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At least 109 records · Page 6Linked to original sources
PubMed2004

Lung volume in mechanically ventilated patients: measurement by simplified helium dilution compared to quantitative CT scan.

OBJECTIVE: We describe a simplified helium dilution technique to measure end-expiratory lung volume (EELV) in mechanically ventilated patients. We assessed both its accuracy in comparison with quantitative computerized tomography (CT) and its precision. DESIGN AND SETTING: Prospective human study. PATIENTS: Twenty-one mechanically ventilated ALI/ARDS patients. INTERVENTIONS: All patients underwent a spiral CT scan of the thorax during an end-expiratory occlusion. From the CT scan we computed the gas volume of the lungs (EELVCT). Within a few minutes, a rebreathing bag, containing a known amount of helium, was connected to the endotracheal tube, and the gas mixture diluted in the patient's lungs by delivering at least ten large tidal volumes. From the final helium concentration, EELV could be calculated by a standard formula (EELVHe). MEASUREMENT AND RESULTS: The results obtained by the two techniques showed a good correlation (EELVHe=208+0.858xEELV(CT), r=0.941; P<0.001). Bias between the two techniques was 32.5+/-202.8 ml (95% limits of agreement were -373 ml and +438 ml), with a mean absolute difference of 15%. The amount of pathological tissue did not affect the difference between the two techniques, while the amount of hyperinflated tissue did. Bias between two repeated helium EELV measurements was -24+/-83 ml (95% limits of agreement were -191 ml and +141 ml), with a mean absolute difference of 6.3%. CONCLUSIONS: The proposed helium dilution technique is simple and reproducible. The negligible bias and the acceptable level of agreement support its use as a practical alternative to CT for measuring EELV in mechanically ventilated ARDS patients.

Adult↗
PubMed1998

Helium and carbon dioxide pneumoperitoneum in patients with pheochromocytoma undergoing laparoscopic adrenalectomy.

Insufflation with helium is used to prevent respiratory acidosis, hypercapnia, and cardiovascular instability associated with carbon dioxide (CO2) pneumoperitoneum. The aim of this prospective study was to compare CO2 with helium pneumoperitoneum with special reference to respiratory and hemodynamic changes at different times during the operation. Altogether 22 pheochromocytoma patients undergoing laparoscopic adrenalectomy (LpA) were included using CO2 in 11 patients (CO2LpA) and helium in 11 patients (HeLpA). The insufflation pressure was 12 mmHg. The two groups were comparable with regard to demographic data and preoperative management. CO2 and helium insufflation were associated with similar catecholamine increase. The most striking significant increase compared with the baseline was observed during tumor isolation: The mean plasma epinephrine (EPI) and norepinephrine (NE) levels increased 32.86-fold and 25.92-fold, respectively, in the CO2LpA patients and 27.43-fold and 18.46-fold, respectively, in the HeLpA patients. HeLpA did not result in significant hypercarbia or acidosis at any measured intraoperative point; this was without any alteration in minute ventilation to maintain these normal PaCO2, excess base (EB), and pH values. Significant increases of mean arterial pressure, pulmonary arterial pressure, pulmonary vascular resistance index, PaCO2, EB, and acidosis were seen in the CO2LpA patients at the time of tumor isolation and tumor removal compared with those in HeLpA patients. No patient required conversion to open surgery. There were no significant differences between CO2LpA and HeLpA regarding mean operative time (117.50 +/- 93.68 vs. 106.87 +/- 16.60 minutes), mean blood loss (168.54 +/- 78.63 vs. 142.02 +/- 109.26 ml), hospital stay (4 days), the need for analgesics, or mean time required to return to normal activity (12 days). There was one wound infection in the HeLpA group and one wound hematoma and one case of atelectasis in the CO2LpA group. Helium may be the agent of choice for abdominal insufflation in patients undergoing LpA for pheochromocytoma, eliminating the adverse hemodynamic and respiratory changes associated with CO2 insufflation.

Adrenal Gland Neoplasms↗
PubMed2006

Exposure to carbon dioxide and helium reduces in vitro proliferation of pediatric tumor cells.

