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

BACKGROUND: 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. METHODS: 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). RESULTS: 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. CONCLUSION: 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.

Evaluation of five oxygen delivery devices in spontaneously breathing subjects by oxygraphy.

Oxygen supply systems may be divided into constant and variable performance systems. As the variable performance systems are widely used, it is relevant to investigate the variation in performance between devices and the influence of oxygen supply on the inspired oxygen fraction. Data were collected from 10 healthy volunteers during the use of one constant performance system and four variable performance systems at different gas flows and inspired oxygen fractions. A thin sampling catheter was placed in the nasopharynx to allow the measurement of the end-tidal oxygen fraction. When oxygen was supplied to variable performance systems, end-tidal oxygen fraction values measured in this way varied less and were more easily quantifiable than inspired oxygen fraction. End-tidal oxygen fraction was used to calculate inspired oxygen fraction. With the variable performance systems, inspired oxygen fraction varied considerably between subjects whereas a constant and equal rise was found for each subject with the fixed performance system. A large nasal catheter was capable of delivering the highest inspired oxygen fraction, whereas the Venturi mask delivered the most precise inspired oxygen fraction. We found oxygraphy useful in the interpretation of measurements made in patients receiving unknown inspired fractions of oxygen.

The Oxygen Status Algorithm on-line with the pH-blood gas analyzer.

BACKGROUND: The Oxygen Status Algorithm is a computer program for interpretation of pH-blood gas measurements. Recently the facility for on-line transfer of measured data from the pH-blood gas analyzer (ABL 520) to the computer with instant calculation, graphical display, and print-out of the oxygen status and the acid-base status of the blood has been implemented. OBJECTIVE: To describe experiences with routine application of the Oxygen Status Algorithm in an intensive care unit and to describe recent improvements of the program. DATA SOURCES: Routine pH-blood gas analyses during a two year period with an average of 40 analyses per day. RESULTS: Several unexpected results were disclosed, especially with respect to abnormal haemoglobin-oxygen affinity, causing suspicion of low 2,3-diphosphoglycerate concentration and hypophosphatemia. The criteria for routine administration of oxygen could be revised on the basis of the oxygen extraction tension. The program was expanded to allow the printing of a cumulated patient report, and modified to allow calculation of the oxygen consumption rate on the basis of simultaneous measurements on the arterial and the mixed venous blood. The program and the computer hardware functioned well in continuous operation during the whole study. It proved to be difficult, however, to ensure that all measurements were supplemented by information on the patient temperature and the fraction of inspired oxygen. CONCLUSION: The Oxygen Status Algorithm provides a more detailed description of the oxygen status and the acid-base status of the blood than currently employed. The interaction between the arterial oxygen tension, the haemoglobin oxygen capacity and the haemoglobin oxygen affinity is displayed graphically and the degree of compensation among these three properties is expressed in terms of a single quantity: the oxygen extraction tension. The program also provides an interactive interpretation, allowing a rapid prediction of the expected effect of therapeutic intervention. Nevertheless, implementation of the program in the daily routine requires an intensive educational effort among physicians as well as nurses and laboratory technicians.

Erythrocyte 2,3-diphosphoglycerate depletion associated with hypophosphatemia detected by routine arterial blood gas analysis.

OBJECTIVE: To describe a clinical case where an extremely low erythrocyte 2,3-diphosphoglycerate concentration (2,3-DPG) was discovered by routine blood gas analysis supplemented by computer calculation of derived quantities. The finding of a low 2,3-DPG revealed a severe hypophosphatemia. DESIGN: Open uncontrolled study of a patient case. SETTING: Intensive care observation during 41 days. PATIENT: A 44 year old woman with an abdominal abscess. INTERVENTIONS: Surgical drainage, antibiotics and parenteral nutrition. MEASUREMENTS AND RESULTS: daily routine blood gas analyses with computer calculation of the hemoglobin oxygen affinity and estimation of the 2,3-DPG. An abrupt decline of 2,3-DPG was observed late in the course coincident with a pronounced hypophosphatemia. The fall in 2,3-DPG was verified by enzymatic analysis. CONCLUSION: 2,3-DPG may be estimated by computer calculation of routine blood gas data. A low 2,3-DPG which may be associated with hypophosphatemia causes an unfavorable increase in hemoglobin oxygen affinity which reduces the oxygen release to the tissues.

The effect of nasal oxygen flow and catheter position on the accuracy of end-tidal carbon dioxide measurements by a pharyngeal catheter in unintubated, spontaneously breathing subjects.

