Robert K. Stoelting

Monitoring of multimodality evoked potentials during open heart surgery under hypothermia.

Multimodality evoked responses (ERs) were monitored in 16 adults who had cardiac surgery under cardiopulmonary bypass and moderate hypothermia (19-25 degrees C). Cooling affected all sensory ERs by progressively increasing the latencies of the major components. The effect was more profound on the later than on the earlier ER components. Visual evoked responses (VERs) were most inconsistent and always disappeared at temperatures below 25 degrees C. The later components of the long latency somatosensory evoked responses (SERs) also attenuated or disappeared rather early during hypothermia. On the other hand, short latency SERs were more resistant to the effects of hypothermia. They were always recordable at temperatures of 25 degrees C or above; and usually persisted even at temperatures between 20 and 25 degrees C. Brain-stem auditory evoked responses (BAERs) were consistently present at temperatures above 25 degrees C, wave V was recordable in majority between 20 and 25 degrees C. All sensory ERs disappeared with severe hypothermia (20 degrees C or less) except the components generated more peripherally such as N10 of the short latency SERs. We feel that BAERs and short latency SERs may serve as useful intraoperative monitors of brain function during hypothermia.

Haemodynamic changes and circulating histamine concentrations following protamine administration to patients and dogs

Haemodynamic changes and the circulating concentrations of histamine associated with the intravenous infusion of protamine were measured in six adult patients undergoing elective aortocoronary bypass graft. surgery and twelve halothane-anuesthetized dogs. Administration of protamine (4.7 mg-kg-1) over five minutes to patients at the conclusion of cardiopulmonary bypass did not produce haemodynamic changes or alterations in the arterial or mixed venous concentrations of histamine, Likewise, the administration of protamine (4.5 mg-kg~’) over five minutes to six dogs produced no haemodynamic changes or alterations in the arterial concentrations of histamine. Conversely, administration of protamine (4.5 tng-kg-1) as a rapid intravenous injection to six other dogs produced a decrease (about 30 per cent below control) in systolic, diastolic and mean arterial pressure (p < 0.05) at 2.5 minutes following the injection. These decreases in blood pressure were paralleled by increases in the arterial concentration of hi stamine from 295 ± 71 pg.(mean ± SD) before protamine to 860 ±6 465 pg.(p < 0.05)2.5 minutes after protamine. Haemo-dynamic changes and the arterial concentration of histamine were not different from control five minutes after protamine administration.It is concluded that administration of protamine over five minutes to patients or dogs does not evoke significant haemodynamic changes or alterations in circulating concentrations of histamine. Conversely, rapid injection of protamine to dogs evokes transient decreases in blood pressure that are paralleled by increases in the arterial concentrations of histamine.RésuméOn a mesuré les répercussions sur l’ hémodynamique et les concentrations plasmatiques d’histamine occasionnées par I’infusion de protamine chez six patients adulles opérés pour aorto-coronarien et chez douze chiens anesthésiés a I’ha/othane.Chez les patients à I’arrêt de la circulation extra-corporelle, I’infusion de protamine (4.7 mgkg-1) n’a en aucun effet sur I’hémodynamique ou les concentrations artérielles et veineuses dhistamine. De la méne façon, I’infusion d’une dose de 4.5 mg-kg-1 de protamine sur une période de cinq minutes chez six chiens n’a en aucun effet. Cependant lorsque la dose a été administrée en injection intraveineuse rapide à six autres chiens, on a observé une réduction de t’ordre de 30 pour cent de la pression artérielle systolique et diastolique et moyenne (p < 0.05)2.5 minutes après I’injection. Ces modifications de pression artérielle s’accompagnaient de facon paral-lile d’une augmentation de la concentration arterielle d’ histamine, concentration qui passait de295 ± 77 pg-ml (M ± DS) à 860 ± 465 pg-ml-1 (p < 0.05) 2.5 minutes apres l’injection. Ces mesures d’ hhnodynamie et d’histamine avaient retrouvé les valeurs de contrôle cinq minutes après léadministration de protamine.On en conclut que l’injection de protamine sur un période de cinq minutes aux patients comme aux chiens ne suscite pas de modifications hémodynamiques notables ou de changements de concentration de I’histamine plasmatique. Cependant, I’injection rapide de protamine chez des chiens provoque une diminution fugace de la pression artérielle, diminution qui s’accompagne de concentration à la hausse d’histamine dans le sang artériel.

Choice of muscle relaxants in patients with heart disease

Summary The presence or absence of circulatory effects induced by muscle relaxants is often cited in the decision process for selection for the most appropriate drug for production of skeletal muscle paralysis in patients with heart disease undergoing surgery. With the exception of pancuronium, all the other currently available nondepolarizing muscle relaxants are devoid of circulatory effects or evoke histamine release only when large doses (about 3×ED95) are administered rapidly. Indeed, it seems undeniable that the circulatory effects of muscle relaxants, when they do occur, are modest, transient, and rarely of clinical significance. More important than muscle-relaxant-induced circulatory effects is their recovery profile and the likelihood that residual (“subclinical”) skeletal muscle paralysis will persist despite drugassisted antagonism. In this regard, when the issue of patient safety is considered, the higher cost of short-acting and intermediate-acting nondepolarizing muscle relaxants seems justifiable. What a difference 10 years can make!29

Aortocoronary Vein Graft Flow in Response to Peripheral Venous Administration of Sodium Nitroprusside or Diazepam

Vein graft flow (VGF) in response to peripheral venous administration of sodium nitroprusside (SNP) or diazepam was studied in 13 anesthetized patients following cardiopulmonary bypass for aortocoronary vein bypass graft operations. SNP (0.5 microgram/kg/min) significantly reduced mean arterial pressure (p less than 0.05). VGF paralleled the decreased blood pressure, but the reduction was not significant (p greater than 0.05). Diazepam (0.1 mg/kg) did not significantly alter blood pressure or VGF. We conclude that peripheral venous administration of SNP or diazepam is not a pharmacologically reliable method by which to increase VGF in the period immediately following a graft operation.

The Evolution of Premedication

Morton’s demonstration of the anesthetic effects of diethyl ether (ether) made painless surgery possible, but ether irritated the airways, often initiating laryngospasm and stimulating production of secretions. Premedication’the administration of drugs before induction of anesthesia’alleviated such problems. Over the latter half of the nineteenth century, clinicians increasingly injected morphine and scopolamine or atropine before ether anesthesia. The capacity of morphine to depress breathing was of limited concern because ether did not appear to depress breathing. The rationale for using premedication before chloroform, was less compelling. Chloroform depressed breathing and did not irritate the airway or promote secretions. However, morphine plus scopolamine could decrease preoperative apprehension before anesthesia with either ether or chloroform. Introduced in 1934, pentobarbital might be given as premedication in place of or in addition to morphine. It offered two advantages over morphine: greater sedation and much less postoperative nausea and vomiting.