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Blood Gases (Arterial & Venous) Collection Technique & Interpretation > Arterial Blood Gas Components > Flashcards

Arterial Blood Gas Components Flashcards

1
Q

PaO2

Definition

A

A value that represents the partial pressure of O2 dissolved in arterial blood. The PaO2 is the primary indication of whether the patient is hypoxemic or not, and is used in the diagnosis of acute respiratory failure.

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2
Q

PaO2

Interpretations

A
  1. A Normal PaO2 for our altitude is 64-84 mmHG
  2. If the PaO2 is < 64, the patient is hypoxemic
  3. In General, if PaO2 levels are < 50 mmHg, the patient is in acute respiratory failure, and requires immediate intervention.
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3
Q

Acid Definition

A

A substance that liberates hydrogen ions (H+) in a solution

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4
Q

Acid Effects

A
  1. An Acid is used to neutralize a base
  2. Too much acid in the blood will lower the blood pH to < 7.35
  3. A blood pH < 7.35 is considered Acidotic
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5
Q

Acidemia Definition

A

A state where the blood has a pH < 7.35 (clinical condition of disease state causing the pH to be < 7.35 is unknown)

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6
Q

Acidosis Definition

A

A clinical condition or disease process producing a state that tends to decrease the blood pH.

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7
Q

Base Definition

A

A substance that accepts hydrogen ions (H+) in a solution

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8
Q

Base Effects

A
  1. A Base cand neutralize and acid
  2. Too much base in the blood will raise the pH to > 7.45.
  3. A blood pH > 7.45 is considered alkalotic
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9
Q

Alkalemia Defintion

A

A state where the blood has a pH > 7.45 (clinical condition or disease state causing the pH to be > 7.45 is unknown.)

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10
Q

Alkalosis Definition

A

A clinical condition or disease process that tends to increase the blood pH.

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11
Q

pH Definition

A

A Term used to indicat the hydrogen ion (H+) concentration in a solution

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12
Q

pH effects

A
  1. pH is the prime director when asessing an acidotic or alkalotic state of the blood
  2. The pH tells you only the direction of th the acid-base disturbance
  3. THe normal range of blood pH is 7.35 - 7.45, with a mean value of 7.4. Values under 7.4 are on the “acid” side of thes mean, and values over 7.4 are on the “alkaline” or “base” side of the mean. THis is important when evaluation the presence of compensation.
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13
Q

paCO2 Definition

A

A value that represents the partial pressure of Carbon Dioxide in arterial blood (Generally, PCO2 is used with venous blood samples)

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14
Q

PaCo2 effects

A
  1. CO2 represents the acid (essentially reflecting the carbonic acid content) side of the acis-base balance.
  2. It is normally regulated by the lungs (respiratory), in response to body metabolism.
  3. The normal PaCO2 range for our facility is 32-40 mmHG
  4. A PaCO2 > 40 indicates hypercapnia
  5. A PaCO2 < 32 indicates hypocapnia
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15
Q

Type I Respiratory Failure

A

Hypoxemic Respiratory Failure

  1. Present when the PaO2 is low (less that 50) and the PaCO2 is low to normal.
  2. Type I respiratory failure is the most common and may be secondary to many acute illnesses that cause dfluid fiilling or collapse of the alveoli.
  3. Example Causes: pulmonary edema (cardiogneic or noncardiogenic) pneumonia, atelectasis, or pulmonary hemorrhage.
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16
Q

Type II Respiratory Failure

A

Present when the PaCO2 is 50 mmHg or greater, hypoxemia is seen in this group as well. If the PaCO2 production of the body is constant, then a rise in PaCO2 indicates a reduction in alveolar ventolation.

  • drug overdoses (reducing respiratory drive)
  • neuromuscular disease
  • abnormalities of the chest wall
  • some airway diseases (ex Asthma and COPD)
17
Q

NaHCO3 Definition

A

A value that represents the bicarbonate content of the blood

18
Q

NaHCO3 Interpretations

A
  1. NaHCO3 is a base. Normally it is generated in the kidneys
  2. HCO3 reflects the metabolic regulatin of pH
  3. The Normal HCO3 at our altitude is 18 - 26 mEq/L
  4. A HCO3 < 18 indicates acidemia (i.e. not enough base)
  5. A HCO3 > 26 indicates alkalemia (i.e. too much base)
19
Q

Acid-Base Balance Definition

A

This balance is maintained by a ration of bicarbonate (metabolic) to acid (respiratory) of 20:1

20
Q

Acid Base Interpretations

A
  1. The normal acid-base ration is 20 bicarbonate to 1 carbonic acid
  2. If the ratio is not 20:1, the body begins to compensate to bring the pH within normal limits
  3. Lungs compensate relatively quickly for the kidneys
  4. Kidneys and other buffer systems compensate slowly for the lungs
  5. When all the buffer compensation mechanisms (which occur simultaneeously) fail to correct the pH, we must interven to correct for the patient
21
Q

O2 Saturation (SaO2) Definition

A

Represents the percent of oxygen that is bound to hemoglobin in conjunction with the number of sites on the hemoglobin molecule available for binding, and the affinity those sites have for oxygen. This then gives the percentage of hemoglobin saturated by oxygen.

