arterial blood gas analysis

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Information about arterial blood gas analysis

Published on January 21, 2009

Author: aSGuest11078


Slide 1: ynm dduh 1 Slide 2: ynm dduh 2 ARTERIAL BLOOD GASES By Dr Y.N MAURYA M.B.B.S D.C.H Medical Officer Deen Dayal Upadhyay Hospital Govt. of NCT New Delhi- 64 ARTERIAL BLOOD GASES : ynm dduh 3 ARTERIAL BLOOD GASES Arterial blood gas sampling is a medical technique used to check gas levels in the blood. It typically involves using a thin needle and syringe to puncture an artery, This technique is commonly used on patients whose breathing is controlled by a mechanical respirator or who are having serious difficulties with breathing. A.B.G SAMPLE COLLECTION : ynm dduh 4 A.B.G SAMPLE COLLECTION ULNER,RADIAL BRACHIAL DORSALIS PEDIS FEMORAL ARTERIES CAN BE USED. ARTERIAL LINE ---- FREQUENT SAMPLING INTERMITENT STAB---INFREQ. SAMPLING UNDER FULL ASEPTIC CONDITION IF ULNER/RADIAL ART IS USED ---MODIFIED ALLEN’S TEST MODIFIED ALLEN’S TEST : ynm dduh 5 MODIFIED ALLEN’S TEST 1. INSTRUCT PATIENT TO CLENCH HIS FIST 2. USING YOUR FINGER APPLY OCCLUSIVE PRESSURE ON BOTH RADIAL & ULNER ARTERY 3. WHILE APPLYING OCCLUSIVE PRESSURE TO BOTH ARTERY,HAVE THE PATIENT RELAX HIS HAND.BLANCHING OF PALM &FINGER SHOULD OCCUR MODIFIED ALLEN’S TEST : ynm dduh 6 MODIFIED ALLEN’S TEST 4. RELEASE THE OCCLUSIVE PRESSURE ON ULNER ARTERY & NOTICE FLUSHING OF HAND WITHIN 7-10 SEC.THIS DENOTE THAT ULNER ARTERY SUPPLY IS ADEQUATE &IT’S SAFE TO PRICK RADIAL ARTERY. IF IT DOES’T OCCUR IT MAENS ULNER ARTERY SUPPLY IS NOT SUFFICIENT & RADIAL ARTERY IS NOT SAFE TO PRICK. SAMPLE SIZE & PRECAUTION : ynm dduh 7 SAMPLE SIZE & PRECAUTION ABOUT 2 ml BLOOD IN AIR TIGHT HEPARINISED SYRINGE/ VIAL GLASS CAPILLARY CAN ALSO BE USED COTINUOUS AGITATION BY ROLLING FIO2 SHOULD BE WRITTEN ON SAMPLE CONTRAINDICATION FOR ARTERIAL PUNCTURE : ynm dduh 8 CONTRAINDICATION FOR ARTERIAL PUNCTURE INFECTION AT SITE. ALLEN’S TEST NEGATIVE. ON ANTICOAGULANT THERAPY. SEVERE PERIPHERAL VASCULAR DISEASE. DISTAL TO SURGICAL SHUNT. SpO2 and SaO2 : ynm dduh 9 SpO2 and SaO2 SpO2 and SaO2 are often used interchangeably, but they are not same When O2 saturation is measured by pulse oximeter..... SpO2 When O2 saturation is measured by CO- oximeter..... SaO2 SpO2 is also called functional arterial O2 saturation and SaO2as fractional arterial O2 saturation Only true CO-oximeter can determine an accurate value for SaO2 SpO2 and SaO2 : ynm dduh 10 SpO2 and SaO2 SpO2 == HbO2 HbO2 + Hb SaO2 == HbO2 HbO2+ Hb+COHb+MetHb+SfHb+COSfHb SaO2 == SpO2[1-SaCO]… (Nellcor equation) Non functional Hb is 2-3% In heavy smoaker it may be up to 15% O2 Saturation & Pulse oximetry : ynm dduh 11 O2 Saturation & Pulse oximetry We can know arterial blood gases and arterial oxygen saturation from ABG machine with help of O2 DISSOCIATION CURVE . O2 DISSOCIATION CURVE : ynm dduh 12 O2 DISSOCIATION CURVE O2 Saturation & Pulse oximetry : ynm dduh 13 O2 Saturation & Pulse oximetry ABG machine calculates o2 saturation based on pH, PaCO2,temp,by using normal adult o2 dissociation curve o2 dissociation curve in presence of 1) fetal Hb ,low 2,3 DPG……curve shifts Lt 2)sickle cell, chr. Hypoxia, cyanotic H D, chr. Asthama, high altitude…. curve shifts Rt. And ABG machine becomes inaccurate O2 Saturation & Pulse oximetry : ynm dduh 14 O2 Saturation & Pulse oximetry If