The Blood Gas Analyzer
The blood gas analyzer is a device that is used to measure pH, blood gas, electrolytes, and some metabolic processes in the blood. Blood analyzers can record the partial pressure of oxygen and carbon dioxide, pH, and the levels of various ions such as bicarbonates, chloride, potassium, and sodium. Besides, the device can also measure metabolites such as lactate, glucose, magnesium, and calcium (World Health Organization 1). Blood analyzers can also identify errors in metabolites, electrolytes levels, the amount of oxygen/carbon dioxide exchange, and acid-base balance. The device can be in the form of a bench-top or a hand-held device. It has an LCD screen, a keypad for entering information, and a slot through which samples are inserted. Some blood gas analyzers come with additional features such as touch-pens, alarms, USB ports, memory functions, and storage compartments (World Health Organization 1).
Blood gas analyzers are fitted with electrodes that measure the partial pressure of oxygen and carbon dioxide in the blood, and the pH. Analyzers that determine blood chemistry are fitted with a pad that contains the reagent needed for a specific test. Analyzers that measure electrolytes in the blood use the ion-selective electrode method that measures the activities of the ions in the solution (World Health Organization 1). The first step in using a blood analyzer is placing the blood samples in test tubes and placing them on the analyzer. The operator can then determine the type of test to be performed from the keypad or a computer connected to the device. The analyzers then channel the blood into a measuring chamber that has specific electrodes that capture the variables being measured (World Health Organization 1). For instance, electrodes sensitive to pH work by comparing the electric potential registered at their tip with a set potential, and the difference is the measure of the concentration of hydrogen ions H+. Electrodes sensitive to carbon dioxide are fitted with a semipermeable membrane made of silicon or Teflon that covers their tip (Sood, Paul, and Puri 57). At the point where the electrode and the membrane meet, a reaction takes place whereby water molecules combine with carbon dioxide molecules, releasing hydrogen ions that are equal in pressure to the carbon dioxide molecules. The voltmeter normally measures H+, but it is calibrated with the pCO2 symbol.
In electrodes that measure oxygen, the gas passes through a membrane made of polypropylene and reacts with a buffer made of phosphate molecules. Water molecules react with oxygen molecules in the phosphate buffer, and this produces an electric current that is proportional to the oxygen molecules (Sood, Paul, and Puri 57). Blood gas analyzers then measure the current and convey the results in form of the initial oxygen pressure. After the measurements are recorded, the blood that remains in the equipment is removed as waste, and the measuring apparatus is cleaned in readiness for the next test. The units of measure used in blood gas analyzers include kilo Pascals (kPa) and millimeters of mercury (mmHg) (Sood, Paul and Puri 58).
The blood gas analyzer is an important equipment in monitoring the acid-base balance in patients, the efficiency of gas exchange, and the status of their respiratory system. Some of the patients that are monitored using gas analyzers include patients that have just left surgery, patients on oxygen therapy, patients in intensive care, and patents with diseases such as diabetes, cardiovascular malfunctions, and kidney disorders (Sood, Paul, and Puri 58).
The human body functions within a narrow optimum alkaline environment with normal pH falling between 7.35-7.45, and maintaining an optimum physiological function requires the maintenance of a normal pH. The two key processes that maintain pH in the body are metabolic and respiratory functions. Blood pH is considered low if it is below 7.35, and this means that the blood is acidic (Uyanki, Sertoglu and Kayadibi 104). If the pH is above 7.45, the blood is considered alkalotic. Respiration interferes with blood pH by releasing CO2 that is a by-product of metabolism into the blood stream. The CO2 is transported to the lungs where it is eliminated through breathing (Singh, Khatana, and Gupta 136). However, the excessive carbon dioxide is absorbed in water to form carbonic acid. Blood pH will change depending on the amount of carbonic acid in the blood, and consequently, the rate and depth of breathing also change. Carbon dioxide is considered a respiratory acid because as the blood pH declines as CO2 is eliminated, and if the blood pH goes up CO2 is retained (Singh, Khatana, and Gupta 136). The renal system is another metabolic function that affects blood pH. The kidneys discharge hydrogen ions and retake bicarbonates. Bicarbonates are a product of metabolism and are considered as alkaline. As the blood pH declines, it becomes acidic, and the body responds by retaining bicarbonates. On the contrary, if the blood pH goes up, the blood becomes alkaline, and the body responds by eliminating bicarbonates through urine (Singh, Khatana, and Gupta 136).
