Magnesium deficiency increases ketamine sensitivity in rats

PURPOSE

Inhibition of the NMDA receptor likely contributes to ketamine's neurodepressive properties. Magnesium also inhibits the NMDA receptor by binding to a site associated with the ketamine-binding domain. Electrophysiological studies suggest that magnesium prevents ketamine from binding to the NMDA receptor and thereby prevents ketamine inhibition. We undertook an in vivo study to determine if magnesium deficiency was associated with an increased sensitivity to ketamine.

METHODS

Weanling rats were maintained on a Mg(2+)-deficient or control diet for 14 days. In Study I, rats were anaesthetized then sacrificed and the Mg2+ concentrations in the brain and plasma were measured. In a second prospective study, experimental animals were rendered hypomagnesaemic and the potency of 125 mg.kg-1 ip ketamine was evaluated. Animals were then were fed a Mg(2+)-containing diet and ketamine sensitivity was re-examined 14 days later.

RESULTS

The Mg(2+)-deficient diets rendered the rats hypomagnesaemic as indicated by the brain and plasma concentration of Mg2+. In Study 2, the time to loss of righting reflex was shorter; 1.9 +/- 0.3 min (n = 12) and 2.6 +/- 0.2 min (n = 16, P < 0.05), whereas the latency to toe pinch was prolonged: 25.0 +/- 5.8 min (n = 12) vs 3.1 +/- 2.1 min (n = 16, P < 0.05) in the Mg(2+)-deficient compared with age-matched control animals, respectively. The hypomagnesaemic animals had a higher death rate following ketamine injection. The increased sensitivity to ketamine was no longer apparent when the animals were re-tested following replenishment of Mg2+.

CONCLUSION

Hypomagnesaemia is associated with an increased sensitivity to ketamine.

Objective predictors of response for staple versus laser emphysematous lung reduction

Recently described surgical approaches to the treatment of emphysema, including buttressed stapled volume reduction and laser coagulation, are associated with variable clinical outcomes. We examined objective preoperative factors as predictors of response to treatment in patients enrolled in a randomized trial of staple versus laser volume-reduction surgery in order to help define patient selection criteria for these procedures. Seventy-two patients with severe symptomatic emphysema without bullae were entered into the protocol (39 staple, 33 laser). Preoperative objective variables (pulmonary function tests, smoking history, demographics, and graded chest computed tomographic [CT] scans) were evaluated as predictors of response to treatment (defined as a change in FEV1) at 3- to 6-mo follow-up, using linear and multivariate regression analysis. Follow-up pulmonary function was obtained on 90% of the 68 patients surviving at 6 mo. Overall improvement was significant only for staple-treated patients, and improved outcome correlated with greater smoking history and younger age for staple-treated patients. When physiologic variables were analyzed, greater smoking history, lower DL(CO), and younger age predicted improved outcome for laser-treated patients. Preoperative FEV1 and gas-exchange variables did not predict outcome in staple-treated patients. When CT scan grading was included in multivariate regression analysis, hyperinflation (increased thoracic gas volume) was the primary predictor of response for laser-treated patients. These findings suggest that younger patients with evidence of advanced emphysematous lung disease and hyperinflation are optimal candidates for lung-volume-reduction surgery, particularly by staple-reduction techniques. Additional studies with long-term follow-up, bilateral procedures, and assessment of other outcome measures must be performed to further define operative criteria for lung-volume-reduction surgery for emphysema.

Predictors of carbon monoxide and hydrogen cyanide exposure in smoke inhalation patients

OBJECTIVE

A prospective study of civilian (nonfirefighter) smoke inhalation patients was carried out to test the hypotheses that: 1) absorption of carbon monoxide and hydrogen cyanide from smoke can be predicted by clinical examination and historical data; and, more specifically 2) a history of exposure to burning synthetic polymers is an important predictor of systemic cyanide levels.

METHODS

The study was conducted over a three-year period at six urban hospitals. Patients with or without burns who were exposed to smoke within five hours of hospital arrival were sampled for carboxyhemoglobin, whole blood cyanide, urine cotinine and urine creatinine. Controls consisted of a smaller group of smoking status-matched, nonsmoke-exposed burn patients.

