形成单侧硬膜外阻滞的原因.doc

Topic of the Day I(for Interns and CA-2s)Oct 26 - Discuss unilateral epidural block - explain this result形成单侧硬膜外阻滞的原因Discussion point.A unilateral anesthetic block may result from the administration of local anesthetic in the epidural space secondary to the plica mediana dorsalis, a connective tissue band in the epidural space that extends in a vertical direction between the ligamentum flavum and dura mater dividing the epidural space in half. 由于背正中皱襞的存在，在硬膜外腔注入局部麻醉药后可造成单侧阻滞。背正中皱襞作为连接黄韧带和硬膜的带状结缔组织在硬膜外腔垂直延伸，并把其一分为二。Oct 27 - Compare sympathetic, motor & sensory block of epidurals vs spinals比较硬膜外麻醉和脊髓麻醉的交感、运动和感觉神经阻滞Discussion points.Epidural anesthesia results in sympathetic nerve blockade, sensory nerve blockade, and motor nerve blockade just as in spinal anesthesia. In epidural anesthesia, however, the levels of each are different than they are in spinal anesthesia. First, sympathetic nerve blockade is at a level equal to sensory nerve blockade, rather than the two to six segments higher that is seen in spinal anesthesia. Second, motor nerve blockade may average four segments lower than sensory nerve blockade, rather than the two segments seen in spinal anesthesia.The major site of action of local anesthetics administered in the epidural space is at the spinal nerve roots. At the spinal nerve roots the dura mater is relatively thin, allowing for the easiest diffusion of local anesthetic through the dura mater to the nerves.There is often a delayed onset in anesthesia at the Sl-S2 nerve root region during an epidural anesthetic. This may be due to the covering of these nerve roots with connective tissue, slowing the diffusion of local anesthetic to these nerve roots.The diffusion of local anesthetic from the epidural space to the subarachnoid space is a minor contributor to the anesthetic effects of local anesthetic solutions in the epidural space. 正如脊髓麻醉一样，硬膜外麻醉亦可阻滞交感、感觉和运动神经。但是，各神经被阻滞的平面在硬膜外麻醉与脊髓麻醉中有所不同。首先，硬膜外麻醉中交感阻滞与感觉阻滞的平面相同，而脊髓麻醉中前者要比后者高26个节段。其次，硬膜外麻醉中运动阻滞平面平均比感觉阻滞平面低4个节段，而脊髓麻醉中前者比后者低2个节段。脊神经根是硬膜外腔注入的局部麻醉药的主要作用部位。脊神经根附近的硬膜相对较薄，使局部麻醉药容易经此扩散至神经而发挥作用。在硬膜外麻醉过程中，骶12神经根支配区域的麻醉起效常有延迟。这可能是因为包裹这些神经根的结缔组织减慢了局部麻醉药向神经根的扩散。在硬膜外麻醉中，局麻药液从硬膜外腔扩散至蛛网膜下腔而产生的麻醉效果所占比例很小。Oct 28- Discuss potential side effects of epidural anesthesia硬膜外麻醉的潜在并发症Discussion points.The potential side effects of spinal anesthesia also apply to epidural anesthesia. Additional side effects of an epidural anesthetic that do not apply to spinal anesthesia include the risks of accidental dural puncture, local anesthetic toxicity, subdural injection, and epidural hematoma formation. The risk of epidural hematoma formation resulting from an epidural anesthetic is extremely low. Patients on anticoagulants are considered to be at the greatest risk, although the incidence is extremely low even in patients with bleeding abnormalities. There are multiple reviews in the literature of patients who received anticoagulation intraoperatively and postoperatively without any neurologic sequelae. Nevertheless, the American Society of Regional Anesthesia published their consensus statement titled Neuraxial Anesthesia and Anticoagulation in May 1998 with