Acid-Base Balance
Metabolic activities rely on regulation of acid-base of ECF
pH of ECF normal is 7.35-7.45
Terms
Acid- molecule that can dissociate and release a hydrogen ion (H+) when combined with water
Base- molecule that can accept or combine with hydrogen ion (H+) when combined with water
pH-the concentration of H+ of solution
pH inversely related to H+ concent
pH balance
Body cells are extremely sensitive to their environment
Slight changes in pH can affect normal cell functioning
pH refers to the measurement of relative balance between acids and bases in solution
pH is a negative logarithm of H+ in mEq/L
Acid-Base
Exist as buffer pairs
Mix of weak acid and base OR
Mix of weak base and acid OR
Mix of strong acid/base
Mix of strong base/acid
Negative Logarithm
-When acid is added to solution, pH will go down. <7.35
-When base is added to solution, pH will go up. >7.4
Arterial Blood
Human blood is considered slightly alkalotic
normal pH is between 7.35-7.45
Human blood normally maintains ratio of 1 acid to 20 bases
Primary acid is CO2
Primary base is HCO3
-The less H2CO3= Acidodic , the more HC03-= Alkalotic. The more CO2= Acidodic,
Regulation of pH
1) Chemical Buffer Systems
2) Respiratory Control Mechanisms
3) Renal Control Mechanisms
Chemical Buffer Systems
*Bicarbonate Buffer System
Exchange of acids/bases within ICH and ECF to regulate pH. Kidneys will either dump or retain bicarb and hydrogen ion to regulate acid-base.
*Hydrogen/Potassium Exchange System: -When there's too much hydrogen on board, potassiu
Acid-Base and Potassium Imbalances
Acidosis:
H+ diffuses into cells and drives out K+, elevating K+ concentration in ECF-- hyperkalemia
Alkalosis:
H+ diffuses out of cells and K+ diffuses in-- hypokalemia
Respiratory Control Mechanism
-Eliminating or retaining CO2 by the lungs also regulates acid-base balance.
CO2 + H2O H2CO3 (carbonic acid)
-The respond is rapid, occur within minutes by altering the rate and depth of respiration
-Carbon Dioxide is a powerful stimulator of the respirat
Respiratory Regulation
PaC02 represents partial pressure of carbon dioxide in arterial blood.
The normal PaCo2 is 35 to 45 mm Hg
Increasing ventilation increases pH by eliminating C02 (makes it alkalotic)
Decreasing ventilation decreases pH by retaining C02.
An acute rise in PC
Renal Control Mechanism (Metabolic)
Kidney regulate pH of ECF:
Elimination of H+ in urine
Reabsorption of HCO3
Production of new bicarbonate
Acid-Base Imbalances
Metabolic Acidosis
Metabolic Alkalosis
Respiratory Acidosis
Respiratory Alkalosis
Laboratory Tests
Arterial Blood Gases
-Can assess respiratory component of pH balance
CO2 & Bicarbonate levels on electrolyte panels
Arterial Blood Gases
pH normal 7.35-7.45
Acidosis: < 7.35
Alkalosis: >7.45
Paco2 normal 35-45 (Resp. component)
Bicarbonate normal 21-28 (Metabolic component)
Metabolic Acidosis
pH decreases, HC03 decrease, PCO2 is the same, (H increases?)
Low HCO3
Decreased bicarbonate with low pH
Caused by:
-Increased metabolic acids
-Inability of kidneys to excrete acid
-Excess loss of bicarbonate via kidneys/GI
-Increased Chloride
-If you los
Clinical Causes of Metabolic Acidosis
Overproduction of Acids:
Diabetic ketoacidosis
Starvation ketoacidosis
Anaerobic metabolism
Overdose of salicylic acid or ferrous sulfate
Renal failure, uremia
Severe body loss of bicarbonate
Diarrhea
Pancreatic secretions lost via pancreatic fistulas
Exc
Body's Compensation for Metabolic Acidosis
-Hyperactive breathing to "blow off" CO2 (acid)
-Kidney's conserve bicarbonate and eliminate H ions in urine
-Lactate solution used in therapy is converted to bicarbonate ions in liver
Metabolic Alkalosis
pH is high, C02 has no change, HC03 increases (H decreases?)
