Biomedical subjects

K Geiger

Publications and source records attributed to K Geiger.

At least 19 recordsLinked to original sources

PubMed2001

[Anaplastic astrocytomas of the medulla oblongata. A rare differential diagnosis in orthostatic hypotension].

HISTORY AND PHYSICAL EXAMINATION: A 39-year-old women was admitted for evaluation of dizziness and hypotension. During standing the blood pressure dropped from 130/80 to 80/40 mmHg. Ten weeks before admission she had recurrent cerebral convulsions. Neurological evaluation showed a slight left hemiparesis. Computed tomography of the brain revealed a 1.5 +/- 1 cm cyst in the left tempral region. It was thought that the cause of the recurrent convulsions was alcohol abuse. During the next few weeks orthostatic hypotension increased and she was not able to work. INVESTIGATIONS: At admission abnormal findings included hypotension, horizontal nystagmus, and deviation of the soft palate to the right. After the patient was brought to an upright position during standardized passive tilt testing she showed a defect in the sympathetic limb of the baroreceptor reflex arc. Head magnetic resonance tomography showed a signal-enhancing tumour in the cervicomedullary region. TREATMENT AND CLINICAL COURSE: Before a planned biopsy could be performed the patient died of respiratory arrest. Postmortem examination revealed an anaplastic grade III astrocytoma extending form the pons to the medulla oblongata. CONCLUSION: Upright tilting leads to pooling of blood in the legs. One of the normal compensatory responses is a reflex tachycardia which our patient did not show as a sign of an afferent defect. Patients with orthostatic hypotension as a prominent symptom should be investigated with a standardized tilt test. In special patients, additional neurological investigations are necessary.

Adult↗

PubMed2001

Is pulmonary resistance constant, within the range of tidal volume ventilation, in patients with ARDS?

When managing patients with acute respiratory distress syndrome (ARDS), respiratory system compliance is usually considered first and changes in resistance, although recognized, are neglected. Resistance can change considerably between minimum and maximum lung volume, but is generally assumed to be constant in the tidal volume range (V(T)). We measured resistance during tidal ventilation in 16 patients with ARDS or acute lung injury by the slice method and multiple linear regression analysis. Resistance was constant within V(T) in only six of 16 patients. In the remaining patients, resistance decreased, increased or showed complex changes. We conclude that resistance within V(T) varies considerably from patient to patient and that constant resistance within V(T) is not always likely.

Adolescent↗

PubMed2001

Volume-dependent compliance and ventilation-perfusion mismatch in surfactant-depleted isolated rabbit lungs.

OBJECTIVE: Volume-dependent alterations of lung compliance are usually studied over a very large volume range. However, the course of compliance within the comparably small tidal volume (intratidal compliance-volume curve) may also provide relevant information about the impact of mechanical ventilation on pulmonary gas exchange. Consequently, we determined the association of the distribution of ventilation and perfusion with the intratidal compliance-volume curve after modification of positive end-expiratory pressure (PEEP). DESIGN: Repeated measurements in randomized order. SETTING: An animal laboratory. SUBJECTS: Isolated perfused rabbit lungs (n = 14). INTERVENTIONS: Surfactant was removed by bronchoalveolar lavage. The lungs were ventilated thereafter with a constant tidal volume (10 mL/kg body weight). Five levels of PEEP (0-4 cm H2O) were applied in random order for 20 mins each. MEASUREMENTS AND MAIN RESULTS: The intratidal compliance-volume curve was determined with the slice method for each PEEP level. Concurrently, pulmonary gas exchange was assessed by the multiple inert gas elimination technique. At a PEEP of 0-1 cm H2O, the intratidal compliance-volume curve was formed a bow with downward concavity. At a PEEP of 2 cm H2O, concavity was minimal or compliance was almost constant, whereas higher PEEP levels (3-4 cm H2O) resulted in a decrease of compliance within tidal inflation. Pulmonary gas exchange did not differ between PEEP levels of of 0, 1, and 2 cm H2O. Pulmonary shunt was lowest and perfusion of alveoli with a normal ventilation-perfusion was highest at a PEEP of 3-4 cm H2O. Deadspace ventilation did not change significantly but tended to increase with PEEP. CONCLUSIONS: An increase of compliance at the very beginning of tidal inflation was associated with impaired pulmonary gas exchange, indicating insufficient alveolar recruitment by the PEEP level. Consequently, the lowest PEEP level preventing alveolar atelectasis could be detected by analyzing the course of compliance within tidal volume without the need for total lung inflation.

