How is an intrathecal injection administered?

Appeared in: KGMU 2023

Explanation

An intrathecal injection involves administering medication directly into the subarachnoid space.
This space contains the cerebrospinal fluid (CSF) that surrounds the spinal cord and brain.
This route is used to bypass the blood-brain barrier for targeted delivery of drugs like anesthetics, chemotherapy agents, or pain medications to the central nervous system.
The term 'intrathecal' literally means 'within the sheath,' referring to the theca or dura mater, the outermost layer of the meninges.

Option B: This describes an intramuscular (IM) injection, where medication is injected into a muscle for systemic absorption.
Option C: This describes an epidural injection. The epidural space is located outside the dura mater, not within the subarachnoid space.
Option D: This describes an intravenous (IV) injection, which delivers medication directly into the systemic circulation via a vein.

Visual 1: Diagram - A cross-section of the spinal column showing the vertebrae, meningeal layers (dura, arachnoid, pia mater), the epidural space, and the subarachnoid space containing the spinal cord and CSF. An arrow should indicate the needle path for an intrathecal injection, piercing the dura and arachnoid mater to enter the subarachnoid space.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Administration route of intrathecal injections as background academic context rather than a clinical decision trigger.
Correct identification of anatomical landmarks is critical for nurses assisting with or monitoring patients after an intrathecal injection to ensure medication is delivered to the correct space and to prevent complications.
Complications can include post-dural puncture headache (PDPH), infection, bleeding, or nerve damage. Nurses must monitor for signs of these complications.
What if? - If the needle is inserted into the epidural space instead of the subarachnoid space, the intended spinal anesthesia will fail, and the patient will not have adequate pain relief. The procedure would need to be repeated, or an alternative anesthetic plan would be required.

How to Approach the Question

First, identify the key term in the question: 'intrathecal injection'.
Recall the definition of 'intrathecal'. The prefix 'intra-' means 'within' and 'theca' refers to the sheath (meninges) surrounding the spinal cord.
This definition directly points to an injection within the meningeal layers.
Evaluate the options based on this definition. 'Subarachnoid space' is the fluid-filled space within the meninges.
Eliminate the other options by defining their routes: 'into the muscle' is intramuscular, 'into the epidural space' is epidural (outside the dura mater), and 'into a vein' is intravenous.

Concept Tested & Keywords

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Practise the full KGMU 2023

Attempt every question from this paper in a timed mock, then review the full solution for each one.