Humidification during anesthesia

Humidification during anesthesia is important to prevent adverse changes in the upper airways and possible pulmonary compromise. These changes may take place in less than 1 hour using dry nonhumidified anesthetic gases. Consequently, some method of humidification should be employed for all but the shortest of surgical procedures requiring general anesthesia. Methods of humidification include the anesthesia breathing system itself, passive humidification or conservation of moisture (the use of HMEs), and active humidification. The simplest system providing good levels of humidification and warming of anesthetic gases is the Circle system, which uses a fresh gas flow of less than 2 L/min. Its success can be further enhanced by use of a coaxial circuit. The minimum levels of water output or humidity required in the breathing circuit remain controversial. It may be preferable to have a gas with a lower temperature and higher relative humidity because a warmer gas that is less saturated may result in increased desiccation from the upper airways. Humidification for neonatal and pediatric patients requires special consideration of resistance, work of breathing, and dead space. Further work is necessary with regard to the use of HMEs in this population of patients undergoing general anesthesia.     

Effect of sucrose acetate isobutyrate (SAIB) ingestion on the hepatobiliary function of normal human male and female volunteers

Monitoring of oxygen uptake during general anesthesia would have several benefits, but unfortunately, this is usually not available in the clinical routine situation. The herein proposed formula to calculate oxygen uptake (.VO2) necessitates only the accurate measurement of FIO2 as well as fresh gas flow and composition. Additionally, this method is not affected by the presence of anesthetic gases. The calculation uses the difference in oxygen content between the delivered fresh gas and the resulting FIO2 in the anesthesia circle system. This gap originates from oxygen uptake (that is mainly caused by metabolic oxygen consumption) and is more pronounced if low fresh gas flows are administered. In order to obtain representative results, calculation of .VO2 should be performed only after achievement of respiratory steady state conditions. Due to its simplicity and wide availability, it has the potential to become a valuable extension in anesthesia monitoring during the performance of routine general anesthesia.     

Ginsenoside Rf2, a new dammarane glycoside from Korean red ginseng (Panax ginseng)

A patient with bronchial asthma was scheduled for an operation under nitrous oxide-isoflurane anesthesia. We monitored isoflurane concentrations continuously using an anesthetic gas analyzer (BK 1304). Upon puffing procaterol hydrochloride aerosol for 4 times, the analyzer showed a rapid increase in end-tidal isoflurane concentration. The BK 1304 uses infrared photoacoustic spectrophotometry and it is susceptible to interferences caused by Freon propellants in bronchodilator aerosols. We should take care in monitoring inhalational anesthetics when using aerosols containing Freon propellants.     

Economic considerations of the use of new anesthetics: a comparison of propofol, sevoflurane, desflurane, and isoflurane

Cost control in anesthesia is no longer an option; it is a necessity. New anesthetics have entered the market, but economic differences in comparison to standard anesthetic regimens are not exactly known. Eighty patients undergoing either subtotal thyroidectomy or laparoscopic cholecystectomy were randomly divided into four groups, with 20 patients in each group. Group 1 received propofol 1%/sufentanil, Group 2 received desflurane/sufentanil, Group 3 received sevoflurane/sufentanil, and Group 4 received isoflurane/sufentanil (standard anesthesia) for anesthesia. A fresh gas flow of 1.5-2 L/min and 60% N2O in oxygen was used for maintenance of anesthesia, and atracurium was given for muscle relaxation. Concentrations of volatile anesthetics, propofol, and sufentanil were varied according to the patient's perceived need. Isoflurane, desflurane, and sevoflurane consumption was measured by weighing the vaporizers with a precision weighing machine. Biometric data, time of surgery, and time of anesthesia were similar in the four groups. Times for extubation and stay in the postanesthesia care unit (PACU) were significantly longer in the isoflurane group. Use of sufentanil and atracurium did not differ among the groups. Propofol patients required fewer additional drugs in the PACU (e.g., antiemetics), and thus showed the lowest additional costs in the PACU. Total (intra- and postoperative) costs were significantly higher in the propofol group ($30.73 per patient; $0.24 per minute of anesthesia). The costs among the inhalational groups did not differ significantly (approximately $0.15 per minute of anesthesia). We conclude that in today's climate of cost savings, a comprehensive pharmacoeconomic approach is needed. Although propofol-based anesthesia was associated with the highest cost, it is doubtful whether the choice of anesthetic regimen will lower the costs of an anesthesia department. IMPLICATIONS: Cost analysis of anesthetic techniques is necessary in today's economic climate. Consumption of the new inhaled drugs sevoflurane and desflurane was measured in comparison to a standard anesthetic regimen using isoflurane and an IV technique using propofol. Propofol-based anesthesia was associated with the highest costs, whereas the costs of the new inhaled anesthetics sevoflurane and desflurane did not differ from those of a standard, isoflurane-based anesthesia regimen.     

