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Safer local anesthesia
local anesthesia Rudolph H de Jong, MD
Local anesthetics are amazingly safe drugs, as attested by their widespread use, but they occasionally cause toxic effects. Except for hypersensitivity reactions that take place soon after injection, local anesthetic toxicity generally develops rather slowly because the drug must first be absorbed. Operating and recovery room nurses should be acquainted with the etiology and symptomatology of these reactions. Cool and quick thinking may well avert difficulties for your patient. General considerations. A very important qualification is that local anesthetics block nerves in a reversible manner. When the block wears off, normal function returns to the nerve and it is none the worse for the experience. Locally, these anesthetics may be considered essentially nontoxic. This is not so once they are absorbed. Like any other substance injected into the human body, local anesthetics are eventually picked up by the cir-
292
culatory system and metabolized and/ or excreted. Drugs absorbed by the bloodstream will reach all organ systems. This is desirable for metabolism and excretion, but i t can create pmblems. When the concentration of the drug, its blood level, exceeds a critical minimum, certain organ systems may be adversely affected. Excessively high blood level is the usual culprit in local anesthetic toxicity. With some drugs, and certain local anesthetics are among them, a minute quantity can incite a violent response or hypersensitivity reaction. Its milder forms are allergies, but a fulminant hypersensitivity reaction can lead to death. Hypersensitivity. A hypersensitivity reaction to local anesthetics can be seen with even a minute dose. Fortunately, such reactions are quite rare, especially with the newer local anesthetics.
AORN Journal, August 1973, Vol 18, N o 2
Procaine is the one local anesthetic best known to cause occasional hypersensitivity reactions. Repeated exposure to this drug has caused contact dermatitis and massive hypersensitivity reactions. Sensitivity to penicillin may involve procaine, which is widely used in the procaine-penicillin combination.
Emergency treatment. If the patient suddenly collapses after local anesthetic injection, put him on his back, slightly elevate the feet if you can, and then attend to his respiration and circulation. Edema of the airways and asthma-like bronchial constriction may impede breathing. If available, oxygen is the first step. Circulation may be impeded, and external cardiac compression must be instituted if there is no pulse and heart sounds are inaudible. Hypersensitivity reactions are virtually unheard of with newer local anesthetics such as lidocaine or mepivacaine. Hypersensitivity to these amide-linked anesthetics has never been convincingly documented; I consider them essentially non-allergenic. Many patients are branded allergic to local anesthetics. Questioning often reveals that the patient received local anesthetics in a dental office and felt faint, had palpitations or developed a severe headache. However, he reacted not to the local anesthetic but to the epinephrine usually incorporated with the local anesthetic. (Of course, he may just have been needle shy.) Interestingly, patients truly allergic to procaine will not cross-react with amide-type local anesthetics such as Iidocaine or mepivacaine.
Cardiovascular toxicity. Local anesthetics can affect the cardiovascular
system in two ways. One is by direct action of the drug on the heart and/or blood vessels. The other is indirectly, by blocking the nerve supply to the organ. You may have observed an occasional severe hypotension following spinal or peridural anesthesia. Such post-block hypotension is due to blockade of preganglionic autonomic nerve fibers innervating the blood vessels of the legs and viscera; it has nothing to do with toxicity. In years past we were quite concerned about the possibility of profound cardiovascular depression from a local anesthetic overdose. Increasingly, however, cardiologists are using local anesthetics such as lidocaine or procainamide to treat cardiac arrhythmias, such as after a myocardial infarction. Lidocaine, perhaps the most widely used local anesthetic, shows almost no harmful effects even when a rather large intravenous bolus is given to a very sick patient. It appears that the direct cardiovascular effects of local anesthetics concern us only rarely.
Central nervous system toxicity. Although we see this complication infrequently, it can occur frighteningly fast. Local anesthetics have unusual and rather baffling dose-dependent effects on the brain. Generalized convulsions are the ultimate manifestation of local anesthetic toxicity, but are seen only when the blood level is very high. Other signs of cerebral irritability such as excitement, confusion and hysterics range below convulsions and are associated with lower blood levels. At other times, we may see cerebral depressioh instead of excitement; the patient may become drowsy and even drop off to sleep.
