Acid-Base Balance & Arterial Blood Gases PDF

ACID-BASE BALANCE ARTERIAL BLOOD GASES PREPARED BY: ADRIAN JUSTIN G. MARASIGAN, RTRP  PRESENTATION OUTLINE ADRIAN JUSTIN GALLO ACID-BASE BALANCE ACID-BASE DISTURBANCES ARTERIAL BLOOD GAS SAMPLING OTHER METHODS FOR SAMPLING MARASIGAN ARTERIAL BLOOD GAS ANALYSIS OTHER TECHNIQUES F...

ACID-BASE BALANCE ARTERIAL BLOOD GASES PREPARED BY: ADRIAN JUSTIN G. MARASIGAN, RTRP  PRESENTATION OUTLINE ADRIAN JUSTIN GALLO ACID-BASE BALANCE ACID-BASE DISTURBANCES ARTERIAL BLOOD GAS SAMPLING OTHER METHODS FOR SAMPLING MARASIGAN ARTERIAL BLOOD GAS ANALYSIS OTHER TECHNIQUES FOR MONITORING BLOOD GASES INTERPRETATION OF ARTERIAL BLOOD GAS RESULT RTRP 2024  ACID-BASE BALANCE ADRIAN JUSTIN Refers to physiologic mechanisms that keep [H+] of body fluids in a range that supports life Body fluids must be kept in a narrow pH range of 7.35 to 7.45 to GALLO function normally This corresponds to [H+] of 45 to 35 nmol/L [H+] ions formed in the body come from either volatile or fixed acids MARASIGAN RTRP 2024  ACID ADRIAN JUSTIN A chemical that gives off/donates [H+] proton donator The body constantly produces acids as a byproduct of metabolism GALLO Carbonic Acid (H2CO3): Formed from the breakdown of carbohydrates and fats Lactic Acid: Produced during intense exercise MARASIGAN Ketoacids: Generated during the breakdown of fats RTRP 2024  BASE ADRIAN JUSTIN A molecule in an aqueous solution that can accept protons or donate electrons Blood is normally slightly basic, with a normal pH range of about 7.35 GALLO to 7.45 Alkaline Reserve: to counteract metabolic process that produce acid MARASIGAN RTRP 2024  BUFFER SOLUTION ADRIAN JUSTIN Resists changes in pH when an acid or a base is added to it Are aqueous mixtures of acid and bases Acid Component: [H+] cation GALLO Base Component: remaining anion Blood buffers are classified as bicarbonate or nonbicarbonate buffer systems MARASIGAN RTRP 2024  BICARBONATE BUFFER SYSTEM ADRIAN JUSTIN OPEN BUFFER SYSTEM H2CO3 is in equilibrium with dissolved CO2, which is readily removed by ventilation GALLO consists of H2CO3 and its conjugate base, HCO3- When H+ is buffered by HCO3-, the product, H2CO3, is broken down into H2O and CO2 as long as ventilation removes CO2 MARASIGAN Buffers only H+ produced by fixed acids; cannot buffer volatile acid RTRP 2024  BICARBONATE BUFFER SYSTEM ADRIAN JUSTIN Bicarbonate buffer systems cannot buffer carbonic acid (volatile acid), which accumulates in the blood whenever ventilation fails to eliminate CO2 as fast as it is produced (hypoventilation) GALLO The resulting accumulation of CO2 drives the hydration reaction in the direction that produces more carbonic acid, H+, and HCO3- MARASIGAN RTRP 2024  NONBICARBONATE BUFFER SYSTEM ADRIAN JUSTIN CLOSED BUFFER SYSTEM All the components of acid-base reactions remain in the system All nonbicarbonate buffer systems are grouped together and GALLO represented as Hbuf/Buf- Hbuf: Weak Acid Buf-: Conjugate Base MARASIGAN Hb is most important simply because it is the most abundant Buffers both H+ of volatile acids and fixed acids RTRP 2024 ADRIAN JUSTIN GALLO MARASIGAN RTRP 2024  BUFFER SYSTEMS ADRIAN JUSTIN Both systems are physiologically important, each playing a unique and essential role in maintaining pH homeostasis Bicarbonate buffers have the greatest buffering capacity because GALLO they function in an open system MARASIGAN RTRP 2024  BUFFER SYSTEMS ADRIAN JUSTIN GALLO MARASIGAN RTRP 2024 HENDERSON-HASSELBACH EQUATION ADRIAN JUSTIN The H-H equation allows the