Podcast
Questions and Answers
What is the generally accepted guideline for the volume of local anesthetic required per segment to be blocked in adults?
What is the generally accepted guideline for the volume of local anesthetic required per segment to be blocked in adults?
Which of the following agents is commonly used for short- to intermediate-acting surgical anesthesia?
Which of the following agents is commonly used for short- to intermediate-acting surgical anesthesia?
What is a primary consideration when using additives to local anesthetics in epidural procedures?
What is a primary consideration when using additives to local anesthetics in epidural procedures?
In which scenario is caudal anesthesia commonly employed?
In which scenario is caudal anesthesia commonly employed?
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What must be ensured when using local anesthetic solutions for epidural or caudal use?
What must be ensured when using local anesthetic solutions for epidural or caudal use?
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What is a clinical manifestation associated with the neuroendocrine stress response?
What is a clinical manifestation associated with the neuroendocrine stress response?
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Which of the following is a major contraindication to neuraxial anesthesia?
Which of the following is a major contraindication to neuraxial anesthesia?
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What effect does neuraxial block have on gastrointestinal function?
What effect does neuraxial block have on gastrointestinal function?
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Which anticoagulant requires documentation of a normal prothrombin time and INR prior to neuraxial block?
Which anticoagulant requires documentation of a normal prothrombin time and INR prior to neuraxial block?
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What is the recommended action regarding the use of aspirin before neuraxial blockade?
What is the recommended action regarding the use of aspirin before neuraxial blockade?
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Which of the following is a relative contraindication to neuraxial anesthesia?
Which of the following is a relative contraindication to neuraxial anesthesia?
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What is the expected outcome of a neuraxial block-induced sympathectomy?
What is the expected outcome of a neuraxial block-induced sympathectomy?
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What is one of the potential benefits of using neuraxial anesthesia during surgery?
What is one of the potential benefits of using neuraxial anesthesia during surgery?
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How long should potent antiplatelet agents like clopidogrel be stopped prior to neuraxial blockade?
How long should potent antiplatelet agents like clopidogrel be stopped prior to neuraxial blockade?
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What structure contains cerebrospinal fluid (CSF)?
What structure contains cerebrospinal fluid (CSF)?
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What is the typical termination point of the spinal cord in adults?
What is the typical termination point of the spinal cord in adults?
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Which type of surgery is neuraxial anesthesia especially useful for?
Which type of surgery is neuraxial anesthesia especially useful for?
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What is a characteristic of spinal anesthesia compared to epidural anesthesia?
What is a characteristic of spinal anesthesia compared to epidural anesthesia?
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What is one reason why upper abdominal procedures are less commonly performed with spinal or epidural anesthesia?
What is one reason why upper abdominal procedures are less commonly performed with spinal or epidural anesthesia?
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What layers make up the meninges?
What layers make up the meninges?
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Which space is better defined and bounded by the dura and ligamentum flavum?
Which space is better defined and bounded by the dura and ligamentum flavum?
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What is the duration of action for hyperbaric bupivacaine when used for spinal anesthesia?
What is the duration of action for hyperbaric bupivacaine when used for spinal anesthesia?
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Which technique provides a broader range of applications than a traditional spinal anesthetic?
Which technique provides a broader range of applications than a traditional spinal anesthetic?
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What is a common gauge size of the standard epidural needle used?
What is a common gauge size of the standard epidural needle used?
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What is a potential risk when a full epidural dose is mistakenly injected intrathecally?
What is a potential risk when a full epidural dose is mistakenly injected intrathecally?
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Which of the following local anesthetics has a rapid onset and shorter duration when compared to others?
Which of the following local anesthetics has a rapid onset and shorter duration when compared to others?
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Which part of the epidural technique provides continuous infusion for anesthesia?
Which part of the epidural technique provides continuous infusion for anesthesia?
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What is the purpose of a test dose administered during epidural anesthesia?
What is the purpose of a test dose administered during epidural anesthesia?