we can know arterial blood gases and arterial oxygen saturation with help of ABG machine, then what is need of pulse oximeter ? O2 Saturation & Pulse oximetry : ynm dduh 15 O2 Saturation & Pulse oximetry ADVANTAGE OF PULSE OXIMETRY Noninvasive Portability Continuous monitoring Ease of use (no calibration) Rapidity (warn decr. in saturation before sign and symptom) Principle of Pulse oximetry : ynm dduh 16 Principle of Pulse oximetry It is based on different absorption coefficients of oxyHb & deoxyHb for different wavelength of lights (BEER’S LAW) For oxyHb & deoxyHb 805nm is isobestic point. Above 805 nm oxyHb absorbs more light than deoxyHb & below it deoxyHb absorbs more light than oxyHb. Because of this fact by using two wavelength of lights actual o2saturatn level can be measured. Pulse oximeter uses two wavelength of light red(660nm) and infrared (950nm). Principle of Pulse oximetry : ynm dduh 17 Principle of Pulse oximetry Absorption Spectrum of Hemoglobin Pulse Oximetry : ynm dduh 18 Pulse Oximetry 1)Pulse oximeter emits two wavelength of lights (red & infrared) from Xenon LED.These lights are sensed by photodiodes just opposite to LED or adjacent to LED. 2)It measures %saturation of deoxyHb with O2 (not PaO2) based on absorption spectrum of Hb in pulsatile arterial blood. 3) Sensitivity rapidly decreases at SpO2 >90% 4) Normally in blood dysfunctional Hb is 2-3% hence all oximeters are standardized against known standard CO-oximeter & adjusted, so that it can display SpO2close to SaO2. Pulse Oximetry : ynm dduh 19 Pulse Oximetry 4)Accuracy depends on a) % of dysfunctional Hb. b) age of LED. (Aging of LEDcauses change in peak wavelength). c) LED from same batch & same manufacturer may vary by 30nm in peak wavelength. d) Good red & infrared waveform i.e signal strength (tissues are easily penetrated by infrared but not so easily by red. Thus red waveform is lost first, this is why false reading is given when signal is weak) Pulse Oximetry : ynm dduh 20 Pulse Oximetry There are two types of probes 1) Transmission probe……Finger type 2) Reflectance probe…… Rectal type Do’t provide accurate reading in CO-poisoning, methemoglobinemia, decreased cut. perfusion, strong vasoconstriction, deep pigmentation, nail polish, intravascular dye, movement, venous pulsation, infrared heating lamp & strong colored lights. ECG synchronization technique can be used to remove movement artifact. Hypoxia & Pulse Oximetry : ynm dduh 21 Hypoxia & Pulse Oximetry Hypoxic hypoxia…. Register low saturation Anaemic hypoxia…. Normal saturation Circulatory hypoxia… Low signal strength Histotoxic hypoxia… Normal saturation SaO2 and Pulse CO- Oximetry : ynm dduh 22 SaO2 and Pulse CO- Oximetry Pulse oximeter do’t measure methemoglobin & carboxyHb.So becomes inaccurate in these cases. IL-282 CO-oximeter is gold standard for o2 saturation measurement. Pulse CO-oximeter emits at least four wavelength of light which measures oxyHb, deoxyHb, methemoglobin & carboxyHb For infants pulse oximeter is more useful because CO-oximeter show false elevation of CO-Hb.