Acid base disorders Flashcards
Where is H+ reabsorbed
Via distal tubule and collecting duct
Where does HCO3 enter/leave the body
HCO3 enter/leaves body via kidneys
Via proximal tubule
Henderson-Hasselbalch equation
pH= 6.1 + log (serum bicarb/0.03 x PaCO2)
Consequences of acidosis: cardiovascular
Impaired contractility…7.2
Decreased contractility
Decreased arterial blood pressure
Sensitive to re-entry dysrhythmias
Decreased threshold for v-fib
Decreased responsiveness to catecholamines=7.1
Consequences of acidosis: Nervous system
Obtundation
Coma
Consequences of acidosis: pulmonary
Hyperventilation
Dyspnea
Respiratory muscle fatigue
Consequences of acidosis: metabolism
Hyperkalemia
Insulin resistance
Inhibition of anaerobic glycolysis
Respiratory acidosis definition
“An acute decrease in alveolar ventilation results in increase PaCO2”
To decrease pH to < 7.35
“resp failure”- extended number of days
Acute hypercarbia compensation
↑ PaCO2 of 10 mmHg = ↑ plasma HCO3- of 1 mmol/L (1meq/L)
Chronic hypercarbia compensation
↑ PaCO2 of 10 mmHg = ↑ plasma HCO3- by 3 mmol/L (3 meq/L)
Tx for resp acidosis
Mechanical ventilation
If hypercarbia marked and CO2 narcosis present
Caution with chronic hypercarbia reversal….excessive bicarb causes CNS irritability…seizures
Metabolic acidosis definition
“ a lowered blood pH which stimulates the respiratory center to hyperventilate”
Respiratory compensation does not fully counter excessive acid production
Equations for compensated metabolic acidosis
1.5 x HCO3- + 8
If PaCO2 is higher than 26, compensation is inadequate; concomitant problem
For every 1 mEq/L ↓ in BE, PaCO2 should fall 1.2 mm Hg
High anion gap
Additional acid is added to extracellular space
Acid dissociates, H+ ion combines with bicarb….carbonic acid…decreased available measurable bicarb= decreasing anion concentration
Causes of high anion gap
Lactic acidosis
Ketoacidosis
Renal failure
Poisonings
Simple anion gap equation
Na+ - (Cl- + HCO3-) = 12-14 mEq/L
Conventional anion gap equation
(Na+ + K+) - (Cl- + HCO3-) = 14-18 mEq/L
Treatment for metabolic acidosis
Treat the cause!!!
Ketoacidosis: insulin and fluids
Lactic acidosis: improve tissue perfusion
r/t renal failure: dialysis
Full bicarb Correction Dos
Full Correction Dose (mmol) = 0.3 x base deficit (mmol/L) x wt(kg)
Give ½ dose and reassess
Urgent/Emergent treatment for metabolic acidosis
consider hemodynamic monitoring
Guide fluid admin
Monitors cardiac function
Frequent lab
Respiratory alkalosis definition
an acute increased alveolar ventilation
Results in decreased PaCO2
pH > 7.45
Causes of resp alkalosis
Pregnancy
High altitude
Iatrogenic hyperventilation (during perioperative period)
Salicylate overdose
Symptoms of resp alkalosis
Vasoconstriction;
lightheaded
Visual disturbance
Dizziness
Greater binding of calcium to albumin
Signs/Sx of hypocalcemia due to resp alkalosis
Paresthesia, muscle spasm, cramps, tetany, circumoral numbness, seizures
Trousseau’s sign; bp cuff -> carpopedal spasm
Chvostek’s sign; facial nerve tap -> irritability
Branches of facial nerve
two chickens bit my zebra
temporal
cervical
buccal
marginal mandibular
zygomatic
Anesthesia management of resp alkalosis
Consequence of pain, anxiety, full bladder, agitation
Poor mechanical ventilation strategy
Therapeutic hyperventilation?
