Ebook Evidence-based critical care (3rd edition): Part 2
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Ebook Evidence-based critical care (3rd edition): Part 2
Chapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2 randomized controlled study has ever been performed evaluating the benefit of ABG analysis in the ICU. it is likely that this technology stands alone as that diagnostic test which has had the greatest impact on the management of critically ill patients: this has likely been translated into improved Ebook Evidence-based critical care (3rd edition): Part 2 outcomes. Prior to the 1960s clinicians were unable to detect hypoxemia until clinical cyanosis developed. ABG analysis became available in the lateEbook Evidence-based critical care (3rd edition): Part 2
1950s when techniques developed by Clark. Stow and coworkers, and Severinghaus and Bradley permitted the measurement of the partial pressures of oxygeChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2on. ABG analysis is the only clinically applicable method of assessing a patient’s acid-base status. ABGs are the most frequently ordered test in the ICU and have become essential to the management of critically ill patients [4]. Indeed, a defining requirement of an ICƯ is that a clinical laboratory Ebook Evidence-based critical care (3rd edition): Part 2 should be available on a 24-11 basis to provide blood gas analysis (5].Indications for ABG SamplingABGs are reported to be the most frequently perforEbook Evidence-based critical care (3rd edition): Part 2
med test in the ICƯ (4]. There are however no published guidelines and few clinical studies which provide guidance as to the indications for ABG samplChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2 line and ABG sampling (7]. These authors demonstrated that patients* with an arterial line had more ABGs drawn than those who did not regardless of the value of the PaO2. PaCO2. APACHE II score or the use of a ventilator. In this study, multivariate analysis demonstrated that the presence of an art Ebook Evidence-based critical care (3rd edition): Part 2erial line was the most powerful predictor of the number of ABGs drawn per patient independent of all other measures of the patient’s clinical© SpringEbook Evidence-based critical care (3rd edition): Part 2
er International Publishing Switzerland 2015 DCrMoai ran, nnt in inn-71 •»!<■» limn 7 7732933022 Arterial Blood Gas Analysisstatus. Roberts and OstryzChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2e ubiquitous use of pulse oximetry in the ICƯ has made the need for frequent ABG sampling to monitor arterial oxygenation unnecessary. Furthermore (as discussed below), venous blood gas analysis can be used to estimate arterial pH and bicarbonate (HCOr) but not arterial carbon dioxide tension (PaCOj Ebook Evidence-based critical care (3rd edition): Part 2). Previously. ABGs were drawn after every ventilator change and with each step of the weaning process: such an approach is no longer recommended. TheEbook Evidence-based critical care (3rd edition): Part 2
indications for ABG analysis should be guided by clinical circumstances. However, as a “general rule” all patients should have an ABG performed on adChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2y 24-48 h. Patients with type II respiratory failure will require more frequent ABG sampling than those with type I respiratory failure. Furthermore, patients with complex acid-base disorders and patients undergoing permissive hypoventilation will require more frequent ABG sampling.ABG SamplingABG s Ebook Evidence-based critical care (3rd edition): Part 2pecimens may be obtained from an indwelling arterial catheter or by direct arterial puncture using a heparinized 1-5 mL syringe. Indwelling arterial cEbook Evidence-based critical care (3rd edition): Part 2
atheters should generally not be placed for the sole purpose of arterial blood gas sampling as they are associated with rare but serious complicationsChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2tives. Serious complications from arterial puncture are uncommon: the most common include pain and hematoma formation at the puncture site. Laceration of the artery (with bleeding), thrombosis and aneurismal formation are rare but serious complications |8. 9].ABG analysis is typically performed on w Ebook Evidence-based critical care (3rd edition): Part 2hole blood. The partial pressure of oxygen (PaO>). partial pressure of carbon dioxide (PaCOj). and pH are directly measured with standard electrodes aEbook Evidence-based critical care (3rd edition): Part 2
