Neuraxial Detailed Flashcards
What are the order of meningeal layers surrounding the spinal cord?
Dura Mater, Arachnoid Mater, Pia Mater.
Which meningeal layer is the innermost and directly covers the spinal cord?
Pia Mater.
Where is the Epidural Space located in relation to the dura mater?
The Epidural Space is located outside the dura mater.
What is found in the Epidural Space?
The Epidural Space contains fat and small blood vessels (epidural veins).
Describe the Subarachnoid Space and its contents.
The Subarachnoid Space is between the arachnoid mater and pia mater, filled with cerebrospinal fluid (CSF) that cushions and protects the spinal cord.
What are the boundaries of the Epidural Space?
Cranial border near the foramen magnum, caudal border near the sacrococcygeal ligament, anterior border lined by posterior longitudinal ligament, lateral borders marked by vertebral pedicles, and posterior borders framed by ligamentum flavum and vertebral lamina.
What are the contents of the Epidural Space?
The Epidural Space contains nerves, fatty tissue, lymphatics, and blood vessels.
How does the fatty tissue in the Epidural Space affect drug absorption?
Fatty tissue can absorb drugs, leading to decreased drug availability; for example, bupivacaine is absorbed more than lidocaine, fentanyl, or morphine.
Describe the characteristics of Epidural Veins (Batsons Plexus).
Epidural veins are valveless and form a plexus to drain blood from the spinal cord and its linings. The density of veins increases laterally.
How do conditions like obesity or pregnancy affect Epidural Veins?
Under conditions like obesity or pregnancy, Epidural Veins can become engorged, increasing the risk during needle procedures in the Epidural Space.
What is the controversy surrounding the existence of Plica Mediana Dorsalis?
The presence of Plica Mediana Dorsalis is controversial and not definitively confirmed.
Where is the Plica Mediana Dorsalis located?
Plica Mediana Dorsalis is thought to be a band of connective tissue located between the ligamentum flavum and the dura mater.
How might the potential existence of Plica Mediana Dorsalis impact the Epidural Space?
If it exists, the Plica Mediana Dorsalis might act as a barrier within the Epidural Space, affecting how medications spread when injected.
In what clinical scenarios is the Plica Mediana Dorsalis relevant?
The Plica Mediana Dorsalis is considered in catheter insertion, potentially causing complications, and in cases of unilateral blocks where both sides are not equally affected.
Where is the subarachnoid space located?
It is situated deep to the arachnoid mater in the spinal cord.
What are the contents of the subarachnoid space?
It contains cerebrospinal fluid (CSF), nerve roots, and the spinal cord itself.
Why is the subarachnoid space the primary target during spinal anesthetic procedures?
It is the primary target as it contains CSF and is where spinal anesthesia is typically administered.
What risk is associated with advancing the needle too far anteriorly in the subarachnoid space?
Advancing the needle too far may lead to passing through multiple layers (pia mater, spinal cord, ligaments) before reaching bone.
What characteristic sensation is often felt during spinal anesthesia as the needle traverses the outer membrane?
A distinct ‘pop’ sensation is often felt when the needle traverses the dura mater.
Where is the subdural space located?
It is a potential space between the dura mater (outer layer) and the arachnoid mater (middle layer) surrounding the spinal cord.
What effect can occur if local anesthetic is inadvertently injected into the subdural space during an epidural?
It can lead to a ‘high spinal’ effect, causing the medication to affect a larger area than intended.
What consequence may result from an accidental injection into the subdural space during spinal anesthesia?
It can result in a failed spinal block if the injection occurs in this space.
What is the function of the Dura Mater within the meninges?
It is a tough fibrous shield protecting the spinal cord.
Where does the Dura Mater begin and end within the spinal cord?
It starts at the foramen magnum and extends to the dural sac.
Which meningeal layer is the first encountered by a needle in the epidural space?
The Dura Mater is the first layer encountered in the epidural space.
Describe the Arachnoid Mater in terms of its location and function.
It is a thin layer of connective tissue beneath the Dura Mater, acting as a protective middle layer between the Dura Mater and Pia Mater.
What are the characteristics of the Pia Mater within the meninges?
It is a highly vascular, delicate innermost layer covering the spinal cord.
Why should the Pia Mater never be punctured during spinal anesthesia procedures?
It should not be punctured as it is directly attached to the surface of the spinal cord.
How many pairs of spinal nerves are found in the spinal cord?
There are 31 pairs of spinal nerves in the spinal cord.
Where do the Cervical nerves exit in relation to their corresponding vertebrae?
Each Cervical nerve exits above its corresponding vertebra except for C8, which exits below the C7 vertebra.
