Der Anaesthesist
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Understanding the mismatching of ventilation and perfusion (VA/Q) is of special interest in the intensive care setting because - given a stable cardiac output and a given inspiratory oxygen fraction - it allows one to explain certain essential respiratory problems in critically ill patients, namely hypoxemia and hypercarbia. Several different methods are available today for the evaluation VA/Q mismatching. Analysis of the PCO2 and PO2 in arterial and mixed venous blood and mixed expired gas yields information about the quality and the degree of the mismatching present. ⋯ The multiple inert gas elimination technique permits virtually continuous ventilation-perfusion distributions to be described over the whole range of VA/Q ratios and has contributed to explaining the pathophysiological mechanisms in various pulmonary diseases. This method, however, is technically very complex and hence will remain a sophisticated investigational tool. Scintigraphic approaches allow the description of regional topographic VA/Q distributions, but their application is still difficult in the intensive care setting.
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The main task of the cardiorespiratory system is to deliver enough oxygen (O2) to meet the metabolic requirements of the body. Of all metabolic substrates, O2 has the highest percentage of extraction at 25%, and O2-reserves are therefore exhausted within a few minutes. Arterial O2-content and cardiac output (CO) are the determinants of O2-delivery (DO2). ⋯ Routinely measured hemodynamic parameters such as heart rate, systemic arterial pressure, etc. only poorly reflect O2-transport to the tissues. O2-consumption (VO2), the best mirror of the actual metabolic activities of the tissues, can be measured either noninvasively by the difference between inspiratory and expiratory O2-concentrations in connection with minute ventilation or invasively using arterial-venous O2-content difference and CO, which requires pulmonary artery catheterization. VO2 determination by respiratory gas analysis is very difficult at a high or changing FiO2.(ABSTRACT TRUNCATED AT 250 WORDS)
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Randomized Controlled Trial Comparative Study Clinical Trial Controlled Clinical Trial
[Better acceptance of measures for induction of anesthesia after rectal premedication with midazolam in children. Comparison of results of an open and placebo-controlled study].
The rectal administration of midazolam for premedication of children before induction of anesthesia by mask was investigated in two clinical studies. In 62 children aged between 2 and 10 years, midazolam was given by open design at various dosages (0.15 mg.kg-1, 0.25 mg.kg-1, 0.30 mg.kg-1, 0.35 mg.kg-1, 0.40 mg.kg-1) to evaluate the most effective dose for optimal acceptance of the mask and gas mixture. An additional 40 children between 3 and 9 years received 0.2 mg midazolam.kg-1 body weight or placebo in a double-blind design to estimate the lower limit of efficacy of midazolam. ⋯ The rectal administration of 0.35-0.4 mg midazolam.kg-1 is most suitable for the preoperative medication of children between 2 and 10 years. Due to the degree of sedation and the relief of anxiety toward the surroundings and the operation, the induction of anesthesia is optimally accepted by the child. In contrast, the effect of a dose around 0.2 mg midazolam.kg-1 body weight is not much different from that of placebo and is not sufficient for effective premedication.
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Randomized Controlled Trial Comparative Study Clinical Trial
[Hemodynamic action profile of propofol in comparison with midazolam. A study in coronary surgical patients].
Propofol, a rapid and short-acting i.v. anesthetic, was associated with the risk of anaphylactic reactions in its original cremophor-EL formulation. It has been reformulated in a soybean emulsion with satisfactory anesthetic properties. A former study of hemodynamic changes after i.v. induction with propofol, thiopental, methohexital, etomidate, and midazolam in patients with coronary artery disease demonstrated that in comparison to other induction agents propofol depressed systolic and diastolic arterial pressures more severely, compromising coronary perfusion. ⋯ Propofol decreased systolic and diastolic pressures (-27%, -22%) more than midazolam (-10%, -9%). Cardiac index and stroke volume index were diminished following both drugs (propofol: -14%, -9%; midazolam: -15%, -11%); total systemic resistance was reduced significantly by propofol (-22%). Dp/dtmax was compromised more markedly by propofol (-24%) than by midazolam (-18%), but there was no significant difference.(ABSTRACT TRUNCATED AT 250 WORDS)
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Randomized Controlled Trial Clinical Trial
[Hemodynamics under propofol-nitrous oxide anesthesia: effects of premedication with lormetazepam and of additional fentanyl].
Propofol, in both its new oil-in-water emulsion and the former cremophor-EL solution, is known to produce significant decreases in arterial blood pressure. The aim of this study was to obtain a precise hemodynamic profile of anesthesia induction with propofol under conditions of daily routine (additional 70% nitrous oxide) and to evaluate the influence of (1) premedication with lormetazepam and (2) additional i.v. injection of fentanyl. Forty patients (ASA classes I and II) were randomly assigned to one of four groups (A, B, C, and D). ⋯ The following parameters were determined immediately prior to induction of anesthesia and 1, 3, 5, 8, and 10 min after the start of the propofol injection: heart rate (HR), mean arterial blood pressure (MAP), mean pulmonary artery pressure (PAP), central venous pressure (CVP), pulmonary occlusion pressure (POP), cardiac output (CO), stroke volume (SV), and systemic vascular resistance (SVR). In all four groups a slight decrease in HR and SVR occurred while a marked decrease in arterial blood pressure (SAP, MAP, DAP) and cardiac output was seen. PAP and preload pressures showed no significant changes.(ABSTRACT TRUNCATED AT 250 WORDS)