Force originating when the heart's pumping pushes the blood against the walls of the blood vessels. Their stretching and contraction help maintain blood flow. Usually measured over an arm or leg artery in humans, blood pressure is expressed as two numbers; normal adult blood pressure is about 120/80 mm of mercury. The higher number (systolic) is measured when the heart's ventricles contract and the lower (diastolic) when they relax. Seealso hypertension, hypotension.
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The test is used to determine the concentrations of gases like carbon dioxide and oxygen, bicarbonate, as well as the pH of the blood. Many blood gas analyzers will simultaneously determine the concentration of lactate, hemoglobin, several electrolytes, oxyhemoglobin, carboxyhemoglobin and methemoglobin. Thus, it provides more information than pulse oximetry. Its main use is in pulmonology, to determine gas exchange levels in the blood related to lung function, but it is also used in nephrology, and used to evaluate metabolic disorders such as acidosis and alkalosis.
Combinations of disorders can be complex and difficult to interpret, so calculators , nomograms, and rules of thumb are commonly used.
Arterial blood for blood gas analysis is usually extracted by a phlebotomist, nurse, or respiratory therapist. Blood may be taken from an easily accessible artery (typically the radial artery, but during unusual or emergency situations the brachial or femoral artery may be used), or out of an arterial line.
The syringe is pre-packaged and contains a small amount of heparin, to prevent coagulation or needs to be heparinised, by drawing up a small amount of heparin and squirting it out again. Once the sample is obtained, care is taken to eliminate visible gas bubbles, as these bubbles can dissolve into the sample and cause inaccurate results. The sealed syringe is taken to a blood gas analyzer. If the sample cannot be immediately analyzed, it is chilled in an ice bath in a glass syringe to slow metabolic processes which can cause inaccuracy. Samples drawn in plastic syringes should not be iced and should always be analyzed within 30 minutes.
The machine used for analysis aspirates this blood from the syringe and measures the pH and the partial pressures of oxygen and carbon dioxide. The bicarbonate concentration is also calculated. These results are usually available for interpretation within five minutes.
|pH||7.35 - 7.45||The pH or H+ indicates if a patient is acidemic (pH < 7.35; H+ >45) or alkalemic (pH > 7.45; H+ < 35).|
|H+||35 - 45 nmol/l (nM)||See above.|
|PO2||9.3-13.3 kPa or 80-100 mmHg||2 is 70-100 mmHg (age-dependent). >A low O2 indicates that the patient is not respiring properly, and is hypoxemic. At a PO2 of less than 60 mm Hg, supplemental oxygen should be administered. At a PO2 of less than 26 mm Hg, the patient is at risk of death and must be oxygenated immediately.|
|PCO2||4.7-6.0 kPa or 35-45 mmHg||The carbon dioxide and partial pressure (PCO2) indicates a respiratory problem: for a constant metabolic rate, the PCO2 is determined entirely by ventilation. A high PCO2 (respiratory acidosis) indicates underventilation, a low PCO2 (respiratory alkalosis) hyper- or overventilation. PCO2 levels can also become abnormal when the respiratory system is working to compensate for a metabolic issue so as to normalize the blood pH.|
|HCO3-||22–26 mmol/l||The HCO3- ion indicates whether a metabolic problem is present (such as ketoacidosis). A low HCO3- indicates metabolic acidosis, a high HCO3- indicates metabolic alkalosis. HCO3- levels can also become abnormal when the kidneys are working to compensate for a respiratory issue so as to normalize the blood pH.|
|SBCe||21 to 27 mmol/l||the bicarbonate concentration in the blood at a CO2 of 5.33 kPa, full oxygen saturation and 37 degrees Celsius.|
|Base excess||-2 to +2 mmol/l||The base excess indicates whether the patient is acidotic or alkalotic. A negative base excess indicates that the patient is acidotic. A high positive base excess indicates that the patient is alkalotic.|
|HPO42−||0.8 to 1.5 mM|
|total CO2 (tCO2 (P)c)||25 to 30 mmol/l|| This is the total amount of CO2, and is the sum of HCO3- and PCO2 by the formula: |
tCO2 = [HCO3-] + α*PCO2, where α=0.226 mM/kPa, HCO3- is expressed in molar concentration (M) (mol/l) and PCO2 is expressed in kPa
|total O2 (tO2e)||This is the sum of oxygen solved in plasma and chemically bound to hemoglobin.|
Contamination with room air will result in abnormally low carbon dioxide and (generally) normal oxygen levels. Delays in analysis (without chilling) may result in inaccurately low oxygen and high carbon dioxide levels as a result of ongoing cellular respiration.
Agency Reviews Patent Application Approval Request for "Systems and Methods for Estimating Central Arterial Blood Pressure of a Patient"
Sep 13, 2012; By a News Reporter-Staff News Editor at Politics & Government Week -- Pacesetter, Inc. has been issued patent application serial...