Flashcards in Neuraxial Analgesia Deck (28)
T or F: Epidural infusions lasting < 24 hours do not appear to offer any clear cardiovascular advantages.
T or F: Epidurally administered opioids have the distinct advantage of producing analgesia without causing significant sympatholytic effect or motor blockade.
True- analgesia occurs by way of a spinal mechansim, which occurs following diffusion of the drug into the spinal fluid.
T or F: Opioids with intermediate lipophilicity have the ability to easily move between aqueous and lipid regions of arachnoid membrane.
Morphine has the greater bioavailability in spinal cord.
Thoracic epidural catheter placement is recommended for both thoracic and upper abdominal surgical procedures because of observed:
- improvement in coronary artery blood flow
- attenuation of pulmonary complications
- reduction in duration of postoperative ileus
Epidural administration of hydrophilic opioids vs lipophilic opioids
- in general, epidural administration of hydrophilic opioids tends to have slow onset, long duration, and mechanism of action that is primarily spinal in nature.
- epidural administration of lipophilic opioids has quick onset, short duration, and supraspinal mechanism of action secondary to rapid systemic uptake.
What is the CSF volume in humans?
Approximately 100-160 mL
What is the rate of CSF production in humans?
How frequently is the entire CSF volume replaced?
Every 6 hours
True or false: CSF cannot be relied on to distribute drugs in the subarachnoid space.
True or false: CSF does not circulate, rather it oscillates in the cephalocaudal axis with a frequency equal to the heart rate.
True or false: spinal blockade leads to decreased sympathetic outflow, leading to unopposed parasympathetic influences.
True or false: Cardiac arrest in healthy patients following spinal anesthesia has been thought to be mediated by unopposed vagal influences on the heart when the cardioaccelerator fibers (T1-T4) are blocked in susceptible individuals.
What does differential block refer to?
Refers to the clinically important phenomenon in which nerve fibers have different sensitivities to local anesthetic blockade.
An example would be that sympathetic nerve fibers appear to be blocked by the lowest concentration of local anesthetic followed in order by fibers responsible for pain, temperature, touch, and motor function.
True or false: Spinal and epidural anesthesia differential block is manifested as a spatial separation that is believed to be a result of a gradual decrease in local anesthetic concentration within the CSF as a function of distance from the site.
True or false: central neuraxial block produces sedation, potentiates the effects of sedative hypnotic drugs, and markedly decreases the MAC of volatile anesthetics.
What are the most important and most common physiologic changes during spinal and epidural anesthesia?
Blockade of sympathetic efferents is the principle mechanism by which spinal anesthesia produces cardiovascular derangements.
Spinal anesthesia will predictably decrease preload and afterload due to the interruption of sympathetic tone.
True or false: hypotension during spinal anesthesia is the result of both arterial and venodilation.
True. Venodilation increases volume in capacitance vessels, thereby decreasing venous return and right sided filling pressures (end-diastolic pressure).
The fall in preload is thought to be the principal cause of decreased cardiac output during high spinal anesthesia.
True or false: high blocks associated with abdominal and intercostal muscle paralysis can impair ventilatory functions requiring active exhalation.
True: expiratory reserve volume, peak expiratory flow, and maximum minute ventilation may be sigificant reduced by high spinal and epidural blocks. The negative impact of high blocks on active exhalation suggests caution when using spinal or epidural anesthesia in patients with COPD who rely on accessory muscles of respiration to maintain a clear airway or adequate ventilation.
True or false: Spinal anesthesia will affect both inspiratory and expiratory mechanics.
True. Neuraxial anesthesia affects intercostal (inspiration and expiration) and abdominal (expiration/cough) muscles and decrease pulmonary reserve.
In a severe COPD'er, which is preferable: general or spinal anesthesia?
Neuraxial anesthesia. In a severe COPD'er, tracheal intubation and general anesthesia have many many many deleterious postoperative effects on pulmonary function.
In spinal anesthesia, what affects the degree of sympathetic block:
- Pt size?
- compression of dural sac?
- degree of sympathetic block is proportional to the dose
- The greater the pt size, the less the sympathetic block
- yes, pregnancy can decrease CSF volume
- degree of sympathetic block is greater in supine position vs upright position for hyperbaric anesthetic
Which property of local anesthetics correlates with potency?
Which property of local anesthetics correlates with duration?
Which property of local anesthetics correlates with onset?
List the rate of absorption for local anesthetics from greatest to least.
IV > tracheal > intercostal > caudal > paracervical > epidural > brachial plexus > sciatic > subq
What are respiratory changes under neuraxial analgesia without general anesthesia? Address the following:
2- Expiratory volume
3- Accessory muscles
4- Feedback from chest wall
5- Gas exchange and respiratory drive
6- Sensitivity to PaO2 and PCO2
7- Blood pressure
8- Intrathoracic blood volume
9- lung volume and ventilatory control
1- FRC is preserved due to the lower diaphragmatic position
2- Reduced expiratory volume that may hamper sputum and secretion clearing
3- paralysis and weakness of accessory muscles
What are classic symptoms of a high spinal?
Numbness and/or tingling in the hands and shortness of breath. High spinals may occur up to 20-30 min after the onset of the block. You must monitor the patient to assess for a continually rising spinal block.