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Lääkärikirja Duodecim 12.9.2012
Finnish Obstetris Anesthetists Association anesthetist Johanna Sarvela and anesthetist Petri Volmanen
The intensity of labor pain is different with every parturient and it is effected by the size and position of the fetus, the magnitude of contractions, the parturients threshold for pain and previous experiences on labor and pain. As the delivery progresses the contractions become more frequent and more painful. Most of the parturients experience the labor pain either as intense or unbearable. The pain in labor can’t always be totally removed but it can be eased with many different ways.
The methods used to treat labor pain are individually selected for every parturient. Sometime the wellbeing of the baby or the stage of the labor can affect so that parturients is not able to receive the pain relief method she or the treating personnel have been planning. The most important thing is that the delivery is as safe as possible and that the wellbeing of the baby or the parturient is not compromised at any stage.
There are different methods that can be used to assess the intensity of labor pain. One method is a verbal classification (for example no pain – excruciating pain), another so called pain line (the intensity of pain is marked to a line witch length is 100mm) and there is also a numerical score (0-10). “0” represents in these non-existing pain and the other end of the pain line (100mm) or numerical score “10” represents the worst pain imaginable. With these simple measurement methods we can better assess the effectiveness of the parturients pain management.
Medical pain relief methods can be divided in to two categories, ones affecting the whole body and ones affecting only some part of the body. The first ones are nitrous oxide and strong painkillers. They don’t take away the pain but they suppress the sensation of pain. The latter methods include different types of local anesthesia, which are usually used as the delivery progresses and the need for pain relief increases. The local anesthesia methods are
spinal anesthesia
epidural anesthesia (in which the medication is injected between the spinal cod and the bony spinal canal)
combination of spinal and epidural anesthesia
paracervical block (local anesthesia of the cervix)
pudendal nerve block
Nitrous oxide is one of most commonly used pain relief methods giving its safety, simple dosing ethod and inexpensiveness. The combination of oxygen and nitrous oxide (50%) is inhaled through a mask periodically before the beginning of contraction. Because the nitrous oxide is used in addition to oxygen it is not harmful to the fetus.
The effect of the gas comes only after about half a minute after the beginning of the inhaling and that is why the mother has to be able to predict the beginning of the contraction. The effect of nitrous oxide will fade after a few minutes but it can frequently cause short term mental confusion and dizziness as well as nausea. Many parturients feel that the nitrous oxide is not efficient enough as pain relief method. It is, however, frequently the only possible pain reliving method in situations where the delivery has progressed so fast that local blocks can not be performed.
Strong morphine like painkillers are called opioids. he most frequently used ones of these are pethidine, oxycodone and tramadol, which are given either injections to muscle, suppositories or per orally. In addition to pain relieving effect they also cause mild tiredness and are therefore especially suitable for mothers who long for some rest at the beginning of labor. The possible side effect is nausea. Pethidine also effects the new born and delays the start of breast feeding, but mainly only if it is given 1-4 hours before the birth. This is why it is suitable mainly in the very beginning of the first stage of labor. All of these painkillers can be used if the fetal heartbeat in the cardiotocography is normal.
More short-term effecting opioids, fentanyl and remifentanyl, can be used also as the delivery progresses. They can also be used in situations in which local anesthesia methods are for some reason unsuitable. These medications are given intravenously and the use requires close monitoring of both the parturient and the new born. They can only be used within delivery units that are prepared for the use of this pain reliving method.
Epidural and spinal anesthesia as well as their combination are the most efficient method of pain relief in labor. The purpose in these methods is to anesthetize the nerves that transmit the pain impulses from the uterus and the area of birthing canal. The neuraxial block are used as addition to other pain relieving methods because they are performed by an anesthesiologist whose immediate availability at any time of the day is unfortunately not always possible.
Picture 1 shows where the local anesthetic is injected in epidural and spinal blocks
Benefits of neuraxial blocks:
Local anesthesia doesn’t cause tiredness for the parturient like opioids
Intense pain and contractions can occasionally decrease the oxygenation of the mother and there for also reduce the oxygenation of the fetus. The efficient pain relief of the mother frequently improves the oxygenation of the fetus.
Sometimes local anesthesia can improve the inefficient pushing by the mother
Local anesthesia decreases the secretion of stress hormones. This is especially useful for example with toxemic (pre-eclampsia) parturients or the parturients who have a serious pulmonary or heart disease.
