Anesthetic Gas Analyzer Research Articles

Evaluation of isoflurane inhalation -anesthesia machines available in Switzerland for on farm piglet -castrations

The present study analyzed piglet castration under isoflurane anesthesia in ten farms. The data of 202 male piglets in the age between three to eleven days and with a body weight of 1 - 4,7 kg were collected. The aim of this study was to compare the PorcAnest®, Pignap® and Pigsleeper® anesthesia machines used in Switzerland. Isoflurane, carbon dioxide (CO2) and oxygen (O2) values were measured in relation to their significance for anesthesia quality. Therefore, preoperative stress level and movements were assessed during skin incision and the dissection of the spermatic cords. Isoflurane, CO2 and O2 values were recorded in the inhaled and exhaled gases next to the nostrils at 30, 60, 75 and 90 seconds after the start of anesthesia. Movements to the skin incisions and dissection of the spermatic cord were observed in 32 % and 37 % respectively. Movements increased with the decrease of measured inspiratory and expiratory isoflurane values (FIIso and ETIso). Significantly lower inspiratory O2 values (FIO2: 12 - 21 volume % vs 21 - 95 volume %) and stronger movements were measured in anesthesia machines using room air compared to machines operated with medical oxygen. Results indicate a potential for improvement in anesthesia deph piglet castration under isoflurane inhalaton anesthesia and THE measured isoflurane, CO2 and O2 values differ significantly between PorcAnest®, Pignap® and Pigsleeper® anesthesia machines. These fluctuations could be recognized and reduced by annual professional maintenance and / or the addition of an anesthetic gas analyzer. In addition, a change to medical oxygen is indicated for all anesthetic machines. Anesthesia machines have to be optimized in consultation with the manufacturers as soon as possible and the farmers have to be trained and sensitized to ensure pain-free castration.

Assessing the depth of isoflurane anaesthesia during cardiopulmonary bypass.

Bispectral index (BIS) and monitoring of end-tidal concentration may be associated with a reduction in the incidence of awareness during volatile-based general anaesthesia. An analogue of end-tidal concentration during cardiopulmonary bypass (CPB) is measuring exhausted isoflurane concentration from the oxygenator as an estimate to blood and, so, brain concentration. The aim of this study was to determine the relationships between oxygenator exhaust and blood concentrations of isoflurane and the BIS score during CPB when administering isoflurane into the sweep gas supply to the oxygenator. Seventeen patients undergoing elective cardiac surgery using CPB and isoflurane with BIS monitoring were recruited in a single-centre university hospital. Isoflurane gas was delivered via a calibrated vaporiser at the beginning of anaesthetic induction. Radial arterial blood samples were collected after the initiation of CPB and before aortic cross-clamping, which were analysed for isoflurane by gas chromatography and mass spectrometry. The BIS score and the concentration of exhausted isoflurane from the oxygenator membrane, as measured by an anaesthetic gas analyser, were recorded at the time of blood sampling. The mean duration of anaesthetic induction to arterial blood sampling was 90 min (95%CI: 80,100). On CPB, the median BIS was 39 (range, 7-43) and the mean oxygenator exhaust isoflurane concentration was 1.24 ± 0.21%. No significant correlation was demonstrated between BIS with arterial isoflurane concentration (r=-0.19, p=0.47) or oxygenator exhaust isoflurane concentration (r=0.07, p=0.80). Mixed-venous blood temperature was moderately correlated to BIS (r=0.50, p=0.04). Oxygenator exhaust isoflurane concentration was moderately, positively correlated with its arterial concentration (r=0.64, p<0.01). In conclusion, in patients undergoing heart surgery with CPB, the findings of this study indicate that, whilst oxygenator exhaust concentrations were significantly associated with arterial concentrations of isoflurane, neither had any association with the BIS scores, whereas body temperature has moderate positive correlation.

