Articulated Numbness (Spinal Anesthesia)
(Update: ) - general subjects
Spinal anesthesia is a form of regional anesthesia that involves injecting a local anesthetic or opioid into the subarachnoid space with a thin needle. The needle is usually 9 cm long.
ICON_PLACEHOLDEREstimated reading time: 8 minutes
It is also called spinal block, subarachnoid block, intradural block and intrathecal block. In latin Spinal anesthesia (short for SP).
The subarachnoid space is the space normally located between the arachnoid and the pia mater and is filled with cerebrospinal fluid and continues up to the spinal cord.
This type of anesthesia is a safe and effective form of anesthesia preferred in under-umbilical surgery. Local anesthetic with or without opioids injected into the cerebrospinal fluid (CSF) provides locoregional anesthesia (i.e. true analgesia, motor, sensory and autonomic - sympathetic blockade). Administration of analgesics (opioid, alpha2-adrenoreceptor agonist) in the cerebrospinal fluid without local anesthetic produces locoregional analgesia (i.e. reduced pain sensation, somewhat autonomic - parasympathetic blockade), but no sensory or motor block. Locoregional analgesia may be preferred to locoregional anesthesia in some postoperative care settings, especially since there is no motor and sympathetic block.
There is a small bend at the tip of the spinal needle. Recently, pencil-point needles have been introduced (Whitacre, Sprotte, Gertie Marx and others).
Spinal anesthesia alone or sedation or general anesthesia It is a technique commonly used in combination with. Most commonly in under-umbilical surgery It is used, but more recently, its use has extended to some supra-umbilical surgery and postoperative analgesia. Procedures using spinal anesthesia include:
- Oropedia: Orthopedic surgery in the pelvis, hip, femur, knee, tibia and ankle, including arthroplasty and joint replacement
- Heart and Vascular:
- Vascular surgery in the legs
- Endovascular aortic aneurysm repair
- General Surgery:
- Urology cases
- Nephrectomy and cystectomy with general anesthesia
- Transurethral resection of the prostate (TUR) and transurethral resection of bladder tumors
- Women's diseases
- Hysterectomy in different techniques used
- Cesarean operations
- Pain management during vaginal delivery and delivery
- Examinations under anesthesia
Spinal anesthesia is the preferred technique for cesarean section because it eliminates the risk of general anesthesia and unsuccessful intubation. It also means that the mother is conscious and the spouse can be present at the birth of the child. In addition to nonsteroidal anti-inflammatory drugs, postoperative analgesia from intrathecal opioids is also good.
Spinal anesthesia is a viable alternative for patients with severe respiratory disease such as COPD as it prevents the possible respiratory consequences of intubation and ventilation when the surgical site is suitable for spinal blockade. It may also be useful when the surgical site is suitable for spinal block in patients where anatomical abnormalities can make tracheal intubation very difficult.
Spinal anesthesia in pediatric patients is particularly beneficial in children with difficult airways and in those who are poor candidates for endotracheal anesthesia, such as increased respiratory risks or the presence of a full stomach.
This can also be used to effectively treat and prevent postoperative pain, especially thoracic, abdominal pelvic and lower limb orthopedic procedures.
Before receiving spinal anesthesia, it is important to have a thorough medical evaluation to make sure there are no absolute contraindications and to minimize risks and complications. Although contraindications are rare, some of the following are:
- Refusal of the person, rejection of the patient
- Local infection or sepsis at the injection site in the waist
- Bleeding disorders, thrombocytopenia or systemic anticoagulation (secondary to increased risk of spinal epidural hematoma)
- Severe aortic stenosis
- Increased intracranial pressure
- Space-occupying lesions of the brain
- Anatomical disorders of the spine
- Hypovolemia, for example after massive bleeding, including obstetric patients
- Special circumstances (controversial): Ehlers Danlos Syndrome or other disorders causing resistance to local anesthesia
Risks and complications
Complications of spinal anesthesia may result from physiological effects on the nervous system or may be related to the insertion technique. While most common side effects are minor and self-resolving or easily treatable, major complications can result in more serious and permanent neurological damage and rarely death. These symptoms may occur immediately after anesthesia administration or up to 48 hours after surgery.
Common and minor complications include:
- Mild hypotension
- Slowing of the heart (bradycardia)
- Nausea and vomiting
- Transient neurological symptoms (low back pain with pain in the legs)
- Post-dural puncture headache or spinal headache - Associated with the size and type of spinal needle used. The 2020 meta-analysis concluded that the use of a 26-G atraumatic hypodermic needle is recommended to reduce the risk of PDDH.
Serious and persistent complications are rare, but are usually related to physiological effects on the cardiovascular and neurological system or to the unintentional misplacement of the injection. The following are some important complications:
- Nerve injuries: Cauda equina syndrome, radiculopathy
- Cardiac arrest
- Severe hypotension
- Spinal epidural hematoma with subsequent neurological sequelae or previously absent due to compression of the spinal nerves.
- Epidural abscess
- Infection (eg meningitis)
Regardless of the drug (anesthetic agent) used, the desired effect is to prevent the transmission of afferent nerve signals from peripheral nociceptors. Sensory signals from the body are blocked, eliminating pain. The degree of neuronal blockage depends on the amount and concentration of local anesthetic used and the properties of the axon. The thin unmyelinated C-fibers associated with pain are blocked first, while the thick, heavily myelinated A-alpha motor neurons are moderately blocked. The heavily myelinated, small preganglionic sympathetic fibers are blocked last. The desired result is the total fit of the region. Therefore, although patients do not feel pain during surgery, they may sense some pressure applied to tissues (due to incomplete blockage of thick A-beta mechanoreceptors). This allows surgical procedures to be performed without causing any painful sensation to the person undergoing the surgery.
