Monday, March 22, 2021

Routine Cesarean Section and Local Anesthetic Toxicity Case File

Posted By: Medical Group - 3/22/2021 Post Author : Medical Group Post Date : Monday, March 22, 2021 Post Time : 3/22/2021
Routine Cesarean Section and Local Anesthetic Toxicity Case File
Lydia Conlay, MD, PhD, MBA, Julia Pollock, MD, Mary Ann Vann, MD, Sheela Pai, MD, Eugene C. Toy, MD

Case 34
A 23-year-old woman, Gravida (G) 2 Para (P)1 with a footling breechpresentation and not in labor, presents to the labor and delivery suite for an elective cesarean section (c-section). She is in excellent physical condition, maintains a healthy lifestyle and only takes prenatal vitamins for medications. The patient is interested in discussing the options for anesthesia prior to the surgery. She has heard “bad things” about spinals. She has been fasting (NPO) since midnight, the night prior.

➤ What are the benefits of general versus regional anesthesia for this patient?

➤ What regional anesthetic techniques are available in this setting?

➤ What are the complications associated with regional anesthesia?


ANSWERS TO CASE 34:
Routine Cesarean Section and Local Anesthetic Toxicity

Summary: This is a healthy woman who presents for a routine, elective c-section.
Benefits of general versus regional anesthesia: Regional anesthesia relieves the pain of surgery, and minimizes the concentration of drugs within the maternal circulation, which could affect the fetus. It also avoids the drowsiness seen following general anesthesia, as well as that observed postoperatively with parenteral narcotics. Less drowsiness allows for an improved interaction between the mother and the baby. In the absence of complications, paralysis and end-tracheal intubation are not required with regional anesthesia. This is desirable because the physiologic changes of pregnancy may render the airway prone to injury, or intubation difficult due to edema and increased vascularity of the glottic and supra glottic structures. If a patient has a bleeding diathesis, if especially high concentrations of oxygen need to be administered, or if a patient is unable to cooperate during the operation, or unwilling to give consent for a regional technique then a general anesthetic is indicated.

Types of regional anesthesia available: Neuraxial blockade, both spinal and epidural, are types of regional anesthesia available for a routine cesarean section.

➤ Complications of neuraxial blockade: These techniques are very safe, but can cause significant morbidity. These include nerve damage, local anesthetic toxicity, high or total spinal, accidental subdural injection of local anesthetic, post-dural puncture headache (PDPH), infection from the site of injection, epidural abscess, and meningitis.


ANALYSIS

Objectives
1. Understand the changes of pregnancy and their implications regarding the choice of anesthetic.
2. Appreciate the differences in, and the indications for epidural and spinal anesthesia.
3. Understand complications of regional anesthesia as it relates to pregnancy.


Considerations
This is a healthy 23-year-old woman who presents for a c-section. She has received appropriate prenatal care, and has no other comorbidities. In discussion with the patient regarding the anesthetic plan, the advantages of regional anesthesia are emphasized, and she agrees to a spinal technique with general anesthesia as backup. A large-bore intravenous is placed; since bleeding might occur, the patient is brought to the operating room, and standard ASA monitors are applied. A spinal with bupivacaine is performed uneventfully with the patient in the sitting position, and she is asked to lie supine. Left uterine displacement is achieved by placing a pillow or “bump” under the left hip, to displace the gravid uterus from the aorta and inferior vena cava. This is an important maneuver, since aorto-caval compression is a common cause of decreased venous return and subsequent hypotension, leading to uteroplacental insufficiency.


APPROACH TO
Routine Cesarean Section and Local Anesthetic Toxicity

Data suggest that use of general anesthesia with end-tracheal intubation is decreasing across the country, and the preferred anesthetic for an uncomplicated cesarean section is a “single shot” spinal. Commonly known as subarachnoid block (SAB), a spinal anesthetic is a type of neuraxial blockade that involves dural puncture with a small needle, and the injection of a small amount of local anesthetic into the subarachnoid space which contains cerebrospinal fluid. A spinal anesthetic has a quick onset, a limited duration action, and a dense sensory and motor block.

Epidural anesthesia is also a type of neuraxial blockade. It involves using a large needle to enter the epidural space, and then injecting a large volume of a dilute concentration of local anesthetic into the space. The epidural space lies outside the dura, and contains nerve roots, and blood vessels which include Batson venous plexus, engorged in pregnancy and morbid obesity. In considering the engorged venous plexus and the large needle used, an inadvertent intravascular injection of local anesthetic is a common complication of an epidural anesthetic.

