Blood gas analysis (BGA) is a determination of the gas distribution of the gases oxygen and carbon dioxide in the blood (partial pressure). In addition, pH, oxygen saturation (SaO2), standard bicarbonate (HCO3-), and base excess (BE, base excess) are also measured. In special cases, the gas distribution of carbon monoxide or nitrogen, etc. is also determined. The determination of blood gases can be carried out with different methods such as volumetric or manometric. Blood gas analysis provides a variety of indications of any acid-base balance disorders that may be present. Physiological aspects of the acid-base balance
In order to maintain the physiological hydrogen ion concentration in the blood, the systems of buffering (mainly via bicarbonate), exhalation of carbon dioxide via the lungs and excretion of hydrogen ions via the kidneys are regulated. However, various disorders can occur due to an imbalance in these regulatory systems:
- Metabolic (metabolic) disorders – caused by disturbances in buffering.
- Respiratory (respiratory-related) disorders – due to disturbances in the exhalation of carbon dioxide.
- Mixed disorders – caused by a combination of the above disorders.
The procedure
Material needed
- Capillary blood (from earlobe, 10 min after hyperemia) → immediate analysis required.
- Arterial blood → immediate analysis required.
Preparation of the patient
- Not necessary
Disruptive factors
- Not known
Normal values – blood
| Parameter | Standard values |
| pH value | 7,36-7,44 |
| Oxygen partial pressure (pO2; PaO2) | 75-100 mmHg |
| Oxygen saturation (SaO2) | 94-98 % |
| Carbon dioxide partial pressure (pCO2; PaCO2) | 35-45 mmHg |
| Standard bicarbonate (HCO3-) | 22-26 mmol/l |
| Base excess (BE) | -2 – +2 mmol/l |
At a pH of < 7.36, one speaks of acidosis. At a pH of > 7.44, one speaks of alkalosis.
Indications
- Assessment of acid-base balance
- Assessment of pulmonary function in
- Acute dyspnea (shortness of breath).
- Respiratory insufficiency (respiratory weakness).
- Resuscitation situation (resuscitation measures).
- Anesthesia monitoring‘or invasive ventilation.
- Other indications include circulatory instability/shock, cardiac arrhythmias, polytrauma, acute abdomen, impaired consciousness/seizures syncope, acute confusional states.
Interpretation
| Respiratory insufficiency (respiratory weakness). | pO2 (PaO2) | pCO2 (PaCO2) |
| Partial insufficiency | ↓ | Normal or still being compensated |
| Globla insufficiency | ↓ | ↑ |
| Acid-base disorder | pH value | pCO² | HCO3- |
| Metabolic acidosis | ↓ | ↓ | ↓ |
| Metabolic alkalosis | ↑ | ↑ | ↑ |
| Respiratory acidosis | ↓ | ↑ | ↑ |
| Respiratory acidosis | ↑ | ↓ | ↓ |
Interpretation
Metabolic acidosis
- Endogenous acidosis:
- Ketoacidosis – hyperacidity of the blood due to increased levels of ketone bodies in the blood; occurs in diabetic coma.
- Lactic acidosis – hyperacidity of the blood due to an increased level of lactate in the blood; occurs in hypoxia of the tissues
- Exogenous acidosis:
- Salicylate intoxication (salicylate poisoning).
- Bicarbonate loss:
- Renal insufficiency (renal dysfunction; renal weakness).
- Renal tubular acidosis (type 2)
- Severe diarrhea (diarrhea)
- Decreased renal excretion:
- Renal insufficiency
- Renal tubular acidosis (type 1)
Metabolic alkalosis
- Acid loss:
- Chronic (persistent) vomiting
- Discharge of gastric juice
- Medications:
- Diuretics (diuretic medications) such as furosemide.
- Mineralocorticoids (high doses) such as fludrocortisone.
Respiratory acidosis
- Hypoventilation (decreased respiration):
- Pulmonary emphysema – lung disease with non-functioning alveoli.
- Pulmonary edema (accumulation of water in the lungs)
- Pneumonia (pneumonia)
Respiratory alkalosis
- Hyperventilation (breathing in excess of demand):
- Psychogenic genesis
- Cerebral genesis
- Altitude stay
For extensive data on the etiology (causes) and pathogenesis (disease development) of acid-base disorders, see the individual topics on acid-base disorders.
