Labour analgesia by single shot spinal for any parturient?—A retrospective one‐year single centre audit

Single shot spinal (SSS) provides effective analgesia for multiparous parturients during advanced labour. Its utility in early labour or primiparous parturients may be limited by the insufficient duration of action. Regardless, SSS may offer a reasonable labour analgesia option in certain clinical scenarios. In this retrospective study, we analyse the failure rate of SSS analgesia by assessing pain after the SSS and by determining the need for additional analgesic interventions in primiparous or early‐stage multiparous parturients compared to multiparous parturients in advanced labour (cervix ≥6 cm).

(SSS) to be a reasonable option for labour pain when EDA/CSE is unavailable. SSS can provide satisfactory analgesia in both primi-and multiparous parturients, also in the early stage of labour. These findings are very interesting and should initiate prospective, randomised multicentre studies in order to better understand the true effect of SSS on labour analgesia.

| INTRODUCTION
Intrathecal analgesia provides a rapid and effective analgesia during labour. Side effects such as motor block, nausea, sedation and pruritus set restrictions to the dosage of these drugs. 1 The anticipated effective analgesic time is approximately 2-3 h with a safely usable combination of lipophilic opioid and local anaesthetic, 1-3 while effective times of less than 2 h have also been reported. 4 Single shot spinal analgesia (SSS) was used in 11% of all deliveries in Finland in 2021 and it is the most common labour analgesia method in some hospitals, such as Seinäjoki regional hospital (Seinäjoki, Finland), where it has been used for over 20 years, particularly for multiparous parturients whose labour is progressing well. 5,6 On a national level, the use of neuraxial labour analgesia has doubled over the past 20 years. 5 The use of single shot spinal analgesia has expanded outside its original intended target group, and it is used in both primiparous as well as multiparous parturients in an earlier stage of labour. Since the duration and outcome of labour are difficult to predict particularly in these parturient populations, the use of SSS analgesia without the possibility to extend the analgesia is questionable.
While SSS has been seen as a viable choice for resource-limited settings, 7-9 recent reports on global shortages of epidural supplies, such as loss-of-resistance syringes, may force delivery units into rationing the use of epidural analgesia. 10,11 In this context, a review of the utility of SSS analgesia in different parturient groups seems warranted.
In this retrospective audit, our aim is to compare the efficacy of a single shot spinal analgesia in primiparous and early-stage multiparous parturients with the later-stage multiparous parturients. The hypothesis for the audit is that the short duration of action of SSS is not sufficient in many of the primiparous or early-stage multiparous parturients as demonstrated by documented reports of pain after initially satisfactory SSS analgesia and subsequent analgesia-related interventions. The primary outcome measure is the incidence of documented pain during delivery after the SSS and the secondary outcome measure is the rate of subsequent analgesia-related peripheral or neuraxial labour analgesia interventions after the SSS analgesia.

| The parturients
Following institutional ethical board approval, a list of parturients that received SSS analgesia at the labour ward was retrieved from the hospital patient management system (Effica, Tieto-Evry OY, Espoo, Finland).
Thereafter all patient files were manually searched for details on the analgesic intervention, any potential neuraxial interventions before the SSS analgesia and particularly for any subsequent interventions either at the labour ward or in the operating room after the SSS was administered. Some parturients received more than one neuraxial analgesia procedure, in which case the first SSS was considered as the recorded analgesia and subsequent interventions as additional interventions.
The patient files were analysed for maternal weight, height, duration of pregnancy, cervical status at the time of SSS, midwife's assessment on the effect of analgesia after the SSS, any requests for subsequent analgesic interventions and potential completed analgesic interventions. The mode of delivery (vaginal or operative) and anaesthesia for any operation at the operating room was also noted. The analgesia was considered initially ineffective if there was documented pain or a request for subsequent analgesia within a 30-60-min window following the initial SSS. The duration of action of the SSS was considered insufficient if there was a note on pain by the midwife after an initially effective SSS, or requests for analgesic interventions at any point over a 60-min period following the SSS.

