Evolution of Blood Gas Analysis - Acid-Base Balance and the - PowerPoint PPT Presentation

Evolution of Blood Gas Analysis - Acid-Base Balance and the Practical Applications of the Acid-Base Chart Ellis Jacobs, Ph.D, DABCC, FACB Associate Professor of Pathology, NYU School of Medicine Director of Pathology, Coler-Goldwater Hospital and Nursing 17/ 10/ 2013 Facility

2 Agenda Part 1 (Today)  Why measure blood gases  Overview of acid-base disturbances  Use of the Acid-Base Chart Part 2  Full value of the p O 2 assessment via  Oxygen uptake, Oxygen transport, Oxygen release  Why a measured saturation is the best  Assessment of tissue perfusion - Lactate

3 What is ABG?  Arterial Blood Gas - ABG:  pH, p O 2 and p CO 2  An ABG is routinely used in the diagnosis and monitoring of predominantly critically/ acutely ill patients  Additionally, ABG is useful in delivery of clinical care to some patients with acute and chronic respiratory disease

4 Information Provided by Blood Gas and CO-oximeter Data Cellular Production PCO 2 Blood pH vs Ventilatory Rem oval Acidity of CO 2 O 2 sat Hem oglobin PO 2 Oxygenation Blood Oxygenation HCO 3 Hb levels Oxy-Hb, deoxy-Hb, carboxy-Hb, m et-Hb Buffering Capacity

Gas Pressures in the Pulmonary 5 and Systemic Circulation Tracheal Air: PO 2 150mmHg PCO 2 0.2 mmHg Alveolar Air: PO 2 100 mmHg PCO 2 36 mmHg Venous Circulation: Arterial Circulation: PO 2 40 mmHg PO 2 90 mmHg Tissue Surface: PCO 2 40 mmHg PCO 2 46 mmHg PO 2 20 mmHg PCO 2 60 mmHg

6 Examples of reference intervals  pH  Children and adults: 7.35 - 7.45 (7.3 – 7.5)*  p CO 2  Male: 35 – 48 mmHg (4.7 - 6.4 kPa) (30 – 50 mmHg)*  Female: 32 - 45 mmHg (4.3 - 6.0 kPa)  p O 2  2 days - 60 years: 83 – 108 mmHg (11.0 - 14.4 kPa) (> 80)* * Clinically acceptable values

7 ABG  ABG allows assessment of  Pulmonary gas exchange: facility of the lungs to simultaneously add oxygen and remove carbon dioxide  Acid-base balance: ability of the body to maintain the pH of blood within narrow healthy limits  But there is much more information that can be obtained from a BG sample  Oxygen transport, energy supply, kidney function, intoxication and a lot more

8 Acid-base  The organism is depending on the acid-base balance to maintain a pH around 7.4 by excreting  CO 2 in the lungs  Non-carbonic acid or base via the kidneys  An acid-base imbalance may be caused by  Respiratory regulation  Metabolic regulation  Mixture of both

9 Acid-base disturbances – main causes  Disease of, damage to, one of the three organs whose function is necessary to maintain pH within normal interval:  Lungs  Kidney  Brain  Disease, or condition that results in increased production of metabolic acids - like lactic acid and keto acids - such that mechanisms for maintenance of normal pH are overwhelmed  Medical intervention (ventilation or drugs)

10 Acid-Base Balance  Normally, acid-base balance is maintained by 3 primary functions: Chemical Buffering Blood pH Respiratory Renal Control Regulation - ) (CO 2 ) (HCO 3

11 The synergistic role of lungs and kidney  pH is primarily regulated by the factors in the Henderson- Hasselbalch equation - ] pH = pK + log [HCO 3 α × p CO 2  Bicarbonate: p CO 2 ratio must be preserved to maintain pH within the normal range  If pH goes up, p CO 2 goes down and vise- versa

12 Regulation of p CO 2  If p CO 2 - ↑ then ventilation of the lungs will increase  If p CO 2 ↓ then ventilation of the lungs will decrease  The regulation of p CO 2 takes place within minutes  p CO 2 reflects how well the lungs are functioning

13 CO 2 transport 5 5 Bicarbonate pCO2 Bound to HgB Carbonic Acid 90

14 Diseases or conditions that effect Acid-Base Balance respiratory failure/ distress burns caused by COPD sepsis pneumonia cardiac arrest liver failure pulmonary edema fetal distress pulmonary embolism asthma traumatic brain injury acute respiratory distress cerebral edema syndrome brain tumor Guillain Barre syndrome drug overdose/ toxic poisoning traumatic chest injury (e.g. salicylate, antacids, acute/ chronic renal failure opiates, barbiturates, diabetic ketoacidosis diuretics, methanol, circulatory failure (shock) due to ethanol and ethylene glycol) severe hemorrhage mechanical ventilation etc.

