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Thread: How well can you interpret acid-base disturbances?

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    Arrow How well can you interpret acid-base disturbances?

    Arterial blood gas analysis: ABG


    Definition

    Blood gases is a test done to measure how much oxygen and carbon dioxide is in your blood. It also looks at the acidity (pH) of the blood. Usually, blood gases look at blood from an artery. In rarer cases, blood from a vein may be used.
    How the Test is Performed

    The test is performed using a small needle to collect a sample of blood from an artery. The sample may be collected from the radial artery in the wrist, the femoral artery in the groin, or the brachial artery in the arm.

    Before blood is drawn, the health care provider may test circulation to the hand (if the wrist is the site). After the blood is drawn, pressure applied to the puncture site for a few minutes stops the bleeding.

    The test must be sent to the laboratory for analysis quickly to ensure accurate results.
    How to Prepare for the Test

    There is no special preparation. If the person having the test is on oxygen, the oxygen concentration must remain constant for 20 minutes before the test. If the test is done without oxygen, the oxygen must be turned off for 20 minutes before the sample is taken to ensure accurate test results.

    How the Test Will Feel

    The health care provider will insert a needle through the skin into the artery. You can choose to have anesthesia at the site. You may feel brief cramping or throbbing at the puncture site. The needle will be withdrawn after the sample is collected.

    Pressure applied over the site for 5 - 10 minutes helps prevent bleeding. A bandage will be placed over the puncture site. The health care provider will watch the site for signs of bleeding or circulation problems.
    Why the Test is Performed

    The test is used to evaluate respiratory diseases and conditions that affect the lungs. It helps determine the effectiveness of oxygen therapy. The acid-base component of the test also gives information about kidney function.

    Normal Results

    Values at sea level:
    • Partial pressure of oxygen (PaO2) - 75 - 100 mm Hg
    • Partial pressure of carbon dioxide (PaCO2) - 35 - 45 mm Hg
    • A pH of 7.35 - 7.45
    • Oxygen saturation (SaO2) - 94 - 100%
    • Bicarbonate - (HCO3) - 22 - 26 mEq/liter

    Note: mEq/liter = milliequivalents per liter; mm Hg = millimeters of mercury

    At altitudes of 3,000 feet and above, the oxygen values are lower.
    What Abnormal Results Mean
    Abnormal results may indicate respiratory, metabolic, or renal diseases. The results may also be abnormal with head or neck injuries, or other traumas that affect breathing.

    Risks
    In general, there is a very low risk when the procedure is done correctly. There may be bleeding or bruising at the puncture site, or delayed bleeding from the site. Circulatory impairment in the area of the puncture may occur, although it is rare.

    Blood gases test




    The blood gases test is performed by collecting a sample of blood through a needle from an artery. The test is used to evaluate respiratory diseases and conditions that affect the lungs, and it is used to determine the effectiveness of oxygen therapy. The acid-base component of the test also gives information on how well the kidneys are functioning.



    How well can you interpret acid-base disturbances?



    Questions:


    1.A 60 year old man was admitted with an exacerbation of chronic obstructive pulmonary disease. His arterial blood gases on air showed pH 7.29, Paco2 8.5 kPa (65.3 mm Hg), Pao2 8.0 kPa (62 mm Hg), and standard bicarbonate 30.5 mmol/l. What is the acid-base disturbance and what is the management?


    2.A 30 year old man was admitted with status epilepticus. He is given intravenous diazepam. Arterial blood gases on 15 l/min via reservoir bag mask showed pH 7.05, Paco2 8 kPa (61.5 mm Hg), Pao2 15 kPa (115 mm Hg), and standard bicarbonate 16 mmol/l. His other results were sodium 140 mmol/l, potassium 4 mmol/l, and chloride 98 mmol/l. What is the acid-base disturbance and why?