their recommendations on how epidural catheters should be managed in the perioperative period in the presence of anticoagulation. Accidental puncture of the dura mater during attempted localization of the epidural space can be recognized by the anesthesiologist by the appearance of cerebrospinal fluid in the hub of the epidural needle. The flow of cerebrospinal fluid from the large-bore needle is rapid and continuous. Cerebrospinal fluid is warm, distinguishing it from saline used for the loss of resistance technique for localization of the epidural space. Cerebrospinal fluid will also dipstick test positive for glucose.The accidental subarachnoid injection of the large volumes of local anesthetic intended for epidural anesthesia results in a rapidly evolving total spinal. The accidental subdural injection of the large volumes of local anesthetic intended for epidural anesthesia results in a slowly evolving total spinal. A subdural injection of local anesthetic may be difficult to recognize. The potential for local anesthetic systemic toxicity with epidural anesthesia is high because of the high doses of local anesthetic that must be given to produce epidural anesthesia, coupled with the numerous venous plexuses found in the epidural space that lend themselves to systemic absorption of the local anesthetic. Even so, blood levels of local anesthetic administered in the epidural space are rarely in the toxic range. The risk of systemic toxicity from the systemic absorption of local anesthetic administered in the epidural space is decreased by the addition of epinephrine to the local anesthetic solution. Epinephrine in the local anesthetic solutions slows the rate of systemic absorption of the local anesthetic in the epidural space.Epidural anesthesia results in less abrupt hypotension than spinal anesthesia, owing to the slower onset of sympathetic nervous system blockade in epidural anesthesia. The treatment for hypotension resulting from epidural anesthesia is placing the patient in a modest head-down position, the administration of intravenous fluids, and, if necessary, the administration of sympathomimetics.The accidental intravascular injection of the large volumes of local anesthetic intended for epidural anesthesia can result in local anesthetic toxicity. This may manifest as cardiovascular collapse, apnea, seizures, and unconsciousness. In the event this occurs, rapid treatment of the seizures and cardiovascular and ventilatory support are indicated.脊髓麻醉潜在的并发症同样也会出现在硬膜外麻醉中。硬膜外麻醉独有的并发症包括意外刺破硬膜、局麻药中毒、硬膜下注射和硬膜外血肿。在硬膜外麻醉中发生硬膜外血肿的机率极低。尽管硬膜外血肿在即使伴有出血异常的病人发生率也极低，正在使用抗凝药仍然被认为是最大的风险。尽管多个文献综述提示术中和术后接受抗凝治疗的病人未出现任何神经病学结局，美国局部麻醉协会在1998年5月发表了以“神经轴索阻滞与抗凝”为标题的一致声明，对围术期应该如何管理正在接受抗凝治疗的病人硬膜外导管提出了建议。在尝试定位硬膜外腔过程中出现意外刺破硬膜可因硬膜外穿刺针针孔出现脑脊液而被发现。脑脊液从大口径穿刺针流出迅速且呈持续性。脑脊液是有热度的，这与用于“阻力消失”技术定位硬膜外腔的生理盐水不同。脑脊液也可通过葡萄糖试纸的阳性反应来确认。意外地在蛛网膜下腔注射原计划用于硬膜外麻醉的大容量局麻药会迅速出现全脊髓麻醉。同样的情况发生在硬膜下腔则会缓慢演变为全脊髓麻醉。局麻药的硬膜下注射可能较难辨别。必须注射高剂量的局麻药来实现硬膜外麻醉，但硬膜外腔同时存在的大量静脉丛使局麻药的全身吸收成为可能，因此硬膜外麻醉所带来的全身局麻药中毒可能性很高。即便如此，硬膜外腔注射局麻药所达到的血药浓度极少在中毒范围。在药液中加入肾上腺素可降低局麻药全身吸收带来的全身毒性风险。加入的肾上腺素可延缓局麻药在硬膜外腔的全身吸收。硬膜外麻醉导致的突发的低血压较脊髓麻醉少见，主要是因为其产生的交感神经阻滞起效较慢。低血压的治疗包括将病人的体位改为中度头低位，静脉补液，必要时可给予拟交感药物。