Effect of anaesthesia with nitrous oxide in oxygen and fentanyl on renal function in the artificially ventilated dog

The effect on renal function of a large dose (25 micrograms kg-1) of fentanyl was investigated in 10 labrador dogs. The animals were anaesthetized with nitrous oxide in oxygen and a small supplement of fentanyl 0.4 microgram min-1 throughout the experiment, and muscular relaxation was provided by alcuronium, pulmonary ventilation being controlled. In the initial phase of each experiment, estimated renal plasma flow, glomerular filtration rate, urine volume, mean arterial pressure and renal vascular resistance were measured at 30-min intervals, three sets of samples being taken. Then the large dose of fentanyl was given over a 10-min period and the measurements were repeated at 30-min intervals for 90 min. Changes in renal function lasted for about 90 min; there was a significant decrease in estimated renal plasma flow (P less than 0.01), glomerular filtration rate (P less than 0.001), urine volume (P less than 0.01) and mean arterial pressure (P less than 0.001) together with an increase in renal vascular resistance (0.05 greater than P greater than 0.02). These changes were accompanied by bradycardia, but were still present when atropine was given.     

The effects of large volume intravenous fluid infusion on neonatal renal function

Twenty healthy infants weighing less than 2,000 gm were studied at low (3.6 ml/kg/hr) or high (10.3 ml/kg/hr) rates of intravenous infusion. Inulin clearance determined by the constant infusion method was greater at the high rate of infusion (p = less than 0.05). Inulin clearance in two groups of infants over 2,000 gm studies at the same low or high rates of infusion did not increase at the higher rate of infusion. Since the GFR in infants less than 2,000 gm depends partially on the rate of intravenous infusion, small, healthy preterm infants may benefit from a rate of fluid administration greater than the low rate. When studies at low and high rates of infusion were compared in the 20 infants less than 2,000 gm, the fractional urinary sodium excretion increased with the increased fluid load. Delivery of fluid from the proximal tubule (CH2O =Na per dl GFR) increased (p less than 0.005). Free-water clearance and the absolute volume of urine increased at the high rate of infusion. These data indicate that the healthy preterm infant less than 2,000 gm, like the adult, compensates by increasing free-water clearance and urine volume when challenged with a large fluid load. Although fluid changes of short duration are appropriately handled, the effect of continuous rapid infusion on water and sodium balance in infants of this size remains to be determined.     

The effects of idazoxan combined with 30% nitrous oxide on the jaw-opening reflex in the rat

In rats, the jaw-opening reflex is elicited by activation of a nociceptive receptor by the electric stimulation of the tooth pulp. This study was undertaken to assess the effects of 30% nitrous oxide and 30% nitrous oxide with idazoxan, an alpha 2-adrenergic antagonist, on this reflex. Each rat received electric stimulation for the jaw-opening reflex at 3, 5, 7, 10, 15, and 20 min after both the start of inhalation and the withdrawal of 100% oxygen or 30% nitrous oxide in oxygen. Idazoxan, 400 micrograms/ kg, was administered intravenously at the start of the inhalation period. Amplitudes significantly decreased during inhalation of nitrous oxide, but they returned gradually to control levels after cessation of nitrous oxide inhalation. In the cases of 100% oxygen, 100% oxygen with idazoxan, and 30% nitrous oxide in oxygen with idazoxan, amplitudes did not change from controls during and after 30% nitrous oxide inhalation. The latency remained unchanged irrespective of the treatment. Since in rats the degree of inhibition by 30% nitrous oxide in oxygen is partially diminished by administration of idazoxan, we conclude that nitrous oxide affects an alpha 2-adrenergic receptor in the central nervous system.     

The relationship between respiratory function and the change in end-tidal nitrous oxide concentration

The aim of the present study is to clarify the relationship between respiratory function and the rate of change in alveolar anesthetic concentration. We measured the concentration of end-tidal nitrous oxide (N2O) when 50% N2O was administered to 15 patients of ASA I possessing normal respiratory function during the course of propofol-100% oxygen anesthesia. All patients were ventilated at a rate of 8-10 ml.kg-1 x 8 times per minute using a conventional anesthetic ventilator with semi-closed circuit and 4 l.min-1 inflow of fresh gas. Arterial CO2 partial pressure was maintained at 36.2 +/- 1.8 mmHg and no significant circulatory change was observed while N2O was administered. The rate of increase of end-tidal N2O concentration in poor FEV1.0/FVC% group was significantly slower than that in high FEV1.0/FVC% group, while there was no relation between %VC and the end-tidal N2O concentration change. Since N2O is an inhaled anesthetic, it is well considered that the effect of FEV1.0/FVC% may be observed in other inhaled anesthetic although the magnitude of the effect may vary. The present result suggests that respiratory function, especially FEV1.0/FVC%, is an important factor affecting the rate of change in alveolar anesthetic concentration and, in lower FEV1.0/FVC% group, it takes more time to achieve the intended alveolar concentration.     

