Needle Selection for Neuraxial Anesthesia

Neuraxial anesthesia is frequently employed for surgeries involving the lower abdomen and lower extremities. This type of anesthesia encompasses spinal, epidural, and combined spinal-epidural techniques. Typically, the procedure involves inserting a needle between the vertebrae to administer medication into either the epidural space (as in epidural anesthesia) or the subarachnoid space (as in spinal anesthesia). Neuraxial anesthesia causes blockade of sympathetic, motor, and sensory nerves. The extent and rapidity of resulting physiological effects are influenced by the level and speed of the block’s onset, along with individual patient factors. Considering the complexity and delicacy of spinal anatomy, needle selection is critical to successful neuraxial anesthesia.

Appropriate needle selection for neuraxial anesthesia involves several key considerations, including the needle’s tip, length, gauge, and bevel. Needles are categorized into cutting needles and pencil point needles. Cutting needles, like the Quincke style, have a sharp point designed to cut through dural and arachnoid structures. In contrast, pencil point needles, such as the Green, Whitacre, Sprotte, and Gertie-Marx types, feature a rounded, non-cutting tip. These needles are utilized to access the subarachnoid space for administering medication during spinal anesthesia. Nerve injury can result from direct nerve penetration or from forceful contact between the needle and the nerve.

The bevel of a needle significantly influences the extent of damage when inserted near a nerve. Short-beveled needles may reduce nerve damage caused by cutting or penetrating the nerve, while long-beveled needles are more likely to penetrate the perineurium and cause fascicular injury. However, short-beveled needles can also cause more severe injury if they penetrate a nerve or fascicle. Blunt, noncutting needles offer better feedback and an enhanced sensation of the “pop” when puncturing the fascia. Nonetheless, a needle that is excessively blunt may complicate fascial puncture, leading to increased pressure and the risk of “overshooting” after puncturing the fascia. Pencil-point needles can also lead to greater post-traumatic inflammation, myelin damage, and intraneural hematoma.

The specific type of block being performed determines the selection of needle length. For example, deeper peripheral blocks like a sciatic nerve block necessitate longer needles. Ultrasound can assist in measuring the distance to the target nerve, ensuring accurate needle placement. If the needle is too short, it won’t reach the target site; if it’s too long, it may be hard to control and could be inserted too deeply. Needles should have depth markings to monitor the penetration depth into the tissue. Choosing the correct needle length (the shortest possible) facilitates better handling and maneuverability.

When selecting needle size, it is important to balance patient comfort with the potential for the needle to bend during insertion. Longer needles are more prone to bending and can be difficult to maneuver, so a larger-gauge needle may be necessary. Smaller-gauge needles, while less rigid

and more prone to bending, can be inserted intrafascicularly, posing serious risks. Larger-gauge needles should be used cautiously due to their association with increased tissue injury and hematoma formation. Additionally, smaller-gauge needles tend to increase resistance during injection and take longer for blood aspiration if the tip is intravascular.

For spinal anesthesia, a small-diameter (24 to 27 gauge) pencil-point spinal needle with an introducer is typically used. Larger-diameter needles and those with cutting tips have a higher risk of causing postdural puncture headaches compared to smaller-diameter and pencil-point needles. Appropriate needle selection for neuraxial anesthesia increases success rates and decreases the risk of postdural puncture headache.

Since the advent of ultrasound guidance for injections, there has been a push to create needles with enhanced visibility under ultrasound. Echogenic needles achieve this by reflecting ultrasound beams through various mechanisms. Some are designed with a special coating that captures micro-air bubbles near the needle tip. These enhanced echogenic needles can reduce the time required for visualization during ultrasound-guided procedures. Clear visibility of needles on ultrasound enables practitioners to perform procedures more efficiently while minimizing the risk of damage to surrounding tissues.

References

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