The current situation of labor analgesia in "The 70th American Knowledge Update Essence"

The current status of labor analgesia technology Kenneth E.
Nelson's theme of this year's Anesthesia Week is "Respect for Life, Pay Attention to Anesthesia - Epidemic Prevention and Control to Save the Severe, Childbirth Analgesia and Nursing Newborns".
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PIEB combined with PCEA is superior to continuous infusion combined with PCEA2.
The reported efficacy of opioids without capping effect is mixed and often unsatisfactory, and respiratory depression should be paid attention to when using remifentanil and fentanyl
.

3.
Saline is recommended for resistance loss experiments 4.
The "epidural perforation" technique appears to improve analgesia without increasing side effects
.

5.
To avoid accidental "pulling out" of this catheter, allow the patient to return to a relaxed position before securing the catheter to the skin
.

6.
It is difficult to conclusively determine whether the use of ultrasound can reduce the incidence of these complications by reducing the number and duration of needle attempts required to enter the epidural space
.

7.
Successful identification of the epidural space has been demonstrated in animal models using an ultrasound source from the tip of the puncture needle, which will visualize the tissue plane and epidural space in real time
.

INTRODUCTION Over the past few decades, methods of labor pain relief have continued to evolve, culminating in the current state of the art
.

Although there are many topics, questions, and controversies regarding labor analgesia, the discussion in this chapter focuses on three main topics: labor analgesia maintenance, debate, and technical approaches
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Maintenance of labor analgesia 1 Patient controlled epidural analgesia/programmed intermittent epidural bolusing (PCEA/PIEB) Porous epidural catheters are commonly used to maintain labor analgesia , local anesthetics can produce "differential flow" through a porous epidural catheter
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At clinically relevant continuous infusion rates, the vast majority of local anesthetics exits through the proximal port (Figure 35.
1)
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Only when the infusion pressure is significantly increased does the local anesthetic begin to flow through the medial and distal orifices, which occurs with a rapid single injection
.

As expected, application of a technique that allows local anesthetic to flow through all three holes improved analgesia
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Current studies have confirmed that PIEB combined with PCEA is superior to continuous infusion combined with PCEA; to take advantage of this advantage, this analgesic pump is currently being developed
.

Future studies will guide its application of the optimal combination of basal infusion and programmed intermittent single-dose
.

2 Intravenous opioids Partial agonists of opioid receptors such as butorphanol have a capping effect on respiratory depression, so theoretically the risk of maternal side effects and neonatal depression is low and can be applied to mothers
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However, its analgesic effect is limited
.


The reported efficacy of pethidine without a capping effect has been mixed and often unsatisfactory
.

Fentanyl rarely causes allergic reactions and has relatively few drug interactions, but its respiratory depressant effect has no capping effect, so it must be used with caution in the delivery room
.

The drug has an accumulating effect, so pay close attention to neonatal respiratory depression
.


Remifentanil is a new type of opioid analgesic with fast onset and short duration of action.
Its unique pharmacodynamic characteristics make its application in labor analgesia very popular in the early days
.

Even with its rapid onset of action, it is almost impossible to administer remifentanil to achieve analgesic effects that fully correspond to uterine contractions
.

However, remifentanil caused more reduction in maternal oxygen saturation, and fentanyl caused more neonatal suppression
.

Controversy 1 Use air or saline for resistance loss experiments When entering the epidural space, either air or normal saline can be safely used to test resistance loss
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The recent debate on this issue has shed light on the reasons for avoiding the use of air, while the arguments against the use of saline are less so
.


Inadequate analgesia has been reported in paediatric patients due to the presence of air bubbles in the epidural space
.

The same problem occurs in obstetrics
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Venous air embolism and pneumocephalus may even occur with air; although a small amount of venous air is rarely a problem, resistance loss experiments with air are more likely to cause headaches than saline, presumably due to pneumocephalus
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Finally, other potential complications include nerve root compression and subcutaneous emphysema
.


However, it is still worth mentioning that it is theoretically possible to confuse normal saline with cerebrospinal fluid (CSF) during combined spinal epidural anesthesia (CSE)
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In a recent study comparing the use of air and saline to detect resistance loss during CSE procedures, there was no significant difference in failure rates between the two methods, nor was there a case of confusing saline for CSF
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The scientific report is consistent with expectations in this case, where saline is injected into the epidural space and distributed into tissues such as fat and blood vessels without being aspirated by subsequent spinal needle aspiration
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2 Accidental dural puncture: what to do next The risk of accidental dural puncture (ADP) can be minimized, but not completely eliminated, with an overall risk of about 1/200
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Once ADP occurs, there are two basic options: ①replace the epidural puncture; or ②indwelling the subarachnoid catheter
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When choosing an indwelling subarachnoid catheter, potential complications to keep in mind include the risk of infection, spinal cord injury, neurotoxicity, and the risk of inappropriate medications or fluids being injected through the catheter
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Potential complications include inadequate analgesia (vs.
subarachnoid catheters), increased risk of headache (again, compared to subarachnoid catheters), and unexpectedly high steric resistance when re-insertion of the epidural catheter is chosen at a different location Lag risk
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Whether choosing a subarachnoid catheter or re-epidural catheterization, perhaps the most important consideration is to clearly label the catheter at the proximal connector to minimize the risk of inappropriate drugs or fluids being injected
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Technical method 1 CSE combined spinal-epidural analgesia is a method that combines the two technical characteristics of subarachnoid analgesia and epidural analgesia, that is, it combines the reliability and fast onset of subarachnoid analgesia.
Sustainability and flexibility of epidural analgesia
.