Animals↗

PubMed2001

Breathing pattern and perception at different levels of volume assist and pressure support in volunteers.

OBJECTIVE: Volume assist (VA) amplifies the breathing effort whereas pressure support ventilation (PSV) provides a fixed, effort-independent ventilatory support. According to the concept of VA, its level should compensate for the pathologically increased (additional) elastance (Eadd). However, it is unclear whether breathing subjects prefer an exact compensation of Eadd and whether they are able to adjust the support level by themselves. DESIGN: Prospective, interventional study. SETTING: Laboratory. SUBJECTS: Twelve healthy volunteers, nine females, three males, aged 21-33 yrs. INTERVENTIONS: Increased Eadd was generated by banding of the thorax and abdomen. Volunteers breathed via a mouthpiece with VA or PSV using a positive end-expiratory pressure of 5 cm H2O (0.5 kPa). The study was subdivided into two parts. In part I, volunteers were instructed to adjust the level of VA and PSV themselves starting from three different, randomly applied levels in each mode (2, 8, 14 cm H2O or cm H2O/L; 0.2, 0.8, 1.4 kPa[/L]). In part II, 20 levels of VA and PSV (1-20 cm H2O or cm H2O/L, 0.1-2 kPa[/L]) were randomly selected by an investigator and estimated by the volunteers using a visual analog scale. Additionally, the breathing pattern was characterized. MEASUREMENTS AND MAIN RESULTS: Eadd (7.1 +/- 1.5 cm H2O/L [0.7 +/- 0.2 kPa/L], mean +/- sd) corresponded almost exactly to the "self-adjusted" VA level of part I (7.0 +/- 3.3 cm H2O/L [0.7 +/- 0.3 kPa/L]) and to the adequate level of part II (8-9 cm H2O/L [0.8-0.9 kPa/L]). The accordant PSV levels were 5.7 +/- 2.6 cm H2O (0.6 +/- 0.3 kPa) and 6-7 cm H2O (0.6-0.7 kPa). The breathing pattern was less influenced by changes of the support level with VA compared with PSV, which may explain in part the greater comfort of VA. CONCLUSIONS: We confirmed the theoretical assumption that VA should be adapted to Eadd. Furthermore, we demonstrated that conscious subjects are able to adjust the level of VA and PSV themselves.

Adult↗

PubMed2001

CO(2)-controlled sampling of alveolar gas in mechanically ventilated patients.

A newly designed gas-sampling device using end-tidal CO(2) to separate dead space gas from alveolar gas was evaluated in 12 mechanically ventilated patients. For that purpose, CO(2)-controlled sampling was compared with mixed expiratory sampling. Alveolar sampling valves were easily controlled via CO(2) concentration. Concentrations of four volatile substances were determined in the expired and inspired gas. Isoflurane and isoprene, which did not occur in the inspired air, had ratios of end-tidal to mixed expired concentrations of 1.75 and 1.81, respectively. Acetone and pentane, found in both the inspired and expired air, showed ratios of 0.96 and 1.0, respectively. Precision of concentration measurements was between 2.4% (isoprene) and 11.2% (isoflurane); reproducibility (as coefficient of variation) was 5%. Because the only possible source of isoflurane and isoprene in this setting was patients' blood, selective enrichment of alveolar gas was demonstrated. By using the new sampling technique, sensitivity of breath analysis was nearly doubled.

Acetone↗

PubMed2001

Radioisotope albumin flux measurement of microvascular lung permeability: an independent parameter in acute respiratory failure?

AIM: To evaluate the extent to which single measurements of microvascular lung permeability may be relevant as an additional parameter in a heterogenous clinical patient collective with Acute Lung Injury (ALI) and Acute Respiratory Distress Syndrome (ARDS). METHODS: In 36 patients with pneumonia (13), non pneumogenic sepsis (9) or trauma (14) meeting the consensus conference criteria of ALI or ARDS double-isotope protein flux measurements (51Cr erythrocytes as intravascular tracer, Tc-99m human albumin as diffusible tracer) of microvascular lung permeability were performed using the Normalized Slope Index (NSI). The examination was to determine whether there is a relationship between the clinical diagnosis of ALI/ARDS, impaired permeability and clinical parameters, that is the underlying disease, oxygenation, duration of mechanical ventilation and mean pulmonary-artery pressure (PAP). RESULTS: At the time of study, 25 patients presented with increased permeability (NSI > 1 x 10(-3) min-1) indicating on exudative stage of disease, and 11 patients with normal permeability. The permeability impairment correlated with the underlying disease (p > 0.05). With respect to survival, there was a negative correlation to PAP (p < 0.01). Apart from that no correlations between the individual parameters were found. Especially no correlation was found between permeability impairment and oxygenation, duration of disease or PAP. CONCLUSION: In ALI and ARDS, pulmonary capillary permeability is a diagnostic parameter which is independent from clinical variables. Permeability measurement makes a stage classification (exudative versus non exudative phase) of ALI/ARDS possible based on a measurable pathophysiological correlate.