Reliable recordings of carbon dioxide concentrations during spontaneous respiration can be obtained from a catheter positioned in the hypopharynx. The present study investigated the possible influence on end-tidal carbon dioxide measurement of nasal oxygen administration, position of the sampling catheter and mouth breathing. The study demonstrated that not only can reliable capnographic tracings be obtained from a thin catheter placed in the unintubated airway, but the subject may also receive up to 6 l.min-1 of oxygen via the nasal route without interference with the accuracy of the measurements. Furthermore, the exact position of the sampling catheter tip in the airway is not critical, which means that it may be placed where it causes the patient least discomfort. Finally, mouth breathing caused a mean decrease in end-tidal carbon dioxide of 0.25 kPa compared to nose breathing.

Oxygen status of arterial and mixed venous blood.

OBJECTIVES: To describe system requirements for determination of the oxygen status of the blood using the oxygen status algorithm, a computer program. To define the oxygen extractivity, a term we propose, of the arterial blood and the oxygen extraction tension. To describe the different causes of tissue hypoxia, and the clinical interpretation of mixed venous oxygen tension and oxygen consumption rate. DATA SOURCES: Previous physiological and clinical studies related to oxygen status of the blood. DATA SYNTHESIS: The oxygen status algorithm calculates the oxygen extraction tension and generates the oxygen graph as an aid in interpreting oxygen status of the patient. A cybernetic scheme explains the causes of tissue hypoxia and forms the basis for the interpretation of changes in the mixed venous oxygen tension. A diagram with the mixed venous oxygen tension on the abscissa and the oxygen consumption rate on the ordinate illustrates the oxygen flux dependent oxygen consumption rate. A graph shows the relationship between mixed venous oxygen tension and oxygen delivery. CONCLUSIONS: The oxygen status of arterial blood comprises three groups of quantities related to arterial oxygen tension, hemoglobin oxygen capacity, and hemoglobin oxygen affinity. Disturbances in one of these groups may be compensated by opposite changes in one or both of the other. The oxygen extraction tension indicates the degree of compensation, and mixed venous oxygen tension is the key parameter in evaluating the presence of a state of oxygen flux-dependent oxidative metabolism.

Reliability of CO2 measurements from the airway by a pharyngeal catheter in unintubated, spontaneously breathing subjects.

Although several short communications have appeared describing attempts to record the concentrations of carbon dioxide (cCO2) from the unintubated airway by a catheter placed in the nose, so far only few reports have documented the reliability of the method. To evaluate the reliability of CO2 measurements by a catheter in the open, unintubated airway during spontaneous respiration, a 12 CH PVC catheter was forwarded through the nostril to the hypopharynx and connected to a capnograph in nine healthy volunteers. Another capnograph was connected to a tightly fitting face mask and simultaneous CO2 recordings were attained from the two parts of the airway during normoventilation, hyperventilation and rebreathing. A corresponding blood sample was drawn from the radial artery for blood gas analysis. The configurations of the capnograms recorded from the pharyngeal catheter were similar to those recorded from the face mask. The results were analysed by a multifactor analysis of variance. The carbon dioxide tension (pCO2) was significantly influenced by degree of ventilation (P < 0.0001), subject (P < 0.0001), measurement site (P = 0.030) and interaction subject-ventilation (P = 0.015). In spite of the significant influence of the measurement site, the difference between end tidal carbon dioxide tension (pCO2(ET)) and carbon dioxide tension in arterial blood (pCO2(a)) was small. The mean differences between paired measurements (pCO2(ET)-pCO2(a)) were -0.10 kPa +/- 0.41 kPa (mean +/- SD) for the catheter and -0.20 kPa +/- 0.43 kPa for the face mask. The study demonstrates that reliable recordings of CO2 concentrations during spontaneous respiration can be obtained by a thin catheter positioned in the hypopharynx.

Venous blood gas analysis for evaluation of blood circulation of the hand during continuous axillary block.

Computer analysis of blood gas measurements was used to evaluate the effect of a continuous axillary block on the circulation of the hand of a patient suffering from regional circulatory insufficiency due to ligation of the brachial artery. Venous blood samples drawn from the cephalic vein were analysed at 0, 1, 2.5 and 18 hours after the blockade. Improved circulation of the hand was indicated by decreased arterio-venous oxygen difference and increased venous oxygen partial pressure following the blockade. The advantage in using the extended blood gas analysis is the possibility of estimating the main factors influencing tissue oxygenation: oxygen capacity, oxygen partial pressure and the haemoglobin oxygen affinity.

Lactate, pH, and blood gas analysis in critically ill patients.

