King H K, Wooten D J
Department of Anesthesiology, King/Drew Medical Center, Los Angeles, CA 90059, USA.
Reg Anesth. 1995 Jan-Feb;20(1):45-9.
Factors governing the spread of local anesthetic in the subarachnoid space have been controversial because of failure to consider the drug related and physical factors. Most studies of isobaric spinal anesthesia in the literature were made using plain bupivacaine which is slightly hypobaric. In this study the effects of drug dose, volume, and concentration were investigated employing isobaric tetracaine (IT).
One hundred twenty patients were randomly allocated to four groups to receive IT diluted to appropriate concentrations with cerebrospinal fluid. Drugs were administered in lateral position at L3-4 level, with the patient remaining horizontal (supine) during the study. Neural block was assessed by pinprick and the Bromage scale. Except for the factor under investigation, identical techniques were used.
Data indicated that volume was the immediate major factor affecting the extent of spread reflected by the significant difference in peak levels between group 1 and group 2 patients. When volume remained constant, increasing dose (mass) concomitantly increased concentration resulting in a faster onset, longer block, and a higher peak level. However, this effect was not prominent and often limited as increasing the dose from 15 mg to 20 mg had no significant effect on the peak levels in group 3 and group 4 patients.
In IT spinal anesthesia, the role of baricity/posture interaction no longer exists, the volume appears the most significant factor by simple bulk displacement or area of contact. Next in significance is the dosage. Increased dose in the same volume implies an increase in concentration that results in faster onset and longer duration and, to a less extent, the peak level.
由于未能考虑药物相关因素和物理因素，蛛网膜下腔局部麻醉药扩散的影响因素一直存在争议。文献中大多数关于等比重脊麻的研究使用的是略为低比重的普通布比卡因。在本研究中，采用等比重丁卡因（IT）研究了药物剂量、容量和浓度的影响。
120例患者随机分为四组，接受用脑脊液稀释至适当浓度的IT。药物在L3 - 4水平侧卧位给药，研究期间患者保持水平（仰卧）位。通过针刺和布罗麻量表评估神经阻滞情况。除研究因素外，采用相同技术。
数据表明，容量是影响扩散范围的直接主要因素，这体现在1组和2组患者峰值水平的显著差异上。当容量保持恒定时，增加剂量（质量）会相应增加浓度，从而导致起效更快、阻滞时间更长和峰值水平更高。然而，这种效应并不显著，而且通常有限，因为将剂量从15 mg增加到20 mg对3组和4组患者的峰值水平没有显著影响。
在IT脊麻中，比重/体位相互作用的作用不再存在，容量似乎是通过简单的体积置换或接触面积起作用的最显著因素。其次重要的是剂量。在相同容量下增加剂量意味着浓度增加，这会导致起效更快、持续时间更长，在较小程度上还会使峰值水平升高。