An epidural block may be performed as a “single shot,” whereby the epidural space is identified, the local anesthetic is injected, and the needle removed. Alternatively, a small-bore catheter can be inserted into the epidural space. This allows the periodic assessment of the adequacy of the block, and the administration of additional doses of local anesthetic once the anesthesia starts to recede. An epidural block has a slower onset, needs a greater volume of drug, and a variable duration since the catheter allows for repeated doses of local anesthetic.

Some of the nerve roots which are anesthetized by the local anesthetic during epidural anesthesia are quite large. Hence, it takes a high concentration and volume of drug, and a long time for the anesthetic to penetrate the nerve fiber and for the block to become effective. Because of this factor, as well as the unpredictable position of the catheter, which is “blindly” threaded, an epidural block is sometimes associated with a “patchy” blockade.

Yet another neuraxial technique is a “spinal/epidural.” This block involves a spinal anesthetic followed by placement of an epidural catheter. This type of block has the benefits of quick onset and a dense block, as well as extended duration with the presence of a catheter. It obviously carries risks of both spinal and epidural anesthesia.


CLINICAL APPROACH
The physiologic changes of pregnancy significantly affect and alter the anesthetic plan. These changes occur as a combination of hormonal effects, mechanics of the gravid uterus, increased metabolic and nutritional demands, fetal requirements, and the placental circulation. The salient ones are mentioned below.

Cardiovascular system: There is an increase in plasma volume without an increase in red cell mass resulting in a dilutional anemia. This increased volume results in increased stroke volume and heart rate, with a resultant increase in cardiac output. There is a reduction in peripheral vascular resistance; hence there is no real change in blood pressure to accommodate the increased cardiac output.

Supine hypotension syndrome: Ten percent of parturients develop severe hypotension, and indeed, a shock state in the supine position as a result of vena caval compression by the gravid uterus. This can be avoided by positioning a pillow under the left lower back. This maneuver results in left uterine displacement and the cava is decompressed.

Respiratory system: Pregnancy is associated with an increase in both minute ventilation and work of breathing to accommodate the increased metabolic demands. Hormones, and an increase in carbon dioxide production drives the increased ventilatory demand. As the pregnancy advances, the breathing pattern becomes more diaphragmatic. Closing capacity remains unchanged, but since functional residual capacity is reduced, the small airways are more prone to collapse and atelectasis. This phenomenon manifests under anesthesia as early desaturation during induction of general anesthesia. Parturients should undergo prolonged preoxygenation (3-5 minutes) to counter the effects of small airway collapse resulting in oxygen desaturation.

Changes in the airway: Capillary engorgement of the oropharynx, vocal cords, and the airway mucosa makes tracheal intubation challenging. Minor manipulations of the airway may result in trauma and significant bleeding, producing further airway compromise.

Hematologic changes: Pregnancy induces a hypercoagulable state by increasing most of the clotting factors. An increased risk of deep vein thrombosis and pulmonary embolism result. There is a relative decrease in platelet count in the third trimester due to an increase in platelet activity. Thrombocytopenia is a relative contraindication for performing a neuraxial block.

Gastrointestinal system: There is an increased risk of pulmonary aspiration of gastric contents due to a number of hormonal and mechanical changes of pregnancy. Progesterone decreases the tone of the lower esophageal sphincter, while the gravid uterus decrease the angle of the lesser curvature and labor pain delays gastric emptying. All of these factors increase the risk of aspiration during induction of general anesthesia. All parturients are considered to be strict “full stomachs” no matter when they last ate.

Central nervous system: Pregnant women are more susceptible to the effects of both regional and general anesthetics. This is particularly true for local anesthetics. Less local anesthetic is required than the nonparturient to achieve the same anesthetic level. In addition to hormonal changes which render the parturient more susceptible, the gravid uterus also contributes by compressing the venous plexus in the epidural space. This relative reduction of the epidural space displaces epidural drugs displacement cephalad, resulting in a higher sensory level from a local anesthetic block.


The Fetoplacental Unit
The placenta is composed of intervillous tissue derived from both mother and fetus, which transmits about 80% of the uterine blood flow. Approximately 40% to 50% of the fetal cardiac output traverses the placenta. Hence, changes in uterine blood flow affect fetal circulation. Uterine blood flow lacks autoregulation, so any changes in maternal blood flow are transmitted directly to the fetus. Vasopressors such as α-adrenergic agonists (phenylephrine) cause increased uterine vascular resistance, and reduce uterine blood flow.

