202501041450

Status:

Tags: Obstetrics

Intra-op pain during CS

Documented rates for ‘inadequate’ neuraxial anaesthesia vary widely depending on the definition used, ranging from <5% to as high as 24%

Breakthrough pain may occur despite an apparently adequate block

Pain during CS can have devastating consequences, including ↑ risk of

OAA information site:

Pain during CS seems to occur more with extension of labour EA compared with de novo SA

Risk factors

Key risk factors for breakthrough pain include

Risk factor Spinal anaesthesia Epidural conversion Comments
Patient-related factors
Substance use disorder X X In a prospective observational study using multivariate regression analysis, substance use disorder was associated with a higher risk of intraoperative pain during CS (aOR 4.77, 95% CI 1.72–13.21).
Low BMI X In a retrospective study using multivariate regression analysis, low BMI was found to be the third most important predictor for requiring an alternate anaesthetic (aOR 0.94, 95% CI 0.90–0.98). The proposed mechanism suggested is larger subarachnoid spaces because of reduced intra-abdominal pressure, which may potentially increase the risk of spinal anaesthesia failure.
High BMI X In a prospective observational study, higher weight before pregnancy (P = 0.019), weight at the end of pregnancy (P = 0.003) and BMI at the end of pregnancy (P = 0.0004) were identified as risk factors for failure, defined as the need to convert to GA at any time during CS, when converting labour epidural analgesia to epidural anaesthesia for CS. A possible explanation is that women with higher BMI have been found to have a more complicated and prolonged surgery.
Taller height X In a meta-analysis of observational studies, taller maternal height was associated with increased need to convert to GA for CS after converting labour epidural analgesia (weighted mean difference in height 0.893 cm higher, 95% CI 0.018–1.767 cm).
Young age X A meta-analysis found that younger maternal age was associated with increased need to convert to GA for CS after existing labour epidural analgesia (weighted mean difference in age −1.571 yrs lower in the failure group, 95% CI −2.166 to −0.975)
Surgical factors
Degree of urgency CS X X In a prospective audit of neuraxial anaesthesia for CS, Class I CS was associated with a higher risk of preoperative failure (conversion to another anaesthetic or failure to achieve a satisfactory block) aOR 2.45 (95% CI 1.36–4.40)
Bilateral tubal ligation X A concomitant tubal ligation was identified as the second most important predictor of failed spinal anaesthesia requiring an alternate anaesthetic technique for CS in a retrospective study, with an OR of 8.23 (95% CI 3.12–19.20) on multivariate analysis. Failure of spinal anaesthesia was defined as the need to provide an alternative anaesthetic, such as a repeat spinal, a new epidural or CSE, or conversion to GA, within 1 h of the initial spinal
Longer duration of surgery X X The duration of time from incision to wound closure was the only significant predictor of intraoperative pain during CS under spinal or combined spinal–epidural anaesthesia in a prospective observational study, with an aOR 1.04 (95% CI 1.01–1.06), after controlling for patient height, intrathecal bupivacaine dose and time of day of the procedure. Other studies have also shown that prolonged surgery increased the risk of spinal anaesthesia failure
Preterm delivery X In a retrospective cohort study, earlier gestational age was found to be a significant predictor of failed spinal anaesthesia requiring alternative anaesthetic technique such as a repeat spinal, a new epidural or CSE, or conversion to GA, within 1 h of the initial spinal (aOR 0.91 per week, ranking 8th out of 12 predictors).
Another study has also shown that preterm parturients show higher rates of spinal anaesthesia failure. A possible explanation is that a smaller fetus causes less aortocaval compression, potentially expanding epidural and subarachnoid spaces
Anaesthesia-related factors
Non-obstetric anaesthetist X According to two retrospective studies included in a meta-analysis, the epidural conversion failure rate for nonspecialist anaesthetists was 7.2% compared with 1.6% for obstetric anaesthetists (OR 4.6; 95% CI 1.8–11.5), where failure was defined as the need to provide an alternative anaesthetic such as GA
High VAS scores in 2 h before CS X One prospective observational trial reported that a higher mean visual analogue scale score for pain in the 2 h before CS was associated with an increased risk of failed epidural anaesthesia requiring conversion to GA at any time after surgery commenced (aOR 4.39, 95% CI 1.6–12.2)
More than two epidural top-ups X In a systematic review and meta-analysis of observational studies, an increased number of clinician-administered top-ups during labour was associated with a three-fold higher risk of failed conversion of epidural analgesia to anaesthesia for CS (OR 3.2, 95% CI 1.8–5.5)

