One of the outstanding features of obstetric surgical procedures carried out under regional anaesthesia is that the patients are seldom given premedication, peroperative sedation or light general anaesthesia which might mask any deficiencies in the local anaesthetic block. Before delivery this is in the interests of the fetus, which may be affected by any drugs given to the mother. For procedures carried out after delivery, sedation or anaesthesia interferes with the mother's enjoyment of her new baby, and may even jeopardize her safety if her respiratory protective reflexes are depressed. This is in contrast with other branches of anaesthesia in which regional techniques are popular—especially orthopaedics, where supplementary sedation or anaesthesia is commonplace. It is in obstetric anaesthesia, therefore, that the differences between extradural and spinal block may be most apparent, and in choosing between them it is necessary that the anaesthetist understands the relative merits of the two techniques.

Extradural, spinal or combined block for obstetric surgical anaesthesia

This double-blind study investigated the effect of adding 1.4% bicarbonate to 0.5% bupivacaine on onset time of sensory and motor blockade after epidural administration. Forty patients were randomly divided into one of two groups. Group 1 received 20 mL of 0.5% bupivacaine (pH, 5.58 +/- 0.12) and group 2 received 20 mL of 0.5% bupivacaine + 0.6 mL of 1.4% bicarbonate (pH, 6.53 +/- 0.06). Onset of temperature sensation loss occurred at L-1 after 5 min in both groups. The first signs of motor impairment were seen after 4 min in three patients in group 1 and two patients in group 2. Maximum motor blockade was reached after 30 min in group 1 and after 36 min in group 2. No difference in motor blockade or upward spread of anesthesia was noted between the two groups. The authors conclude that alkalinization of 0.5% bupivacaine offers no improvement in the onset of epidural blockade.

Onset of epidural blockade after plain or alkalinized 0.5% bupivacaine.

Modification of local anaeshetics by the addition of agents such as sodium bicarbonate has been practised for a long time. The article by Gaggero e t al. ~ studies the effect of adding sodium bicarbonate to lidocaine 2% when used in epidural anaesthesia for Caesarian section. Modification of a local anaesthetic is usually carried out to either try to speed the onset of blockade, i.e., by adding sodium bicarbonate or prolonging the duration of block, i.e., by adding epinephrine. As yet, there is no local anaesthetic available that combines reliable quick onset (in 10 minutes or less for an epidural block) with a length of action of several hours. The theory behind the practice of adding sodium bicarbonate is that most local anaesthetics, while being weak bases with pKa's varying from 7.7 to 8.90, are supplied in solutions that are acidic. 2 This is done to improve the stability of the local anaesthetic preparations. Local anaesthetics when used in nerve blockade must cross the perineural sheath and nerve membrane. These structures are only permeable to the drug when in its non-ionised form. 3 Thus when injected in an acidic preparation the local anaesthetic will exist mostly in the ionised form and therefore will probably achieve nerve block slower than if a solution is used with a pH that more closely approximates the pKa and contains more of the non-ionised drug. A typical preparation of lidocaine 2% is supplied at a pH of 6.4 and bupivacaine 0.5% is at a pH of 6.0. 2 At these pH's the proportion of the non-ionlsed form is less than 5%. If the pH of lidocaine is raised to 7.0 (pKa is 7.6) the proportion of the non-ionised drug increases to 11%. 3 The pKa of bupivacaine is 8.0 and therefore even less non-ionlsed drug is available in the supplied preparation. A number of studies have reported comparisons between alkalinized and plain (unalkalinized) preparations of local anaesthetics. ~,3-J0 It is difficult to compare the results of these studies as either the local anaesthetic solutions differ, i.e., both bupivacaine and lidocaine have been studied or differing blocks were studied, i.e., epidural for analgesia in labour or Caesarean section and

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Alkalinization of local anaesthetics.

Eighty patients of groups ASA I and II, havingepidural anesthesia in their operations were investigated in 4 different groups. Group I patients were given a commercially prepared 0.5 % bupivacaine solution plus 0.2 cc 8.4% NaHC03 per 20 cc of bupivacaine at 20°C; (pH: 6.90). Group II patients were given a commercially prepared 0.5 % bupivacaine solution plus 0.2 cc of 8.4 % NaHC03 per 20 cc of bupivacaine at +4° C; (pH: 5,68) Group III patients were given a commercially prepared 0.5 % bupivacaine solution plus 0.2 cc of 8.4 % NaHC03 per 20 cc of bupivacaine at+4° C; (pH: 7.05). Group IV patients were given a commercially prepared 0.5 % bupivacaine solution at +4° C; (pH:5,67) Times of onset of analgesia and anesthesia in different bupivacaine solutions according to temperature and pH values were investigated. There were no significant effects observed on cardiovascular system. There was no significant difference in motor blockade. There was difference among groups in onset of analgesia and anesthesia. It was concluded that onset of analgesia and anesthesia is more rapid in group III. [Turk J Med Res 1993; 11(6): 277-281]

The use of alkalinized bupivacaine for epidural anesthesia at different temperatures

The highly-dosed infusion with Procaine-HCl with sodium-bicarbonate as additive was firstly published twenty years ago. The method advanced to a routine in many centers for pain treatment, rehabilitation and natural medicine. The aim of the procedure is the systemic use of the various pharmacological features of Procaine, especially to inhibit pain and inflammation, for vasodilatation, anti-oxidation and to harmonize the vegetative nervous system. On one hand shall the addition of sodium-bicarbonate balance the common latent pH-decrease in the periphery. On the other hand also the degradation products of Procaine (DAE and PABA) have a systemic effect. For the safety of the patients and to improve the success rate of the method it was shown that the classic Procaine-Base-infusion should be only realized on the base of a prior acid-base-diagnostic. Review Article Citation: Ralf Oettmeier, Uwe Reuter. The Procaine-Base-Infusion: A Review after Twenty Years of Use. J Med Clin Res & Rev. 2017;

The procaine-(base)-infusion: A review after twenty years of use

&NA; pH adjustment of lidocaine and 2‐chloroprocaine has been reported to decrease the latency of epidural anesthesia (EA). The effect of alkalinization of bupivacaine on onset of surgical anesthesia has not been adequately studied to date. To determine what effect raising the pH of 0.5% bupivacaine has on the latency of EA in patients undergoing lower extremity surgery, we performed a randomized, double‐blind study. Forty patients were randomly divided into two groups. Group I patients received 15 ml of a local anesthetic (LA) solution containing 0.5% bupivacaine and 0.15 mEq of NaHCO3. Group II patients received 15 ml of a standard solution of 0.5% bupivacaine. Both solutions contained freshly added epinephrine (1:200,000). After injection of LA via Tuohy needle, sensory testing was conducted using a safety pin. The pH of the LA used for Group I was 6.96 ± 0.01 and for Group II was 5.33 ± 0.11. No statistically significant difference was found between the anesthetic parameters tested in each group. On this basis, we find no advantage of pH adjustment of 0.5% bupivacaine for EA.

R. A. Stevens

Papers

The Effect of pH Adjustment of 0.5% Bupivacaine on the Latency of Epidural Anesthesia

pH-Adjustment of 2-Chloprocaine Quickens the Onset of Epidural Anesthesia