-Increased bicarbonate with elevated pH
Caused by:
-Increased bicarb administration
-Loss of Cl and Potassium
-Excess loss of acid via kidneys/GI
-Increased bicarb levels by contraction of ECF v
Clinical Causes of Metabolic Alkalosis
Excess base loading:
Antacids
Ringer's lactate
Loss of acid:
Gastric suctioning
Vomiting
Thiazide/loop diuretics
Contraction of ECF:
Decrease in ECF due to vomiting/NGT suction leads to loss of CL and reabsorbtion of NA and Bicarb
Body's compensation for Metabolic Alkalosis
Breathing suppressed to hold CO2
Alkaline Urine-Kidneys conserve H ions and eliminate HCO3 in urine
-Chloride-containing solution where HCo3 ions are replaced by Cl
Respiratory Acidosis
Increase in CO2 (acid) with decreased pH, (HC03 no change)
Caused by:
Acute disorders of ventilation
Chronic disorders of ventilation
Increased Carbon dioxide production
Clinical Causes of Respiratory Acidosis
Acute Disorders of Ventilation
Impaired function of respiratory center in medulla
Lung disease
Chest injury
Weakness of respiratory muscles
Airway obstruction
Chronic Disorders of Ventilation
COPD
Pulmonary fibrosis
Increased PCO2 Production
Exercise
Feve
Respiratory Alkalosis
Decrease PCO2 with increased pH
Caused by:
Hyperventilation
Central stimulation of respiratory center
Stimulation of peripheral pathways to respiratory center
Clinical Causes of Respiratory Alkalosis
Central Stimulation
Anxiety
Pain
Pregnancy
Febrile states
Sepsis
Encephalitis
Salicylate toxicity
Hypoxemia
Stimulation of chemoreceptors in carotid bodies due to high altitudes
Hyperventilation
Anxiety
Mixed Acidosis or Alkalosis
Results when 2 or more primary acid-base disorders are present simultaneously.
pH may change more dramatically in direction of acidosis or alkalosis depending on specific disorders involved
Examples of Mixed
Renal failure + Narcotic-induced respiratory depression = metabolic acidosis + respiratory acidosis
COPD + diarrhea=respiratory acidosis + metabolic acidosis
Compensation
The body's attempt to return the ratio of acid to base back toward 1:20 to maintain the pH between 7.35-7.45
The patient is not considered to be compensated unless pH is within normal range.
If changes in that direction are noted either in PaCo2 or HCO3 w
Arterial Blood Gas Interpretation
Normal Values:
pH 7.35-7.45
PaCO2 35-45 mm Hg
HCO3 22-26 mEq/L
PaO2 80-100 mm Hg
O2 Sat. 95% or greater
Analysis
Evaluation of components
Respiratory component: PaCO2
Regulated by the lungs
Normal: 35-45 mm Hg
Low: <35 mm Hg (Respiratory alkalosis)
-Hyperventilation
-Decrease carbonic acid
-Increase in pH
High:>45mm Hg (Respiratory Acidosis)
-Hypoventilation
-increa
Analysis
Acidosis /Alkalosis is determined by pH
Causes reflected by changes in PaCO2 and/or HCO3
PaCO2 reflects respiratory changes
HCO3 reflects metabolic processes
Analysis
Alkalosis Respiratory:
pH>7.45
Decreased PaCO2
Metabolic Alkalosis:
pH>7.45
Increased HCO3
Mixed Alkalosis:
pH>7.45
Decreased PaCO2
Increased HCO3
Acidosis Respiratory:
pH<7.35
Increased PaCO2
Metabolic Acidosis:
pH<7.35
Decreased HCO3
Mixed Acidosis:
pH<