Coronary Sinus Isoflurane Concentration in Cardiac Surgery

Volatile anesthetic agents such as isoflurane may be associated with fewer adverse myocardial events compared with total intravenous anesthesia in cardiac surgery. The authors aimed to determine whether reasonable isoflurane concentrations at tissue level were being achieved to protect the myocardium using this agent. The isoflurane concentration in myocardium has never been measured. The primary aim was to sample coronary sinus (CS) blood and measure its isoflurane concentration. Secondary aims were to determine whether the CS blood concentration would equilibrate with the arterial blood concentration and the relationship of CS blood concentration with oxygenator exhaust isoflurane concentrations during cardiopulmonary bypass (CPB). Prospective, observational study. Single-center university hospital. The study comprised 23 patients undergoing cardiac surgery using CPB and isoflurane. Shortly after initiation of CPB and insertion of a CS retrograde cardioplegia catheter but before aortic cross-clamping, CS blood was aspirated, followed by radial artery blood, which then were analyzed for isoflurane with gas chromatography and mass spectrometry. The oxygenator exhaust isoflurane level was measured with an anesthetic gas analyzer. The mean arterial and CS isoflurane concentrations were 87.7 ± 50.1 and 73.0 ± 42.9 μg/mL, respectively. There was a significant mean difference of 14.7 μg/mL (95% confidence interval 6.7-22.8) between CS and arterial isoflurane concentrations. Oxygenator exhaust isoflurane levels were correlated positively with those in the CS blood (r = 0.68, p < 0.001) and arterial blood (r = 0.72, p < 0.001). This was the first study in which CS blood was sampled and measured for isoflurane concentration. The CS isoflurane concentration could be estimated from the isoflurane concentration in the oxygenator exhaust gas. However, the value of this relationship is limited because the CS isoflurane concentration does not accuratelyrepresent its myocardial levels during CPB.

Intra operative awareness due to malfunctioning of anaesthesia machine - A rare incidence

A 15 year old female patient of ASA class I was posted for implant removal from left forearm under general anaesthesia. Intraoperative period was uneventful. In the immediate postoperative period, she became restless which subsided after administration of haloperidol and promethazine intramuscularly. On interview, she complained of intraoperative awareness. Thorough checking of the anaesthesia machine revealed that the floats in both oxygen and nitrous oxide rotameters were moving up even when both nitrous oxide cylinders were closed and one oxygen cylinder was kept open. The diaphragm of oxygen failure safety valve was found to be ruptured which allowed oxygen to flow through nitrous oxide flow meter. Preoperative checking of the anaesthesia machine could not identify these abnormalities. Thus, meticulous checking of anaesthesia machine including the oxygen failure safety valve, intraoperative monitoring of depth of anaesthesia, use of oxygen and end-tidal anesthetic gas analyzer may be helpful to prevent such an incident. DOI: http://dx.doi.org/10.4038/slja.v21i2.5235

Comparison of air‐sealing characteristics of tapered‐ vs. cylindrical‐shaped high‐volume, low‐pressure tube cuffs

This study aimed at comparing air-sealing characteristics of the new tapered-shaped tracheal tube cuffs with cylindrical tube cuffs. Tracheal tubes with tapered-shaped polyurethane (PU) and polyvinyl chloride (PVC) cuffs as well as standard cylindrical-shaped cuffs made of PU and PVC (Covidien, Athlone, Ireland) were investigated. A tracheal model attached to a test lung was intubated, and cuffs were inflated to 10, 15, 20, 25 and 30 cm H(2)O. The test lung was ventilated with intermittent positive pressure ventilation at peak inspiratory pressures (PIPs) of 20 and 25 cm H(2)O. Air leakage was assessed by spirometry and measurement of sevoflurane concentration passing the cuff at the upper cuff border using an anaesthetic gas analyser. Experiments were repeated four times with new tracheal tubes for each run. Statistical comparisons were done using Mann-Whitney U-test with level of significance at P < 0.05. The tapered-shaped PVC tube cuff demonstrated a significantly lower air leakage determined by spirometry than the cylindrical-shaped cuff at both PIPs (20 and 25 cm H(2)O). Similarly, sevoflurane leakage was less with the tapered PVC cuff particularly at higher cuff pressures. With the PU cuff, reduction in air leakage by a tapered-shaped compared with a cylindrical-shaped tube cuff was not significant. A tapered-shaped tube cuff considerably improves air-sealing characteristics of PVC tube cuffs and allows thereby reducing cuff pressure required for sufficient ventilation. In tube cuffs made of PU that exhibits superior sealing characteristics compared with PVC, a tapered shape failed to result in a further reduction of air leakage.

