spinal anaesthesia
Oct 13, 2025
Into the Space: Understanding Spinal Anaesthesia
Spinal anaesthesia 🏥 is a neuraxial technique which involves local anaesthetic, either with or without an adjunct such as fentanyl, being injected into the cerebrospinal fluid in the lumbar subarachnoid space. Spinal’s can also be referred to as a subarachnoid block or an intrathecal block.
A spinal is performed with the patient either sitting or lying in a lateral position, and is always done under strict aseptic conditions. The chlorhexidine wash used to prep the skin should be kept away from the sterile field of the spinal setup at all times to avoid inadvertent administration, which would be catastrophic for a patient ⚠️. After local infiltration to the skin, a fine gauge spinal needle, typically 25-G pencil point, is inserted at the L3/4 or L4/5 interspace.
🔹 The anaesthetic solution used for the block may be:
Hyperbaric – heavier than CSF (usually achieved with a glucose additive like with heavy marcaine); affected by gravity and can be manipulated with patient positioning
Isobaric – same density as CSF, meaning gravity has minimal effect (plain solutions)
Hypobaric – lighter than CSF (often done by diluting with sterile water); the solution rises against gravity, not commonly used
🔸 Indications for a spinal include:
Lower limb surgeries
Urological surgeries
Hernia repairs and other lower abdominal/pelvic procedures
Caesarean section
Other obstetric and gynaecological procedures
🔹 Contraindications can be separated into absolute and relative:
Absolute: Patient refusal, allergy to local anaesthetics, infection at injection site, severe bleeding/coagulation disorders, severe hypovolaemia, raised intracranial pressure, spinal anomalies
Relative: Cardiovascular instability, mild coagulopathy, spinal deformities, previous spinal surgery
Once the intrathecal injection has occurred, a profound sensory and motor block is established. This also leads to vasodilation and possible hypotension, with higher blocks affecting respiratory muscles 🌬️. The height of the block corresponds to the spread of local anaesthetic along nerve roots that supply specific areas of skin, known as dermatomes. Assessment of block levels can be performed bilaterally using ice to determine the level at which the “cold” sensation is lost as reported by the patient — bearing in mind that block heights can vary from side to side.
Build Knowledge✅
Improve Safety ✅
References:
Australian Society of Anaesthetists. (n.d.). Epidural and Spinal Anaesthesia and Analgesia. ASA. https://asa.org.au/epidural-and-spinal-anaesthesia-and-analgesia
OpenAnesthesia. (2023, December 19). Spinal Anaesthesia in Adults: Anatomy, Indications, and Physiological Effects. OpenAnesthesia. https://www.openanesthesia.org/keywords/spinal-anesthesia-in-adults-anatomy-indications-and-physiological-effects/
Stay connected with news and updates!
Join our mailing list to receive the latest news and updates from our team.
Don't worry, your information will not be shared.
We hate SPAM. We will never sell your information, for any reason.