Influence of nitrous oxide on rat skin allograft.

Adult male Lewis/f Mai rats underwent skin allografts and the time for complete loss of the graft was compared among different groups treated with different methods. The rats were exposed in isolation chambers to an atmosphere of either room air (control groups I and IV for nitrous oxide-exposed groups, 20% and 40%, respectively); or an atmosphere of oxygen supplemented respectively with 20% and 40% nitrous oxide (the balance being nitrogen) continuously after transplant surgery (Groups II and V respectively); or 48 hours prior to transplantation and with air exposure only after surgery (Groups III or VI respectively). Results indicated that nitrous oxide-exposed rats had significantly prolonged skin allograft survival.

Suppression of chemotaxis to corneal inflammation by nitrous oxide.

Immune competency is depressed in the perioperative period. The role of anesthetic agents in immune reactivity remains unclear. The chemotactic migration of polymorphonuclear leukocytes (PMNs) to the cornea of rabbits injured by clove oil was studied. PMNs were previously radiolabeled with tritiated (3H) thymidine. Immediately following injury, the rabbits entered isolation chambers and breathed either air or air containing 10%, 20% or 40% nitrous oxide (N2O) for 24 hours. After sacrifice, the radioactivity of a 10 mm corneal button, removed by trephination, was determined by scintillation counting technique. Peripheral blood was obtained for hemoglobin, white cell and platelet count. The N2O dosage affected on the migration of PMNs to the cornea. 3H was decreased 15.4% by 20% N2O and 38.8% for 40% N2O-exposed rabbits. Peripheral blood values did not differ. N2O can suppress chemotaxis of PMNs in the rabbit, thereby adversely affecting the inflammatory component of immune defense.

Histamine release by four narcotics: a double-blind study in humans.

Histamine release and hemodynamic changes associated with four narcotics were studied in 60 adults (28 men, 32 women) scheduled for general surgery under balanced anesthesia. Under double-blind conditions, incremental equipotent doses of meperidine, morphine, fentanyl, or sufentanil were administered IV for induction of anesthesia, prior to thiopental, succinylcholine, and intubation. Arterial blood samples were drawn before and 1, 6, and 20 min after narcotic administration. Of the 16 patients given meperidine (mean dose 4.3 +/- 0.2 (SEM) mg/kg), five (31%) had clinical signs (hypotension, tachycardia, erythema) and elevations in plasma histamine levels ranging from 3.2 to 49.7 ng/ml 1 min after narcotic administration. Plasma epinephrine levels at this time were also elevated in these five patients. One of the ten patients given morphine (0.6 +/- 0.02 mg/kg) developed hypotension, tachycardia, and an increase in plasma histamine level to 12.4 ng/ml. None of 34 patients given either fentanyl (7 +/- 0.4 micrograms/kg) or sufentanil (1.3 +/- 0.1 microgram/kg) had clinical signs of histamine release or elevations of plasma histamine levels. In the six patients in whom histamine release occurred, there was a significant correlation between the histamine levels at 1 min and the magnitude of change in heart rate, blood pressure, and plasma epinephrine level. All six histamine releasers were young women, ranging in age from 18 to 35 yr. Histamine release occurred more frequently after meperidine than after the other narcotics, including morphine, and the degree of hemodynamic compromise was related to the increase in plasma histamine concentration.

Comparison of morphine, meperidine, fentanyl, and sufentanil in balanced anesthesia: a double-blind study.

A double-blind study comparing four narcotic analgesics of different potencies, meperidine, morphine, fentanyl, and sufentanil, was performed on consenting patients undergoing general or orthopedic surgery under balanced anesthesia. Blood pressure, measured through an indwelling arterial catheter, was recorded continuously, as were ECG and heart rates. The narcotics, made up in equipotent concentrations, were given as indicated by hemodynamic and clinical signs. Arterial blood samples were taken before and after induction, after intubation, before and after incision, at intervals during the operation, and postoperatively. Hemodynamic values and plasma levels of catecholamines during and after induction, intubation, incision, and throughout the operation were least in patients given sufentanil and greatest in those who received morphine or meperidine. Heart rates increased significantly after induction with meperidine and were significantly higher after intubation in morphine-treated and meperidine-treated patients than they were in patients receiving sufentanil. Intraoperatively, mean arterial blood pressure, rate-pressure product, and plasma norepinephrine levels were lowest in patients receiving sufentanil. Intraoperative plasma epinephrine levels were lowest in patients receiving sufentanil and meperidine. Because of increases in blood pressure, heart rate, or both to greater than 15% above control values, supplementation with a potent inhalational agent was necessary in 38%, 30%, and 29% of the patients given meperidine, morphine, and fentanyl, respectively. No sufentanil patient required supplementation. Side effects, including histamine release accompanied by tachycardia and hypotension, were most frequent and most severe in patients who received meperidine. After extubation, marked increases in heart rate, blood pressure, and plasma norepinephrine and epinephrine occurred in some patients in each group. The incidence of postoperative respiratory depression was greatest in patients given morphine (mean dose of naloxone 8.6 micrograms/kg) and least with sufentanil (mean dose of naloxone 1.8 micrograms/kg) and fentanyl (3.2 micrograms/kg naloxone).