Profilaxia antiemética em cirurgia de abdome agudo: estudo comparativo entre droperidol, metoclopramida, tropisetron, granisetron e dexametasona

It is calculated that the incidence of postoperative nausea and vomiting (PONV) is approximately 30%. The prophylaxis of PONV has been the subject of several studies, both to decrease this problem and to compare the cost-benefit ration of the treatment used. The objective of this study was to compare the efficacy of 5 antiemetic drugs with a control group in emergency appendectomy. A controlled, double-blind, prospective study with 150 patients, ASA I and II, BMI < 30, undergoing appendectomy, was undertaken. Patients were divided in six groups: Group 1 (n = 25): 5 mL of normal saline; Group 2 (n = 25): 0.625 mg of droperidol; Group 3 (n = 25): 20 mg of metoclopramide; Group 4 (n = 25): 5 mg of tropisetron; Group 5 (n = 25): 1 mg of granisetron; Group 6 (n = 25): 4 mg of dexamethasone. Monitoring included ECG non-invasive blood pressure, O2 saturation, P(ET)CO2, anesthetic gas analyzer and peripheral nerve stimulator. The presence of PONV complications and the degree of satisfaction in the first 48 hours were evaluated. The incidence of PONV in the droperidol group was 4% while in the granisetron, tropisetron and metoclopramide groups it was 12% (p < 0.05). The dexamethasone group had a 24% incidence and the control group 28%. Low doses of droperidol were more effective in the prophylaxis of PONV in emergency appendectomy than the other drugs.

ANESTHETIC PRECONDITIONING CONFERS ACUTE CARDIOPROTECTION VIA UP-REGULATION OF MANGANESE SUPEROXIDE DISMUTASE AND PRESERVATION OF MITOCHONDRIAL RESPIRATORY ENZYME ACTIVITY

The cellular and molecular mechanisms that underlie cardioprotection against I/R by anesthetic-induced preconditioning (APC) require further elucidation. Using isoflurane as a representative anesthetic, we evaluated the hypothesis that APC induces myocardial protection against I/R by attenuation of excessive reactive oxygen species and restoration of mitochondrial bioenergetics through postischemic up-regulation of manganese superoxide dismutase (MnSOD) expression and preservation of respiratory enzyme activity. Pentobarbital anesthetized open-chest Sprague-Dawley rats were subject to 30-min left coronary artery occlusion, followed by 120-min reperfusion. Before ischemia, rats were randomly assigned to receive 0.9% saline, two cycles of brief coronary artery occlusion and reperfusion, or a 30-min exposure to 1.0 minimum alveolar concentration isoflurane in the absence or presence of a specific mitochondrial adenosine triphosphate-sensitive potassium (KATP) channel blocker, 5-hydroxydecanoate; a membrane-permeable superoxide scavenger, 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl; or a NOS inhibitor, N(G)-nitro-L-arginine methyl ester. Isoflurane exposure induced an initial increase in myocardial superoxide (O2-), but not NO level. It also significantly decreased infarct size and restored mitochondrial respiratory enzyme activity or ATP production in I/R rat hearts, along with suppression of the O2- surge at reperfusion and increase in MnSOD expression or enzyme activity. These protective effects were abrogated by 5-hydroxydecanoate or 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl, but not by N(G)-nitro-L-arginine methyl ester pretreatment. These results suggest that opening of mitochondrial KATP channel, followed by O2- signaling, induces postischemic augmentation of MnSOD and preservation of mitochondrial respiratory enzyme activities, leading to attenuated cardiac O2- surge and restored ATP production during reperfusion, and underlie APC-induced cardioprotection.