Adult↗

PubMed2001

Analysis of volatile disease markers in blood.

BACKGROUND: The diagnostic potential of breath analysis has been limited by a lack of knowledge on origin, distribution, and metabolism of the exhaled substances. To overcome this problem, we developed a method to assess trace amounts of hydrocarbons (pentane and isoprene), ketones (acetone), halogenated compounds (isoflurane), and thioethers (dimethyl sulfide) in the blood of humans and animals. METHODS: Arterial and venous blood samples were taken from mechanically ventilated patients. Additional blood samples were taken from selected vascular compartments of 19 mechanically ventilated pigs. Volatile substances were concentrated by means of solid-phase microextraction (SPME), separated by gas chromatography, and identified by mass spectrometry. RESULTS: Detection limits were 0.02-0.10 nmol/L. Venous concentrations in pigs were 0.2-1.3 nmol/L for isoprene, 0-0.3 nmol/L for pentane, and 1.2-15.1 nmol/L for dimethyl sulfide. In pigs, substances were not equally distributed among vascular compartments. In humans, median arteriovenous concentration differences were 3.58 nmol/L for isoprene and 1.56 nmol/L for pentane. These values were comparable to pulmonary excretion rates reported in the literature. Acute respiratory distress syndrome (ARDS) patients had lower isoprene concentration differences than patients without ARDS. CONCLUSIONS: The SPME method can detect volatile substances in very low concentrations in the blood of humans and animals. Analysis of volatile substances in vascular compartments will enlarge the diagnostic potential of breath analysis.

Acetone↗

PubMed2000

Extracorporeal membrane oxygenation: a ten-year experience.

BACKGROUND: Extracorporeal membrane oxygenation (ECMO) is a supportive therapy used for severe acute respiratory distress syndrome (ARDS). We present outcome, clinical parameters, and complications in a cohort of 245 ARDS patients of whom 62 were treated with ECMO. METHODS: Data of all ARDS patients were prospectively collected between 1991 and 1999. Outcome and clinical parameters of patients treated with and without ECMO were evaluated. RESULTS: One hundred thirty-eight patients were referred from other hospitals, 107 were primarily located in our hospital. About one fourth of these patients were treated with ECMO. The survival rate was 55% in ECMO patients and 61% in non-ECMO patients. CONCLUSIONS: ECMO is a therapeutic option for patients with severe ARDS, likely to increase survival. However, a randomized controlled study proving its benefit is still awaited. Until the development of a causal or otherwise superior therapy ECMO should be used in selected patients.

Adult↗

PubMed2000

Transthyretin and transferrin in hemangioblastoma stromal cells.

Hemangioblastoma, a rare benign tumor of the CNS, consists of two main components: capillaries and stromal cells. Despite many efforts, the histogenesis of stromal cells is still unknown. We took a new approach to clarify the origin of stromal cells using immunohistochemical methods. Paraffin-embedded tissue of 24 surgically removed hemangioblastomas of the CNS was examined with antibodies against transthyretin, transferrin, vimentin, NSE, protein S-100, CK 8, KL-1, EMA, CD34, factor VIII rAg, and collagen IV. Stromal cells showed a positive reaction with anti-transthyretin in 12 of 24 hemangioblastomas, a positive reaction with anti-transferrrin, to a different extent, in 13 of 24 cases, and many stromal cells expressed basal membrane collagen IV on the cell surface in 19 of 24 cases. The expression of transthyretin and transferrin in stromal cells of hemangioblastomas is reported for the first time, thus providing an antigenic profile of hemangioblastoma stromal cells that is very similar to that of immature choroid plexus epithelium. These findings support the notion that hemangioblastoma stromal cells may originate from the embryonal plexus epithelium. We discuss our results with special regard to stromal cell histogenesis, including a review of the literature.

