[Rectal anesthesia with methohexital in pediatric ophthalmology].
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Dose-response-curves for rectal induction of anaesthesia in children with 1%- or 5%-methohexitone-solutions and dosages of 5, 10, 15, 20 and 25 mg/kg body wt. were obtained in 10 groups of 20 children. Methohexitone and hydroxy-methohexitone serum-levels were compared in another 23 children after application of 1%- or 5%-methohexitone-solutions at dosages of 15 and 20 mg/kg body wt. The sleep induction quota after 1%-methohexitone-solution in the 20 and 25 mg/kg body wt.-dosages was significantly higher, 20% and 25% respectively, and the mean sleep induction time shorter, 37% and 45% respectively compared with results after 5%. The change after 15 mg/kg body wt. was not significant. A study of dosages 5 and 10 mg/kg body wt. was discontinued due to insufficient effect. Methohexitone serum-levels ranged from 0.7-8 mg/l. All of the children after the use of 1%-methohexitone-solution, and only 60% after 5%-methohexitone had serum concentrations above the sleep inducing "borderline" concentration of 2 mg/l. The differences between mean methohexitone and hydroxy-methohexitone-serum-levels were not significant due to the small groups and the wide range of results. We conclude that individual dosages of 15 or 20 mg/kg body wt. 1%-methohexitone-solution should be applied according to clinical criteria such as physical and psychic status of the child.
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Rectal administration of drugs has become a standard procedure in clinical anesthesia, most notably for anorectal induction in children. Limitations of this method include low bioavailability, a wide scatter of pharmacokinetic and pharmacological results, and poor predictability of the clinical effect in any particular patient. Historically, the rectal route has been used for the administration of smoke ("fumigation") for resuscitation and various other purposes. An ether boiler for rectal application was developed by Pirogoff as early as 1847. The pharmacokinetics of rectally administered drugs are determined by the anatomical properties of the rectum and, owing to interindividual variance, this adds to the inconsistency of absorption. Aspects that can be better controlled include the drug preparation and the vehicle, with hydrophilic solutions resulting in improved absorption. Larger volumes such as are associated with lower concentrations increase the bioavailability by enlarging the mucosal surface in contact with the drug. In contrast to the hypothetical assumption that hepatic circulation may be circumvented--thus avoiding first-pass metabolism--by direct venous drainage from the rectum into the systemic circulation via the vena cava, it has been shown that hepatic clearance is the main factor affecting bioavailability. This may be due to blood flow through anastomoses interconnecting the superior, medium and inferior rectal venous systems. Resorption from the rectum is also determined by physicochemical properties of drugs. According to the pH-partition hypothesis, only the non-ionized moiety of a compound will be available for transmucosal diffusion. The degree of ionization is a function of the local (or microclimate) milieu pH and pKa of the drug; the former is close to neutral in adults but alkaline in most children. Adsorption of feces, intraluminal degradation by microorganisms, metabolism within the mucosal cell, and lymphatic drainage do not significantly affect the fate of rectally administered drugs. In clinical practice, the rectal administration of methohexital and midazolam is an established method of premedication or induction of anesthesia in children; so far, midazolam appears to be associated with fewer complications. Ketamine has been shown to be as effective and as quick-acting as methohexital, but at least in one study its use as sole induction agent was associated with respiratory distress in some cases. However, painful diagnostic or therapeutic procedures in children may be indications for the rectal administration of ketamine. Early trials with rectally administered etomidate have been abandoned since its implication in suppression of cortisol synthesis. Narcotic analgesics in a hydrogel vehicle are effective in adult pain management.(ABSTRACT TRUNCATED AT 400 WORDS)
Rectal application of methohexital for induction of anaesthesia takes into consideration the child's psychological state. However, quite a lot of side effects may occur that are not dependent on age or body weight but on dosage. A clinical study with 66 children from nine months to seven years of age was performed to find out the most adequate dose of methohexital for rectal application. Three groups of children were given, 20, 25 and 30 mg methohexital/kg BW, respectively. Results obtained suggest 25 mg methohexital/kg BW to be the most adequate dose. Failure of induction was seen in 6%. Side effects like respiratory depression, excitation and unexpectedly high plasma levels of methohexital should be considered possible. Methohexital plasma levels of more than 22 micrograms/ml were obtained. Correlation between the effect and side effects of methohexital on the one hand, and maximal plasma levels on the other, were not seen. Since rectal application of methohexital in fact means induction of anaesthesia it should be given only in the presence of an anaesthesiologist and adequate anaesthesia equipment.