Neuraxial blocks can’t be performed in the following situations:
Skin infection at the lower back
Possible coagulating disorder or use of anticoagulation medications (for example heparin or varfarin)
Some rare neural disorders or back problems
Tattoo at the lower back does not usually prevent the neuraxial lock although the needle can’t be inserted directly through the ink.
Epidural block can be performed when the delivery is efficiently ongoing. The performing of epidural goes as follows:
The parturient is positioned either to her side or in sitting position for the block to be performed. It is crucial that the parturient is as still as possible during the insertion of the block. The rounding of the parturients back also makes it easier to find the correct place to insert the block.
After the disinfection on the skin the puncture site is numbed by infiltration with a thin needle. After that the anesthesiologist will place a thin and flexible catheter through a special needle to the epidural space. The epidural space lies in the immediate surrounding of the spinal cord space inside the central canal of the bone formed spine. Sometimes the parturient may feel a short-term electric shock like sensation or twitch on one of her legs as the catheter is been placed. When the catheter has been correctly placed, the needle is removed and the catheter is taped to stay in its place. The catheter isn’t removed until the end of the delivery.
From the epidural space the local anesthetic is absorbed to the spinal cord level where it the effects the neural roots innervating the uterus. By this manner a well specified and effective pain management is achieved especially at the first stage of labor.
The pain starts to ease little by little as the anesthetics reach the nerves. This usually takes about 5 – 15 minutes. After this the contractions are usually felt only as tightening in the abdominal wall and pressure towards the birthing canal as the delivery progresses. The local anesthetic used is given either as single doses or as continuing infusion through the same catheter all the way through the first stage of labor until the start of the pushing. The effect of a single dose of local anesthetic usually last for about 2 hours. According to the latest studies epidural block has only very little effect on the new born.
Even though the epidural block is mainly used at the first stage of labor, a decent pain relief can also be achieved during the second stage if the length of the block has been long-lasting and the doses of the local anesthetic are big enough.
The spinal block is the newest local anesthesia method used in pain relief during labor. It is used especially with women with previous labors because it’s effect comes faster and its more efficient towards the pain in second stage of labor. Spinal block is performed as a single shot block and it’s duration is limited and clearly shorter than that of the epidural block.
The spinal block is also performed by an anesthesiologist. In this pain relieving method the anesthesiologist gives the local anesthetic – painkiller –mixture straight to the spinal fluid space. The manners of delivering the medications are quite similar to those of the epidural block. The doses of the anesthetics used however are much smaller than in the epidural block.
In the spinal block the pain relief accrues usually faster than in the epidural block. At the beginning of the block there can be a passing sensation of numbness at the lower limbs and at this time the strength of pushes can also be impaired. The tingling and numbness will however shortly parish.
Because the duration of the spinal block is quite short, it is possible to first place a spinal block to the parturient through the epidural needle and then insert the epidural catheter to the epidural space (the combined spinal-epidural block). Hence, if needed, the analgesia can be continued via the epidural catheter without additional procedures.
Some of the milder side-effects are quite common but the more serious ones are very rare.
Effect on muscle strength. Modern diluted local anesthetic-opioid –mixtures make it possible to affect mainly the nerves conducting the pain from uterus so that the function of the muscles is preserved. This enables the parturient to stand up when 30 minutes has passed since the dosing of the analgetic mixture. The possible blocking effect on the lower limbs however is very individual with every parturient. That is why it’s important to make sure that the strength in the lower limbs is adequate before getting up and that the parturient doesn’t leave the bed without a companion.
Tremor and itching. Local anesthesia may increase the harmless tremor and light itching of the skin. The itching is more common after spinal than epidural block.
Difficulties in urination. Delivery itself as well as local anesthesia can cause difficulties in urination. This is why the midwife regularly evaluates the fullness of the bladder during the labor.
Effect on progress of the delivery. Epidural block may decrease the urge to push and prolong the second stage of labor. In this case it may be necessary to use vacuum extraction to deliver the baby. When using the modern diluted local anesthetic – opioid -mixtures these undesired side-effects have significantly decreased and it’s very probable that the labor progresses normally. Local anesthesia hasn’t been shown to increase the need for cesarean section.
Inadequate pain relief. Sometimes the pain relief remains inadequate or becomes for example one-sided. In most cases the situation can be corrected by altering the depth of the catheter or increasing the dose. It may also be necessary to replace the existing catheter with a new one.
Parturients blood pressure and heart rate of the fetus. Neuraxial blocks usually lower the blood pressure a bit and because on this an intravenous fluid transfusion is started. Sometimes the fast-acting pain relief can cause temporary deceleration on the fetal heart rate. These rarely cause any trouble, but monitoring of the parturients blood pressure and fetal heart rate are important when local anesthesia is used.
