Acid-Base

Define and recognize acid/base disorders

  • Arterial pH usually 7.35 - 7.45 

    • less acidosis and more alkalosis

    • disturbances affect several organ systems and etiology can be drug related changing drug therapy and therapeutic plan 

  • Physiology HCO3- + H+ ⇆ H2CO3 ⇆ CO2 + H2O

    • HCO3- basic retain in kidneys more basic/alkalotic

    • CO2 - acidic retain in lungs more acidic/acidosis  


Disorder

pH

PaCO2

HCO3-

Causes

Normal

7.35-7.45

35-45 mmHg

22-26 mEq/L


Metabolic Acidosis

lower

lower (compensate)

lower

elevated AG M.U.D.P.I.L.E.S. normal AG G.R.E.E.D

Metabolic Alkalosis

higher

higher (compensate)

higher

D.C. N.E.V.E.R

Respiratory Acidosis

lower 

higher

higher (compensate)

hard or difficulty breathing

Respiratory Alkalosis

higher

lower

lower (compensate)

Huffed & P.U.F.T

  • pH matches underlying disorder telling clinically 

    • Same metabolic Different respiratory

  • compensation is the one that does not match disorder

    • younger can compensate for longer elderly cannot 

Metabolic Acidosis low pH low HCO3-

  • Reduced excretion of H+ and exogenous sources of Cl-

  • Anion Gap secondary marker to help tell cause of acidosis 

    • AG = Na+ - (Cl- + HCO3-) usually 7-16 

  • Treatment - correct underlying cause maybe Sodium Bicarbonate controversial 

    • ADR hypernatremia, volume overload, over-alkalinization, hypokalemia  

      • CKD chronic bicarb tablets to offset disease 

    • Dialysis 

Elevated AG Metabolic Acidosis 

  • Causes - M.U.D.P.I.L.E.S

    • methanol, metformin

    • uremia

    • diabetic ketoacidosis —> glucose and ketones 

    • propylene glycol

    • ischemia,intoxication

    • lactic acidosis —> lactate 

    • ethanol,ethylene glycol —> SCr/BUN

    • salicylates,starvation —>plasma osmolal gap 

Normal AG Metabolic Acidosis 

  • Causes - G.R.E.E.D

    • GI loss (diarrhea) 

    • renal loss (renal tubular acidosis)

    • endocrine (hypoaldosteronism)

    • excess Cl-

    • drug (acetazolamide)

Metabolic Alkalosis high pH high HCO3- 

  • loss of H+/Cl- and net increase in HCO3- a

  • Causes - D.C N.E.V.E.R

    • diuretics

    • contraction (intravascular volume)

    • nasogastric suctioning 

    • endocrine (hyperaldosteronism, mineralocorticoids)

    • vomiting 

    • excess alkali 

    • refeeding (hypokalemia)

  • Treatment - correct underlying cause 

    • fix fluid deficits and replace Cl - and/or K+ as appropriate 

    • acetazolamide (carbonic anhydrase inhibitor) dumps the bicarb 

    • hydrochloric acid replaces the Cl-

Respiratory Acidosis low pH high CO2

  • respiratory failure leading to reduced CO2 excretion

  • Causes - things that make you stop or hard breathing

    • Pulmonary - COPD, Asthma, Aspiration, Mechanical ventilation

    • Cardiopulmonary - Cardiac arrest , Edema, Embolism

    • Neurologic - CNS depressants, cerebral vascular accident, seizure

    • Neuromuscular - multiple sclerosis, GBS, myasthenia gravis 

  • Treatment - correct underlying cause and respiratory support 

Respiratory Alkalosis high pH low CO2 

  • hyperventilation leading to increased CO2 excretion

  • Causes - Huffed & P.U.F.T

    • hyperventilation,hypoxia

    • pregnancy, pneumonia 

    • uncus (CNS pathology)

    • fever, heart failure 

    • trauma 

  • Treatment - correct underlying cause and rebreathe expelled air 

Mixed Acid-base disorders 

  • mixed metabolic and respiratory disorders 

    • identify primary disorder and access compensation