AORN Journal, August 1973,Vol 18, No 2
293
Often, when the blood level is rising, fine twitching of the small muscles of the face and eyelids can be noticed and the patient feels “shaky.” Sometimes these symptoms forewarn of an impending convulsion, and decisive action at this stage may avert more serious problems. (Small doses of local anesthetics have been used to treat status epilepticus. Depending on dosage, local anesthetics thus can be anticonvulsants as well as convulsants.) As is so often the case, prevention is the best cure. Evidence dealing with CNS toxicity of local anesthetics is available only from experiments carried out in animals, but the results probably apply to man. One important finding is that hyperventilation raises the brain’s seizure thresho1d.l More local anesthetic is needed to produce a convulsion in a hyperventilated animal than in a normally ventilated one. Thus, when you suspect an imminent reaction tell the patient to take some good, deep breaths. The other observation is that diazepam doubles the local anesthetic seizure threshold in cats, monkeys and r a t s 2 Many of my colleagues therefore premedicate their patients with diazepam prior to local anesthetic injection. If the patient develops generalized convulsions in spite of your efforts, try to be level-headed about the approach. The cardinal rule should be to prevent the patient from injuring himself. If you are alone with a convulsing patient, lay him flat and restrain him as best you can. If handy, oxygen is beneficial, because the respiratory and
294
laryngeal muscles also contract spasmodically during the convulsion. Gas exchange essentially halts at the height of a convulsion. If the patient is not breathing at all, mouth-tomouth respiration becomes essential unless you have some respirating device handy and in working order. Probably by this time convulsions will have stopped, because generally the local anesthetic blood level rapidly drops. Even if not, you must now check the circulation. Feel the pulse and listen to the heart sounds. How pale is the patient? Even convulsive doses of local anesthetic are unlikely to cause cardiac arrest, but they can decrease cardiac output and compromise peripheral circulation. About the best you can do, assuming help is not immediately available, is to elevate the legs trying to improve venous return to the heart. If help is available, and you have taken the important emergency measures outlined, then someone might start an IV to have a pathway for drug administration. However, if you are alone, worry about the other things first. Venipuncture in a thrashing patient is so flustering that you may easily overlook some simpler and more effective means of handling the situation. With an IV going, and if the patient is still convulsing, usual treatment is to give about 50 to 75 mg of a quickacting barbiturate such as thiopental. Anesthesiologists recently have turned to using diazepam instead, injecting about 2.5 mg increments. Convulsions usually are self-limiting, and heroic therapy rarely will be necessary. Summary. Side effects from local anesthetic injection include hyper-
AORN Journal, August 1973, V o l 1 8 , No 2
sensitivity reaction, cardiovascular depression and central nervous system toxicity. Although local anesthetic toxicity occurs only occasionally, knowledge of the etiology and symptomatology of these reactions enables the Operating room and recovery room nurse to administer patient care
that may prevent further complications. FOOTNOTES
R H
de Jong, I H Wagman, and D A Prince, "Effect of Carbon Dioxide on the Cortical Seizure
I.
Threshold to Lidocaine," € x p Neurol,
17 (1967),
221-231. 2. R H d e Jong and
J E Heavner, "Diazepam Prevents Local Anesthetic Seizures,'' Anesthesiology,
3 4 ( I 97 I ) , 523-53 I .
Elecfron microscope insfulled The world's first electron microscope for biomedical research has been installed a t the University of Wisconsin. Capable of magnifying specimens a million times, the equipment enables microscopists to study the ultrastructure of organisms in a continuing effort to fathom the organization and function of the human cell. A second million-volt electron microscope facility i s scheduled to be put into operation a t the University of Colorado, Boulder. Both facilities, supported by grants totaling
$1.7 million from the National Institutes of Health's Division of Research Resources, offer three significant features considered critical for further in-depth biomedical cell research: a) greater specimen penetration, b) reduced specimen damage, and c) greater image resolution. According to Dr Hans Ris, microscopist and program director of the Wisconsin facility, one of the major advantages of the new microscope is the possibility of obtaining images with high resolution of much thicker specimens than was formerly feasible. "For instance, intact cells or sections of plastic-embedded cells one or two micrometers thick show detail to about 20 angstroms with excellent contrast on the million-volt microscope," he said. Dr Ris has been studying chromosomes for some 33 years. He thinks the new electron microscope will move him closer to his goal of unraveling the inner workings of chromosomes. He i s particularly following the DNA fiber "which probably continues through the whole chromosome." The resolution of the electron microscope allows detailed study of intact cells or cell organelles. "The great depth of field of the electron microscope allows stereoscopic imaging through specimen titling,'' pictures never before achieved."
Dr Ris explained. "This provides three dimensional
The instrument a t the University of Wisconsin weighs 28 tons and i s mounted on a 60-ton cement block. The 88-ton installation floats on three compound plastic bags inflated by compressed air. A four-ton crane removes the covers of the generator and accelerator when service is required. Dr Keith Porter i s program director for the Colorado facility. He intends to concentrate on the organization of the nucleolus. Noting that scientists know nothing about this subject, he said, "It's responsible for the organization, shape and function of the cell center. It is an apparatus which we can describe now only in the grossest terms." Both facilities will be available to scientists in the United States who want to delve further into their various specialized cell studies.