Urethane anesthesia in adult female rats: preliminary observations

Urethane is widely used as a rodent anesthetic in the laboratory setting, and is characterized as producing long-lasting anesthesia. The purpose of this study was to evaluate the quality of anesthesia provided by a single dose of urethane based on the response to a noxious stimulus. If the quality of anesthesia was insufficient to prevent gross purposeful movement (GPM), isoflurane was also administered until no response to noxious stimulation occurred. Five adult Harlan Sprague Dawley rats (6 months of age, 250–300 g) were given urethane (1.4 g kg−1 IP) and evaluated for 120 minutes post-injection. If the rats became laterally recumbent by 20 minutes post-injection, a large hemostat was positioned around the tail and the response to tail clamping was assessed. If no GPM occurred, an additional 20 minutes was allowed to elapse. If the rats were not laterally recumbent or GPM was present, they were placed in a chamber and isoflurane in oxygen was administered. Inspired isoflurane concentrations (ISO) were measured using a S/5 anesthetic gas analyzer (Datex-Ohmeda Division, Helsinki, Finland) calibrated before each experiment with a standardized calibration gas mixture (DOT-34 NRC 300/375 m1014, Datex-Ohmeda Division, Helsinki, Finland). A period of 20 minutes was allowed for equilibration to inspired ISO. The tail-clamp stimulus was then re-applied and the animal's response recorded. If GPM was absent, ISO was lowered by 10–20% and an additional 20 minute interval elapsed. In contrast, if GPM was present, ISO was increased by 10–20%. This procedure was repeated until the ISO required to prevent GPM was determined in duplicate. The position within the estrus cycle influenced pain thresholds in the rats. As such, a vaginal smear was prepared from each rat and the position in the estrus cycle was determined based on vaginal cytology. Rats were euthanatized at the end of the study period. All values were mean ± SD. Four rats became recumbent after urethane injection (time to recumbency: 45 ± 17 seconds). Of these, two rats (one estrus, one metestrus) did not require isoflurane supplementation for the duration of the study. The three remaining rats (two metestrus, one estrus) required isoflurane supplementation. The mean ISO required to prevent GPM was 0.26 ± 0.16%. Position within the estrus cycle did not appear to affect the animal's response to urethane. These results indicate that urethane anesthesia is not long lasting in all rats and provides variable quality of anesthesia. This is of particular concern in the laboratory setting where muscle relaxants are often administered to rats shortly after urethane injection.

Assessment of the respiratory exchange ratio in mechanically ventilated patients by a standard anaesthetic gas analyser

The respiratory exchange ratio (R) is the CO2 production divided with O2 consumption. R is an essential factor included in several formulas during routine blood gas analysis. Instant and individual measurement of R may be of particular interest to improve the evaluation of each single patient. A standard anaesthetic gas analyser has been recommended for measurement of R among spontaneously breathing healthy subjects, but there is no experience using this method among mechanically ventilated critically ill patients. This study validates the assessment of R by a Brüel & Kjaer gas analyser (B & K) during positive pressure ventilation of intensive care patients. The B & K sampled gas from 11 mechanically ventilated patients over a period of 5 min. The recordings of end-tidal values of O2 and CO2 based on fractions (RF) allowed for calculation of RF by the alveolar equation solved for R. The continuous recordings of corresponding values were depicted into an O2-CO2 diagram. A developed computer program calculated estimates of R as the slope of the regression lines related to the full cycle (Rfull) and the expiratory phase only (Rexp). Corrected values of the full respiratory cycle (Rfull*) were also calculated assuming changes of CO2 and O2 volumes during gas exchange. The different estimates of R were compared with simultaneous measurement of a Deltatrac indirect calorimeter (Rdelta). Ten values of RF were within the expected interval of 0.72 < R < 1.00. For the full respiratory cycles, the mean R-value was 0.94 +/- 0.07 and for the expiratory phase the mean R-value was 0.82 +/- 0.08. The O2-CO2 diagram appeared as a convexo-convex loop during each cycle. The agreement of Rexp and Rdelta (Rexp-Rdelta: 0.01 +/- 0.13) were good. This study demonstrates that gas measurements by a standard anaesthetic gas monitor can be used for determination of R, and thereby we present an alternative to R calculation made by the Deltatrac monitor.