Prevention

Optimal prevention of intraoperative pain during CS centres on three key principles—

Preop education / counselling

build rapport
effective communication
expectation management

Optimising neuraxial anaesthesia

One study found the ED95 of intrathecal hyperbaric bupivacaine to be 11.5 mg

use of a prophylactic infusion of phenylephrine may ↑ ED95 by ∼20%

Pregnancy-induced increased intraabdominal pressure leads to epidural venous engorgement and reduced lumbar CSF volume, decreasing the required intrathecal local anaesthetic dose.
phenylephrine infusion may counteract this effect by constricting epidural veins and restoring lumbar CSF volume, thus ↑ necessary intrathecal dosage

supplementation with preservative-free fentanyl decreased the need for intraoperative supplemental analgesia by 82%

Surgical duration → d/w obs

For conversion of labour EA, the most important factor is identifying those epidural catheters at high risk of failure.
Studies have reiterated the fact that persistent high pain scores during labour despite an indwelling catheter, or multiple top-ups, may suggest a poorly functioning catheter

both alkalinised lidocaine combined with adrenaline (epinephrine) and fentanyl, and chloroprocaine provide fast onset times
chloroprocaine was shown to be associated with more intraoperative pain

addition of epidural fentanyl decreased onset times but did not decrease need for intraoperative supplementation.

Testing the block

controversial topic

Although the innervation of the uterus from T10–L1 and S2–S4 suggests that a low thoracic sensory level should suffice, the involvement of visceral organs sending afferent impulses to T4–L2 necessitates a higher thoracic block

Other challenges in the assessment of adequate sensory block include

In addition to testing sensory levels, testing motor blockade is also considered mandatory and it is recommended to test sensory level only after some motor weakness is evident

The ability to straight leg raise indicates inadequate anaesthesia, regardless of the extent of sensory loss

Complete S1 motor block (plantar flexion) is typical with spinal but not epidural anaesthesia. Normal ankle function during epidural anaesthesia may suggest insufficient sacral anaesthesia, risking intraoperative pain

The timing and frequency of block assessment should be performed in a way to alleviate anxiety and increase patient confidence

Management

The surgical team must be informed, and the surgery should be paused if possible, to address the issue

In the presence of an EA catheter, the anaesthetist should reassess the block and consider giving top-ups with fast-acting local anaesthetics such as alkalinised lidocaine containing adrenaline, or chloroprocaine, to improve the block and alleviate the patient's pain

If pain occurs early, especially before delivery, and extending the block or performing another neuraxial technique is not possible, switching to GA should be considered.
If the patient declines, fast-acting opioids (fentanyl 25–50 μg, alfentanil 250–500 μg) or ketamine (10 mg boluses) should be used

Pain should not be treated with sedatives or anxiolytics

In cases where the surgery continues under neuraxial anaesthesia, minimising surgical stimuli is crucial, and uterine exteriorisation should be avoided

Limited data exist regarding other analgesic options including the intraperitoneal instillation of local anaesthetics (e.g. 2-chloroprocaine 3%) for reducing intraoperative pain after delivery

It is crucial to acknowledge the patient's pain promptly and discuss the option of GA. If pain remains unrelieved, even before delivery, timely conversion to GA is recommended

Events, treatments and responses should be thoroughly documented

Guidelines

The Obstetric Anaesthetists’ Association recommends that the upper and lower limit of the sensory block and motor block should be tested, that complaints of pain should be acknowledged and managed with IV supplementation of opioids that have rapid onset including fentanyl(25-50µg) or remifentanil with low-dose ketamine (10mg).

Follow up

Follow up is crucial for women who experience pain and distress during CS under neuraxial anaesthesia to minimise the development of long-term psychological sequelae

During the postpartum period, follow-up screening for signs of post-traumatic stress should be conducted, with a senior anaesthetist visiting the patient. An explanation for the intraoperative pain should be provided, and any questions or concerns should be addressed fully

References

Prevention and Management of Intraoperative Pain During Caesarean Section - BJA Ed