Backache. There may be some tenderness at the area in which the needle has been inserted. Back pain is also common during pregnancy and after labor. It hasn’t been shown that neuraxial block increase the risk of back pain.
Headache. It is relatively rare (about 1 parturient in 100) that the puncture of the spinal membrane causes a headache that gets worse as the parturient gets up (“post-spinal headache”). As the block is bee performed this membrane is punctured intentionally in spinal and sometimes unintentionally in epidural blocks. The hole in the membrane closes by itself with time, but if the headache is agonizing it can effectively be treated by the anesthesiologist by placing of so called blood patch.
Increase on the body temperature. When used for a long time, an epidural can cause a slight increase in the parturients body temperature.
Effects on the fetus, new born and breast feeding. Sometimes the fast-acting pain relief can cause short-term decelerations on the fetal heart rate. However the studies show that oxygenation of the fetus improves during the local anesthesia. Effects of the local anesthetics on the new born are lesser than with strong painkillers. Parturients receiving epidural analgesia seem to need support with breast feeding more often – even though the causal connection can’t be proven – than those parturients that don’t need any effective pain relief at all.
Nerve root and spinal cord injuries. During the delivery the head of the fetus compresses the nerves that lie near the birthing canal and this can sometimes cause temporary alterations in sensations of lower limbs and pelvis. This may happen in approximately one parturient per hundred. These usually don’t have any connection to the local anesthesia methods used. Severe and permanent nerve injuries that are caused by bleeding, mechanical damage or infection are extremely rare. In the entire Finland these damages are estimated appear less frequently than once a year.
Medicine overdose. If the medical cocktail used in epidural block is by accident partly delivered into a blood vessel or the spinal fluid, symptoms of drug overdose can present (for example dizziness, heart palpitation or feeling of strong numbness in the legs). This is very rare and usually easily manageable.
The paracervical block is performed by the obstetrician. In this type of local anesthesia the neural plexus is blocked at the both sides of the cervix.
The paracervical block can be used to ease the pain at the end part of the first stage of labor. The success rate of paracervical block is not as high as in epidural. The effect of the block begins quickly but the duration is shorter than in epidural, about 60 – 90 minutes. Quite rarely the block may cause decelerations in the fetal heart rate. Paracervical block is best suited as a pain relieving method for parturients who have previous deliveries, whose pregnancy is at full term and the fetus is healthy.
With the pudendal nerve block, performed by the obstetrician, the pain orienting from the lower part of the birthing canal and the vulva can be eased at the second stage of labor. The second stage and the saturation of the possible episiotomy are usually rather painless with the pudendal nerve block. The risks for the mother and the baby are quite small. The pudendal nerve block is usually used as addition to other blocks.
Both epidural and spinal block, the combination of these to or general anesthesia can be used safely as anesthesia method during the cesarean section. The decision of what method Is to be used is depending on many mainly medical reasons, and the aim is always to perform the surgery in the urgent cases as quickly and as safely as possible, both for the mother and the baby.
Epidural block is commonly used in non-elective section when the parturient already has the epidural catheter at place. The medications used for section anesthesia are much stronger than those used for labor pain relief. Spinal block is usually slightly faster than epidural block and the amounts of local anesthetic used are much smaller because the drugs are injected straight to the spinal fluid. The duration of the spinal block is limited. When the combined spinal-epidural block is used the fast start of the spinal block is achieved and if needed the block can be continued via the epidural catheter. The epidural catheter also enables the management of postoperative pain with medical infusions to the epidural space.
General anesthesia is used when neuraxial blocks are not an option or in a case of true emergency cesarean section. One of the biggest concerns in general anesthesia is the vomiting of the patient and the aspiration of stomach content to the lungs at the beginning or the end of anesthesia. This may lead to development of severe pneumonia. For this reason every parturient is given a medication neutralizing the acid in the stomach before the general anesthesia is conducted. Also other precautions are used during the anesthesia.
Before any surgical procedures requiring anesthesia one must be without any food for 6 hours and drinks for 2 hours. Approximately one in ten parturients undergoing vaginal birth requires an unexpected surgical operation during the labor (cesarean sections, ruptures, bleedings etc.). Because of this it is rational from safety’s point of view not to eat any solid food when the labor is in progress. It is however possible to consume clear fluids and energy containing drinks. We hope, that once the labor is in progress, the parturient doesn’t eat anything without first consulting the treating personnel.
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