Alon P. Winnie

THE SUBCLAVIAN PERIVASCULAR TECHNIQUE OF BRACHIAL PLEXUS ANESTHESIA.

The prevertebral fascia envelops the brachial plexus from the cervical vertebrae to the distal axilla, forming a subclavian perivascular space that is continuous with the axillary perivascular space. By applying the concept of the axillary perivascular technique to the supraclavicular approach, the authors have developed the subclavian perivascular technique which affords greater simplicity) safety and consistency of results than presently used supraclavicular technique. Just as with peridural technique, once the space has been entered only a single injection is necessary and the extent of anesthesia will depend on the volume of anesthetic and the level at which it is injected. Sufficient volumes by either approach will produce cervical as well as brachial plexus anesthesia since the cervical plexus travels in the same space at a higher level.

Santayana's prophecy fulfilled

In most training programs today there is little interest in and little attention paid to the history of anesthesia, to the individuals who shaped the specialty of anesthesiology, to the techniques that allowed surgical (and obstetrical) horizons to expand, and to the agents that allowed anesthesia to become progressively less dangerous. Even such catastrophies as the deaths due to the use of pentothal in treating those injured in the bombing of Pearl Harbor1 or the paralyses of Wooley and Roe by spinal anesthesia2 tend to be forgotten as the problems causing them are resolved, despite the fact that their very occurrences provided lessons that should be remembered rather than forgotten. Such are the cases of neurotoxicity reported after the unintentional intrathecal injection of 2-chloroprocaine in the early 1980s. They represent a serious problem that arose over 20 years ago; but once resolved, the problem and its solution have already been forgotten. As a result, anesthesiologists unaware of the past “are condemned to repeat it”; but in medicine, it is the patients who will suffer from their physicians’ failure to remember. In 1952, 2-chloroprocaine, an analog of procaine, was introduced by Foldes and McNall,3 who showed that the simple substitution of a chlorine atom on the second carbon (in the ortho position) of the benzene ring of procaine results in more rapid enzymatic hydrolysis and, hence, decreased toxicity.4 Foldes and McNall3 believed that this simple change provided anesthesiologists with an agent having many of the characteristics of “the ideal local anesthetic,” namely, rapid onset of action, increased potency (21⁄2 times that of procaine), decreased neural and systemic toxicity (half that of procaine), and an adequate duration of action (twice that of procaine) that could be increased significantly by the addition of epinephrine. Because of the rapid onset, potency, and safety of this new agent, anesthesiologists quickly began to use the drug clinically, especially for epidural anesthesia. During the next decade, several large series of cases were reported attesting to the efficacy and safety of Nesacaine, as the commercial preparation became known (then manufactured by Maltbie Laboratories, a division of Wallace & Tiernan, Belleville, NJ), for both major abdominal surgery5 and obstetrics.6 Interestingly, Colavincenzo et al.7 demonstrated the usefulness of such a short-acting agent for outpatient anesthesia, an asset that would be rediscovered over 30 years later.8,9 However, while 2-chloroprocaine was used for all types of surgical procedures, the characteristics of the drug were so well suited to the anesthetic requirements of the pregnant woman and her fetus, it was for obstetrical anesthesia that the drug was most widely used, with a special preparation for epidural anesthesia (without methylparaben) designated as Nesacaine-CE (Strasenburg Laboratories, Rochester, NY). As Gissen et al.10 pointed out, “It is rapid in onset, has the lowest potential for toxicity, and is the most rapidly hydrolyzed of all the local anesthetics. The fetal circulation is exposed to the lowest concentrations of 2CP because of rapid drug hydrolysis, which minimizes the possibility of fetal drug depression. Finally, the metabolic products of 2CP hydrolysis are nontoxic both to the maternal and fetal organism.” Then, in 1980, after nearly 30 years of clinical use, two reports of persistent neurological deficit after epidural Nesacaine-CE appeared in the literature,11,12 followed by an additional report 2 years later.13 These articles reported a total of 8 patients, *Santayana G. The Life of Reason: Reason in Common Science. New York, NY: Scribner; 1903.

The search for a pharmacologic ventilator.