To obtain information about the relationship between different types of circulatory insufficiency, a series of oxygen parameters and plasma lactate, we have performed a pilot study comprising five patients with circulatory insufficiency. Plasma lactate was measured on a Stat Profile 7 (NOVA Biomedical, USA) and pH/blood gases on an ABL 520 (Radiometer Medical A/S, Denmark). Plasma lactate seems to be inversely related to base excess (BE), whereas no relationship to venous oxygen tension pO2(v) of the vein draining the inadequately perfused region seemed to exist. In one patient we made simultaneous measurements from v. cava inferior., v. cava superior., a. pulmonalis and a. radialis. Simultaneously sampled plasma lactate from different sites differed up to 0.6 mmol/L with the highest value obtained from v. cava inferior. This pilot study indicates that the increase of plasma lactate may vary with the type of circulatory disturbance and the sampling site.

The influence of patent blue V on pulse oximetry and haemoximetry.

Patent Blue V (PBV) is a blue dye solution which is used to visualize lymphatic vessels for surgical procedures. There has been some conflicting reports about the influence of this dye solution on pulse oximetry and haemoximetry, why we decided to: 1) produce a spectrum of PBV in plasma, 2) measure absorbances of full blood before and after addition of PBV and 3) to record the effect on the pulse oximeter and haemoximeter of an intradermal injection of PBV to a patient. Computer analysis of the blood gas measurements were carried out by the Oxygen Status Algorithm (OSA). The spectrum of PBV demonstrated a peak absorption at 640 nm and correspondingly the absorbances of the haemoximeter increased most significantly at 622 and 636 nm. These changes invalidated the determination of haemoglobin pigments, and the results should not be used. Computer analysis interpreted the measurements as a shift of the haemoglobin oxygen binding curve.

Oxygraphy in spontaneously breathing subjects.

BACKGROUND: Continuous monitoring of O2 and CO2 in the airways of spontaneously breathing patients can be carried out by sampling air to a gas monitor through a catheter placed in the upper airway. The graphical display of O2 (oxygraphy) is a rather new facility. OBJECTIVE: To describe the photo-acoustic and magneto-acoustic technique for CO2 and O2 monitoring in the open unintubated airway, to evaluate the efficacy of oxygen therapy by oxygraphy and to determine alveolar gas tensions and alveolar-arterial partial pressure gradients. DATA SOURCES: O2 and CO2 fractions in the airways were monitored in 9 healthy subjects. Blood samples were drawn from the radial artery. METHODS: The Multigas Monitor 1,304 (Brüel and Kjaer, Naerum, Denmark) was used; end-expiratory measurements were considered as representative for the alveolar gas composition. Arterial blood was analysed by ABL520 (Radiometer Medical A/S, Copenhagen, Denmark). RESULTS: Reliable tracings of gas fractions (FCO2 and FO2) were obtained during the respiratory cycle in all subjects. When oxygen was supplied, FO2 of the airway varied considerably during the inspiratory phase whereas it remained almost constantly during the expiratory phase. The end-expiratory FO2 increased from 0.15 breathing atmospheric air to 0.41 breathing oxygen 15 L/min through a Hudson mask. Alveolar-arterial partial pressure differences were: pO2(A-a): 1.07 +/- 0.85 kPa and pCO2(A-a): -0.04 +/- 0.33 kPa during normoventilation in atmospheric air. CONCLUSION: Continuous monitoring of CO2 and O2 in the airway gives information about the pulmonary gas exchange and the efficacy of oxygen supply. Combined with arterial blood gas analysis the method allows determination of alveolar-arterial CO2 or O2 gradients.

Oxygen status determined by the photo-electric method--a circular finger-probe constructed for detection of blood oxygen content, blood flow and vascular density.

Three factors are the major determinants of tissue oxygenation: blood oxygen content, blood flow and vascular density. Blood oxygen content can be measured in vitro by haemoximetry or in vivo by oximetry. The blood flow and the vascular density may be estimated by a further development of pulse oximetry, based on the photo-electric method separating the signal into an AC and DC-part. A circular finger-probe was constructed to analyse the propagation of light through blood perfused tissue by the photo-electric method. The AC and DC-signals were compared at different positions around the finger. The detectors were placed at -45 degrees, 45 degrees, 90 degrees, 180 degrees and 215 degrees in relation to the light source. The preliminary results have shown that it is possible to record AC and DC-signals from the different angles. The size and configuration of the AC-signals are very similar but the levels of the DC-signals decrease with the distance between source and detector. It is our suggestion that blood flow can be estimated from the area of the AC-signal and the vascular density from the relationship between the DC-levels at different positions.

[Cannulation of the radial artery. Risks, effective examination methods and monitoring of the circulation in the hand during the procedure]. / Kanylering af a. radialis. Risici, relevante undersøgelsesmetoder og monitorering af håndens kredsløb i forbindelse med proceduren.