What is the exception in the exit pattern of the Cervical nerves in comparison to the others?
The C8 nerve exceptionally exits below the C7 vertebra unlike other Cervical nerves.
What types of nerves are formed by the joining of different nerve roots in each spinal nerve?
Each spinal nerve consists of an Anterior (Ventral) Nerve Root and a Posterior (Dorsal) Nerve Root.
What information does the Anterior (Ventral) Nerve Root carry?
It carries motor and autonomic information from the spinal cord to the body.
What information is transmitted by the Posterior (Dorsal) Nerve Root?
It transmits sensory information from the body back to the spinal cord.
What is a dermatome?
A dermatome is an area of skin innervated by sensory nerves from a single spinal nerve root.
Explain the misconception related to dermatomes and spinal nerves.
Despite physical appearances, a dermatome may not align with the corresponding part of the spine but may be connected to a different spinal nerve root.
Provide an example of a dermatomal discrepancy.
The umbilicus (belly button) is typically associated with the L3 nerve but is actually served by the T10 nerve.
How is sensory information from the face transmitted?
Sensory information from the face is not carried by spinal nerves but is transmitted via the trigeminal nerve (Cranial Nerve V).
What areas does the V1 - Ophthalmic Nerve of the trigeminal nerve innervate?
The V1 - Ophthalmic Nerve is responsible for sensation from the forehead, scalp, and upper eyelids.
Which regions are served by the V2 - Maxillary Nerve of the trigeminal nerve?
The V2 - Maxillary Nerve handles sensory input from the lower eyelids, cheeks, nostrils, upper lip, and upper teeth.
What sensations are conveyed by the V3 - Mandibular Nerve of the trigeminal nerve?
The V3 - Mandibular Nerve conveys sensations from the lower jaw, lower teeth, lower lip, and part of the tongue.
Where is the site of action for local anesthetics in the spinal cord?
Local anesthetics act on the myelinated preganglionic fibers in the subarachnoid space of the spinal cord.
Describe the location of the spinal epidural space in relation to the dura mater.
The spinal epidural space is located outside the dura mater surrounding the spinal cord.
How do local anesthetics reach nerve roots in the epidural space?
Local anesthetics diffuse through the dural cuff and can also leak through the intervertebral foramen to reach nerve roots.
List controllable factors affecting local anesthetic distribution in the spinal space.
Controllable factors include baricity, patient position, dose, and site of injection.
What are non-controllable factors that influence local anesthetic distribution in the spinal space?
Non-controllable factors include volume of cerebrospinal fluid, increased intra-abdominal pressure, and age.
How does a low cerebrospinal fluid volume impact the spread of local anesthetics?
Low cerebrospinal fluid volume correlates with extensive spread of local anesthetics in the intrathecal space.
Why is dose considered crucial in affecting the spread of local anesthetic?
Dose is crucial as it is the most reliable factor influencing the spread of anesthetic using hypo- or isobaric solutions.
What role does baricity play in determining the spread of local anesthetics?
Baricity matters, as the relative density of the anesthetic compared to CSF determines its spread, especially for hyperbaric solutions.
How does advancing age affect the vulnerability of neural nerves to local anesthetics?
In advanced age, neural nerves become more vulnerable to local anesthetics as cerebrospinal fluid volume decreases.
What impact does pregnancy have on cerebrospinal fluid volume and local anesthetic distribution?
Pregnancy leads to decreased cerebrospinal fluid volume due to increased intraabdominal pressure, affecting local anesthetic spread.
What is the most important drug-related factor affecting local anesthetic spread and block height?
The local anesthetic volume is the most important drug-related factor.
Which factor is considered the most important procedure-related factor influencing local anesthetic spread and block height?
The level of injection is the most important procedure-related factor.
Name a non-controllable factor that can affect local anesthetic spread and block height.
Pregnancy is a non-controllable factor.
How does the local anesthetic concentration impact local anesthetic spread and block height?
It is a controllable factor that can influence the distribution and block height.
What role does the patient’s position play in local anesthetic spread and block height?
Patient position is a controllable factor that can affect the spread and block height.
In what way can the additives in the anesthetic impact local anesthetic spread and block height?
Additives can modify onset time or duration but not the spread of the local anesthetic.
How does the direction of the bevel of the needle affect local anesthetic spread?
The needle bevel direction does not influence the spread of the local anesthetic.
What factors do not affect the spread of spinal anesthetic?
The speed of injection, barbotage, direction of bevel, gender and vasoconstrictors
What determines the block height in the spinal or epidural space?
The spread of the local anesthetic in the spinal is determined by the dose. In the epidural space the volume determines the block height.
