Lumbar epidural anesthesia (LEA) is one of the most widely used forms of central neuraxis blockade. For surgical anesthesia, LEA may be used either as the sole technique or in combination with general anesthesia. Although the combined spinal epidural technique is gaining popularity, lumbar epidural analgesia is still the first choice for pain relief during labor and delivery in many centers. In acute and chronic pain treatment, lumbar epidural analgesia is used both as a diagnostic and therapeutic tool.

loss of resistance

For LEA, the loss of resistance technique (LOR) as described by Dogliotti (1) is the golden standard for identifying the epidural space.

The technique is based on the anatomical principle that the advancing needle is passing through the ligamentum flavum before entering the epidural space.

After the epidural needle has been introduced through the skin, the needle stylet is removed and a syringe is attached to the needle.

The ligamentum flavum is a very dense tissue, offering a high resistance to injection, whereas the epidural space offers a very low to absent resistance to injection. When the advancing needle tip crosses from the ligamentum flavum into the epidural space, the sudden loss of resistance to injection confirms the correct needle position.

LOR being the key to identifying the epidural space, it is not surprising that Dogliotti used saline rather than air in his syringe. Unlike air, saline or any other fluid is non-compressible, and consequently a high pressure can be placed on the syringe when the needle tip is entering the ligamentum flavum. Upon entering the epidural space, the sudden loss of resistance is therefore usually very clear and unambiguous. When using a compressible medium such as air, the pressure that can be built up is not as high as when using a non-compressible medium, and consequently the LOR when using air is not as clear.

This elementary fact notwithstanding, LOR using air has gained popularity as well for a variety of reasons. The most important reason is historical; until the seventies, syringes were made from glass and non-disposable. A well-known drawback of these syringes is that when filled with a fluid, the plunger of the syringe may stick to the glass wall, falsely indicating a high resistance to injection when in fact there is none (the “sticky syringe”). In order to avoid this, a completely “dry” technique with air as the medium was developed and for a while, generations of anesthesiologists were trained using air rather than a fluid for LOR. However, with the advent of the disposable, plastic syringe the raison d'être for this modification has vanished.

There is a natural tendency for people to resist change, and one who has performed LOR with air successfully for a long time is not likely to change his habits. Advocates of air have put several arguments forward to justify the practice of not using a fluid; the most frequently cited reasons are that the prior injection of saline into the epidural space may dilute the local anesthetic and slow the onset of anesthesia. While this may be true when injecting a significant volume of saline, this argument ignores the fact that with proper technique, the amount of fluid used to identify the epidural space can easily be limited to less than 1 mL and the perceived problem is thus non-existent.

By contrast, several studies have demonstrated the disadvantages of air as compared to a fluid for LOR, including a higher incidence of inadvertent dural puncture and patchy anesthesia; a recent study confirming the superiority of a fluid and including a review of the available literature is recommended for the interested reader (2).

In summary, when identifying the epidural space, using a fluid for LOR is the logical choice. There are no evidence-based arguments supporting the use of air. While people experienced in performing LOR with air should make their own decision whether or not they want to change their habit or continue a practice they feel comfortable with, the teaching of the LOR technique to residents should be based on the proven superiority of fluid.

Median or paramedian approach

 The median approach to the lumbar epidural space is the most widely used. If the midline can be identified properly, the path of the needle is straightforward, requiring little three-dimensional insight. The ligamentum flavum is thickest in the midline, adding to the tactile feedback obtained from the needle tip.

In certain patients however, the midline route may be difficult or even impossible to achieve due to anatomical variations. Inability to properly flex the spine or malformations of the bony structures in the midline may narrow or obstruct the route to the epidural space to the point where lumbar puncture may be impossible. By avoiding the midline, the paramedian approach offers a better alternative in those patients.

The paramedian approach has some additional advantages: Probably due to the steeper angle of entry, epidural catheter insertion is easier and associated with a lower incidence of paresthesia (3-5); in a cadaver study comparing epidural catheter insertion via the midline and paramedian route, the latter was associated with fewer technical problems, absence of dural tenting and a predictable cephalad direction of the catheter (6).

The point of paramedian needle insertion is approximately 1.5 cm lateral and 1.5 cm caudal to the point of the median needle insertion, with the needle angled in an upward and medial direction.

Disadvantages of the paramedian approach are that it calls for more three-dimensional insight and is more painful than the midline approach.

Indications & Dose

LEA is indicated for lower abdominal and lower limb surgery. The third lumbar (L3/L4) and the second lumbar interspace ( L2/L3) are the most frequently used. The fourth lumbar interspace is a possibility, but extension of sensory block may be too low at this level. The first lumbar interspace is more comparable to thoracic epidural anesthesia because of the columna extending to the second lumbar vertebra. For the indications mentioned above, this interspace is therefore not recommended.

If LEA is used as a sole technique, sensory block has to be dense and high concentrations of local anesthetic should be used (levobupivacaine 0.75 %, ropivacaine 1 %, lidocaine 2 %). When using lidocaine, the addition of epinephrine 5 micrograms/mL is necessary in order to minimize absorption and to obtain motor block.

Dose varies inversely with age. For the mentioned local anesthetics, volumes of 15 – 20 mL are recommended, to be reduced to 12 – 15 mL in the elderly.

If LEA is combined with general anesthesia, lower concentrations can be used (levobupivacaine 0.5 %, ropivacaine 0.75 %).

Sitting or lateral decubitus position

The advantage of the lateral decubitus position is that it is more comfortable to the patient and there is a lower tendency to vasovagal collapse. However in the sitting position, anatomical landmarks are more easily identified, especially in case of anatomic malformations such as scoliosis and in cases of (morbid) obesity. In addition, a paramedian approach is more easily accomplished with the patient in the sitting position.

Sedation

Many patients find lumbar puncture threatening, and for that reason most anesthesiologists prefer to administer sedation unless there is a contra-indication. When performing lumbar puncture with the patient in the sitting position, there is a greater tendency for vasovagal collapse, especially in young, male patients. Adequate sedation greatly reduces the incidence of vasovagal collapse.

Monitoring

Establishing prior intravenous access and non-invasive monitoring are a conditiones sine qua non when performing lumbar puncture. Standard monitoring consists of an electrocardiographic trace, peripheral oxygen saturation and non-invasive blood pressure. Mandatory emergency equipment readily available includes a means to ventilate and administer oxygen, laryngoscope and an endotracheal tube. Mandatory drugs readily available include drugs for a rapid sequence induction such as thiopental and suxamethonium, drugs to treat convulsions such as thiopental or midazolam, and drugs to treat bradycardia and or vasovagal collapse such as atropine and ephedrine.

Vasovagal collapse

Preliminary symptoms heralding the imminence of a vasovagal collapse are anxiety and/or confusion, and sweating. One of the most prominent signs of vasovagal collapse is bradycardia, followed by loss of consciousness and often convulsions.

Treatment consists of placing the patient in Trendelenburg position to promote venous return, and the administration of intravenous drugs and fluid.

Bradycardia is a symptom, not the cause of vasovagal collapse; collapse ensues as the result of massive loss of sympathetic tone, resulting in arterial and venous vasodilatation. The resultant decrease in cardiac output and sharp decrease in arterial blood pressure are the cause of cerebral hypoperfusion and loss of consciousness. For this reason, atropine is not the drug of first choice in the treatment of vasovagal collapse. Indicated is a drug that promotes vasoconstriction and increases cardiac output, such as ephedrine. The combination of the Trendelenburg position and intravenous administration of 5-10 mg ephedrine is usually sufficient to restore blood pressure and heart rate.