Local anesthetics cross membranes, including the uteroplacental membrane, in their ionized form. In the event that they cross into a fetus with acidosis, the local anesthetic becomes ionized from the H+ circulating in the fetus, and then cannot cross back into the mother to maintain equilibrium. This syndrome is called “ion-trapping,” and since local anesthetics also have general anesthetic properties, can result in an exacerbation of fetal distress.

Significant features of other drugs that cross the placenta and cause effects on the fetus are small size, high-lipid solubility, and low protein binding. Maternal drug levels and maternal and fetal pH also play a role in placental drug transfer.


Anesthetic Techniques for Cesarean Section
Table 34–1 presents the effects of neuraxial blockade. Regional anesthetic techniques result in lower circulating drug concentrations in the mother to be potentially transmitted to the fetus. In addition, physiologic changes

Table 34–1 EFFECTS OF NEURAXIAL BLOCKADE

SYSTEM

SPINAL

EPIDURAL

Cardiovascular

Sympathectomy resulting

in a decreased heart rate

and blood pressure

With spinal the

sympathectomy extends

about 2-6 dermatomes

above the level of

sensory anesthesia.

With epidural, the

sympathectomy is at the

same dermatomal level as

the sensory anesthesia.

Also, the blood pressure drop

is more gradual and of less

magnitude. It also can be

modified by decreasing the

dose of the drug.

Respiratory

Inspiratory muscles

control ventilation while

expiratory muscles control

cough and clearing of

secretions from the lung.

Respiratory arrest, while

rare, is usually secondary to

medullary hypoperfusion

rather than muscle paralysis

Decrease in vital

capacity with decrease

in tidal volume (usually

secondary to decreased

expiratory reserve

volume because of

abdominal muscle

paralysis).

Similar to spinal, except the

level is dose dependent hence

can be modified with a

catheter in place.

Gastrointestinal

Hyperperistalsis

secondary to

unopposed vagal

activity usually presents

as nausea during a SAB.

Protective effect on gastric

mucosa in the postoperative

stage, as intramucosal pH is

higher with epidural than

systemic analgesia.

Renal

Urinary retention may

need a Foley catheter.

Urinary retention usually

occurs secondary to

paralysis of bladder

function. Lower doses of

local anesthetic paralyze

bladder function, than

doses that paralyze lower

extremity nerves.

No difference with spinal


are observed in the airway which increase the risk of pulmonary aspiration and difficult intubation. Spinal or epidurals are the most common techniques used for routine c-sections. However, there are well-documented complications of neuraxial blockade.

Post-dural puncture headache is the most common complication of a spinal block. It usually presents 24 hours to 7 days after the spinal has been administered, as a severe headache, positional in nature. Rising to sitting from laying down, or even walking to the bathroom precipitates the headache. It is not associated with signs of infection or photophobia. PDPH may be very painful. Supportive management such as hydration and bed rest helps in mild cases of PDPH. Adjuvant therapies such as caffeine and painkillers have met with varying degrees of success.

For severe cases of PDPH, a blood patch has been recommended. One hypothesis for mechanism of pain in PDPH is a continuous leakage of cerebrospinal fluid from the subarachnoid space, worsened by rising from a supine position. The blood patch uses autologous blood from a sterile venipuncture to supposedly seal off the puncture site by forming a clot. This is accomplished by epidural puncture and injecting the autologous blood. Reports have credited the blood patch with 96% success in the sure of PDPH. However, this technique remains controversial within the pain management community, since no outcome studies have been conducted to assess the true risks of this procedure.

Nerve injury is an uncommon complication of neuraxial blockade. The incidence of injury increases if the patient experiences an “electric shock” like pain during spinal or epidural place. This pain signals intraneural needle placement which could lead to nerve injury. If intraneural injection occurs, then the needle must be promptly removed and the patient questioned about continued pain. The neural injury often results in a transient paresthesia lasting up to several months, at the area of distribution of the nerve. Regrowth of the nerve results in recovery. Long-term nerve damage is very rare.

In the laboring patient under neuraxial blockade, there is no painful feedback from the possible overstretching of lumbar muscles which maybe implicated in the occurrence of back pain after spinal or epidural anesthesia. Although back pain is not uncommon, there have no reports of anatomic causes of back pain or lower back injury after neuraxial blockade.

Local anesthetic (LA) toxicity may manifest as central nervous system (CNS) or cardiovascular system (CVS) complications, usually related to an overdose of LA. Cardiovascular complications, particularly hypotension or bradycardia, are often the only manifestation of severe local anesthetic toxicity, and can even occur an hour or more after injection. In addition to progressive hypotension, bradycardia can lead to asystole. Ventricular ectopy, multiform ventricular tachycardia, and ventricular fibrillation are also indicative of cardiotoxic injury.