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.     

Anesthetic and cardiorespiratory effects of tiletamine-zolazepam-medetomidine in cheetahs

OBJECTIVE: To evaluate anesthetic and cardiorespiratory effects of an intramuscular injection of a tiletamine-zolazepam-medetomidine combination in cheetahs. DESIGN: Prospective study. ANIMALS: 17 adult captive cheetahs. PROCEDURE: The anesthetic combination was administered intramuscularly via a dart. Induction quality, duration of lateral recumbency, duration of recovery, and quality of anesthetic reversal with atipamezole were assessed. Cardiorespiratory variables (arterial blood gas partial pressures, arterial blood pressure, heart and respiratory rates, end-tidal CO2, oxygen saturation, and rectal temperature) were measured during anesthesia. RESULTS: Sedation and lateral recumbency developed within 1.9 +/- 1.0 (mean +/- SD) and 4.3 +/- 2.0 minutes of drug administration, respectively. Clinically acceptable cardiorespiratory and blood gas values were recorded for at least 87 minutes after drug administration in all but 1 cheetah. Hypoxemia and arrhythmias developed in 1 cheetah breathing room air but resolved after treatment with oxygen. Hypertension developed in all cheetahs. Significant differences in heart and respiratory rates, mean arterial blood pressure, arterial pH, partial pressure of oxygen, and hemoglobin saturation were found between cheetahs that did and did not receive oxygen supplementation. After administration of atipamezole, sternal recumbency and mobility returned within 6.9 +/- 5.8 and 47.5 +/- 102.2 minutes, respectively. Postreversal sedation, which lasted approximately 4 hours, developed in 4 cheetahs. CLINICAL IMPLICATIONS: Tiletamine-zolazepam-medetomidine delivered via a dart provided an alternative method for induction and maintenance of anesthesia in cheetahs. Atipamezole at the dose used was effective for reversal of this combination in the initial phase of anesthesia.     

Dependence of surgical trauma in aortic interventions on the approach chosen. A prospective study

A study was undertaken to assess the performance of the Komesaroff vaporizer, placed within the circuit, in ventilated patients during maintenance of closed circuit anaesthesia with halothane or isoflurane. Following intravenous induction, anaesthesia was maintained by inhalation. This was achieved using a conventional vaporizer outside the circle for the first 10 minutes to manage the fast uptake phase. The fresh gas flow was then reduced to the basal oxygen requirement with the Komesaroff vaporizer within the circle maintaining inhalational anaesthesia. Complete isolation of the circuit was achieved by returning all anaesthetic gases to the circuit following analysis and using a bag-in-bottle ventilator. The Komesaroff vaporizer dial was positioned at between the first and second division and end-tidal volatile anaesthetic agent levels were measured. This study demonstrated that at dial positions 1 or 1.5 with either agent, the end-tidal volatile concentration plateaued at clinically acceptable levels. The Komesaroff vaporizer can therefore be used safely in ventilated patients to maintain closed circuit anaesthesia provided clinical observation and monitoring are meticulous.     

Relation of PaCO2 to fresh gas flow in a circle system

Recent reports have described methods of controlling the level of CO2 during anesthesia with a N2O-relaxant sequence and controlled ventilation. This paper describes a method of predicting and controlling the PaCO2, using body weight for determination of the fresh gas flow from the anesthetic machine, removing the absorbent from the canister while leaving the canister in the circuit, and controlling ventilation at 12 ml/kg and at 12/min.     

