Acid-Base Homeostasis Flashcards
what is the normal [H+] in blood?
0.0004mEq/L or 40x10-9 Eq/L or 40nEq/L
what is the [H+] range and pH range compatible with life?
25-100nEq/L
7.0-7.7
where does the daily acid load come from?
CO2 from oxidation of glucose and fatty acids during aerobic cellular metabolism
CO2+H2O<->H2CO3<->H++HCO3-
what are the three phases of defense against loss of acid base homeostasis?
buffering
compensation
correction
what is the order of action from the three phases of defense against loss of acid base homeostasis?
buffering: immediate
compensation: minutes to days
correction: days or more
what equation shows the equilibrium relationship of carbonic acid dissociation?
Henderson-Hasselbalch
what are the buffers?
H2CO3/HCO3-
inorganic phosphates and plasma proteins
major intracellular is hemoglobin
how can the lungs regulate pH?
effectively removes H+ by blowing CO2 off
what receptors lead to a change in ventilation?
chemoreceptors in medulla, carotid body, and aortic arch
how does the renal system contribute to buffering?
regulates Na+ and Cl- loss
H2O
reabsorption filtered HCO3-
excrete H+ (titratable acid or ammonia)
what are the normal ranges of pH, PCO2, and base excess [HCO3-] in an arterial blood gas?
7.37-7.43
36-44 mmHg
22-26 mEq/L
what are the two indirect methods for determination of [HCO3-]?
Siggard-Andersen nomogram using pH and PCO2
biochemical measurement of total blood CO2
what is base excess?
mEq of acid that would be needed to bring 1 L of blood in the sample to a pH of 7.4, if PCO2 held at 40 mmHg
evaluation of non-respiratory component of acid-base
what is anion gap?
estimates amount of strong anions in plasma not accounted for by inorganic ions measurement
what does an increased anion gap indicate?
unmeasured anions present: ketoacids, lactate, sulfates, phosphate, albumin
what are normal anion gaps?
with K+: 17-19 mEq
without K+: 12-14 mEq
what is metabolic acidosis with a normal anion gap?
changes in [Cl-] usually
what is respiratory acidosis due to (not disease processes)?
impaired pulmonary elimination of CO2 due to alveolar hypoventilation
what can cause respiratory acidosis?
pulmonary disease
impaired chest wall or respiratory muscle function
severe CNS depression
inadequate ventilation during anesthesia
how does renal compensation work with respiratory acidosis?
increased H+ excretion
what is respiratory alkalosis due to?
inappropriate CO2 elimination due to hyperventilation
what can cause respiratory alkalosis?
hypoxia, pain or fear, gram negative sepsis, strenuous exercise, overzealous assisted ventilation, hyperthermia, hypoxemia, hypotension
what does renal compensation of respiratory alkalosis consist of?
diminished HCO3- recovery
what can cause metabolic acidosis?
diarrhea or renal failure leading to HCO3- loss
renal failure
increased endogenous acid production
exogenous acid load
what is metabolic acidosis due to?
HCO3- loss
retention of acid
how does the respiratory system compensate for metabolic acidosis?
increased CO2 removal
what is metabolic alkalosis due to?
acid loss
HCO3- retention
what can cause metabolic alkalosis?
vomiting: acid loss
volume depletion, K+ wasting diuretics
how can the respiratory system compensate for metabolic alkalosis?
hypoventilation
what is the normal range for bicarbonate?
22-26 mEq/L
what is the normal range for pH?
7.37-7.43
what is the normal range for PCO2?
36-44 mmHg
do we routinely measure inorganic ions in plasma?
yes, but not organic ions
what does a positive base excess indicate?
alkalemia
what is the equation for the equilibration for the concentration of hydrogen ions in plasma?
[H+]=24*PCO2/[HCO3-]
how much carbonic acid does alveolar ventilation remove daily?
24,000 mEq
how can the kidneys regulate acid loss?
titratable acid
ammonia