Rectal temperatures and heart rates of American river otters (Lutra canadensis) decreased significantly (P less than 0.05) during chemical immobilization with i.m. ketamine hydrochloride in combination with xylazine hydrochloride and acepromazine and during inhalation anesthesia with isoflurane. Anesthetized otters showed a tendency for apnea during induction and while dorsally recumbent, which was reflected by a respiratory acidosis on arterial blood gases. Declines in rectal temperatures and heart rates were not found to be a function of dosage (mg/kg) of the ketamine combination used except for rectal temperatures of otters in relatively poor body condition (inanition). The electrocardiograms of isoflurane-anesthetized otters were similar to those recorded on immobilized otters with the exception of an r' deflection in the ventricular depolarization complex (RSr'). Electrocardiographic criteria were not found which predicted the degree of right ventricular or generalized cardiac enlargement seen radiographically.
The rectal administration of midazolam for premedication of children before induction of anesthesia by mask was investigated in two clinical studies. In 62 children aged between 2 and 10 years, midazolam was given by open design at various dosages (0.15 mg.kg-1, 0.25 mg.kg-1, 0.30 mg.kg-1, 0.35 mg.kg-1, 0.40 mg.kg-1) to evaluate the most effective dose for optimal acceptance of the mask and gas mixture. An additional 40 children between 3 and 9 years received 0.2 mg midazolam.kg-1 body weight or placebo in a double-blind design to estimate the lower limit of efficacy of midazolam. All children were classified as ASA I and had to undergo a surgical procedure. Within the two studies the children were not different with respect to their general data, age, weight, and sex. In both studies more boys than girls were included. Parameters of efficacy were the degree of sedation before and at 10, 20, and 30 min after midazolam as well as acceptance of the mask and the gas mixture at induction of anesthesia. In all groups, including placebo, a sedative and tranquilizing effect of the premedication was found. The rectal administration of 0.35-0.4 mg midazolam.kg-1 is most suitable for the preoperative medication of children between 2 and 10 years. Due to the degree of sedation and the relief of anxiety toward the surroundings and the operation, the induction of anesthesia is optimally accepted by the child. In contrast, the effect of a dose around 0.2 mg midazolam.kg-1 body weight is not much different from that of placebo and is not sufficient for effective premedication.
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Halothane-anesthetized Mongolian gerbils were submitted to 5-min bilateral carotid artery occlusion. After ischemia, halothane anesthesia was continued for various periods of up to 85 min, and the degree of CA1 neuronal injury was estimated 7 days later by counting the number of surviving pyramidal cells. During ischemia and postischemic halothane anesthesia, rectal and cranial temperature was kept at control level (37.7 and 37.0 degrees C, respectively) using a feedback-controlled heating system. When anesthesia was discontinued after ischemia, transient hyperthermia occurred. In animals with 0- and 15-min postischemic halothane anesthesia, both cranial and rectal temperature rose by approximately 1.5 degrees C, and the number of surviving CA1 neurons amounted to less than 25% of control. After 45- or 85-min postischemic anesthesia, hyperthermia was significantly reduced and the number of surviving neurons increased to 65 and 89%, respectively. The protective effect of postischemic anesthesia was lost when anesthetized animals were submitted to the same hyperthermic profile as nonanesthetized ones, using a feedback-controlled heating system (16% surviving neurons in hyperthermia vs. 89% in normothermia, respectively). These observations demonstrate that postischemic anesthesia with 1% halothane protects against delayed neuronal death by preventing postischemic hyperthermia and not by its anesthetic effects.