Changing from isoflurane to desflurane toward the end of anesthesia does not accelerate recovery in humans

BACKGROUND: In an attempt to combine the advantage of the lower solubilities of new inhaled anesthetics with the lesser cost of older anesthetics, some clinicians substitute the former for the latter toward the end of anesthesia. The authors tried to determine whether substituting desflurane for isoflurane in the last 30 min of a 120-min anesthetic would accelerate recovery. METHODS: Five volunteers were anesthetized three times for 2 h using a fresh gas inflow of 2 l/min: 1.25 minimum alveolar concentration (MAC) desflurane, 1.25 MAC isoflurane, and 1.25 MAC isoflurane for 90 min followed by 30 min of desflurane concentrations sufficient to achieve a total of 1.25 MAC equivalent ("crossover"). Recovery from anesthesia was assessed by the time to respond to commands, by orientation, and by tests of cognitive function. RESULTS: Compared with isoflurane, the crossover technique did not accelerate early or late recovery (P > 0.05). Recovery from isoflurane or the crossover anesthetic was significantly longer than after desflurane (P < 0.05). Times to response to commands for isoflurane, the crossover anesthetic, and desflurane were 23 +/- 5 min (mean +/- SD), 21 +/- 5 min, and 11 +/- 1 min, respectively, and to orientation the times were 27 +/- 7 min, 25 +/- 5 min, and 13 +/- 2 min, respectively. Cognitive test performance returned to reference values 15-30 min sooner after desflurane than after isoflurane or the crossover anesthetic. Isoflurane cognitive test performance did not differ from that with the crossover anesthetic at any time. CONCLUSIONS: Substituting desflurane for isoflurane during the latter part of anesthesia does not improve recovery, in part because partial rebreathing through a semiclosed circuit limits elimination of isoflurane during the crossover period. Although higher fresh gas flow during the crossover period would speed isoflurane elimination, the amount of desflurane used and, therefore, the cost would increase.     

Effects of three different types of management on the elimination kinetics of volatile anaesthetics. Implications for malignant hyperthermia treatment

The effectiveness of three types of management on the elimination kinetics of volatile anaesthetics was studied prospectively in 45 patients randomised to one of three groups. Patients were anaesthetised using isoflurane. Inspiratory and expiratory isoflurane concentrations were measured. After reaching a steady-state isoflurane concentration, the vaporizer was turned off. In group 1, only the fresh gas flow was increased from 40 to 120 ml.kg-1 x min-1. Patients in group 2, in addition to the increase in the fresh gas flow, had a charcoal filter connected in the inspiratory limb of the circuit. Patients in group 3 had the fresh gas flow increased and the anaesthetic machine and breathing system changed. There was a statistically significant difference in the isoflurane washout from the anaesthetic machines between group 1 (90% elimination time 39 [10] s) and group 2 (90% elimination time 25 [5] s) (p < 0.01). However, there was no significant difference in the isoflurane washout from the patients in any of the groups. Thus the use of a charcoal filter or a change of the anaesthetic machine and breathing system proved to be of no clinical advantage.     

Cardiopulmonary and anesthetic effects of propofol in wild turkeys

OBJECTIVE: To determine safety, anesthetic variables, and cardiopulmonary effects of i.v. infusion of propofol for induction and maintenance of anesthesia in wild turkeys. ANIMALS: 10 healthy, adult wild turkeys. PROCEDURE: Anesthesia was induced by i.v. administration of propofol (5 mg/kg of body weight) over 20 seconds and was maintained for 30 minutes by constant i.v. infusion of propofol at a rate of 0.5 mg/kg/min. Heart and respiratory rates, arterial blood pressures, and arterial blood gas tensions were obtained prior to propofol administration (baseline values) and again at 1, 2, 3, 4, 5, 10, 15, 20, 25, and 30 minutes after induction of anesthesia. All birds were intubated immediately after induction of anesthesia, and end-tidal CO2 concentration was determined at the same time intervals. Supplemental oxygen was not provided. RESULTS: Apnea was observed for 10 to 30 seconds after propofol administration, which induced a decrease in heart rate; however, the changes were not significant. Compared with baseline values, respiratory rate was significantly decreased at 4 minutes after administration of propofol and thereafter. Systolic, mean, and diastolic pressures decreased over the infusion period, but the changes were not significant. Mean arterial blood pressure decreased by 30% after 15 minutes of anesthesia; end-tidal CO2 concentration increased from baseline values after 30 minutes; PO2 was significantly decreased at 5 minutes after induction and thereafter; PCO2 was significantly (P < 0.05) increased after 15 minutes of anesthesia; and arterial oxygen saturation was significantly (P < 0.05) decreased at the end of anesthesia. Two male turkeys developed severe transient hypoxemia, 1 at 5 and the other at 15 minutes after induction. Time to standing after discontinuation of propofol infusion was 11 +/- 6 minutes. Recovery was smooth and unremarkable. CONCLUSION: Propofol is an effective agent for i.v. induction and maintenance of anesthesia in wild turkeys, and is useful for short procedures or where the use of inhalational agents is contraindicated.     