15 Signs and symptoms of Acid-Base disturbance coma/ reduced consciousness drowsiness, confusion convulsions/ seizures combativeness lethargy headache reduced blood pressure breathlessness/ shortness of breath/ difficulty breathing wheezing/ chronic cough reduced or increased respiratory rate cardiac arrhythmia anuria/ polyuria, muscle spasm/ tetany electrolyte disturbance

16 - Bicarbonate - HCO 3  Bicarbonate is the principal buffer in blood plasma  90 % of CO 2 is transported as bicarbonate  The kidneys are vital for a well-regulated pH  The concentration of bicarbonate indicates the buffering capacity of blood  Low bicarbonate indicates that a larger pH change will occur for a given amount of acid or base produced  Bicarbonate is classified as the metabolic component of acid-base balance

17 - Bicarbonate - HCO 3  In the blood gas analyzer bicarbonate is calculated from the measurement of pH and p CO 2 via the Henderson- Hasselbalch equation: - ] pH = pK + log [HCO 3 α × p CO 2  This is the actual bicarbonate, and the standard bicarbonate is corrected from deviation from normal of the respiratory component of acid-base balance ( p CO 2 = 40 mmHg, p O 2 = 100 mmHg and at 37 ° C)

18 Actual or standard bicarbonate? - •Standard HCO 3 •More precise measure of metabolic (non-respiratory) component - •Eliminates effect of respiratory component on HCO 3 Wettstein R Wilkins R I nterpretation of Blood Gases (Chapter 8) I n: Clinical Assessment in Respiratory Care (6 th ed) Mosby: St Louis Missouri 2010

19 - Bicarbonate - HCO 3 - in 1. Consumption of HCO 3 buffering excessive acid production - from the body 2. Loss of HCO 3 - 3. Failure to regenerate HCO 3 - 1. I ncreased generation of HCO 3 consequent of excessive loss of hydrogen ions and/ or chloride ions 2. Excessive administration/ ingestion - of HCO 3

20 Some terms for acid base disorders Acidosis Alkalosis  Clinical term for the process that  Clinical term for the process that gives rise to acidemia, typically gives rise to alkalemia, typically associated with pH < 7.35 initially. associated with pH > 7.45 initially. Acid-base disturbance that results from primary increase in p CO 2 . Respiratory acidosis Associated with reduced pH (in the absence of metabolic compensation). Acid-base disturbance that results from primary decrease in p CO 2 . Respiratory alkalosis Associated with increased pH (in the absence of metabolic compensation). Acid-base disturbance that results from primary reduction in HCO 3 - . Metabolic acidosis It is associated with reduced pH. - . Acid-base disturbance that results from primary increase in HCO 3 Metabolic alkalosis It is associated with increased pH.

21 Respiratory disorders Respiratory acidosis Respiratory alkalosis pH p CO 2 pH p CO 2 Emphysema, COPD, Hyper-ventilation, Pneumonia, depression Anxiety attacks, of respiratory center stimulation of brain respiratory center

22 Metabolic disorders Metabolic alkalosis Metabolic acidosis HCO 3 - HCO 3 - pH pH Renal failure, Bicarbonate diabetic administration, ketoacidosis, potassium depletion circulatory failure

23 Acid-base disturbances and its compensation Respiratory acidosis Respiratory alkalosis Metabolic acidosis Metabolic alkalosis Prim ary issue Primary increase Primary decrease Primary decrease Primary increase in p CO2 in p CO2 in bicarb. in bicarb. Som e com m on Emphysema, COPD, Hyper-ventilation, Renal failure, diabetic Bicarbonate causes pneumonia, depression anxiety attacks, ketoacidosis, administration, of respiratory center stimulation of brain circulatory failure Potassium depletion respiratory center I nitial blood gas pH decreased pH increased pH decreased pH increased results - p CO 2 increased p CO 2 decreased p CO 2 normal p CO 2 normal uncom pensated Bicarbonate normal Bicarbonate normal Bicarbonate decreased Bicarbonate increased Com pensatory RENAL: RENAL: RESPIRATORY: RESPIRATORY: m echanism increase bicarbonate decrease bicarbonate decrease p CO 2 increase p CO 2 but limited compensation in metabolic alkalosis Blood gas results pH decreased but pH increased but closer pH decreased but Limited compensation after partial closer to normal to normal closer to normal in metabolic alkalosis com pensation p CO 2 increased p CO 2 decreased p CO 2 marginally Bicarbonate increased Bicarbonate marginally decreased decreased Bicarbonate decreased Blood gas pH normal pH normal pH normal Limited compensation results after p CO 2 increased p CO 2 decreased p CO 2 decreased in metabolic alkalosis full com pensation Bicarbonate increased Bicarbonate decreased Bicarbonate decreased