BACKGROUND: Minimally invasive techniques are increasingly applied to children with malignant tumors. We showed previously that CO(2) used for pneumoperitoneum modulates the function of macrophages and polymorphonuclear cells via direct effects and via acidification. Numerous in vitro and small animal model studies also confirmed an alteration of the behavior of several types of adult tumor cells by CO(2). The impact of CO(2) and other gases used for pneumoperitoneum on the behavior of various pediatric tumors has not yet been determined. METHODS: Cell lines of neuroblastoma (IMR 32, SK-N-SH, Sy5y), lymphoma (Daudi), hepatoblastoma (Huh 6), hepatocellular carcinoma (Hep G2), and rhabdomyosarcoma (Te 671) were incubated for 2 h. Incubation was performed with 100% CO(2), 100% helium, and 5% CO(2) as control. Cell proliferation was determined by the MTT-assay [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] by actively growing cells to produce a blue formazan product. The MTT-assay was performed before, directly after incubation, and daily for 4 days. Vitality of the cells was determined by trypan blue. The extracellular pH during incubation was measured during gas exposition every 10 min using Bayer Rapid Lab 855. RESULTS: CO(2) for 2 h significantly decreased the proliferation of neuroblastoma, lymphoma, hepatoblastoma, and hepatocellular carcinoma cells. This decrease persisted over 4 days in neuroblastoma, lymphoma, and hepatocellular carcinoma cells. The CO(2) had no impact on hepatoblastoma and rhabdomyosarcoma cells. Helium had a similar effect on neuroblastoma cells. After 4 days, a significant decrease of cell activity was found in two neuroblastoma cell lines and in hepatoblastoma cells. Helium had no effect on lymphoma and hepatocellular carcinoma cells. The extracellular pH was 6.2 during incubation with CO(2), and 7.6 during incubation with helium. CONCLUSION: CO(2) and helium may affect the proliferation of some pediatric tumor cell lines in vitro. However, some of these effects and the impact on the extracellular pH are differential. The role of pH modulation, hypoxia and direct effects of gases remain to be investigated before a general recommendation on the use of minimally invasive techniques in pediatric oncology can be given.

Carbon Dioxide↗
PubMed2000

Cardiopulmonary changes during laparoscopy and vessel injury: comparison of CO2 and helium in an animal model.

BACKGROUND: Injury of venous vessels during elevated intraperitoneal pressure is thought to cause possible fatal gas embolism, and helium may be dangerous because of its low solubility. METHODS: Twenty pigs underwent laparoscopy with either CO2 (n=10) or helium (n=10) with a pressure of 15 mm Hg and standardized laceration (1 cm) of the vena cava inferior. After 30 s, the vena cava was clamped, closed endoscopically by a running suture and unclamped again. During the procedure changes of cardiac output (CO), heart rate (HR), mean arterial pressure (MAP), central venous pressure (CVP), pulmonary artery pressure (PAP), pulmonary artery wedge pressure (PAWP), end tidal CO2 pressure (PETCO2), and arterial blood gas analyses (pH, pO2 and pCO2) were investigated. RESULTS: No animal died during the experimental course (mean blood loss during laceration: CO2, 157+/-50 ml; helium, 173+/-83 ml). MAP and CO values showed a decrease after laceration of the vena cava in both groups that had already been completely compensated for before suturing. PETCO2 increased significantly after CO2 insufflation (P<0.01), while helium showed no effect. Laceration of the vena cava caused no significant changes in PETCO2 values in either group. Significant acidosis and an increase of pCO2 were only found in the CO2 group. CONCLUSIONS: The incidence of gas embolism during laparoscopy and accidental vessel injury seems to be very low. With the exception of acidosis and an increase of PETCO2 in the CO2 group, there were no differences in cardiopulmonary function between insufflation of CO2 and helium.

Animals↗
PubMed2001

The influence of CO2 versus helium insufflation or the abdominal wall lifting technique on the systemic immune response.

BACKGROUND: Both laparoscopic and conventional surgery result in activation of the systemic immune response; however, the influence of the laparoscopic approach, using CO2 insufflation, is significantly less. Little is known about the influence of alternative methods for performing laparoscopy, such as helium insufflation and the abdominal wall lifting technique (AWLT), and the systemic immune response. METHODS: Thirty-three patients scheduled for elective cholecystectomy were randomly assigned to undergo laparoscopy using either CO2 or helium for abdominal insufflation or laparoscopy using only the AWLT. The postoperative inflammatory response was assessed by measuring the white blood cell count, C-reactive protein (CRP) and interleukin-6 (IL-6). The postoperative immune response was assessed by measuring monocyte HLA-DR expression. RESULTS: CRP levels were significantly higher 1 day after helium insufflation when compared with CO2 insufflation; however, no differences were observed 2 days after surgery. The AWLT resulted in significantly higher levels of CRP both 1 and 2 days after surgery when compared with either CO2 or helium insufflation. A small increase in postoperative IL-6 levels was observed in all groups, but no significant differences were seen between the groups. After both helium insufflation and AWLT a significant decrease in HLA-DR expression was observed, in contrast to the CO2 group. CONCLUSION: Carbon dioxide used for abdominal insufflation seems to limit the postoperative inflammatory response and to preserve parameters reflecting the immune status. These findings may be of importance in determining the preferred method of laparoscopy in oncologic surgery.