CNS symptoms usually lag behind CVS complications, and are often subtle at onset or absent. CNS excitation (agitation, confusion, twitching, seizure), depression (drowsiness, obtundation, coma, or apnea), or nonspecific neurologic symptoms (metallic taste, circumoral paresthesias, diplopia, tinnitus, dizziness) are each typical of LA toxicity.

An intravascular injection may present with nonspecific signs such as a metallic taste or tinnitus, and is unrelated to the dose of local anesthetic. However, if undetected, an intravascular injection can lead to the CNS and CVS complications described earlier. Indeed, to facilitate the diagnosis of possible intravascular injection with epidural, epinephrine is often added to the local anesthetic test dose. If the test does is associated with tachycardia, the injection is aborted.

Should a bloody tap or an intravascular injection occur with spinal or epidural injection, the injection should be aborted and the procedure repeated at another interspace. If these complications occur, treatment is supportive, and includes airway management and resuscitation. The arrhythmias or seizures should be treated pharmacologically as indicated.

A subdural injection of local anesthetic, or a “high” or “total” spinal is detected by the sudden, unexpected loss of consciousness, apnea, and cardiovascular collapse, sometimes accompanied by seizures. Treatment is supportive.


Comprehension Questions

34.1. A 22-year-old patient presents to the OB suite for a vaginal delivery and is interested in labor analgesia. She wants to know possible complications of a labor epidural. She claims her cousin had a labor epidural and now has long-term back pain and wants to know if she is likely to experience the same type of back injury. Back pain following an epidural is most likely due to which of the following?
A. Direct result of injury to a nerve by the needle
B. Can portend impending paralysis
C. Results from an inadvertent stretching of muscles
D. Long lasting, as experienced by her cousin

34.2. During injection of local anesthetic in the epidural space, the patient loses consciousness. You suspect which of the following?
A. Vagal reaction
B. Drug overdose
C. Subdural injection
D. Dehydration

34.3. A 28-year-old woman is wheeled into the operating room for a c-section, and placed on the operating room table. As monitors are placed, her blood pressure is 68/40 and she reports feeling dizzy. You first response is which of the following?
A. Left uterine displacement
B. Fluid administration
C. Pressor administration
D. Oxygen by nasal cannula


ANSWERS
34.1. A. Back pain is associated with but not caused by neuraxial blockade. A laboring patient who is free from labor pains due to a neuraxial blockade is likely to stretch muscles, leading to back pain. There is small incidence of nerve injury associated with neuraxial blockade. It usually manifests as paresthesia over the region of nerve supply, is usually temporary in duration, and may last as long as 3 months. Nerve regrowth usually causes cessation of symptoms. Paralysis is a complication of spinal cord injury, site of neuraxial blockade for labor analgesia or for c-section is at L3 to L4 level. The spinal cord ends at L1 in adults and cord injury is rare.

34.2. C. Subdural injection of the local anesthetic causing a total spinal with loss of consciousness. The treatment is supportive.

34.3. A. The hypotension is almost certainly caused by aorto-caval syndrome, secondary to compression of the aorta and/or inferior vena cava by the gravid uterus. Once left uterine displacement is performed, there is decompression and resumption of venous return and resolution of the hypotension. If the patient had recently received a local anesthetic bolus via a spinal or epidural injection, vasodilatation from the local anesthetic maybe implicated in the cause of hypotension.


Clinical Pearls
➤ Left uterine displacement relieves inferior vena caval and/or aortic compression and restores venous return and establishes maternal and fetal perfusion.
➤ General anesthesia is associated with significant maternal morbidity such as failed airway management, aspiration, inadequate ventilation, and a lower Apgar score in the fetus.
➤ Spinal or epidural anesthesia is the preferred anesthetic technique for caesarian section with few complications to the fetus.
➤ The gravid uterus causes epidural venous congestion, which may increase the spread of local anesthetic, hence drug dosing needs to be adjusted appropriately.
➤ Hypotension associated with neuraxial techniques can be avoided with fluid replacement and careful dosing of local anesthetic.

References

Anesthesia for obstetrics. In: Miller RD. Miller’s Anesthesia. 6th ed. Churchill Livingstone; 2005:Chapter 58. 

Chestnut DH. Obstetric Anesthesia—Principles and Practice. 3rd ed. Elselvier Mosby.

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