Acute effects of exercise on cerebrovascular response and cognitive performance in individuals with stable coronary heart disease.

BACKGROUND: Individuals with coronary heart disease (CHD) exhibit cognitive deficits and cerebrovascular dysfunctions, and are at higher risk of developing dementia. Cognitive function in individuals with CHD has never been studied during acute aerobic exercise. Given the increasing popularity of training at high peak power output (PPO), its impact on cerebrovascular and cognitive functions in individuals with CHD should be further studied. METHOD: Thirty-eight individuals with CHD and 16 healthy controls completed two exercise bouts at 30% and 70% of their individualized PPO on an ergocycle while performing a cognitive task including non-executive and executive conditions. Variations of oxy- deoxy-hemoglobin, and total hemoglobin concentrations were measured on left prefrontal cortex at both PPO using near-infrared spectroscopy. RESULTS: Cognitive task performances were equivalent between groups at all intensity levels. Individuals with CHD exhibited larger variation of deoxyhemoglobin in the executive condition and larger variation in total hemoglobin concentration in all task conditions compared to healthy controls at 70% of PPO. CONCLUSION: Exercising at high intensity seems to have a larger impact on cerebral blood volume in CHD patients compared to healthy age-matched controls. Higher exercise intensity has negative impacts on cerebral blood volume variations during a cognitive task in CHD patients and could potentially lead to other neurocognitive dysfunctions. Other studies are needed to determine if a cognitive task administered during an exercise test could help identify individuals with CHD at higher risk of developing cognitive decline.

Fentanyl in 2% mepivacaine compared with fentanyl in 0.5% bupivacaine: two parallel controlled double blind studies.

The efficacy of epidural mepivacaine and bupivacaine, combined with fentanyl to enhance blockade, was compared in two parallel controlled, double-blind clinical trials. Patients in the studies (n = 91) were scheduled for orthopedic surgery of the legs and a tourniquet was used in all cases. Those patients receiving mepivacaine attended day surgery only, whereas patients receiving bupivacaine were hospitalised. Epidural puncture was performed with a Tuohy needle at the L3-4 level in the lateral decubitus position. Levels of sensory and motor blockade were assessed; adverse reactions and pain during surgery were recorded. There were four groups of patients: 1) 26 received 2% mepivacaine with placebo; 2) 26 received 2% mepivacaine with 0.1 mg fentanyl; 3) 19 received 0.5% bupivacaine with placebo and 4) 20 patients received 0.5% bupivacaine with 0.1 mg fentanyl. The levels of the sensory blockade was comparable in all groups. The degree of motor-blockade was more intense in the mepivacaine groups, but the blockade by mepivacaine lasted shorter. Addition of fentanyl did not change the sensory and motor blockade. Intraoperative pain was reported by: 7 patients in the mepivacaine/placebo group; 4 patients in the mepivacaine/fentanyl group; 4 patients in the bupivacaine/placebo group; and by one patient in the bupivacaine/fentanyl group. These results indicate that fentanyl enhances the quality of epidural blockade when combined with either mepivacaine or bupivacaine.

Ascorbic acid prevents cimetidine-induced decrease of serum hydrocortisone concentrations.

A blind, parallel, prospective, clinical study was conducted to investigate the effect of ascorbic acid on human serum hydrocortisone concentrations which were decreased by the administration of cimetidine. The study population included 16 male adults scheduled for major abdominal vascular surgery. The study was conducted in surgical patients under anaesthesia, in which steroidogenesis was inhibited by cimetidine. The results showed a reduction in serum hydrocortisone concentrations in patients receiving a placebo. In patients receiving ascorbic acid, there was a significant increase in serum hydrocortisone concentration. This reflects the normal serum hydrocortisone profile for this operation and anaesthetic technique. Cimetidine can bind to cytochrome P-450 covering the active haem group, the cytochrome proves to be of vital importance for hydroxylation reactions, involved in human steroidogenesis. Serum hydrocortisone concentrations will decrease when cytochrome P-450 becomes blocked. Intravenous administration of ascorbic acid was supposed to cause relief for this decrease. The reasons are undetermined yet. This investigation proved that ascorbic acid can prevent cimetidine-induced decrease of human serum hydrocortisone concentrations.