The blood gas analyzers used in modern hospitals are a product of several years of gradual improvement. The basic technology used in blood analyzers is the same, but their size has reduced significantly. Nevertheless, the reduction in the size of analyzers has presented a challenge, which is to fit sensors in the reduced analyzer sizes and design (Singh, Khatana, and Gupta 137). The pioneering blood gas analyzers used pH electrode that was developed at the start of the 19th century. Scientists had discovered that when a fine glass membrane is placed in between two solutions with different pH, a small difference in terms of electrical potential developed. Scientists faced a challenge in measuring the difference in electrical potential, but with the development of electrical devices, instruments that could measure pH were made (Singh, Khatana, and Gupta 137).
The second generation of blood gas analyzers was developed fifty years after the pioneering one. Second generation blood analyzers used pCO2 sensors that were covered with plastic membranes. The membrane covered a mercury/mercury chloride reference electrode, but later, a bicarbonate ion was added to the electrolyte solution (Dev, Hillmer, and Ferri 7). This enabled an association of the partial carbon dioxide pressure outside the membrane with pH through a basic mathematical equation that is referred to as the Henderson-Hasselbalch equation. The partial oxygen pressure sensor was developed and integrated into the analyzer to form an integrated instrument. The partial oxygen pressure sensor was an electrode covered by a membrane (Dev, Hillmer, and Ferri 7).
Despite the improvement in the design and accuracy of blood gas analyzers over the years, scientist still face challenges in designing the device to-date. One of the challenges faced in designing the instrument is comprehensive understanding of the electrochemistry and physical chemistry used in the sensors (Singh, Khatana, and Gupta 138). A second challenge is the selection of the best materials that provide the best sensor functions. Lastly, a physical method of evaluating the property of materials such as chemical impurities and surface texture used to make gas analyzers is still missing. Solving these challenges is more important today because of the trend to create smaller devices. Scientists hope that smaller gas analyzers will lead to an improved analysis (Singh, Khatana, and Gupta 138).
Most gas analyzers utilize several sensors that are placed in a complex flow of cells. The time it takes for the gases and liquids to flow through the cells is lengthy, and this sometimes leads to an incomprehensible measurement cycle. On the contrary, the recording of the sensor signals needed to produce the result takes place during a very small window, for example, a fraction of a second (Singh, Khatana, and Gupta 138). The device uses the remaining time in the reading cycle to identify a suitable starting point for the next reading. This means that the time that is allocated for the sensors to respond is very small, and the solution is having faster sensors. Ideally, the sensor should be very fast to enable them to attain an equilibrium within the time the signal is acquired. In reality, it is difficult to create faster sensors, and even faster sensors sometimes change dismally when acquiring signals (Singh, Khatana, and Gupta 139).
Dealing with the above challenge means that medical practitioners will have to determine the end points of the reactions, that is, predict what the responses/reactions would have been if they were allowed to proceed to completion. The prediction should be made based on mathematical formula suitable for the sensor used; however, in some cases, empirical predictions can be made (Singh, Khatana, and Gupta 138). Improving the efficacy and speed of blood gas analyzers can also be achieved through selecting the most suitable material for the membrane that measures partial carbon dioxide. In the previous years, the material used to make partial carbon dioxide membrane was polypropylene, Teflon or polyethylene. Blood gas analyzers that had membranes comprising materials as mentioned earlier took tens of seconds before responding. This means that the first generation blood gas analyzers were very slow (Singh, Khatana, and Gupta 138).
