Arterial Blood Gases Flashcards
Overall Fct, ABG
Determine respiratory vs metabolic disorder
Define ABG
“Evaluation of lungs’ ability to move oxygen into blood and remove carbon dioxide from blood”
ABG Aquisition
Anatomic: ABG is a blood test taken from the radial artery
Logistic: Usually, a respiratory therapist will take collect the blood. The procedure is painful and difficult (deep artery c proximity to radial vn and nerves) and they are better practiced than most other clinicians
Indications, ABG
(4)
- Assess oxygenation capacity of lungs
- Assess respiratory adequacy
- Assess acid-base balance
- Evaluate pt primary state, compensatory mechanisms, and efficacy of tx
Respiratory Microphysiology
See picture.
Note that alveolar elasticity allows for 100% or near 100% concentration gradients and efficient gas exchange. COPD pts lack this, thus decreasing affinity for gas exchange
ABG Measurements and Normal Ranges
(6 values)
- PaO2 (partial pressure of oxygen) = 80-100 mmHg
- PaCO2 (partial pressure of carbon dioxide) = 35-45 mmHg
- pH = 7.35-7.45
- HCO3 = 24-28 meq/L
- SO2 = 95-100% (critical <90% due to change in dissociation curve)
- Base Excess = -2 - +2 mmol/L
Base Excess
(define, use, value interpretation)
Def: Amt of acid necessary to achieve optimal pH
Use: measure bicarb and overall metabolic acid-base state of pt
Interpretation: units = “equivalents”
- <0 = acidosis (you must take away acid to reach balance)
- >0 = alkalosis (you must add acid to reach balance)
ABG Analysis Algorhythm
Evaluate ABG results in this order
- Acid - base balance
- pH - normal or abnormal?
- PaCO2 - normal or abnormal?
- HCO3 - normal or abnormal?
- PaCO2 and HCO3 - correlate c pH?
- Ventilatory/Respiratory adequacy
- PaO2, SO2 - normal or abnormal?
ABG Signs, Primary Respiratory Distrubance
pH - high
PaCO2 - low
ABG Signs, Metabolic Acidosis
Abnormal Values:
- pH
- HCO3
- B.E.
Primary ABG Distrubances
(4)
- Respiratory Acidosis
- Respiratory Alkalosis
- Metabolic Acidosis
- Metabolic Alkalosis
*Note, these will all couple c compensatory mechanisms, making laboratory interpretation more difficult *
Compensatory Mechanisms
(4 categories, 2/2/3/3 specifics)
- Respiratory Acidosis (high CO2)
- Renal H+ excretion
- Renal HCO3 reabsorption
- Respiratory Alkalosis (low CO2)
- Renal HCO3 excretion
- Renal H+ excretion decrease
- Metabolic Acidosis
- Initial RR increase
- Renal H+ excretion
- Renal HCO3 reabsorption
- Metabolic Alkalosis
- Initial RR decrease
- Renal HCO3 excretion
- Renal H+ retention
Respiratory Acidosis
(Uncompensated and Compensated)
Uncompensated:
- pH < 7.35
- PaCO2 >45 mmHg
- HCO3 - normal
Compensated:
- pH - normal
- PaCO2 >45 mmHg
- HCO3 > 28 meq/L
*General Tx - add bicarb *
Respiratory Alkalosis
(Cause, Uncompensated, Compensated, Tx)
Cause: due to decrease in acid concentration, very rarely due to increase in bases
Uncompensated:
- pH > 7.45
- PaCO2 <35 mmHg
- HCO3 - normal
Compensated:
- pH - normal
- PaCO2 <35 mmHg
- HCO3 <24 meq/L
Tx: Ctrl diarrhea to keep bases in
Metabolic Acidosis
(Associated Condition, Pathophys, Uncompensated, Compensated)
Asst Condition: DKA
Pathyphys: Bicarb is primary distrubance due to metabolic nature (lack of bicarb makes you more acidic)
Uncompensated:
- pH < 7.35
- PaCO2 - normal
- HCO3 - <24 meq/L
- BE < -2
Compensated: (via ventilation changes)
- pH normal
- PaCO2 <35 mmHg
- HCO3 < 24 meq/L
- BE > +2
Metabolic Alkalosis
(pathophys, uncompensated, compensated)