How does the spread of local anesthetic differ in the lumbar region during an epidural injection?
It mostly spreads cephalad in the lumbar region during an epidural injection.
Describe the spread dynamics of local anesthetic in the mid-thoracic region during an epidural injection.
The spread is balanced both cephalad and caudad in the mid-thoracic region.
In which direction does local anesthetic spread in the cervical region during an epidural injection?
In the cervical region, the local anesthetic spreads caudad.
What is meant by the term ‘differential blockade’ in the context of nerve fibers?
Differential blockade refers to varying sensitivities of nerve fibers to local anesthetics, affecting block levels.
How does sensory blockade differ from autonomic blockade in terms of local anesthetic sensitivity?
Sensory blockade occurs at lower concentrations, while autonomic blockade requires even lower concentrations.
Which nerve fibers are associated with autonomic preganglionic function and venodilation?
The B fibers are related to autonomic preganglionic function and venodilation.
What functions are attributed to A-delta fibers in the context of nerve sensitivity?
A-delta fibers are associated with pain and temperature sensation.
Identify the nerve fiber type responsible for motor tone.
A-gamma fibers are responsible for motor tone.
Which nerve fibers are linked to touch and pressure sensation?
A-beta fibers are associated with touch and pressure sensation.
What functions are attributed to A-alpha fibers in the context of nerve sensitivity?
A-alpha fibers are related to motor function and proprioception.
What happens at lower concentrations of Local Anesthetic in Sensory Blockade?
Sensory Blockade occurs, affecting sensory neurons but not motor neurons.
How does Sensory Blockade compare to motor blockade in terms of block level?
Sensory level is 2 levels higher than motor level
At what concentrations does Autonomic Blockade occur in relation to Local Anesthetic?
Autonomic Blockade requires even lower concentrations of Local Anesthetic.
Which neurons are affected by Autonomic Blockade?
Autonomic Blockade does not affect sensory or motor neurons.
What level of blockade does Autonomic Blockade lead to?
Autonomic Blockade leads to the highest level of blockade.
How does the sensory level compare to the motor level in Differential Blockade Zones?
The sensory level is 2 levels higher than the motor level in Differential Blockade Zones.
What are the functions of Type B-fibers?
B-fibers are associated with sympathetic function.
What type of sensation is lost with C and A-delta fibers in nerve fiber classification?
Loss of pain and temperature sensation occurs with C and A-delta fibers.
What is the impact of A-gamma fibers being affected in nerve fiber classification?
Loss of motor tone occurs when A-gamma fibers are affected.
Which sensations are affected by A-beta fibers in nerve fiber classification?
A-beta fibers are associated with the loss of touch and pressure sensation.
What functions are impaired when A-alpha fibers are affected according to nerve fiber classification?
Motor function and proprioception are lost when A-alpha fibers are affected.
What is the clinical progression stage characterized by Nerve Block Onset?
Nerve Block Onset order:
Type B (sympathetic)
Type C and Type A-delta (pain and temp)
Type A-gamma (motor tone)
Type A-beta (touch/pressure)
Type A-alpha (motor function/proprioception)
What does Nerve Block Recovery signify in the clinical progression of differential blockade?
Nerve Block Recovery refers to the regaining of nerve function post-local anesthesia, indicating the resolution of nerve block effects.
Which sense is typically the first to be blocked during anesthesia?
Temperature sensation is the first sense to be blocked during anesthesia.
How can the loss of temperature sensation be demonstrated in a patient under anesthesia?
Patients may not feel cold from an alcohol pad as a demonstration of the loss of temperature sensation under anesthesia.
What is the second sense to be blocked during anesthesia?
Pain sensation is the second sense to be blocked during anesthesia.
How can pain sensation be assessed in a patient under anesthesia?
Pain sensation can be assessed using stimuli like a pinprick.
Which sense is typically the last to be blocked during anesthesia?
Touch or pressure sensation is the last sense to be blocked during anesthesia.
What is utilized for monitoring sensory block during anesthesia?
The Modified Bromage Scale is utilized for monitoring sensory block during anesthesia.
What does a level of ‘0’ on the Modified Bromage Scale indicate?
A level of ‘0’ indicates no motor block according to the Modified Bromage Scale.
Describe the motor block at level ‘1’ on the Modified Bromage Scale.
Level ‘1’ reflects a slight motor block where the patient cannot raise an extended leg but can still move the knees and feet.
What does a level of ‘2’ on the Modified Bromage Scale represent?
A level of ‘2’ represents a moderate motor block where the patient cannot raise an extended leg or move the knee but can move the feet.
What does a level of ‘3’ signify on the Modified Bromage Scale?