Metabolic alkalosis definition
“marked increase in plasma bicarb usually compensated for by an increase in carbon dioxide”
Causes of metabolic alk
Hypovolemia
Vomiting
NG suction
Diuretic therapy
Bicarb administration
Hyperaldosteronism
Renal or extrarenal causes
Net loss of H+ or net gain of bicarb
Treatment for metabolic alk
depends on cause
Volume depletion: saline fluid resuscitation
Gastric loss: PPI’s
Loop diuretics: add K+ sparing diuretics
pH 7.35, PCO2 48, HCO3 24
resp acidocis
Increase bicarb
pH 7.58, PCO2 38, HCO3 29
Metabolic alkalosis
Increase acid
pH 7.28, PCO2 42, HCO3 18
metabolic acidosis
Increase bicarb
pH 7.48, PCO2 32, HCO3 22
resp alkalosis
Decrease bicarb to make comp
PaO2= 80 -100 mmhg on 21%.
on 100% oxygen pao2 should be ______
500 mmHg
factor of 5
Excess production of H+ (in relation to hydroxyl ions)
Acidemia
Excess production of OH- (in relation to hydrogen ions)
Alkalemia
If both PaCO2 and/or HCO3 change in same direction
primary disorder with secondary compensation
If both PaCO2 and/or HCO3 change in different direction
mixed acid/base disorder
what is metabolic acidosis associated with
Assoc with alterations in transcellular ion pumps and ↑ ionized calcium
Problems with ion pumps
Causes of R shift
decreased affinity for O2.
increase pCO2
increase H+ (dec pH)
inc 2,3 DPG
inc Temp
Causes of L shift on oxy hb dissociation curve
Bicarb equation for calculating metabolic acidosis
(1.5 x HCO3-) + 8
If PaCO2 is higher than calculated CO2, compensation is inadequate; concomitant problem
Base excess equation for calculating metabolic acidosis compensation
hyperchloremic metabolic acidosis
Bicarb loss is countered by net gain of chloride ions
what can cause metabolic acidosis with a normal anion gap
Sodium chloride infusions
Diarrhea
Early renal failure
hyperchloremic metabolic acidosis
Bicarb loss is countered by net gain of chloride ions
Causes of L shift on oxy hb dissociation curve
increased affinity for O2
dec PCO2
dec H+
dec 2,3 DPG
dec temp
fetal hbg
what is metabolic acidosis associated with
Assoc with alterations in transcellular ion pumps and ↑ ionized calcium
Problems with ion pumps
what can cause metabolic acidosis with a normal anion gap
Sodium chloride infusions
Diarrhea
Early renal failure
Bicarb equation for calculating metabolic acidosis compensation
(1.5 x HCO3-) + 8
If PaCO2 is higher than calculated CO2, compensation is inadequate; concomitant problem
Causes of R shift
decreased affinity for O2.
increase pCO2
increase H+ (dec pH)
inc 2,3 DPG
inc Temp
Base excess equation for calculating metabolic acidosis compensation
For every 1 mEq/L ↓ in BE, PaCO2 should fall 1.2 mm Hg
if this is true then it is compensated
Otherwise compensation inadequate
Base excess equation for calculating metabolic acidosis compensation
For every 1 mEq/L ↓ in BE, PaCO2 should fall 1.2 mm Hg
if this is true then it is compensated
Otherwise compensation inadequate
what is metabolic acidosis associated with
Assoc with alterations in transcellular ion pumps and ↑ ionized calcium
Problems with ion pumps
hyperchloremic metabolic acidosis
Bicarb loss is countered by net gain of chloride ions
Causes of R shift
decreased affinity for O2.
increase pCO2
increase H+ (dec pH)
inc 2,3 DPG
inc Temp
Causes of L shift on oxy hb dissociation curve
increased affinity for O2
dec PCO2
dec H+
dec 2,3 DPG
dec temp
fetal hbg
Bicarb equation for calculating metabolic acidosis compensation
(1.5 x HCO3-) + 8
If PaCO2 is higher than calculated CO2, compensation is inadequate; concomitant problem
what can cause metabolic acidosis with a normal anion gap
Sodium chloride infusions
Diarrhea
Early renal failure
what can complicate using the anion gap equations
Complicated by hypoalbuminemia, hypophosphatemia
the equations Frequently underestimates extent of disturbance
Levels to treat with sodium bicarbonate
pH < 7.1 or Bicarb < 10 meq/L
How does giving bicarb affect the acid base status
- Reacts with H+… generates CO2 …diffuses intracellularly and decreases pH more
- In chronic metabolic acidosis, acute pH changes negates right shift of curve (Bohr effect) and causes tissue hypoxia
Other names for Metabolic alkalosis
Volume depletion or volume overload alkalosis
