Stanski D R
Stanford University School of Medicine, Anesthesiology Service, CA.
Eur J Anaesthesiol Suppl. 1987;1:3-11.
Alfentanil has a different pharmacokinetic and pharmacodynamic profile compared to fentanyl. Alfentanil is approximately five to eight times less potent than fentanyl when given as a single i.v. dose. The onset of alfentanil effect is five to six times more rapid than fentanyl because of a more rapid blood: brain equilibration. The rapid dissipation of alfentanil's effect occurs due to both redistribution from the brain to other tissues and rapid elimination from the body, secondary to the short elimination half-life. The short alfentanil elimination half-life arises from the marked reduction in steady-state distribution volume from a limited tissue distribution. Higher plasma concentrations are needed for endotracheal intubation and skin incision than skin closure and post-operative ventilation. Upper abdominal surgical procedures require higher plasma concentrations than lower abdominal or breast surgery. Optimal alfentanil anaesthesia occurs when plasma concentrations are maintained relatively constant at therapeutic values using infusion techniques. Age and hepatic disease alter alfentanil pharmacokinetics. Age and other CNS depressants can lower the alfentanil plasma concentrations needed for adequate clinical anaesthesia. In spite of adjusting for these factors that affect alfentanil pharmacokinetics and pharmacodynamics, unexplained pharmacokinetic variability of 30-50% exists. Alfentanil infusions must be titrated and adjusted in each patient, based upon the clinical response to circumvent this pharmacokinetic and pharmacodynamic variability.
与芬太尼相比，阿芬太尼具有不同的药代动力学和药效学特征。单次静脉注射时，阿芬太尼的效力约为芬太尼的五分之一至八分之一。由于血脑平衡更快，阿芬太尼起效比芬太尼快五至六倍。阿芬太尼作用的快速消散是由于从脑到其他组织的再分布以及因消除半衰期短而从体内快速消除。阿芬太尼消除半衰期短源于有限的组织分布导致稳态分布容积显著降低。气管插管和皮肤切开所需的血浆浓度高于皮肤缝合和术后通气。上腹部手术所需的血浆浓度高于下腹部或乳腺手术。使用输注技术将血浆浓度维持在治疗值相对恒定水平时，可实现最佳的阿芬太尼麻醉。年龄和肝脏疾病会改变阿芬太尼的药代动力学。年龄和其他中枢神经系统抑制剂可降低充分临床麻醉所需的阿芬太尼血浆浓度。尽管对影响阿芬太尼药代动力学和药效学的这些因素进行了调整，但仍存在30% - 50%无法解释的药代动力学变异性。必须根据临床反应对每位患者的阿芬太尼输注进行滴定和调整，以规避这种药代动力学和药效学变异性。