Desflurane: a new inhalation anesthetic]

Desflurane is a new fluoride-only halogenated inhalational anesthetic. It differs from other halogenated anesthetics, in having a lower solubility in all tissues and greater molecular stability in all media. These traits mean, on the one band, that desflurane affords rapid achievement of depth of anesthesia, recovery and management during surgery, and on the other, that its potential toxicity is low and that it is safe for use in low flow circuits. The pharmacodynamic effects of desflurane are similar to those of isoflurane in the blood stream, airways and brain. Sympathetic hyperactivity with increased heart rate and arterial pressure may be triggered when concentration is increased quickly, but this effect is partially abolished when fentanyl is administered. Induction of anesthesia with desflurane causes irritation of the airways, particularly in children, and its use in pediatric surgery is therefore inadvisable. Desflurane potentiates the action of neuromuscular relaxants, much like isoflurane. Desflurane represents a step forward in the search for the ideal anesthetic.     

Prevention of contamination with a heat-and-moisture-exchanger (HME) and bacterial filter during clinical anesthesia

Although the use of HME and bacterial filter is a common practice to protect the anesthesia machine as well as the patients from bacterial contaminants, there is no report demonstrating the effectiveness of this filter in clinical anesthesia setting. We evaluated the actual effectiveness of the filter during clinical use. While the anesthesia breathing circuit, two bacterial filters (BB 50 T, Nihon PALL) and anesthesia bag, which were sterilized with ethylen oxide gas (EOG), were connected to the anesthesia machine and used continuously for one week, EOG sterilized HME and bacterial filter (BB 25 A, Nihon PALL) were changed before each anesthesia. Culture samples were taken from the BB 25 A, the breathing circuit and the machine side of the BB 50 T. Of the 117 BB 25 A samples taken, 6 were positive for Micrococcus, alpha-Streptococcus, Bacillus, and Staphylococcus epidermidis. From 21 breathing circuit "internal" samples, one was positive for Bacillus, Staphylococcus epidermidis. But the contamination from outside sources was suspected, since all the BB 25 as used with this circuit were negative. Use of BB 25 A prevents contamination of the breathing circuit for a period of one week. If we use BB 25 A in every anesthesia case, the changing of the breathing circuit is unnecessary, reducing the cost and simplifying procedures during clinical practice.     

Preservation of hypoxic pulmonary vasoconstriction during sevoflurane and desflurane anesthesia compared to the conscious state in chronically instrumented dogs

BACKGROUND: The authors' objective was to assess the extent to which sevoflurane and desflurane anesthesia alter the magnitude of hypoxic pulmonary vasoconstriction compared with the response measured in the same animal in the conscious state. METHODS: Left pulmonary vascular pressure-flow plots were generated in seven chronically instrumented dogs by continuously measuring the pulmonary vascular pressure gradient (pulmonary arterial pressure-left atrial pressure) and left pulmonary blood flow during gradual (approximately 1 min) inflation of a hydraulic occluder implanted around the right main pulmonary artery. Pressure-flow plots were generated during normoxia and hypoxia on separate days in the conscious state, during sevoflurane (approximately 3.5% end-tidal), and during desflurane (approximately 10.5% end-tidal) anesthesia. Values are mean+/-SEM. RESULTS: In the conscious state, administration of the hypoxic gas mixture by conical face mask decreased (P < 0.01) systemic arterial PO2 from 94+/-2 mmHg to 50+/-1 mmHg and caused a leftward shift (P < 0.01) in the pressure-flow relationship, indicating pulmonary vasoconstriction. The magnitude of hypoxic pulmonary vasoconstriction in the conscious state was flow-dependent (P < 0.01). Neither anesthetic had an effect on the baseline pressure-flow relationship during normoxia. The magnitude of hypoxic pulmonary vasoconstriction during sevoflurane and desflurane was also flow-dependent (P < 0.01). Moreover, at any given value of flow the magnitude of hypoxic pulmonary vasoconstriction was similar during sevoflurane and desflurane compared with the conscious state. CONCLUSION: These results indicate that hypoxic pulmonary vasoconstriction is preserved during sevoflurane and desflurane anesthesia compared with the conscious state. Thus, inhibition of hypoxic pulmonary vasoconstriction is not a general characteristic of inhalational anesthetics. The flow-dependent nature of the response should be considered when assessing the effects of physiologic or pharmacologic interventions on the magnitude of hypoxic pulmonary vasoconstriction.     