Although CSE technology is very mature, its role in labor analgesia remains to be determined
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For example, the use of CSE in high-risk patients for cesarean delivery remains somewhat controversial because of the "untested" catheter position immediately after catheter placement
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Once analgesic doses have been administered to the subarachnoid space and an epidural catheter is placed, it is appropriate to use local anaesthetic to test whether the catheter is in the subarachnoid space, but it becomes problematic to exclude the catheter from entering the vein
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Intrathecal opioids can also cause pruritus, which is usually not enough to avoid, but is sometimes painful enough to cause patients to request treatment or even refuse CSE in later pregnancies
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However, the CSE technique has many advantages over epidural alone, including rapid onset of action, reliable results, and minimal motor block
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Also, the use of CSE increased the rate of cervical dilation compared with epidural and systemic analgesia
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2 Epidural perforation Obstetric anesthesiologists have recently introduced a technique called "epidural perforation"
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This technique is to make a small hole in the dura during the epidural operation, but does not use drugs in the subarachnoid space, and aims to improve the quality and reliability of epidural analgesia
.

After the catheter is placed, the effectiveness of the catheter can be completely tested, and a small amount of epidural drug can be passed through the perforated dural hole to improve the analgesic effect
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This technique, although not yet widely used, has been well-studied and appears to improve pain relief without increasing side effects
.

In addition, the technique "proved" that the epidural catheter was fully functional in the event of an unplanned cesarean delivery, thereby addressing the theoretical shortcomings of the CSE technique described above
.

3.
Unintentional "pulling out" of the catheter Regardless of the epidural catheter technique, the length of catheter fixation can significantly affect the length of catheter that remains in the epidural space (Fig.
35.
2)
.

The distance from the skin to the ligamentum flavum is minimal when the patient is seated and the lumbar spine is in maximal flexion
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When the patient returns to a relaxed sitting position, this distance increases and the skin and soft tissues move caudally
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Therefore, if the catheter is secured to the skin before the patient returns to the relaxed position, the epidural catheter will be pulled out of the external lumen by the same distance as the soft tissue has moved, even if the catheter's markings on the skin remain the same
.

This distance traveled is further magnified in obese patients and, if this effect is not recognized, can lead to complete failure of the epidural catheter
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To avoid accidental "pulling out" of the catheter, the patient should be allowed to return to a relaxed position before securing the catheter to the skin
.

Placing the patient in a lateral decubitus position should also be considered before securing the catheter, as this allows for further soft tissue stretch, especially in obese patients
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4 Ultrasound-guided neuraxial block Ultrasound technology adds a visual tool to the anesthesiologist that can be used to locate landmarks and measure the depth from the skin surface to the epidural space before the procedure begins
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However, the use of ultrasound to guide intraspinal blocks in real time is problematic because the narrow "window" between the spinous processes requires the simultaneous application of an ultrasound probe and an epidural stylus
.

Proponents of the technology hope that the use of ultrasound will improve safety
.

Fortunately, epidural hematomas and infections are extremely rare, so it is difficult to conclusively determine whether the use of ultrasound can reduce the incidence of complications by reducing the number and duration of needle attempts required to enter the epidural space
.


Previous studies have shown that even experienced anesthesiologists often make mistakes in determining anatomical landmarks and estimating the intervertebral space by hand palpation, often higher than the estimated intervertebral space
.

Ultrasound can accurately determine the level of the intervertebral space, thus avoiding unnecessary intraspinal manipulation above the level of the cauda equina
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Compared with peripheral nerve blocks, ultrasound still has a lower prevalence in the maternity and delivery room; this is likely due to the high success rates achieved without ultrasound and the limitations of using ultrasound procedures
.

"Routine" use of ultrasound can prolong the time from the patient's request for analgesia to the first painless contraction, which can lead to some resistance to the use of ultrasound by anesthesiologists and patients
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Despite some limitations, ultrasound is emerging as a tool for lumbar epidural procedures
.

5.
A new method of epidural space localization The use of an ultrasonic source from the tip of a puncture needle to successfully locate the epidural space has been demonstrated in animal models, and this technology is expected to enter clinical trials in the future
.

Another similar technique utilizes spectral absorption at different tissue planes instead of acoustic waves
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Hopefully, one day, our current "blind" method of determining the epidural space by the loss of resistance will be replaced by advanced technology that will visualize the tissue plane and epidural space in real time
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What is the "state of the art labor analgesia"? As research and clinical experience guide changes in techniques for analgesics, neuraxial adjuvants, maintenance of epidural analgesia pumps, and access to epidural and subarachnoid spaces, The definition is also constantly evolving
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In this evolutionary process, controversy is inevitable
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Anesthesiologists need to be aware of the pros and cons of choosing different techniques, such as air versus saline for resistance loss determination, placement of a subarachnoid catheter or repositioning of an epidural catheter after an accidental dural rupture
.

Technological changes are also indicative of the current state of labor analgesia as devices evolve and improve, making access to the epidural space easier while minimizing complications
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