L9: ABGs Flashcards
What’s an Arterial Blood Gas?
used to detect and monitor indices of: oxygenation, ventilation, acid-base balance
→ also quantify: carboxyhemoglobin, methemoglobin
Procedure: draw blood from an artery→ usually radial (+/- brachial, femoral) with an anticoagulant→ place on ice→ analysis in lab→ results in 5-15 minutes
Normal pH
7.35-7.45 (use 7.4)
Normal pO2
80-100 mmHg
Normal O2 saturation
> 95
Normal pCO2
35-45 mmHg
Normal HCO3
22-26 mmol/L
Is oxygenation/pO2 used to determine acid-base conditions?
NO
Why bother with pO2?
More reliable than pulse ox
Acidemia
pH<7.35
Alkalemia
pH>7.45
In a mixed disorder
pCO2 and HCO3 move in opposite directions
High anion gap metabolic acidosis
“MUDPILES” Methanol Uremia Diabetic ketoacidosis Propylene glycol Iron/Isoniazid Lactate (lactic acidosis) Ethanol/Ethylene glycol Salicylates (ASA)/Starvation
General rules for acid-base disorders
It is only possible to have one respiratory disorder at a time, but 2 metabolic disorders can be present at once
Normal pH does not mean there is not an acid-base disorder: could have acidosis+alkalosis
Low bicarb is usually pathologic
MUDPILES: M
Methanol
MUDPILES: U
Uremia
MUDPILES: D
Diabetic ketoacidosis
MUDPILES: P
Propylene glycol
MUDPILES: I (2)
Iron/Isoniazid
MUDPILES: L
Lactate (lactic acidosis)
MUDPILES: E (2)
Ethanol/Ethylene glycol
MUDPILES: S (2)
Salicylates (ASA)/Starvation
Non anion gap metabolic acidosis is caused by (3)
GI bicarb loss
Renal bicarb loss
Hyperchloremia
Treat metabolic acidosis:
Treat underlying cause +/- sodium bicarbonate (immediate period), allow for normal respiratory compensation
Hyperchloremia is due to
due to normal saline resuscitation
Renal bicarb loss is due to
Early renal failure
Renal tubular acidosis
Carbonic anhydrase inhibitors (acetazolamide)
Aldosterone inhibitors (spironolactone)
GI bicarb loss is due to
Diarrhea
GI fistulas
Utererosigmoidostomy
Effects of vomiting vs diarrhea
Vomiting: lose acid= metabolic alkalosis
Diarrhea: lose bicarb= metabolic acidosis
Urine chloride <25= chloride/fluid responsive metabolic alkalosis is caused by
GI losses: vomiting, NG suction
Diuretics→ contraction alkalosis
Cystic fibrosis
Treat with fluids
Urine chloride >25= non-chloride responsive metabolic alkalosis is caused by
Barter’s syndrome Cushing’s Hyperaldosteronism Potassium depletion Citrate toxicity→ massive blood transfusion protocol Chronic diuretics Renin secreting tumor Treat underlying cause +/- potassium
Hyperchloremia
Non-anion gap metabolic acidosis
Diarrhea
Non-anion gap metabolic acidosis
Cushing’s
non-chloride responsive metabolic alkalosis
Hyperaldosteronism
non-chloride responsive metabolic alkalosis
Diabetic ketoacidosis
High anion gap metabolic acidosis
Potassium depletion
non-chloride responsive metabolic alkalosis
Citrate toxicity
non-chloride responsive metabolic alkalosis
Ethanol
High anion gap metabolic acidosis
Diuretics
chloride/fluid responsive metabolic alkalosis
contraction alkalosis
Renin secreting tumor
non-chloride responsive metabolic alkalosis
Chronic diuretics
non-chloride responsive metabolic alkalosis
Barter’s syndrome
non-chloride responsive metabolic alkalosis
Methanol
High anion gap metabolic acidosis
Ethylene glycol
High anion gap metabolic acidosis
Isoniazid
High anion gap metabolic acidosis
Uremia
High anion gap metabolic acidosis
Treatment for chloride/fluid responsive metabolic alkalosis
Fluids
Cystic fibrosis
chloride/fluid responsive metabolic alkalosis
Aldosterone inhibitors (spironolactone)
Non-anion gap metabolic acidosis
non-chloride responsive metabolic alkalosis treatment
Treat underlying cause +/- potassium
Carbonic anhydrase inhibitors (acetazolamide)
Non-anion gap metabolic acidosis
Renal tubular acidosis
Non-gap metabolic acidosis
Carbonic anhydrase inhibitors (acetazolamide)
Non-anion gap metabolic acidosis
Respiratory acidosis
poor ventilation causing accumulation of CO2
Causes of Respiratory acidosis
Acute airway obstruction: foreign body, tumor, laryngospasm/bronchospasm
Lung disease: severe pneumonia/PE/COPD exacerbation, pulmonary edema, pulmonary fibrosis
CNS depression: narcotics, CNS event, trauma, central sleep apnea
Neuromuscular disorder: Guillain-Barre, Myasthenia Gravis, Brain stem/spinal cord injury,
Impaired lung motion
Inappropriate mechanical ventilation settings
Respiratory alkalosis
excess elimination of CO2 from the lungs→ pCO2<35
lightheadedness, palpitations, tachypnea, +/- paresthesias
Causes of Respiratory alkalosis
Hyperventilation Compensatory mechanism in sepsis Anxiety, pain CNS: neurogenic hyperventilation Salicylate overdose Pregnancy High altitude, Hypoxemia Hepatic encephalopathy
Hyperventilation
Respiratory alkalosis
Acute airway obstruction: foreign body, tumor, laryngospasm/bronchospasm
Respiratory acidosis
Compensatory mechanism in sepsis
Hyperventilation causing Respiratory alkalosis
Inappropriate mechanical ventilation settings
Respiratory acidosis
CNS depression: narcotics, CNS event, trauma, central sleep apnea
Respiratory acidosis
Anxiety, pain
causes Hyperventilation causing Respiratory alkalosis
Impaired lung motion
Respiratory acidosis
CNS: neurogenic hyperventilation
Respiratory alkalosis
Neuromuscular disorder: Guillain-Barre, Myasthenia Gravis, Brain stem/spinal cord injury
Respiratory acidosis
Lung disease: severe pneumonia/PE/COPD exacerbation, pulmonary edema, pulmonary fibrosis
Respiratory acidosis
Salicylate overdose
causes Hyperventilation causing Respiratory alkalosis
High altitude, Hypoxemia
causes Hyperventilation causing Respiratory alkalosis
Hepatic encephalopathy
causes Hyperventilation causing Respiratory alkalosis
Pregnancy
causes Hyperventilation causing Respiratory alkalosis
Pregnancy
causes Hyperventilation causing Respiratory alkalosis
Treat respiratory acidosis
Treat underlying cause, respiratory support (BiPAP)
Differentiate from chronic acidosis→ more stable (COPD) especially if with good compensation, won’t need BiPAP
Treat respiratory alkalosis
Treat underlying cause