The use of analeptics in medicine is currently condemned in the United States for several seemingly sound reasons. First of all, the respiratory stimulation caused by such agents is usually but a part of generalized stimulation of the central nervous system. Secondly, the dose of analeptic needed to produce a significant increase in ventilation is all too frequently very close to the dose that will cause convulsions. And thirdly, the principal areas where analeptics have been used in the past have been situations of central depression either due to or associated with hypoxia, and under such conditions stimulation of the central nervous system merely serves to create an even greater oxygen debt. Because of this lack of specificity, narrow margin of safety and increase in oxygen consumption the use of analeptics to try to induce arousal and to support pulmonary and cardiocirculatory function in drug-induced depression has properly been abandoned and more appropriately replaced by mechanical support of ventilation and specific drug therapy for cardiocirculatory failure when indicated. However, recent work in pulmonary physiology, which has placed increasing emphasis on the importance of the physiologic sigh, would seem to indicate possible new indications for a drug that could selectively stimulate deep breathing if this could be done without adverse side effects. In addition, the last two decades have seen the synthesis of several agents with proven increased margins of safety but with unproven claims of increased specificity of respirogenic activity. The present study is part of a continuing study that undertakes to compare under a controlled clinical situation the relative potency, specificity, and safety of these newer agents in man, and to compare their activity with the older drugs that have been rejected. Hopefully then, this is a search for a pure pharmacologic ventilator.

Effect of Bupivacaine and Levobupivacaine on Exocytotic Norepinephrine Release from Rat Atria

Background: The cardiotoxic mechanism of local anesthetics may include interruption of cardiac sympathetic reflexes. The authors undertook this investigation to determine if clinically relevant concentrations of bupivacaine and levobupivacaine interfere with exocytotic norepinephrine release from cardiac sympathetic nerve endings. Methods: Rat atria were prepared for measurements of twitch contractile force and 3[H]-norepinephrine release. After nerve endings were loaded with 3[H]-norepinephrine, the tissue was electrically stimulated in 5-min episodes during 10 10-min sampling periods. After each period, a sample of bath fluid was analyzed for radioactivity and 3[H]-norepinephrine release was expressed as a fraction of tissue counts. Atria were exposed to buffer alone during sampling periods 1 and 2 (S1 and S2). Control atria received saline (100 &mgr;l each, n = 6 atria) in S3-S10. Experimental groups (n = 6 per group) received either bupivacaine or levobupivacaine at concentrations (in &mgr;M) of 5 (S3-S4), 10 (S5-S6), 30 (S7-S8), and 100 (S9-S10). Results: Bupivacaine and levobupivacaine decreased stimulation-evoked fractional 3[H]-norepinephrine release with inhibitory concentration 50% values of 5.1 ± 0.5 and 6.1 ± 1.3 &mgr;m. The inhibitory effect of both local anesthetics (∼70%) approached that of tetrodotoxin. Local anesthetics abolished the twitch contractions of atria with inhibitory concentration 50% values of 12.6 ± 5.0 &mgr;m (bupivacaine) and 15.7 ± 3.9 &mgr;m (levobupivacaine). In separate experiments, tetrodotoxin inhibited twitch contractile force by only 30%. Conclusions: The results indicate that clinically relevant cardiotoxic concentrations of bupivacaine and levobupivacaine markedly depress cardiac sympathetic neurotransmission. A possible mechanism of local anesthetics in reducing evoked norepinephrine release from sympathetic endings is blockade of tetrodotoxin-sensitive fast sodium channels.

Supraclavicular approaches to brachial plexus anesthesia

The concept of a continuous perineural and perivascular space surrounding the brachial plexus from roots to terminal nerves simplifies conduction anesthesia of the upper extremity. As with peridural techniques, the space may be entered at any level, and following the injection of a local anesthetic, the extent of anesthesia will depend on the volume of anesthetic and the level at which it is injected. The single injection techniques based on this concept have resulted in both an increased incidence of success and a decreased incidence of serious complications as compared to the multiple injection techniques used previously. The space above the clavicle, the interscalene space, is potentially just such a space; and it is only after the injection of a local anesthetic that it expands to become a true, fluid-filled compartment. Furthermore, this space is quite extensive in its vertical and horizontal axes but very narrow in its anteroposterior axis. It was for this reason that the original subclavian perivascular and interscalene techniques both called for the needle to be introduced in one of the long axes of the space, whereas the more recently introduced parascalene techniques all call for the needle to be inserted in the very narrow anteroposterior axis. As a result, the chance of the needle leaving the space during the performance of the block is minimized with the subclavian perivascular and interscalene techniques, whereas with the parascalene techniques the slightest movement of even the properly placed needle may cause it to leave the space, resulting in the injection of local anesthetic outside of the fascial compartment. In short, the subclavian perivascular and interscalene techniques of brachial plexus block can provide simple, safe, and effective anesthesia for all types of surgery on the upper extremity and shoulder.

Shock: Recognition and Modern Treatment

In a modern approach to treatment of shock, an adequate blood volume is primary, but certain adjuncts are necessary to facilitate its distribution to the body and to perfuse and oxygenate the tissues. Such adjunctive therapy is discussed.Treatment should be directed at correcting the three basic pathophysiologic changes associated with the development of shock. These changes involve the vascular, intravascular and extravascular components.