pH, HCO3-, or PCO2, to be computed if two of these three variables are known Blood gas analyzers measure pH and PCO2, but compute HCO3- GALLO useful in checking a clinical blood gas report to see if the pH, PCO2, and HCO3- values are compatible with one another MARASIGAN RTRP 2024  ACID EXCRETION ADRIAN JUSTIN Lungs and Kidneys are the primary acid-excreting organs Lungs: Can only excrete volatile acids (CO2) Kidneys also remove fixed acids but at a slow pace GALLO Individuals affected by disease, failure of one system can be partially offset by a compensatory response MARASIGAN RTRP 2024  LUNGS ADRIAN JUSTIN Because the volatile acid H2CO3 is in equilibrium with dissolved CO2, the lungs can decrease blood H2CO3 concentration through ventilation GALLO Elimination of CO2 is crucial because normal aerobic metabolism produces large quantities of CO2, which reacts with H2O to form H2CO3 MARASIGAN Approximately 24,000 mmol/L of CO2 is removed from the body daily through normal ventilation RTRP 2024  KIDNEYS ADRIAN JUSTIN The kidneys physically remove H+ from the body by: Excretion: elimination of substances from the body in the urine Secretion GALLO Reabsorption Kidneys excrete less than 100 mEq/L of fixed acid per day MARASIGAN Compared with the ability of lungs to change the blood PCO2 in seconds, the renal process is slow, requiring hours to days Kidneys influence blood pH by reabsorbing or excreting HCO3- RTRP 2024 if pCO2 is high: Kidneys excrete more H+ and absorbs HCO3- if pCO2 is low: Kidneys excrete less H+ and more HCO3-  ADRIAN JUSTIN GALLO ARTERIAL BLOOD GAS SAMPLING AND ANALYSIS MARASIGAN RTRP 2024  ABG ADRIAN JUSTIN ABGs are considered the “gold standard” of gas exchange analysis Blood gas analysis monitors the following physiologic variables GALLO PaO2: Arterial Oxygenation PaCO2: Alveolar Ventilation pH: Acid-Base status MARASIGAN PvO2: Tissue Oxygenation other components: Bicarbonate (HCO3-) RTRP 2024 Base Excess  ARTERIAL OXYGENATION ADRIAN JUSTIN PaO2 (Arterial PO2) is the portion of O2 that is dissolved in the plasma of blood GALLO For every 1 mmHg of PaO2, there is 0.003 mL of dissolved O2 PAO2 - (Alveolar PO2) Is calculated by the following formula MARASIGAN RTRP 2024  ARTERIAL OXYGENATION ADRIAN JUSTIN GALLO MARASIGAN RTRP 2024  ARTERIAL OXYGENATION ADRIAN JUSTIN P(A-a)O2 Difference between alveolar O2 Tension and arterial O2 tension GALLO Formula: PAO2-PaO2 Normal Value: 4-12 mmHg P/F ratio or PaO2/FiO2 ratio MARASIGAN Used in determination of acute lung injury (ALI) or Acute Respiratory Distress Syndrome Measures the efficiency of oxygen transfer across the lung Formula: PaO2/FiO2 (in decimals) RTRP 2024 NORMAL VALUE: >300 mmHg  ARTERIAL OXYGENATION ADRIAN JUSTIN Arterial Oxygen Saturation (SaO2) The percentage of the hemoglobin that is bound by oxygen GALLO SaO2 value reported by a blood gas analyzer is calculated actual saturation can be measured using hemoximeter or co- oximeter Large differences between the calculated and measured values MARASIGAN may be due to elevated carbon monoxide (COHb) levels Normal Value: 95-100% Formula: PaO2 = SaO2 - 30 RTRP 2024  ARTERIAL OXYGENATION ADRIAN JUSTIN Arterial Oxygen Content (CaO2) Most effective method for determining the O2-carrying capacity GALLO of a patient’s blood Blood Carries O2 in two ways Bound to Hb: 1g of Hb is capable of carrying 1.34mL of O2 Formula: (1.34 x Hb x SaO2) MARASIGAN Dissolved in Plasma: 0.003 mL of O2 dissolves in plasma for every 1mmHg of O2 tension (PaO2) Formula: (0.003 x PaO2) Cao2 formula : RTRP 2024 NORMAL VALUE: 16-20 %VOL (mL/dL)  ARTERIAL OXYGENATION ADRIAN JUSTIN GALLO MARASIGAN RTRP 2024  HbO2 Dissociation Curve ADRIAN JUSTIN This curve plots the relationship between PaO2 and SaO2 and the affinity that Hb has for O2 at various saturation levels GALLO Shift to the Left Increase oxygen affinity Higher O2 content for any PO2 Shift to the Right MARASIGAN Decrease oxygen affinity Lower O2 content for any PO2 RTRP 2024  HbO2 Dissociation Curve ADRIAN JUSTIN SHIFT TO LEFT (INCREASED AFFINITY) SHIFT TO RIGHT (DECREASED AFFINITY) GALLO Increased pH Decrease pH Decrease PCO2 Increase PCO2 Decrease Temperature Increase Temperature MARASIGAN Decrease 2-3 DPG Increase 2-3 DPG Decrease P50 Increase P50 RTRP 2024 HaLdane Effect COHb, MetHb, HbF BohR Effect  HbO2 Dissociation Curve ADRIAN JUSTIN P50 O2 tension at which 50% of the Hb is saturated when the blood is GALLO at 37*C, has a PCO2 level of 40 mmHg a pH level of 7.40 Used to describe the affinity of Hb for O2 Normal Value: 26.6 MARASIGAN RTRP 2024  LEVELS OF HYPOXEMIA ADRIAN JUSTIN PaO2 GALLO 80-100 mmHg 60-79 mmHg Normal Mild Hypoxemia MARASIGAN 40-59 mmHg Moderate Hypoxemia Severe 45 mmHg Hypocapnia: 7.45 Decreased PCO2 levels RTRP 2024 Increased HCO3- levels ADRIAN JUSTIN GALLO ACID BASE DISTURBANCES MARASIGAN RTRP 2024  NORMAL ACID BASE BALANCE ADRIAN JUSTIN Kidneys keep the arterial [HCO3-] in the range of: 22- 26 mEq/L Lung ventilation keeps the arterial PCO2 in the range of 35 to 45 mmHg GALLO These normal values produce an arterial pH range of 7.35 to 7.45 As shown by the H-H equation When [HCO3-] is 24 mEq/L and PaCO2 is 40 mmHg, the pH is MARASIGAN exactly 7.40 RTRP 2024  NORMAL ACID BASE BALANCE ADRIAN JUSTIN Plasma pH is determined by the ratio of [HCO3-] to dissolved CO2 As long as the ratio of [HCO3-] buffer to dissolved CO2 is 20:1, the pH is normal GALLO MARASIGAN An increase in HCO3- or decrease in PCO2 increases the pH Alkalemia Ratio > 20:1 RTRP 2024 A decreased HCO3- or an increase PCO2 decreases the pH Acidemia Ratio < 20:1 PRIMARY RESPIRATORY DISTURBANCES ADRIAN JUSTIN RESPIRATORY ACIDOSIS A high PCO2 increases dissolved CO2, decreasing the pH Hypoventilation GALLO MARASIGAN RESPIRATORY ALKALOSIS A low PCO2 decreases dissolved CO2, raising the pH Hyperventilation RTRP 2024  PRIMARY METABOLIC DISTURBANCES ADRIAN JUSTIN METABOLIC ACIDOSIS Build-up of a fixed acid in the body is buffered by HCO3-, decreasing the plasma [HCO3-] and the pH GALLO Loss of HCO3- MARASIGAN METABOLIC ALKALOSIS Ingesting too much alkali (e.g., NaHCO3 or other antacids) increases [HCO3-] and the pH Processes that increase arterial pH by losing fixed acid or gaining RTRP 2024 HCO3- ADRIAN JUSTIN GALLO MARASIGAN RTRP 2024  PRIMARY METABOLIC DISTURBANCES ADRIAN JUSTIN METABOLIC ACIDOSIS Build-up of a fixed acid in the body is buffered by HCO3-, decreasing the plasma [HCO3-] and the pH GALLO Loss of HCO3- MARASIGAN METABOLIC ALKALOSIS Ingesting too much alkali (e.g., NaHCO3 or other antacids) increases [HCO3-] and the pH Processes that increase arterial pH by losing fixed acid or gaining RTRP 2024 HCO3-  RESPIRATORY ACIDOSIS ADRIAN JUSTIN Any physiologic process that increases PaCO2 (>45 mmHg) with an accompanying decreased arterial pH ( 10% HbCO  HEMOXIMETRY ADRIAN JUSTIN Also known as Co-oximetry. is a method of measuring the O2 carrying state of Hb in the blood It can measure HbCO and metHb GALLO MARASIGAN RTRP 2024  PULSE OXIMETRY ADRIAN JUSTIN Are portable noninvasive monitors that estimate arterial blood HbO2 saturation levels Combines the principle of spectrophotometry with GALLO photoplethysmography Uses two wavelengths of light Red (approx. 