Abdominal Muscles↗
PubMed2003

Influence of different gases used for laparoscopy (helium, carbon dioxide, room air, xenon) on tumor volume, proliferation, and apoptosis.

BACKGROUND: Previous reports suggest that helium pneumoperitoneum used for laparoscopic surgery suppresses postoperative tumor growth. The present study was designed to determine the effects of gases used in laparoscopy on tumor volume, proliferation, and apoptosis in rats with implanted malignoma. METHODS: In 36 rats Morris hepatoma 3294A cells were implanted intrahepatically. Then, after 5 days, they underwent laparoscopy using helium ( n = 7), CO(2) ( n = 7), room air ( n = 7), or xenon ( n = 8). One group received anesthesia only ( n = 7). Rats were killed 10 days after implantation to assess tumor volume, proliferation, and apoptosis. RESULTS: Helium pneumoperitoneum caused a significant smaller tumor volume compared to other groups (Kruskal-Wallis test: p = 0.001; median tumor volume: control: 44 mm3; helium: 19 mm3). There was no significant difference in tumor cell proliferation (PCNA) and apoptosis (TUNEL reaction) between the groups. CONCLUSIONS: There was a significant decrease of tumor volume using helium pneumoperitoneum compared to the other gases, but no decreased tumor cell proliferation or increased tumor cell apoptosis.

Air↗
PubMed2001

Helium and other alternative insufflation gases for laparoscopy.

BACKGROUND: Carbon dioxide (CO(2)) is currently the insufflation gas of choice for laparoscopy. It fulfills most of the requirements for an ideal insufflation gas, being colorless, noninflammable, and rapidly excreted from the circulation. However, its use is associated with adverse cardiorespiratory effects, especially in patients with preexisting cardiorespiratory compromise. METHODS: The descriptive review of relevant literature, moreover, has been proposed that it increases the incidence of port site (wound) metastases from abdominal cancers when used during oncological surgery. In addition, it may cause postoperative pain due to peritoneal irritation, and its use is associated with physiological and immunological impairment. Hence, there is scope for the investigation of alternative insufflation gases. Other possibilities include gasless laparoscopy, helium, nitrous oxide, (N(2)O), and argon. Helium insufflation has been used extensively in animal models but only to a limited extent in humans. In experimental studies, it has been shown to produce fewer changes in cardiorespiratory and intraperitoneal immunological status than CO(2) insufflation, and its use is associated with less spread of tumors to port sites in a variety of small animal tumor models. However, helium also has the potential for some adverse effects. Helium pneumothorax probably resolves more slowly than CO(2) pneumothorax, and helium gas embolism is tolerated poorly in animal models. The clinical significance of these potential problems has yet to be determined. CONCLUSIONS: Although the use of alternative gases appears to be promising, further evaluation is needed within both clinical and laboratory settings before their routine clinical use can be supported.

Abdominal Neoplasms↗
PubMed1999

Videoscopic surgery under local and regional anesthesia with helium abdominal insufflation.

BACKGROUND: High-risk patients may not be good candidates for laparoscopic surgery due to the metabolic consequences of transperitoneal absorption of insufflated CO(2) gas and the necessity of general anesthesia because CO(2) insufflation produces pain. Helium gas is metabolically inert and does not produce pain. Thus it permits an alternative approach to performing laparoscopic surgery in high-risk patients. METHODS: Laparoscopic cholecystectomy, appendectomy, hernia repair, and peritoneal dialysis catheter procedures were performed under local or regional anesthesia in high-risk patients utilizing helium gas as the insufflation agent. RESULTS: Twenty-one patients underwent laparoscopic procedures under local or regional anesthesia. None of the procedures initiated under local-regional anesthesia required abandonment of the laparoscopic approach or conversion to general anesthesia. There were no operative or perioperative mortalities. Two incidences of pneumothorax occurred with extraperitoneal hernia repair; one required a tube thoracostomy. CONCLUSIONS: Helium gas should be considered the agent of choice for intraperitoneal insufflation in high-risk patients not only because helium avoids the metabolic consequences of CO(2) insufflation but also because it permits selected procedures to be performed under local-regional anesthesia. Helium may be contraindicated for laparoscopic procedures involving extraperitoneal insufflation due to the increased risk for pneumothoraces.

