ABG Analysis

what 5 components do ABGs examine

1. arterial pH (acid-base balance)

2. PaCO2 (ventilation)

3. PaO2 (oxygenation)

4. bicarbonate (HCO3-)

5. base excess

what is the normal value for ARTERIAL pH

7.35-7.45

what is the normal value for PaCO2

35-45 mmHg

what is the normal value for PaO2

80-100 mmHg

what is the normal value for HCO3-

22-26 mEq/L

how are ABGs reported

PaO2/PaCO2/pH/HCO3-

followed by a +/- number (BE)

what is HIGH pH called

alkalosis

what is LOW pH called

acidosis

ALKALOSIS (high pH) is caused by (2)

1. decreased PaCO2

2. increased HCO3-

ACIDOSIS (low pH) is caused by (2)

1. increased PaCO2

2. decreased HCO3-

what is PaCO2

partial pressure of carbon dioxide in plasma

what does PaCO2 reflect

adequacy of alveolar ventilation

what do HIGH PaCO2 LEVELS cause

low pH (acidic) = hypoventilation

what do LOW PaCO2 LEVELS cause

high pH (basic) = hyperventilation

what does HYPOVENTILATION result in

low pH (acidic)

what does HYPERVENTILATION result in

high pH (basic)

what is PaO2

partial pressure of oxygen in plasma

what does PaO2 reflect

circulating oxygen available for tissues to use

what does HCO3- act as

a buffer to prevent extreme fluctuations in acid-base balance

what do significant changes in blood pH >7.8 or <6.8 interfere with

cellular functioning

(if uncorrected = death)

what 2 ORGANS take on the role of REGULATING ACID-BASE BALANCES

1. lungs

2. kidneys

how do the LUNGS regulate acid-base balance

by blowing off (hyperventilation)/retaining (hypoventilation) PaCO2

when does RESPIRATORY COMPENSATION begin

within second by alveolar hyper/hypoventilation

how do the KIDNEYS regulate acid-base balance

by retaining/excreting bicarbonate + hydrogen ions

what does RENAL COMPENSATION require to significantly effect pH

at least 12-24 hours

what are 4 ACID-BASE STATES

1. respiratory acidosis

2. respiratory alkalosis

3. metabolic acidosis

4. metabolic alkalosis

what is the MAJOR CAUSE of RESPIRATORY ACIDOSIS

high PaCO2

what is HIGH PaCO2 due to

alveolar hypoventilation

what are 2 FEATURES of RESPIRATORY ACIDOSIS

1. pH < 7.35

2. PaCO2 > 45 mmHg

what are 5 COMMON CAUSES of RESPIRATORY ACIDOSIS

1. CNS depression (TBI, narcotics, sedatives, anesthesia)

2. impaired respiratory muscle function (SCI, neuromuscular diseases)

3. pulmonary disorders (atelectasis, pneumonia, pneumothorax, pulmonary edema, bronchial obstruction, COPD)

4. massive pulmonary embolus

5. hypoventilation (pain, chest wall injury/deformity, rib fractures, abdominal distention, sleep apnea)

what are 3 SIGNS + SYMPTOMS of RESPIRATORY ACIDOSIS

1. pulmonary

- dyspnea

- respiratory distress

- shallow respirations

2. neurological

- HA

- restlessness

- drowsiness

- lethargy

- confusion

- altered mental status

- tremor

- coma

3. cardiovascular

- tachycardia

- dysrhythmia

- HTN

what is the MAJOR CAUSE of RESPIRATORY ALKALOSIS

low PaCO2

what is LOW PaCO2 due to

alveolar hyperventilation

what are 2 FEATURES of RESPIRATORY ALKALOSIS

1. pH > 7.45

2. PaCO2 < 35 mmHg

what are 6 COMMON CAUSES of RESPIRATORY ALKALOSIS

1. psychological responses (anxiety/fear)

2. pain

3. increased metabolic demands (fever, sepsis, pregnancy)

4. medications (respiratory stimulants)

5. CNS lesions

6. cardiopulmonary (CHF, PE, asthma, ARDS, hypoxia)

what are 4 SIGNS + SYMPTOMS of RESPIRATORY ALKALOSIS

1. neurological

- light-headedness

- numbness/tingling

- confusion

- inability to concentrate

- blurred vision

2. cardiovascular

- palpitations

- dysrhythmia

- diaphoresis (excessive sweating)