A level of ‘3’ signifies a complete motor block where the patient cannot move the legs, knees, or feet.
What aspect of nerve function does the Modified Bromage Scale evaluate?
The Modified Bromage Scale evaluates the function of lumbosacral nerves.
Which regions does the Modified Bromage Scale focus on during assessment?
The Modified Bromage Scale focuses on the lower spine and sacral nerve areas during assessment.
What areas are not assessed by the Modified Bromage Scale?
The Modified Bromage Scale does not assess movement above the lower spine and sacral nerve areas.
How does sympathectomy affect preload in the cardiovascular system?
Sympathectomy causes veins to dilate, leading to blood pooling in the periphery and reducing blood return to the heart.
What effect does sympathectomy have on afterload in the cardiovascular system?
Sympathectomy partially dilates arterial circulation, decreasing afterload.
How does Systemic Vascular Resistance (SVR) change in healthy patients under neuraxial anesthesia?
Healthy patients experience a decrease in SVR by approximately 15%.
In elderly or cardiac patients, by how much can Systemic Vascular Resistance (SVR) decrease under neuraxial anesthesia?
In elderly or cardiac patients, SVR can decrease by up to around 25%.
How does a decrease in venous return and SVR impact Cardiac Output (CO) under neuraxial anesthesia?
The decrease in venous return and SVR leads to reduced stroke volume and subsequently reduced Cardiac Output.
Describe the initial response of Cardiac Output (CO) to changes caused by neuraxial anesthesia.
Cardiac Output may initially increase, then decrease over time due to changes in blood vessel dilation speeds.
What causes a decrease in heart rate under neuraxial anesthesia?
Blockade of Cardiac Accelerator Fibers reduces sympathetic tone, leading to decreased heart rate.
How does the Bezold-Jarisch Reflex contribute to changes in heart rate during neuraxial anesthesia?
The Bezold-Jarisch Reflex responds to ventricular underfilling, potentially causing significant bradycardia and asystole.
What is the Reverse Bainbridge Reflex, and how does it affect heart rate?
The Reverse Bainbridge Reflex is triggered by reduced stretching of the heart’s right atrium, influencing heart rate.
What are the potential consequences of unopposed parasympathetic tone during neuraxial anesthesia?
Unopposed parasympathetic tone can lead to profound bradycardia, hypotension, and sudden cardiac arrest.
When does sudden cardiac arrest typically occur after the onset of spinal anesthesia?
Sudden cardiac arrest typically occurs 20 to 60 minutes after the onset of spinal anesthesia.
What ratio of occurrence is observed for sudden cardiac arrest in relation to spinals and epidurals?
In young adults with high parasympathetic tone, the ratio is 7 in 10,000 for spinals and 1 in 10,000 for epidurals.
What factors are associated with sudden cardiac arrests during neuraxial anesthesia?
Sudden cardiac arrests are often associated with large blood loss and orthopedic cement placement.
Why is delaying treatment for spinal-anesthesia induced hypotension dangerous?
Delaying treatment can lead to increased mortality.
How does phenylephrine help prevent spinal-anesthesia induced hypotension?
Vasopressors like phenylephrine maintain blood pressure by constricting blood vessels.
Which drug can mitigate reflexes causing hypotension in spinal-anesthesia?
5-HT3 antagonists like ondansetron can mitigate reflexes like the Bezold-Jarisch reflex that lead to hypotension.
What is the recommended method of fluid administration immediately after a spinal block to prevent hypotension?
Co-loading with intravenous fluids (around 15 mL/kg) is recommended to prevent drops in blood pressure.
Why is pre-block hydration not routinely recommended for preventing spinal-anesthesia induced hypotension?
Pre-block hydration is not routinely recommended due to its minimal impact on preventing hypotension.
How does excessive fluid intake impact patients at risk of spinal-anesthesia induced hypotension?
Excessive fluid can overload the circulatory system, especially in patients with heart problems.
What role does positioning play in preventing spinal-anesthesia induced hypotension?
Positioning, like slight pelvic tilting, optimizes blood flow and reduces risks of hypotension.
How are ephedrine and epinephrine used in the treatment of spinal-induced hypotension?
They are utilized based on the patient’s heart rate and symptoms. Ephedrine preferred hypotension with bradycardia.
Phenylephrine preferred for hypotension with elevated or normal heart rate.
What anticholinergic medication may be administered for bradycardia in spinal-induced hypotension?
Atropine may be given to patients experiencing bradycardia.
What types of fluids are commonly used for maintaining adequate blood volume in spinal-induced hypotension?
Crystalloids or colloids are employed in fluid management for maintaining blood volume.