| The spinal analgesia intervention
The SSS analgesia routinely used in our hospital is carried out by a pencil point G27 needle, which is occasionally replaced by a G25 needle, if necessary. A combination of bupivacaine 2.5 mg and sufentanil 5 μg is given at the L2/L3 or L3/L4 interspace in either a sitting or lateral position in a total volume of 2 mL. The blood pressure is monitored every 5 min for 30 min after the intervention, along with continuous foetal heart-rate monitoring.

| Statistical analysis
The data was collected into SPSS version 25 software (IBM, Armonk, NY, USA) for analysis. The parturients were allocated into three different groups: primiparous parturients, multiparous parturients at cervical dilatation of below 6 cm, and multiparous parturients that had reached the cervical dilatation of 6 cm. Continuous variables such as age and BMI were analysed by one-way ANOVA for intergroup differences and dichotomous variables were analysed by Fisher exact test against the advanced labour multiparous group. The unadjusted odds ratios were calculated for labour analgesia outcomes.
The use of SSS analgesia was known to be about three times more common in multiparous parturients compared to primiparous parturients. Based on the prior study 6 from the same hospital, the incidence of additional analgesic interventions was anticipated to be in the range of 3%. This audit was powered to detect an increase of additional analgesic interventions to 12%, which was considered clinically significant and was calculated to require 77 primiparous and 233 multiparous parturients. While the exact proportion of welladvancing multiparous parturients (cervix ≥6 cm) was not known it was deemed to include approximately twice the number of multiparous parturients required to ensure sufficient statistical power to detect the potential difference between the groups.  Table 1

| The outcome of SSS labour analgesia
The initial success rate of SSS analgesia was 96.6% without any differences between the studied groups. However, based on the notes made by the midwives, the duration was more likely to be considered insufficient in both primiparous parturients ( Primiparous parturients were also more likely to receive subsequent peripheral analgesic interventions (pudendal and paracervical blocks), while early-stage multiparous parturients were more likely to receive either new neuraxial or peripheral analgesic interventions. The outcome of labour SSS analgesia in the three groups is shown in Figure 1 and Table 2. A total of 76 (14.2%) of the 535 parturients were subjected to more neuraxial interventions than one single shot spinal. There were four (0.7%) cases of documented headache of which two received an epidural blood patch. In two cases of headache, there was an attempt to place an epidural prior to SSS, and one of these parturients received an epidural blood patch. One case with headache that did not require a blood patch was noted after two SSS, and one epidural blood patch was placed due to headache after a single uneventful SSS during labour.