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What is a key feature of the Tuohy needle used in epidural anesthesia?
What is a key feature of the Tuohy needle used in epidural anesthesia?
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What does a hyperbaric spinal anesthetic solution do when the patient is in a head-down position?
What does a hyperbaric spinal anesthetic solution do when the patient is in a head-down position?
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Which type of spinal needle decreases the incidence of postdural puncture headache?
Which type of spinal needle decreases the incidence of postdural puncture headache?
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What is the preferred time frame for administering neuraxial anesthesia after the last dose of Low-Molecular-Weight Heparin (LMWH)?
What is the preferred time frame for administering neuraxial anesthesia after the last dose of Low-Molecular-Weight Heparin (LMWH)?
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What factor primarily affects the migration of local anesthetic in CSF?
What factor primarily affects the migration of local anesthetic in CSF?
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Which position is described as maximizing the “target” area for neuraxial blocks due to spinal flexion?
Which position is described as maximizing the “target” area for neuraxial blocks due to spinal flexion?
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What standard should be applied during the performance of neuraxial blocks?
What standard should be applied during the performance of neuraxial blocks?
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Which spinal needle type is characterized by a cutting design and end injection?
Which spinal needle type is characterized by a cutting design and end injection?
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Which position can help achieve a 'saddle block' after spinal anesthesia?
Which position can help achieve a 'saddle block' after spinal anesthesia?
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In which position do patients typically assume a 'fetal position' for neuraxial blocks?
In which position do patients typically assume a 'fetal position' for neuraxial blocks?
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What is the effect of increasing the dosage of local anesthetic during spinal anesthesia?
What is the effect of increasing the dosage of local anesthetic during spinal anesthesia?
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What is a critical consideration for the facility where neuraxial blocks are performed?
What is a critical consideration for the facility where neuraxial blocks are performed?
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What is a disadvantage of using Buie's (Jackknife) position for neuraxial procedures?
What is a disadvantage of using Buie's (Jackknife) position for neuraxial procedures?
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What type of local anesthetic solutions are used for spinal anesthesia?
What type of local anesthetic solutions are used for spinal anesthesia?
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Which of the following is NOT a benefit of nonpharmacologic patient preparation before neuraxial blocks?
Which of the following is NOT a benefit of nonpharmacologic patient preparation before neuraxial blocks?
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What is a common consequence of using a hyperbaric solution when the patient is supine?
What is a common consequence of using a hyperbaric solution when the patient is supine?
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Which spinous process is generally noted to be at the same level as the inferior angle of the scapulae?
Which spinous process is generally noted to be at the same level as the inferior angle of the scapulae?
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Study Notes
Neuraxial Anesthesia
- Studies indicate that using neuraxial blockade (alone or with general anesthesia) can reduce postoperative complications and mortality.
- Neuraxial blocks can decrease the incidence of venous thromboembolism, cardiac complications, bleeding, transfusion requirements, vascular graft occlusion, pneumonia, and respiratory depression in high-risk patients undergoing upper abdominal or thoracic surgery.
- The spinal column forms a double C shape, convex anteriorly in cervical and lumbar regions.
- The meninges consist of three layers: pia, arachnoid, and dura mater.
- Cerebrospinal fluid (CSF) is located between the pia and arachnoid layers in the subarachnoid space.
- The epidural space is a potential space within the spinal canal, bounded by the dura and ligamentum flavum.
Spinal Cord Anatomy
- The spinal cord extends from the foramen magnum to L1 in adults.
- In children, the spinal end is at L3 and moves upwards with age.
Mechanism of Neuraxial Blockade
- The principal site of action for neuraxial blockade involves the nerve roots.
- Local anesthetic is injected into the CSF (spinal anesthesia) or epidural space (epidural/caudal anesthesia).
- Spinal anesthesia uses a relatively small dose/volume of local anesthetic to achieve a dense sensory and motor block.