AORN Journal, August 1973,Vol 18, N o 2
295
Local anesthetics are amazingly safe drugs, as attested by their widespread use, but they occasionally cause toxic effects. Except for hypersensitivity reactions that take place soon after injection, local anesthetic toxicity generally develops rather slowly because the drug must first be absorbed. Operating and recovery room nurses should be acquainted with the etiology and symptomatology of these reactions. Cool and quick thinking may well avert difficulties for your patient. General considerations. A very important qualification is that local anesthetics block nerves in a reversible manner. When the block wears off, normal function returns to the nerve and it is none the worse for the experience. Locally, these anesthetics may be considered essentially nontoxic. This is not so once they are absorbed. Like any other substance injected into the human body, local anesthetics are eventually picked up by the cir-
292
culatory system and metabolized and/ or excreted. Drugs absorbed by the bloodstream will reach all organ systems. This is desirable for metabolism and excretion, but i t can create pmblems. When the concentration of the drug, its blood level, exceeds a critical minimum, certain organ systems may be adversely affected. Excessively high blood level is the usual culprit in local anesthetic toxicity. With some drugs, and certain local anesthetics are among them, a minute quantity can incite a violent response or hypersensitivity reaction. Its milder forms are allergies, but a fulminant hypersensitivity reaction can lead to death. Hypersensitivity. A hypersensitivity reaction to local anesthetics can be seen with even a minute dose. Fortunately, such reactions are quite rare, especially with the newer local anesthetics.
AORN Journal, August 1973, Vol 18, N o 2
Procaine is the one local anesthetic best known to cause occasional hypersensitivity reactions. Repeated exposure to this drug has caused contact dermatitis and massive hypersensitivity reactions. Sensitivity to penicillin may involve procaine, which is widely used in the procaine-penicillin combination.
Emergency treatment. If the patient suddenly collapses after local anesthetic injection, put him on his back, slightly elevate the feet if you can, and then attend to his respiration and circulation. Edema of the airways and asthma-like bronchial constriction may impede breathing. If available, oxygen is the first step. Circulation may be impeded, and external cardiac compression must be instituted if there is no pulse and heart sounds are inaudible. Hypersensitivity reactions are virtually unheard of with newer local anesthetics such as lidocaine or mepivacaine. Hypersensitivity to these amide-linked anesthetics has never been convincingly documented; I consider them essentially non-allergenic. Many patients are branded allergic to local anesthetics. Questioning often reveals that the patient received local anesthetics in a dental office and felt faint, had palpitations or developed a severe headache. However, he reacted not to the local anesthetic but to the epinephrine usually incorporated with the local anesthetic. (Of course, he may just have been needle shy.) Interestingly, patients truly allergic to procaine will not cross-react with amide-type local anesthetics such as Iidocaine or mepivacaine.
Cardiovascular toxicity. Local anesthetics can affect the cardiovascular
system in two ways. One is by direct action of the drug on the heart and/or blood vessels. The other is indirectly, by blocking the nerve supply to the organ. You may have observed an occasional severe hypotension following spinal or peridural anesthesia. Such post-block hypotension is due to blockade of preganglionic autonomic nerve fibers innervating the blood vessels of the legs and viscera; it has nothing to do with toxicity. In years past we were quite concerned about the possibility of profound cardiovascular depression from a local anesthetic overdose. Increasingly, however, cardiologists are using local anesthetics such as lidocaine or procainamide to treat cardiac arrhythmias, such as after a myocardial infarction. Lidocaine, perhaps the most widely used local anesthetic, shows almost no harmful effects even when a rather large intravenous bolus is given to a very sick patient. It appears that the direct cardiovascular effects of local anesthetics concern us only rarely.
Central nervous system toxicity. Although we see this complication infrequently, it can occur frighteningly fast. Local anesthetics have unusual and rather baffling dose-dependent effects on the brain. Generalized convulsions are the ultimate manifestation of local anesthetic toxicity, but are seen only when the blood level is very high. Other signs of cerebral irritability such as excitement, confusion and hysterics range below convulsions and are associated with lower blood levels. At other times, we may see cerebral depressioh instead of excitement; the patient may become drowsy and even drop off to sleep.
