Anesthesia Flashcards
A woman with preeclampsia with severe features undergoes epidural anesthesia. Following anesthesia induction she complains of numbness and weakness in her fingers bilaterally. The most likely diagnosis is:
A. Allergic reaction
B. Stroke
C. Severe features of preeclampsia
D. High epidural
E. Lumbar hematoma
D. Numbness and weakness of the fingers and hands following regional anesthesia indicate that the level of anesthesia has reached the cervical level (C6-C8) which is dangerously close to the innervation of the diaphragm (C3-C5). Optimally with epidural the level should be T10 for a vaginal delivery and T4 for a cesarean delivery. The putative reasons for high epidural include a miscalculated drug dose or subarachnoid injection. If the diaphragm is not paralyzed, the patient is breathing and cardiovascular stability is maintained, administration of oxygen and reassurance may suffice. Total spinal anesthesia occurs when the level of anesthesia rises dangerously high, resulting in paralysis of the respiratory muscles including the diaphragm, which will require respiratory support with a bag mask or possibly intubation. The incidence of total spinal anesthesia after epidural anesthesia is 1 in 16,200. A true allergic reaction to amide-type local anesthetic (lidocaine, bupivacaine) is extremely rare. Lumbar hematomas present as severe back or neck pain. A stroke most often presents unilaterally. Severe features of preeclampsia include headache, blurry vision, or right upper quadrant pain. Gabbe Obstetrics 6th edition. Chapter 17, page 371-372
To which dermatomal level is regional anesthesa required for cesarean delivery?
A. T2
B. T4
C. T6
D. T8
E. T10
Answer:
B. Pain during the first stage of labor results from a combination of uterine contractions and cervical dilation. Painful sensations travel from the uterus through visceral afferent (sympathetic) nerves that enter the spinal cord through the posterior segments of thoracic spinal nerves 10, 11, and 12. During the second stage of labor, additional painful stimuli are added as the fetal head distends the pelvic floor, vagina, and perineum. The sensory fibers of sacral nerves 2, 3, and 4 (i.e., the pudendal nerve) transmit painful impulses from the perineum to the spinal cord during second stage and during any perineal repair. During cesarean delivery, although the incision is usually around thoracic spinal nerve 12 (T12) dermatome, anesthesia is required to a level of thoracic spinal nerve 4 (T4) to completely block peritoneal discomfort, especially during uterine exteriorization. Pain after cesarean delivery is due to both incisional pain and uterine involution.
. Which of the following is the mechanism underlying maternal hypotension in the setting of regional anesthesia?
A. Sympathetic block
B. Decreased catecholamine release
C. Decreased heart rate
D. Sedation
Answer:
A. Hypotension is defined variably, but most often as a systolic blood pressure of less than 100 mm Hg or a 20% decrease from baseline. It occurs after about 10% of spinal or epidural blocks given during labor. Hypotension occurs primarily as a result of the effects of local anesthetic agents on sympathetic fibers, which normally maintain blood vessel tone. Vasodilation results in decreased venous return of blood to the right side of the heart, with subsequent decreased cardiac output and hypotension. A secondary mechanism may be decreased maternal endogenous catecholamines following pain relief. Once diagnosed, hypotension is corrected by increasing the rate of intravenous fluid infusion and exaggerating left uterine displacement. If these simple measures do not suffice, a vasopressor is indicated. The vasopressor of choice has evolved from ephedrine, given in 5- to 10-mg doses, to phenylephrine, in 50- to 100-mcg increments. Ephedrine is a mixed α- and β- agonist, and was thought to be less likely to compromise uteroplacental perfusion than the pure α-agonists. Of concern, ephedrine is associated with fetal tachycardia. Recent clinical studies have suggested that phenylephrine may be given safely to treat hypotension during neuraxial anesthesia for cesarean delivery, and the drug indeed may lead to higher umbilical artery pH values in the fetus and less maternal nausea and vomiting. Gabbe, Normal and Problem Pregnancies, 6 Edition.
A 24 yo G1P0 with a past medical history of opiate abuse (now on methadone maintenance therapy) presents in active labor at 6 cm. Which narcotic is contraindicated?