Brain Neoplasms↗

PubMed2000

Breathing pattern associated with respiratory comfort during automatic tube compensation and pressure support ventilation in normal subjects.

BACKGROUND: Automatic tube compensation (ATC) is a new option to support spontaneously breathing tracheally intubated patients. We have previously demonstrated an increased respiratory comfort compared to pressure support ventilation (PSV) in volunteers. Here we characterized the breathing pattern during ATC associated with respiratory comfort in comparison to PSV. Furthermore, we studied whether ATC can be substituted by a simple modification of PSV. METHODS: We exposed 10 volunteers breathing through a 7.5 mm endotracheal tube via mouthpiece to PSV with 1) immediate and 2) delayed pressure rise and to 3) ATC. Immediate changes of the respiratory pattern after mode shifts were analyzed in detail. Furthermore, the volunteers were instructed to indicate changes in comfort after transitions between these modes as increased, unchanged, or decreased. RESULTS: Decreased comfort was associated with a substantial increase of tidal volume, minute ventilation, gas flow, and pressure. No differences in respiratory comfort were perceived between immediate and delayed pressure rise during PSV. CONCLUSION: PSV resulted in excessive tidal volumes and airflow, which was perceived as discomfort. This cannot be avoided by a delayed pressure rise but can be by the more comfortable ATC. ATC seems to adapt better to the ventilatory demand than PSV.

Adult↗

PubMed2000

Continuous calculation of intratracheal pressure in the presence of pediatric endotracheal tubes.

OBJECTIVE: To measure the pressure-flow relationship of pediatric endotracheal tubes (ETTs) in trachea models, to mathematically describe this relationship, and to evaluate in trachea/lung models a method for calculation of pressure at the distal end of the ETT (Ptrach) by subtracting the flow-dependent pressure drop across the ETT from the airway pressure measured at the proximal end of the ETT. DESIGN: Trachea models and trachea/lung models. SETTING: Research laboratory in a university medical center. INTERVENTIONS: The pressure-flow relationship of pediatric ETTs (inner diameter, 2.5-6.5 mm) was determined using a physical model consisting of a tube connector, an anatomically curved ETT, and an artificial trachea. The model was ventilated with sinusoidal gas flow (12-60 cycles/min). The coefficients of an approximation equation considering ETT resistance and inertance were fitted separately to the measured pressure-flow curves for inspiration and expiration. Calculated Ptrach was compared with directly measured Ptrach in mechanically ventilated physical trachea/lung models. MEASUREMENTS AND MAIN RESULTS: The pressure-flow relationship was considerably nonlinear and showed hysteresis around the origin caused by the inertia of accelerated gas. ETT inertance ranged from 0.1 to 0.4 cm H2O/L x sec2 (inner diameter, 6-2.5 mm). The abrupt change in cross-sectional area at the tube connector caused an inspiration-to-expiration asymmetry. Calculated and measured Ptrach were within +/- 1 cm H2O. Correspondence between measured and calculated Ptrach is improved even further when the ETT inertance is taken into account. CONCLUSIONS: Ptrach can continuously be monitored in the presence of pediatric ETT by combining ETT coefficients and the flow and airway pressure continuously measured at the proximal end of the ETT.

Adolescent↗

PubMed2000

Respiratory comfort and breathing pattern during volume proportional assist ventilation and pressure support ventilation: a study on volunteers with artificially reduced compliance.

OBJECTIVE: To assess respiratory comfort and associated breathing pattern during volume assist (VA) as a component of proportional assist ventilation and during pressure support ventilation (PSV). DESIGN: Prospective, double-blind, interventional study. SETTING: Laboratory. SUBJECTS: A total of 15 healthy volunteers (11 females, 4 males) aged 21-31 yrs. INTERVENTIONS: Decreased respiratory system compliance was simulated by banding of the thorax and abdomen. Volunteers breathed via a mouthpiece with VA and PSV each applied at two levels (VA, 8 cm H2O/L and 12 cm H2O/L; PSV, 10 cm H2O and 15 cm H2O) using a positive end-expiratory pressure of 5 cm H2O throughout. The study was subdivided into two parts. In Part 1, volunteers breathed three times with each of the four settings for 2 mins in random order. In Part 2, the first breath effects of multiple, randomly applied mode, and level shifts were studied. MEASUREMENTS AND MAIN RESULTS: In Part 1, the volunteers were asked to estimate respiratory comfort in comparison with normal breathing using a visual analog scale. In Part 2, they were asked to estimate the change of respiratory comfort as increased, decreased, or unchanged immediately after a mode shift. Concomitantly, the respiratory pattern (change) was characterized with continuously measured tidal volume, respiratory rate, pressure, and gas flow. Respiratory comfort during VA was higher than during PSV. The higher support level was less important during VA but had a major negative influence on comfort during PSV. Both modes differed with respect to the associated breathing pattern. Variability of breathing was higher during VA than during PSV (Part 1). Changes in respiratory variables were associated with changes in respiratory comfort (Part 2). CONCLUSIONS: For volunteers breathing with artificially reduced respiratory system compliance, respiratory comfort is higher with VA than with PSV. This is probably caused by a better adaptation of the ventilatory support to the volunteer's need with VA.

