Sickle Cell Disease
Sickle cell disease is a common genetic disorder. This week we'll discuss the disease and its implications for anesthesia. This week we'll discuss the anesthetic concerns of the disorder.
1. When should transfusions be considered in patients with sickle cell disease?
2. Can tourniquets be used in patients with sickle cell disease?
3. What are possible concerns regarding the use of regional anesthesia techniques?
本周我们讨论镰状细胞病相关的麻醉问题：
1、 镰状细胞病患者什么情况下考虑输血？
2、 止血带能否用于镰状细胞病患者？
3、 使用区域阻滞时主要考虑哪些问题？
参考答案：
1、 镰状细胞病患者什么情况下考虑输血？
对于镰状细胞病相关的标准血管阻塞性危象或疼痛，输血治疗常没有必要，且不推荐使用。然而，紧急血液置换常被用于突发的严重再生障碍性危象，常发生在脾肿大的患儿出现严重感染时，这些患儿的血液聚集在肿大的脾脏内[1]。
通过输血治疗镰状细胞病的一些严重的并发症。选择2-16岁的患儿，通过输血2年以上，使血红蛋白S水平达到不低于全血红蛋白浓度的30%水平（其它成分不考虑），结果发现中风的发生率降低[2]。另外一项研究，与通过血液置换输血使全血红蛋白S达到30%的患者相比，对接受全身麻醉的镰状细胞病成年患者，术前输血使HCT增加到30%，结果有一半出现输血的并发症（但镰状细胞病并发症的发生率相似）[3]。
虽然以上结果是有益的，但输血并非没有风险，可发生感染、铁离子蓄积、血液粘度增加和异源免疫。因此，必须进行更进一步的研究以评估何时输血最有效，血红蛋白达到什么水平最有益。
2、 止血带能否用于镰状细胞病患者？
一般而言，预防血液停滞是目标之一，包括注意体位、心血管稳定性（局麻和全麻诱导时很重要）以及容量状况。不使用止血带就不能获得最佳的手术状况时，方使用止血带。使用止血带可导致酸中毒、血流减少以及低氧导致细胞镰状并发生进一步的损伤。然而，在镰状细胞病患者行矫形外科和血管外科手术时，有限制的使用止血带并未发现产生有意义的后遗症[4]。
3、 使用区域阻滞时主要考虑哪些问题？
虽然区域麻醉，特别是中枢传导阻滞可产生有效的交感神经阻滞并增加肢体血流，但是非麻醉部位发生代偿性血管收缩，可能使这些部位发生血管阻塞性危象[5]。如此而言，硬膜外镇痛的使用可使患者下腹部和远端部位镰状细胞危象得到有效的改善[6]。
When should transfusions be considered in patients with sickle cell disease?
Transfusions are usually not required nor recommended for standard vaso-occlusive crises or pain associated with sickle cell disease. However, urgent blood replacement may be required for sudden and severe aplastic crises, usually observed in the setting of severe infection in children with blood sequestered in an enlarged spleen (1).
Transfusions have been evaluated to treat certain severe complications of sickle cell disease. Using an arbitrary transfusion goal of a hemoglobin S level of less than 30% of the total hemoglobin concentration (other levels have not been evaluated), a decrease in strokes were noted in children ages 2-16 years of age over a two year period (2). In another study, using adults affected with sickle cell disease undergoing general anesthesia, increasing the hematocrit to 30% through a preoperative transfusion was noted to result in half as many transfusion related complications (but similar incidence of sickle cell complications) when compared to exchange transfusing patients to a total hemoglobin S fraction of 30% (3).
While these may represent beneficial results, transfusions are not without risks: infections, iron accumulation, increased blood viscosity, and alloimmunization can all occur. As such, further work must be conducted to evaluate when and to what hemoglobin goals, transfusions will be the most beneficial.
Can tourniquets be used in patients with sickle cell disease?
In general, prevention of circulatory stasis is a goal which includes attention to body positioning, cardiovascular stability (important with the induction of regional and general anesthesia), and volume status. Tourniquets should only be used when optimal surgical conditions cannot be achieved without their use, as the resultant production of acidosis, reduced blood flow, and hypoxia creates sickling and further injury. However, the limited use of tourniquets for orthopedic and vascular surgeries have been reported to be without significant sequelae in the sickle cell population (4).
What are possible concerns regarding the use of regional anesthesia techniques?
Although regional anesthesia, especially central conduction blockade, produces a favorable sympathectomy and increased limb blood flow, compensatory vasoconstriction in non-anesthetized areas may actually produce vaso-occlusive crises in these areas (5). This being said, the use of epidural analgesia has been observed to result in favorable recovery in patients with lower abdominal and extremity sickle cell crises (6).
References:
1. Behrens RJ, Cymet TC. Sickle Cell Disorders: Evaluation, Treatment, and Natural History. Hosp Phys 2000;17-28.
2. Adams RJ, McKie VC, Hsu L, et al. Prevention of the first stroke by transfusions in children with sickle cell anemia and abnormal results on transcranial Doppler ultrasonography. N Engl J Med 1998;339:5-11.
3. Vichinsky EP, Haberkern CM, Neumayr L, et al. A comparison of conservative and aggressive transfusion regimens in the perioperative management of sickle cell disease. The Preoperative Transfusion in Sickle Cell Disease Study Group. N Engl J Med 1995;333:206-13.
4. Adu-Gyamfi Y, Sankarankutty M, Marwa S.Use of a tourniquet in patients with sickle-cell disease. Can J Anaesth. 1993;40:24-7.
5. Bridenbaugh PO, Moore DC, Bridenbaugh LD. Alterations in capillary and venous blood gases after regional-block anesthesia. Anesth Analg 1972;51:280-6.
6. Finer P, Blair J, Rowe P. Epidural analgesia in the management of labor pain and sickle cell crisis--a case report. Anesthesiology. 1988;68:799-800.
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