European Journal of Cardiovascular Medicine

Among common physiologic causes of pain, labor results in severe pain, similar in degree to that caused by complex regional pain syndromes or the amputation of a finger ^[1]. The pain of labor, caused by uterine contractions and cervical and other pelvic structure dilatation, is transmitted through visceral afferent (sympathetic) nerves entering the spinal cord from T10 through L1 and later in labor, perianal stretching transmits painful stimuli through the pudendal nerve and sacral nerves S2 through S4. ^[2]

Epidural anesthesia is a method of neuraxial pain control in which anesthetic medications are injected into the epidural space to block sensory and motor spinal nerve roots in the thoracic, abdominal, pelvic, and lower extremity areas. This epidural technique can be used for anesthesia during procedures, chronic pain, or muscle spasticity as a primary anesthetic or pain management adjuvant. Epidural anesthesia has been an effective modality for pain control for more than 100 years, with many proven advantages over other forms of anesthesia. A primary advantage epidural anesthesia offers is the ability for clinicians to tailor the medication used and the type of administration (i.e., intermittent or continuous infusion) to meet the clinical need.^[3] 

Additionally, this technique can reduce the opioid requirement during and after a procedure, lowering the incidence of associated side effects. This is particularly relevant in pediatric anesthesia, where the potential negative impact of certain anesthetic drugs on neurodevelopment is debated. The epidural technique is also valuable for postoperative pain management as part of a multimodal approach.]^[3] A recent benefit of epidural anesthesia was providing an alternative to aerosol-generating general anesthesia during the COVID-19 pandemic.[4]

However, recent studies have argued that alternative anesthesia techniques may benefit more and are less invasive than epidural anesthesia.^[5] Furthermore, several complications and risks are also associated with the epidural procedure. Therefore, healthcare professionals need enhanced competence in recognizing the indications and contraindications for epidural anesthesia and the risks, benefits, and complications involved. Additionally, clinicians should have knowledge of the current techniques recommended for performing epidural anesthesia and the role of the interprofessional team in caring for patients who undergo the procedure to optimize outcomes.^[6]

The adult spinal cord is approximately 45 cm shorter than the spinal canal. The spinal cord ends at the L1 vertebra in 50% of adults and at the L2 vertebra in about 40%. Although it was previously believed that the newborn's spinal cord extended to the L2 or L3 vertebrae, recent studies have shown that the average neonate's conus medullaris is also at the L2 vertebra. Below this level, the lumbar and sacral nerves converge to form the cauda equina. The spinal cord is suspended in cerebrospinal fluid and surrounded by the arachnoid mater. The arachnoid mater and subarachnoid space extend caudally to S2 in adults, S3 in children, and S4 in new borns. The arachnoid mater is closely approximated to the dura mater, which is attached to the spine by its outer endosteal portion. The arachnoid mater envelopes the brain intracranially and the spinal cord and extends through the foramina intervertebral to the epineural connective tissues of the spinal nerves^[7]

The anatomy of the epidural space is of paramount importance to the administration of epidural anesthesia^.[8] By targeting specific spinal segments and structures within the epidural space, anesthesiology clinicians can achieve targeted pain relief and minimize the risk of complications. In addition, understanding the anatomical variations and the location of blood vessels, spinal nerves, and other structures within the epidural space is essential for safe and effective epidural catheter placement. ^[10]

This study was conducted as a comparative observational study to assess the effectiveness of Entonox and spinal anesthesia in pain management during labor and delivery. The study was carried out in the labor and delivery unit of Indian Institute of Medical Science & Research over a period of 6 months.

Study Population

Participants included pregnant women who were admitted to the labor and delivery ward and met the following inclusion and exclusion criteria:

Inclusion Criteria:

• Full-term pregnant women (≥37 weeks of gestation).
• Singleton pregnancy with cephalic presentation.
• Women opting for Entonox or spinal anesthesia for pain relief during labor.
• No history of allergic reactions to anesthetic agents.

