Chapter 22A. Mechanisms and Management of Failed Spinal Anesthesia
The most likely reason for lack of cerebrospinal fluid (CSF) flow despite correct needle placement in the subarachnoid space is:
A. Absence of CSF (a “dry tap”)
C. Manufacturing problems leading to a blocked needle lumen
D. Obstruction of the needle lumen by clot or tissue
D is correct. Obstruction of the needle lumen by clot or tissue. Fine-bore spinal needles may become easily obstructed by a plug of tissue or clot, particularly if advanced without the stylet properly placed. In the case of any doubt, it is recommended to flush the needle or replace with fresh equipment.
A is incorrect. A true “dry tap” is rare but has been reported in cases with very low CSF volumes or when the subarachnoid space is obliterated—by a compressive lesion in the cauda equina or lumbar arachnoiditis.1
B is incorrect. Low CSF pressure—for example in patients with a CSF leak following neurosurgery or accidental dural puncture during an epidural procedure—may result in very slow flow of CSF through the needle.
C is incorrect. Such manufacturing issues are rare and should be easily identifiable by use of the stylet.
Regarding the use of ultrasound in neuraxial blockade:
A. It has not been shown to improve success rates.
B. Real-time scanning of needle placement is a technically simple skill.
C. It can be used to aid the identification of the midline and lumbar level in patients with difficult anatomy.
D. It is recommended as best practice for neuraxial block in all patients.
C is correct. It can be used to aid the identification of the midline and lumbar level in patients with difficult anatomy. Ultrasound has been shown to be superior to palpation of anatomical landmarks in identifying the vertebral level land midline.2
A is incorrect. Data from randomized controlled trials have shown an improvement in success rates of both epidural and spinal procedures using ultrasound guidance.
B is incorrect. Real-time ultrasound-guided neuraxial blockade is an advanced technique requiring an experienced operator.
D is incorrect. For this reason its use is often reserved for certain subgroups of “difficult” patients.
Aspiration of cerebrospinal fluid (CSF) through the spinal needle:
A. Decreases the height of the resultant block