Airway obstruction during anaesthesia in a child with a mediastinal mass

Molecular scale modeling approach to evaluate stability and dissociation of methane and carbon dioxide hydrates

An analysis of carbon/oxygen gas bubble formation in some nickel alloys

Hyperoxia-induced Tissue Hypoxia

Electrodes for blood pO2 and pCO2 determination.

Bispectral index (BIS) and entropy measure electroencephalographic voltage between electrodes placed on the forehead. BIS is used to monitor and quantify depth of hypnosis1and to guide anesthetic drug administration during general anesthesia.2Entropy assesses loss of consciousness by the quantification of the degree of spatial and temporal integration of cerebral neuronal activity.3An entropy monitor has been introduced recently; it provides two indices, state entropy and response entropy, that decrease in healthy volunteers receiving propofol with a brief intervening period of wakefulness4and in surgical patients during propofol anesthetic induction.5We report two cases of perioperative gas embolism encountered during laparoscopic surgery while patients were being monitored simultaneously by BIS (Aspect A-2000 XP®, version 3.11; Aspect Medical Systems, Newton, MA) and entropy of electroencephalogram (S/5™ M-Entropy plug-in Module; Datex-Ohmeda Company, Limonest, France).In our first case, an 83-yr-old man was scheduled for a laparoscopic hemicolectomy under general anesthesia. Target-controlled infusion of propofol and remifentanil was achieved using a computer-assisted infusion device6while atracurium was administered continuously after a bolus. Standard monitoring was used as was BIS and entropy monitoring. Pneumoperitoneum was achieved with carbon dioxide. The first 90 min of anesthesia and surgery were uneventful. Suddenly, BIS and entropy indices dropped to zero as shown in figure 1. Partial pressure of end-tidal carbon dioxide decreased a few seconds later from 28 mmHg to 19 mmHg and arterial hypotension of 80/45 mmHg was noted (it was previously 149/85 mmHg). The surgeon reported no bleeding. Gas embolism was suspected, and the dramatic change in electroencephalographic-derived indices led to immediate exsufflation and conversion to laparotomy. BIS and entropy remained at low values for approximately 25 min with almost 100% burst suppression even after hemodynamic stability was restored. The colectomy was completed, the anesthetic was discontinued, and the patient awoke. Neurologic examination was performed and was normal. Transesophageal echocardiography performed the day after surgery confirmed a patent foramen ovale.In our second case, a 46-yr-old woman was scheduled for a laparoscopic cholecystectomy. Anesthesia and monitoring were similar to case 1. Shortly after the onset of carbon dioxide insufflation, partial pressure of end-tidal carbon dioxide suddenly decreased from 32 to 10 mmHg and arterial pressure decreased to less than 60 mmHg. BIS and entropy values decreased to approximately 20 and the burst suppression ratio was 80% within seconds. Laparoscopy showed a tear in the surface of the liver. The pneumoperitoneum was immediately exsufflated, and a laparotomy was performed. BIS and entropy values regained their former values within 5 min, but arterial pressure and partial pressure of end-tidal carbon dioxide remained low for 15 min. Cholecystectomy was performed. Transesophageal echocardiography performed during anesthesia revealed no septal defect. Anesthesia was discontinued at the end of the procedure and the patient awoke. Neurologic examination was normal.Sudden decreases in BIS have been reported at the onset of clinical deterioration. England was the first to describe the changes in BIS during a hypovolemic cardiac arrest.7An acute decrease in BIS can reflect cerebral hypoperfusion8–10or cerebral embolization.11An alternative explanation for an acute decrease in electroencephalographic-derived indices is an increase in plasma concentration of an anesthetic drug, especially propofol, as a result of rapid alteration of its elimination.12Our two cases showed simultaneous acute and profound decrease of BIS and entropy indices that forced the anesthesiologist to react quickly. After verification of good signal quality, the low level of electromyogram, the stability of anesthetic drug concentrations and the absence of acute bleeding, the diagnosis of gas embolism was made; this is a known complication of laparoscopic surgery. Using transesophageal echocardiography, a very sensitive method of detection, Derouin et al. reported gas embolism in 11 of 16 patients undergoing laparoscopic cholecystectomy.13The clinical impact of gas embolization can be as serious as cardiac arrest;14however, in most instances there are no lasting effects, probably because of the high solubility of carbon dioxide bubbles. Electroencephalographic monitoring modified the surgical and anesthetic management in our two cases. The chronology of events varied between the cases. In the first case, carbon dioxide bubbles reached the brain very rapidly through the patent foramen ovale; BIS and entropy values decreased before any significant changes in other parameters. Other methods of early detection of paradoxical gas embolism have been reported during laparoscopic cholecystectomy; by transesophageal echocardiography15and by transcranial Doppler.16In our second case, in which a patent foramen ovale was ruled out, the decrease of BIS and entropy was observed after hemodynamic and respiratory parameters changed and was transient, reflecting a decrease in cardiac output as a result of gas embolization.Finally, anesthesiologists should be aware of the potential for venous gas embolization during routine laparoscopic procedures; BIS or entropy monitoring may play a role in early detection and could complement routine monitoring.* Foch Hospital, Suresnes, France. m.fischler@hopital-foch.org.

