DR..ALI A. ALLAWI
CONSULTANT INTERNIST&NEPHROLOGIST COLLEGE OF MEDICINE BAGHDAD UNIVERSITYRegulation 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 pHRegulation 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 actionsChemical 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 bicarbBiological Regulation
Buffer actions that occurExchange of K+ and H+Carbon dioxide goes into RBCcarbonic acid (HCO3-)HCO3 ready to exchange with Cl-Chloride shift within RBC K+K+
K+
H+
H+
H+
H+
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 pHPhysiological Regulators
Lungs Regulate by altering H+ ions Metabolic acidosis Metabolic alkalosis Kidneys Regulate by altering HCO3 and H+ ionsH+
H+
H+
H+
HCO3
HCO3
HCO3
HCO3
Respiratory acidosis
pH ↓PaCO2 ↑HCO3 ↓ Respiratory alkalosispH ↑PaCO2 ↓HCO3 ↑ Metabolic acidosis
pH ↓PaCO2 HCO3 ↓ Metabolic alkalosis
pH ↑PaCO2HCO3 ↑
Increase pH – alkalosisDecrease pH – acidosisRespiratory – CO2Metabolic (kidneys)– HCO3CO2 has an inverse relationship with pHWhen pH goes down, CO2 goes upHCO3 follows pH. If pH goes up so does HCO3CO2 increases, pH decreases – resp. acidosisCO2 decreases, pH increases – resp. alkalosisHCO3 increases, pH increases – metabolic alkalosisHCO3 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 - 7.54, PaCO2 – 28, HCO3 – 222. pH – 7.32, PaCO2 – 46, HCO3 – 243. pH – 7.31, PaCO2 – 35, HCO3 – 204. pH – 7.5, PaCO2 – 37, HCO3 - 28Review
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 disturbancesAssessment Cont’d. Environmental factors affecting fluid/electrolyte alterationsDietLifestyle – smoking, ETOHMedicationsPhysical AssessmentDaily weightsI&OVital signsLaboratory Studies
Acid-Base Disturbances��pH must be within small range��Normal is 7.4��Large acid loads are produced by normalmetabolism
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 (7.35-7.45) 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 ofCO2 results in a �� pCO2 which thencauses renal retention of bicarbonate
Respiratory Acidosis: Causes�� �� respiratory exchange�� CNS Depressiontrauma/infections/tumorcerebrovascularaccidentsdrug overdose�� Neuromuscular disordersMyopathies�� Thoracic disordershydrothoraxpneumothorax�� Lung disorderbronchial obstructionemphysema (chronicobstructive airwaydisease)severe pulmonary edema
Respiratory Acidosis: Compensation��Problem: �� pCO2 and this results in a ��blood pH (high H+)��[H+] stimulates kidney to generate andretain bicarbonate��respiratory acidosis.is compensated for by thedevelopment of a metabolic alkalosis
Respiratory Acidosis: Compensation��Compensation is complete ([HCO3] levelsout) in 2-4 days��Final HCO3 can be calculated from thefollowing equation:��HCO3 mmol/L = 0.44 X pCO2 mmHg + 7.6 (+/-2).��Limit of compensation is a HCO3 of 45mmol/L
Respiratory Acidosis: Treatment�� Acute: correctunderlying source ofalveolarhypoventilation��Bronchodilators��Oxygen��Antibiotics/Drug therapy��Dialysis�� If it is chronic: try toavoid excessivesupplemental oxygen
Respiratory Alkalosis���� respiratory exchange with loss of CO2results in a �� pCO2 which then stimulatesrenal excretion of bicarbonate
Respiratory Alkalosis: Causes�� �� respiratoryexchange�� CNS disturbances�� Psychogenic (anxiety)�� Pregnancy�� Hypoxia�� Drug toxicity /overdose��Pulmonarydisorders��Embolism��Edema��Asthma��Pneumonia
Respiratory Alkalosis: Compensation��Problem: �� pCO2 causing �� blood pH(low H+)���� pH stimulates the kidney to excretebicarbonate��respiratory alkalosis is compensated for by thedevelopment of a metabolic acidosis
Respiratory Alkalosis: Compensation��If the condition has been present for 7days or more full compensation mayoccur.��Compensation is complete ([HCO3] levelsout) in 7-10 days.��The limit of compensation is a HCO3 of 12mmol/L.
Respiratory Alkalosis: Treatment��Treatment aims to eradicate theunderlying 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 relieveacute anxiety and increases carbon dioxidelevels