Arterial blood gas analysis: Difference between revisions
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==='''pH'''=== | ==='''pH'''=== | ||
*Measurement of acidity or alkalinity of solution . The normal range is 7.35 to 7.45 | *Measurement of acidity or alkalinity of solution . The normal range is 7.35 to 7.45 | ||
*pH > 7.45 = alkalosis | *pH > 7.45 = [[alkalosis]] | ||
*pH< 7.35 = acidosis | *pH< 7.35 = [[acidosis]] | ||
==='''PaO<sub>2</sub>'''=== | ==='''PaO<sub>2</sub>'''=== | ||
The partial pressure of oxygen that is dissolved in arterial | *The partial pressure of oxygen that is dissolved in the arterial serum that is ''not'' carried by hemoglobin. The normal range is 80 to 100 mm Hg. | ||
'''SaO<sub>2</sub>''' | **Used to assess alveolar-arterial (A-a) gradient, or [[P<sub>a</sub>O<sub>2</sub>/FiO<sub>2</sub> ratio]]. | ||
The arterial oxygen saturation | ==='''SaO<sub>2</sub>'''=== | ||
*The arterial oxygen saturation | |||
*The normal range is 95% to 100%. | |||
==='''pCO<sub>2</sub>'''=== | ==='''pCO<sub>2</sub>'''=== | ||
*The amount of carbon dioxide dissolved in arterial blood | *The amount of carbon dioxide dissolved in arterial blood | ||
*pCO<sub>2</sub> >45 = acidosis | *The normal range is 35 to 45 mm Hg. | ||
*pCO<sub>2</sub> <35 = alkalosis | *pCO<sub>2</sub> >45 = primary [[respiratory acidosis]] | ||
*pCO<sub>2</sub> <35 = primary [[respiratory alkalosis]] | |||
==='''HCO<sub>3</sub>'''=== | ==='''HCO<sub>3</sub>'''=== | ||
The calculated value of the amount of bicarbonate in the bloodstream | *The calculated value of the amount of bicarbonate in the bloodstream | ||
HCO3 > 26 = alkalosis | *The normal range is 22 to 26 mEq/liter | ||
HCO3 < 22 = acidosis | *HCO3 > 26 = [[alkalosis]] | ||
*HCO3 < 22 = [[acidosis]] | |||
==='''B.E.'''=== | ==='''B.E.'''=== | ||
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==ABG in Hypothermia== | ==ABG in [[Hypothermia]]== | ||
*Blood gas analyzers typically warm blood to 37°C before making calculations however physicians should simply interpret the values as given by the lab | *Blood gas analyzers typically warm blood to 37°C before making calculations however physicians should simply interpret the values as given by the lab | ||
*At any temperature, a pH of 7.4 and a PCO2 of 40 mm Hg represent normal acid-base balance | *At any temperature, a pH of 7.4 and a PCO2 of 40 mm Hg represent normal acid-base balance | ||
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Oxygen and carbon dioxide increase in solubility as water temperature lowers, so warmed ABGs from hypothermic patients with show a higher PaO2, higher PaCO2 and a lower pH than what is actually present in the patient’s blood although the clinical implications of this change is not significant.<ref>Ashwood ER, Kost G, Kenny M. Temperature correction of blood-gas and pH measurements. Clin Chem. 1983 Nov;29(11):1877-85. Review. PubMed PMID: 6354511.</ref> | Oxygen and carbon dioxide increase in solubility as water temperature lowers, so warmed ABGs from hypothermic patients with show a higher PaO2, higher PaCO2 and a lower pH than what is actually present in the patient’s blood although the clinical implications of this change is not significant.<ref>Ashwood ER, Kost G, Kenny M. Temperature correction of blood-gas and pH measurements. Clin Chem. 1983 Nov;29(11):1877-85. Review. PubMed PMID: 6354511.</ref> | ||
*PO2 is 5 mmHg lower for each degree below 37C° | *PO2 is 5 mmHg lower for each degree below 37C° | ||
*PCO2 is 2mmHg | *PCO2 is 2mmHg lower for each degree below 37C° | ||
==ABG after Cardiac Arrest== | ==ABG after [[Cardiac Arrest]]== | ||
pH of blood dependent on: | pH of blood dependent on: | ||
*cause of arrest | *cause of arrest | ||
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*insufficient oxygenation during resuscitation | *insufficient oxygenation during resuscitation | ||
*aspiration | *aspiration | ||
*pulmonary edema | *[[pulmonary edema]] | ||
*PE | *[[PE]] | ||
*primary respiratory pathology | *primary respiratory pathology | ||
Latest revision as of 15:30, 11 October 2019
Basics
pH
- Measurement of acidity or alkalinity of solution . The normal range is 7.35 to 7.45
- pH > 7.45 = alkalosis
- pH< 7.35 = acidosis
PaO2
- The partial pressure of oxygen that is dissolved in the arterial serum that is not carried by hemoglobin. The normal range is 80 to 100 mm Hg.
- Used to assess alveolar-arterial (A-a) gradient, or [[PaO2/FiO2 ratio]].
SaO2
- The arterial oxygen saturation
- The normal range is 95% to 100%.
pCO2
- The amount of carbon dioxide dissolved in arterial blood
- The normal range is 35 to 45 mm Hg.
- pCO2 >45 = primary respiratory acidosis
- pCO2 <35 = primary respiratory alkalosis
HCO3
- The calculated value of the amount of bicarbonate in the bloodstream
- The normal range is 22 to 26 mEq/liter
- HCO3 > 26 = alkalosis
- HCO3 < 22 = acidosis
B.E.
- The base excess indicates the amount of excess or insufficient level of bicarbonate in the system.
- The normal range is -2 to +2 mEq/liter.
- A negative base excess indicates a base deficit in the blood.
ABG in Hypothermia
- Blood gas analyzers typically warm blood to 37°C before making calculations however physicians should simply interpret the values as given by the lab
- At any temperature, a pH of 7.4 and a PCO2 of 40 mm Hg represent normal acid-base balance
The best (simplest) approach is to use uncorrected ABG values compared with the normal values at 37°C[1]
TEMPERATURE CORRECTION OF PO2 and PCO2
Oxygen and carbon dioxide increase in solubility as water temperature lowers, so warmed ABGs from hypothermic patients with show a higher PaO2, higher PaCO2 and a lower pH than what is actually present in the patient’s blood although the clinical implications of this change is not significant.[2]
- PO2 is 5 mmHg lower for each degree below 37C°
- PCO2 is 2mmHg lower for each degree below 37C°
ABG after Cardiac Arrest
pH of blood dependent on:
- cause of arrest
- duration of arrest when ABG is taken
- the quality of the CPR and ventilation the patient is receiving
- temperature of the patient when ABG taken
- drugs administered during arrest (ie. Adrenaline and NaHCO3)
Elevated pCO2
- often due to inadequate ventilation during resuscitation
Low PaO2
- insufficient oxygenation during resuscitation
- aspiration
- pulmonary edema
- PE
- primary respiratory pathology
Hyperkalemia Causes
- cell death
- loss of cell membrane integrity and acidosis
- other sources such as missed dialysis
References
- ↑ Burnett RW, Noonan DC. Calculations and correction factors used in determination of blood pH and blood gases. Clin Chem. 1974 Dec;20(12):1499-506. Review.
- ↑ Ashwood ER, Kost G, Kenny M. Temperature correction of blood-gas and pH measurements. Clin Chem. 1983 Nov;29(11):1877-85. Review. PubMed PMID: 6354511.