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Sixty-one children, ASA physical status I, aged 2-14 years, admitted for strabismus surgery were studied. All were premedicated with diazepam and atropin rectally. Anesthesia was induced with thiopental or with halothane on a facemask, and succinylcholine was given to facilitate tracheal intubation. Anesthesia was maintained with halothane and nitrous oxide. Each child was randomly assigned to receive either no antiemetic prophylaxis (control), droperidol 0.075 mg/kg, or dixyrazine 0.25 mg/kg. The drugs were injected intravenously at the end of surgery. The incidence of vomiting during the following 24 h was 65% in the control group, 48% in the droperidol group, and 25% in the dixyrazine group (P less than 0.05 as compared to the control group). Four hours after the operation, six children in the droperidol group and none in the dixyrazine group (P less than 0.05) were difficult to arouse. It is concluded that dixyrazine reduces the incidence of postoperative vomiting without causing heavy sedation.
To characterise the response in the plasma concentration of Zn a total of 60 male Wistar rats (250 g) were divided into six groups of ten rats each. One group did not exercise; the five other groups swam at constant temperature (32/34 degrees C) and were respectively studied after 30, 60, 90, 120 min and at exhaustion. After anesthesia, rectal temperature (RT) was measured and arterial blood was obtained from the abdominal aorta. Acidbase balance, arterial blood gases and plasma concentration of Zn, Cu, Mg, Ca and Hb were measured. The swimming time at exhaustion was (mean +/- SD) 284 +/- 66 min. RT only changed after exhaustion. (H+) increased significantly at 30 min then did not change until exhaustion. (Hb) increased slightly at 90 and 120 min of swimming and after exhaustion. No changes of Mg and Ca except at exhaustion were observed (+7 and +50% respectively). On the other hand, Cu (30 min = +16%; 60 min = +29% exhaustion = +36%) and Zn (30 min = +26%; 60 min = +39%; 120 min = +66% and exhaustion = +76%) increased significantly through the two first hours of exercise. Haemoconcentration, acidosis and RT did not explain the progressive increase of Zn, which seems to be time-dependent and probably related to some degree of stress.
In cancer surgery, operating time, tissue trauma and other stress should be minimized because circulating dormant tumor cells may be reactivated by stress, including that of anesthesia. Rectal polyps and Sertoli-cell tumors should be removed as soon after diagnosis as possible. Neutering is recommended to reduce the risk of certain tumors. Biopsies should contain tissue from the center and periphery of the lesion. Laparotomy or thoracotomy may be necessary to visually inspect internal tumors. Debulking or partial resection of large tumors may render them more susceptible to chemotherapy or irradiation. Palliative surgery may be desirable to comfortably prolong an animal's life. In curative surgery, enlarged local lymph nodes should also be resected, hemorrhage controlled and lavage used to prevent tumor-cell seeding. Complete resection should take precedence over reconstructing the defect created by resection.
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The authors evaluated the efficacy of rectally administered midazolam for preinduction (i.e., premedication/induction) of anesthesia in 67 pediatric patients, ASA physical status 1 or 2, undergoing a variety of elective surgical procedures. In phase 1, 41 children weighing 12 +/- 3 kg (range 7-20 kg) and 31 +/- 16 months (range 8-67 months) of age (mean +/- SD) received midazolam, 0.4-5.0 mg.kg-1, in an attempt to produce unconsciousness. Only one child lost consciousness (4.5 mg.kg-1). However, at all doses, inhalational induction of anesthesia was facilitated because children were tranquil and calmly separated from their parent(s). There were no clinically significant changes in arterial blood pressure, heart rate, oxyhemoglobin saturation, and end-tidal carbon dioxide concentration, 10 min after drug administration. In phase 2, 26 children weighing 17 +/- 4 kg (range 10-26 kg) and 44 +/- 19 months (range 17-84 months) months of age undergoing tonsil and/or adenoid surgery were studied to determine the optimal sedative dose of rectally administered midazolam. Patients received 0.3, 1.0, 2.0, or 3.0 mg.kg-1 of midazolam in a randomized, double-blind fashion. One third (3 of 9) of patients receiving 0.3 mg.kg-1 struggled during mask induction. All patients receiving greater than or equal to 1.0 mg.kg-1 were adequately sedated (P less than 0.008). Discharge from the postanesthesia care unit (PACU), however, was delayed (greater than 60 min) in children receiving greater than or equal to 2.0 mg.kg-1 (P less than 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)
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