Epidural labor analgesia-causes and countermeasures of insufficient analgesia

Sun Chuanjiang Department of Anesthesiology, Jinghu Hospital, Macau Since the British obstetrician and gynecologist Simpson successfully used chloroform to relieve labor pain in 1847, people have been continuously researching and exploring labor pain relief for more than a century. Various drugs and methods have been reported frequently, but each Pros and cons. To date, there is no method that can make childbirth completely painless without affecting the safety of mother and baby. At present, it is recognized that the combined epidural and lumbar epidural analgesia has the best analgesic effect and has the least side effects. The former of the two is more common. 　　

        Epidural block analgesia is the longest application history of intraspinal block analgesia. Its advantages are that the maternal vital signs are stable, the analgesia time is flexible, and it can be adjusted in time with the length of labor. Anesthesia can be extended to cesarean section if necessary. But after all, obstetric epidural analgesia is different from epidural anesthesia during surgery. It not only has to achieve effective sensory nerve block and minimal motor nerve block, but also has the least impact on the birth process and mother and baby. Previous studies of epidural labor analgesia focused on the methods of administration—comparing the advantages and disadvantages of continuous epidural infusion and intermittent injection, the effects of different

        concentrations of local anesthetics on labor or production methods, and epidural It is possible to use other drugs (opioids, clonidine, neostigmine, etc.) in the cavity. These studies have significantly improved the safety of the parturient (preventing a large amount of local anesthetics from entering the blood vessels or subarachnoid space by mistake); the use of low-concentration local anesthetics has reduced the numbness of the lower limbs of the parturient and can even walk freely, which improves comfort and reduces Movement block, as far as possible to reduce the interference to the labor process

        (1). 　　 The disadvantages of epidural labor analgesia are slower effect, large dosage, and a certain percentage of analgesia failure rate. It has been reported in the literature that the failure rate of obstetric epidural analgesia is 3.5-13.5%, or even higher 24-32%, compared with the failure rate of surgical epidural anesthesia of 2-4%

        (2). 　　 analgesia effective sign: the visual analog analgesia score when the uterus contracts 30 minutes after the first dose is less than 10mm (3); 　　 The definition of analgesia failure in the first stage of labor: two consecutive additions of the same dose of local anesthetic within 30 minutes; such as 0.125% bupivacaine 12-18ml or 0.2% ropivacaine 10ml. 　　

        The definition of analgesia failure in the second stage of labor: VAS> 30 mm when holding the breath downward. 　　

        Ghislaine Le (3) et al. studied the risk factors for the failure of epidural analgesia in 456 primiparas. Analgesia method 0.125% simple bupivacaine 10-14ml/h continuous infusion. After multivariate analysis, it was found that the following factors are related to epidural insufficiency: epidural analgesia time exceeds 6h, the analgesia time of the entire labor process is less than 1h, radicular pain occurs when a hard external catheter is placed, and the analgesic effect of the first dose Poor, when the fetal position is abnormal (posterior occipital position or breech position). The authors found that the failure rate of hard external analgesia in the first stage of labor was 5% and that in the second stage of labor was 20%. 　　

        Pain during childbirth is affected by many factors, and the factors related to the parturient are age <18 years old or age> 35 years old, and primiparous women. 　　

        1. Factors related to the fetus: macrosomia, abnormal fetal position. 　　

        Studies have shown that when the fetal position is abnormal, the pain of the parturient is more severe, the labor process is longer, and the situation of insufficient analgesia is prone to occur. When the labor process is longer, the mother’s physical exhaustion has a worse tolerance for pain, leading to uncoordinated contractions of the uterus. Susan Ponkey

       (4) studied the effect of continuous posterior occipital position on the delivery method, labor process and newborns. The percentage of persistent posterior occipital position among 3315 primiparous women was 7.2%, and the incidence of transverse occipital position was 2.7%. The natural delivery rate of primiparous women in posterior occipital position is only 26%-29%, and that of post-occipital women is 55-57%. The rate of epidural analgesia for parturients in the continuous posterior occipital position was 86.1%, and that in the anterior occipital position was 73.1%. The effect of continuous posterior occipital position on the process of labor and the way of delivery: the first and second stages of labor are prolonged; oxytocin is needed to strengthen contractions in the labor process; the rate of delivery in the second stage of labor increases; the rate of caesarean section increases. At present, there are two views on the relationship between epidural analgesia and continuous posterior occipital position: one is that epidural analgesia leads to continuous posterior occipital position; the other is that the mother has pain due to continuous posterior occipital position. Early, long lasting and severe pain, so analgesia is required. 　　

        Although studies have shown that epidural analgesia is related to abnormal fetal position during labor, it is impossible to conclude that there is a causal relationship between the two. 　　

        2. When uterine muscle acidosis occurs, the maternal pain is severe and the chance of dystocia is greatly increased. 　　

        Women who have undergone a cesarean section due to dystocia have a lowered blood oxygen partial pressure in the uterine blood vessels while the PH value drops to 7.35, and women who have undergone an elective cesarean section 　　

        PH value is 7.48(5). In vitro tests confirmed that when the PH value drops from 7.5 to 7.3, the contractility of the uterus decreases and the contraction frequency decreases. When oxytocin is used improperly during labor, frequent uterine contractions cause the decrease of blood supply to the uterus, the decrease of oxygen partial pressure, the accumulation of lactic acid, and finally cause uncoordinated uterine contractions and even dystocia.

 　　3. Related to different stages of labor. 　　

        When the cervix dilates 7-8cm, the fetal presentation begins to decrease. Due to the coexistence of visceral pain and physical pain, the pain score at this time is higher than before, and the amount of PCA used by the mother is the largest.

