ISSN:0003-3022    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Halothane in humans depresses the ventilatory response to hypoxemia in a manner that suggests a selective action on one or more components of the peripheral chemoreflex arc. To test the hypothesis that this action is at the carotid bodies themselves, the authors studied the ventilatory response to subanesthetic concentrations of halothane (0.15–0.30% inspired) in six fit volunteers maintained in a steady state of isocapnic hypoxemia (PEo250 mmHg). Upon exposure to halothane, hypoxemia-driven ventilation decreased promptly and progressively (from 7.5 · 1.2 1 · min−1· m−2in the control state to 5.9 · 0.9 and 4.8 · 0.7 1 · min−1· m−2at 30 s and 60 s of inhalation respectively, means · SEM). The relationship of hypoxemia-driven ventilation to end-tidal halothane tensions at 30 and 60 s of halothane wash-in (PEHal0.4 and 0.6 mmHg, respectively) approached the relationship observed in near steady states of halothane inhalation. The results are interpreted as indicating that the site of selective action is at a tissue that accumulates halothane very rapidly during the first minute of inhalation. To make possible such pharmacokinetics, that tissue would require 1) a location having a brief circulatory transit time from the lungs, and 2) an extremely high rate of perfusion in relation to its capacity for uptake of halothane. The only tissue of the peripheral chemoreflex pathway that can satisfy these requirements is that of the carotid bodies.

ISSN:0003-3022    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Various animal models have been used for studies of bupivacaine cardiovascular toxicity. These studies are difficult to relate to the clinical situation, since the disposition of bupivacaine in the various species is unknown. The serum protein binding of bupivacaine, therefore, was determined in human, sheep, monkey, dog, and rat at physiologicpH using ultrafiltration. Since a mixed acidosis results during a systemic toxicity reaction to bupivacaine, the influences of an acidicpH, resulting from the addition of lactic acid, also was examined. All sera exhibited two classes of binding sites, a high-affinity, low-capacity class (class 1) and a low-affinity, high-capacity class (class 2). When compared to human serum at physiologicpH, a significantly higher (P< 0.05) affinity constant for the class 1 sites was observed for all species studied, with the exception of the rat. All species studied exhibited a significantly lower (P< 0.05) capacity for the class 1 sites. The binding parameters of the class 2 sites displayed no significant difference. An acidpH resulted in a decrease in bupivacaine protein binding over the entire concentration range studied for all species, with the exception of the monkey. Monkey serum exhibited no change in bupivacaine binding with a decrease inpH. Since protein binding explains only a portion of the total disposition of bupivacaine, further delineation of each animal model under both acidotic and physiologic conditions needs to be accomplished before the animal studies currently under investigation can be extrapolated to the clinical situation.

ISSN:0003-3022    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

The influence of hyperkalemia on the central nervous system and cardiac toxicity of bupivacaine and lidocaine was studied in open-chested mechanically ventilated dogs. The seizure and cardiotoxic doses of intravenously administered lidocaine and bupivacaine were determined in two separate groups of normokalemic (2.7 · 0.05 SEM mEq/1) dogs. In the case of both anesthetics, the cardiotoxic dose was found to be approximately four times the seizure dose. Under conditions of hyperkalemia (5.4 · 0.08 SEM mEq/1), however, the cardiotoxic doses of both anesthetics were decreased significantly to approximately two times the seizure dose. Hyperkalemia did not change the seizure dose for either anesthetic. The cardiac to seizure dose ratio was decreased significantly for bupivacaine but not for lidocaine. The results of this study suggest that hyperkalemia enhances the cardiotoxic effects of both lidocaine and bupivacaine, with this enhancement being more pronounced in the case of bupivacaine.

