Spinal anaesthesia (or spinal anesthesia), also called spinal analgesia, spinal block or subarachnoid block (SAB), is a form of regional anaesthesia involving injection of a local anaesthetic into the subarachnoid space, generally through a fine needle, usually 9 cm long (3.5 inches). For extremely obese patients longer needles are available (12.7 cm / 5 inches). The tip of the spinal needle has a point or small bevel. Recently, pencil point needles have been made available (Whitacre, Sprotte, Gertie Marx & others)Epidural anesthesia is a technique whereby a local anesthetic drug is injected through a catheter placed into the epidural space. This technique has some similarity to spinal anesthesia, both are neuraxial, and the two techniques may be easily confused with each other. Differences include:
The injected dose for an epidural is larger, being about 10–20 mL compared to 1.5–3.5 mL in a spinal.
In an epidural, an indwelling catheter may be placed that serves for additional injections, while a spinal is almost always a one-shot only.
The onset of analgesia is approximately 25–30 minutes in an epidural, while it is approximately 5 minutes in a spinal.
An epidural often does not cause as significant a neuromuscular block as a spinal, unless specific local anesthetics are also used which block motor fibres as readily as sensory nerve fibres.
An epidural may be given at a cervical, thoracic, or lumbar site, while a spinal must be injected below L2 to avoid piercing the spinal cord. |
