Arterial blood gas test

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The arterial-blood gas test measures the amount of arterial gas, such as oxygen and carbon dioxide. The ABG test requires that a small amount of blood be drawn from the radial artery with a syringe and a thin needle, but sometimes femoral arteries in the groin or elsewhere are used. Blood can also be taken from the arterial catheter. The ABG test measures the blood gas voltage values ​​of the arterial oxygen partial pressure, and the partial pressure of the carbon dioxide artery, and the pH of the blood. In addition, arterial oxygen saturation can be determined. Such information is essential when treating patients with critical illness or respiratory diseases. Therefore, the ABG test is one of the most common tests performed on patients in the intensive care unit. At another level of care, pulse oximeter plus transcutaneous carbon dioxide measurement is a less invasive alternative method for obtaining similar information.

The ABG test can also measure the level of bicarbonate in the blood. Many blood gas analyzers will also report concentrations of lactate, hemoglobin, some electrolytes, oxyhemoglobin, carboxyhemoglobin, and methemoglobin. ABG testing is primarily used in the treatment of pulmonology and critical care to determine the exchange of gas across the alveolar-capillary membrane. ABG Testing also has a variety of applications in other medical fields. The combination of disorders can be complicated and difficult to interpret, so calculators, nomograms, and rules of thumb are generally used.

The ABG sample was initially sent from the clinic to the medical laboratory for analysis. Today, the analysis can be done in the laboratory or as a testing place of care, depending on the equipment available in each clinic.

Video Arterial blood gas test

Sampling and analysis

Arterial blood for blood gas analysis is usually taken by respiratory therapists and occasionally phlebotomist, nurse, paramedic or physician. Blood is most often taken from the radial artery because it is easily accessible, compressed to control bleeding, and has less risk for occlusion. The selection of radial arteries to draw from is based on the results of the Allen test. Brachial artery (or more rarely, femoral artery) is also used, especially during emergency situations or with children. Blood can also be taken from arterial catheters that have been placed in one of these arteries.

There are plastic and glass syringes used for blood gas samples. Most syringes come pre-packaged and contain small amounts of heparin, to prevent clotting. Other syringes may need to be heparin, by pulling out a small amount of heparin and spraying it again to remove air bubbles. Once the sample is obtained, care is taken to remove visible gas bubbles, since these bubbles can dissolve into the sample and cause inaccurate results. The sealed needle is taken to a blood gas analyzer. If a blood gas syringe is used, the sample must be transported and stored at room temperature and analyzed in 30 minutes. If a long delay is expected (ie, more than 30 minutes) before analysis, the sample should be drawn in a glass syringe and placed immediately on the ice. Standard blood tests can also be performed on arterial blood, such as measuring glucose, lactate, hemoglobin, dys-hemoglobin, bilirubin and electrolytes.

Calculation

The machine used for analysis of blood aspiration is from syringe and measures the pH and partial pressure of oxygen and carbon dioxide. Bicarbonate concentration is also calculated. These results are usually available for interpretation in five minutes.

Two methods have been used in the treatment of patient blood gases in hypothermia: pH-stat method and alpha-stat method. Recent studies have shown that the -stat method is superior.

• pH-stat: pH and other ABG results are measured at the patient's actual temperature. The goal is to maintain a pH of 7.40 and arterial carbon dioxide pressure (paCO ₂ ) at 5.3 kPa (40 mmHg) at the actual patient temperature. You need to add CO ₂ to oxygenator to achieve this goal.
• ? - stat (alpha-stat): pH and other ABG results are measured at 37 Ã, Â ° C, despite the patient's actual temperature. The goal is to keep arterial carbon dioxide pressure at 5.3 kPa (40mmHg) and pH at 7.40 when measured at 37Ã, Â ° C.

Both stat-stat and stat stat stat have theoretical flaws. The -stat method is the preferred method for optimal myocardial function. The pH-stat method can cause loss of autoregulation in the brain (coupling cerebral blood flow with metabolic rate in the brain). By increasing cerebral blood flow beyond metabolic requirements, the pH-stat method can lead to brain microembolization and intracranial hypertension.

Guidelines

1. The change of 1 mmHg in PaCO ₂ above or below 40 mmHg produces a change of 0.008 units in pH in the opposite direction.
2. PaCO ₂ will be reduced by about 1 mmHg for every 1 mEq/L reduction in [ HCO ^-
   ₃ ] under 24 mEq/L
3. Changes in [ HCO ^- ₃ ] of 10 mEq/L will produce a pH change of about 0.15 pH units in the direction that same.
4. Value of pCO ₂ relationship with pH: If pCO ₂ & amp; pH moves in the opposite direction ie, pCO ₂ ? when pH is & lt; 7.4 or pCO ₂ ? when pH & gt; 7.4, it is a primary respiratory disorder. If pCO ₂ & amp; pH moves in the same direction ie, pCO ₂ ? when pH is & gt; 7.4 or pCO ₂ ? when pH & lt; 7.4, it is a primary metabolic disorder.

