acid base Flashcards
what is a normal pH?
7.4 (7.35-7.45)
how is pH regulated?
buffers (bicarbonate and carbon dioxide)
respiration (lungs)
metabolic (kidneys)
lower pH= more _____ (acidic/basic)
acidic
pH is the inverse of ___
how much acid (-log H)
definition of an acid
H+ donor
CO2 is ____
acid
definition of a base
H+ acceptor
HCO3- is ___
base
definition of buffer
ability of a weak acid + anion (base) conjugate pair to resist pH changes after the addition of a strong acid or base
role of carbonic anhydrase
enzyme that converts CO2 to carbonic acid
“emia” refers to
objective sign in the blood
(abnormal pH)
“osis” refers to
the disease process
(metabolic or respiratory process led to abnormal pH)
normal PaCO2
35-45
normal HCO3-
22-26
how is arterial blood gas documented
pH/PaCO2/PO2/HCO3/SaO2
disorder when pH < 7.35
acidemia
disorder when pH > 7.45
alkalemia
disorder when PCO2 < 35
respiratory alkalosis
disorder when PCO2 > 45
respiratory acidosis
disorder when HCO3- < 22
metabolic acidosis
disorder when HCO3 > 26
metabolic alkalosis
how do the lungs try to regulate pH?
they either “blow off” or retain CO2 by altering minute ventilation
how do the kidneys try to regulate pH?
they either increase or decrease reabsorption of HCO3-
how will the lungs try to compensate in metabolic alkalosis?
try to retain CO2 by decreasing minute ventilation to decrease the pH
how will the lungs try to compensate in metabolic acidosis?
try to blow off CO2 by increasing minute ventilation to increase the pH
how will the kidneys compensate for respiratory alkalosis?
try to absorb less bicarb to decrease the pH
how will the kidneys compensate for respiratory acidosis?
try to retain bicarb to increase the pH
what is anion gap
calculation used to find causes of metabolic acidosis
Na - (HCO3 + Cl)
normal range is 4-12
adjust for albumin: add 2.5 to gap for every 1g/dL of albumin below 4
what if anion gap >12?
MUDPILES
Methanol
Uremia
Diabetic ketoacidosis
Propylene glycol
Ingestion
Lactic acidosis
Ethylene glycol
Salicylates
what if anion gap normal?
USEDCAR
Ureteral diversion
Saline infusion
Exogenous acid
Diarrhea
Carbonic anhydrase inhibitors
Adrenal insufficiency
Renal tubular acidosis
what are some signs of respiratory acidosis?
pH < 7.35
CO2 > 45
decreased respiratory rate (retaining acid)
altered mental status, tachycardia
how to treat respiratory acidosis?
mechanical ventilation: make them breathe (hyperventilate them to get them to blow off CO2)
treat underlying cause (opiate antagonist, bronchodilators, etc)
objective signs of metabolic acidosis
pH < 7.35
HCO3 < 22
hyperventilation (from lungs trying to compensate)
+/- elevated anion gap (MUDPILES if elevated, USEDCAR if normal)
what are some potential causes of lactic acidosis?
increased oxygen demand (extreme exercise or seizures)
decreased oxygen delivery (hypotension, severe anemia, severe HF)
drugs (metformin and salicylates)
decreased lactate clearance (hypoperfusion, liver failure)
toxins (methanol, ethanol)
treatment of metabolic acidosis
- correct the underlying cause (whether that is gap or non gap. examples: give antidote, give insulin, dialysis)
- give some base: IV sodium bicarbonate in SEVERE cases when pH <7.15
IV sodium bicarbonate dosing?
(0.5 L/kg x IBW) x (desired bicarb- actual bicarb)
administer 1/2 dose stat push, then give the rest over 4-6 hours
when to give oral bicarb?
in mild case of metabolic acidosis where pH is 7.2-7.4
signs of respiratory alkalosis
pH > 7.45
CO2 < 35
respiratory rate increased (from blowing off CO2)
can happen from altitude, setting mechanical ventilation too fast, hyperventilation.
how to treat respiratory alkalosis
mechanical ventilation, “re-breathing” (brown paper bag), sedatives
prevention of altitude sickness with acetazolamide 1-2 days before ascent and continuing 2 days after arrival at altitude.
signs of metabolic alkalosis
pH > 7.45
HCO3 > 26
2 different etiologies of metabolic alkalosis
Chloride responsive (Cl urine < 15)
Chloride resistant (Cl urine > 25)
what to do if chloride responsive metabolic alkalosis?
calc chloride deficit
(0.2 L/kg x kg) x (103- actual Cl)
replace chloride deficit with normal saline: Chloride deficit (mEq)/ 154 mEq/L
what to do if chloride resistant metabolic alkalosis?
decrease/change corticosteroids
+/- spironolactone 100-400 mg/day in 1-2 divided doses
replete magnesium then potassium
acetazolamide 500 mg IV/PO daily
