Neuraxial techniques have long been established as the anesthetic techniques of choice for cesarean section because with their application, risks inherent in the use of general anesthesia, such as failed intubation, regurgitation, aspiration of gastric contents, and untoward awareness are avoided. However, on some occasions neuraxial techniques may fail, leading to maternal discomfort and pain. This could lead to the development of adverse psychological sequelae and even to medicolegal claims against obstetric anaesthetists.
Risk factors for failure of neuraxial anesthesia for cesarean section
There is no consensus as to what constitutes failure of neuraxial anesthesia. ‘Failure’ might either be complete (accompanied by total lack of sensorimotor block) or partial (manifested as unilateral block or inadequate block height). The need for intraoperative supplementation by additional analgesics or the need for conversion to general anesthesia is also a manifestation of failure of neuraxial anesthesia. Therefore, failure might be evident preoperatively (as inability to achieve a satisfactory block) or intraoperatively, as pain experienced intraoperatively by the parturient and as a request on her behalf for analgesic supplementation. Risk factors associated with preoperative failure include high BMI, operative urgency (associated with acute fetal distress or maternal medical condition) and being a primiparous parturient. Risk factors for intraoperative failure include allowing the cesarean section to start in spite of an inadequate block as well as increased duration of surgery. Spinal anesthesia is thought to require lower intraoperative supplementation than epidural anesthesia and is associated with lower failure rates. Additionally, the use of spinal opioids in the context of spinal anesthesia is associated with less intraoperative failure. When labor epidural analgesia is converted to anesthesia for caesarean section, there are some well identified risk factors for failed conversion such as the urgency of cesarean section, the provision of anesthetic care by a non-obstetric anaesthetist and the need for an increased number of administered boluses for management of labor pain. In specific, obstetric anaesthetists in contrast to non-obstetric anaesthetists are more likely to manage labor epidurals more proactively, ensuring well-functioning catheters. This is because they are more likely to manipulate or replace suboptimal epidural catheters while non-obstetric anaesthetists are less likely to manipulate the epidural catheter or opt for alternative techniques if conversion fails. Also, frequent epidural boluses due to breakthrough pain throughout labor suggest a poorly functioning epidural catheter, which is more likely to fail if used for epidural conversion. Finally, the urgency of the cesarean section is a risk factor for epidural conversion failure, as there is not much time to wait for a satisfactory and well-established block. Conversely, the need for a lower epidural top up volume and the use of adrenaline in the local anesthetic mixture is associated with less intraoperative failure when a labor epidural is converted for cesarean section. Among the measures undertaken to prevent pain during cesarean section, the most important is to ensure the presence of an adequate block, of appropriate height and density.
Block assessment before cesarean section
Since the innervation of the uterus comes from sympathetic nerves originating from the inferior hypogastric plexus (T10-L1) and parasympathetic nerve fibers originate from pelvic splanchnic nerves (S2-S4), one would assume that the level required for the skin incision for the cesarean section is the one corresponding to the T10 dermatome. However, a block height to lower thoracic levels is not sufficient for cesarean section and this should reach much higher thoracic dermatomes, since several visceral organs send afferent impulses to higher levels of the thoracic spinal cord (up to T4). However, there is a lack of consensus as to how to perform an objective assessment of the neuraxial block before cesarean section and how this should be tested as various surveys have revealed inconsistency in practice and a lack of standardized approach as to methods of testing the neuraxial block. There is also considerable variation in the sensory block considered adequate among clinicians as well as whether the block should be tested from blocked to unblocked areas or the other way around. Additionally, there is a lack of consensus about the stimulus that should be used to test the height of the block with some using loss of cold sensation, some others using loss of sharp pin prick sensation and lastly some using loss to touch sensation. This is reflected in the various sensory modalities used to assess the block height such as ethyl chloride (cold), calibrated Neuropen (sharp), cotton wool (light touch) etc. There is also an inconsistent relation between cold, sharp pinprick and touch sensation, meaning that one cannot be safely predicted by assessing the other. To compound things more, anaesthetists are not always able to correlate anatomical landmarks with the correct dermatome. There is evidence however by surveys of anesthetic practice worldwide that loss of cold sensation to T4 (or alternatively to light touch) is the most common practice for testing the sensory block and thus reaching this level is required to minimize the risk of pain during cesarean section. Additionally, the required height of the block is no different if a spinal or an epidural is used. When checking the sensory level of the block, additional recommendations are to test the also the lower level apart from the higher level and to allow sufficient time for the woman to respond when moving along dermatomes, especially when there are language barriers. Additionally, a dense bilateral motor block of the lower limbs is necessary to prevent pain during cesarean section and most textbooks suggest using the