DR..ALI A. ALLAWI CONSULTANT INTERNIST&NEPHROLOGIST COLLEGE OF MEDICINE BAGHDAD UNIVERSITY

Regulation of Acid-Base Balance Lungs and kidneys are our buffering systems A buffer is a substance that can absorb or release H+ to correct an acid-base imbalance Arterial pH is an indirect measure of hydrogen ion concentration Greater concentration of H+, more acidic, lower pH

Regulation of Acid-Base Balance Lower concentration of H+, more alkaline, higher pH The pH is also a reflection of the balance between CO2 (regulated by lungs) and bicarb (regulated by kidneys) Normal H+ level is necessary to –Maintain cell membrane integrity –Maintain speed of cellular enzymatic actions

Chemical Regulation Carbonic acid-bicarbonate buffer system is the first to react to change in the pH of ECF H+ and CO2 concentrations are directly related ECF becomes more acidic, the pH decreases, producing acidosis ECF receives more base substances, the pH rises, producing alkalosis Lungs primarily control excretion of CO2 resulting from metabolism Kidneys control excretion of hydrogen and bicarb

Biological Regulation 1.Buffer actions that occur 1.Exchange of K+ and H+ 2.Carbon dioxide goes into RBC  carbonic acid (HCO3-) 1.HCO3 ready to exchange with Cl- 3.Chloride shift within RBC K+ H+

Acidosis vs Alkalosis Acidosis –Acids have high H+ ions in solution Alkalosis –Bases have low H+ ion concentration Acidity or Alkalinity of a solution measured by pH

Physiological Regulators Lungs –Regulate by altering H+ ions –Metabolic acidosis –Metabolic alkalosis Kidneys –Regulate by altering HCO3 and H+ ions H+ HCO3

Respiratory acidosis pH ↓ PaCO2 ↑ HCO3 ↓ Respiratory alkalosis pH ↑ PaCO2 ↓ HCO3 ↑ Metabolic acidosispH ↓ PaCO2 HCO3 ↓ Metabolic alkalosis pH ↑ PaCO2 HCO3 ↑

Increase pH – alkalosis Decrease pH – acidosis Respiratory – CO2 Metabolic (kidneys)– HCO3 CO2 has an inverse relationship with pH When pH goes down, CO2 goes up HCO3 follows pH. If pH goes up so does HCO3 CO2 increases, pH decreases – resp. acidosis CO2 decreases, pH increases – resp. alkalosis HCO3 increases, pH increases – metabolic alkalosis HCO3 decreases, pH decreases – metabolic acidosis

Question An older man comes to the emergency department experiencing chest pain and shortness of breath. An arterial blood gas is ordered. Which of the following ABG results indicates respiratory acidosis? 1. pH , PaCO2 – 28, HCO3 – pH – 7.32, PaCO2 – 46, HCO3 – pH – 7.31, PaCO2 – 35, HCO3 – pH – 7.5, PaCO2 – 37, HCO3 - 28

Review Acid/Base Imbalance Tutorial How do we assess for acid-base balance?

Assessment clinical history –Age Prior Medical History –Acute illness –Surgery –Burns increase fluid loss –Resp. disorder predisposes to resp. acidosis –Head Injury can alter ADH secretion –Chronic illness Cancer CVD Renal disorders GI disturbances

Assessment Cont’d. Environmental factors affecting fluid/electrolyte alterations Diet Lifestyle – smoking, ETOH Medications Physical Assessment –Daily weights –I&O –Vital signs Laboratory Studies

Acid-Base Disturbances pH must be within small range Normal is 7.4 Large acid loads are produced by normal metabolism

Some definitions… pH defines the blood [H+] concentration Low (<7.35) = Acidemia High (>7.45) = Alkalemia

Some definitions… [HCO3] defines the metabolic component Low (<20 mmol/L) = Metabolic acidosis High (>33 mmol/L) = Metabolic alkalosis

Basic Evaluation High pH (>7.45) suggests: Respiratory alkalosis - pCO2 < 35mmHg Metabolic alkalosis - [HCO3] > 33 mmol/L.

Basic Evaluation Low pH (<7.35) suggests: Respiratory acidosis - pCO2 > 45 mmHg Metabolic acidosis - [HCO3] < 23 mmol/L

Normal pH? Normal pH ( ) suggests: No acid-base disturbance Chronic respiratory alkalosis Chronic respiratory acidosis (mild) Mixed disturbance

Buffer Systems Bicarbonate – carbonic acid system Lungs excrete Proteins and phosphates Kidneys excrete

Respiratory Acidosis respiratory exchange with retention of CO2 results in a pCO2 which then causes renal retention of bicarbonate

Respiratory Acidosis: Causes respiratory exchange CNS Depression trauma/infections/tumor cerebrovascular accidents drug overdose Neuromuscular disorders Myopathies Thoracic disorders hydrothorax pneumothorax Lung disorder bronchial obstruction emphysema (chronic obstructive airway disease) severe pulmonary edema

Respiratory Acidosis: Compensation Problem: pCO2 and this results in a blood pH (high H+) [H+] stimulates kidney to generate and retain bicarbonate respiratory acidosis.is compensated for by the development of a metabolic alkalosis

Respiratory Acidosis: Compensation Compensation is complete ([HCO3] levels out) in 2-4 days Final HCO3 can be calculated from the following equation: HCO3 mmol/L = 0.44 X pCO2 mmHg (+/- 2). Limit of compensation is a HCO3 of 45 mmol/L

Respiratory Acidosis: Treatment Acute: correct underlying source of alveolar hypoventilation Bronchodilators Oxygen Antibiotics/Drug therapy Dialysis If it is chronic: try to avoid excessive supplemental oxygen

Respiratory Alkalosis respiratory exchange with loss of CO2 results in a pCO2 which then stimulates renal excretion of bicarbonate

Respiratory Alkalosis: Causes respiratory exchange CNS disturbances Psychogenic (anxiety) Pregnancy Hypoxia Drug toxicity / overdose Pulmonary disorders Embolism Edema Asthma Pneumonia

Respiratory Alkalosis: Compensation Problem: pCO2 causing blood pH (low H+) pH stimulates the kidney to excrete bicarbonate respiratory alkalosis is compensated for by the development of a metabolic acidosis

Respiratory Alkalosis: Compensation If the condition has been present for 7 days or more full compensation may occur. Compensation is complete ([HCO3] levels out) in 7-10 days. The limit of compensation is a HCO3 of 12 mmol/L.

Respiratory Alkalosis: Treatment Treatment aims to eradicate the underlying condition removal of ingested toxins treatment of fever or sepsis (toxin) treatment of CNS disease In severe respiratory alkalosis: breathing into a paper bag, which helps relieve acute anxiety and increases carbon dioxide levels

IV. Mixed acid-base disturbance 1. dual acid-base disturbance 1) metabolic acidosis plus respiratory acidosis heart beat [HCO - 3 ] respiration stop character PaCO 2 pH 2) metabolic alkalosis plus respiratory alkalosis hepatic NH 3 PaCO 2 failure diuretic character [HCO - 3 ] pH 3) respiratory acidosis plus metabolic alkalosis pulmonary heart disease diuretic pH ±

4) respiratory alkalosis plus metabolic acidosis infective shock fever pH ± 5) metabolic acidosis plus metabolic alkalosis ketoacidosis(diabetes) vomiting pH ± 2. triple acid-base disturbance 1) respiratory acidosis; metabolic acidosis and alkalosis pulmonary heart disease; vomiting 2) respiratory alkalosis; metabolic acidosis and metabolic alkalosis fever; vomiting; diarrhea (food poisoning)