Pathphys: usually due to a change in bicarb concentration; amount of acid will stay the same
Uncompensated:
- pH > 7.45
- PaCO2 - normal
- HCO3 > 28 meq/L
- B.E. > +2
Compensated: (via ventilation changes)
- pH - normal
- PaCO2 > 45 mmHg
- HCO3 > 28 meq/L
- B.E. < -2
Clinical Respiratory Acidosis
(4 disease states, 4 s/sx, 4 dx tests, 8 tx)
Disease States: All reflective of change in ventilation status
- Lung disease
- Airway obstruction
- Respiratory center depression
- Neuromuscular problems
Signs and Symptoms:
- Dyspnea
- **Shallow, rapid ventilations **(in attempt to blow off more CO2, but not usually very helpful)
- Diaphoresis
- Warm, flushed skin
Laboratory Tests:
- ABG
- CXR
- Electrolyte levels, esp K+>5 meq/L
- Other blood tests - tox screen (TCA’s are most common cause)
Treatment:
- Maintain airway
- Bronchodilators
- Supplimental oxygen
- Treat hyperkalemia
- Antibiotics for infection
- Tracheal suctioning
- Monitor cardiac rhtythm
- Observe for neuro changes
Purpose of Compensation
Regulate the body pH. Therefore, other ABG values may change from normal to abnormal when a patient is compensating in order to maintain a safe pH
Potassium Change c Acidosis
K+ is one of the primary intracellular electrolytes. If H+ ions enter the cell, a K+ leaves to maintain intracellular charge.
If done in high amounts hyperkalemia is a risk
Clinical Respiratory Alkalosis
(5 disease states, 8 s/sx, 4 dx studies, 6 tx)
Disease States:
- Hyperventilation
- Acute hypoxia c altitude change
- Severe anemia
- Pulmonary embolus
- Drugs - nicotine, salicylates
S/Sx:
- Tachycardia
- Syncope
- Dyspnea
- Tachypnea
- Diaphoresis
- Anxiety
- Confusion
- Parethesias
Dx Tests:
- ABG
- EKG
- Electrolye analysis (esp K+ for hypokalemia)
- Drug screen (for compensation from ASA overdose)
Treatment:
- Treat underlying cause
- Supplimental oxygen
- Sedative for causative anxiety
- Rebreathe CO2 via paper bag
- VS monitoring
- Observe for neuro changes
Clinical Metabolic Acidosis
(4 disease states, 8 s/sx, 4 dx tests, 6 tx)
Disease States:
- Ketone overproduction - diabetes, alcoholism, hyperthyroidism
- Lactic acidosis - shock, CHF, seizures, liver disease
- Kidney disease
- Drugs - ASA, methanol, ethanol
S/Sx:
- Diarrhea, vomiting
- Muscle weakness
- Hypotension
- Warm, dry, flushed skin
- Lethargy
- Anorexia
- Blindness (c methanol overdose)
- Confusion
- **Kussmal’s respirations **
Dx Studies:
- ABG
- EKG
- Tall T waves
- Wide QRS
- Prolonged PR
- Electrolytes - hyperkalemia
- Glucose and keytones
Treatment:
- Mechanical ventilation, if necessary
- Monitor K+
- Admin rapid acting insulin (get glucose into cells - change pH)
- Dialysis (renal failure only)
- Antidiarrheal med
- Monitor neurologic status
Clinical Metabolic Acidosis
(3 disease states, 6 s/sx, 3 dx studies, 5 tx)
Disease States:
- Diuretics (losing NaCl, reabsorbing more bicarb)
- Excessive acid loss from GI tract (vomiting, NG suctioning)
- Drugs (antacids, diuretics)
S/Sx:
- Hypotension
- Cyanosis
- N/V/anorexia
- Weakness
- Paresthesias
- Confusion
Lab Tests:
- ABG
- EKG (low T waves)
- Electrolytes
- hyperkalemia
- hypercalcemia
Treatment:
- D/C diuretics/NG suctioning
- Antiemetic
- Supplimental O2
- Seizure precautions
- Monitor for muscle weakness, tetany
Name the Condition:
pH - 7.55
PaCO2 - 37 mmHg
PaO2 - 99 mmHg
SO2 - 98%
HCO3 - 31 meq/L
Metabolic Alkalosis, uncompensated
Name the Condition:
pH - 7.36
PaCO2 - 32 mmHg
PaO2 - 44 mmHg
SO2 - 78%
HCO3 - 17 meq/L
Compensated Metabolic Acidosis