Haemodynamic effects of massive doses of hydrocortisone and the interaction with phenoxybenzamine in controlled haemorrhagic shock in the dog

Haemorrhagic shock was produced in anaesthetized dogs by bleeding into a blood reservoir system. The blood level of the reservoir was adjusted at a level above the heart, corresponding to a mean arterial blood pressure of 6.7 kPa (50 mm Hg). The dogs were treated with hydrocortisone and the adrenergic alpha-receptor blocking agent phenoxybenzamine during the hypotension period. Hydrocortisone (80-160 mg kg-1) was found to induce vasodilation, which, however, was of a very small magnitude and was of short duration. Phenoxybenzamine given after hydrocortisone caused very pronounced vasodilation. Hydrocortisone (80 mg kg-1) given after phenoxybenzamine also showed a vasodilator activity, which seemed to be greater than that of the same dose of hydrocortisone given alone. Thus, the vasodilator action of hydrocortisone does not seem to be due to an alpha-receptor blockade of the drug. The vasodilator action of phenoxybenzamine given after hydrocortisone was greater than that of even higher doses of the drug given alone. From the present findings and the fact that corticosteroids are known to potentiate the sympathomimetic action of catecholamines, it is suggested that the hydrocortisone-induced potentiation of the vasodilation action of phenoxybenzamine found is related to an increased vascular adrenergic beta-receptor tone.     

The haemodynamic effects of adrenergic receptor blockade or stimulation druing nitrous oxide anaesthesia in dogs

The effects of ventilation with nitrous oxide in oxygen on myocardial blood flow any oxygen metabolism were investigated in 31 mongrel dogs. The results of this study showed that, compared with controls, hyperoxic nitrous oxide mixtures did not cause any great changes in myocardial haemodynamics, despite a decrease in cardiac output and an increase in systemic vascular resistance. Normoxic nitrous oxide mixtures produced an increase of the coronary blood flow due to decreased coronary vascular resistance. To what extent this coronary vasodilatation resulted from a increased myocardial metabolism or from a direct effect of nitrous oxide on the coronary vascular bed cannot be quantified from the present results.     

Closed system with agent-specific vaporizers and nitrous oxide

Through judicious use of nitrous oxide the closed system can be quite effectively used with currently available equipment including both agent-specific direct-reading percentage vaporizers and suitable devices for the measurement of end-tidal concentrations of oxygen, carbon dioxide and anaesthetic agents. It is only necessary to think in terms of required volumes of fresh gases and vapours added to the system as well as the appropriate concentrations of oxygen and anaesthetic in the respired mixture. When used as described the inspired concentration of nitrous oxide in the closed system should never exceed 50% (usually about 40%). Therefore nitrous oxide will not pose the threat of hypoxaemia unless misused. Experience in teaching this method during the previous decade supports a belief that learning the use of a truly closed circle absorption anaesthesia system is fundamentally important to the development of clinical skills and also facilitates understanding of basic concepts related to respiratory physiology and the uptake and distribution of inhalation anaesthetics. It follows that students and residents should be introduced to this method in the early weeks of their learning experience.     

Effects of information on the reinforcing, subjective, and psychomotor effects of nitrous oxide in healthy volunteers

One method of quality control which has recently been recommended by professional bodies in the UK is the 'rapid review' method. This involves the microscopic 30 s review of all negative cervical smears with the intention of flagging potential missed abnormalities. Although it has been suggested that rapid review is better than 10% random rescreening of negative smears, the efficiency and efficacy of this method of quality control have not been thoroughly evaluated. We have used the AxioHOME system, which can record the area of a slide covered and the screening time, to investigate slide coverage during rapid review quality control, as performed by 15 cytoscreeners and MLSOs reviewing a test set of 22 slides each. The test set comprised 18 negative slides, three positive slides, and one unsatisfactory slide. We have recorded two distinct methods of rapid review in use amongst cytotechnologists, the step method and the whole slide method. The data show that rapid review takes longer on average than the recommended 30 s, the mean screening times being 76 s and 82 s for the step and whole slide methods, respectively. Abnormal smears were missed on three of 15 occasions by the step method (sensitivity 80%, positive predictive value 85%), and on seven of 30 occasions by the whole slide method (sensitivity 76.6%, positive predictive value 45%). However, the 95% confidence intervals were wide (57.7-90.7% for the step method, and 51.9-95.7% for the whole slide method). Analysis of scanning tracks and screening rates shows significant flaws in the methodology of rapid review. Abnormal cells were not identified, although dyskaryotic cells were included in the scanning track on nine occasions, seven using the whole slide method and two using the step method. On one occasion (using the step method) abnormal cells were not identified because they were not included in the scanning track. Further research is in progress to determine optimal methods of rapid review, and whether the rapid review technique is as effective as automated screening systems for quality assurance in cytology.     