 　　 Moeen K (6) and others prospectively studied the changes in the minimum effective concentration of local anesthetics during the first stage of labor as the labor progressed. According to whether oxytocin is needed for epidural analgesia, 57 parturients are divided into 4 groups; natural vaginal delivery                   group (oxytocin is not required), natural vaginal delivery group (oxytocin is required), and caesarean section (oxytocin is not required) ), Caesarean section group (need oxytocin). In this study, the parturients did not enter the active phase when they were selected, and the parturients who were clinically diagnosed as normal labor in the early stage of labor would eventually be delivered by caesarean section; their local anesthetic dosage was relatively large. 　　 30 minutes after the first dose, if the analgesia is insufficient, an additional remedial dose of 0.25% bupi 6-12 ml can be added. If the vaps is not less than 10 mm after 15 minutes, it will be considered as an analgesia failure and eliminated.

 　　 The results showed that women who had a final cesarean section had higher MLAC in the early stages of labor, and women who had already taken oxytocin during analgesia had higher MLAC.

 　　 Women who need oxytocin at the beginning of analgesia may have weak uterine contractions, and when the labor process is blocked, the pain becomes worse. Severe pain may be one of the signs of dystocia.

  　　Wuitchik reported that women who experienced severe pain during the incubation period had longer labor and more caesarean sections.

 　　 The literature reports that the MLAC of bupivacaine ranges from 0.065-0.069, 0.083, 0.104%. The different data of MLAC are related to different research objects, and the beginning of analgesia at different stages of labor.

 　　 According to reports, with the continuous progress of labor, MLAC increased from 0.048 to 0.14%.

  　　Hess reported that if the position of the epidural catheter is good and the mother still needs more than 3 additional doses, the chances of caesarean section or device-assisted delivery are greatly increased.

 　　 This study shows that the mothers suffer severe pain during dystocia and the demand for local anesthetics increases. There may be a large fetus, abnormal pelvic structure, abnormal fetal position, etc. There may be uncoordinated uterine contractions during dystocia, or ineffective contractions (undilated cervix).

  　　Countermeasures:

  　　1) Correctly assess whether it is a normal labor process, and be familiar with the characteristics of pain changes in different labor processes. If it is a normal labor and the cervix dilates 7-8cm, there is insufficient analgesia, and the PCA settings can be adjusted in time to increase the single load or shorten the lock-in time.

 　　 If the labor is normal, evaluate the analgesic efficacy of the first dose. After giving the epidural test dose (1.5% lidocaine 3ml), if the analgesic effect of the first dose is not good, even if the amount of local anesthetic is increased continuously at a constant rate, the analgesic effect cannot be improved. One of the reasons for the failure of extra-membrane analgesia. In clinical practice, satisfactory analgesic effects can be obtained by the following methods: 　　          A) Adjust the depth of the epidural catheter.

 　　 Bromage believes that when the lumbar epidural tube is placed 3 – 4 cm, the risk of blood vessel insertion, unilateral block, and tube loss can be minimized.

  　　Robert et al.

        (7) randomly grouped 800 parturients and placed tubes 2, 4, 6, and 8 cm, respectively, to evaluate the incidence of blood vessel insertion, unilateral block, and decoupling. The results of the study show that when the catheter is placed 2 cm, the risk of insertion of the blood vessel and unilateral block can be reduced, but it is prone to detubation. When the catheter is placed 6 cm, the risk of blood vessel insertion and de-catheterization can be reduced, but 13.5% have unilateral block, 19.5% need to adjust the position of the catheter, and 6% need to re-insert the catheter. 

　　 The author believes that the ideal depth of the epidural catheter cannot be concluded. He suggests that if the postpartum woman has no previous adverse birth history and the labor is expected to be fast, the catheter can be inserted 2 cm. If the labor process is prolonged (the tube is more likely to fall off) or the risk of transiting to caesarean section is higher, a 6cm tube can be placed.

 　　 After the catheter is inserted into the blood vessel by mistake or unilateral block, you can pull out 1cm and then inject the loading dose. After 20 minutes, evaluate the pain score. If the VAS is greater than 30 mm, you need to reinsert the catheter.

  　　B) When the dilatation of the uterine orifice is greater than 6 cm, the combined spinal-epidural analgesia can reduce the incomplete analgesia that may occur with simple epidural analgesia. Abouleish studied that when the average uterine orifice was 6.2 cm dilated, the subarachnoid cavity gave bupivacaine 2.5mg + 10μg sufentanil, less than 5 minutes VAPS <10mm, the analgesic effect was good and the maternal satisfaction was greatly improved. Improve, thereby enhancing the confidence of natural childbirth.

         2) If the increase in pain is related to abnormal conditions in the obstetric department, such as persistent posterior occipital position and uterine muscle acidosis, after reconfirming that the epidural catheter is in good position, the  anesthesiologist should inform the obstetrician in time and assist the obstetrician to make correct judgments and deal with. To sum up, compared with surgical epidural anesthesia, when insufficient analgesia occurs during epidural analgesia during labor, under the premise of excluding the poor catheter position, appropriate consideration can be given to whether the obstetric abnormalities are also complicated and deal with them in time These abnormal conditions ensure the safety of mothers and babies. The author graduated from Beijing Institute of Tuberculosis and Thoracic Tumor in 2004, majoring in anesthesia (Master), and went to work in the Department of Anesthesiology, Jinghu Hospital, Macau in 2005, in charge of labor analgesia, and helped Jinghu Hospital to officially start standardization of epidural in June 2006 Labor pain relief work.