Adult↗
PubMed1988

The influence of helium pressure on the reduction induced in field potentials by various amino acids and on the GABA-mediated inhibition in the CA1 region of hippocampal slices in the rat.

In a previous study, it was shown that helium pressure depressed excitatory synaptic transmission mediated by the Schaffer-commissural afferents and increased the intrinsic excitability of pyramidal cells, in the CA1 region of hippocampal slices in the rat. In the present study, the neurochemical bases of these changes was investigated. Various excitatory amino acids were studied under normal and up to 80 atm of helium. At normal pressure, the amino acids tested induced a decrease in the field excitatory postsynaptic potential (EPSP) and antidromic field potential of CA1 pyramidal cells. These changes probably resulted from the well known depolarizing effect of the compounds. Quisqualate is supposed to activate the synaptic receptors of the pathway tested. Since the effect of this amino acid and other agonists were not significantly affected by helium pressure, it is suggested that the depressed hippocampal synaptic potentials under pressure did not result from reduced sensitivity of synaptic receptors. On the other hand, helium pressure enhanced the action of N-methyl-D-aspartate (NMDA) and depressed the GABA-mediated inhibition of CA1 pyramidal cells. Given that the excitability of these neurones is modulated by NMDA-related events and GABA inhibition, these results indicate that both neurochemical systems were probably involved in the helium pressure-induced hyperexcitability of the cells studied.

Action Potentials↗
PubMed1995

Theoretical validation of the respiratory benefits of helium-oxygen mixtures.

A theoretical analysis of convective gas transport validates the clinically demonstrated advantage of using helium-oxygen mixtures in treating patients with respiratory problems. Previous studies have attributed that advantage to the ability of helium-oxygen to stay laminar at higher velocities than nitrogen-oxygen. The present work shows that helium-oxygen does not need to be laminar to provide higher flow rates and that its benefits persist under turbulent conditions. The analysis is applied to steady flow through the lungs and through a circular airway obstruction. A simplified model of the lungs gives pressure-flow relations that show a significant increase in oxygen flow rate when nitrogen is substituted by helium. A similar improvement is found for flow through an obstruction. For a given pressure difference across the lungs or across an obstruction, the turbulent flow rate of oxygen increases by approximately 50% when nitrogen is replaced by helium in a mixture containing 20% oxygen.

Helium↗
PubMed2005

Dose tolerance at helium and nitrogen temperatures for whole cell electron tomography.

Electron tomography is currently the only method that allows the direct three-dimensional visualization of macromolecules in an unperturbed cellular context. In principle, tomography should enable the identification and localization of the major macromolecular complexes within intact bacteria, embedded in amorphous ice. In an effort to optimize conditions for recording data that would bring us close to the theoretical limits, we present here a comparison of the dose tolerance of Caulobacter crescentus cells embedded in amorphous ice at liquid helium versus liquid nitrogen temperature. The inner and outer cell membranes, and the periodic structure of the S-layer of this Gram-negative bacterium provide ideal features to monitor changes in contrast and order as a function of dose. The loss of order in the S-layer occurs at comparable doses at helium and nitrogen temperatures. Macroscopic bubbling within the cell and the plastic support develops at both temperatures, but more slowly at helium temperature. The texture of the bubbles is finer in initial stages at helium temperature, giving an impression of contrast reversal in some parts of the specimen. Bubbles evolve differently in different organelles, presumably a consequence of their different chemical composition and mechanical properties. Finally, the amorphous ice "flows" at helium temperature, causing changes in the relative positions of markers within the specimen and distorting the cells. We conclude that for cryo-electron tomography of whole cells liquid nitrogen temperature provides better overall data quality.

Animals↗
PubMed2003

Anomalous effects of helium head pressure carbon dioxide in supercritical fluid chromatography and extraction.

