported that despite a median BIS of less than 70 (range of 42–68) on all parts of general anesthesia in Caesarean section, hemodynamic parameters increased significantly in some patients especially during laryngoscopy and intubation, where routine dose of 4–5 mg/kg thiopental dose was used.[5]

Although thiopental dose of 5–7 mg/kg has been described safe for induction of anesthesia in Caesarean section,[4,15] the dosage of medication should be adjusted so that the mother can benefit from satisfactory anesthesia, while the safety of the fetus in provided as well. We designed this randomized clinical trial to compare the effects of higher versus lower doses of STP on the depth of anesthesia with IFT and BIS (primary outcome) in the parturient and its side effects measured by Apgar score and neurobehavioral test (secondary outcomes) in the newborns immediately after delivery.