Nitrogen dioxide exposure--influence on rat testes.

Prolonged intermittent exposure to subanesthetic concentrations of nitrous oxide (N2O) can impair spermatogenesis in the LEW/f mai rat. USP purity standards state that N2O used for medical purposes may contain other oxides of nitrogen such as NO and NO2 as impurities at concentrations up to one part per million (ppm) each. The question thus arises as to whether prolonged exposure to N2O may be associated with adverse health effects from oxides of nitrogen other than N2O, particularly NO2. NO2 has demonstrated biological toxicity at concentrations as low as 0.3 ppm. In this study, rats were exposed to filtered air with and without 1 ppm NO2 for 7 hr/day, 5 days/week, for 21 days. No gross or light microscopy abnormality was found in the testes of NO2-exposed rats. Serum vitamin B12 levels were within normal limits. The findings indicate that NO2 exposure under the test conditions does not in itself impair spermatogenesis or alter B12 levels.

Association of post-anaesthetic hyperthermia with abnormal muscle characteristics: a case report.

A previously healthy 18-year-old male, following appendectomy developed post-anaesthetic hyperthermia (42.1 degrees C) with an elevation of serum creatine kinase and activated partial thromboplastin time. Repeated arterial blood gases were normal. Cooling and anti-pyretic medication did not control the fever. In contrast, sodium dantrolene appeared effective in lowering the patient's temperature and normalizing the vital signs, both acutely and over the following three days. Subsequent muscle biopsy revealed a normal contracture response to caffeine alone or in the presence of halothane. However, the muscle had a larger than normal potentiation of evoked twitch tension in the presence of caffeine and halothane. Electrophoresis of the muscle revealed a marked increase of an unidentified low molecular weight protein. The patient's clinical course, and the results of the muscle studies, suggest that an abnormality of skeletal muscle.

Postoperative nitrous oxide analgesia and the functional residual capacity.

Surgery of the upper abdomen is associated with the greatest demand for postoperative analgesia and also is marked by depressed pulmonary function, arterial hypoxemia, and pulmonary complications. Nitrous oxide (N2O) in concentrations of 15-25% is a potent analgesic and is relatively free of untoward side effects if administered for a maximum of 48 h. In the present study, the effect of N2O analgesia on postoperative lung function, in particular, the functional residual capacity (FRC), is examined. Eighteen cholecystectomy patients received either a narcotic (N = 11) or N2O (N = 7) for postoperative analgesia. N2O-treated patients had satisfactory analgesia and maintained FRC at normal levels. Narcotic treated patients had a fall of 22% in FRC. N2O had no effect on the formed elements in peripheral blood.

Helium meter correction equations for oxygen and nitrous oxide.

Helium detectors utilizing thermal conductivity are sensitive to the presence of nitrous oxide (N2O) and oxygen (O2). Measurement of the level of these gases within the spirometer may be used to obtain the true helium concentration for use in the calculation of functional residual capacity (FRC). Linear relationships were obtained relating the change (delta) in reading of the helium meter by nitrous oxide and oxygen. The regression equations are: delta O2 = 0.027 (%O2) - 0.513; delta N2O = -0.276 (%N2O). Failure to correct the helium reading for N2O will overestimate lung volume; elevations of O2 above 21% will underestimate the lung volume.

Histological evaluation of cutaneous wound healing in presence of nitrous oxide in rats.

Three-centimetre linear incisions were made in 90 young male Lew/f Mai rats by scalpel through skin to the investing fascia of the left flank. The skin was undermined sharply for a distance of 0.5 cm along both sides of the entire length of the incision. The wound site was closed per primam with Michel clips and left uncovered. Following emergence from anesthesia, rats were randomly allocated to one of three groups of 30 rats each: one group breathed air only and acted as control; the second was exposed to 20% N2O for 24 hours daily until sacrificed (continuous group); the third was exposed to 20% N2O for 8 hours daily until sacrificed (intermittent group). Ten rats from each of the three groups were sacrificed after 3, 7, or 10 days postincision. After sacrifice, sections from the wound stained with hematoxylin and eosin or reticulin were examined microscopically. No histological evidence of an effect on wound healing of skin occurred in rats exposed to 20% N2O.