ANALYSIS

Historical information was obtained on SMOKING status, FIRETYPE (structural vs other), MATERIAL burned (natural vs synthetic) and LAGTIME (from exposure to sampling). A smoke inhalation SCORE (0-10) was assigned to each case, based on physical examination findings and changes on chest X ray, and carboxyhemoglobin and cyanide levels were entered into various multivariate linear regression models.

RESULTS

A total of 40 cases and 9 controls were recruited, ranging in age from 15 to 92 years. Thirty-four cases were discharged alive and six expired in-hospital. Observed carboxyhemoglobin levels ranged from 1.2% to 41.6% in cases (mean 8.6%), and from 0.5 to 7.3% in controls (mean 2.9%). Observed cyanide levels ranged from nondetectable (< 0.05 micrograms/mL) to 2.79 micrograms/mL in cases (mean 0.25 micrograms/mL), and from nondetectable to 0.11 micrograms/mL in controls (mean 0.03 micrograms/mL). Among cases, linear regression models explained up to 35% of the observed variance in carboxyhemoglobin levels (p < 0.001) and up to 48% of the variance in cyanide levels (p = 0.0001).

CONCLUSIONS

SCORE was the strongest predictor of both carboxyhemoglobin and cyanide levels; LAGTIME also explained significant variance for [log-transformed] carboxyhemoglobin. Historical factors, such as FIRETYPE, MATERIAL, and SMOKING status, did not explain significant variance in most of the statistical models employed.

Infrared emission from reactions of high-velocity atomic oxygen with black surfaces: Z306 paint, anodized aluminum, and Teflon

Large optical telescopes are being placed into orbit at altitudes where the residual atmosphere can interact with the spacecraft to produce optical emissions, such as the visible shuttle glow. The near-field emissions produced from these interactions will reduce the far-field detection limits of these instruments. Here we present laboratory data on the intensities and spectral distributions of the infrared emissions created in the interaction at orbital velocity of the dominant atmospheric constituent, atomic oxygen, with optical baffle coating materials used on space observatory platforms: Z306 Chemglaze paint, black anodized aluminum, and black Teflon. Data over the 1.0-5.4-µm spectral region are presented. Adsorbed contaminants dominate the spectra of the less reactive coatings. We present data on contaminant removal with oxygen fluence. We also include a simple assessment, based on these data, of the magnitude of this interaction and its effect on mission performance.

Crohn's ileitis in a patient with longstanding HIV infection

The differential diagnosis of diarrhea in patients infected with HIV is broad, and includes a variety of bacterial, viral, and parasitic pathogens, as well as malignancies including lymphoma and Kaposi's sarcoma. Idiopathic non-specific inflammatory bowel disease rarely occurs in association with HIV infection. A recent case report described a patient with longstanding Crohn's disease who experienced remission of his bowel disease upon infection with HIV (6). The authors inferred that the remission was secondary to a depressed CD4 (T helper) lymphocyte count. We report the first case of Crohn's ileitis developing in a patient with established HIV infection, depressed CD4 lymphocyte count, and no prior history of inflammatory bowel disease. This case raises questions about the role of CD4 cells in the pathogenesis of Crohn's disease.

Langerhans' cell histiocytosis presenting with the superior vena cava syndrome: a case report

A case of Langerhans' cell histiocytosis confined to the mediastinum and presenting with de novo superior cava syndrome is reported. The causes of superior vena cava syndrome in childhood are discussed as is the importance of obtaining pathologic diagnosis prior to initiating therapy.

Cardiovascular effects of human insular cortex stimulation

Recent investigations indicate a site of cardiac representation within the left insular cortex of the rat. Moreover, the results of lesion studies suggest left-sided insular dominance for sympathetic cardiovascular effects. It is unclear whether similar representation exists within the human insular cortex. Five epileptic patients underwent intraoperative insular stimulation prior to temporal lobectomy for seizure control. On stimulation of the left insular cortex, bradycardia and depressor responses were more frequently produced than tachycardia and pressor effects (p less than 0.005). The converse applied for the right insular cortex. We believe this to be the first demonstration of cardiovascular changes elicitable during insular stimulation in humans, and of lateralization of such responses for a cortical site. In humans, unlike the rat, there appears to be right-sided dominance for sympathetic effects. These findings may be of relevance in predicting the autonomic effects of stroke in humans and in the explanation of sudden unexpected epileptic death.