Helium head pressure carbon dioxide cylinders are commonly used to facilitate the delivery of liquid CO2 to supercritical fluid extraction and chromatographic pumps. It is usually tacitly assumed that the helium used to increase the delivery pressure of the CO2 cylinders is completely insoluble in liquid CO2 and thus remains isolated in the head space of the delivery cylinder. This assumption is invalid because up to 5 mol% helium can be entrained in the liquid CO2 delivered from helium head pressure cylinders. Significantly, contamination of liquid CO2 with even small amounts of helium can cause many unforeseen and usually deleterious effects in supercritical fluid chromatography and extraction schemes. The observed anomalies include decreased density of the fluid phase, irreproducible extraction and retention, ghost peaks, and even phase separation within the column or extraction vessel.

Carbon Dioxide↗
PubMed1996

A comparison of the hemodynamic and ventilatory effects of abdominal insufflation with helium and carbon dioxide in young swine.

Abdominal CO2 insufflation has been shown to cause hypercarbia, acidemia, and decreased oxygenation in a pediatric animal model. Such metabolic derangements have prompted a search for alternative insufflation gases. This study compares the hemodynamic and ventilatory changes that occur during pneumoperitoneum with CO2 and helium. Four juvenile swine were intubated and given general anesthesia. Minute ventilation was adjusted to obtain a baseline Pco2 of between 32 and 36 mm Hg, and was kept constant for the duration of the experiment. The subjects initially were insufflated with CO2 or helium at a pressure of 10 mm Hg. Peak ventilatory pressure, end-tidal CO2 (ETCO2) arterial pH, Pco2, Po2, and right atrial and inferior vena caval pressures were measured before and during a 1-hour insufflation period. After desufflation, Pco2 and pH were restabilized. The same parameters were then measured during reinsufflation with the alternate gas. CO2 insufflation caused significant decreases in pH, from 7.51 +/- 0.03 to 7.32 +/- 0.06, and Po2 increased from 261 +/- 49 to 189 +/- 33 mm Hg. Pco2 increased from 35.0 +/- 1.4 to 57.9 +/- 6.3 mm Hg. ETCO2 also increased, from 29.0 +/- 2.2 to 47.2 +/- 5.0 mm Hg. Helium insufflation caused pH to decrease from 7.51 +/- 0.01 to 7.42 +/- 0.04. Pco2 increased from 32.8 +/- 0.8 to 43.5 +/- 3.9 mm Hg, and ETCO2 increased from 27.8 +/- 0.5 to 36.8 +/- 3.1 mm Hg. These alterations were significantly less than those with CO2 pneumoperitoneum. Po2 decreased as well-from 266 +/- 30 to 212 +/- 21 mm Hg. During insufflation with both gases, peak ventilatory pressure and right atrial pressure increased significantly. Abdominal insufflation with CO2 or helium causes hypercarbia, acidemia, and increased ETCO2 in this juvenile animal model. These derangements are significantly less with helium. This gas may prove to be the more suitable insufflation agent for pediatric patients.

Acid-Base Equilibrium↗
PubMed1993

Helium ions versus iodine 125 brachytherapy in the management of uveal melanoma. A prospective, randomized, dynamically balanced trial.

PURPOSE: Optimal radiation therapy for uveal melanoma is uncertain, and the relative efficacies of radioactive plaques and charged particles are unclear. METHODS: The authors prospectively studied helium-ion irradiation and iodine 125 (125I) brachytherapy in a randomized, dynamically balanced trial. Of the 184 patients who met the eligibility criteria, 86 were treated with helium ions and 98 with 125I brachytherapy. RESULTS: No patients with uveal melanoma had a history of systemic malignancy. Tumors were less than 15 mm in maximum diameter and less than 10 mm in thickness. A minimum tumor dose of 70 GyE was delivered to the tumor apex. There was a significantly higher local recurrence rate after 125I brachytherapy than after helium-ion irradiation. Enucleations occurred more frequently after brachytherapy (relative risk = 1.99; 95% confidence interval, 0.78-5.78). More anterior segment complications occurred after helium-ion irradiation. To date, there has been no measurable impact on survival. CONCLUSIONS: Most uveal melanomas can be managed with radiation with retention of the eye. There was better tumor control with helium-ion irradiation; however, there were more anterior segment complications.

Adult↗
PubMed2003

Calibration of three capnographs for use with helium and oxygen gas mixtures.

