The buffer reactions are:

  
    
      
        
          
            H
            
              +
            
          
          +
          
            HCO
            
              3
            
            
              −
            
          
          
            
              
                
                  
                    
                      ↽
                    
                    
                    
                    
                      −
                    
                  
                
              
              
                
                  
                    
                      −
                    
                    
                    
                    
                      ⇀
                    
                  
                
              
            
          
          
            H
            
              2
            
            
              
            
          
          
            CO
            
              3
            
            
              
            
          
          
            
              
                
                  
                    
                      ↽
                    
                    
                    
                    
                      −
                    
                  
                
              
              
                
                  
                    
                      −
                    
                    
                    
                    
                      ⇀
                    
                  
                
              
            
          
          
            CO
            
              2
            
            
              
            
          
          +
          
            H
            
              2
            
            
              
            
          
          O
        
      
    
    {\displaystyle {\ce {H+ + HCO3- <=> H2CO3 <=> CO2 + H2O}}}
  The Henderson-Hasselbalch equation mathematically describes the relationship between blood pH and the components of the bicarbonate buffering system:

  
    
      
        
          pH
        
        =
        
          
            pK
          
          
            a
          
        
        +
        
          
            L
            o
            g
          
        
        ⁡
        
          
            
              [
              
                
                  HCO
                
                
                  3
                
                
                  −
                
              
              ]
            
            
              [
              
                
                  CO
                
                
                  2
                
              
              ]
            
          
        
      
    
    {\displaystyle {\text{pH}}={\text{pK}}_{a}+\mathop {\mathrm {Log} } {\frac {\left[{\text{HCO}}_{3}^{-}\right]}{\left[{\text{CO}}_{2}\right]}}}
  

Using Henrys law, we can say that [CO2] = 0.03 × PaCO2
(PaCO2 is the pressure of CO2 in arterial blood)
Adding the other normal values, we get
  
    
      
        
          pH
        
        =
        6.1
        +
        
          
            L
            o
            g
          
        
        ⁡
        
          [
          
            
              24
              
                0.03
                ×
                40
              
            
          
          ]
        
      
    
    {\displaystyle {\text{pH}}=6.1+\mathop {\mathrm {Log} } \left[{\frac {24}{0.03\times 40}}\right]}
  

  
    
      
        =
        6.1
        +
        1.3
      
    
    {\displaystyle =6.1+1.3}
  

  
    
      
        =
        7.4
      
    
    {\displaystyle =7.4}

Consequences
Acute Metabolic Acidosis
Acute Metabolic Acidosis most often occurs during hospitalizations, and acute critical illnesses.
Increased anion gap
Causes of increased anion gap include: 

Lactic acidosis
Ketoacidosis (e.g., Diabetic, alcoholic, or starvation)
Chronic kidney failure
Transient 5-oxoprolinemia due to long-term ingestion of high-doses of acetaminophen (often seen with sepsis, liver failure, kidney failure, or malnutrition)
Intoxication:
Salicylates, methanol, ethylene glycol
Organic acids, paraldehyde, ethanol, formaldehyde
Carbon monoxide, cyanide, ibuprofen, metformin
Propylene glycol (metabolized to L and D-lactate and is often found in infusions for certain intravenous medications used in the intensive care unit)
Massive rhabdomyolysis
Isoniazid, iron, phenelzine, tranylcypromine, valproic acid, verapamil
Topiramate
SulfatesNormal anion gap
Causes of normal anion gap include
Inorganic acid addition
Infusion/ingestion of HCl, NH4Cl
Gastrointestinal base loss
Diarrhea
Small bowel fistula/drainage
Surgical diversion of urine into gut loops
Renal base loss/acid retention:
Proximal renal tubular acidosis
Distal renal tubular acidosisHyperalimentation
Addison disease
Acetazolamide
Spironolactone
Saline infusionTo distinguish between the main types of metabolic acidosis, a clinical tool called the anion gap is considered very useful. It is calculated by subtracting the sum of the chloride and bicarbonate levels from the sum of the sodium and potassium levels. As sodium is the main extracellular cation, and chloride and bicarbonate are the main anions, the result should reflect the remaining anions. Normally, this concentration is about 8–16 mmol/L (12±4). An elevated anion gap (i.e. > 16 mmol/L) can indicate particular types of metabolic acidosis, such as types caused by certain poisons, lactate acidosis, and ketoacidosis. It is important to note that the anion gap can be spuriously normal in sampling errors of the sodium level, e.g. in extreme hypertriglyceridemia. The anion gap can also be increased due to relatively low levels of cations other than sodium and potassium (e.g.