AORN Journal, August 1973,Vol 18, No 2
293
Often, when the blood level is rising, fine twitching of the small muscles of the face and eyelids can be noticed and the patient feels “shaky.” Sometimes these symptoms forewarn of an impending convulsion, and decisive action at this stage may avert more serious problems. (Small doses of local anesthetics have been used to treat status epilepticus. Depending on dosage, local anesthetics thus can be anticonvulsants as well as convulsants.) As is so often the case, prevention is the best cure. Evidence dealing with CNS toxicity of local anesthetics is available only from experiments carried out in animals, but the results probably apply to man. One important finding is that hyperventilation raises the brain’s seizure thresho1d.l More local anesthetic is needed to produce a convulsion in a hyperventilated animal than in a normally ventilated one. Thus, when you suspect an imminent reaction tell the patient to take some good, deep breaths. The other observation is that diazepam doubles the local anesthetic seizure threshold in cats, monkeys and r a t s 2 Many of my colleagues therefore premedicate their patients with diazepam prior to local anesthetic injection. If the patient develops generalized convulsions in spite of your efforts, try to be level-headed about the approach. The cardinal rule should be to prevent the patient from injuring himself. If you are alone with a convulsing patient, lay him flat and restrain him as best you can. If handy, oxygen is beneficial, because the respiratory and
294
laryngeal muscles also contract spasmodically during the convulsion. Gas exchange essentially halts at the height of a convulsion. If the patient is not breathing at all, mouth-tomouth respiration becomes essential unless you have some respirating device handy and in working order. Probably by this time convulsions will have stopped, because generally the local anesthetic blood level rapidly drops. Even if not, you must now check the circulation. Feel the pulse and listen to the heart sounds. How pale is the patient? Even convulsive doses of local anesthetic are unlikely to cause cardiac arrest, but they can decrease cardiac output and compromise peripheral circulation. About the best you can do, assuming help is not immediately available, is to elevate the legs trying to improve venous return to the heart. If help is available, and you have taken the important emergency measures outlined, then someone might start an IV to have a pathway for drug administration. However, if you are alone, worry about the other things first. Venipuncture in a thrashing patient is so flustering that you may easily overlook some simpler and more effective means of handling the situation. With an IV going, and if the patient is still convulsing, usual treatment is to give about 50 to 75 mg of a quickacting barbiturate such as thiopental. Anesthesiologists recently have turned to using diazepam instead, injecting about 2.5 mg increments. Convulsions usually are self-limiting, and heroic therapy rarely will be necessary. Summary. Side effects from local anesthetic injection include hyper-
AORN Journal, August 1973, V o l 1 8 , No 2
sensitivity reaction, cardiovascular depression and central nervous system toxicity. Although local anesthetic toxicity occurs only occasionally, knowledge of the etiology and symptomatology of these reactions enables the Operating room and recovery room nurse to administer patient care
that may prevent further complications. FOOTNOTES
R H
de Jong, I H Wagman, and D A Prince, "Effect of Carbon Dioxide on the Cortical Seizure
I.
Threshold to Lidocaine," € x p Neurol,
17 (1967),
221-231. 2. R H d e Jong and
J E Heavner, "Diazepam Prevents Local Anesthetic Seizures,'' Anesthesiology,
3 4 ( I 97 I ) , 523-53 I .
Elecfron microscope insfulled The world's first electron microscope for biomedical research has been installed a t the University of Wisconsin. Capable of magnifying specimens a million times, the equipment enables microscopists to study the ultrastructure of organisms in a continuing effort to fathom the organization and function of the human cell. A second million-volt electron microscope facility i s scheduled to be put into operation a t the University of Colorado, Boulder. Both facilities, supported by grants totaling
$1.7 million from the National Institutes of Health's Division of Research Resources, offer three significant features considered critical for further in-depth biomedical cell research: a) greater specimen penetration, b) reduced specimen damage, and c) greater image resolution. According to Dr Hans Ris, microscopist and program director of the Wisconsin facility, one of the major advantages of the new microscope is the possibility of obtaining images with high resolution of much thicker specimens than was formerly feasible. "For instance, intact cells or sections of plastic-embedded cells one or two micrometers thick show detail to about 20 angstroms with excellent contrast on the million-volt microscope," he said. Dr Ris has been studying chromosomes for some 33 years. He thinks the new electron microscope will move him closer to his goal of unraveling the inner workings of chromosomes. He i s particularly following the DNA fiber "which probably continues through the whole chromosome." The resolution of the electron microscope allows detailed study of intact cells or cell organelles. "The great depth of field of the electron microscope allows stereoscopic imaging through specimen titling,'' pictures never before achieved."
Dr Ris explained. "This provides three dimensional
The instrument a t the University of Wisconsin weighs 28 tons and i s mounted on a 60-ton cement block. The 88-ton installation floats on three compound plastic bags inflated by compressed air. A four-ton crane removes the covers of the generator and accelerator when service is required. Dr Keith Porter i s program director for the Colorado facility. He intends to concentrate on the organization of the nucleolus. Noting that scientists know nothing about this subject, he said, "It's responsible for the organization, shape and function of the cell center. It is an apparatus which we can describe now only in the grossest terms." Both facilities will be available to scientists in the United States who want to delve further into their various specialized cell studies.
AORN Journal, August 1973,Vol 18, N o 2
295