    3.A 45 year old lady with previous peptic ulcer disease was admitted with persistent vomiting. She looked dehydrated. Her blood results were sodium 140 mmol/l, potassium 2.5 mmol/l, chloride 86 mmol/l, pH 7.5, Paco2 6.0 kPa (50 mm Hg), Pao2 14 kPa (107 mm Hg), standard bicarbonate 40 mmol/l. What is the acid-base disturbance and why? How would you treat this patient?



    4.A 40 year old man with pleurisy for five days was assessed. A moderately sized pneumothorax was seen in a chest radiograph. His arterial blood gases on air showed pH 7.44, Paco2 3.0 kPa (23 mm Hg), Pao2 30.5 kPa (234.5 mm Hg), standard bicarbonate 16 mmol/l. How can you explain the clinical picture.


    5.A 50 year old man with type 1 diabetes and diabetic nephropathy was recovering on a surgical ward after a total colectomy and ileostomy. He had persistent metabolic acidosis and the surgeons were concerned about his high potassium concentration and that there may have been some ischaemia in the abdomen causing the acidosis. However, the patient appeared well perfused and had normal vital signs.

    He had normal fluid balance and his results showed sodium 130 mmol/l, potassium 6.5 mmol/l, creatinine 180 µmol/l (2.16 mg/dl), chloride 109 µmol/l, 8 am cortisol 500 nmol/l (18 µg/dl), pH 7.29, Paco2 3.5 kPa (27 mm Hg), Pao2 14 kPa (107 mm Hg), standard bicarbonate 12 mmol/l. What is the acid-base disturbance and why?
    Answers

    [HIDE]
    1.This patient had an acidosis with a high Paco2 and normal standard bicarbonate--respiratory acidosis. This is a common finding in acute exacerbations of chronic obstructive pulmonary disease. Doctors gave medical treatment (nebulisers, steroids, and antibiotics) and non-invasive ventilation.

    2.This patient had acidosis with both a high Paco2 and a low standard bicarbonate--a mixed acidosis. The anion gap was 26 mmol/l (increased). The Pao2 is lower than expected because the patient was breathing around 70% oxygen. Does this fit with the clinical picture? Yes, he had a lactic acidosis from prolonged fitting and a respiratory acidosis from intravenous diazepam. This disturbance will return to normal with attention to A--airway manoeuvres and oxygen, B--assisted ventilation if needed, C--treatment with fluids.

    3.This patient had alkalosis due to a high standard bicarbonate-metabolic alkalosis. The Paco2 was appropriately low in compensation. This was hypokalaemic hypochloraemic metabolic acidosis because of potassium and chloride loss from vomiting. Treatment was of the underlying cause (pyloric stenosis) and intravenous sodium chloride with potassium.

    4.This patient had a normal pH but had both a low Paco2 and a low standard bicarbonate. How do we know if this was a compensated respiratory alkalosis or a compensated metabolic acidosis? Easy. The history indicates five days of hyperventilation, so this is a compensated respiratory alkalosis. What if this were a diabetic patient who was unwell with fever, vomiting, and high glucose? Then it would have been a compensated diabetic ketoacidosis.

    5.This patient had acidosis due to low bicarbonate. The Paco2 was appropriately low in compensation. The anion gap was normal (13.5 mmol/l). This makes intra-abdominal ischaemia (which causes lactic acidosis) unlikely. Was this a gastrointestinal problem or a kidney problem? If this were a gastrointestinal problem, you would expect low potassium. This man had diabetic nephropathy which predisposes to renal tubular acidosis. Type 4 (hyporeninaemic hypoaldosteronism) is typically associated with high potassium and is found in diabetic and hypertensive renal disease.
    [/HIDE]

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    Last edited by trimurtulu; 03-03-2009 at 07:14 AM.

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    Hi Good Work

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    there is no thanx button here!!!

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    Quote Originally Posted by uditdalmia View Post
    there is no thanx button here!!!
    Check inferolateral of each post.


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    thanks
    i realy need them

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