The severity of acid-base disturbances in diarrhoeic calves was investigated and a simple, inexpensive method of monitoring them was evaluated. The Harleco apparatus measures the 'total carbon dioxide' in a blood sample, mostly generated from the bicarbonate present, and any abnormalities are mainly due to metabolic acidosis or alkalosis. Its performance was tested against a standard blood gas analyser by comparing the results obtained by both methods with nearly 2000 blood samples from healthy or diarrhoeic calves. After technical modifications, the technique gave excellent precision and accuracy for the clinical evaluation of acid-base balance, using venous whole blood. The samples were very stable, especially at 0 degrees C, but also at room temperature. The normal range (mean +/- 1.96 sd) for total carbon dioxide in whole blood from calves was 21 to 28 mmol/litre. For samples corresponding to mild, moderate or severe acidosis, 79 per cent were correctly classified by the Harleco apparatus and only 0.1 per cent were beyond the adjacent degree of severity. After four days of diarrhoea, the calves which later died had twice the deficit in plasma bicarbonate of those which survived. As death approached, the deficit was almost three times that in surviving calves and the blood pH shortly before death was as low as 6.79 +/- 0.08. The Harleco apparatus was less successful with alkalotic samples, but metabolic alkalosis is less common and usually less severe.

The processes of solution and hydrate formation behind a shock wave of moderate amplitude were studied experimentally in water with bubbles of nitrogen — carbon dioxide mixture at different initial static pressures in the medium and surfactant concentrations. It is shown that these bubbles do not affect significantly the processes of solution and hydrate formation behind a shock wave during the considered periods. The hypothesis about partial hydration of nitrogen from the gas mixture at intense formation of carbon dioxide hydrate was suggested for the conditions, when the pressure behind the wave is less than the equilibrium pressure of nitrogen hydrate formation at a given temperature.

Double contrast examination of the colon has proved itself an important roentgenologic procedure for the detection of early neoplasms and for the demonstration of gross structural changes of the mucosa occurring in other types of disease. Since the original description of this technic by Fischer (1) in Germany and its development and refinement by Weber (2), Stevenson (3, 4), and others, it has remained, essentially, a method whereby air is introduced to distend the barium-coated walls of the colon. In our attempts to produce uniformly satisfactory examinations with the least inconvenience to the patient and examiner, we have resorted to the use of compressed carbon dioxide instead of air. We believe this to be a refinement of technic which possesses several advantages. Method After a preliminary barium enema study and evacuation of the barium, the patient is again observed fluoroscopically. If there has been adequate emptying of the bowel, additional routine postero-anterior and lateral films are made. Spot-films and other views are taken as indicated. It must be emphasized that satisfactory double-contrast films cannot be obtained if too much barium remains in the colon. A catheter is inserted into the rectum and carbon dioxide is allowed to flow into the bowel. The carbon dioxide is supplied by a small tank of the compressed gas (Fig. 1) , which is equipped with two gauges—one, a flow meter on a reduction valve; the other, a tank pressure gauge. The flow of gas is regulated, by turning the regulator on the reduction valve, to a rate of 1.0 to 1.5 liters per minute. When the proper rate of flow is obtained, the gas supply is shut off by turning the main valve on the tank. The regulator on the reduction valve must not be disturbed. As a precautionary measure, the rate of flow must be regulated before the catheter is inserted into the rectum. Filling of the colon with gas is observed fluoroscopically, additional films are made, and the patient is then permitted to go to the toilet. In preparing barium suspension for an enema, we have found the optimum temperature of the water to be 41 °F. In our geographical area, water at this temperature is readily obtained from the cold water faucet in winter; at other times, the water is cooled to the proper temperature. The use of cool water has two advantages: First, the colon shows a greater tolerance for the enema, possibly because the mucosa is subjected to the slight anesthetizing effect of cold. Second, all gases are more soluble in cold liquids than in warm liquids, so that the tendency for bubble formation is reduced by the lower temperature in the colon. Advantages 1. The absorption rate of gas from the colon depends largely on the partial pressure gradient between the bowel lumen and the venous blood. The average partial pressure of carbon dioxide in venous blood, with the subject at rest, is 46 mm. Hg, while the average partial pressure of nitrogen in venous blood is 573 mm. Hg (5).