Adult↗

PubMed1999

[In Process Citation]

Soaring health care costs are also forcing surgeons and anaesthesiologists to introduce practice patterns that allow more efficient use of expensive hospital resources. Because perioperative ward expenditures account for approximately one-third of the hospital costs incurred for surgical inpatients, with personnel costs being a major component, interventions that decrease the length of stay can result in considerable savings without affecting the quality of care. Interventious that can reduce the length of stay are outpatient preoperative evaluation and same-day admission, improvement of OR efficiency and sufficient cost-effective facilities for qualified postoperative care.

Journal Article↗

PubMed1999

Volume-dependent compliance in ARDS: proposal of a new diagnostic concept.

OBJECTIVE: Adaptation of ventilator settings to the individual's respiratory system mechanics requires information about the pressure-volume relationship and the change of compliance which is dependent on inflated volume. Unfortunately, established methods of obtaining this information are invasive and time-consuming, and, therefore, not well suited for clinical routine. We propose a new standardized diagnostic concept based on the recently developed slice method. This multiple linear regression method (MLR) determines volume-dependent respiratory system compliance (C(SLICE)) within the tidal volume (V(T)) during ongoing mechanical ventilation. The impact of a ventilator strategy, recommended by a consensus conference, on the course of compliance within V(T) was investigated in patients with the acute respiratory distress syndrome (ARDS) or acute lung injury (ALI). DESIGN: Prospective observational study. SETTING: Intensive care unit of a university hospital. PATIENTS: 14 ARDS patients, 2 patients with ALI. INTERVENTIONS: None. MEASUREMENTS AND RESULTS: After measurement of flow and airway pressure and calculation of tracheal pressure, C(SLICE) was determined. The resulting course of C(SLICE) within V(T) was estimated using a mathematical algorithm. C(SLICE) data were compared to those obtained by standard MLR. We found decreasing C(SLICE) mainly in the upper part of V(T) in all patients. In 7 patients, we found an additional increasing C(SLICE) mainly in the lower part of V(T). CONCLUSIONS: C(SLICE) was not constant in patients with ARDS/ALI whose lungs were ventilated according to consensus conference recommendations. The proposed diagnostic concept may serve as a new tool to obtain a standardized estimation of respiratory system compliance within V(T) non-invasively without interfering with ongoing mechanical ventilation.

Adolescent↗

PubMed1999

[Importance and perspectives of breath analysis].

Quantitative chemical analysis of volatile constituents in exhaled gas can provide useful insights into biochemical processes in the body. Relations between the chemical composition of human exhaled air and inflammatory processes, states of high oxidative activity, inhalation or ingestion of various noxious substances as well as diseases like ARDS, pneumonia or sleep apnea have been described. Clinical interpretation of these findings, however, remains difficult because definite marker substances for certain diseases could not yet be identified, substance concentrations in the exhaled air change under various conditions, and results vary in a wide range. Because of very low substance concentrations in the exhaled air sophisticated analytical techniques are necessary. Analyses are hampered by high water content and numerous contaminants in the samples. A clear distinction has to be made between substances originating from within the patient and those coming from outside of the body. Despite all these limitations there is no doubt that relations exist between the chemical composition of human exhaled air and clinical parameters. Upcoming new analytical techniques will allow more efficient extraction and preconcentration of substances in minute concentrations. Fast track bedside analyses will shortly become possible with the introduction of miniature gas chromatographic and mass spectrometric equipment. This will open a new area for clinical and basic research.

Air↗

PubMed1999

Unintended inhalation of nitric oxide by contamination of compressed air: physiologic effects and interference with intended nitric oxide inhalation in acute lung injury.

