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Biomedical subjects

F Mertzlufft

Publications and source records attributed to F Mertzlufft.

At least 73 records · Page 4Linked to original sources
PubMed1993

Perioperative respiratory monitoring of oxygen transport.

Oximetry nowadays is understood as the in vitro measurement of O2 saturation (sO2, %) and hemoglobin (Hb) derivatives (%) using 4-7 wavelengths (CO- and Hem-oximeters). Pulse oximeters, using only 2 wavelengths, are designed for the continuous noninvasive measurement of the arterial partial O2 saturation (psO2, %) in vivo. Light-emitting diodes allow light to pass through the peripheral site of measurement with red and infrared light to enable a distinction between oxygenated and deoxygenated hemoglobin during a recorded pulse wave. In case of physiological concentrations of Hb derivatives the determination of psO2 is performed with clinically relevant accuracy of +/- 2-3%. However, at carboxyhemoglobin (COHb) concentrations above normal, under normoxia as well as under hypoxia the accuracy of measurement varies considerably among the instruments from different manufacturers. In the case of elevated methemoglobin (MetHb) concentrations, the situation is completely different. With increasing cMetHb, the psO2 is still the value required, but success depends on the concentration of MetHb: under normoxia psO2 is increasingly underestimated, whereas under hypoxia increasing overestimation must be anticipated. Provided there is a constant Hb concentration, knowledge of the initial sO2, and absence of the derivatives COHb and MetHb as well as of severe perfusion disorders, pulse oximetry is suitable for perioperative respiratory monitoring of oxygen transport.

Carboxyhemoglobin↗
PubMed1993

[The behavior of arterial and mixed venous oxygen and carbon dioxide partial pressure and the pH value during and following intubation apnoea. Studies on the occurrence of the Christiansen-Douglas-Haldane effect].

The Christiansen-Douglas-Haldane effect describes the reduced CO2 binding capacity of oxygenated compared to deoxygenated haemoglobin. Under the condition of a "closed system", for example hyperoxic apnoea after adequate preoxygenation (continuous O2 uptake with lack of CO2 delivery), specific effects on the arterial and mixed venous blood gas status, due to the Haldane effect, are seen: within 30 s after onset of apnoea, "paradoxical pCO2" (paCO2 exceeds pvCO2) and "pH reversal" (pHa falls under pHv) can be observed. It was the aim of this study to demonstrate how fast arterial and mixed venous pCO2 and pH normalize when a change from apnoea ("closed system") to controlled ventilation ("open system") takes place. METHODS. 12 patients (ASA II-IV, NYHA II-III) scheduled for coronary artery bypass grafting were studied. Premedication consisted of flunitrazepam 2.0 mg p.o. given the evening before operation and another 2.0 mg p.o. given 90-120 min before induction of anaesthesia. Routine preparation for induction consisted of venous and arterial cannulas, pulmonary artery catheter and continuous pulse oximetry. Following standardized preoxygenation, induction of anaesthesia was performed with fentanyl, pancuronium and etomidate. After cessation of spontaneous respiration, controlled ventilation was continued with 100% O2 until intubation. Intubation and insertion of stomach tube and oesophageal temperature probe were undertaken after exactly 2 min. After reconnection to the semi-closed circle breathing system, controlled ventilation was continued with 100% O2. Eighteen arterial (a) and 18 mixed-venous (v) blood samples were drawn simultaneously in a sequential manner immediately before and during the last 20 s of apnoea, as well as within 4 min after onset of controlled ventilation (Table 1). The pO2 (mmHg), pCO2 (mmHg) and pH were determined using a Stat Profile 5 blood gas analyser. RESULTS. During apnoea and within the first 35 s of controlled ventilation the paO2 showed a total decrease of 131.5 mmHg that was followed by an almost linear increase of 29.7 mmHg/min (Fig. 1a). In the course of apnoea and controlled ventilation the pvO2 remained relatively stable, with values ranging from 42 to 43 mmHg (Fig. 1b). During apnoea the paCO2 showed an increase of 12.5 mmHg that was followed by a biphasic decrease (first 13.8 mmHg/min and then 0.75 mmHg/min) beginning 15 s after the onset of controlled ventilation (Fig. 2a). With an increase of 4.2 mmHg, the pvCO2 showed about a third of the increase of the paCO2 during apnoea, reaching a maximum 45 s after the onset of controlled ventilation and then being followed by a linear decrease of 0.86 mmHg/min (Fig.2b). Comparing the course of paCO2 and pvCO2 during apnoea as well as during the period of controlled ventilation, pHa and pHv changed in a reciprocal manner (Fig. 3a/b). The so-called normalization of pCO2 (paCO2 falls under pvCO2) and pH (pHa exceeds pHv) began 18.2 s and 23.2 s respectively after the onset of controlled ventilation (Fig. 4a, b). CONCLUSION. Considering the expected decrease of paO2 during hyperoxic apnoea, insufficient pulmonary N2 elimination prior to the onset of apnoea, as well as direct N2 delivery into the alveoli, due to the so-called a ventilatory mass flow, will limit unrestricted pulmonary O2 uptake. The continuing decrease of the paCO2 after the onset of controlled ventilation can be regarded as indirect proof of a ventilatory mass flow. The course of pCO2 and pH after the onset of controlled ventilation shows that normalization in arterial and mixed-venous blood gas status takes place in about 18.2 s after the cessation of apnoea.