In 1837 Cormack (1) reported that he blew the contents of his twice-filled chest into the jugular vein of a horse and that the animal exhibited “only moderate signs of uneasiness.” This probably represents the first time that the right heart of any animal experienced more than its usual quota of carbon dioxide. Needless to say, physicians have felt considerable uneasiness in the intervening one hundred and twenty years when any free gas arrived in the heart. In the last two years intracardiac carbon dioxide has been shown to be of definite diagnostic aid in cardiovascular radiology. Experimental animal studies by Oppenheimer et al. (2) in 1955 revealed that relatively large amounts of this gas could reach the right heart and pulmonary circulation without producing embolic phenomena. Human application was first carried out by Stauffer (3), who visualized the heart valves and chambers in two infants. In the course of these studies Durant, Stauffer, Paul, and Oppenheimer (4, 5) found that carbon dioxide in the right atrium could be used to differentiate pericardial effusion from cardiac enlargement. The limitations of plain-film examination in this problem are well known. Kymography may show blunting of pulsations in both entities, and fluoroscopy in the recumbent position may demonstrate widening of the base of the cardiac silhouette in both. Opaque angiography will reveal the presence of surrounding pericardial effusion but carries with it the risk of allergic reaction. Reliance on pericardiocentesis to establish the diagnosis entails the hazard of myocardial laceration and hemopericardium. In order, therefore, to evaluate the carbon-dioxide method, a series of 22 patients have now been examined by the authors. It is with the rationale, technic, results, and safety of intravenous carbon-dioxide insufflation that this paper deals. Rationale It has been pointed out that carbon dioxide is twenty times more soluble in blood than oxygen or air. This property of the gas allows the formation of a transient gas-blood level and serves as the crux of the method. It may be calculated that small intravenous injections of carbon dioxide, 50 to 100 C.C., alter the carbon-dioxide content of the blood approximately 5 to 10 volumes per cent, and this effect is of only several minutes duration. In this time the change produced in the blood pH is insignificant. This amount of carbon dioxide is equivalent to the amount of the gas formed in one minute during minimal exercise, such as eating or turning over in bed. If a patient is placed in left decubitus (left side down, right side up), carbon dioxide, once in the right atrium, will rise and outline its uppermost surface. In this position the atrium is seen as a hemispherical shadow extending at its summit 4 to 5 cm. above the spine. The opaque shadow or band, as we have come to call it, outlined between the carbon-dioxide bubble and the overlying lung, consists of pleura, pericardium, and atrial wall.

Dissolved carbon dioxide flotation-emulsification microextraction technique coupled with high-performance liquid chromatography was developed for separation and determination of fat-soluble vitamins (A, D3 , E, and K3 ) in multivitamin pharmaceutical preparations. Dissolved carbon dioxide flotation was used to break up the emulsion of extraction solvent in water and to collect the extraction solvent on the surface of aqueous sample in narrowed capillary part of extraction cell. Carbon dioxide bubbles were generated in situ through the addition of 300μL of concentrated hydrochloric acid into the alkaline sample solution at pH=11.5 (1% w/v sodium carbonate), which was sonicated to intensify the carbon dioxide bubble generation. Several factors affecting the extraction process were optimized. Under the optimal conditions, the limits of detection were 0.11, 0.47, 0.20 and 0.35μg/L for A, E, D3 , and K3 vitamins in water samples, respectively. The inter-day and intra-day precision of the proposed method were evaluated in terms of the relative standard deviation and were <10.5%.