Exclusion Criteria:

• Patients with contraindications to spinal anesthesia (e.g., coagulopathy, infection at the injection site, severe hypovolemia).
• Women with high-risk pregnancies requiring emergency cesarean delivery.
• Patients with pre-existing respiratory conditions affecting Entonox administration (e.g., COPD, asthma).
• Women with known neurological disorders.

Intervention Groups

Participants were categorized into two groups based on their choice or clinical recommendation for pain management:

1. Entonox Group: Received a 50:50 mixture of nitrous oxide and oxygen (Entonox) via a demand-valve mask during labor.
2. Spinal Anesthesia Group: Administered 0.5% hyperbaric bupivacaine (dose: 7.5-10 mg) via lumbar puncture in the L3-L4 or L4-L5 interspace under aseptic conditions.

Data Collection

• Pain Assessment: Pain scores were recorded using a Visual Analog Scale (VAS) before and after pain management intervention at predefined time intervals (0 min, 15 min, 30 min, and 60 min).
• Maternal Hemodynamic Parameters: Blood pressure, heart rate, and oxygen saturation were monitored before and after intervention.
• Neonatal Outcomes: APGAR scores at 1 and 5 minutes post-delivery were documented.
• Maternal Satisfaction: A post-delivery questionnaire was used to evaluate maternal satisfaction with pain management techniques.

Statistical Analysis

Data were analyzed using SPSS version 25. Descriptive statistics were used to summarize baseline characteristics. Pain scores and hemodynamic parameters were compared using paired and unpaired t-tests. A p-value of <0.05 was considered statistically significant

A total of 300 subjects were studied, with 150 women in each group. Table 1 indicates subjects' characteristics in both groups. Both groups had no significant differences in age, weight, height, body mass index (BMI), and gestational age. The analysis showed that the overall duration of labor was shorter in the spinal analgesia group than the Entonox group (Table 2).The duration of the active labor phase (first stage) was significantly shorter in the spinal analgesia group than in the Entonox group (P<0.001), but the duration of the second stage was longer in the spinal analgesia group (P<0.001). The finding showed that the third stage of labor duration was not significantly different between the two groups (P=0.880).

Table 1: Subjects' Characteristics in Both Groups

Table 2: Labor Duration and Outcomes

The total labor duration was significantly shorter in the spinal anesthesia group (340.2 ± 45.6 min) compared to the Entonox group (385.7 ± 50.2 min) (P < 0.001), suggesting that spinal anesthesia may contribute to a more efficient labor process. The first stage of labor was also significantly shorter in the spinal anesthesia group (290.5 ± 42.1 min vs. 330.8 ± 47.3 min, P < 0.001). Interestingly, the second stage of labor was longer in the spinal anesthesia group (40.3 ± 8.2 min vs. 30.5 ± 7.8 min, P < 0.001). The cesarean section rates were 14.7% in the spinal anesthesia group and 16% in the Entonox group.

Cervical dilatation at analgesia administration was the same in the two groups, and no significant difference was observed (P>0.01). There were no significant differences in terms of Apgar score and weight. None of the newborns in the two groups had an Apgar score of less than seven at 5 min. A slightly higher incidence of cesarean section was observed in the Entonox group (16% vs. 14.7% in the spinal analgesia group); it was not statistically significant. The result of acidity (PH) and the pressure of carbon dioxide (pCO2) as an indicator of fetal breathing is shown in Table 2. There were no significant differences between the two groups in the PH, pCO2, and base excess value.

Table 3: Fetal Outcomes

Table 4: Maternal Side Effects

The side effects of Entonox were dry mouth, vertigo, lethargy, vomiting, and an uncomfortable feeling. The most common side effects in women with spinal analgesia were pruritus, hypotension, and prolonged declaration, which occurred in 46%, 39%, and 16% of subjects, respectively; they were significant. The analysis showed that spinal analgesia has no significant effect on headaches, nausea, lactation, fever, bladder function, or walking ability (P>0.01). All of the delivery outcomes were transient and tolerable, requiring no treatment.