3. dry mouth

4. tetanic spasm of arms/legs

what is the MAJOR CAUSE of METABOLIC ACIDOSIS

low HCO3-

what are 2 FEATURES of METABOLIC ACIDOSIS

1. pH < 7.35

2. HCO3- < 22 mEq/L

what are 5 COMMON CAUSES of METABOLIC ACIDOSIS

1. renal failure

2. diabetes/DKA

3. anaerobic metabolism (lactic acidosis)

4. starvation

5. alcoholism

6. diarrhea

7. ostomy drainage

8. parenteral nutrition (extended need)

9. salicylate intoxication (aspirin)

what are 4 SIGNS + SYMPTOMS of METABOLIC ACIDOSIS

1. pulmonary

- Kussmaul respirations

2. neurological

- HA

- restlessness

- drowsiness

- lethargy

- confusion

- coma

3. cardiovascular

- dysrhythmia

4. warm + flushed skin

what are KUSSMAUL RESPIRATIONS

deep desperate breathing

- attempt to increase pH by removing CO2

what is the MAJOR CAUSE of METABOLIC ALKALOSIS

high HCO3-

what are 2 FEATURES of METABOLIC ALKALOSIS

1. pH >7.45

2. HCO3- > 26 mEq/L

what are 4 COMMON CAUSES of METABOLIC ALKALOSIS

1. excess base

- excess ingestion of antacids

- excess use of bicarbonate

- use of lactate in dialysis

2. loss of acids

- vomiting

- nasogastric suction

- hypochloremia (decreased Cl-)

- hypokalemia

- excess diuretics

- high levels of aldosterone (steroids)

3. banked blood transfusions

4. cushing's syndrome (overactive adrenal gland)

what are 4 SIGNS + SYMPTOMS of METABOLIC ALKALOSIS

1. neurological

- dizziness

- lethargy

- disorientation

- seizures

- coma

2. pulmonary

- respiratory depression (try to retain PaCO2 to decrease pH)

3. musculoskeletal

- weakness

- muscle twitching

- muscle cramps

- tetany

4. gastrointestinal

- nausea

- vomiting

what are 2 features of FULLY COMPENSATED ABGs

1. pH normal range

2. both PaCO2 + HCO3- out of range

what are 2 features of PARTIALLY COMPENSATED ABGs

1. pH out of normal range (but moving near normal)

2. both PaCO2 + HCO3- out of range

what are 2 features of UNCOMPENSATED ABGs

1. pH out of normal range

2. only PaCO2 or HCO3- out of range (not both)

practice #1

pH: 7.30

PaCO2: 55 mmHg

HCO3-: 26 mEq/L

uncompensated respiratory acidosis

explanation:

pH: low

PaCO2: high

HCO3-: normal range

- respiratory acidosis = high PaCO2 + low pH (acidic)

- uncompensated = only PaCO2 out of range + pH out of range

practice #2

pH: 7.48

PaCO2: 44 mmHg

HCO3-: 32 mEq/L

uncompensated metabolic alkalosis

explanation

pH: high

PaCO2: normal range

HCO3-: high

- metabolic alkalosis = high pH + high HCO3-

- uncompensated = pH out of range + only HCO3- out of range

practice #3

pH: 7.38

PaCO2: 56 mmHg

HCO3-: 35 mEq/L

fully compensated respiratory acidosis

explanation:

pH: normal (lower end of range)

PaCO2: high

HCO3-: high

- respiratory acidosis = high PaCO2 + pH lower end of range

- full compensated = pH normal range + both PaCO2 and HCO3- out of range

practice #4

pH: 7.33

PaCO2: 62 mmHg

HCO3-: 35 mEq/L

partially compensated respiratory acidosis

explanation

pH: low

PaCO2: high

HCO3-: high

- respiratory acidosis = high PaCO2 + low pH

- partially compensated = pH outside normal (moving to normal) + both PaCO2 and HCO3- out of range

practice #5

pH: 7.29

PaCO2: 30 mmHg

HCO3-: 18 mEq/L

partially compensated metabolic acidosis

explanation:

pH: low

PaCO2: low

HCO3-: low

- metabolic acidosis = low HCO3- + low pH

- partially compensated = pH outside normal (moving to normal) + both PaCO2 and HCO3- out of range