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ABG is useful for:

*For monitoring treatment, adjusting oxygen settings and evaluating client response
-Partial pressure of oxygen (PaO2).
-Partial pressure of carbon dioxide (PaCO2).
-Bicarbonate (HCO3).
-Oxygen saturation (O2Sat)


*pH - Measurement of acidity or alkalinity, based on the hydrogen (H+) ions
-The normal range is 7.35 to 7.45
pH greater than 7.45 = alkalosis
pH less than 7.35 = acidosis


The partial pressure of oxygen that is dissolved in arterial blood.
- The normal range is 80 to 100 mm Hg.


The arterial oxygen saturation.
- The normal range is 95% to 100%.


*The amount of carbon dioxide dissolved in arterial blood.
- The normal range is 35 to 45 mm Hg.
- Remember:
PCO2 greater than 45 = acidosis
pCO2 less than 35 = alkalosis


*The calculated value of the amount of bicarbonate in the
- The normal range is 22 to 26 mEq/liter
- Remember:
HCO3 greater than 26 = alkalosis
HCO3 less than 22 = acidosis


*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.
- Remember:
A negative base excess indicates a base deficit in the blood.

Normal range: pO2


Normal range: pCO2


Normal range: HC03


Rates of correction

-Buffers function almost instantaneously
-Respiratory mechanisms take several minutes to hours
-Renal mechanisms may take several hours to days

The Bodys' Buffer system includes:

-Bllood (protteiin)
-Lungs (Co2)

The arterial blood gas is used to evaluate ___.

Both acid-base balance and oxygenation, each representing separate conditions.

Acid-base evaluation requires ___.

A focus on three of the reported components: pH, PaCO2 and HCO3.

Steps to an Arterial Blood Gas Interpretation: Step 1

*Step one: Identify whether the pH, pCO2 and HCO3 are
abnormal. For each component, label it as "normal",
"acid" or "alkaline".
* The two matching values determine what the problem is.

Steps to an Arterial Blood Gas
Interpretation: Step 1

*If the ABG results are abnormal, determine if the abnormality is due to the kidneys (metabolic) or the lungs (respiratory).
*Match the two abnormalities: Respiratory (lung problem) + Acidosis = Respiratory Acidosis.

What happens when an acid-base imbalance exists
over a period of time?

The body attempts to compensate.

Compensated vs. Uncompensated

*A patient can be uncompensated, partially compensated, or fully compensated.
*When an acid-base disorder is either uncompensated or partially compensated, the pH remains outside the normal range.

The body response to acid-base imbalance is called___.


May be ___ if brought back within normal limits


___ if range is still outside norms.

Partial compensation


*If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation.
*If problem is respiratory, renal mechanisms can bring about metabolic compensation.


*Principal effect of acidosis is depression of the CNS through in synaptic transmission.
*Generalized weakness
*Deranged CNS function the greatest threat
*Severe acidosis causes
- Disorientation
- coma
- death


*Alkalosis causes over excitability of the central and peripheral nervous systems.
*It can cause :
- Nervousness
- muscle spasms or tetany
- Convulsions
- Loss of consciousness
- Death

Respiratory Acidosis

*Carbonic acid excess caused by blood levels of CO2 above 45 mm Hg.
*Hypercapnia - high levels of CO2 in blood
*Chronic conditions:
- Depression of respiratory center in brain that controls breathing rate - drugs or head trauma
- Paralysis of respiratory or chest muscles
- Emphysema

Respiratory Acidosis - Acute conditons:

- Adult Respiratory Distress Syndrome
- Pulmonary edema
- Pneumothorax

Compensation for Respiratory Acidosis

Kidneys eliminate hydrogen ion and retain bicarbonate ion

Signs and Symptoms of Respiratory Acidosis

-Lethargy and disorientation
-Tremors, convulsions, coma
-Respiratory rate rapid, then gradually depressed
-Skin warm and flushed due to vasodilation caused by excess CO2

Treatment of Respiratory Acidosis

-Restore ventilation
-IV lactate solution
-Treat underlying dysfunction or disease

Respiratory Alkalosis

-Carbonic acid deficit
-pCO2 less than 35 mm Hg (hypocapnea)
-Most common acid-base imbalance
-Primary cause is hyperventilation

Respiratory Alkalosis: Conditions that stimulate respiratory center include:

- Oxygen deficiency at high altitudes
- Pulmonary disease and Congestive heart failure - caused by hypoxia
- Acute anxiety
- Fever, anemia
- Early salicylate intoxication
- Cirrhosis
- Gram-negative sepsis

Compensation of Respiratory Alkalosis

-Kidneys conserve hydrogen ion
-Excrete bicarbonate ion

Treatment of Respiratory Alkalosis

-Treat underlying cause
-Breathe into a paper bag
-IV Chloride containing solution - Clions replace lost bicarbonate ions

Metabolic Acidosis: Bicarbonate deficit

Blood concentrations of bicarb drop below 22mEq/L

Bicarbonate deficit Causes:

- Loss of bicarbonate through diarrhea or renal dysfunction
- Accumulation of acids (lactic acid or ketones)
- Failure of kidneys to excrete H+

Symptoms of Metabolic Acidosis

-Headache, lethargy
-Nausea, vomiting, diarrhea

Compensation for Metabolic Acidosis

-Increased ventilation
-Renal excretion of hydrogen ions if possible
-K+ exchanges with excess H+ in ECF
-( H+ into cells, K+ out of cells)
*IV lactate solution
- IV lactate turns to bicarbonate ions in the liver

Metabolic Alkalosis: Bicarbonate excess

Concentration in blood is greater than 26 mEq/L

Bicarbonate excess causes

- Excess vomiting = loss of stomach acid
- Excessive use of alkaline drugs
- Certain diuretics
- Endocrine disorders
- Heavy ingestion of antacids
- Severe dehydration

Compensation for Metabolic Alkalosis

-Alkalosis most commonly occurs with renal dysfunction, so can't count on kidneys
-Respiratory compensation difficult - hypoventilation limited by hypoxia

Symptoms of Metabolic Alkalosis

-Respiration slow and shallow
-Hyperactive reflexes ; tetany
-Often related to depletion of electrolytes
-Atrial tachycardia

Symptoms of Metabolic Alkalosis

-Respiration slow and shallow
-Hyperactive reflexes ; tetany
-Often related to depletion of electrolytes
-Atrial tachycardia

Treatment of Metabolic Alkalosis

-Electrolytes to replace those lost
-IV chloride containing solution
-Treat underlying disorder

Diagnosis of Acid-Base Imbalances

1. Note whether the pH is low (acidosis) or high (alkalosis)
2. Decide which value, pCO2 or HCO3 - , is outside the normal range & could be the cause of the problem. If the cause is a change in pCO2, the problem is respiratory. If the cause is HCO3 - the problem is metabolic.
3. Look at the value that doesn't correspond to the observed pH change. If it is inside the normal range, there is no compensation occurring. If it is outside the
normal range, the body is partially compensating for the problem.

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