Effect of breathing a heliox gas mixture on cardiopulmonary function in horses-anesthetized immediately following exercise

The purpose of this study was to determine the cardiopulmonary effects of breathing a heliox (60% He: 40% O2) carrier gas mixture in horses anesthetized immediately following treadmill exercise. Using a randomized crossover design, six healthy, Thoroughbred horses (five males, one female) weighing 517 ± 36.9 kg were instrumented to enable measurement of heart rate (HR), systolic (SAP), mean (MAP) and diastolic (DAP) carotid arterial pressures, mean pulmonary arterial pressure (PAP), central venous pressure (CVP), pulmonary arterial temperature (TEMP), and cardiac output. Horses were warmed up for 3 minutes at 4 m second−1, then exercised to the point of fatigue at 115% VO2max and immediately anesthetized using detomidine (0.04 mg kg−1 IV) followed by tiletamine-zolazepam (1.25 mg kg−1 IV). Anesthesia was maintained using 1.3 MAC isoflurane (ISO) vaporized in either 100% O2 (O), 60% N2 : 40% O2 (N), or 60% He : 40% O2 (H). End-tidal ISO concentration was measured using a RASCAL II anesthetic gas analyzer. Minute ventilation (MV) was measured during ISO anesthesia using a heated, calibrated pneumotachometer and differential pressure transducer. Ventilation during ISO anesthesia was controlled to maintain constant, similar minute ventilation between the O, N and H treatment groups. Cardiovascular data and samples for arterial and mixed venous blood gas analysis were recorded while the horse stood quietly prior to exercise, 30 seconds after the point of fatigue, immediately prior to isoflurane anesthesia and 15, 30, 45 and 60 minutes after initiating isoflurane anesthesia. Data were analyzed using repeated measures anova with posthoc differences between means identified using Bonferroni's method (p < 0.05). Exercise was associated with significant increases in HR, SAP, MAP, DAP, PAP, CVP, TEMP and significant decreases in pH, HCO3– and BE. Anesthesia was associated with a return of HR, SAP, MAP, DAP, PAP and CVP to pre-exercise values. MV measured during ISO was not different between groups. Horses in the O group had significantly higher values for PaO2 (156.7 mm Hg, 20.9 kPa) compared to the N group (93.6 mm Hg, 12.5 kPa) or the H group (90.4 mm Hg, 12.1 kPa). No other differences between treatments were identified. We conclude that use of H as a carrier gas does not improve gas exchange in horses anesthetized immediately following exercise.

The Hemodynamic and Adrenergic Effects of Perioperative Dexmedetomidine Infusion after Vascular Surgery

We tested dexmedetomidine, an alpha(2) agonist that decreases heart rate, blood pressure, and plasma norepinephrine concentration, for its ability to attenuate stress responses during emergence from anesthesia after major vascular operations. Patients scheduled for vascular surgery received either dexmedetomidine (n = 22) or placebo (n = 19) IV beginning 20 min before the induction of anesthesia and continuing until 48 h after the end of surgery. All patients received standardized anesthesia. Heart rate and arterial blood pressure were kept within predetermined limits by varying anesthetic level and using vasoactive medications. Heart rate, arterial blood pressure, and inhaled anesthetic concentration were monitored continuously; additional measurements included plasma and urine catecholamines. During emergence from anesthesia, heart rate was slower with dexmedetomidine (73 +/- 11 bpm) than placebo (83 +/- 20 bpm) (P = 0.006), and the percentage of time the heart rate was within the predetermined hemodynamic limits was more frequent with dexmedetomidine (P < 0.05). Plasma norepinephrine levels increased only in the placebo group and were significantly lower for the dexmedetomidine group during the immediate postoperative period (P = 0.0002). We conclude that dexmedetomidine attenuates increases in heart rate and plasma norepinephrine concentrations during emergence from anesthesia. The alpha(2) agonist, dexmedetomidine, attenuates increases in heart rate and plasma norepinephrine concentrations during emergence from anesthesia in vascular surgery patients.