nd digital analyzers: oxygen saturation is calculated from standard Oj dissociation curves or may be directly measured with a cooximeter. The bicarbonChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2e dissociation constant of carbonic acid. The base excess is defined as the quantity of strong acid required to titrate blood to pH 7.40 with a PaCO2 of 40 mmHg at 37 °C. In practice, acid is not titrated as suggested but calculated using a variety of established formulae or nomograms. The base exce Ebook Evidence-based critical care (3rd edition): Part 2ss thus ‘removes’ the respiratory element of acid-base disturbanceABG Analysis331and identifies the metabolic contribution to interpret with pH and [HEbook Evidence-based critical care (3rd edition): Part 2
*]. The standard bicarbonate is broadly similar and is the calculated [HCO.r] at a PaC'O2 of 40 mmHg. Although the base excess and standard bicarbonatChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2it is important that the specimen be collected and processed correctly and that quality assurance methods exist to ensure the accuracy of the measurements. Aside from inter-laboratory variation, errors in calibration and electrode contamination with protein or other fluids may alter results. Heparin Ebook Evidence-based critical care (3rd edition): Part 2 is usually added to the blood to prevent coagulation and dilution with older liquid solutions previously caused spuriously low PaCO2. Sample preparatEbook Evidence-based critical care (3rd edition): Part 2
ion is important because air bubbles falsely elevate PaO2.The following points must be considered before obtaining sample to avoid errors in blood gasChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2ilatory parameters in patients on mechanical ventilation. In most ICƯ patients a steady state is reached between 3 and 10 min and in about 20-30 min in patients with chronic airways obstruction [10].•Anticoagulants: Excess of heparin may affect the pH. Only 0.05 mL is required to anticoagulate I inL Ebook Evidence-based critical care (3rd edition): Part 2 of blood.•Delay in processing of the sample: Because blood is a living tissue. 02 is being consumed and co2 is produced in the blood sample. Red blooEbook Evidence-based critical care (3rd edition): Part 2
d cell glycolysis may generate lactic acid and change pH. Significant increases in PaCO2 and decreases in pH occur when samples are stored at room temChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2be processed up to 2 11 without affecting the blood gas values.•Hypothermia. Blood gas values are temperature dependent, and if blood samples are warmed to 37 °C before analysis (as is common in most laboratories), PO2 and PCO2 will be overestimated and pH underestimated in hypothermic patients. The Ebook Evidence-based critical care (3rd edition): Part 2 following correction formulas can be used:-Subtract 5 mmHg PO2 per I °C that the patient’s temperature is <37 °C-Subtract 2 mmHg PCO2 per I °C that tEbook Evidence-based critical care (3rd edition): Part 2
he patient’s temperature is <37 °C-Add 0.012 pH units per 1 °C that the patient’s temperature is <37 °C.ABG AnalysisAn ABG provides a rapid and accuraChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2ne process will affect the other two. However, for the sake of simplicity and ease of understanding each will be discussed separately.22 Arterial Blood Gas Analysis332Alveolar VentilationThe arterial co2 content as reflected by arterial co2 tension (PaCO2) at any given moment depends on the quantity Ebook Evidence-based critical care (3rd edition): Part 2 of co2 produced and its excretion through alveolar ventilation (VA) and can be expressed by the equation. PaCO2~CO>/VA. Hie alveolar ventilation is tEbook Evidence-based critical care (3rd edition): Part 2
hat portion of total ventilation that participates in gas exchange with pulmonary blood. If it is assumed that co2 production is constant, then co2 hoChapter 22Arterial Blood Gas AnalysisArterial blood gas (ABG) analysis plays a pivotal role in the management of critically ill patients. Although no Ebook Evidence-based critical care (3rd edition): Part 2alveolar hypoventilation and low PaC0> (<35 mmHg) implies alveolar hyperventilation.OxygenationThe ultimate aim of the card io-respiratory system is to provide adequate delivery of oxygen to the tissues. This is largely dependent upon cardiac output, hemoglobin concentration and hemoglobin saturatio Ebook Evidence-based critical care (3rd edition): Part 2n. The PaO2 is a measure of the oxygen tension in plasma: while the dissolved fraction makes a negligible contribution to oxygen delivery (<2 %) it isEbook Evidence-based critical care (3rd edition): Part 2
a major factor affecting hemoglobin saturation. In turn the PaO2 is dependent on the concentration of oxygen in the inspired air (FiO?). oxygen exchaGọi ngay
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