Acid-base Imbalances Flashcards
What is the normal blood pH?
7.35-7.45
What are the 3 mechanisms of maintaining normal blood pH?
~ maintaining H+ ions to keep cell membrane integrity ~
1) Buffer systems (to respond instantly)
- Prevents drastic changes
- Rapidly changes strong acids and bases into weaker ones
- Located in intra & extracellular fluid
- Carbonic acid + hemoglobin + proteins and phosphates
2) Respiration (mins)
- CO2 is produced by cellular respiration
- HCO3- binds to excess H+ in the body to form CO2 again which will be exhaled from body
- H+ is more acidic than H2CO3 by-product
- If body is in alkalosis, rate of breathing dec to retain CO2 and ^ H+ conc to ^ acidity
- Occurs within 1-3 mins
3) Kidney excretion (hrs)
- Acids can only be excreted by kidney
- Kidneys can adjust blood HCO3 by ^ or dec secretion/absorption and producing new bicarbonate
What are acidosis and alkalosis?
Both can be either due to respiratory or metabolic reasons
Acidosis:
- ^ H+ ions
- Causes nervous system depression
- Respiratory (hypoventilation)
- Metabolic (^ metabolic acids)
Alkalosis:
- Dec H+ ions
- Causes nervous system irritability
- Respiratory (hyperventilation)
- Metabolic (excessive loss of H+ or ^ HCO3-)
What are the pH, PCO2 and HCO3 lab results for respiratory and metabolic acidosis/alkalosis?
RAc: Dec pH, ^ pCO2, N HCO3-
MAc: Dec pH, N pCO2, Dec HCO3-
RAlk: ^ pH, Dec pCO2, N HCO3-
MAlk: ^ pH, N pCO2, ^ HCO3-
How does respiratory acidosis occur?
- Hypoventilation (Accumulation of CO2 forms carbonic acid which dissociates into H+ ions)
- pH 7.35, PaCO2 > 45 mmHg
- Due to brainstem trauma, CNS depressant drugs, impaired respiratory muscle function, lung disorders
- If renal buffer (mechanism 3) is ineffective, may need ventilator support
What is the treatment for respiratory acidosis?
- Hold any respiratory depressant drugs
- Improve ventilation
- Opiates (NALOXONE) PRN
~ Response within 10 mins - BZP (FLUMAZENIL) PRN (max x5 every 20 mins)
- ABG every 2-5 hrs initially, then12-24 hrs
- Basic metabolic panel needed
How does metabolic acidosis occur?
- Certain conditions cause generation of excess acids (eg lactic acids, salicylic acid)
~ Body ^ RR to try to excrete excess acids in the form of CO2
~ Kidneys may also have impaired ability to excrete H+
What is the treatment for metabolic acidosis?
- HCO3- replacement (ie sodium bicarb)
~ Only if chronic
~ Not used for acute (DKA, lactic acidosis, septic shock) - Treat underlying condition instead
How does respiratory alkalosis occur?
- Hyperventilation (due to respiratory stimulus, ^ metabolic demands etc)
- pH >7.45 PaCO2 < 35 mmHg
What is the treatment for respiratory alkalosis?
- Correct underlying disorders
- Hold any suspected drugs
- Initiate ocygen therapy in px with severe hypoxemia (pO2 < 40 mmHg)
- Treat theophylline overdoses
How does metabolic alkalosis occur?
- Excessive loss of H+ or excessive HCO3- loss
- Prolonged vomiting, gastric suction
- Excessive antacid usage
How is metabolic alkalosis treated?
- Correct underlying conditions
- Hold any suspected drugs
If ECF volume dec:
- NS for fluid resus
- Replace K+ and Cl-
If ECF overload:
- w no renal insufficiency: ACETAZOLAMIDE
- but w ARF/ESRD: HD or PD
- but w hyperaldosteronism: SPIRONOLACTONE or AMILORIDE
~ use K+-sparing diuretics instead of loop diuretics
What are the normal results of an ABG?
pH: 7.35 - 7.45
PaO2: 80 - 100 mmHg
PaCO2: 35 - 45 mmHg
HCO3: 22 - 26 mEq/L
Base excess (BE): -3 to +3
SaO2: 95% - 100%
What does base excess represent?
^ in metabolic alkalosis
Dec in metabolic acidosis
Why is ABG sent down in ice?
To slow down metabolism of RBC
