Spinal anesthesia (1)

Spinal anesthesia Capt. Wiriya Homhuan Anesthesiology department Phramongkutklao hospital

Spinal anesthesia• Overview Outline • Pharmacology• Indications • Physiology• Anatomy • Contraindications• Techniques • Complications

AnesthesiaGeneral Regional- Endotracheal tube - Spinal anesthesia- Laryngeal mask airway- Total intravenous anesthesia (Spinal block) (Subarachnoid block) - Epidural anesthesia - Peripheral nerve block

Definition of regional anesthesia• Local anesthetic applied around a peripheral nerve at any point along the length of the nerve (from spinal cord) Reducing or preventing impulse transmission

How to choose choice of anesthesia ?General VS Regional Patient Doctor Operation

Advantages of spinal anesthesia over GA• Lower cost• Patient satisfaction• Decrease risk for aspiration• Alternative to GA for certain poor risk patient – esp : difficault airway, respiratory disease• Less intraoperative blood loss• Post operative pain control

Indications• Spinal anesthesia can be used to provide surgical anesthesia for all procedure carried out on the lower half of the body. – Lower limbs – Pelvis – Genitalia – Perineum – Urologic procedure• Can be used analgesia ( intrathecal opioid).

Vertebrae

Vertebrae

Ligaments

Ligaments

Spinal Cord- First trimester Begins: Foramen Magnum Ends: Sacrum- Newborn Begins: Foramen Magnum Ends: L3- Adult Begins: Foramen Magnum Ends: L1

Spinal Cord- Terminal End : Conus Medullaris- Filum Terminale : Anchors in sacral region- Cauda Equina : Nerve group of lower dural sac

Membranes surrounding the spinal cord• Pia mater - highly vascular, covers the spinal cord and brain• Arachnoid mater - non vascular and attached to the dura mater. - principal anatomic barrier for drugs moving between the epidural space and the spinal cord• Dura mater - extension of the cranial dura mater, extends from the foramen magnum to S2 (ending at the filum terminale)



Cerebrospinal fluid (CSF)• Clear fluid that fills the subarachnoid space• Produced by plasma ultrafiltration in the choroid plexus within the cerebral ventricles.• Made up of 99% water and other molecules including electrolytes, proteins, glucose, neurotransmitters, neurotransmitter metabolites, cyclic nucleotides, amino acids.

Cerebrospinal fluid (CSF)• The CSF volume is approximately 100 to 160 mL in adult humans and it is produced at the rate of 20 to 25 mL/hr.• Specific gravity is between 1.003-1.009 (this will play a crucial role in the barocity of local anesthetic that one chooses).• Absorbed by the arachnoid villi in the superior sagittal sinus and/or into lymphatics via perineural sheaths of cranial and spinal nerves.

Sensory dermatomes - The spinal cord gives rise to 31 pairs of spinal nerves, each composed of an anterior motor root and a posterior sensory root. - The skin area innervated by a given spinal nerve and its corresponding cord segment is called a dermatome.

Spinal anesthesia technique• Preparation • Patient positioning – Spinal needle – Lateral decubitus – Sterile spinal preparation set – Sitting – Antiseptic solution – Prone – Local anesthetic agent• Monitoring – NIBP – Pulse Oximeter – EKG

Needle • Spinal needles are classified by the design of their tips. -Pencil point - Cutting point

Landmark • iliac crests • A line drawn between the iliac crests crosses the body of L5 or the L4 to L5 interspace.

Position• Lateral decubitus

Position• Sitting

Anatomical approach• Midline The spinal needle is inserted with a slight cephalad angulation and should advance in the midline without contacting bone (B). If bone is contacted, it may be either the caudad (A) or the cephalad spinous process (C).

Anatomical approach• Paramedian • Useful in situations where the patient’s anatomy does not favor the midline approach such as : - inability to flex the spine - heavily calcified interspinous ligaments • This approach can be used with the patient in any position. •The first significant resistance encountered should be the ligamentum flavum.

Pharmacology• Successful spinal anesthesia requires a block that is high enough to block sensation at the surgical site and last for the duration of the planned procedure.• The clinician must understand the factors governing spinal block height and duration to individualize local anesthetic dose for each patient and procedure.





Baricity• Baricity is defined as the ratio of the density (mass/volume) of the local anesthetic solution divided by the density of CSF : which averages 1.0003 ± 0.0003 g/mL at 37°C. – Isobaric solutions : Same density as CSF have a baricity of 1 – Hyperbaric solutions : More denser than CSF – Hypobaric solutions : Less denser than CSF

Baricity and Patient Position• Baricity is important in determining local anesthetic spread and thus block height by gravity – hyperbaric solutions to low downward in CSF to the most dependent regions of the spinal column – hypobaric solutions tend to rise in CSF – truly isobaric solutions : gravity has no effect on the distribution.• Anesthesiologist can exert considerable influence on block height by choice of anesthetic solution and proper patient positioning.