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Blood gas analysis is a procedure that is associated with high dependency, intensive care and respiratory units, but equipment used to carry out blood gas analysis is now commonplace on hospital wards and in some community services. It is, therefore, important for nurses in primary and secondary care to understand the significance of blood gas analysis.
Blood gas analysis provides valuable information about both the extracellular acid-base status and gas exchange. A blood gas analyzer measures pH, partial pressure of oxygen(pO(2)), partial pressure of carbon dioxide (pCO(2)), O(2) saturation, and hemoglobin concentration. A number of calculated parameters can be derived from these direct measurements such as bicarbonate concentration, base excess, oxygen content, etc. This contribution introduces the basic technical aspects of a blood gas analyzer and then describes some of the parameters that facilitate evaluation of the acid-base status and the oxygenation status of the blood. Finally, proper sampling and handling of blood gas samples is addressed.
Blood gas analysis is a time-consuming procedure, taking up to 30 minutes from obtaining a blood sample from the patient to receiving the results. The process can involve as many as three health care professionals: the doctor, nurse and a member of the pathology department. The result is that it is difficult to provide continual monitoring of blood gas levels on patients with acute respiratory problems.
Arterial blood gas analysis is used to evaluate oxygen and carbon dioxide gas exchange and acid-base status. Few studies identify indications for arterial blood gas analysis, especially with regard to optimizing the quality of patient care. General indications in severely ill adults usually include pathophysiologic abnormalities that can alter gas exchange or acid-base disturbances. Most commonly identified general indications have not been prospectively studied to determine if this analysis is necessary for diagnosis or management. Clinical settings where analysis is indicated involve patients with acute asthma in the emergency room, postoperative treatment of patients who have had coronary artery bypass graft surgery, stable patients in the intensive care unit, and patients receiving prophylactic supplemental low-flow oxygen by nasal cannula. Advances in noninvasive monitoring have suggested other possible clinical settings. However, further prospective, controlled clinical studies are needed to establish indications for arterial blood gas analysis and the role of noninvasive monitoring.
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UNLABELLED: Prehospital blood gas analysis is a new method in out-of-hospital emergency care. In a prospective pilot study we evaluated the feasibility of prehospital compensation of severe acidosis relying on different monitoring systems to evaluate patients oxygen, carbon dioxide or acid-base status, respectively. METHODS: With the help of arterial blood gas checks taken at the site of the emergency, the acid base status of patients undergoing out of hospital cardiopulmonary resuscitation was analysed. The values derived from the first arterial puncture were used to determine the presence and the type of acidosis. The data of the arterial blood gas checks were set into relation with the time elapsed since the beginning of resuscitation and they were compared with end-tidal CO2. RESULTS: During the observation period 26 blood gas analyses from patients who had out-of-hospital resuscitation because of cardiac arrest were done. Twenty three patients had severe acidosis (pH range < 6.9 to 7.31), one had alkalosis (pH 7.51). Only two had an arterial pH within normal range. The pCO2 was variable (range: 24 to 97 mm Hg). The correlation of pH with time from the beginning of resuscitation to arterial puncture was poor (r = 0.407, p < 0.05). There was no correlation between pH and BE (r = 0.267) or pH and pCO2, (r = 0.016) respectively. Prehospital capnometry had a poor correlation with arterial pCO2 in most emergency patients. Only patients with respiratory disturbances of extrapulmonary origin showed a good correlation between end-tidal CO2 and the arterial pCO2. In severely ill patients the arterio-alveolar CO2-difference was unexpectedly high (> 15 mm Hg). In four patients resuscitation was not successful until compensation of an unexpectedly severe acidosis based upon the findings from blood-gas analysis had been performed. CONCLUSIONS: Arterial blood gas analysis proved to be helpful in the optimal management of out of hospital cardiac arrest. The incidence of severe acidosis in patients undergoing cardiopulmonary resuscitation was 80%. The probability of developing acidosis was found to increase slightly depending on the time elapsed since the beginning of CPR. The application of a calculated buffering of acidosis with sodium bicarbonate showed a good outcome in selected cases. In emergency patients alternative methods fail to detect severe disturbances of the patients oxygen and/or carbon dioxide status and the acid-base balance. Management of prehospital cardiac arrest could be optimized by the routine use of blood gas analysis.
Arterial blood gas analysis can be complex. However, in many clinical areas the nurse is one of the first to see the results so they need to know whether immediate action is required. This article identifies a simple four-step approach that enables ABG interpretation even when all the complexities are not fully understood.