(fetal Hb absorb more than two wavelength of lights) SaO2 and oxygen content : ynm dduh 23 SaO2 and oxygen content Tissues need a requisite amount of oxygen molecules for metabolism. Neither the PaO2 nor the SaO2 tells how much oxygen is in the blood. It is provided by the oxygen content, CaO2 (units = ml O2/dl). CaO2 is calculated as:CaO2 = quantity O2 bound + quantity O2 dissolved to hemoglobin in plasmaCaO2 = (Hb x 1.34 x SaO2) + (.003 x PaO2) Hb = hemoglobin in gm%; 1.34 = ml O2 that can be bound to each gm of Hb; SaO2 is percent saturation of hemoglobin with oxygen; .003 is solubility coefficient of oxygen in plasma: .003 ml dissolved O2/mm Hg PO2. Oxygen dissociation curve: SaO2 vs. PaO2 : ynm dduh 24 Oxygen dissociation curve: SaO2 vs. PaO2 O2 content The Key to Blood Gas Interpretation: : ynm dduh 25 The Key to Blood Gas Interpretation: Equation Physiologic Process 1) PaCO2 equation Alveolar ventilation 1) Alveolar gas equation Oxygenation 2) Oxygen content equation Oxygenation 3) Henderson-Hasselbalch equation Acid-base balance PaCO2 equation : ynm dduh 26 PaCO2 equation PaCO2 =0.863VCO2/VA VCO2,ml of CO2 produced/ min; VA, alveolar ventilation VA is increased……. PaCO2decreases VA is decreased…. …PaCO2increases Alveolar Gas Equation : ynm dduh 27 Alveolar Gas Equation PAO2 = PIO2 - PaCO2/R , R= resp. quotient PAO2 = PIO2 - PaCO2/ O.8 PAO2 = PIO2 - 1.2 (PaCO2), PIO2 = FIO2 (PB – 47 mm Hg) PAO2 = FIO2 (PB – 47 mm Hg) - 1.2 (PaCO2) Alveolar Gas Equation PAO2 = FIO2 (PB – 47 mm Hg) - 1.2 (PaCO2) : ynm dduh 28 Alveolar Gas Equation PAO2 = FIO2 (PB – 47 mm Hg) - 1.2 (PaCO2) Except in a temporary unsteady state, alveolar PO2 (PAO2) is always higher than arterial PO2 (PaO2). Thus, If FIO2 & PB are constant, as PaCO2 increases both PAO2 and PaO2 will decrease (hypercapnia causes hypoxemia). If PB & PaCO2 are constant, as FIO2 decreases both PAO2 and PaO2 will decrease (suffocation causes hypoxemia). If PaCO2 & FIO2 are constant, as PB decreases (e.g., with altitude), both PAO2 and PaO2 will decrease (mountain climbing causes hypoxemia). P(A-a)O2 : ynm dduh 29 P(A-a)O2 P(A-a)O2 is the alveolar-arterial difference in partial pressure of oxygen. it actually results from gravity-related blood flow changes within the lungs (normal ventilation-perfusion imbalance). PAO2 is always calculated, based on FIO2, PaCO2 and barometric pressure. PaO2 is always measured, in a ‘blood gas machine’. Normal P(A-a)O2 ranges from @ 5 to 25 mm Hg at room air (it increases with age). A higher P(A-a)O2 means the lungs are not transferring oxygen properly from alveoli into the pulmonary capillaries. Except for right to left cardiac shunts, an elevated P(A-a)O2 signifies some sort of problem within the lungs. If P(A-a)O2 is negative---there is error in calculation/measurement Ventilation-Perfusion imbalance : ynm dduh 30 Ventilation-Perfusion imbalance A normal amount of ventilation-perfusion (V-Q) imbalance accounts for the normal P(A-a)O2. Most common cause of low PaO2 is an abnormal degree of ventilation-perfusion imbalance Virtually all lung disease lowers PaO2 via V-Q imbalance, e.g., asthma, pneumonia, atelectasis, pulmonary edema, COPD. Diffusion barrier is seldom a major cause of low PaO2 (it can lead to a low PaO2 during exercise). Henderson - Hasselbalch equation : ynm dduh 31 Henderson - Hasselbalch equation Weak acid ionizes as, HA=H++ A- pH = pK+ log[A-] / [HA] Causes of low PaO2 : ynm dduh 32 Causes of low PaO2 NON-RESPIRATORY P(A-a)O2Cardiac right to left shunt Increased Decreased PIO2 NormalLow mixed venous oxygen content* Increased RESPIRATORYPulmonary right to left shunt IncreasedVentilation-perfusion imbalance IncreasedDiffusion barrier IncreasedHypoventilation (increased PaCO2) Normal *Unlikely to be clinically significant unless there is right to left shunting or ventilation-perfusion imbalance NORMAL A.B.G VALUES : ynm dduh 33 NORMAL A.B.G VALUES HB -- 12-15gm/dl HCT -- 35-55 FIO2 ----- PaO2 – 80(60)-100mmHg PaCO2 – 35-45mmHg pH – 7.35-7.45 K+ -- 3.5-4.5 mmol/L Na+ -- 135-145 mmol/L HCO3¯ -- 22-26 mmol/L BE -- ±2 mmol SaO2 -- >90% ABG Interpretation : ynm dduh 34 ABG Interpretation First, does the patient have an acidosis or an alkalosis. Second, what is the primary problem – metabolic or respiratory. Third, is there any compensation by the patient – respiratory compensation is immediate while renal compensation takes time. ABG Interpretation : ynm dduh 35 ABG Interpretation It would be extremely unusual for either the respiratory or renal system to overcompensate The pH determines the primary problem After determining the primary and compensatory acid/base balance, evaluate the effectiveness of oxygenation Abnormal Values : ynm dduh 36 Abnormal Values pH < 7.35 Acidosis (metabolic and/or respiratory) pH > 7.45 Alkalosis (metabolic and/or respiratory) paCO2 > 45 mm Hg Respiratory acidosis (alveolar hypoventilation) paCO2 < 35 mm Hg Respiratory alkalosis (alveolar hyperventilation) HCO3 < 22 meq/L Metabolic acidosis HCO3 > 26 meq/L Metabolic alkalosis Putting It Together - Respiratory : ynm dduh 37 Putting It Together - Respiratory So, paCO2 > 45 with a pH < 7.35 represents a respiratory acidosis paCO2 < 35 with a pH > 7.45 represents a respiratory alkalosis For a primary respiratory problem, pH and paCO2 move in the opposite direction For each deviation in paCO2 of 10 mm Hg in either direction, 0. 08 pH units change in the opposite direction Putting It Together - Metabolic : ynm dduh 38 Putting It Together - Metabolic And HCO3 < 22 with a pH < 7.35 represents a metabolic acidosis HCO3 > 26 with a pH > 7.45 represents a metabolic alkalosis For a primary metabolic problem, pH and HCO3 are in the same direction, and paCO2 is also in the same direction Compensation : ynm dduh 39 Compensation The body’s attempt to return the acid/base status to normal (i.e. pH closer to 7.4) Primary Problem Compensation respiratory acidosis metabolic alkalosis respiratory alkalosis metabolic acidosis metabolic acidosis respiratory alkalosis metabolic alkalosis respiratory acidosis Compensation : ynm dduh 40 Compensation HOW KNOW THE DISORDER : ynm dduh 41 HOW KNOW THE DISORDER Slide 42: ynm dduh 42 Effectiveness of Oxygenation : ynm dduh 43 Effectiveness of Oxygenation Further evaluation of the arterial blood gas requires assessment of the effectiveness of oxygenation of the blood Hypoxemia – decreased oxygen content of blood - paO2 less than 60 mm Hg and the saturation is less than 90% Hypoxia – inadequate amount of oxygen available to or used by tissues for metabolic needs Causes of Hypoxemia : ynm dduh 44 Causes of Hypoxemia Inadequate inspiratory partial pressure of oxygen Hypoventilation Right to left shunt Ventilation-perfusion mismatch Incomplete diffusion equilibrium Assessment of Gas Exchange : ynm dduh 45 Assessment of Gas Exchange Alveolar-arterial O2 tension difference A-a gradient PAO2-PaO2 PAO2 = FIO2(PB - PH2O) - PaCO2/RQ* arterial-inspired O2 ratio PaO2/FIO2 P/F ratio *RQ=respiratory quotient= 0.8 Slide 46: ynm dduh 46 THANK YOU

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