Cannulization of the radial artery with the object of continuous measurement of the blood pressure or repeated analyses of the arterial blood gases is an easy and relatively safe procedure. Thrombosis is observed in 25-40% of the cases. The frequency depends upon the condition of the patient, the cannula and technique of cannulization and duration of this. Permanent ischaemic damage resulting from thrombosis is, however, rare. Other complications of clinical significance are infections and vascular lesions which are, similarly, rare. Allen's test for assessing the collateral circulation of the hand has a high negative predictive value while the positive predictive value is so low that a positive test result does not exclude cannulization. In these cases, better assessment of the perfusion of the hand may be obtained by combining the test with pletysmography. After cannulization, it should be possible to monitor perfusion distal to the site of cannulization employing more recent pulse oximeters with the aid of the pletysmographic curve.

Spirometry in healthy adult never-smokers.

Spirometry was performed in 277 female and 240 male subjects constituting a random, unbiased population sample representative for the population of Denmark. Equipment, calibration and measurement procedures conformed strictly with established standards. Statistical analysis showed that certain power transformations (cubic, quadratic or square root) of the data produced models that fitted the data statistically significantly better than linear models, where no transformations are applied, or logarithmic models where a logarithmic transformation is applied to the response variable. Differences between predictions obtained with the three models were, however, small and without practical significance. Neither rigid adherence to established, well documented standards nor elaborate statistical analysis reduced the inter-individual variance significantly in comparison to previous investigations. The results emphasize that it is important that reference values are appropriate for the methods and populations in question.

Ketanserin in the treatment of traumatic vasospastic disease.

The specific serotonin receptor blocker ketanserin was given orally to 12 patients with traumatic vasospastic disease in a double blind crossover study. The effect of treatment was assessed by measuring finger systolic pressure and rewarming time after cold provocation and by medical interview and diaries. Median (range) percentage change in finger systolic pressure after cooling was 50 (0-100)% after treatment with ketanserin compared with 0 (0-90)% after placebo. Median (range) rewarming time after cooling decreased from 320 (236-972)s with placebo to 160 (88-404)s after treatment with ketanserin. These changes were not significant. Ninety five percent confidence intervals for difference between the treatments, however, showed that finger systolic pressure may be 80% better and rewarming time 256 seconds faster after treatment with ketanserin than after placebo. The number of attacks did not differ significantly between the two treatments. Two patients had a feeling of warmth in their hands during treatment with ketanserin. The results suggest that orally administered ketanserin may improve digital circulation in patients with traumatic vasospastic disease, but larger numbers of patients are required to assess the true effect of treatment with ketanserin in this disease.

Postoperative pain relief and respiratory performance after thoracotomy: a controlled trial comparing the effect of epidural morphine and subcutaneous nicomorphine.

Twenty patients scheduled for lateral thoracotomy were randomly allocated to receive either epidural morphine at regular intervals or subcutaneous nicomorphine on demand for postoperative pain relief. The daily dose of opiate administered was greater in the group receiving subcutaneous nicomorphine than in the epidural group although four patients in the latter needed additional subcutaneous injections of opiate. During the first three days of the postoperative course, a profound decrease of the forced vital capacity (FVC), the forced expiratory volume in one second (FEV1), peak expiratory flow rate (PEF) and the arterial oxygen tension (PaO2) was found in both groups, whereas the visual analogue pain score showed a marked increase, and the arterial pH and carbon dioxide tension (PaCO2) remained unchanged. No significant difference could be demonstrated between the group;s. The conclusion is that epidural morphine may produce sufficient pain relief after thoracotomy, but compared with conventional pain treatment the benefits are limited.

Postoperative pain treatment after upper abdominal surgery with epidural morphine at thoracic or lumbar level.

Thirty patients undergoing upper laparotomy were entered into a randomized trial, comparing the effect of midthoracic (T) and lumbar (L) epidural morphine on postoperative pain and pulmonary function. Five mg morphine was injected through the catheter at the end of the operation, and subsequently three times a day. Six, 30 and 54 h postoperatively, the following tests were performed: linear analogue pain score, arterial gas tensions (PaO2, PaCO2 and pH), forced ventilatory capacity (FVC), forced expiratory volume in 1s (FEV1) and peak expiratory flow rate (PEF). The changes in pain score (increase of the median): T: 21, 6, 5, and L: 24, 15, 8 per cent of full scale), PaO2 (decrease of the tension: T: 1.7, 2.1, 2.4, and L: 2.0, 2.8, 2.0 kPa), PaCO2, pH, FVC (decrease of the volume: T: 1.3, 1.1, 0.9, and L: 1.3, 1.3, 1.21), FEV1 and PEF from the preoperative tests were not significantly different. It is concluded that the clinical effect of epidural morphine for postoperative pain treatment is the same or little different whether the administration takes place at the thoracic or lumbar level.