Week 8: Acid-Base Balance

what creates acids and CO2?

metabolic reactions

blood pH normal range

7.35-7.45

what is the first line of defense against pH changes?

blood buffers → weak acid + conjugate base

what systems maintain pH in the body

• blood buffers

• respiratory system

• renal system

H+ and HCO3- form what?

H2CO3 = carbonic acid

4 main buffers in body

1. bicarbonate-carbonic acid = principle plasma buffer

2. phosphate buffers

   • HPO2- and H2PO4- = renal

   • 2,3-DPG = RBCs

3. hemoglobin

4. plasma proteins

   • negatively charged

   • bind H+

how do kidneys use phosphate as a buffer?

• excretion of H+

• HPO42- = basic form

• H2PO4- = acidic form

• protons bind basic form to make acidic form → flushed out in urine

isohydric shift

• H+ is shifted among acid-base pairs

• [H+] remains the same

• plasma

  • CO2 combines with H2O

  • proteins bind

• RBC

  • most CO2 enters cells and combines with H2O

carbonic anyhydrase

converts CO2 and H2O → carbonic acid

____ is buffered by oxyhemoglobin (HbO2-)

H+

oxyhemoglobin and deoxyhemoglobin

• oxyhemoglobin is transported to tissues

• O2 diffuses to tissues

• tissues release CO2 → RBCs with deoxyhemoglobin

deoxyhemoglobin has a higher affinity for ____

H+

chloride shift in RBCs

• HCO3- accumulates in RBCs, and is pumped out into plasma in exchange for Cl-

• maintains electroneutrality

in RBCs at the _________, CO2 enters and HCO3- is pumped out in exchange for Cl-

tissues

in RBCs at the _________, HCO3- enters the cell in exchange for Cl-, and CO2 is pumped out

lungs

oxyhemoglobin has a much lower affinity for _____

H+

renal acid-base balance is the _________ defense against changes in body pH

final

mechanisms of renal acid-base balance

• acid excretion

• HCO3- reabsorption

renal acid excretion is done through ________ exchange

Na+ / H+

in renal acid excretion, H+ is reacted with buffer base: ______________

PO4, NH3

HCO3- reabsorption in the renal system is generally _____________ to Na+ reabsorption

proportional

Na+ / H+ exchange in renal acid excretion, ______ is secreted and ______ is reabsorbed (active exchange)

H+, Na+

______ and H+ compete for exchange in the renal tubules

K+

with hyperkalemia, there is more ______ in RBCs, and more ______ in plasma

H+, K+

with hypokalemia, there is more _____ in RBCs, and more ______ in plasma

K+, H+

how does metabolic acidosis affect potassium concentration?

hyperkalemia

how does metabolic alkalosis affect potassium concentration?

hypokalemia

H+ combines with dibasic sodium phosphate to form what compound that is excreted in urine?

monobasic sodium phosphate (NaH2PO4)

H+ combines with NH3 to form what compound that is excreted in urine?

NH4+, which is excreted as ammonium salt NH4Cl

henderson-hasselbalch equation

blood pH = 6.1 * log [bicarbonate ions] / [carbonic acid]

blood pH is controlled by what ratio?

[bicarbonate ions] / [carbonic acid]

what is the normal ratio of blood [bicarbonate ions] / [carbonic acid]

20/1

an increased [HCO3-] / [H2CO3] ratio causes…

increased pH (alkalosis)

a decreased [HCO3-] / [H2CO3] ratio causes…

decreased pH (acidosis)

the following are described as which type of acid-base disorder?

• increased CO2 (acidosis)

• decreased CO2 (alkalosis)

• renal system compensates

respiratory disorders

the following are described as which type of acid-base disorder?

• decreased HCO3- (acidosis)

• increased HCO3- (alkalosis)

• respiratory system compensates

metabolic disorders

in respiratory acidosis, pCO2 __________ and HCO3- ____________

increases, stays the same

in metabolic acidosis, pCO2 __________ and HCO3- ____________

stays the same, decreases

in respiratory alkalosis, pCO2 __________ and HCO3- ____________

decreases, stays the same

in metabolic alkalosis, pCO2 __________ and HCO3- ____________

stays the same, increases

what does compensation look like?

opposite factor moves in same direction as the primary problem to normalize pH (bring back to 20:1 ratio)

for example, if there is decreased pCO2 (respiratory alkalosis), what will be altered for compensation (bring back to 20:1 ratio)?

HCO3- will decrease

when we have compensation to bring back the normal 20:1 ratio, the pH may become normal BUT…

now BOTH factors are abnormal

which type of compensatory mechanism is immediate, short-term, and often incomplete?

respiratory compensation

what is the respiratory compensatory response to metabolic alkalosis?

• increase CO2 retention

• hypoventilation

what is the respiratory compensatory response to metabolic acidosis?

• eliminate CO2

• hyperventilate (“blow off”)

which type of compensatory mechanism is slower, long-term, and potentially complete?

renal compensation

what is the renal compensatory response to respiratory alkalosis?

• increase H+ retention

• lower HCO3- retention

what is the renal compensatory response to respiratory acidosis?

• decrease H+ retention

• increase HCO3- retention

metabolic acidosis results from a primary bicarbonate _________

deficit

in a normochloremic type of metabolic acidosis, the increased acids consume __________

HCO3-

what types of acids become increased in a normochloremic type of metabolic acidosis?