意外地血管内注射原计划用于硬膜外麻醉的大容量局麻药会导致局麻药中毒，可表现为心血管虚脱，呼吸暂停，惊厥和无意识。一旦出现毒性反应，应快速控制惊厥，进行心血管和呼吸系统支持治疗。References. Stoelting RK, Miller RD: Basics of Anesthesia, 4th ed. Philadelphia, Churchill Livingstone, 2000; p. 182, 183; Miller RD: Anesthesia, 5th ed. Philadelphia, Churchill Livingstone, 2000; p. 1513-1514, 1497.Spinal Anesthetic SEs脊髓麻醉的并发症Some side effects associated with spinal anesthesia include hypotension, bradycardia, postdural puncture headache, total spinal, nausea, urinary retention, backache, neurologic sequelae, and hypoventilation.脊髓麻醉的并发症包括低血压，心动过缓，硬膜穿破后头痛，全脊麻，恶心，尿潴留，腰背痛，神经病学结局和低通气。References. Stoelting RK, Miller RD: Basics of Anesthesia, 4th ed. Philadelphia, Churchill Livingstone, p. 176. Miller RD: Anesthesia, 5th ed. Philadelphia, Churchill Livingstone, 2000; pp. 1506-1507. Oct 29 - Discuss the dx and management of an accidental dural puncture意外穿破硬膜的诊断与处理Discussion point.Accidental puncture of the dura mater during attempted localization of the epidural space can be recognized by the anesthesiologist by the appearance of cerebrospinal fluid in the hub of the epidural needle. The flow of cerebrospinal fluid from the large-bore needle is rapid and continuous. Cerebrospinal fluid is wann, distinguishing it from saline used for the loss of resistance technique for localization of the epidural space. Cerebrospinal fluid will also dipstick test positive for glucose. Once accidental dural puncture during attempted epidural anesthesia has occurred, the anesthesiologist may convert to a spinal anesthetic. Alternatively, the needle may be removed and reattempt an epidural anesthetic at another interspace. The development of a postdural puncture headache after accidental dural puncture with an 18-gauge epidural needle is likely, given the size of the hole in the dura mater produced by the relatively large needle. For this reason the patient should be informed about the possibility of a postdural puncture headache and should be instructed as to whom to contact for evaluation and treatment should a postdural puncture headache occur.（前面重复，不作叙述）一旦意外穿破硬膜，麻醉医生可改行脊髓麻醉。另外一种方法是拔出穿刺针后在另一个间隙试行硬膜外麻醉。假如硬膜破口正是18G硬膜外穿刺针所造成的，意外穿破硬膜就极有可能发生硬膜穿破后头痛。因此应该告知病人发生硬膜穿破后头痛的可能性，而且应说明一旦出现硬膜穿破后头痛病人可联系哪位医生进行评估和治疗。References. Stoelting RK, Miller RD: Basics of Anesthesia, 4th ed. Philadelphia, Churchill Livingstone, 2000; p. 182; Miller RD: Anesthesia, 5th ed. Philadelphia, Churchill Livingstone, 2000; p. 1513-1514. Oct 30 - Discuss caudal anesthesia - anatomy, technique, etc.骶管麻醉相关的解剖、技术及其他Discussion points.To facilitate the administration of a caudal anesthetic the adult patient should be in the prone position, whereas the pediatric patient may be in the lateral decubitus position.The sacral hiatus is located between the sacral cornua approximately 5 cm from the tip of the coccyx.For the administration of a caudal anesthetic the needle is first introduced through the sacrococcygeal ligament perpendicular to the skin. After contact with the sacrum, the needle is withdrawn slightly and redirected at a slightly reduced angle about 2 cm into the caudal canal. The needle is then appropriately placed for the administration of the local