Concentration of Hydrogen ions in extracellular fluid is determined by ratio of bicarbonates to carbonic acid . The normal ratio is 20:1 , even when arterial blood gases are abnormal , if the ratio remains 20:1 , no imbalance will occcur .
Types of acid base Imbalance
1. Respiratory Acidosis
2. Respiratory Alkalosis
3. Metabolic Acidosis
4. Metabolic Alkalosis
1. Respiratory Acidosis
In respiratory Acidosis , the total concentration of buffer bae is lower than normal with relative increase in hydrogen ion concentration , so there will greater no. of hydrogen ions in circulating blood .
- Always remember in acidosis, pH is decreased.
ABG OR LAB VALUE IN RESPIRATORY ACIDOSIS
pH : Decreased
Hco3 : Normal
Pao2 : Decreased
Paco2 : Increased
K+ : Increased
Causes of Respiratory Acidosis
- Asthma
- Atelactasis
- Brain trauma
- Bronchiectasis
- Bronchitis
- Emphysema
- Hypoventilation
- pnemonia
- pulmonary edema
- pulmonary emboli
2. Respiratory Alkalosis
A deficit of carbonic acid and decrease in hydrogen ions concentration that results from accumulation of base or from loss of acids .
- In Alkalosis, pH is Increased .
ABG OR LAB VALUE IN RESPIRATORY ALKALOSIS
pH : Increased
Hco3 : Normal
Pao2 : Usually Normal
Paco2 : Decreased
K+ : Decreased
Causes of Respiratory Alkalosis
- Fever
- Hyperventilation
- Hypoxia
- Hysteria
- over ventilation by mechanical ventilators
- Pain
3. Metabolic Acidosis
A total concentration of buffer base that is lower than normal , with relative increase in hydrogen ion concentration.
ABG OR LAB VALUE IN METABOLIC ACIDOSIS
pH : Decreased
Hco3 : Decreased
Pao2 : usually Normal
Paco2 : Normal
K+ : Increased
Causes of Metabolic Acidosis
- Diabetes mellitus or Diabetic Ketoacidosis DKA
- Excessive ingestion of acetylsalicylic acid
- High fat diet
- Malnutrition
- Severe diarrhea
- acute kidney injury or chronic kidney disease.
4. Metabolic Alkalosis
A deficit of carbonic acid and decrease in hydrogen ion concentration that results from accumulation of base or from loss of acid without a comparable loss in the body fluid .
ABG OR LAB VALUE IN METABOLIC ALKALOSIS
pH : Increased
Hco3 : Increased
Pao2 : usually Normal
Paco2 : Normal
K+ : Decreased
Causes of Metabolic Alkalosis
- Diuretics
- Excessive vomiting or gastrointestinal suctiong
- Hyperaldosteronism
- Massive transfusion of whole bloog
- Infusion of excess sodium bicarbonate
Arterial Blood Gas analysis (ABG)
Important Point to remember
- In acidosis , pH is Decreased
- In alkalosis , pH is elevated
- The respiratory function indicator os the Pco2
- The Metabolic function indicator is bicarbonate ion Hco3
Acid Base imbalance chart ( ABG interpretation chart )
Steps in Arterial Blood Gas analysis (ABG) analysis
Step 1 :
- Look at the blood gas report
- Look at the pH . Is the pH is elevated or decreased ?
- If the pH is elevated , it reflects Alkalosis
- or if pH is decreased , it reflects Acidosis
Step 2 :
- Look at the pco2 . Is the pco2 elevated or decreased ?
- If the Pco2 reflects opposite relationship to pH then the condition is respiratory imbalance ( Eg. PH decreased and pCo2 increased or pH increased pco2 decreased ) .
- if the Pco2 does not reflect opposite relationship to pH , go to step 3 .
Step 3:
- Look at the HCO3 .
- Does HCO3 reflects corresponding relationship with pH ? ( Eg . pH decreased HCO3 decreased or pH increased HCO3 also increased ) .
- Then the condition is a metabolic imbalance .
Step 4 :
- Full compansation has occured if the pH in a normal range of 7.35 to 7.45 .
- If the is not within normal range , look at respiratory or metabolic function indicators.
- If the condition is respiratory imbalance , look at HCO3 to determine state of compensation .
- If the condition is metabolic imbalance , look at the Pco2 to determine the state of compensation .
Also Read : Ryles Tube procedure and different type of ryles tube