Anesthesia for neonatal surgical emergencies

In this review of the anesthetic considerations for the neonate who requires anesthesia for emergency surgery, the authors discuss preoperative, intraoperative, and postoperative management from an anesthetic perspective. Monitoring the cardiorespiratory and metabolic status of neonates during anesthesia is usually difficult because the neonate is not physically accessible. Specific monitoring techniques that provide accurate measurements are discussed. General anesthesia is usually required for the surgery, the airway must be secured and anesthesia managed with a combination of inhalational and intravenous agents. Regional anesthesia and opioids may be included to decrease the intraoperative anesthetic requirements and prevent pain in the postoperative period. The pharmacology of specific anesthetic and adjuvant agents are discussed.     

Endobronchial intubation causes an immediate increase in peak inflation pressure in pediatric patients

Our purpose was to determine whether endobronchial intubation always causes an immediate increase in peak inflation pressure and, if so, the magnitude of the increase. Fourteen children scheduled for central line placement for prolonged antibiotic administration comprised the study group. After routine premedication and induction of anesthesia (halothane in oxygen), an endotracheal tube was inserted, and its position was verified by auscultation and fluoroscopy. Children were mechanically ventilated using a preset volume pressure-limited ventilator with a 5-L fresh gas flow. All children received a constant tidal volume using a similar circuit, similar tubing, and a similar compression volume. The lowest peak inflation pressure to deliver a tidal volume of 15 mL/kg was used. After adjusting the respiratory rate (end-tidal CO2 30 mm Hg) and anesthetic level (halothane end-tidal 1.2%), the peak inflation pressure at this endotracheal position was recorded. The endotracheal tube was advanced into a bronchus, the position was verified as above, and peak inflation pressure was recorded. The endobronchial tube was then pulled back into the trachea, and placement of the central line proceeded. The peak inflation pressure at the endobronchial position was significantly greater than the peak inflation pressure at the endotracheal position (P < 0.0001). The increase was instantaneous at the endobronchial position. Monitoring peak inflation pressure while inserting an endotracheal tube and during anesthesia can help to diagnose endobronchial intubation. Implications: Monitoring peak inflation pressure while inserting an endotracheal tube and during anesthesia can help to diagnose endobronchial intubation.     

Absence of renal and hepatic toxicity after four hours of 1.25 minimum alveolar anesthetic concentration sevoflurane anesthesia in volunteers

Sevoflurane is degraded by CO2 absorbents to Compound A. The delivery of sevoflurane with a low fresh gas flow increases the generation of Compound A. The administration of Compound A to rats can produce injury to renal tubules that is dependent on both the dose and duration of exposure to Compound A. The present study evaluated renal and hepatic function in eight volunteers after a 1-L/min delivery of 3% (1.25 minimum alveolar anesthetic concentration) sevoflurane for 4 h. Volunteers gave their informed consent and provided 24-h urine collections before and for 3 days after sevoflurane anesthesia. Urine samples were analyzed for glucose, protein, albumin, and alpha- and pi-glutathione-S-transferase. Daily blood samples were analyzed for markers of renal and liver injury or dysfunction. Circuit Compound A and plasma fluoride concentrations were determined. During anesthesia, the average maximal inspired Compound A concentration was 39 +/- 6 (mean +/- SD). The median mean arterial pressure, esophageal temperature, and end-tidal CO2 were 62 +/- 6 mmHg, 36.5 +/- 0.3 degrees C, and 30.5 +/- 0.5 mm Hg, respectively. Two hours after anesthesia, the plasma fluoride concentration was 50 +/- 9 micromol/L. All markers of hepatic and renal function were unchanged after anesthesia (repeated-measures analysis of variance P > 0.05). Low-flow sevoflurane was not associated with renal or hepatic injury in humans based on unchanged biochemical markers of renal and liver function. IMPLICATIONS: Sevoflurane delivered in a 3% concentration with a fresh gas flow of 1 L/min for 4 h generated an average maximal Compound A concentration of 39 ppm but did not result in any significant increase in sensitive markers of renal function or injury, including urinary protein, albumin, glucose, and alpha- and pi-glutathione-S-transferase.     