Anesthetic Gas Analyzer Pressure Readings Could Drift

Anesthetic Gas Analyzer Pressure Readings Could Drift

Ventilatory effects, blood gas changes, and oxygen consumption during laparoscopic hysterectomy.

We evaluated the ventilatory effects and blood gas changes of prolonged CO2-pneumoperitoneum in nor-moventilated patients and examined the respiratory and gas exchange consequences of head-down positioning (25-30 degrees) and CO2 insufflation into the peritoneal cavity in 20 patients without major cardiorespiratory disorders in various phases of laparoscopic hysterectomy. The patients received general anesthesia with isoflurane, fentanyl, and vecuronium, and minute ventilation (MV) was adjusted to maintain the PETCO2 at 33-36 mm Hg throughout the entire procedure, either by increasing the tidal volume (TV) and keeping the respiratory rate (RR) at 12/min (10 patients) or by changing the RR and maintaining the TV at 8 mL/kg (10 patients). Arterial and mixed venous blood samples were collected simultaneously for blood gas analysis and for measurements of oxygen consumption, and respiratory mechanics and gases were recorded by an anesthetic gas analyzer and side stream spirometry device. Oxygen consumption decreased with anesthesia, remained stable to the end of the laparoscopy, increased soon after deflation of the pneumoperitoneum, and reached preanesthetic values during recovery. The MV requirement increased by approximately 30% after the start of CO2 insufflation, then increased somewhat further toward the end of the laparoscopy, reaching the highest level a few minutes after deflation of the intraabdominal gas. The compliance decreased by 20% with the head-down position and by an additional 30% with the increased intraabdominal pressure. PaCO2 and mixed venous PCO2 increased with CO2 insufflation, and the arterial to end-tidal PCO2 (a-etPCO2) gradient increased by 1.5 mm Hg during laparoscopy. A mild metabolic acidosis developed.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventilatory Effects, Blood Gas Changes, and Oxygen Consumption During Laparoscopic Hysterectomy

We evaluated the ventilatory effects and blood gas changes of prolonged CO (2)-pneumoperitoneum in normoventilated patients and examined the respiratory and gas exchange consequences of head-down positioning (25-30 degrees) and CO2 insufflation into the peritoneal cavity in 20 patients without major cardiorespiratory disorders in various phases of laparoscopic hysterectomy. The patients received general anesthesia with isoflurane, fentanyl, and vecuronium, and minute ventilation (MV) was adjusted to maintain the PETCO2 at 33-36 mm Hg throughout the entire procedure, either by increasing the tidal volume (TV) and keeping the respiratory rate (RR) at 12/min (10 patients) or by changing the RR and maintaining the TV at 8 mL/kg (10 patients). Arterial and mixed venous blood samples were collected simultaneously for blood gas analysis and for measurements of oxygen consumption, and respiratory mechanics and gases were recorded by an anesthetic gas analyzer and side stream spirometry device. Oxygen consumption decreased with anesthesia, remained stable to the end of the laparoscopy, increased soon after deflation of the pneumoperitoneum, and reached preanesthetic values during recovery. The MV requirement increased by approximately 30% after the start of CO2 insufflation, then increased somewhat further toward the end of the laparoscopy, reaching the highest level a few minutes after deflation of the intraabdominal gas. The compliance decreased by 20% with the head-down position and by an additional 30% with the increased intraabdominal pressure. PaCO2 and mixed venous PCO2 increased with CO2 insufflation, and the arterial to end-tidal PCO2 (a-etPCO2) gradient increased by 1.5 mm Hg during laparoscopy. A mild metabolic acidosis developed. The MV requirement was more among patients whose RR was changed to maintain normocapnia. In conclusion, there was a small increase in the a-etPCO2 gradient, indicating some increase in alveolar dead space during laparoscopy. Normocapnia during laparoscopy in healthy patients was achieved by maintaining the PETCO2 at a somewhat lower level than normal, preferably by increasing the TV of controlled ventilation. (Anesth Analg 1995;80:961-6)

Anesthetic Gas Analyzer Measurements Could Drift

Anesthetic Gas Analyzer Measurements Could Drift

Erroneous data from an infrared anesthetic gas analyzer

Erroneous data from an infrared anesthetic gas analyzer

American monitoring: standard and state of the art.