The role of ascorbic acid in etomidate toxicity.

Etomidate, a short-acting hypnotic used in anaesthesia, has been shown to block steroidogenesis in man. The free imidazole radical in etomidate binds to cytochrome P450. Serious side-effects of etomidate have only been observed in guinea-pigs and in man, both species relying for restoration of ascorbic acid pools upon resynthesis and upon the daily dietary intake of vitamin C. It has been shown that ascorbic acid and not ACTH can increase serum cortisol concentration during etomidate infusion. Ascorbic acid even restores the ACTH/cortisol ratio to pre-operative values. It is therefore suggested that etomidate blocks ascorbic acid metabolism. Resynthesis of ascorbic acid cannot occur because of the blockade of cytochrome P450. Depletion of the ascorbic acid pool would then cause inhibition of steroidogenesis. This is the case in man and probably also in the guinea-pig. All other species can synthesize their own ascorbic acid from alpha ketogluconic acid.

Modification of corticosteroid synthesis by etomidate/fentanyl and air anesthesia.

The characteristics of cortisol synthesis blockade by an etomidate/fentanyl combination was explored in a group of seven patients undergoing major abdominal vascular surgery. Cortisol, androstene-dione 11-deoxy cortisol (compound S) and ACTH were measured during surgery for three hours. In the fourth hour an ACTH1-24 stimulation test was performed and the reaction of the corticosteroid synthesis was assessed. ACTH and androstene-dione showed a stable concentration during the study, the reaction of androstene-dione to ACTH1-24 was blunted but normal. Compound S and cortisol concentrations decreased during anesthesia and showed no significant increase after stimulation with ACTH1-24. These results indicate that the infusion of etomidate and fentanyl may cause a blockade of the corticosteroid synthesis. The blockade is situated at the place where the conversion of cholesterol to pregnenolone occurs. Because the study was done in clinical setting the results should be interpreted carefully, and confirmed by experimental laboratory results.

Can etomidate cause an Addisonian crisis?

The purpose of this study was to assess if it could have been possible to discover the side effects of etomidate by infusion in an earlier phase of its introduction on the market, using the routine parameters of everyday anesthesiological practice. The study was undertaken in twelve patients scheduled for major abdominal vascular surgery. The effect of etomidate-fentanyl and air anesthesia was compared with the effects of neurolept anesthesia. Arterial blood-pressure, central venous blood pressure, pulse rate, peripheral and central body temperature were recorded continuously. Blood samples were taken every two hours during anesthesia for the estimation of arterial blood gases, cortisol, sodium, potassium and chloride. Significant differences were found mainly for the peripheral-, core temperature difference, the cumulative sodium and cumulative fluid balance from which the diagnosis addisonian crisis could have been made. There were also differences in the incidence of early and late complications and in the recovery rate of the patients after etomidate infusions.

Inhibition of corticosteroidogenesis by etomidate.

The effects of the intravenous anesthetic etomidate have been investigated on ACTH-induced steroidogenesis in vitro, using purified isolated rat adrenal cells. It was found that etomidate almost completely blocked corticosterone production induced by physiological concentrations of ACTH at doses of 200 ng or greater. The mean inhibitory etomidate concentration resulting in 50% inhibition approximated 1.5 X 10(-7)M which is in the range of concentrations measured after clinical doses of etomidate.

Serum levels of cortisol in man during etomidate, fentanyl and air anesthesia, compared with neurolept anesthesia.

The effects of etomidate and fentanyl given as a mixture in continuous infusion and of a classical neuroleptanalgesia, with droperidol and fentanyl, on the serum cortisol levels were compared during and after anesthesia in sixteen patients who were to undergo major abdominal surgery. The results showed that the postoperative increase of serum cortisol levels which occurred in the neurolept group was absent in the group receiving etomidate and fentanyl infusion. During etomidate-fentanyl anesthesia there was a more significant decrease of serum cortisol and no rise in serum cortisol levels in response to synthetic ACTH injection. Etomidate and fentanyl, given as a continuous infusion during major abdominal surgery, block the adrenal mechanism to secrete endogenous cortisol in response to stress or after the administration of adreno-corticotrope hormone.

Airway patency in the unconscious patient.