Aged↗
PubMed1992

[Checking the precision of capnometers].

Capnometry, i.e. measurement of CO2 concentration (cCO2, vol%) and calculation of the respective CO2 partial pressure (pCO2, mmHg), is simple to apply, but the user must understand its principles of operation in order to appreciate its power and its limitations. However, sidestream capnometers use to dry the humidified respired gas (37 degrees C, pH2O 47 mmHg) for methodological reasons, thus increasing pCO2 by ca. 6% which, in turn, requires correction. With infrared spectroscopy, overestimation of pCO2 in presence of N2O and underreporting of pCO2 in presence of O2 also require to be corrected. These require either knowledge of the respective gas concentrations (mainstream analyzers) or adequate (i.e. correct) measurement (some sidestream capnometers). Changes in barometric pressure (pB) must be also either known or be measured automatically. Evaluation of the precision of capnometers must therefore focus on, (1) the possible pH2O correction, (2) the possible effects exercised by O2 and N2O, and (3) the possible dependence on barometric pressure. Two mainstream (Capnolog D/Dräger; Sirecust 404-1/Siemens) and eight sidestream capnometers (AGM 1304/Brüel & Kjaer; SARAcap A. G. and SARA-trans/Biomedical Systems/Hellige; Capnomac and Normocap 200/Datex/Hoyer; CO2 Monitor/Dräger; Nellcor N-1000/Nellcor/Dräger; Multinex/Datascope) were investigated. Dry and humidified gases (37 degrees C) of defined composition in respect of CO2, O2, N2, N2O, and H2O, were used for evaluation. The results prove reproducibility of ca. =/- 1 mmHg for the 10 capnometers within the 30-50 mmHg pCO2 range.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesiology↗
PubMed1991

[The meaningfulness of central venous blood samples. Central venous versus mixed venous O2 status].

Both mixed-venous and "central-venous" oxygen status (O2 partial pressure [pO2], O2 saturation [sO2], O2 concentration [cO2], hemoglobin concentration [cHb]) are often considered to adequately represent total-body oxygen supply. Since modern technology has made continuously in vivo measurement possible, mixed-venous O2 saturation (svO2) and partial O2 saturation (psO2) have become extensively used for that purpose. Both venous sites of measurement are used as diagnostic adjuncts regarding hemodynamic status. However, both are associated with certain problems. There is a lack of any clear definition of a "central-venous" site of the catheter tip (right atrium, superior vena cava, inferior vena cava). Instead, the location of the catheter tip depends upon the approach to the central venous system. One must also be aware of significant migrational tendencies of the catheter tip. Thus, "central-venous" samples can only represent the situation in a single portion of the circulation, whereas the respective organ areas may vary considerably with the same catheter from one time point to another. Furthermore, the state of the coronary circulation never can be evaluated. The frequently postulated correlation of mixed-venous and "central-venous" values decreases with increasing deterioration of the cardiovascular system, especially in patients with high cardiovascular risks. The main overall parameters of mixed-venous oxygen status are oxygen content (cvO2), cardiac output (C.O.), and oxygen consumption (QO2) of the tissues. The relation between arterial and mixed-venous O2 status is given by Fick's principle: caO2-cvO2 = QO2/C.O. From this, it becomes obvious that a relation between cvO2 and C.O. may only be presumed if QO2 and caO2 remain constant. Evaluation of O2 availability (AO2) using cvO2 or the determining components of cvO2 seems reasonable only if the modulating influences of C.O. and QO2 are taken into consideration. Therefore, any empirically deduced relation between svO2 and C.O. (regardless of the origin, i.e., linear or nonlinear) must be viewed as being accidental. This implies that svO2 and cvO2 per se are only partly helpful in evaluating the hemodynamic situation. The best parameters for interpreting the cardiovascular situation seem to be arteriovenous O2 difference (avDO2) and C.O. In particular, the avDO2 can be accepted as an integrating parameter for AO2 and QO2, and may therefore serve as a diagnostic indication of cardiovascular imbalance.

Humans↗
PubMed1990

Oxygen parameters of blood: definitions and symbols.

Definitions and symbols for relevant parameters of the oxygen status of arterial blood are recommended. The recommendations are as simple as possible, easy to understand, and devoid of misinterpretations and double meanings. The authors propose no new definitions for limited new methods, no combination of symbols and methods, and no association between definition, symbol and commercial name.

Abbreviations as Topic↗