Cold water immersion modulates the reinforcing effects of nitrous oxide in healthy volunteers.

The purpose of this study was to determine if a contextual variable manipulation, water temperature of a bath in which a forearm was immersed, would modulate the reinforcing effects of nitrous oxide (N?O) in healthy volunteers (N?=?12). Each of 2 separate choice experiments consisted of a lukewarm water session and a cold water session. Each session consisted of 3 trials: The 1st 2 were sampling trials in which participants inhaled either 100% oxygen or 40% N?0 for 25 min, and the last trial was a 25-min choice trial, in which participants chose between the 2 agents. In each of the 3 trials, participants immersed their forearm in either ice-cold or lukewarm water for 3 min. A variant of the McNemar test revealed that participants were more likely to choose N?O on cold water sessions than on warm water sessions. The authors conclude that N?O was more reinforcing when participants forearms were immersed in ice-cold water than when immersed in lukewarm water. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioural effects induced by nitrous oxide in rats performing a vigilance task

Nitrous oxide (N2O) effects were evaluated, as a behavioural model of inert gas narcosis, in rats performing a vigilance task in which they were required to respond to a slight luminous increment of the house-light. A dose-related decrease of correct responses was produced by the tested range of concentrations of N2O (from 30 to 70% N2O), with a parallel increase of anticipatory responses up to 60% N2O and a dramatic increase of omissions at 70% N2O. The influence of preparatory period duration on hits delays suggested a 'conditional probability effect' conserved under N2O. Pretreatment of animals with flumazenil (a central benzodiazepine receptor antagonist) did not improve performance under 40% N2O. Naltrexone, an opiate receptor antagonist, however, increased the N2O-induced deficits. These results suggest that benzodiazepine receptors are not involved in N2O-induced impairments in this attentional task, but opiate mechanisms may be implicated.     

Long-term effects of antihypertensive agents on proteinuria and renal function

BACKGROUND: Although many studies have examined the effects of antihypertensive agents on proteinuria and glomerular filtration rate in patients with kidney disease, many questions remain unresolved. These questions include whether the effects of agents differ, whether their effects are similar in diabetic and nondiabetic patients with renal disease, and whether the effects of any agents are independent of blood pressure reductions. METHODS: We conducted a meta-analysis of studies obtained with MEDLINE and bibliographies from comprehensive reviews but included only investigations with follow-up times of at least 6 months. We combined data (1) in an analysis of randomized controlled trials, (2) in a separate univariate analysis of controlled and uncontrolled trials, and (3) using weighted multiple linear regression. RESULTS: In 14 randomized controlled trials, angiotensin-converting enzyme inhibitors caused a greater decrease in proteinuria (pooled mean [95% confidence intervals], -0.51[-0.68 to -0.35], ln [treatment/control]), improvement in glomerular filtration rate (0.13 mL/min per month [0.10 to 0.16 mL/min per month]), and decline in mean arterial pressure (-4.0 mm Hg [-4.9 to -3.0 mm Hg]) compared with controls. In a multivariate analysis of controlled and uncontrolled trials, each 10-mm Hg reduction in blood pressure decreased proteinuria (regression coefficient [95% confidence interval] -0.14 [-0.22 to -0.06] ln [after/before]), but angiotensin-converting enzyme inhibitors (-0.45 [-0.58 to -0.32]) and nondihydropyridine calcium antagonists (-0.38 [-0.70 to -0.06]) were associated with additional declines in proteinuria that were independent of blood pressure changes and diabetes. Each 10-mm Hg reduction in blood pressure caused a relative improvement in glomerular filtration rate (0.18 mL/min per month [0.04 to 0.31 mL/min per month]), but among diabetic patients there was a tendency for dihydropyridine calcium antagonists to cause a relative reduction in glomerular filtration rate (-0.68 mL/min per month [-1.31 to -0.04 mL/min per month]). CONCLUSIONS: Long-term beneficial effects of antihypertensive agents on proteinuria and glomerular filtration rate are proportional to blood pressure reductions and are similar in diabetic and nondiabetic patients with renal disease. In addition, angiotensin-converting enzyme inhibitors, and possibly nondihydropyridine calcium antagonists, have additional beneficial effects on proteinuria that are independent of blood pressure reductions.     

Oxygen contamination of the nitrous oxide pipeline supply

Venlafaxine, a structurally novel antidepressant that combines mechanisms of action of both the cyclic antidepressants and SSRIs, may be effective in the treatment of panic disorder. Thirteen patients with DSM-IV panic disorder with or without agoraphobia participated in an open-label, fixed-flexible dose treatment study with venlafaxine. All patients who completed the 10-week trial exhibited statistically significant decreases in scores on anxiety symptoms as well as complete cessation of panic attacks at an effective mean daily dose of 47 mg per day. Venlafaxine was well tolerated in all completers. Venlafaxine may be an effective antipanic agent, even at lower than typical antidepressant dosages.