Airway patency was explored in patients breathing spontaneously under deep halothane anaesthesia. Opening and closing of the airway was observed with a flexible bronchoscope looking proximally from the nasopharynx at the epiglottis and the tongue. With the occiput elevated at various angles the smallest angle of retroflexion of the neck necessary to open the airway was measured. The influence of artificial airways on this angle of retroflexion was measured. Cadaveric preparations of the upper airway were studied to assess the mechanisms involved in airway patency. The results indicate that the epiglottis and not the tongue is the main cause of obstruction of the upper airway. When methods are applied to displace the hyoid anteriorly, the airway will be cleared on most occasions.

Steroid response to ACTH and to ascorbinic acid during infusion of etomidate for general surgery.

The characteristics of the steroid response during an etomidate-fentanyl combination was explored in two groups of five patients undergoing major abdominal vascular surgery. Cortisol, androstene-dion, compound-S and ACTH were measured during surgery for three hours. In the fourth hour, an ACTH1-24 stimulation test was performed in one group and the steroid response was assessed. The other group received ascorbinic acid intravenously and the reaction of the adrenals was measured in the same way. The result indicates that etomidate causes a blockade of the adrenal corticosteroid synthesis at the site of the hydroxylation of cholesterol. This blockade is due to the interaction of the imidazole structure with the cytochrome p-450. Ascorbinic acid is able to overcome this blockade, indicating that cytochrome p-450 is involved in the ascorbinic acid metabolism which is obligatory for the hydroxylation of cholesterol.

Mechanical ventilators for emergency medical care using. A manual resuscitation bag.

It is possible to construct a mechanical ventilator from the parts of a selfinflating resuscitation bag, in combination with a magnetic valve. These ventilators prove to be very helpful for transport of critically ill patients, of all categories, under various conditions. These ventilators can be used by paramedical and medical personnel, but experience in ventilation of patients is mandatory. The ventilators are cheap and reliable, with a stable performance but more sophisticated patterns of ventilation necessitate the use of volume and pressure monitoring. The mode of action of the ventilator, the compliance of different reservoir bags and the place of the mechanical monitor devices are discussed in this article.

Influence of different heparin solutions upon blood gas analysis and biochemical values measured in plasma.

Three types of heparin solutions and their effect on blood gas analysis were investigated in four series of dilutions. pCO2, bicarbonate and pH are related to changes caused by the addition of heparin solution to the sample. These changes may simulate respiratory compensation of a metabolic acidosis. The effects of addition of different volumes and types of heparin solution were investigated. The accuracy of other routine biochemical values were also assessed in plasma and compared with serum. We found significant differences in lactate dehydrogenase, inorganic phosphorus and total protein results. This may be due to the clotting process in the serum samples.

A portable PEEP valve for 0-20 cm H2O.

Positive end expiratory pressure (PEEP) ventilation is a valuable method in modern critical care therapy. Nevertheless it is often necessary to take patients off the ventilator for routine physiotherapy as well as for special investigations and transport. Portable ventilators or manual bag ventilators are used during the offventilator periods. In order to keep the expiratory pressure in the therapeutic range it is desirable to have a portable PEEP valve available. This valve has to be lightweight, small, easy to use, stable and cheap. AMBU Danmark has designed such a PEEP valve which fits onto adult and pediatric Non-Return (NR) valves. The latest design is a green PVC-spring type valve with a pressure range of 0-20 cm H2O. We have evaluated this valve in the laboratory for different flows, temperature, humidity and position, and in the clinic in various situations. We found the AMBU PEEP valve to be accurate and easy to use with a stable performance meeting all requirements for emergency medical care (EMC).

Controlled administration of oxygen with self inflating resuscitation bags.

Resuscitation bags were originally developed to ventilate patients under emergency conditions. Under circumstances where oxygen is available one should make full use of it. The problem of exact air enrichment for these bags has not been satisfactory solved until now. Therefore a system has been developed which furnishes controlled delivery of FIO2 during ventilation with self inflating resuscitation bags. This is obtained via a venturi device connected to the air inlet of the manual resuscitation bag. The FIO2 delivered to the patients from a self inflating bag was tested for values of 24, 30, 40 and 50% oxygen. The new system proved to be capable to delivery exact FIO2 in contrast with previously applied methods of oxygen delivery where this could never be achieved.