Acid-Base Flashcards by Renee DeAngelis

In what 2 ways is acid-base status of a patient determined? What is measured and calculated in each?

biochemistry profile - measured = TCO2; calculated anion gap —> NO INFORMATION ON RESP ACID-BASE DISTURBANCES OR COMPENSATION
blood gas profile - measured = pH, pCO2, pO2; calculated = HCO3-, base excess

How well did you know this?

Not at all

Perfectly

What is TCO2?

estimate of plasma bicarbonate concentration, with 95% of it accounting in the form of HCO3-

How well did you know this?

Not at all

Perfectly

What are the 4 contributors to blood pH?

pCO2 - changes with ventilation
addition or removal of acids (H+) - lactated metabolites of ethylene glycol or loss of H+
strong ion movements - Na, K, Cl
serum proteins, phosphates, and other weak acids

How well did you know this?

Not at all

Perfectly

Why is pH maintenance important?

proper pH is necessary for the maintenance of protein structure, metabolism, and enzyme conformation/action

How well did you know this?

Not at all

Perfectly

What keeps hydrogen ion concentration in check? What are 3 examples?

buffers and regulatory systems

bicarbonate system: HCO3-, pCO2
non-bicarbonate system: PO4, NH3-, Hgb, albumin, plasma proteins
renal excretion (H+) and alveolar ventilation (CO2)

How well did you know this?

Not at all

Perfectly

What are the 3 classifications of acid-base disturbances?

metabolic acidosis - titrational vs. secretional metabolic acidosis
metabolic alkalosis
mixed - both metabolic acidosis and alkalosis

How well did you know this?

Not at all

Perfectly

How is pH interpreted on biochemistry? Metabolic disturbances?

ALKALEMIA = increased pH
ACIDEMIA = decreased pH

METABOLIC ACIDOSIS = decreased HCO3-/TCO2
METABOLIC ALKALOSIS = increased HCO3-/TCO2

How well did you know this?

Not at all

Perfectly

What is base excess?

characterizes the overall metabolic acid-base status independent of the respiratory acid-base status (accounts for all arterial bases

the amount of bases that must be added or removed to return the pH to normal

How well did you know this?

Not at all

Perfectly

What does HCO3- represent on biochemistry profiles?

amount of CO2 gas that is released from plasma/serum when mixed with a strong acid

How well did you know this?

Not at all

Perfectly

What is an anion gap? How is it calculated?

the difference in cations and anions that is used to further characterize metabolic acidosis and approximate unmeasured anions and/or cations in circulation

AG = [Na + K] - [Cl + HCO3]

How well did you know this?

Not at all

Perfectly

What does an increased anion gap indicate?

metabolic acidosis with a high number of unmeasured anions:

Ketones
Lactate
Uremic acid
Ethylene glycol metabolites
salicylates
hyperalbuminemia

How well did you know this?

Not at all

Perfectly

What does metabolic acidosis with an elevated anion gap mean?

titrational metabolic acidosis

How well did you know this?

Not at all

Perfectly

What does a decreased anion gap indicate? What are 2 causes?

metabolic alkalosis with increased cations —> RARE, not clinically significant

decreased unmeasured anions - hypoalbuminemia
increased unmeasured cations - hyperalbuminemia and hypermagnesemia

How well did you know this?

Not at all

Perfectly

What is the law of electroneutrality?

the sum of all positively charged ions (cations) must be equal to the sum of all negatively charged ions (anions) in the body

HCO3- is excreted into the urine and Cl- is retained/reabsorbed
Na+ is reabsorbed, so H+ or K+ is excreted

How well did you know this?

Not at all

Perfectly

What machinery is used for blood gas data? What blood is preferred? What tube should it be collected in?

electrochemical analyzers (in-house common)

arterial blood allows for complete evaluation of blood oxygenation; venous blood is common an adequate, too

whole blood collected into heparinized tube

How well did you know this?

Not at all

Perfectly

What should be avoided so that pH of blood is not altered before blood gas data is collected? When should it be processed?

avoid exposure of blood to room temperature and gas bubbles during collection

process within 10 mins or put on ice and process within an hour if not immediate

How well did you know this?

Not at all

Perfectly

What happens on blood gas analysis if there is a delay in sample processing? Air exposure?

DELAY = decreased pH and PO2

AIR EXPOSURE = increased pH and PO2, decreased PCO2 and HCO3-

(caused by continued glycolysis of RBCs)

How well did you know this?

Not at all

Perfectly

What analytes are measured and calculated on blood gas analysis?

Study These Flashcards

MEASURED - pH (H+ ions), pCO2 (respiratory), electrolytes (Ca, Mg, etc.), pO2

CALCULATED - HCO3-, base excess

Why isn’t base excess commonly used to determine metabolic differences? What do different values mean?

Study These Flashcards

doesn’t really add information —> can be used to guide fluid bicarbonate therapy

< 0 = metabolic acidosis
> 0 = metabolic alkalosis

What do levels of pCO2 above/below RI indicate?

Study These Flashcards

ABOVE RI = hypercapnia/hypercarbia, usually from hypoventilation —> RESPIRATORY ACIDOSIS

BELOW RI = hypocapnia/hypocarbia, usually from hyperventilation (panting) —> RESPIRATORY ALKALOSIS

What is the normal blood pH?

Study These Flashcards

7.35 - 7.45 —> 7.4 average

What are the compensatory mechanisms used to control respiratory and metabolic changes that alter pH?

Study These Flashcards

RESP = when changes in HCO3- occur, the lungs compensate by altering ventilation to change pCO2 - FAST

MET = when changes in pCO2 occur, the kidneys compensate by retaining or excreting HCO3- - SLOW

What occurs during acidemia/alkalemia? How are they compensated?