Isoflurane for refractory status epilepticus: a clinical series

General anesthesia has been recommended to control convulsive status epilepticus that is refractory to conventional anticonvulsant therapy. Halothane has been the recommended agent, but without experimental justification. Isoflurane, which has no reported organ toxicity and produces electrographic suppression at clinically useful concentrations in normal humans, should be a better volatile anesthetic for this purpose. The efficacy and safety of isoflurane administered to control convulsive status epilepticus were assessed on 11 occasions in nine patients in seven North American hospitals. Isoflurane, administered for 1-55 h, stopped seizures in all patients and was able to be titrated to produce burst-suppression patterns on electroencephalograms. Blood pressure support with iv fluids and/or pressor infusions was required in all of the patients. Seizures resumed upon discontinuation of isoflurane on eight of 11 occasions. Six of the nine patients died. The three survivors sustained cognitive deficits. In one patient urine fluoride concentrations were elevated, although not to nephrotoxic levels. These cases suggest that isoflurane 1) is an effective, rapidly titratable anticonvulsant; 2) does not reverse underlying causes of the refractory seizures; and 3) usually necessitates hemodynamic support with fluids and/or pressors. Isoflurane may be administered for seizures, but only when iv agents in anesthetic doses are ineffective or produce unacceptable side effects.

Angiostrongyliasis: a rare cause of gastrointestinal hemorrhage

Angiostrongylus costaricensis is an intestinal nematode, endemic to Central and South America. Affecting mostly children, it causes an eosinophilic gastroenteritis with involvement of the appendix, distal small bowel, and right colon. We report a case of a 41-yr-old man, from a non-endemic area, with the unique presentation of recurrent gastrointestinal bleeding. The diagnosis was made after surgical exploration.

Patient anesthesia and monitoring at a 1.5-T MRI installation

This paper describes the facilities successfully used to provide patient monitoring and anesthesia support in a 1.5-T imaging installation. The requirements for the MRI site for anesthetic gases, shielded power, and radiofrequency ports are outlined. Specific modifications in anesthesia machines, anesthesia cart, laryngoscope, mercury sphygmomanometer, oximeter, and remote blood pressure devices are described. Additional aspects of patient monitoring and support, e.g., electrocardiogram and pressure infusion, are also discussed.

Aminophylline increases the toxicity but not the efficacy of an inhaled beta-adrenergic agonist in the treatment of acute exacerbations of asthma

We studied 40 patients with acute exacerbations of asthma to determine the efficacy of a 3-h intravenous infusion of aminophylline in patients who were already being treated with an inhaled beta-adrenergic agonist (metaproterenol). Each patient was treated with inhaled metaproterenol at hourly intervals for 3 h. In addition, patients were randomly assigned to therapy with either intravenous aminophylline or placebo. Neither the patient nor the house officers and nurses caring for the patient knew whether aminophylline or placebo was given. The FEV1 improved continually throughout the study to a similar extent in both treatment groups, but the patients treated with aminophylline had significantly more adverse effects (p less than 0.025, Mann-Whitney). There was no apparent benefit from aminophylline even in patients who presented to the emergency room with severe airway obstruction (FEV1 less than 0.8L) or with plasma theophylline levels less than 10 mg/L. We conclude that intravenous aminophylline adds to the toxicity but not the efficacy of inhaled metaproterenol in the treatment of acute exacerbations of asthma.

Isospora belli in a patient with acquired immunodeficiency syndrome

Isospora belli is a cause of protracted diarrhea in immunocompromised patients. Acquired immunodeficiency syndrome (AIDS), seen mostly in homosexual men and narcotic addicts, predisposes affected persons to a number of opportunistic infections. As Isospora belli has been reported only once in this group, we report Isospora belli in an AIDS patient with chronic diarrhea.