Technological advances have permitted the development of hand-held gas analyzers. Portable analyzers utilize analytical cartridges that can be disposed of, and they are fitted with optical sensors in some instances. This means that a nurse or physician without technological certification can use hand-held devices. Some hand-held blood gas analyzers are considered less accurate because they are not calibrated, and this increases the cost of analysis (Sood, Paul, and Puri 58).
Blood gas analyzers are vital tools that enable medical practitioners to examine the acid-base balance in patients in order to evaluate how respiratory oxygen is used. The device measures partial oxygen pressure, partial carbon dioxide pressure, and pH using electrodes. The electrode used to measure partial carbon dioxide pressure and pH are potentiometric; that is, the voltage is proportional to CO2 and hydrogen ions produced (Dev, Hillmer, and Ferri 8). Examining patients using blood analyzers has some advantages for medical practitioners. These advantages include helping in making a diagnosis; structuring the treatment plan; assisting managing ventilators; and enhancing acid-base management (Dev, Hillmer, and Ferri 8).
The accuracy of the readings obtained from blood gas analyzers is determined by the how the blood sample was collected, prepared, and analyzed. Experts have noted that clinically significant errors can occur in any of the steps above and interfere with the accuracy of the results (Dev, Hillmer, and Ferri 9). Some of the most common errors include bubbles in the specimen, blood samples not obtained from arteries, and inadequate or too much anticoagulant in the specimen. Errors that are likely to occur before a sample is obtained from a patient include wrong/missing patient identification, the use of incorrect anticoagulant, failure to stabilize the condition of the patient before taking samples, and poor cleaning of the apparatus before taking a sample (Dev, Hillmer, and Ferri 9).
Medical practitioners can also make errors when handling specimen. Some of the errors they make include mixing venous and arterial blood and failing to mix blood specimen with heparin properly. Errors can also occur during the storage process, and some of the errors that can occur include the destruction of the red blood cells and poor storage (Sood, Paul, and Puri 59). If medical practitioners adhere to the proper procedure when using blood gas analyzers, then they are more likely to end up with accurate results. However, medical practitioners are cautioned that they should always take the relevant clinical history of a patient before administering a blood analyzer test (Sood, Paul, and Puri 59). For example, patients suffering from renal failure, hypotension, and diabetes are more likely to have acidic blood. On the other hand, patients suffering from nausea or patients that use diuretics are more likely to have alkaline blood. Medical practitioners using blood gas analyzers are advised to observe standard precaution when dealing with body fluids (Sood, Paul, and Puri 60).
The blood gas analyzer gives a record of oxygen and carbon dioxide levels, which assists medical practitioners in determining whether the kidneys and lungs are functioning effectively. Blood gas analyzers determine the management approach that can be used in dealing with patients with acute diseases (Singh, Khatana, and Gupta 139). Some of the symptoms medical practitioners look for in a patient before performing a blood gas analyzer test include nausea, confusion, breathing problems, and shortness of breath. In most cases, blood analyzer test is prescribed to patients suspected of suffering from neck or head trauma with breathing problems; patients with metabolic diseases, lung problems, and kidney disease (Singh, Khatana, and Gupta 139).
Just like other medical tests and treatments, blood gas analyzers may have some side effects. However, blood analyzer tests are generally considered to be low risk because of the small amount of blood used. Some of the possible side effects of undergoing a blood gas analyzer test include dizziness, infections, bleeding, and blood accumulating under the skin (Singh, Khatana, and Gupta 139). In the future, gas analyzers are likely to improve patient outcomes and assist medical practitioners in providing a speedy treatment. In addition, experts have predicted that in the future, blood analyzers will be used in diagnosing a range of medical conditions. The testing methods that will be included in the gas analyzer in the future are also likely to enhance the manner in which the tests are conducted and the outcomes (Singh, Khatana, and Gupta 140).
