Acid Base Balance Flashcards
Acidosis
Disorder tending to make blood more acid than normal
Alkalosis
Disorder tending to make blood more alkaline than normal
Acidemia
Low blood pH
Alkalemia
High blood pH
Factors affecting pH
Respiratory component: CO2 concentration
Metabolic component:
Intrinsic acid (products of metabolism)
Extrinsic acid (diet, toxins etc)
Buffering capacity: Bicarbonate, other buffers
Central relationship between bicarbonate and CO2
Ph and HCO3- are dependant variables governed by
pCO2
Concentration of weak acids (ATOT)
ATOT = Pi + Pr + Alb
Strong ion difference (SID)
SID = Na+ + K+ + Mg2+ + Ca2+ – Cl- – other strong anions (eg lactate, ketoacids)
What do we measure for Atrial Blood Gas?
pH
pO2
pCO2
HCO3- / Std HCO3-
Base excess
May include other measures (eg lactate, Na+, K+)
Standard bicarbonate
Measures of metabolic component of any acid-base disturbance
Absolute bicarbonate is affected by both respiratory and metabolic components
Standard bicarbonate is the bicarbonate concentration standardised to pCO2 5.3kPa and temp 37
Base excess
Quantity of acid required to return pH to normal under standard conditions
Can be used to calculate bicarbonate dose to correct acidosis: 0.3xWtxBE (but not generally used in practice)
Base excess is negative in acidosis, can be referred to as base deficit
Respiratory acidosis
What it is? CO2 retention – which leads to carbonic acid dissociation
Causes? Inadequate ventilation (hypoventilation, COPD, asthma, resp failure) - due to airway obstruction
Renal compensation? Increased ammonia formation. Therefore, increased renal H+ excretion and ammonium formation and increased bicarbonate reabsorption.
Respiratory alkalosis
What it is? When CO2 is depleted due to hyperventilation. Hyperventilation occurs in response to hypoxia (CO2 elimination then exceeds O2 reabsorption).
Causes? Type 1 respiratory failure, anxiety/panic
Renal compensation? Decreased H+ excretion causing more H+ to be retained to help normalise pH. Less bicarbonate is reabsorbed (more loss/more HCO3- secretion)
Metabolic acidosis
What it is? (Disorders leading to) a loss of HCO3- and/or excess H+ production.
Causes? Renal failure, lactic acidosis, ketoacidosis, dilution of blood (more dissociation of H2O so more H+ in the blood), failure of H+ excretion (e.g., hypoaldosteronism)
Respiratory compensation? The reduction in pH stimulates central Chemoreceptors that enhance respiration. Causes PaCO2 decreases and pH to increase (hyperventilation to increase CO2 excretion)
Metabolic alkalosis
What it is? (Disorders causing) the loss of H+ and/or increased HCO3- reabsorption
Causes? Vomiting (loss of H+), alkali ingestion, hyperaldosteronism
Respiratory compensation? The increased pH inhibits Chemoreceptors, reducing respiration, PaCO2 then increases and therefore decreases the pH. (Hypoventilation causes CO2 excretion to decrease – limited by hypoxic drive)