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Umbilical cord blood gas and pH values should always be obtained in the high-risk delivery and whenever newborn depression occurs. This practice is important because umbilical cord blood gas analysis may assist with clinical management and excludes the diagnosis of birth asphyxia in approximately 80% of depressed newborns at term. The most useful umbilical cord blood parameter is arterial pH. Sampling umbilical venous blood alone is not recommended because arterial blood is more representative of the fetal metabolic condition and because arterial acidemia may occur with a normal venous pH. A complete blood gas analysis may provide important information regarding the type and cause of acidemia and sampling the artery and vein may provide a more clear assessment. The sampling technique is simple and easily mastered by any treatment person in the delivery room. Preheparinized syringes ensure a consistent dose and amount of heparin. Depending on how normality is defined and on the population studied, normal ranges for umbilical cord blood gas values vary (see Table 1). In general, the lower range for normal arterial pH extends to at least 7.10 and that for venous pH to at least 7.20. Many different factors during pregnancy, labor, and delivery can affect cord blood gases. Umbilical blood sampling for acid-base status at all deliveries cannot be universally recommended because many facilities do not have the capabilities to support such a practice and in doing so may impose an excessive financial burden. Considering the costs, the accumulated published data, and the nonspecificity of electronic fetal monitoring in the evaluation of fetal oxygenation, it may be more rational to implement universal cord blood gas analysis. Care providers and institutions with the logistical capabilities in place should consider the cost efficacy of routine cord blood gas analysis because it is the gold standard assessment of uteroplacental function and fetal oxygenation/acid-base status at birth.
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.
UNLABELLED: Within the last few years the use of Point-of-Care Analyzers increased. These testing is primarily performed in the emergency room, intensive care units, and in the operating room using small portable analyzers. The fact of being transportable and working with rechargeable or changable batteries and disposable cartridges caused us to use blood gas analysis in the prehospital setting. METHODS: We tested three available blood gas analyzers: AVL OPTI 1, IRMA Blood Analyzer and the i-Stat Portlab System. All analyzers work with single-use cartridges and the calibration procedure is automatic. The AVL OPTI 1 uses a calibration gas and sucks in the blood by itself. The IRMA and the i-Stat system use a containing calibration gel, which must be removed from the sensory by injecting the blood sample. In all analyzers the results appear within 2-4 min on the screen. The OPTI 1 and the IRMA are able to print out the results automatically, the i-Stat uses an additional printer connected over an infrared adapter. RESULTS: During the observation period of 2 years more than 320 prehospital blood gas analyses were performed (200 with the OPTI 1.70 with IRMA and 50 with the i-Stat). All devices served their purpose. The main problems appeared with the application of the blood samples at the IRMA and the i-Stat. Because of this intricate procedures 21.4% and 20% of all tries failed. The time spent on the measurement was 2 to 5 minutes. CONCLUSIONS: All tested devices worked satisfactorily. Relating to the safety, the performance and the use the AVL OPTI 1 has to become the best notes. But this system is much more bigger and heavier than the others, especially the i-Stat Blood analyzer.
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Analysis of blood gases and blood pH yield important information in many situations of clinical emergencies. We report on a patient in whom pre-analytic errors in blood gas and blood pH measurements resulted in unnecessary further investigations. We therefore studied various pre-analytic sources of error in blood pH and blood gas analysis. Delay in sample processing for more than one hour resulted in an increase of pO2 and pCO2 and a decrease of pH. Excess sodium heparin solution as an anticoagulant (> or = 10% of total volume) led to a significant decrease of pH and pCO2 and to an increase of pO2. Air bubbles (10% of total volume) left in the syringe for 10 min significantly increased pO2. For accurate estimations of pO2, pCO2 and pH, it is necessary to keep the heparin solution below 10% of total volume, to expel all air bubbles from the syringe and to process the blood sample within one hour. Instructions to medical staff on handling blood samples for blood gas analysis should include these possible sources of errors.
Blood gas analysis is fundamental to all intensive care. Although speed is essential for adequate treatment, prognosis and even survival of the patient, precision and consistency of results are equally important prerequisites for correct clinical decision making. Point-of-care testing (POCT) has become one of the predominant fields of blood gas analysis. Although modern technology and instruments are user friendly, special training and continuous updating of staff education are of paramount importance to the reliability of results. The article consists in an outline of quality requirements and discussion of appropriate procedures for assessing and maintaining quality in blood gas analysis.
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Blood gas values were compared in blood collected from cut toenails and femoral arteries in 50 healthy crossbred dogs that were sedated and allowed to breathe room air spontaneously. Blood samples from cut toenails were collected by microcapillary technique with Natelson tubes. Femoral artery samples were collected by arterial puncture. Blood values for PO2, PCO2, pH, and HCO3 were compared. There was good correlation for pH, PCO2, and bicarbonate, but not for PO2. Microcapillary samples should be collected in 10 seconds or less for the most accurate results. A metal mixing "flea" was unnecessary. When properly handled, the Natelson tube technique provides an alternative method for collection of blood gas samples.