ISSN:0003-3022    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

The more rapid rate of rise of alveolar anesthetic partial pressure in children compared with adults may be explained in part by an increasing solubility of volatile anesthetics in blood with age. To investigate this possibility, the authors measured the blood–gas partition coefficients of isoflurane, enflurane, halothane, and methoxy-flurane in four groups of fasting subjects: 10 full-term newborns (at delivery), 11 children (3–7 years old), 11 adults (20–40 years old), and 10 elderly adults (75–85 years old). The blood–gas partition coefficients were greatest in adults: isoflurane 1.46, enflurane 2.07, halothane 2.65, and methoxyflurane 16.0; and least in newborns: 1.19, 1.78, 2.14, 13.3, respectively. The blood-gas partition coefficients in children (1.28, 1.78, 2.39, 15.0, respectively), which were intermediate between those in newborns (P< 0.005) and those in adults (P< 0.005), were not significantly different from those in elderly adults (1.29, 1.79, 2.41, 15.0, respectively). The blood–gas partition coefficients of both isoflurane and enflurane correlated directly with the serum albumin and triglyceride concentrations; that of halothane correlated directly with the serum cholesterol, albumin, triglyceride, and globulin concentrations; and that of methoxyflurane correlated directly with the serum cholesterol, albumin, and globulin concentrations. The authors conclude that 1) age significantly affects blood–gas partition coefficients, and 2) the lower blood–gas partition coefficients in children explain in part the more rapid rise of alveolar anesthetic partial pressure in this age group.

ISSN:0003-3022    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

It is fairly widespread clinical practice to administer large doses of corticosteroids to patients in cases of shock; doses of hydrocortisone as high as 50 mg · kg−1given intravenously have been proposed and used. Hydrocortisone, when administered in this way during surgery, has been implicated in interactions with neuromuscular blocking agents. In order to determine the type and mechanism of this interaction, the authors undertook further investigation. The effects of hydrocortisone were studied in two ways. Firstly, a constant 50% depression of the indirectly elicited twitch tension of the tibialis–anterior muscle was established in cats, using a constant intravenous infusion of either pancuronium (1.0 · 0.2 μg · kg−1· min−1) or succinylcholine (3.6 · 0.8 μg · kg−1· min−1). The effects of intravenous hydrocortisone then were studied on this block. Secondly, cats chronically were treated with 2 mg · kg−1of intramuscular hydrocortisone three times a week for 1 month, and then dose-response curves were constructed for pancuronium or succinylcholine. Acute administration of intravenous hydrocortisone (1–15 mg · kg−1) alone had no affect on the twitch tension of either the tibialis–anterior or soleus muscles, however, the corticosteroid (7 and 15 mg · kg−1) did significantly (P< 0.05) enhance the 50% depression of the indirectly elicited twitch tension of the tibialis–anterior muscle produced by the constant intravenous infusion of pancuronium. The soleus muscle was affected similarly (n = 6). Under the same conditions, with a constant infusion of succinylcholine, hydrocortisone had no effect on the blockade of the tibialis–anterior muscle or the soleus muscle (n = 6). The chronic treatment of male cats with hydrocortisone had no effect on the sensitivity to pancuronium (n = 6) of both the tibialis–anterior and soleus muscles. However, this treatment did produce a significant (P< 0.05) change in sensitivity to succinylcholine (n = 6) on the tibialis–anterior muscle but not on the soleus muscle. Two of the 12 cats chronically treated with hydrocortisone exhibited histologic evidence of myopathy. It is concluded that hydrocortisone can enhance the neuromuscular blocking effect of pancuronium and that chronic hydrocortisone treatment can modify the response to succinylcholine. In either case, monitoring of neuromuscular transmission during anesthesia is suggested when a patient is receiving either high-dose acute or chronic hydrocortisone therapy.

ISSN:0003-3022    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

The effects of nitrous oxide, halothane, ether, isoflurane, thiopental, and thiamylal on the excitatory as well as inhibitory responses of single neurons in the midbrain reticular formation (MRF), believed to be one of the most important sites for the regulation of wakefulness, were studied by long-term, extracellular microelectrode recording in cats and rats. All anesthetics except nitrous oxide suppressed the excitatory responses of MRF neurons evoked by somatosensory stimulation. The inhibitory responses markedly were potentiated by both barbiturates but variously affected by other inhalation anesthetics. Blockade of the inhibitory responses (disinhibition) was observed more frequently with the inhalation agents during the light state of anesthesia. Thus, suppression of excitatory responses is likely to be a general feature of the anesthetic state in terms of the behavior of MRF neurons. Further, potentiation of the inhibitory responses might be characteristic of harbiturate anesthesia.