anesthetic for caudal epidural anesthesia.Confirmation that the needle tip is appropriately placed in the caudal canal for the administration of local anesthetic can be made by injecting about 5 mL of saline or air. If the needle is subcutaneously placed, subcutaneous air or a subcutaneous bulge will appear overlying the tip of the needle. Aspiration on the needle before injection would result in the appearance of cerebrospinal fluid in the syringe if the needle were erroneously placed in the subarachnoid space.为了有助于骶管麻醉的实施，成年人应该采取俯卧位，而小儿则可采取侧卧位。骶管裂孔位于距尾骨尖端约5 cm的两侧骶角之间。实施骶管麻醉时，穿刺针首先垂直刺过皮肤和骶尾韧带，触及骶骨后，针回退少许后稍放低，重新推进2 cm进入骶管腔，然后适当固定穿刺针以注射局麻药。为了确认针尖是否位于骶管腔，可注射5ml生理盐水或空气。如果针位于皮下，可在针尖上面覆有一皮下气肿或皮下隆起。如果针误入蛛网膜下腔，注射前可回抽出脑脊液。References. Stoelting RK, Miller RD: Basics of Anesthesia, 4th ed. Philadelphia, Churchill Livingstone, 2000; p. 183; Miller RD: Anesthesia, 5th ed. Philadelphia, Churchill Livingstone, 2000; p. 1508, 1511-1512, 1525. Topic of the Day II(for CA-2s and CA-3s)Oct 26 - Discuss adrenal insufficiency and supplemental periop steroids肾上腺皮质功能不全和围术期替代治疗Discussion points:Adrenocortical insufficiency can be due to the destruction of the adrenal cortex by cancer, tuberculosis, or hemorrhage; to deficiency in adrenocorticotropic hormone; or to the prolonged exogenous administration of corticosteroids. The adrenal cortex of the adrenal gland synthesizes glucocorticoids, mineralocorticoids, and androgens. Cortisol, a glucocorticoid, is essential for the maintenance of blood pressure and the conversion of norepinephrine to epinephrine in the adrenal medulla. Indeed, acute adrenocortical insufficiency can be life threatening. Cortisol also plays an important role in gluconeogenesis, sodium retention, and potassium excretion and has anti-inflammatory effects. Surgical stimulation normally results in an increase in the amount of circulating cortisol. Patients who are being chronically treated for adrenocortical insufficiency have impaired cortisol secretion and may have cardiovascular compromise because they are unable to respond to the physiologic stress of surgery with the secretion of cortisol. This is the basis for the perioperative administration of supplementary doses of corticosteroids to these patients.造成肾上腺皮质功能不全的原因包括肿瘤、结核或出血引起肾上腺皮质破坏；促肾上腺皮质激素缺乏；长时间应用外源性皮质类固醇。肾上腺皮质可合成糖皮质激素、盐皮质激素和雄激素。皮质醇是一种糖皮质激素，对动脉血压的维持和在肾上腺髓质中去甲肾上腺素向肾上腺素转化相当重要。事实上，急性肾上腺皮质功能不全可危及生命。皮质醇对糖异生、钠潴留和钾排出起着相当重要的作用，同时还具有抗炎作用。外科刺激正常情况下可导致血中皮质醇水平升高。慢性肾上腺皮质功能不全的病人皮质醇分泌受损，由于对外科生理性应激不能反应地引起的皮质醇分泌，病人可出现心血管不良事件。这就是此类病人进行围术期糖皮质激素补充替代治疗的依据。References. Stoelting RK, Miller RD: Basics of Anesthesia, 4th ed. Philadelphia, Churchill Livingstone, 2000; pp. 313-314; Miller RD: Anesthesia, 5th ed. Philadelphia, Churchill Livingstone, 2000; pp. 920-922. Oct 27 - Discuss clinical presentation of acute adrenal insufficiency急性肾上腺皮质功能不全的临床表现Discussion points:Acute adrenal insufficiency, or addisonian crisis, presents as hypovolemia, hyponatremia, and hyperkalemia. Patients may also have hypotension, decreases in systemic vascular resistance, and decreases in left ventricular stroke index severe enough to lead to death. 急性肾上腺皮质功能不全，或称为Addisonian 危象，表现为低血容量，低钠血症，高钾血症。