| DISCUSSION
The single shot spinal (SSS) analgesia has been used at the Seinäjoki regional hospital for over 20 years. It was initially intended for multiparous parturients in advanced labour. 6 Ease of application and high efficacy has led to the expansion of its use to other parturient populations, including primiparous parturients and earlier-stage multiparous parturients. Despite promising reports on the use of SSS also in primiparous parturients, 8,9,12 these parturients along with earlier-stage multiparous parturients can be more challenging to manage with the SSS technique due to its limited duration of action. Therefore, we sought to investigate the outcome of SSS analgesia in these groups compared to the originally intended target group, multiparous parturients whose labour is progressing well.
In our study, we used both subjective clinical documentation and clinical interventions to assess the adequacy of analgesia provided by the SSS analgesia across the different subgroups. The notes by midwives on the efficacy of the analgesia provide a subjective assessment of the efficacy. Based on these notes, the SSS analgesia works initially equally well in all groups of parturients ( Figure 1). However, due to the limited duration of action, both early-stage multiparous parturients and primiparous parturients experience pain that often requires subsequent interventions ( Table 2). These interventions provide a means of T A B L E 1 Parturient baseline characteristics for the different groups receiving spinal analgesia for labour pain-primiparous parturients and multiparous parturients at cervical status below 6 cm or at equal or greater than 6 cm, respectively. Numbers show overall spinal analgesia use and the rate of combined spinal epidural (CSE) analgesia and single shot spinal use in the respective groups. p-values calculated by one-way ANOVA for age and body mass index (BMI), whereas Fischer exact test was used for the CSE use rate in the groups. assessing the duration of the initial SSS analgesia even though their use may be affected by the availability of the different interventions. Even with this limitation, the use of subsequent analgesic interventions reveals the increased risk of insufficient duration of action.
In a prior study, the SSS was used in 39.9% of deliveries in multiparous parturients in our hospital, 6 and its use remains at approximately the same level (42.9%) in the multiparous parturients in our study population. The cervical dilatation was 5.0 ± 0.9 cm in the prior study and did not show a correlation between insufficient duration of analgesia and the cervical dilatation status prior to SSS analgesia. 6 In our multiparous parturients, the cervical dilation state was 6.6 ± 1.7 cm suggesting that the multiparous population overall was in a more advanced stage of labour than the parturients in the prior study. Similarly, the cervix status in the primiparous parturients was at 7.1 ± 2.1 cm ( p < .01 compared to multiparous parturients). This suggests that SSS was generally used in a rather advanced phase of the labour, and therefore, its limited duration of action was not regarded as a great concern.
The SSS produced initially sufficient analgesia in 96-97% of the parturients across all groups in our study (Figure 1), which is higher than the previously published rate of 90% of parturients with initially sufficient analgesia. 6 The prior prospective study may have been more sensitive to detect insufficient analgesia as the efficacy of analgesia was assessed by real-time questioning. In addition, the prior study used a combination of bupivacaine (2.5 mg) and fentanyl (0.025 mg) in a total volume of 1.5 mL, whereas the interventions in this study were done with the same bupivacaine dose and sufentanil (5 μg) in a volume of two millilitres, making it possible that the higher volume of the spinal anaesthetic solution resulted in better spread and a higher initial success rate of the SSS. A similar initial success rate has been published for bupivacaine and sufentanil (7.5 μg) in a volume of 2 mL, 12 while the effect of 5 μg has been shown to be equivalent in terms of time and analgesic efficacy to 7.5 μg. 4 The relative potency difference between sufentanil and fentanyl has been suggested to be 4.4, thus making the 0.025 mg fentanyl dose at least as effective as the 5 μg sufentanil dose. 13 Furthermore, a 10% initial failure rate has been described with various sufentanil doses when given with a 2.5 mg bupivacaine dose in a volume of 1 mL. 4 Therefore, it is highly unlikely that the change of opioid from fentanyl to sufentanil alone could explain the better initial success rate.
Regardless of the better initial success rate of SSS analgesia, the limited duration remains a problem. In the study by Viitanen  Spinal sufentanil has been suggested to result in a longer duration of action as spinal labour analgesia, which would be particularly beneficial when a SSS analgesia is used. 1,3,13 Despite this change in the spinal anaesthetic mixture, a limited duration of action is seen in our contemporary population across all subpopulations in our study, with a marked increase from the prior study even in the well-advanced multiparous parturients. 6 The SSS analgesia used in our hospital has a mean duration of action of 109 ± 7 min until the contraction pain reaches 5 on the 0-10 NRS scale. 3 The national rate of neuraxial labour analgesia has been constantly increasing in Finland, reaching 75% in 2017, 5 which may reflect the attitudes of both parturients and healthcare professionals towards better treatment of labour pain, resulting in a need to reassess our current practices of widespread use of SSS analgesia. The significant increase in the proportion of even advanced-stage multiparous parturients considered by the midwife to experience pain following an initially effective SSS analgesia raises questions about the usability of SSS to treat labour pain in the contemporary times. SSS has been suggested to be a good option to use in resource-limited settings where equipment and staff may not be available for more demanding neuraxial analgesia interventions. [7][8][9] However, according to the Finnish national birth registry, it was used for 11% of all deliveries in 2021. 5 Even if SSS can be seen as a viable choice for analgesia in cases where the delivery is imminent, 12 its use in most primiparous parturients and in the early stages of delivery in multiparous parturients is clearly associated with an increased risk for the insufficient duration of analgesia, resulting in recurrent pain and subsequent analgesia interventions.