- Epidural and caudal anesthesia require much larger volumes of local anesthetic to achieve the same concentration in nerve roots.
Indications for Neuraxial Blocks
- Neuraxial blocks are useful for procedures below the neck, especially lower abdominal, inguinal, urogenital, rectal, and lower extremity surgeries.
- Lumbar spinal surgery can be performed under spinal anesthesia.
- Upper abdominal surgeries (e.g., gastrectomy) are less frequently performed using spinal or epidural anesthesia due to potential challenges in achieving sufficient sensory blockade for patient comfort.
Types of Blocks: Somatic
- Sensory blockade inhibits both somatic and visceral pain signals.
- Differential blockade results in sympathetic blockade, often affecting a segment or two more cephalad than the sensory or motor block.
Types of Blocks: Autonomic
- Interruption of efferent autonomic transmission leads to sympathetic blockade.
- Sympathetic nerves exit the spinal cord from T1 to L2.
- Neuraxial anesthesia does not block the vagus nerve (main parasympathetic pathway).
- The physiological responses to neuraxial blockade stem from decreased sympathetic and/or unopposed parasympathetic tone.
- Neuraxial blocks cause variable drops in blood pressure and heart rate.
- High sympathetic blocks may prevent compensatory vasoconstriction and may cause bradycardia and profound hypotension.
- Unopposed vagal tone can potentially cause cardiac arrest during spinal anesthesia.
Minimizing Hypotension During Neuraxial Blockade
- Patient hydration and volume status are important considerations.
- Volume loading (10-20 mL/kg IV fluid) may not prevent hypotension in healthy patients.
- Left uterine displacement in pregnant patients during the third trimester can minimize physical obstruction to venous return.
- Treat hypotension with vasopressors and symptomatic bradycardia with atropine.
- Ephedrine is a vasopressor that increases heart rate and contractility.
Systemic Neuroendocrine Response to Surgery
- Surgical trauma triggers a systemic neuroendocrine response.
- This includes increased levels of ACTH, cortisol, epinephrine, norepinephrine, and vasopressin, alongside activation of the renin-angiotensin-aldosterone system.
- Clinical signs may include intra-and postoperative hypertension, tachycardia, hyperglycemia, and altered renal function.
- Neuraxial blockade can partially or completely suppress this response.
Effects on Gastrointestinal Function
- Neuraxial block-induced sympathectomy results in a small, contracted gut with active peristalsis.
- Postoperative epidural analgesia, using local anesthetics with minimal systemic opioids, accelerates the return of gastrointestinal function after abdominal procedures.
Urinary Retention
- Loss of autonomic bladder control causes urinary retention until the blockade resolves.
- Perioperative urinary catheterization is often prudent when regional anesthesia might affect bladder function for sustained periods.
Contraindications to Neuraxial Anesthesia
- Major: Patient refusal, bleeding tendency, severe hypovolemia, elevated intracranial pressure, and infection at injection site.
- Relative: Severe valvular heart disease and sepsis or bacteremia (may theoretically increase risk of spreading infection). Preexisting neurological deficits and psychiatric conditions (e.g., dementia, psychosis, emotional instability) should be considered with caution.
Anticoagulants and Antiplatelets
- Oral anticoagulants (e.g., Warfarin): Confirm a normal prothrombin time (PT) and INR before the block.
- Antiplatelet drugs: Discontinue aspirin and other NSAID medications before anesthesia. Discontinue more potent agents (e.g., ticlopidine, clopidogrel) 7-14 days before.
- Heparin: Prophylactic minidose subcutaneous heparin is not a contraindication. However, avoid neuraxial anesthesia in patients taking therapeutic doses of heparin with increased partial thromboplastin time. Low-molecular-weight heparin (LMWH) use should be considered 12 hours after the last dose.
Technical Considerations
- Neuraxial blocks should only be performed in facilities equipped for intubation, resuscitation, and general anesthesia.
- Maintain standard monitoring.