straight leg raise test since if the parturient can straight leg raise, the block will most likely not be adequate and pain can be experienced even if there is a high sensory block. On the other hand, the inability to lift the legs against gravity does not provide information about the density of the block in the mid to upper thoracic segments. Therefore, a combined approach of testing both sensory and motor components of the block is required. It has also been suggested to wait for some evidence of motor block before testing the sensory block for the first time and to start the sensory testing on the side where there is a denser block as evidenced by more motor block. This will help the parturient appreciate differences in a more accurate way as the block ascends. As to autonomic block assessment, most clinicians agree that it can be a useful adjunct to sensory and motor testing to confirm the quality of the block. It is evidenced by the presence of warm dry feet and can be confirmed by feeling the temperature of the underside of the toes. Since autonomic fibers are the most sensitive to the local anesthetic, the absence of autonomic block means that there is little chance of an adequate sensory block. Furthermore, differences in foot temperature suggest an asymmetrical or unilateral block, even if sensory testing does not show differences between the two sides. Importantly, a fall in blood pressure is not an index of sympathetic block since this can be masked by the use of vasopressor infusions. There is also lack of consensus on when and how often the block should be tested after the performance of neuraxial anesthesia. If there is evidence of a successful block at an early stage, this can encourage the parturient but on the other hand, if the block is tested too soon and there is a delay in manifesting its success, this might increase parturient anxiety. Anxiety can also be increased by testing the block multiple times as the parturient might feel that she is under pressure to confirm the adequacy of the block, even if this is not yet satisfactory. Although it is common practice to occasionally ask the surgeon the test the adequacy of the block before starting the operation, the responsibility for block assessment lies with the anaesthetist. The establishment of good communication between the parturient and the anaesthetist is also of paramount importance in ensuring the accuracy of the parturient’s responses and thus of correct block assessment.
Additional considerations helping in preventing pain during cesarean section
In order to provide optimal neuraxial analgesia, it is necessary to administer the correct dose of local anesthetic for spinal anesthesia taking into consideration maternal body weight or height, aortocaval compression and gestational age. Also, consideration should be given to the supplementation of the local anesthetic by a lipid-soluble opioid, which augments the block and increases its duration. A combined spinal-epidural anesthetic offers the advantage of extending the duration of neuraxial anesthesia with supplementation via the epidural catheter in case this is required intraoperatively.
Preventing failed epidural conversion of labor analgesia
Pain during cesarean section can be prevented by preventing and avoiding failed epidural conversion of labor analgesia. The anaesthetist should continuously evaluate epidural block quality, the presence of breakthrough pain and the requirement for additional top ups so that he/she is aware of all the dynamic circumstances occurring during labor and he/she is actively involved in the process. This will provide the opportunity to optimize the epidural block quality, replace poorly functioning epidural catheters and prevent pain during cesarean section or the need to resort to general anesthesia. Continuous active communication with the obstetric team and knowledge of obstetric factors (such as progress of labor, fetal heart rate, maternal well-being, maternal risk factors) is mandatory. Confirmation of the catheter location by visual inspection or by administration of a test dose is highly recommended. In case of absence of progression of the block in the process of conversion, alternative techniques should be considered.
Managing failed epidural conversion of labor analgesia
Even after adequate assessment and active management of the epidural block, this still may fail to provide adequate anesthesia for the cesarean section. Therefore, it is essential to ensure adequate neuraxial blockade before surgical incision with some alternative technique because if inadequate anesthesia is recognized after the operation has been allowed to start, the only options left are intravenous supplementation or conversion to general anesthesia with its accompanying risks. In any case, the anesthetist should always believe the patient if she complains of pain and accept failure. As mentioned before, the most common reason for anaesthetists to face litigation claims after caesarean deliveries is intraoperative pain resulting from failed neuraxial anesthesia. Finally, prompt follow up of the parturient after the operation is absolutely necessary to minimize the development of long-term psychological sequelae.
Plaat F, Stanford SER, Lucas DN, Andrade J, Careless J, Russell R, Bishop D, Lo Q, Bogod D. Prevention and management of intra-operative pain during caesarean section under neuraxial anaesthesia: a technical and interpersonal approach. Anaesthesia. 2022 May;77(5):588-597.
Keita H, Deruelle P, Bouvet L, Bonnin M, Chassard D, Bouthors AS, Lopard E, Benhamou D; French Practice Bulletin Taskforce: ‘Préconisations – insuffisance d’analgésie au cours de la césarienne sous anesthésie périmédullaire: prévention – prise en charge immédiate et différée’. Raising awareness to prevent, recognise and manage acute pain during caesarean delivery: The French Practice Bulletin. Anaesth Crit Care Pain Med. 2021 Oct;40(5):100934.
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