Maps Arterial blood gas test

Parameters and reference range

This is a typical reference range, although various analytical and laboratory tools can use different ranges.

Contamination of the sample with room air will result in abnormally low carbon dioxide and possibly increased oxygen levels, and a simultaneous increase of pH. Delay analysis (without cooling the sample) may result in inaccurate oxygen and high levels of carbon dioxide as a result of ongoing cellular respiration.

pH

The normal range for pH is 7.35-7.45. When pH decreases (& lt; 7.35), it implies acidosis, while if the pH increases (& gt; 7.45) it implies alkalosis. In the context of arterial blood gases, the most common occurrence is respiratory acidosis. Carbon dioxide is dissolved in the blood as carbonic acid, weak acid; However, in large concentrations, it can affect the pH drastically. Whenever there is poor pulmonary ventilation, the levels of carbon dioxide in the blood are expected to increase. This leads to an increase in carbonic acid, which causes a decrease in pH. The first pH buffer is a plasma protein, since it can receive several H ions to try to maintain homeostasis. As the concentration of carbon dioxide continues to increase ( Pa CO ₂ & gt; 45 mmHg), a condition known as respiratory acidosis occurs. The body tries to maintain homeostasis by increasing the rate of breathing, a condition known as tachypnea. This allows more carbon dioxide to come out of the body through the lungs, thereby increasing the pH by having less carbonic acid. If a person is in a critical setting and intubated, one must increase the number of breaths mechanically.

Respiratory alkalosis ( Pa CO ₂ & lt; 35 mmHg) occurs when too little carbon dioxide in the blood. This may be due to hyperventilation or excessive breathing provided through a mechanical ventilator in a critical care setting. The action to be done is to calm the person and try to reduce the amount of breath taken to normalize the pH. The respiratory tract tries to compensate for changes in pH in a matter of 2-4 hours. If this is not enough, the metabolic pathway occurs.

Dalam kondisi normal, persamaan Henderson-Hasselbalch akan memberikan pH darah

$            {\displaystyle                   \text{pH}                =        6.1                {}_{}}$ log                         10                                                  (                                                         [                                                          HCO                                             3                                                                  -                                                                          ]                                                0,03                  ÃÆ' -                  P                  a                                                          CO                                             2                                                                                                                                                                            )                           {\ displaystyle {\ ce {pH}} = 6.1 \ log _ {10} \ kiri ({\ frac {[{\ ce {HCO3 ^ -}}]} {0,03 \ kali Pa {\ ce {CO2}}}} \ right)}   

Where:

• 6.1 is the acid dissociation constant (p K _a ) carbonic acid ( H
  ₂ CO
  ₃ ) at normal body temperature
• HCO ₃ ^- is the concentration of bicarbonate in the blood at mEq/L
• Pa CO ₂ is the partial pressure of carbon dioxide in arterial blood in the torr

Kidney and liver are the two major organs responsible for pH metabolic homeostasis. Bicarbonate is a base that helps to receive excess hydrogen ions whenever acidemia occurs. However, this mechanism is slower than the respiratory tract and may last from several hours to 3 days to be applied. In acidemia, the levels of bicarbonate increase, so they can neutralize the excess acid, while the opposite occurs when there is alkalemia. So when an arterial blood gas test reveals, for example, an increase in bicarbonate, the problem has been present for several days, and metabolic compensation occurs during the blood problem of acedemia.

In general, it is easier to correct acute pH disorders by adjusting respiration. Metabolic compensation occurs at a later stage. However, in a critical setting, a person with normal pH, high CO ₂ , and high bicarbonate means that, despite the high levels of carbon dioxide, there is metabolic compensation. As a result, one must be careful not to artificially regulate the breath to lower carbon dioxide. In that case, suddenly reducing carbon dioxide means that the bicarbonate will be excessive and will cause metabolic alkalosis. In such cases, carbon dioxide levels should slowly decrease.

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See also

• acid-base homeostasis
• Anion gap
• Mechanical Ventilation
• Radial artery function
• Acidosis
• Alkalosis
• Chemical equilibrium
• pCO2
• pH
• pKa
• Open arterial oxygen difference
• oxygen saturation (drug)

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References

src: www.medistudents.com

External links

• An online arterial blood gas calculator
• The online model of arterial blood gas changes with respiration
• Interactive ABG Quiz
• Practice interpreting examples of arterial blood gas presentations

Source of the article : Wikipedia