The determinants for oxygen delivery: is increased fraction of inspired oxygen always crucial? (original) (raw)
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Pathophysiological alterations in oxygen delivery to the tissues
Transfusion and Apheresis Science, 2011
This paper reviews co-factors that impact on oxygen delivery and uptake, in the attempt to unravel the mechanisms underlying the correlation between the decrease in oxygen delivery and oxygen consumption. In sequence, the following factors are analyzed that, besides a decrease in haemoglobin concentration, impair tissue metabolism: (1) lung diffusion and perfusion limitation in oxygen transport, (2) decrease in cardiac output, (3) impairment of peripheral microvascular perfusion and (4) reduced ability of cells to extract oxygen. The contribution of the various factors is modeled aiming to present a decisional flow chart for the functional evaluation of the efficiency of the oxygen transport system.
Paradigms of Oxygen Therapy in Critically Ill Patients
Journal of Intensive and Critical Care, 2017
Oxygen administration to patients has potential advantages and some evident drawbacks. Several clinical settings, mainly critical scenarios, demand high oxygen inspired fractions (FiO 2) in order to assure safe reserve margins for an eventual arterial desaturation (for example before tracheal intubation in operating room). On the other end some evidence shows that maintain high FiO 2 during surgical procedures and/or controlled ventilation in the intensive care units might be more harmful than beneficial. The aim of this revision was to show what type of decision clinicians may make, regarding the amount of oxygen that should be given to patients, with a special focus on the pros and cons of its liberal utilization.
Partial pressure of oxygen in the human body: a general review
The human body is a highly aerobic organism, in which it is necessary to match oxygen supply at tissue levels to the metabolic demands. Along metazoan evolution, an exquisite control developed because although oxygen is required as the final acceptor of electron respiratory chain, an excessive level could be potentially harmful. Understanding the role of the main factors affecting oxygen availability, such as the gradient of pressure of oxygen during normal conditions, and during hypoxia is an important point. Several factors such as anaesthesia, hypoxia, and stress affect the regulation of the atmospheric, alveolar, arterial, capillary and tissue partial pressure of oxygen (PO 2 ). Our objective is to offer to the reader a summarized and practical appraisal of the mechanisms related to the oxygen's supply within the human body, including a facilitated description of the gradient of pressure from the atmosphere to the cells. This review also included the most relevant measuring methods of PO 2 as well as a practical overview of its reference values in several tissues.
Oxygen Therapy in Critical Care: A Double Edged Sword
The oxygen therapy is an universal treatment in the hospital setting, especially in the critical care units. The purpose of this therapy is to avoid hypoxemia and to ensure an adequate supply of oxygen to the tissues. But often we overlook the potential adverse effects of oxygen therapy. Oxygen produces lung damage and induces apoptosis and cell death creating an imbalance between the production of reactive species of oxygen and the antioxidant mechanisms. The oxygen therapy inhibits systemic adaptive changes induced by hypoxia, disrupting compensatory mechanisms and causing deleterious effects. We are faced with a challenge in order to treat patients with respiratory failure, counterbalancing hypoxia with hyperoxia-induced damage and introducing therapy lines that are innovative but not risk-free as permissive hypoxemia. Currently many questions remain unresolved and there are not enough clinical studies that validate the therapeutic optimal oxygenation ranges. These ranges may differ depending on each patient and the underlying disease.
Factors limiting maximal O2 consumption: effects of acute changes in ventilation
Respiration Physiology, 1995
The response of the 02 transport system to acute changes in alveolar ventilation ('qA) was analysed. The fractional limitations to maximal 02 consumption (Vo~ ..... ) imposed by the lungs (ventilation, Fv, and lung-blood transfer, FL), the cardiovascular system (FQ), and peripheral 02 diffusion (Fp) were calculated according to a multifactorial model. A reference set of data, describing the status of 02 transport at maximal exercise in normoxia was used. The effects of'qA on 9% ..... were assessed on the assumption of a constant reference 02 flow in mixed venous blood (0Vo,). The changes in reference data "after given independent changes in VA were calculated by an iterative procedure, until the Vo~in~,~. value compatible with the constant reference Q9% was found, at Plo, values of 150 (normoxia), 130, 110 and 90 Torr. The V o ....... changes in normoxia were less than expected assuming a linear 02 transport system, because of the flatness of the 02 dissociation curve around normoxic P%. This affected the cardiovascular resistance to 02 flow, and its changes counterbalanced the effects on Vo_, ..... of induced changes in VA. This phenomenon was reversed in hypoxia, as the steep part of the O2 dissociation curve was approached. The fractional limitations to 9 o ....... in normoxia resulted as follows: Fv and FL provided between 5 and 12%, FQ between 59 and 78?'0, and Fp between 13 and 19% of the overall %), ...... limitation. In hypoxia, Fv and FL increased and FQ decreased. At PIo, = 90 Torr, when VA was halved. Fv, FL, FQ and Fp amounted to 0.35, 0.31, 0.20 and 0.14, respectively.
Factors in oxygen delivery to tissue
Microvascular Research, 1974
An animal model for evaluating oxygen delivery to tissue is based upon the determination of the intracellular oxygen tension by surface fluorometry of NADH under conditions where the inspired oxygen is reduced through the critical value for the particular organ. This procedure allows the evaluation of the overall efficiency of the pulmonocardiac tissue in delivering oxygen to tissue, and can be useful in new, quantitative measurements of the effect of various factors occurring between the inspired air and the final tissue oxygen tension.
Microcirculation (New York, N.Y. : 1994), 2018
To determine the human dose-response relationship between a stepwise increase in arterial oxygen tension and its associated changes in DO and sublingual microcirculatory perfusion. Fifteen healthy volunteers breathed increasing oxygen fractions for 10 minutes to reach arterial oxygen tensions of baseline (breathing air), 20, 40, 60 kPa, and max kPa (breathing oxygen). Systemic hemodynamics were measured continuously by the volume-clamp method. At the end of each period, the sublingual microcirculation was assessed by SDF. Systemic DO was unchanged throughout the study (P = .8). PVD decreased in a sigmoidal fashion (max -15% while breathing oxygen, SD18, P = .001). CI decreased linearly (max -10%, SD10, P < .001) due to a reduction in HR (max -10%, SD7, P = .009). There were no changes in stroke volume or MAP. Most changes became apparent above an arterial oxygen tension of 20 kPa. In healthy volunteers, supraphysiological arterial oxygen tensions have no effect on systemic DO...