Advancement in technology will also ensure that little training is needed for practitioners to use blood gas analyzers. Nevertheless, the current analyzers are less cumbersome, and they need less maintenance and troubleshooting. Moreover, changing electrodes in the device has become easier, unlike in the earlier versions (Singh, Khatana, and Gupta 140). Modern blood gas analyzers also have inbuilt quality assurance systems unlike in the earlier version that required a practitioner to perform quality control checks after every eight hours manually. For instance, modern blood gas analyzers have the ability to detect clots and remove them from the system automatically. In addition, current analyzers are highly automated, especially when it comes to sampling (Singh, Khatana, and Gupta 140).
Modern hand-held analyzers also have several benefits that include the ease-of-use and faster delivery of results and this makes hand-held devices convenient. Consequently, most medical practitioners prefer hand-held devices. Hand-held analyzers have the benefit of transmitting results automatically and in a secure manner, and this lowers the chances of transcription errors. Cost is another reason why hospitals are opting for hand-held devices. For instance, tabletop blood gas analyzers can cost between $30,000 and $100,000, but hand-held devices can cost about $7,000 (Singh, Khatana, and Gupta 141).
Experts have predicted that in the future, blood gas analyzers are more likely to be integrated with other procedure, for example, pulse oximetry therapy. Integration has some advantages; for instance, gas analyzers examine the specimen at one moment in time, while oximetry therapy has the ability to provide continuous monitoring. Some manufacturers have already developed wireless blood gas analyzer systems (Singh, Khatana, and Gupta 141). The wireless connection enables faster transfer of information, and this means that information is available whenever needed by medical practitioners. Another feature that is likely to be included in future models of gas analyzers is the broad test menu. Researchers are interested in testing several variables when performing a blood gas analysis. The variables that are likely to be included in the future are the levels of lactate, blood urea nitrogen, and creatinine (Dev, Hillmer, and Ferri 9).
Future blood gas
analyzers are also likely to have a compact design, and this will prove crucial
is saving space in hospitals. Laboratory practitioners are looking for blood
gas analyzers that are easy to use in terms of usage instruction and data
entry. Practitioners also prefer analyzers with a small sample capacity because
obtaining enough blood from patients can be challenging, especially when
dealing with infants (Dev, Hillmer, and Ferri 9).
Most medical practitioners want microliter-size gas analyzers as opposed to the
current milliliter-sized analyzers. Hospital administrators are interested in
comparing results from several analyzers in different places. However, this is
made impossible by lack of standard workflow procedures and methods of ensuring
quality. As a result, hospital administrators are advocating for increased
standardization of gas analyzers (Dev, Hillmer,
and Ferri 9). Other special features that some manufacturers are
planning to integrate into their devices include biometric identification. The
current devices uses passwords for security and this can be easily manipulated.
The biometric features that will be used for identification in the future
models include thumb, retina, and voice (Dev,
Hillmer, and Ferri 9). In summary, the technological improvement of
blood gas analyzers will provide crucial information on metabolic diseases and
respiratory problems in the future.
Dev, Shelly P., Melinda D. Hillmer and Mauricio Ferri. “Arterial Puncture for Blood Gas Analysis.” The New England Journal of Medicine (2011): 7-9. Print.
Singh, Virendra, Shruti Khatana and Pranav Gupta. “Blood gas analysis for bedside diagnosis.” Natl J Maxillofac Surg. 4. 2(2013): 136–141 . Print.
Sood, Pramod, Gunchan Paul and Sandeep Puri. “Interpretation of arterial blood gas.” Indian J Crit Care Med. 14. 2 (2010): 57–64 . Print.
Uyanki, Metin, Erdim Sertoglu and Huseyin Kayadibi. “Comparison of blood gas, electrolyte and metabolite results measured with two different blood gas analyzers and a core laboratory analyzer .” Scandinavian Journal of Clinical & Laboratory Investigation. 75 (2015): 97-105. Print.
World Health Organization. “Blood Gas/pH/Chemistry Point of Care Analyzer.” 2011. Print.