BACKGROUND: Compressed air from a hospital's central gas supply may contain nitric oxide as a result of air pollution. Inhaled nitric oxide may increase arterial oxygen tension and decrease pulmonary vascular resistance in patients with acute lung injury and acute respiratory distress syndrome. Therefore, the authors wanted to determine whether unintentional nitric oxide inhalation by contamination of compressed air influences arterial oxygen tension and pulmonary vascular resistance and interferes with the therapeutic use of nitric oxide. METHODS: Nitric oxide concentrations in the compressed air of a university hospital were measured continuously by chemiluminescence during two periods (4 and 2 weeks). The effects of unintended nitric oxide inhalation on arterial oxygen tension (n = 15) and on pulmonary vascular resistance (n = 9) were measured in patients with acute lung injury and acute respiratory distress syndrome by changing the source of compressed air of the ventilator from the hospital's central gas supply to a nitric oxide-free gas tank containing compressed air. In five of these patients, the effects of an additional inhalation of 5 ppm nitric oxide were evaluated. RESULTS: During working days, compressed air of the hospital's central gas supply contained clinically effective nitric oxide concentrations (> 80 parts per billion) during 40% of the time. Change to gas tank-supplied nitric oxide-free compressed air decreased the arterial oxygen tension by 10% and increased pulmonary vascular resistance by 13%. The addition of 5 ppm nitric oxide had a minimal effect on arterial oxygen tension and pulmonary vascular resistance when added to hospital-supplied compressed air but improved both when added to tank-supplied compressed air. CONCLUSIONS: Unintended inhalation of nitric oxide increases arterial oxygen tension and decreases pulmonary vascular resistance in patients with acute lung injury and acute respiratory distress syndrome. The unintended nitric oxide inhalation interferes with the therapeutic use of nitric oxide.

Administration, Inhalation↗

PubMed1999

Ventilation-perfusion mismatch after lung ischemia-reperfusion. Protective effect of nitric oxide.

Lung ischemia-reperfusion provokes pulmonary hypertension and increased microvascular permeability with subsequent edema formation and hypoxemia. We exposed buffer-perfused rabbit lungs to 120 and 180 min of warm ischemia. After reperfusion, gas exchange disturbances were analyzed by the multiple inert gas elimination technique (MIGET). Additionally, ischemic lungs were treated with different doses of inhaled nitric oxide (NO) throughout reperfusion. Reperfusion provoked a transient pulmonary artery pressure elevation, followed by progressive pulmonary edema formation. After 120 min of ischemia, severe ventilation-perfusion (V A/Q) mismatch developed within 15 min of reperfusion, with the appearance of low V A/Q areas and marked broadening of both perfusion and ventilation distribution in the midrange V A/Q regions. In parallel, shunt flow increased from less than 2% to approximately 17%. Inhalation of NO suppressed the pressor response, edema formation, as well as V A/Q mismatch and shunt flow. Concentrations of 10 and 50 ppm NO were equipotent, surpassing the efficacy of 1 or 250 ppm NO. Inhalation of NO, however, did not protect from the overwhelming gas exchange and fluid balance disturbances provoked by 180 min ischemia. In conclusion, severe abnormalities in gas exchange occurred rapidly upon reperfusion of ischemic lungs. Prophylactic NO inhalation may be considered for maintenance of gas exchange in settings of ischemia-reperfusion including lung transplantation.

Administration, Inhalation↗

PubMed1999

In vivo evaluation of a new method for chemical analysis of volatile components in the respiratory gas of mechanically ventilated patients.

Using the volatile anaesthetic isoflurane as a marker substance a gas chromatographic method for analysis of exhaled gas in mechanically ventilated patients was evaluated. Twelve patients with and 10 patients without preceding isoflurane exposure and seven blank respiratory circuits were investigated. Respiratory gas was sampled at four different sites in the respiratory tubing system. Analysis of volatile components was based upon adsorption onto activated charcoal, desorption by means of microwave energy, gas chromatographic separation and flame ionisation or mass spectrometric detection. Isoflurane concentrations in the blank respiratory circuits, in the control group, and in the inspiratory limb of patients with preceding isoflurane inhalation were at the limit of detection (<10(-12) mol/l). In the isoflurane group, isoflurane concentrations in the inspiratory and expiratory limb differed considerably. Using the method described, substances at very low concentrations could be identified as originating in the patient or as coming from the gas delivery system.

Adult↗