Flashcards in Acid Base Disorders Deck (32):
Normal anion gap
5-15 , normal approx 12
How do kidneys help when there is fixed acid in the blood?
Kidneys reabsorb more HCO3 to help turn the free H into CO2 that is formed and removed by lungs thereby maintaining pH
Acidosis vs alkalosis on O2 dissociation curve
acidosis - right shift (decreases affinity of hemoglobin -> increases O2 delivery to tissues)
alkalosis - left shift (increases affinity -> decreases O2 delivery to tissues)
What effects can acidosis and alkalosis both cause?
Effects of acidosis on body
decreased pulmonary blood flow
hyperkalemia (acid pulls K from cells)
impairs myocardial function
Effects of alkalosis on body
decreases cerebral blood flow
causes of anion gap met acidosis
Salicylate OD (aspirin)
What kinds of things can cause ketoacidosis besides diabetes?
prolonged starvation or prolonged alcohol abuse (due to malnutrition)
What kinds of things can cause lactic acidosis?
low tissue perfusion, shock, excessive energy expenditure (strenuous exercise, seizures)
anything that that increases O2 demand
What acid base disturbances does salicylate overdose cause?
primary respiratory alkalosis AND primary metabolic acidosis
What causes normal AG acidosis (aka hyperchloremic metabolic acidosis)
- diarrhea (MCC)
- RTA (type 1 and type 2)
- carbonic anhydrase inhibitors (acetazolamide)
- pancreatic/small bowel fistulas
What clinical features do you see in metabolic acidosis?
- hyperventilation/Kussmaul deep breathing to blow off CO2 for compensation
- decreased CO and tissue perfusion
Winter formula for respiratory compensation
1.5(HCO3) + 8 -> +/-2
if PCO2 falls within expected range -> acute compensated
if below expected range -> met acidosis + resp alkalosis
if higher than expecte range -> met acidosis + resp acidosis -> VERY BAD, (i.e. child with asthma is compensating by lowering pCO2 but then pCO2 becomes normal with no treatment...FUCK THIS IS BAD)
What two general events to consider in metabolic alkalosis
1. event that starts met alk (loss of H via vomiting/gastric drainage, etc or increase of HCO3 concentration due to ECF contraction)
2. event that maintains met alk (kidney can't get rid of extra bicarb)
What other value to look at besides EBG and serum electrolytes in evaluating met alk?
(urine Cl<10) = saline sensitive
(urine Cl>20) = saline resistant
What characterizes saline sensitive met alk?
hypokalemia and ECF contraction
What causes saline sensitive met alk?
- vomiting, nasogastric suction (patient loses HCl so makes extra HCO3 to compensate)
- villous adenoma of colon, diarrhea with high Cl content
What characterizes saline resistant met alk?
ECF EXPANSION and HTN
What causes saline resistant met alk?
- adrenal disorders like primary hyperaldosteronism (MCC) -> excessive mineralcorticoid = increased Na and HCO3 reabsorption and volume expansion = less reabsorption of Cl
- Cushing, severe K deficiency, Bartter syndrome, diuretics
Define respiratory acidosis
lowered blood pH<7.4 due to increased PCO2 (>40)
Acute compensation for resp acd
HCO3 increases by 1 for every 10 increase in PCO2
Chronic compensation for resp acd and what conditions would you usually see this?
HCO3 increases by 4 for every 10 increase in PCO2
you would typically see this in patients with underlying disease like COPD where they're used to not being able to blow off as much CO2
Causes of resp acidosis?
ANYTHING THAT CAUSES ALVEOLAR HYPOVENTILATION
- lung disease (COPD, obstruction)
- respiratory muscle fatigue
- neuromuscular disease like myasthenia gravis
- drugs that depress CNS like morphine, anesthetics, sedatives
Clinical features of resp acidosis
- somnolence, confusion, myoclonus with asterixis
- headaches, confusion, PAPILLEDEMA = acute CO2 retention
How to treat resp acidosis
- if PaO2 is low, give supplemental O2...EXCEPT IN PATIENTS WITH CHRONIC CO2 RETENTION LIKE COPD...this can worsen resp acd
- anything to help alveolar ventilation (ex: pulm toilet, remove obstruction
- intubate in severe cases
If you have drug induced resp acidosis, what antidote will usually help?
What are indications for ventilation/intubation in context of resp acidosis?
- severe acidosis
- pCO2 > 60 or low PO2 even after O2 administration
- AMS, obtunded
- prolonged labored breathing/respiratory fatigue
How does increased PCO2 cause CNS depression?
increased PCO2 -> increased cerebral bloodflow -> increased ICP and generalized CNS depression
Definition of resp alk
increased blood pH due to decreased PCO2
Compensation for resp alk (acute and chronic)
acute: every 10 mmhg decrease in PCO2, HCO3 decreases 1-2
chronic: every 10 mmhg decrease in PCO2, HCO3 decreases 5-6
Causes of resp alk
ANYTHING THAT CAUSES ALEOLAR HYPERVENTILATION
-liver disease (cirrhosis)
-PE, pneumonia, asthma