New perspectives in blood gas measurement assessment and interpretation
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"New Perspectives in Blood Gas Measurement, Assessment and Interpretation" . William J Malley, M.S., RRT, CPFT. “Blood gas and pH analysis has more immediacy and potential impact on patient care than any other laboratory determination.”

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New perspectives in blood gas measurement assessment and interpretation l.jpg

"New Perspectives in Blood Gas Measurement, Assessment and Interpretation"

William J Malley, M.S., RRT, CPFT


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OUTLINE potential impact on patient care than any other laboratory determination.”

  • 1) Review pre-analytical ABG issues and consequences of improper technique.

  • 2) Discuss the value of temperature correction of ABG’s.

  • 3) Use case studies to highlight some key clinical concepts.

  • 4) Explore appropriate clinical ABG targets in different clinical scenarios.


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Interactive potential impact on patient care than any other laboratory determination.”


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Sample Handling potential impact on patient care than any other laboratory determination.”


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Icing blood gas samples potential impact on patient care than any other laboratory determination.”

Routine arterial blood gases in plastic syringes should be iced if they will be run within 30 minutes.

Yes/No


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Rationale for Icing potential impact on patient care than any other laboratory determination.”

  • To minimize the effect of metabolism of living tissue


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. potential impact on patient care than any other laboratory determination.”No

NCCLS. Blood gas and pH analysis and related measurements. C46-A, 2001


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Icing blood gas samples potential impact on patient care than any other laboratory determination.”

PaO2 decreased in a linear fashion when measured up to 30 minutes after the blood sample in a plastic syringe had been placed in an ice-water bath.

YES/NO


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Factors which could theoretically impact results: potential impact on patient care than any other laboratory determination.”

  • 1) Metabolism

  • 2) Diffusion of gases between the sample and the ambient gas

  • 3) The change in gas solubility due to the temperature decrease


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No…PaO potential impact on patient care than any other laboratory determination.”2 actually increased

Liss, HP, Payne, CB. Stability of blood gases in ice and at room temperature. Chest 103:1120, 1993.


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Icing blood gas samples when also measuring electrolytes potential impact on patient care than any other laboratory determination.”

Potassium will tend to be higher in iced samples or samples sent through pneumatic tubes.

Yes/No


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Factors which may falsely elevate plasma potassium levels potential impact on patient care than any other laboratory determination.”

  • Hemolysis

  • Physical Stress on sample

    • Icing

    • Pneumatic Tubes


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Yes potential impact on patient care than any other laboratory determination.”


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Learning Styles potential impact on patient care than any other laboratory determination.”

“I learn best least from facts and figures and most from pictures and stories!”


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A 38 y.o. female patient is admitted to the emergency department with severe pneumonia and a temperature of 41oC.

  • ARTERIAL BLOOD GASES

  • SaO2 85%

  • pH 7.30

  • PaCO2 41 mm Hg

  • PaO2 62 mm Hg

  • [HCO3] 25 mEq/L

  • (data has been temp corrected to 410C)


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NO! department with severe pneumonia and a temperature of 41


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  • ARTERIAL BLOOD GASES department with severe pneumonia and a temperature of 41

  • SaO2 86% 69%

  • pH 7.24 7.30

  • PaCO2 41 mm Hg 32 mm Hg

  • PaO2 62 mm Hg 40 mm Hg

  • [HCO3] 17 mEq/L15 mEq/L

  • 41oC 37oC


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A 51 y.o. male with severe leukemia has a blood gas drawn. He is also on a pulse oximeter which is reading 92%.

  • ARTERIAL BLOOD GASES

  • SaO2 85%

  • pH 7.36

  • PaCO2 37 mm Hg

  • PaO2 50 mm Hg

  • [HCO3] 25 mEq/L


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KEY OBSERVATIONS being picked up by the pulse oximeter.

  • Pulse oximetry reading is satisfactory.

  • There is a discrepancy between the pulse oximeter reading and the PaO2

  • The patient has leukemia


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NO being picked up by the pulse oximeter.

Haynes JM, A case of disparity between pulse oximetry measurements and blood gas analysis values, Resp Care 49,1059-60, 2004


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A 55 year old male patient in the burn unit suffers a cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate.

  • ARTERIAL BLOOD GASES

  • SaO2 91%

  • pH 7.52

  • PaCO2 47 mm Hg PaO2 63 mm Hg

  • [BE] -11 mEq/L


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BICARBONATE THERAPY cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate.