Study These Flashcards

ACIDEMIA:
- pCO2 increased (respiratory acidosis): HCO3- is increased by kidney (metabolic alkalosis)
- HCO3- decreased (metabolic acidosis): pCO2 is decreased by lung ventilation change (respiratory alkalosis)

ALKALEMIA:
- pCO2 decreased (respiratory alkalosis): HCO3- decreased by kidney (metabolic acidosis)
- HCO3- is increased (metabolic alkalosis): pCO2 is increased by lung ventilation change (respiratory acidosis)

What are the 5 steps to approaching blood gas data?

Study These Flashcards

evaluate pH
evaluate HCO3-
evaluate pCO2
determine what mechanism (resp/met) is primary and which is compensatory
determine if compensation is adequate —> pH 7.4-7.6

How can the mechanism of acidosis/alkalosis be determined as primary or compensatory?

- primary mechanism if driving pH away from 7.4 - compensatory mechanism moves in the opposite direction - if a difference is not noted, it is likely a mixed disturbance combined abnormalities between HCO3- and pCO2 ---> least abnormal value is almost always due to compensation response

When are compensatory mechanisms not seen in pH differences?

if the process is very acute

What are 4 common causes of respiratory acidosis? What values differ? How is it compensated?

retention of CO2 ---> hypoventilation 1. anesthesia 2. diffuse pulmonary disease 3. intrathoracic lesions 4. CNS disease decreased pH (acidemia) and increased pCO2 (acidosis) ---> secondary metabolic alkalosis by retaining HCO3-

What are 4 common causes of respiratory alkalosis? What values differ? How is it compensated?

release of CO2 ---> hyperventilation 1. hypoxemia 2. pain, anxiety 3. hyperthermia 4. drugs that stimulate medullary respiratory center increased pH (alkalemia) and decreased pCO2 (alkalosis) ---> secondary metabolic acidosis by renal retention of H+

What are the 2 mechanisms of metabolic acidosis?

1. titrational metabolic acidosis - increase in acid 2. secretional metabolic acidosis - loss of base

What is titrational metabolic acidosis? What differential needs to be considered?

HCO3- lost due to titration of organic acid (it titrates the salt of the acid it titrates) increased nonvolatile acids - Ketones, Lactate, Uremic acids (phosphates, sulfated), Ethylene glycol metabolites (toxins)

What is secretional metabolic acidosis? What are 4 differentials?

HCO3- is lost through bicarbonate-rich fluids (NaHCO3 or KHCO3), resulting in the retention of HCl 1. GI loss from diarrhea 2. intestinal ileus 3. salivation in ruminants 4. urinary loss by tubules

What are the 2 types of metabolic acidosis compensation?

1. SHORT-TERM: respiratory alkalosis by increased ventilation 2. LONG-TERM: increased renal excretion of H+

What are the 3 biochemical findings in titrational metabolic acidosis?

1. decreased TCO2 2. elevated anion gap 3. Cl- within RI

What are the 3 biochemical findings in secretional metabolic acidosis?

1. decreased TCO2 2. normal anion gap 3. Cl- within RI or increased due to excess of Na+ (hyperchloremic metabolic acidosis)

What are the 2 mechanisms of metabolic alkalosis?

1. loss of acid (HCl-rich fluids)* 2. increase in base

What are 3 differentials related to excessive renal loss of H+ causing metabolic alkalosis?

1. diuretics 2. hypokalemia that stimulated H+, K+ ATPase pump ---> K+ retention, H+ secretion, HCO3- generation 3. chronic respiratory acidosis

What are the differentials in hypochloremic metabolic alkalosis in monogastrics and ruminants?

MONOGASTRIC: severe gastric vomiting, pyloric outflow obstruction RUMINANTS: sequestration of fluid in the abomasum due to ileus or displacement

What are 4 findings associated with metabolic alkalosis?

1. increased TCO2 2. normal anion gap 3. decreased Cl- in excess of Na+ 4. hypochloremic metabolic alkalosis

What are the 2 compensatory responses to metabolic alkalosis?

1. SHORT-TERM: respiratory acidosis by decreased ventilation 2. LONG-TERM: increased renal retention of H+

What is paradoxcial aciduria? What causes it? How is it treated?

acidic urinary pH when there is metabolic alkalosis - hypchloremia causes HCO3-, instead of Cl-, to be resorbed along with Na+ - Na+ resorption is coupled with secretion of H+, which acidicfies the urine correcting NaCl deficit with appropriate fluids

What are 3 common cases where mixed acid-base disturbances should be considered?

1. high anion gap with normal TCO2 2. Cl- is lost in excess of Na+, but TCO2 is normal 3. Cl- is high in excess of Na+, but TCO2 is normal

A diabetic ketoacidotic dog is vomiting and has a high anion gap with normal TCO2 and low Cl-. What is likely going on?

titrational metabolic acidosis AND hypochloremic metabolic alkalosis ---> mixed disturbance - acidosis from ketones - alkalosis from vomiting

What are mixed acid-base disturbances? When should patients be suspected of this?

2 primary acid-base disturbances are occurring simultaneously electrolyte disturbances and/or.... - disease associated with an acid-base disturbance, yet has a normal bicarbonate concentration or pH - compensatory response is moving in the wrong direction

CASE: 2 day old female calf is septic. The patient has diffuse diarrhea (scours) and pneumonia. What is going on based on the biochemistry profile and blood gas analysis?

- low pH = acidemia - high pCO2 = primary respiratory acidosis - low HCO3- = primary metabolic acidosis - *2 primary changes are driving the acidemia, not a primary change with compensatory change* high anion gap supports titrational metabolic acidosis, (lactate) and sodium/chloride are decreased proportionally ---> no acid-base change

Acid-Base Flashcards

(44 cards)