Electrolytes and Acid-Base Disturbances

Normal pH of arterial blood is 7.4 and is maintained to within 0.05 (i.e. the normal pH range of the blood is 7.35 to 7.45). 
The main buffering of acids occurs through  Lungs Through the conversion of carbonic acid [H2CO3] to CO2 and H2O and  Kidney  Through the base bicarbonate [NaHCO3].


Respiratory acidosis V/S Respiratory alkalosis



Respiratory acidosis  Respiratory acidosis occurs when the lungs are not exhaling CO2 adequately. 
This can occur with  

• Emphysema  
• Respiratory depressive states such as:  Oversedation, Respiratory insufficiency, and Arrest. 
   

Respiratory alkalosis  Respiratory alkalosis occurs when too much CO2 is expelled 

This can occur with  

• Hyperventilation 
• Neurogenic disorders 
• Salicylate toxicity  (which, interestingly, is accompanied by metabolic acidosis)

Metabolic acidosis V/S Metabolic alkalosis

Metabolic acidosis  Metabolic acidosis is caused by a deficit of the base bicarbonate. 

Normally there is an H2CO3-to-NaHCO3 ratio of 1:20.

To maintain this ratio 

• H+ is excreted in the urine 
• Bicarbonate is reabsorbed into the renal tubules  

With the presence of excess acid, the bicarbonate combines with this source of H+, is excreted, and is therefore no longer available for its usual buffering role.  

This results in an upset of the 1:20 ratio and acidosis. 

Lactic acid from muscle activity or anaerobic conditions, diabetic ketoacidosis , renal failure, or exogenous sources such as methanol, ethanol, or paraldehyde can all serve as the alternative acid source.

A method to determine whether metabolic acidosis is present is to calculate an anion gap (if information on electrolytes is available):
 

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