• endogenous acids

  • ketoacidosis

  • lactic acidosis

• exogenous acids

  • isopropanol

  • salicylate toxicity (late)

in a normochloremic type of metabolic acidosis, there is decreased acid _____________ as a result of renal __________

excretion, failure

what happens to the anion gap during a normochloremic metabolic acidosis?

increased

in a hyperchloremic type of metabolic acidosis, there is a direct loss of ________, and therefore increased Cl- for electroneutrality

HCO3-

what disorders are associated with a hyperchloremic type of metabolic acidosis?

• renal tubular acidosis (RTA)

• diarrhea

what happens to the anion gap during a hyperchloremic type of metabolic acidosis?

stays normal

pyruvate is converted to ____________ in anaerobic conditions instead of acetyl CoA

lactate

what types of lactic acidosis can occur?

• physiologic

  • strenuous exercise

  • lactate/pyruvate ratio unchanged

• pathologic

  • coma and death

  • hypoxic

    • shock

    • hypovolemia

    • heart failure

  • lactate/pyruvate ratio increases

when analyzing specimen for lactic acid, we must minimize in vivo and in vitro _____________ to avoid falsely elevated lactate (pyruvate is stable)

glycolysis

patient prep for lactate specimen

• fasting

• resting for > 2 hours

• no tourniquet/fist

whole blood collection for lactate

• heparinized tube

• on ice

• gray top

• transfer to TCA or perchloric acid tube

plasma collection for lactate

• collect in NaF or K oxalate tube

• on ice

• separate cells within 15 minutes

in metabolic acidosis, pH __________ and HCO3- ____________, and after compensation pCO2 _____________

decreases, decreases, decreases

metabolic alkalosis results from a primbary bicarbonate _________

excess

disorders associated with metabolic alkalosis

• antacid or bicarbonate overdose

• increased H+ excretion or loss

  • vomiting

  • nasogastric suctioning

  • K+ depletion

    • increased Na+ retention (hyperaldosteronism)

    • diuretics

metabolic alkalosis compensation

• hypoventilation

• renal system

  • retains H+

  • excretes HCO3-

lab findings with metabolic alkalosis show that pH ______________, HCO3- ____________, and after compensation pCO2 _____________

increases, increases, increases

urine with metabolic alkalosis may become ____________

alkaline

respiratory acidosis results from a primary CO2 _________

excess

disorders associated with respiratory acidosis

• chronic obstructive pulmonary disease (COPD)

  • asthma

  • pulmonary emphysema

• chemoreceptor depression

  • drugs like heroin and morphine

• rebreathing exhaled air

compensation for respiratory acidosis

• hyperventilation

• renal

  • acid excretion

  • bicarbonate retention

lab findings with respiratory acidosis will show that pH _____________, pCO2 ____________, pO2 ___________, and after compensation HCO3- ____________

decreases, increases, decreases, increases

Cl- may be ___________ with respiratory acidosis

decreased

respiratory alkalosis results from a primary CO2 __________

deficit

disorders associated with respiratory alkalosis

• psychogenic

  • anxiety and hysteria

• hyperstimulation of respiratory center

  • hypoxemia

  • drugs: salicylate toxicity (early)

salicylate poisoning

• mixed acid-base disturbance

• primary respiratory alkalosis = early phase

• high anion gap metabolic acidosis = late phase

compensation mechanisms for respiratory alkalosis

• renal

  • retain H+

  • excrete bicarbonate

• hypoventilation

lab findings with respiratory alkalosis show pH __________, pCO2 ___________, and after compensation HCO3- ______________

increases, decreases, decreases

with respiratory alkalosis the urine may be ____________

alkaline

% oxygen saturation

ratio of O2 bound to Hgb / oxygen-Hbg binding potential

oxygen dissociation is predicted by what?

O2-Hgb dissociation curve

factors that affect oxygen transport

• oxygen availability

• concentration of Hgb and type

• blood pH

• temperature

• concentration of CO2

• carbon monoxide

• concentration of 2,3-DPG

what type of shift is described by the following?

• increased H+

• increased CO2

• increased temperature

shift to the right

what type of shift is described by the following?

• decreased H+

• decreased CO2

• decreased temperature

shift to the left

what is p50?

the pO2 at which Hgb is 50% saturated with oxygen

p50 __________ during a shift to the left

decreases

shift to the left

• Hgb has increased affinity for oxygen

• increased pH, CO, Hgb F

• decreased CO2, 2,3-DPG, temperature

what may happen to the body with a shift to the left?

• tissue hypoxia

• compensatory hyperventilation

during a shift to the left, hemoglobin hold onto oxygen more tightly, therefore…

releasing it less rapidly to peripheral tissues

p50 _________ during shift to the right

increases

shift to the right

• Hgb has a decreased affinity for oxygen

• low pH

• increased CO2, 2,3-DPG, temperature

• low pO2 → increased 2,3-DPG

what can cause a shift to the right?

• adaptation to high altitudes

• chronic hypoxemia

• anemia

measured analytes in blood gas analysis include:

• pH

• pO2

• pCO2

derived parameters in blood gas analysis include:

• H2CO3

• HCO3-

• base excess

• TCO2

• %SO2

H2CO3 calculation

pCO2 × 0.031

the H2CO3 calculation can be substituted into what formula?

henderson-hasselbalch

titratable base excess (BE)

the amount of strong acid or strong base needed to titrate blood back to a neutral pH

BE estimates the ____________ component of an acid-base disorder

metabolic

positive BE suggests metabolic ____________

alkalosis