ISSN:0003-3022    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

The cardiovascular responses to increasing infusion rates of the slow calcium channel inhibitor, verapamil, were studied in three groups of dogs during either enflurane, isoflurane, or halothane anesthesia. Control hemodynamic values and plasma samples were taken after 2 h of anesthesia with the given agent. Increasing infusion rates of verapamil were given to achieve a range of plasma verapamil levels up to approximately 500 ng · ml−1. Each infusion rate was administered for 30 min, at which time repeat measurements and plasma samples for verapamil were taken. Mean arterial blood pressure, cardiac index, and left ventricular dP/dt decreased with increasing plasma verapamil levels in the enflurane and isoflurane groups compared with the control values. The values for the enflurane-verapamil combination were significantly lower than those for the other anesthetics at comparable verapamil levels. Compared with enflurane, higher verapamil levels were required with isoflurane to achieve the equivalent degree of hemodynamic depression. A higher incidence of conduction abnormalities also was noted in the enflurane group. In the halothane group, the only significant change observed at these verapamil levels, achieved by continuous infusion, was a prolongation of the PR interval of the ECG. In this animal model, verapamil was least well tolerated by the cardiovascular system during enflurane anesthesia.

ISSN:0003-3022    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

Depressive effect of halothane on carotid sinus baroreceptor function may be due to direct local action, action in the CNS, or both. Paris of dogs were anesthetized with pentobarbital and ventilated with oxygen. The carotid sinus of the recipient dog was isolated and perfused with blood from the common carotid artery of the donor dog. Blood from the recipient sinus was returned through its external carotid to the donor common carotid. Thus, both carotid sinuses of the donor and the contralateral carotid sinus of the recipient dog received uninterrupted circulation. Carotid sinus nerve action potentials and lingual artery pressure of the isolated recipient sinus were recorded before and during steady state end-tidal halothane concentrations of 0, 0.5, 1.0, 1.5, 2.0, and 2.5% in oxygen, given randomly first to the donor dog (to evaluate direct local effect) and then to the recipient dog (to determine central effect). The dog not given halothane received pentobarbital. Plots of normalized nerve activityversushalothane concentrations showed approximately zero slope when the donor was given halothane but showed significant decrease in nerve activity when the recipient was given halothane. Halothane appears to have no direct local effect but causes depression of baroreceptor nerve activity, possibly via CNS inhibition of sympathetic efferents to the carotid sinus.

ISSN:0003-3022    

出版商:OVID    

年代:1984

数据来源: OVID

摘要:

The confluent sinus pressure was measured in eight mongrel dogs in the head-up position to compare the effectiveness of positive end-expiratory pressure (PEEP) and jugular venous compression in increasing cerebral venous pressure. When the head was elevated 30 cm above the heart, confluent sinus pressure decreased from 9.6 · 1.8 (mean · SEM) to −5.3 · 0.5 mmHg. At constant arterial carbon dioxide tension (Paco2= 28 · 2 mmHg), PEEP (20 cmH2O) did not increase cerebral venous pressure. However, when the jugular veins were compressed with a neck tourniquet with pressures of 20–140 mmHg, cerebral venous pressure increased rapidly. When neck tourniquet pressure was maintained at 40 mmHg, confluent sinus pressure in all dogs was increased and sustained at 2.4 · 0.8 mmHg. Carotid artery pressure measured distal to the tourniquet was not altered. The efficacy of extrathoracic venous pressure elevation (neck tourniquet) is greater than intrathoracic (PEEP), and this may relate to the Starling resistor effects of neck veins and the presence of jugular venous valves. We conclude that prophylactic use of PEEP in the prevention of air embolism during the sitting position may not be as effective as jugular venous compression.

ISSN:0003-3022    

出版商:OVID    

年代:1984

数据来源: OVID