During the procedure, some sedation is sometimes provided to help the patient relax and spend time, but with a successful spinal anesthesia, the operation can be performed while the patient is fully awake.
In spinal anesthesia, the needle is placed in the subarachnoid space beyond the dura mater and between the lumbar vertebrae. To reach this gap, the needle must pierce several layers of tissue and connective tissue (supraspinous ligament, interspinous ligament, and ligamentum flavum). Spinal cord (Spinal cord or conus medullaris) is typically at the L1 or L2 level of the spine, so the needle is placed between the L3 and L4 space or L4 and L5 space below it to prevent injury to the spinal cord.
- Position (Positioning)
Positioning of the patient is crucial to the success of the procedure and can affect how the drug is delivered. There are 3 different positions used: sitting, decubitus to the side and prone. Sitting and side decubitus positions are most common.
Sitting - The patient sits upright on the edge of the examination table, with his back turned back, legs dangling from the end of the table and feet on a stool. The patient emphasizes his shoulders and gives his back a hunchbacked shape.
Lateral decubitus - In this position, the patient is placed on his side with his back turned to the edge of the bed. The patient should bend their shoulders and legs and bend the lower back (fetal position)
Prone: The patient lies face down and looks back up.
Spinal anesthesia is typically used in surgeries involving structures up to the navel level. If applied to higher levels, it can affect breathing and heart function (paralyze the intercostal respiratory muscles and even the diaphragm, slow the heartbeat, and stop the heart). Also, spinal anesthesia injection higher than the L1 level can damage the spinal cord and is therefore usually not done.
- Injected substances
Bupivacaine (Marcaine) is the most commonly used local anesthetic, but lidocaine (lignocaine), tetracaine, procaine, ropivacaine, levobupivicaine, prilocaine, or cinchocaine can also be used. Opioids are commonly added to cure block and provide postoperative pain relief, examples include morphine, fentanyl, diamorphine, and buprenorphine. Non-opioids such as clonidine or epinephrine can also be added to prolong the duration of analgesia (Clonidine may cause hypotension). In European countries, since 2004, the National Institute of Health and Care Excellence has recommended spinal anesthesia for cesarean to be supplemented with intrathecal diamorphine, and this combination is currently the modal form of anesthesia for this indication. Since diamorphine (heroin) is not used in clinical practice in the USA, morphine is used in cesarean sections for the same purpose.
Baricity (Baricity) refers to the density of a substance compared to the density of human cerebrospinal fluid. Baricity is used in anesthesia to determine how a particular drug will diffuse into the intrathecal space. Generally, hyperbaric (eg, hyperbaric bupivacaine) is chosen as it can be effectively and predictably controlled by the anesthesiologist by tilting the patient. Hyperbaric solutions are made denser by adding glucose to the mixture.
Differences between Epidural and Spinal anesthesia
Epidural anesthesia is a technique in which medicine (an anesthetic agent) is injected through a catheter inserted into the epidural space. This technique is similar to spinal anesthesia, but there are some differences between them. It is as follows:
- In spinal anesthesia, the drug is injected into the subarachnoid space, that is, the cerebrospinal fluid (CSF). Hence, it allows it to act directly on the spinal cord. In epidural anesthesia, the drug is given outside the dura (outside the CSF) and its main effect is on the nerve roots that leave the dura at the epidural level.
- In spinal anesthesia, it provides a deep block of all motor and sensory functions below the injection level, while in epidural anesthesia, it blocks the nerve roots around the injection site with normal function above and below the blocked levels.
- The amount of drug used in spinal anesthesia is low (1.5-3.5 mL). In epidural anesthesia, the injected drug dose is larger (10-20 mL).
- Spinal anesthesia is done only once. In epidural anesthesia, a permanent catheter can be placed that allows re-injections. For this reason, spinal anesthesia is used more frequently for short procedures.
- While the effect of spina anesthesia starts in 5 minutes, this period is approximately 25-30 minutes in the epidural.
- Epidural does not cause a neuromuscular block as important as spinal.
- Spinal anesthesia is usually given to the lower back (below L2). Epidural anesthesia can be applied to the neck (cervical), chest (thoracic) and waist (lumbar) regions.
History of spinal anesthesia
The first spinal analgesia was applied in 1885 by James Leonard Corning (1855–1923), a neurologist in New York. He was experimenting with cocaine on a dog's spinal nerves when he accidentally pierced the dura mater.
The first spinal anesthesia planned for surgery in humans was administered by August Bier (1861-1949) on August 16, 1898 in Kiel, where he injected a 34-year-old worker with 3 ml of 0.5% cocaine solution. After using it in 6 patients, he and his assistant injected cocaine into their spine. They recommended this method for leg surgeries, but abandoned it later due to cocaine toxicity.
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Bier A. Versuche über Cocainisirung des Rückenmarkes. Deutsch Zeitschrift für Chirurgie 1899; 51: 361. (translated and reprinted in 'Classical File', Survey of Anesthesiology 1962, 6, 352)
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