Leroy D. Vandam

The unfavourable effects of prolonged anaesthesia

Summary and ConclusionsIn the light of recent investigations I have undertaken to re-examine the thesis that prolonged anaesthesia may be shocking Discussion was confined to the pharmacological properties and manner of administration of anaesthetics, although it is recognized that many effects cannot be distinguished from those produced by operation Not only may anaesthetics alter physiology intra-operatively, but their physical properties suggest that retention in the body can extend untoward effects into the postoperative period As an example of postanaesthetic shock the instance was cited of postoperative hypotension refractory to vasopressor drugs Some of the common abnormalities underlying this condition were enumerated, and each subsequently exammed for possible anaesthetic complicityThrough several mechanisms, anaesthetics may contribute to postoperative diminution in plasma volume Anaesthetic respiratory depression and the pattern of intermittent positive pressure breathing applied may induce significant hypoxia The influence of anaesthetics on renal function leads to water and salt retention Disturbances in intermediary carbohydrate metabolism wrought by anaesthetics may aid in the development of metabolic acidosis Finally under some circumstances anaesthetic administration may introduce infection and the prolonged use of nitrous oxide suppress the bone marrowAlthough the picture has been magnified, the total of the changes cited could add considerably to the burdens of an already chemically ill surgical patient If this thesis is an acceptable one, and operations or other procedures requiring prolonged anaesthesia continue to be necessary, it is apparent that anaesthetics must be selected and given with a view to minimizing their supposed shocking propertiesRésuméA la lumière des récentes recherches, j’ai songé à examiner de nouveau la thèse d’après laquelle l’anesthésie de longue durée peut engendrer le choc L’étude a été limitée aux propriétés pharmacologiques des agents anesthésiques et à la façon de les administrer, bien que l’on ne puisse pas toujours distinguer entre leurs effets et ceux de l’opération Les agents anesthésiques peuvent modifier la physiologie non seulement au cours de l’opération, mais leurs propriétés physiques portent à croire que leur rétention dans l’organisme peut produire des effets indésirables même au cours de la période post-opératoire Comme exemple de choc post-anesthésique, on a cité celui de l’hypotension post-opératoire réfractaire aux substances vasopressives Quelques unes des anomalies les plus fréquentes sous-jacentes à cet état ont été énumérées, puis on a recherché pour chacune d’elles des relations possibles avec l’anesthésie.Par le jeu de plusieurs mécanismes, les agents anesthésiques peuvent contribuer à la diminution postopératoire du volume plasmatique La dépression respiratoire anesthésique et l’application d’un système de respiration à pression positive intermittente peuvent entraîner une hypoxie importanteL’action des agents anesthésiques sur la fonction rénale entraîne une rétention d’eau et de sel Les troubles suscités dans le métabolisme intermédiaire des carbonates par les agents anesthésiques peuvent participer à l’installation de l’acidose métabolique Enfin, en certaines circonstances, l’administration d’agents anesthésiques peut introduire une infection, et l’usage prolongé du protoxyde d’azote arrête l’activité de la moelleBien que tout soit exagéré, l’ensemble des changements mentionnés peut aggraver le pronostic chez un malade déjà chimiquement touché Si cette thèse s’avère plausible, et que la chirurgie continue à requérir des anesthésies de longue durée, il est évident que les agents anesthésiques doivent être choisis et administrés en vue de diminuer leurs effets traumatisants

DIURNAL VARIATION IN BLOOD VOLUME OF MAN.

Summary Isotope dilution with I 131 iodinated human serum albumin was used to measure the blood volume of 12 ambulatory, normally active, healthy young adults during the course of a day. Volumes increased and hematocrit decreased significantly on the average with changes most marked by evening.

UNTOWARD REACTIONS TO RADIODIAGNOSTIC CONTRAST MEDIA.

Untoward reactions to radiodiagnostic contrast media have been known since these techniques were first employed. Unless the reaction is of a maior systemic nature, detection is difficult and the over‐all incidence is unknown. Mortality is said to be as high as 1 in 1,000 during intravenous pyelography and 4 in 1,000 on whom cerebral angiograms are performed. The organic iodides are associated with the highest number of reactions, but there is no satisfactory means of predicting toxicity from chemical structure. Results of experimental studies are not readily applicable to man because of variations in experimental design and species differences. Monitoring of physiological function during diagnostic studies in man would provide not only more information but greater safety. History taking and pretesting are not universally reliable in preventing reactions. Efforts should be made to detect reactions at the earliest moment and to apply resuscitative measures as soon as possible.

Circulatory Response to Intra-abdominal Manipulation During Ether Anesthesia in Man

Of 38 patients studied during a steady state of ether anesthesia before performance of the definitive phase of operation, hypotensive episodes were produced in 8 by deliberate intra-abdominal stimulation of various types. The production of hypotension was therefore not only unpredictable in the group as a whole, but it was also possible that a positive response in each case could have been mediated by a different circulatory mechanism. The protocol of these experiments was not designed either by method employed or time interval chosen to detect rapid or early changes responsible for the final steady-state measurements that were made. Arterial systolic, diastolic, mean, and pulse pressures decreased with a decline in pulse rate in several cases. As a result of a decreased stroke volume or slowing of the pulse, the cardiac output declined and was responsible for the pressure alterations observed. There was no directional change in the calculated overall peripheral resistance. The remainder of the circulatory measurements, including central venous pressure and central blood volumes, suggest that the circulatory changes are by no means simply explained and that vasodilation in peripheral vascular beds cannot be ruled out.