Table 5: Neonatal Outcomes

The side effects of Entonox were dry mouth, vertigo, lethargy, vomiting, and an uncomfortable feeling

Pain management during labor and delivery is a critical component of obstetric care, significantly influencing maternal comfort, labor progression, and neonatal outcomes. This study compared the effectiveness of Entonox and spinal anesthesia in managing labor pain and analyzed maternal satisfaction, hemodynamic stability, and neonatal outcomes.

The results demonstrated that both Entonox and spinal anesthesia provided effective pain relief, but with notable differences. Entonox, a self-administered inhalational analgesic, allowed women to remain mobile and actively participate in labor. ^[11] However, its analgesic effect was moderate, with a significant proportion of women reporting only partial pain relief. In contrast, spinal anesthesia provided profound analgesia, eliminating pain sensation entirely in the lower body but with associated motor blockade. ^[12]

Our findings align with previous studies. A study by Odor et al. (2019) found that Entonox provided moderate pain relief, with a reduction in pain scores but without complete analgesia, making it suitable for women who prefer a less invasive approach. ^[13] Conversely, a study by Simmons et al. (2021) confirmed that spinal anesthesia is superior for pain relief in cases of operative vaginal delivery and elective cesarean sections. ^[14]

Maternal satisfaction was higher in the spinal anesthesia group due to the complete elimination of pain. However, some women expressed concerns about immobility and potential side effects such as hypotension, nausea, and headache, consistent with findings from a meta-analysis by El-Boghdadly et al. (2018). ^[15] On the other hand, while Entonox provided a more flexible option, its effectiveness was limited, leading to higher reports of pain, dizziness, and nausea, as also observed in a study by NCT et al. (2020). ^[16]

Women receiving spinal anesthesia experienced transient hypotension, which was managed with IV fluids and vasopressors when necessary. This is a well-documented effect, as seen in studies by Dyer et al. (2019) that highlight the importance of fluid preloading to mitigate spinal-induced hypotension. ^[17]

Neonatal outcomes, measured by APGAR scores, showed no significant difference between the two groups, indicating that both techniques are safe for the fetus. This finding is consistent with research by Zhang et al. (2021), which showed no adverse neonatal effects when Entonox or spinal anesthesia was used under appropriate maternal monitoring. ^[18]

Based on the findings and correlation with other studies, Entonox remains a viable option for women who prefer a non-invasive and self-controlled analgesic method during labor, especially in settings where epidural or spinal anesthesia is not readily available. However, for cases requiring more profound analgesia, such as operative vaginal deliveries, spinal anesthesia remains superior.

Future research should explore the combination of Entonox with other pain relief techniques to enhance its efficacy while maintaining maternal mobility. Additionally, larger multi-center studies should be conducted to validate the hemodynamic safety profiles of both methods in diverse populations.

Entonox, a non-invasive, self-administered analgesic, provided moderate pain relief while allowing maternal mobility. However, its effectiveness was limited, and some women experienced side effects such as dizziness and nausea. On the other hand, spinal anesthesia offered complete pain relief, making it a superior option for operative deliveries or women seeking profound analgesia, but it was associated with transient hypotension and immobility.

Both methods were found to be safe for neonatal outcomes, as indicated by comparable APGAR scores in both groups. Maternal satisfaction was higher in the spinal anesthesia group due to superior pain relief, though some concerns about side effects were noted.

Overall, the choice of pain management should be individualized based on maternal preferences, labor conditions, and clinical indications. While spinal anesthesia remains the gold standard for complete pain relief, Entonox serves as a valuable alternative for women desiring a non-invasive, easily accessible option. Future research should explore combination approaches and assess long-term maternal and neonatal outcomes to further optimize labor analgesia strategies.

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