![]() Acute changes in PaCO 2 will alter the pH. PaCO 2 reflects alveolar hyperventilation. An elevated PaCO 2 reflects alveolar hypoventilation, whereas a decreased The PaCO 2reflects the state of alveolar ventilation. If the body has compensated for the disorder, the pH may be in the normal range. The pH determines the presence of acidaemia or alkalaemia. N = within normal range ↑ = increased ↓ = decreased Hyperventilation anxiety, pain, febrile illness, hypoxia, pulmonary embolism, pregnancy, sepsis opioids, sedatives), severe asthma, pulmonary oedema chronic obstructive pulmonary disease, respiratory depression from drugs (e.g. antacids)Ĭhronic lung disease with CO 2retention, e.g. Vomiting, prolonged therapy with potassium-wasting diuretics or steroids, Cushing's disease, ingestion/overdose of sodium bicarbonate (e.g. With normal anion gap: diarrhoea, secretory adenomas, ammonium chloride poisoning, interstitial nephritis, renal tubular acidosis, acetazolamide administration ethylene glycol), drug overdoses (paracetamol, aspirin, isoniazid, alcohol) With raised anion gap: diabetic ketoacidosis, lactic acidosis, poisons (e.g. Kussmaul-type breathing (deeper, faster respiration), shock, comaĬhronic: hypoventilation, hypoxia, cyanosisĪcute: hyperventilation, paraesthesia, light-headedness Kilopascals: to convert pressures to kPa, divide mmHg by 7.5Ĭorrelating arterial blood gas results with clinical features Reference ranges for arterial blood gases These measurements should be considered with the patient's clinical features ( Table 1). Bicarbonate (HCO 3ˉ) is also calculated ( Box 1). The automated analysers measure the pH and the partial pressures of oxygen (PaO 2) and carbon dioxide (PaCO 2) in arterial blood. They include prolonged bleeding, infection, thrombosis or arteriospasm. If there is any delay in processing the sample, the blood can be stored on ice for approximately 30 minutes with little effect on the accuracy of the results.Ĭomplications of arterial puncture are infrequent. To ensure accuracy, it is important to deliver the sample for analysis promptly. If repeated arterial blood gas analysis is required, it is advisable to use a different site (such as the other radial artery) or insert an arterial line. ![]() After the puncture, sterile gauze should be placed firmly over the site and direct pressure applied for several minutes to obtain haemostasis. 1The radial artery should be palpated for a pulse, and a pre-heparinised syringe with a 23 or 25 gauge needle should be inserted at an angle just distal to the palpated pulse ( Fig. Local anaesthetic makes arterial puncture less painful for the patient and does not increase the difficulty of the procedure. The puncture site should be cleaned with alcohol or iodine, and a local anaesthetic (such as 2% lignocaine) should be infiltrated. ![]() A towel may be placed under the wrist for support. The patient's arm is placed palm-up on a flat surface, with the wrist dorsiflexed at 45°. Blood is usually withdrawn from the radial artery as it is easy to palpate and has a good collateral supply.
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