660nm) Infrared (approx. 940 nm) MARASIGAN Accuracy of pulse oximetry readings is usually within +/- 2 to 4% of invasive hemoximetry readings Unrealiable at 7.45 STEP 2: INSPECT FOR THE CAUSATIVE COMPONENT Which parameter is responsible for the change in pH MARASIGAN ROME IF RESPIRATORY PaCO2: Normal: 35-45 mmHg RTRP 2024 Respiratory Acidosis (hypoventilation): > 45 mmHg Respiratory Alkalosis (hyperventilation): 26 mEq/L MARASIGAN RTRP 2024 INTERPRETATION OF ACID-BASE STATUS ADRIAN JUSTIN STEP 3: CHECK FOR COMPENSATION Did the noncausative component respond appropriately GALLO MARASIGAN RTRP 2024 INTERPRETATION OF ACID-BASE STATUS ADRIAN JUSTIN STEP 4: ASSESS OXYGENATION (PaO2) For Nonventilated patients Normal (PaO2): 80-100 mmHg GALLO Mild Hypoxemia: 60-79 mmHg Moderate Hypoxemia: 40-59 mmHg Severe Hypoxemia: 100 mmHg INTERPRETATION OF ACID-BASE STATUS ADRIAN JUSTIN SQ 1: pH: 7.21 PaCo2: 43 mmHg GALLO PaO2: 81 mmHg HCO3-: 14 mEq/L SQ2: MARASIGAN pH: 7.36 PaCO2: 62 mmHg PaO2: 58 mmHg RTRP 2024 HCO3-: 36 mEq/L INTERPRETATION OF ACID-BASE STATUS ADRIAN JUSTIN COPD - CHRONIC OBSTRUCTIVE PULMONARY DISEASE ABGs shows Fully Compensated Chronic Respiratory Acidosis with Hypoxemia GALLO pH: Within Normal Range PaCO2: 50-65 mmHg Pao2: 55-65 mmHg HCO3- Increased MARASIGAN RTRP 2024 INTERPRETATION OF ACID-BASE STATUS ADRIAN JUSTIN SQ3: A COPD patient on 40% Venturi mask has the following arterial blood gas results: Patient becomes tired, sleepy, lethargic, and unresponsive. What should the you do? GALLO pH: 7.30 PaCO2: 80 mmHg PaO2: 80 mmHg HCO3-: 38 mEq/L MARASIGAN RTRP 2024 INTERPRETATION OF ACID-BASE STATUS ADRIAN JUSTIN Oxygen-Induced Hypoventilation can result when a patient with COPD is given too much oxygen. The patient will become tired, sleepy, lethargic and then GALLO unresponsive Solution is not mechanical ventilation but instead you should decrease the FiO2 MARASIGAN RTRP 2024 ADRIAN JUSTIN GALLO SAMPLE QUESTIONS MARASIGAN RTRP 2024  SAMPLE QUESTIONS ADRIAN JUSTIN INTERPRET THE ABG VALUE pH: 7.57 GALLO PaCO2: 27 mmHg PaO2: 89 mmHg HCO3-: 24 mEq/L MARASIGAN RTRP 2024  SAMPLE QUESTIONS ADRIAN JUSTIN INTERPRET THE ABG VALUE pH: 7.22 GALLO PaCO2: 51 mmHg PaO2: 71 mmHg HCO3-: 17 mEq/L MARASIGAN RTRP 2024  SAMPLE QUESTIONS ADRIAN JUSTIN A 51-year-old patient on room air has the following ABG results: pH: 7.43 PaCO2: 47 mmHg GALLO PaO2: 169 mmHg Which of the following is the best action to take? A. Report the result to the attending physician MARASIGAN B. Report the results to the patient’s nurse C. Discard the sample and obtain a new one D. Give the patient a bronchodilator treatment RTRP 2024  SAMPLE QUESTIONS ADRIAN JUSTIN Measure the sample’s actual hemoglobin saturation analysis of an arterial blood sample taken from a healthy athlete reveals a pH of 7.36, a PCO2 of 45 mmHg, and a PO2 of 43 mmHg. Which of the following GALLO analytic errors should you suspect? A. Excessive heparin in the sample B. Exposure of the blood sample to air MARASIGAN C. Excessive time since sample collection D. Sample admixture with venous blood RTRP 2024  SAMPLE QUESTIONS ADRIAN JUSTIN A 23 year-old firefighter is admitted with suspected smoke inhalation. You place him on a nonrebreathing mask. What is the most appropriate method of monitoring his oxygenation? GALLO A. Arterial Blood Gas analysis B. Co-oximetry C. Pulse oximetry MARASIGAN D. Calculation of P(A-a)O2 RTRP 2024 Thank you!