病人也可伴有低血压，外周血管阻力降低和严重至足以引起死亡的左室每搏指数下降。References. Stoelting RK, Miller RD: Basics of Anesthesia, 4th ed. Philadelphia, Churchill Livingstone, 2000; p. 314; Miller RD: Anesthesia, 5th ed. Philadelphia, Churchill Livingstone, 2000; p. 921-922. Oct 28- Discuss recommendations for preop steriod administration for at risk pts高风险病人术前应用类固醇的建议Discussion points:Patients at risk for adrenal insufficiency typically receive supplementary doses of corticosteroids in the perioperative period given they cannot respond to the increased stress of surgery with the secretion of cortisol. Perioperative acute adrenal insufficiency occurs rarely but can be severe and potentially fatal. In contrast, the administration of perioperative high-dose corticosteroids places the patient at minimal risk. The precise dose of corticosteroid supplementation has not been studied. There has been a correlation established between the stress of surgery and the natural response of a healthy adrenal gland. Under peri operative conditions the adrenal gland secretes 120 to 185 mg of cortisol per day. Under maximum stressful conditions the adrenal gland may secrete 200 to 500 mg/d. One method of administering supplementary corticosteroids is to mimic the natural response of the adrenal gland. For more stressful surgical procedures hydrocortisone can be administered at a dose of 200 mg/d, while for minor surgical stresses a hydrocortisone dose of 100 mg/d should be adequate in the average-sized adult patient. The dose can be decreased by 25% each postoperative day until the patient is able to take the normal oral dose. 如果对额外的外科应激无法反应性地引起的皮质醇分泌，肾上腺皮质功能不全的高风险病人围术期常需接受皮质类固醇替代治疗。围术期很少出现急性肾上腺皮质功能不全，一旦发生，症状严重甚至可能危及生命。反过来说，围术期使用大剂量的皮质类固醇可使风险降至最低。尚未有人研究出皮质类固醇替代治疗的精确剂量。外科应激和正常肾上腺反应之间关联性已经明确。围术期肾上腺每天可分泌120185mg 皮质醇。最大应激情况下肾上腺每天可分泌200500mg皮质醇。皮质类固醇替代治疗的另一个方法是模拟肾上腺的正常反应。对一个标准身型的成年人来说，更大的外科应激情况下可一天使用氢化可的松200mg,但较小的外科应激情况下一天氢化可的松100mg即已足够。References. Stoelting RK, Miller RD: Basics of Anesthesia, 4th ed. Philadelphia, Churchill Livingstone, 2000; p. 314; Miller RD: Anesthesia, 5th ed. Philadelphia, Churchill Livingstone, 2000; p. 921-922. Oct 29 - Discuss the potential risks of periop steriods administration围术期使用类固醇的潜在风险Discussion points:The potential risks of the administration of supplementary doses of corticosteroids to patients in the peri operative period are few. In theory, patients may have aggravation of hypertension, fluid retention, stress ulcers, and psychiatric disturbances. Of concern are impaired wound healing and an increased rate of infections, because these have been seen to occur clinically. These events still occur rarely, however. It is generally recommended that supplementary corticosteroids are administered to patients at risk in the perioperative period because the potential risks are minimal and rare and are outweighed by its potential benefit. 围术期使用替代治疗剂量的类固醇的潜在风险很小。理论上，可加剧血压升高、液体潴留、应激性溃疡和精神障碍。实际临床工作中更值得关注的是出现伤口愈合不良和增加感染的发生率。但这些现象的发生率也极低。由于潜在的风险极小，发生率低，使用后利大弊，建议常规对高危病人进行皮质类固醇的替代治疗。References. Stoelting RK, Miller RD: Basics of Anesthesia, 4th ed. Philadelphia, Churchill Livingstone, 2000; p. 314; Miller RD: Anesthesia, 5th ed. Philadelphia, Chur