The parturients in our study received a wide range of subsequent analgesic interventions ( Figure 1 and Table 2). The rate of subsequent neuraxial analgesia (SSS or epidural) administration is somewhat alarming as such interventions took place in 12.5% of the primiparous parturients and 14.5% of the early-stage multiparous parturients compared to 7.6% in the later-stage multiparous parturients. Although the documented incidence of suspected post-dural puncture headache (PDPH) was very low (<1%) in our material, any new neuraxial analgesia intervention carries with it increased risks for unwanted adverse effects, such as post-dural puncture headache 14 and complications associated with it. 15 Actions to reduce recurrent neuraxial analgesic interventions should be taken with a view to reducing risks for complications, with the added benefit of a lower workload for the anaesthetic team both during and after the delivery.
Finally, the risk for operative delivery is higher in primiparous parturients compared to multiparous parturients, particularly those whose labour is progressing well. 16,17 The use of catheter-based analgesia methods, such as epidural or CSE analgesia, would facilitate topping up of the labour analgesia to provide safe and effective anaesthesia for most peripartum operative needs. 18 This is a retrospective study and therefore it has some limitations, including potential underreporting of either initial pain after the SSS intervention or recurrent pain after the effect of SSS has worn off.
Therefore, we used a dual detection system including both notes from the midwife and the number of actual subsequent analgesia interventions. Both suggest that in modern times, SSS analgesia does not always meet the expectations of the parturients and the labour room staff. The T A B L E 2 Comparison of the labour analgesia outcome in primiparous parturients and early-stage (cervix (CX) at below 6 cm) multiparous parturients with the advanced-stage multiparous parturients (cervix at or above 6 cm). If the spinal analgesia was noted as having insufficient effect at 30-60 min after administration it was considered initially ineffective, whereas pain following initially effective analgesia was regarded as insufficient duration. The rate of use of subsequent single shot spinal (SSS) analgesia and epidural analgesia is shown along with the rate of peripheral blocks (PDB, pudendal nerve block; PCB, paracervical nerve block). Data shows the number of parturients that received the intervention or condition in question. Some parturients received more than one intervention. p values show Fisher exact test value for intergroup comparison and OR the unadjusted odds ratio compared to multiparous parturients with a minimum cervical dilatation of 6 cm. rate of subsequent neuraxial analgesia interventions has increased from the previously reported 0.5% 6 to 7.6% even in the advanced-stage multiparous parturients and some parturients ended up receiving repeated (up to three) subsequent SSS doses. It should be noted that this data was collected in a delivery hospital with a widespread use of SSS analgesia and therefore both the staff and the local parturient population are expected to be used to SSS analgesia. Also, the incidence of post-dural puncture headache (PDPH) may be underreported in our retrospective chart review as some of the PDPH cases may have become symptomatic only after discharge from the hospital.
Subjective maternal experience on both provision and efficacy of the neuraxial analgesia is often overlooked or neglected in obstetric analgesia studies 19 and these factors are not possible to address in a retrospective study. It must be noted that SSS is often a relatively fast and easy intervention to complete for the anaesthesiologist but also for the parturient experiencing severe pain. Therefore, the maternal perception of both the analgesia administration and the time course of its effect should be addressed in a future prospective study where SSS should be compared against epidural labour analgesia and potential side effects such as PDPH should be actively followed for some time also after discharge from the hospital.
In conclusion, SSS remains a reasonable option in certain clinical scenarios and provides labour analgesia of limited duration for any parturient. However, a proportion of the parturients (7.6% of the later-stage multiparous, 14.5% of the early-stage multiparous and 12.5% of the primiparous) may need additional analgesia, which could be associated with increased risks of adverse effects and complications from these additional interventions or procedures in addition to causing an increased work burden for the staff caring for the parturient.

ACKNOWLEDGEMENT
The work was supported by the authors' home clinics and completed without outside funding. The authors have no conflicts of interest.

AUTHOR CONTRIBUTIONS
Kati Kähkönen: Planning of the study, collection of the data, writing of the manuscript, read the final version of the manuscript. Antti Väänänen: Planning of the study, data validation, statistical analysis, writing of the manuscript, read the final version of the manuscript.

DATA AVAILABILITY STATEMENT
Individual participant data points that underlie the results (figures, tables and text) reported in this article may be shared in deidentified form based on the provision of methodologically sound proposal addressed to the corresponding author.