A. Morphine
B. Nalbuphine (Nubain)
C. Fentanyl
D. Meperidine
E. All of the above
B. Methadone is a synthetic opioid used in the maintenance treatment of opioid dependency due to its long half-life (on average 36 hours). In pregnancy, methadone maintenance therapy has been shown to decrease criminal activity, increase compliance with prenatal visits, and decrease the risk of infections such as hepatitis B, hepatitis C, HIV, STIs, cellulitis, bacterial endocarditis, and tuberculosis. Mixed agonist-antagonists such as nalbuphine (Nubain) and butorphanol (Stadol) are contraindicated because they may displace the maintenance opioid from receptors and precipitate acute opioid withdrawal. Morphine (naturally occurring opioid), fentanyl (synthetic opioid) and meperidine (synthetic opioid) do not have the antagonist effects, thus will not precipitate withdrawal. There is no point in labor when IV narcotics are absolutely contraindicated; though some authors advocate avoiding IV narcotics after 7cm of dilation due to the possibility of respiratory suppression of the neonate at birth. Gabbe (6th edition)page 366-367, 1178-1180. Creasy(7th edition) pages 1139-1411, 1181
Which of the following statements is NOT accurate regarding the essential anesthesia considerations for a pregnant woman with a moderate-sized unrepaired ventricular septal defect (VSD) in labor?
A. Stroke volume is increased by uterine contractions which in turn increases the left to right shunt, risk for arrhythmia, and may increase right ventricular/pulmonary artery pressures
B. Management of pain is important to avoid the catecolamine-driven increase in systemic vascular resistance, which worsens left to right shunting
C. A sudden drop in systemic vascular resistance associated with some regional anesthetics may lead to hypoxemia due to reversal of flow across the VSD
D. Caval compression increases following delivery such that cardiac output decreases in the immediate postpartum period.
D. Small septal defects (either atrial or ventricular) are typically tolerated well in pregnancy and rarely result in changes to pulmonary blood flow. As the size of the defect increases, the volume of left to right shunting increases which may increase right ventricular and pulmonary artery blood flow and pressures. Ultimately, the right and left ventricular pressures may equalize leading to pulmonary vasoconstriction and irreversible pulmonary vascular changes. Anesthesia goals in labor are to maintain cardiac output, euvolemia, stable systemic vascular resistance (after-load), and stable pre-load. During labor, cardiac output increases by an additional 45% above the already increased cardiac output of late gestation. Immediately after delivery, cardiac output increases by as much as 80% due to autotransfusion associated with uterine contractions. The autotransfusion results from an increase in preload secondary to increased uterine muscular tone and release of vena caval obstruction by the enlarged uterus. Thus, the first answer option is correct in that the increased pre-load associated with uterine contractions may increase the left heart chamber dimensions, increase the risk for arrhythmia (due to left atrial dilation), and may increase the left to right shunting. An increase in systemic vascular resistance due to pain-associated catecholamines will increase the left ventricular afterload and may increase left to right shunting as well. A sudden drop in the systemic vascular resistance will reduce the pressure within the left ventricle and may “equalize” the pressures in the two ventricles leading to increased right to left flow and possibly hypoxemia
A patient develops a severe headache postpartum after a vaginal delivery for which she received epidural anesthesia. The headache is more severe when she sits up and is relieved lying down. What is the most likely cause of her pain?
A. Vasoconstriction
B. Small loss of cerebrospinal fluid leading to stretching of the meninges and vessels
C. Increased intracranial pressure
D. Meningitis
Spinal headache may follow uncomplicated spinal anesthesia but is more common when the dura is punctured during the process of administering an epidural, resulting in spinal fluid leakage (i.e., a “wet tap”). The overall incidence is 1-3%, but a spinal headache may occur in as many as 70% of patients who experience a wet tap. The headache is most likely caused by loss of cerebrospinal fluid, which allows the brain to settle, and thus causes the meninges and vessels to stretch. Higher needle gauge (smaller needle bore), orientation of the needle bevel parallel to the longitudinal fibers of the dura, and reinsertion of the stylet prior to needle removal have been shown to decrease the incidence. Conservative therapy is recommended for the first 24 hours. For patients with moderate to severe spinal headache for more than 24 hours, and who are refractory to conservative measures, treatment with an epidural blood patch should be considered.
