pH-Adjustment of 2-chloroprocaine quickens the onset of epidural anaesthesia

Abstract

pH-Adjustment of 2-chloroprocaine quickens the onset of epidural anaesthesia The effect of pH.adjustment of three per cent 2-chloroprocaine (2-CP , Nesacaine MPF | on the onset, duration, and spread of epidural analgesia and anaesthesia was studied in patients undergoing lower extremity surgery. Forty ASA physical status l and II patients were randomized to two groups. In a doubleblinded fashion, patients in both groups received an epidural injection of 15 ml of local anaesthetic (I.A) solution via a Tuohy needle at the Lj_4 interspace. Local anaesthesia for Group I was prepared by adding 3 mEqNaHC03 to 27 ml threeper cent 2-CP and for Group II was prepared by adding 3 ml O.9 per cent NaCl to 27 ml three per cent 2.CP. Both solutions contained epinephrine (1:200,000). The pH of commercially prepared Nesacaine MPF | was 3.19 +-0.02. The pH of the solutions used for Group l and Group H patients were 7.32 +-O.01and 3.2 7 +-0.02, respectively. Times to analgesia and anaesthesia at the 1,2 dermatome were significantly decreased in Group l patients by 2.5 and 6.6 minutes, respectively. Likewise, pH-adjustment accelerated the attainment of maximum level of block by 2.8 rain. No statistical differences were found between groups in the maximum level of epidural block, or in time to 2-segment regression. No precipitation of LA was observed in pH-adjusted

Reversal of lidocaine with epinephrine epidural anesthesia using epidural saline washout

“…Clinical studies have demonstrated a more prolonged onset of epidural analgesia and anesthesia when the pH of local anesthetics has been adjusted away from the physiologic range. 18,19 Elucidation of the mechanism of epidural washout will have to await further study.…”

Extradural, Spinal or Combined Block for Obstetric Surgical Anaesthesia

“…Significant reductions in onset time have been claimed for extradural mepivacaine [28], lignocaine [22], bupivacaine [24] and chloroprocaine [64,75]. All investigators do not agree with these findings, however, especially with respect to bupivacaine [76].…”

From micro- to nanostructured implantable device for local anesthetic delivery

“…10,12 The salt, being a weak base, can exist in solution as an un-ionized free base, which is more lipophilic, or as a positively charged cation; both species are involved in the process of conduction blocking. 10,13 The base crosses the neuronal bilayer more easily, and thus is preferred for optimal penetration. 10 The percentage of drug in the two forms depends on its pK a and the environmental pH.…”

“…Each drug has a characteristic pK a , with ester type LAs typically having a higher value than the amide type. 11 The closer the pK a is to the pH of the tissues, the faster is the onset of action of the drug, 13,14 since the percentage of free base formed increases. For this reason, in infected tissues, the LA effect is reduced or even delayed, as the environment tends to be more acidic than usual and the un-ionized form decreases.…”