Comparison of cuffed and uncuffed endotracheal tubes in young children during general anesthesia

BACKGROUND: Uncuffed endotracheal tubes are routinely used in young children. This study tests a formula for selecting appropriately sized cuffed endotracheal tubes and compares the use of cuffed versus uncuffed endotracheal tubes for patients whose lungs are mechanically ventilated during anesthesia. METHODS: Full-term newborns and children (n = 488) through 8 yr of age who required general anesthesia and tracheal intubation were assigned randomly to receive either a cuffed tube sized by a new formula [size(mm internal diameter) = (age/4) + 3], or an uncuffed tube sized by the modified Cole's formula [size(mm internal diameter) = (age/4) + 4]. The number of intubations required to achieve an appropriately sized tube, the need to use more than 21.min-1 fresh gas flow, the concentration of nitrous oxide in the operating room, and the incidence of croup were compared. RESULTS: Cuffed tubes selected by our formula were appropriate for 99% of patients. Uncuffed tubes selected by Cole's formula were appropriate for 77% of patients (P < 0.001). The lungs of patients with cuffed tubes were adequately ventilated with 2 1.min-1 fresh gas flow, whereas 11% of those with uncuffed tubes needed greater fresh gas flow (P < 0.001). Ambient nitrous oxide concentration exceeded 25 parts per million in 37% of cases with uncuffed tubes and in 0% of cases with cuffed tubes (P < 0.001). Three patients in each group were treated for croup symptoms (1.2% cuffed; 1.3% uncuffed). CONCLUSIONS: Our formula for cuffed tube selection is appropriate for young children. Advantages of cuffed endotracheal tubes include avoidance of repeated laryngoscopy, use of low fresh gas flow, and reduction of the concentration of anesthetics detectable in the operating room. We conclude that cuffed endotracheal tubes may be used routinely during controlled ventilation in full-term newborns and children during anesthesia.     

Exhaled NO during graded changes in inhaled oxygen in man

BACKGROUND: Nitric oxide (NO) is present in the exhaled air of animals and humans. In isolated animal lungs the amount of exhaled NO is decreased during hypoxia. A study was undertaken to determine whether changes in arterial oxygen tension affect levels of exhaled NO in humans. METHODS: Sixteen healthy subjects were randomised to inhale different gas mixtures of oxygen and nitrogen in a double blind crossover study. Eight gas mixtures of oxygen and nitrogen (fractional inspired oxygen concentration (FiO2) 0.1 to 1.0) were administered. Exhaled NO was measured with a chemiluminescence detector from end expiratory single breath exhalation. RESULTS: A dose-dependent change in exhaled NO during graded oxygen breathing was observed (p = 0.0012). The mean (SE) exhaled NO concentration was 31 (3) ppb at baseline, 39 (4) ppb at an FiO2 of 1.0, and 26 (3) ppb at an FiO2 of 0.1. CONCLUSIONS: The NO concentration in exhaled air in healthy humans is dependent on oxygen tension. Hyperoxia increases the level of exhaled NO, which indicates increased NO production. The mechanism behind this phenomenon remains to be elucidated.     

The dumping valve and its clinical application

An open reservoir for the collection and evacuation of anaesthetic gases permits leakage to room air. The use of a closed reservior for the removal of overspill gas from anaesthetic circuits is described. Calibrated gas evacuation is carried out through an ejector flowmeter from the anesthetic circuit or from a closed reservoir, where the gas is collected via a relief valve. In order to eliminate the risk of high or low pressure in the reservoir employed, a relief valve and a dumping valve is included in the system.