Monitoring of the anesthetized patient, the anesthesia machine, and the patient-machine interface is an essential component of anesthetic practice in order to prevent anesthetic-related injuries resulting from equipment failure or human error. While the optimal monitor to detect anesthetic problems (hypoxia, esophageal intubation, hemodynamic compromise, for example) is unclear at present, American standards require continuous presence of qualified personnel who evaluate patient oxygenation, ventilation, circulation, and temperature. A common monitoring array includes electrocardiogram, autosphygmomanometer, pulse plethysmography/oximetry, stethoscope, anesthetic gas analyzer, thermistor, and nerve stimulator. The role of emerging technologies, including transesophageal echocardiography, automated electrocardiographic analysis of ST segments, transcranial Doppler, and transcranial near infrared spectroscopy are discussed.

Monitoring anesthetic vapor concentrations using a piezoelectric detector: evaluation of the Engstrom EMMA.

The Engstrom anesthetic gas analyzer (EMMA) was evaluated to determine the reproducibility, response time, gas interference, water vapor dependence, and sensitivity. The analyzer also was evaluated clinically in 20 children undergoing orthopedic surgery. Difference between the analyzer output and anesthetic gas standard (reproducibility) ranged from 0.013 +/- 0.008 vol % to 0.018 +/- 0.018 vol %. Response times decreased from 710 ms at 5 l X min-1 to 149 ms at 30 l X min-1. Nitrous oxide caused an offset of +0.11 +/- 0.007 vol %. Water vapor caused positive offsets of 0.25 +/- 0.044 vol %, 0.51 +/- 0.027 vol %, and 0.80 +/- 0.037 vol % at 25 degrees C, 30 degrees C, and 34 degrees C, respectively. The analyzer reproducibly measured dry gas concentrations, but compensation had to be made for water vapor when measuring wet gases. The analyzer's usefulness for end-tidal monitoring was questioned because of its slow response time and its sensitivity to water vapor.

A laboratory investigation of a multigas monitor for anaesthesia (EMMA).

A new volatile anaesthetic gas analyser (EMMA) was tested in the laboratory. It was shown to have an accurate, linear response, with minimal zero drift and to be almost unaffected by carrier gases. It is a versatile and sensitive machine with a fast response time indicating that it might be used for breath-by-breath monitoring. The EMMA is a useful new anaesthetic gas analyser than should find widespread clinical usage.

A flueric respiratory and anesthetic gas analyzer.

A unique fluidic-electronic system utilizing flueric jet-edge resonator oscillator sensors has been developed to continuously measure concentrations of oxygen, carbon dioxide, halothane, enflurane, and nitrous oxide in respiratory and anesthetic gases. The sensing unit consists of two flueric jet-edge resonator oscillators operating in parallel. At a constant geometry, flow rate, and temperature, the frequency generated by these oscillators is a function of the molecular weight and specific heat of the gases flowing through them. Oscillator frequencies are detected by pressure transducers. These transducer signals are processed and converted electronically to a.d.c. voltage which is calibrated and displayed in units of constituent concentrations per voltage. The change in frequency of the sensing unit is linear for CO2 and O2 in air and for CO2, N2O, halothane, and enflurane in oxygen. The sensitivity of the sensors is approximately 65 Hz/%CO2 and 20 Hz/%O2 when referenced against air. For these same sensors, sensitivities for CO2, N2O, halothane, and enflurane are approximately 55 Hz/%CO2, 45 Hz/%N2O, 680 Hz/% halothane, and 790 Hz/%enflurane when referenced against oxygen. Time response for the sensor system is 450±10 msec from zero to 90% full scale.