Autonomic hyperreflexia during cystoscopy in patients with high spinal cord injuries.

Cystoscopic procedures were performed on 102 patients with histories of traumatic spinal cord lesion; 57 patients had sensorimotor levels above T7, and the remaining 45 patients had levels below T7. In 40 of the 57 patients (70 per cent) with levels above T7, signs and symptoms of autonomic hyperreflexia were seen during bladder distension and cystoscopy; the remaining 17 of these patients (30 per cent) did not have this response. No autonomic hyperreflexia was seen during cystoscopy in any of the 45 patients with sensorimotor levels below T7.

Naloxone antagonism after narcotic-supplemented anesthesia.

Narcotic-supplemented balanced anesthesia is increasing in popularity; however, the narcotic must frequently be antagonized postoperatively. Authorities differ in their recommendations as to dose and as to mode and duration of administration of the narcotic antagonist. In the present study of 58 patients undergoing narcotic-supplemented anesthesia, 60 percent of 42 fentanyl patients and 81 percent of 16 morphine patients required postsurgical naloxone for respiratory inadequacy. Naloxone dosage was initially 1.5 mug/kg IV, with repeat IV doses of 1.5 mug/kg, when needed, at 3-minute intervals, until a regular respiratory rate greater than 15 breaths/min was attained. None of the fentanyl patients and only 25 percent (4/16) of the morphine patients required additional naloxone in the recovery room. For the latter, the dose of naloxone previously administered was given IM and proved satisfactory. Additional analgesia was needed by 12 percent (7/58) of the patients during the recovery room stay. Judicious naloxone titration permitted respiratory adequacy to coexist with analgesia after narcotic-supplemented anesthesia.

Endotracheal intubation and Venturi (jet) ventilation for laser microsurgery of the larynx.

Meeting the exacting requirements for microsurgery of the larynx is a challenge for the anesthesiologist. To accomplish, the necessary dissection, the otolaryngologist has several requirements. They are a quiet relaxed field, excellent illumination with magnification, binocular vision for depth perception, and, above all, an unobstructed field. The management of anesthesia for suspension microsurgery on the larynx presents many problems, the most vexing of which is the fact that the otolaryngologist and anesthesiologist are in competition for access to the patient's airway. In sharing this, neither has been able to perform with the degree of control that he would like due to either inadequate operating conditions or insufficient access to ventilatory mechanisms. Several anesthetic techniques have been used for inspection or operative laryngoscopy: topical anesthesia, apneic techniques, translaryngeal topical anesthesia, chest respirator, neuroleptanalgesia, and general endotracheal anesthesia with muscle relaxants. The latter has proven most popular, particularly in children, because ventilation and surgical conditions are considered to be most controllable. However, the presence of the requisite endotracheal tube obscures the full view of the larynx and vocal cords, and the tube may itself become obstructed. Additionally, use of the laser involves the further risk of heat effects on the endotracheal tube if the beam hits the tube. This report presents our experience and development of the combined technique of endotracheal intubation and Venturi (jet) ventilation. We believe it represents the safest available approach while providing near ideal working conditions for the otolaryngologist during laser microsurgery of the larynx.

Testicular reaction to prolonged exposure to nitrous oxide.

Male LEW/f Mai rats were exposed to an atmosphere of 20 per cent N2O, 20 per cent O2, and 60 per cent N2 for a maximum of 35 days. Evidence of injury to the seminiferous tubules was found in some animals by the second day. By 14 days, such damage was found in all animals. The toxic effect was confined to the spermatogenic cells, with consequent reduction in mature spermatozoa and appearance of multinucleated forms. Other cells within the testes were resistant to damage. Recovery of spermatogenesis occurred after return to room air for more than three days. Serum testosterone levels were not significantly affected during the prolonged exposure.

Corneal injuries during general anesthesia.

A corneal abrasion is the most common eye complication during general anesthesia and recovery. It is painful, may progress to inflammation of the uveal tract, and in the presence of contamination may lead to a serious infection. Both eyes may be involved, as the two reported cases show. Possible causes include mask friction on the open eye or other careless technics. Treatment includes local application of an antibiotic ointment and an eye pressure patch. In addition, a cycloplegic and mydriatic solution is instilled to prevent synechiae (in the presence of a secondary iridocyclitis) and to relieve the pain associated with spasm of the iris and ciliary muscle. Topical application of local anesthetics should be avoided, as they delay regeneration of corneal epithelium and may promote keratitis.