Capnography is considered essential in the management of mechanically-ventilated patients. Helium, as an adjunct to mechanical ventilation, is the subject of renewed interest and used increasingly. However, helium affects the performance of infrared capnometry. We constructed a simple device to generate variable mixtures of helium, oxygen and carbon dioxide within the normal physiological range, and tested the performance of two side-stream and one in-line capnographs. We found that addition of helium to the gas mixture caused all three capnographs to underestimate the concentration of carbon dioxide. The underestimation increased as the proportion of helium increased. The maximum underestimation (30%) occurred in a 79:21 helium/oxygen mixture.

Calibration↗
PubMed2001

Metabolic and immunologic consequences of laparoscopy with helium or carbon dioxide insufflation: a randomized clinical study.

BACKGROUND: Previous studies using animal models have demonstrated that carbon dioxide (CO2) pneumoperitoneum during laparoscopy is associated with adverse physiological, metabolic, immunological and oncological effects, and many of these problems can be avoided by the use of helium insufflation. The present study was performed in patients to compare the effect of helium and CO2 insufflation on intraperitoneal markers of immunological and metabolic function. METHODS: Eighteen patients undergoing elective upper gastrointestinal laparoscopic surgery were randomized to have insufflation achieved by using either helium (n = 8) or CO2 (n = 10) gas. Intraperitoneal pH was monitored continuously during surgery, and peritoneal macrophage function was determined by harvesting peritoneal macrophages at 5 min and 30 min after commencing laparoscopy, and then assessing their ability to produce tumour necrosis factor-alpha (TNF-alpha), and their phagocytic function. RESULTS: Carbon dioxide laparoscopy was associated with a lower intraperitoneal pH at the commencement of laparoscopy, although this difference disappeared as surgery progressed. The production of TNF-alpha was better preserved by CO2 laparoscopy, but the insufflation gas used did not affect macrophage phagocytosis. Patients undergoing helium laparoscopy required less postoperative analgesia. CONCLUSION: The choice of insufflation gas can affect intraperitoneal macrophage function in the clinical setting, and possibly acid-base balance. The present study suggested no immunological advantages for the clinical use of helium as an insufflation gas. The outcomes of the present study, however, are different to those obtained from previous laboratory studies and further research is needed to confirm this outcome.

Carbon Dioxide↗
PubMed2002

Asphyxial suicide with helium and a plastic bag.

Suicide by helium inhalation inside a plastic bag has recently been publicized by right-to-die proponents in "how to" print and videotape materials. This article reports a suicide performed according to this new and highly lethal technique, which is also a potentially undetectable cause of death. Toxicology information could not determine helium inhalation, and drug screening did not reveal data of significance. The cause of death could be determined only by the physical evidence at the scene of death. Helium inhalation can easily be concealed when interested parties remove or alter evidence. To ensure that their deaths are not documented as suicide, some individuals considering assisted suicide may choose helium methods and assistance from helpers. Recent challenges to Oregon's physician-assisted suicide law may increase interest in helium instead of barbiturates for assisted suicide.

Administration, Inhalation↗
PubMed1998

Minimum alveolar concentrations of noble gases, nitrogen, and sulfur hexafluoride in rats: helium and neon as nonimmobilizers (nonanesthetics)

UNLABELLED: We assessed the anesthetic properties of helium and neon at hyperbaric pressures by testing their capacity to decrease anesthetic requirement for desflurane using electrical stimulation of the tail as the anesthetic endpoint (i.e., the minimum alveolar anesthetic concentration [MAC]) in rats. Partial pressures of helium or neon near those predicted to produce anesthesia by the Meyer-Overton hypothesis (approximately 80-90 atm), tended to increase desflurane MAC, and these partial pressures of helium and neon produced convulsions when administered alone. In contrast, the noble gases argon, krypton, and xenon were anesthetic with mean MAC values of (+/- SD) of 27.0 +/- 2.6, 7.31 +/- 0.54, and 1.61 +/- 0.17 atm, respectively. Because the lethal partial pressures of nitrogen and sulfur hexafluoride overlapped their anesthetic partial pressures, MAC values were determined for these gases by additivity studies with desflurane. Nitrogen and sulfur hexafluoride MAC values were estimated to be 110 and 14.6 atm, respectively. Of the gases with anesthetic properties, nitrogen deviated the most from the Meyer-Overton hypothesis. IMPLICATIONS: It has been thought that the high pressures of helium and neon that might be needed to produce anesthesia antagonize their anesthetic properties (pressure reversal of anesthesia). We propose an alternative explanation: like other compounds with a low affinity to water, helium and neon are intrinsically without anesthetic effect.

Anesthetics↗