- Non-pharmacological preparation of the patient (to reduce anxiety) is helpful.
- Supplemental oxygen may be needed during sedation.
- Maintain standard sterility.
Surface Anatomy
- Spinous processes are palpable landmarks for midline identification.
- Cervical, thoracic, and lumbar landmarks (e.g. spinous processes, scapula, iliac crests) are used for positioning.
Patient Positioning
- Sitting: Useful for general positioning and enhancing access when patients have to be placed in lateral positions for obese patients. Spinal flexion results in superior exposure/ visualization.
- Lateral decubitus (lateral): Preferred position for neuraxial block. Patients lie on their side with knees flexed to the abdomen or chest.
- Buie's (Jackknife): Used often for anorectal procedures.
Spinal Anesthesia Technique
- Spinal anesthetic solutions block nerve conduction by suppressing signals.
- Needle insertion proceeds through skin, ligamentum flavum, and dura-arachnoid membrane to the subarachnoid space.
- Successful dural puncture is confirmed by the free flow of CSF.
Spinal Needles
- Spinal needles come in various sizes, lengths, and bevel/tip designs.
- All needles have a removable stylet to avoid tracking epithelial cells into the subarachnoid space.
- Sharp-tip and blunt-tip designs exist (Sharp-tip [cutting] needles may decrease post-dural puncture headache incidence).
Factors Influencing Spinal Block Level
- Baricity: Density of the anesthetic solution influences its movement in CSF.
- Patient position: Head-down position causes hyperbaric solutions to move cephalad, while the reverse holds true.
- Drug dosage: Higher dosages result in more cephalad blockade.
- Other factors: weight, age, height, pregnancy, and injection site can potentially affect anesthesia spread
- Sitting position (saddle block): The position of the patient may help in achieving caudal blocks.
Spinal Anesthetic Agents
- Only preservative-free solutions are used in spinal anesthesia.
- Adding vasoconstrictors (epinephrine) and opioids enhance the quality or prolong the duration of spinal anesthesia.
- Hyperbaric bupivacaine, tetracaine are commonly used, and these tend to have slower onset but longer duration than others.
- Lidocaine and procaine have faster onset and shorter duration.
Epidural Anesthesia
- Continuous epidural anesthesia is a neuraxial technique with a wider range of applications than a single-dose spinal anesthetic.
- It is performed at the lumbar, thoracic, or cervical level (Sacral epidural anesthesia is a caudal block).
- Epidural blocks are used for surgical procedures, pain control, and chronic pain management (single shot or continuous infusion).
- Epidural anesthesia is slower in onset (10-20 minutes) compared with spinal blocks and may not provide as profound anesthesia. However it avoids the need for motor-blocking anesthetic.
Epidural Needle and Catheter
- Standard epidural needle features a 17-18 gauge, curved tip that helps to avoid puncturing the dura.
- Epidural catheters facilitate continuous infusions for extended pain management.
- Utilizing a 19- or 20-gauge catheter in a 17- or 18-gauge epidural needle allows for easier introduction.
Epidural Anesthesia Considerations
- Toxic effects can occur with intravascular injection of full epidural doses, so incremental dosing is required (test injection and incremental dose adjustments).
- Aspiration prior to injection is not sufficient enough to prevent intravascular injection.
- Factors affecting the level may not be as predictable as with spinal anesthesia.
- Suitable concentrations of local anesthetic are required per segment (in adults).
- Opioids affect the quality of the block more than the duration.
Caudal Anesthesia
- Caudal anesthesia is the sacral portion of the epidural space.
- It is commonly used in pediatric procedures and anorectal surgeries.
- Caudal anesthesia is often combined with general anesthesia for intraoperative and postoperative purposes, in procedures below the diaphragm.
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Test your knowledge on the guidelines and considerations for neuraxial anesthesia. This quiz covers essential aspects including local anesthetic volume, contraindications, and clinical manifestations. Perfect for medical students and professionals in anesthesiology.