22
Q

O2 Saturtion (SaO2) Interpretations

A
  1. Normal SaO2 is 92 - 94% for our altitude
  2. Always correlate SaO2 with the patients hemoglobin status. For Example: A patient with a hemoglobin of 9g with a reported 94% saturation is vastly different than a patient with a hemoglobin of 14 and a 94% saturation. The former will not be delivering as much oxygen to the tissues as the latter patient
  3. SaO2 is most accurate when measured off the ABGs versus non-invasive SpO2
23
Q

Base Deficit and Base Excess

Definition

A

A measurement of how much extra NaHCO3 is lost or created as a response to the respiratory status

24
Q

Base Deficit and Base Excess

Interpretations

A
  1. Normal range is from (-) 2 to (+)2 mEq/L
  2. A (-) negative base level outside this range indicates a base deficit. In patients with respiratory alkalosis, the physiologic compensationis for NaHCO3 to get lost via the urine - this creating the computer calculated base deficit.
  3. A (+) positive base level outside the normal range indicates a base excess in patients with chronic repiratory failure type II, creting a chronic respiratory acidosis, excess NaHCO3 will be produced by the kidneys creating a base excess
  4. Clinical studies indicate that base deficit may be an important marker to evaluate the effectiveness of oxygen delivery and cellular respiration, and therby a predictor of mortality
  5. As the base deficit and excess are in response to another, underlying condition, neither of these two conditions should be treated blindly (i.e. without consideatin fo the casuse of the loss or extra produation of NaCO2 as this may worsen the patients condition)
25
Q

PaO2/FiO2 Ratio

Definition

A

This score reflects the correlation between ventilation and perfusion. is is also known as the:

  • Shunt Equation

or

  • hypoxemic score.
26
Q

PaO2/FiO2 ratio

Interpretations

A
  1. It is now a component recorded on most ABG results
  2. It is a recommended standard of care for Mechanically ventilated patiens as part of a comprehensive assessment
  3. The PaO2/FiO2 ration is not corrected for altitude. Also, “normal” may vary based upon the reference thas is used. The normal PaO2/FiO2 ration most commonly used is > 300

NOTE: Even if the criteria for ARDS are not met, low PaO2/FiO2 scores still represent acute lung injury and shunting

NOTE: The PaO2/FiO2 score DOES NOT indicate if the shunt is secondary to inadequate perfusion (or a combination of the two). This must be based on clinical and hemodynamic assessment of the patient.

27
Q

PaO2/FiO2 ratio

Calculation

A

The PaO2/FiO2 ratio is calculated bu taking the PaO2 obtained from ABG results and dividing this by the FiO2 being delivered to the patient (as a decimal)

  • example: PaO2 of 75 mmHg divided by and FiO2 of 0.21 (21% on room air)

PaO2/FiO2 ratio = 75/0.21

PaO2/FiO2 ratio = 357 (no shunting)

28
Q

PaO2/FiO2 Ratio

Acute Lung Injury (ALI)

A
  • Acute Lung Injury is present whten the PaO2/FiO2 score is 250 or less. This means that the patients lungs are the site of an acute inflammatory response. The lower the score, the more profound the injury to the alvolar capillary membrane, and the more profund the deverity of ventilation perfusion mismatching (or shunt)
  • Example: PaO2 is 75 and the patient is on 35% FiO2
  • PaO2/FiO2 ratio = 75/0.35
  • PaO2/FiO2 ratio = 217 (shunting present)
29
Q

PaO2/FiO2 ratio

Acute Respiratory Distress Syndrome (ARDS)

A
  • A PaO2/FiO2 score of 200 or less should start an evaluation for the diagnosis of ARDS. Four criteria are generally used to diagnose ARDS:
  1. A known trigger
  2. Bilaterall infiltrates on the chest x-ray
  3. A normal left ventricular end-diastolic or pulmonary occlusive pressure (to rule out cardiac etiology)
  4. And the PaO2/FiO2 score of 200 or less
30
Q

Anion Gap

Definition

A

A calculation involving the body’s major cation (sodium) and anions (chloride and bicarbonate). It is calculated to help differentiate the cause of a metabolic acidosis

31
Q

Anion Gap

Calculation and Interpretation

A
  1. The formula for the anion gap is: Serum Sodium (mEq/L) minus (serum chloride + bicarbonate) (mEq/L)
  2. Normal anion gap has a range of 6 - 16 mEq/L (in our laboratory)
  3. Elevation of the anion gap is seen i metabolic acidosis conditions such as diabetic ketoacidosis uremia and salicylate toxicity. It is also correlated with lactic acidosis
  4. A metabolic acidosis without an elevated anion gap is usually due to loss of bicarbonate or chloride ion retention
32
Q

Anion Gap

General Uses

A

Though not usualy part of a blood gas, the anion gap has two general uses in acid-base diagnosis

  1. To indicate the type of an established metabolic acidosis
  2. to detect the presence of a hidden metabolic acidosis in a patient with mixed acid-base abnormalities

Blood Gases (Arterial & Venous) Collection Technique & Interpretation (1 decks)

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