  • Bicarbonate therapy for metabolic acidosis should be directed primarily at the negative base excess.

  • YES/NO


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BICARBONATE THERAPY cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate.

  • May be indicated is metabolic acidosis but is controversial


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NO cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate.


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A 55 year old male patient in the burn unit suffers a cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate.

  • ARTERIAL BLOOD GASES

  • SaO2 91%

  • pH 7.52

  • PaCO2 47 mm Hg PaO2 63 mm Hg

  • [BE] -11 mEq/L


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Blood Gas Interpretation cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate.

  • The blood gas reported is impossible.

  • Yes/NO


If you know two of the three acid base variables ph hco 3 paco 2 you know the third l.jpg

If you know two of the three acid-base variables cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate. (pH- HCO3- PaCO2)you know the third!


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Arterial Blood Gas cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate.

  • pH 7.55

  • PaCO2 40 mm Hg

  • [HCO3] ?


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Blood Gas Interpretation cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate.

  • The blood gas reported is impossible.

  • Yes/NO


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Yes cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate.


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  • ARTERIAL BLOOD GASES cardiac arrest. Blood gases drawn during the arrest are called to the floor. Due to the negative base excess reported the patient is given two ampoules of sodium bicarbonate.

  • SaO2 91%

  • pH 7.52

  • PaCO2 47 mm Hg PaO2 63 mm Hg

  • [BE] +11 mEq/L


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A 25 year old female patient arrives in the emergency room in a coma.

  • ARTERIAL BLOOD GASES

  • SaO2 85%

  • pH 7.16

  • PaCO2 80 mm Hg PaO2 52 mm Hg

  • [BE] blood - 4 mEq/L

  • [HCO3] 28 mEq/L


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METABOLIC INDICES in a coma.

  • It is impossible to have an elevated plasma bicarbonate with a decreased base excess of the blood.

  • YES/NO


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METABOLIC INDICES in a coma.

  • HYPERCAPNIA CAUSES

    • Increased bicarbonate via the hydrolysis reaction

    • Decreased blood base excess because of in vivo – in vitro discrepancies in calculation


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NO in a coma.


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Arterial Blood Gases in a coma.

  • pH 7.38

  • PaCO2 73 mm Hg

  • [HCO3] 42 mEq/L

  • [K] 2.8 mEq/L


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COPD in a coma.

  • This blood gas represents a compensated respiratory acidosis.

  • YES/NO


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NO in a coma.


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HYPOKALEMIA in a coma.

  • Hypokalemia may hamper weaning from mechanical ventilation

  • YES/NO


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CONSEQUENCES OF HYPOKALEMIA in a coma.

  • ARRYTHMIA

  • METABOLIC ALKALOSIS

  • MUSCLE WEAKNESS


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YES in a coma.


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Clinical Blood Gas Targets in a coma.

  • PaCO2 ?

  • PaO2

  • pH


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Permissive Hypercapnia in a coma.

  • PaCO2 as high as 80 – 100 mm Hg

  • Avoidance of Volume / Pressure Induced Lung Injury

  • Avoid hypercapnia patients vulnerable to increased intracranial pressure


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METABOLIC ACIDOSIS in a coma.

  • Some evidence suggests acidosis may actually be protective to cells, but it should be treated in the presence of hyperkalemia.

  • YES/NO


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TREATMENT OF METABOLIC ACIDOSIS in a coma.

  • Treatment of metabolic acidosis has been becoming progressively conservative

  • Metabolic acidosis exacerbates hyperkalemia


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YES in a coma.


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Permissive Acidemia in a coma.

  • pH down to 7.10 surprisingly well tolerated

  • Some evidence that low pH is actually protective to the organism

  • Must treat when acidosis is associated with significant hyperkalemia


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PERMISSIVE HYPOXEMIA ? in a coma.

  • In paraquot poisoning, it is probably best to keep the patient in mild hypoxemia.

  • YES/NO


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PERMISSIVE HYPOXEMIA in a coma.

  • Formation of oxygen free radicals is accelerated in the presence of

    • Paraquot

    • Bleomycin Rx


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YES in a coma.


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Permissive Hypoxemia in a coma.

  • According to Downs, hypoxia may not occur until PaO2 is less than 30 mm HG

  • Downs, JB. Has oxygen administration delayed appropriate respiratory care? Resp Care48:611, 2003.


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