Circulatory effects of halothane in patients with heart disease.

Halothane in an inspired concentration of 0.5 per cent in nitrous oxide and oxygen was given to 10 patients with advanced heart disease who were to undergo open cardiac operation. There was either no change or an elevation in systolic, diastolic, and mean arterial pressures. Higher concentrations of halothane, from 1 to 1.5 per cent, reduced the pressure moderately in some cases, more markedly in others. Pronounced change in pulse rate or increased myocardial irritability was not seen with either concentration. With both concentrations, significant diminution in the cardiac output was observed. This depression may have been enhanced by positive pressure control of respiration. The decrease in cardiac output and the tendency toward lowering of blood pressure were accompanied by an elevation in the over‐all peripheral vascular resistance. Changes in circulation time, central venous pressure, and central blood volume were observed but were not, because of lack of more specific information, helpful in the interpretation of the basic circulatory changes.

Anesthesia for Cardioversion

Abstract A method of anesthesia, essentially amnesia, for patients undergoing cardioversion has been presented. A review of the administration of anesthesia in 150 cases has indicated the safety of the method and the absence of complications in this group of patients presenting with cardiac arrhythmias.

Circulatory dynamics of cardiopulmonary bypass

P HYSIOLOGIC and metabolic changes of varying complexity accompany the use of the heart-lung machine in man. These changes relate to many factors, such as the design of the apparatus, the ventilating gas, the pH of the priming blood, the rate and duration of perfusion, the body temperature and the need for and manner of producing cardiac arrest. Many of the changes in acid-base balance, blood volume and myocardial function are difficult or impossible to duplicate in the laboratory. For these reasons this study presents circulatory and respiratory data obtained during cardiopulmonary bypass in 50 adults undergoing operation for a variety of congenital and acquired diseases of the heart. It attempts to integrate the hemodynamic responses, to indicate some unusual responses, and to present technics that have been found helpful in avoiding serious abnormalities.

Anesthesia in Patients with Heart Disease

Anesthesia for the patient with heart disease has become increasingly safer with the passage of years due to a better knowledge of the physiology of heart disease and of the pharmacologic action of anesthetic agents themselves. There are few statistics to support the clinical impression that patients with cardiac disease tolerate anesthesia and surgery well but reports are not lacking. The difficulty in gathering statistics lies in an inability to compare results in comparable groups of patients. Anesthesia is but a small part of the total operative experience. The patient with serious heart disease usually undergoes a relatively long period of preoperative preparation. When ready, he is given preanesthetic medication and is subjected to the administration of an anesthetic. The surgical operation is superimposed on these preliminary events. Subsequently, convalescence with its many physiologic adjustments completes the surgical experience. Anesthetic problems may originate in any of the aforementioned phases of the operative experience. These problems have been briefly reviewed. The most important factor in minimizing the problems of anesthesia itself is the skill and knowledge with which the anesthetic agents are chosen and administered rather than the actual pharmacologic and physiologic effects of the agents themselves. On a background of thorough medical preperation safe anesthesia for the patient with heart disease consists of the careful selection of preanesthetic medication, flawless technic, and use of minimal quantities of anesthetic agents and adjuncts. Despite the attainment of these goals, circulatory and respiratory problems will be encountered. These may be related to the heart disease itself, to medical preparation, pharmacologic side effects, and to a multitude of undesirable respiratory and circulatory reflexes. The latter in turn reside in anesthetic and surgical manipulation. Knowledge of these factors enables the internist to understand the problems of anesthesia and to prepare the patient for the operative experience.

Pharmacologic discovery by anesthesiologists

The discovery of anesthesia in the 1840s has been said to be the first great contribution of pharmacology: yet pharmacology at the time was hardly in a formative stage. It was only after the Franco‐Prussian War that Schmiedeberg established the first laboratory of pharmacology at Strassburg. It is not as simple to discern when the roots of anesthesiology took hold. John Snow, the first physician to devote all of his time to this field, possessed the intellectual qualities, but at a time when it was not possible to benefit from advances in basic science that would have made experimentation possible. Anesthesiology became a true specialty only when its adherents looked beyond mere technical procedure to engage in teaching and investigation. If a time were to be cited for this transition, it would be the late 1920s when Ralph Waters laid the groundwork for the first academic department of anesthesia at Wisconsin. What have been the anesthesiologic contributions to pharmacology since then? One is at first beset with the problem of definition, to define anesthesiologys role in pharmacology. The contribution of anesthesiology may be found largely in the area of applied pharmacology with an emphasis not unlike that of Claude Bernard on the use of drugs to elucidate physiologic processes. But anesthesiology has not overlooked two other traditional pharmacologic aims: to define the safe limits of usage of drugs and to discover and assist in the evaluation of new agents.