Fiber refractometer to detect and distinguish carbon dioxide and methane leakage in the deep ocean

Blood-gas properties of plateau zokor (Myospalax baileyi)

SummaryThe effects of winter shearing on ewe live weight, body condition score (BCS) and the concentrations of glucose, non-esterified fatty acids (NEFA), 3-hydroxybutyrate, growth hormone (GH), cortisol, insulin and the thyroid hormones in plasma plus that of oxygen and carbon dioxide in jugular vein blood and packed cell volume (PCV) were measured at weekly intervals over the final 7 weeks of pregnancy in two groups of multiple-bearing shorn and unshorn pregnant ewes.Shorn ewes lost 47% more live weight than unshorn controls over the period from the day of being shorn to immediately after lambing. There was a significant decrease in BCS in both groups between 45 and 9 days before lambing. Three days after shearing the plasma NEFA concentration was higher in the shorn group but there were no other significant differences between shorn and unshorn groups in the plasma concentrations of NEFA, cortisol or insulin over the remaining 7 weeks of pregnancy. Both the PCV and concentration of carbon dioxide in blood were higher in shorn sheep throughout the final 6 weeks of pregnancy indicating they were making metabolic adaptations to long-term cold exposure. This response may have been mediated via an increase in thyroid hormone concentrations which were higher throughout the 7-week sampling period in shorn animals compared with unshorn controls. A decrease in ambient temperature was associated with a significant increase in the plasma concentration of GH and glucose in shorn animals. At 2 weeks before lambing there was a decrease in the plasma glucose concentration and an increase in 3-hydroxybutyrate concentration in the unshorn ewes, but these changes were not observed in the shorn animals. It is concluded that winter shearing of the pregnant ewe results in an increased loss of maternal body tissues and metabolic adaptations to long-term cold exposure without any of the changes associated with an increase in energy expenditure during the final third of pregnancy.

Although mild hypothermia improves outcome in patients after out-of-hospital cardiac arrest, the cardiodepressive effects of hypothermia may lead to secondary brain damage. This study was performed to assess the cerebral blood flow, cerebral oxygen extraction, and cerebrovascular reactivity to changes in partial pressure of carbon dioxide in the arterial blood in comatose patients after out-of-hospital cardiac arrest treated with mild hypothermia. Observational study. Tertiary care university hospital. Ten comatose patients after out-of-hospital cardiac arrest. All patients were cooled to 32-34 degrees C for 24 hrs. Cerebrovascular reactivity to changes in carbon dioxide in the arterial blood was measured after increasing or decreasing the minute ventilation by 20%. Mean flow velocity in the middle cerebral artery and pulsatility index were measured by transcranial Doppler at 0, 3, 6, 9, 12, 18, 24, and 48 hrs after admission. Jugular bulb oxygenation was measured at the same intervals. Cerebrovascular reactivity to changes in carbon dioxide in the arterial blood was studied on admission to the intensive care unit and at 6, 12, 18, and 24 hrs by measurement of mean flow velocity in the middle cerebral artery and jugular bulb oxygenation. Mean flow velocity in the middle cerebral artery was low (30.3+/-9.5 cm/sec) on admission and remained relatively stable for the first 24 hrs. After rewarming, it increased to 67.5+/-33.0 cm/sec at 48 hrs after admission from 30.3+/-9.5 at admission (p=.009). Jugular bulb oxygenation at the start of the study was 66.2+/-8.5% and gradually increased to 82.9+/-4.9% at 48 hrs (p<.001). Regression analysis showed a significant correlation between changes in carbon dioxide in the arterial blood, mean flow velocity in the middle cerebral artery (p<.001) and jugular bulb oxygenation (p<.001). The mean percentage change in mean flow velocity in the middle cerebral artery was 3.6+/-2.9% per 1-mm Hg change of carbon dioxide in the arterial blood. The mean flow velocity in the middle cerebral artery, as a parameter of cerebral blood flow, was low during mild hypothermia, whereas cerebral oxygen extraction remained normal, suggesting decreased cerebral metabolic activity. We demonstrated that CO2 reactivity is preserved during hypothermia in these patients.

Methane hydrate exists in huge amounts in certain locations, in sea sediments and the geological structures below them, at low temperature and high pressure. Production methods are in development to produce the methane to a floating platform. There it can be reformed to produce hydrogen and carbon dioxide, in an endothermic process. Some of the methane can be burned to provide heat energy to develop all needed power on the platform and to support the reforming process. After separation, the hydrogen is the valuable and transportable product. All carbon dioxide produced on the platform can be separated from other gases and then sequestered in the sea as carbon dioxide hydrate. In this way, hydrogen is made available without the release of carbon dioxide to the atmosphere, and the hydrogen could be an enabling step toward a world hydrogen economy.