CME - ABG

Dr Manisha Sahay  Currently i/c Professor and HOD, Nephrology Department, OMC/OGH  MBBS Rajasthan  MD Ped Niloufer  DNB Neph ,Osmania General Hospital (Gold medal) 2003  10 gold medals till date  9 best paper awards at zonal and national conferences  Best young researcher award –Indian Society of Nephrology  Executive committee member –Young Nephrologist’s committee International Society of nephrology  Executive committee member Indian society of Nephrology  Executive member of South Zone –Indian society of Nephrology  Young Key Opinion leader in Transplantation –India  Publications in national and international journals

ABC ‘s of ABG Dr. Manisha Sahay i/c Professor & HOD Dept of Nephrology Osmania General Hospital Hyderabad

Collection of sample  use local anaesthesia over the radial artery before puncture. (brachial/femoral)  Use a 20 or 21 gauge needle  Pre heparinised syringe (glass better)  Express the heparin from the syringe before taking the sample  At least 3 ml of blood is required to avoid a dilution effect from the heparin.  Any sample with more than fine air bubbles should be discarded. Manisha Sahay

 Press for 5 minutes  Allen's test. The radial and ulnar arteries are occluded  Avoid contact with air by firm pressure while the fist is clenched.  Put in ice if delay The hand is opened and the arteries released one at a time to check their ability to return blood flow to the hand Manisha Sahay

NORMAL ABG Arterial pH 7.35 - 7.45 ; Venous 7.32 - 7.42 HCO3 art 22 to 26 mEq/L, venous 19 to 25 mEq/l PaCO2 35-45 mm Hg, PvCO2 38-52 mm Hg B.E. –2 to +2 mEq/liter  value outside normal - metabolic acidosis Standard Bicarbonate:  Calculated value. No added info. PaO2 SO2 FiO2 CaO2 A-a Definitely Confusing!

No click Steps for Successful Blood Gas Analysis

ABC’s of ABG  1Acidosis or alkalosis  2 Metabolic or respiratory  3 Compensation  4 Anion gap  5 ∆ AG and ∆ HCO3  6 Urine AG Manisha Sahay

Step 1 Look at the pH (Normal 7.35-7.45) Is the patient acidemic pH < 7.35 or alkalemic pH > 7.45

Step 2 (pH & CO2)  Look at the PCO2 (Normal =35-45 mmHg)  pH and pCO2 change in opposite direction in respiratory problem  pH and pCO2 change in same direction in metabolic problem Manisha Sahay

Step 2 Metabolic OR Respiratory ? Disorder pH PCO2 Metabolic   acidosis Metabolic Metabolic   Same direction alkalosis Respiratory   Respiratory Opposite direction acidosis Respiratory   alkalosis Manisha Sahay

Step 3 Compensation(CO2 & HCO3)  Body tries to compensate to normalise pH  HCO3 and CO2 always move in CO2 HCO3 same direction Manisha Sahay

Step 3 Compensation For compensation HCO3 and CO2 follow each other Primary event Compensation Disorder pH PCO2 HCO3 Respiratory    acidosis Respiratory    alkalosis Metabolic    acidosis Metabolic    alkalosis Manisha Sahay

Step 3: Calculation of compensation Disorder pH Primary Compensatory Equation change Response Metabolic   [HCO3-]  PCO2 ΔPCO2  1.2  ΔHCO3 Acidosis Metabolic   [HCO3-]  PCO2 ΔPCO2  0.7  ΔHCO3 Alkalosis Respiratory   PCO2  [HCO3-] Acute: Acidosis ΔHCO3-  0.1  ΔPCO2 Chronic: ΔHCO3-  0.3  ΔPCO2 Respiratory   PCO2  [HCO3-] Acute: Alkalosis ΔHCO3-  0.2  ΔPCO2 Chronic: ΔHCO3-  0.5  ΔPCO2

Compensation Formula Simplified 1.2 Acidosis Metabolic 0.7 Alkalosis 0.1 Acidosis 0.3 Respiratory 0.2 Alkalosis 0.5 AcuteChronic

Step 4 Check Anion Gap Manisha Sahay

What is anion gap?  [Na+] – ([HC03-] + [Cl-])  140 - (24 + 105) = 11  Normal = 12 + 2 Manisha Sahay

1. Anion gap helps in etiology of Metabolic acidosis High AG (high acid) NAG (loss of HCO3) Cl  (MUDPILES) (DURHAM) M ethanol  Diarrhea U remia Ureterosigmoid fistula D KA P araldehyde Renal tubular acidosis I nfection Hyperalimentation L actic acidosis Acetazolamide E thylene Glycol Miscellaneous conditions: S alicylate - pancreatic fistula, cholestyramine, calcium chloride Manisha Sahay

2. Anion gap may identify hidden acidosis pH may be normal but if Anion gap is high it indicates metabolic acidosis hence always calculate anion gap AG is called the footprint of metabolic acidosis No use of ABG without electrolytes Manisha Sahay

Step 5 check difference bet AG and change in HCO3 Increase in AG should be equal to fall in HCO3 Δ AG = Δ HCO3 Δ AG > Δ HCO3 - metabolic alkalosis Δ AG < Δ HCO3 - metabolic acidosis Manisha Sahay

Step 6-Urine anion gap  Urine Anion-Gap = Na + K – Cl  Normal Positive (+30- + 50) mmol/l  In metabolic acidosis,  if Urine anion gap is negative-acidosis is extrarenal (Kidneys excreting NH4)  Positive - DRTA

Step 7 Oxygenation and ventilation Manisha Sahay

Normal arterio/venous difference No click 0 10 20 30 40 50 60 70 80 90 100 PaO2 100 80 Rt. Shift Oxygen delivered to tissues 60 with normally placed curve Delivered oxygen 40 with Rt. Shift curve Normal 20 Shift of the curve ……changes saturation for a given PaO2

A Oxygenation TCO2 19-20 ml/gm Hb  Hb X SO2 X 1.34 + 0.003X PaO2 PaO2 80-95 mm Hg. Pv 28 - 48 mm  1.34 ml O2 bound to each gm Hb Reflects only dissolved oxygen not  Best measure of hypoxemia bound to Hb Anemia, CO poisoning, type of normal in anemia ,hypoxemia may Hb all affect TCO2 exist with normal O2,not affected by Hb FIO2 - fractional inspired O2. SaO2-95 - 100%; SvO2 50 – 70% N= 21% in room air  only reflects % saturation of Hb FiO2 × 5 = PaO2  normal in anemia ,hypoxemia may 21 × 5 = 100 exist with normal SO2 ,not affected by type of Hb Manisha Sahay

State which of the following situations would be expected to lower PaO2.  a) anemia.  b) carbon monoxide toxicity.  c) an abnormal hemoglobin that holds oxygen with half the affinity of normal hemoglobin.  d) an abnormal hemoglobin that holds oxygen with twice the affinity of normal hemoglobin.  e) lung disease with intra-pulmonary shunting. Manisha Sahay

More on oxygenation….. CONDITION PaO2 SaO2 CaO2 Severe Anemia n n  CO Poisoning n   Severe V-Q    High Altitude    Manisha Sahay

Body needs O2 molecules, so oxygen content (CaO2) takes precedence over partial pressure in determining degrees of hypoxemia Which patient is more hypoxemic? Patient A: PaO2 Patient A CaO2 = .95 x 7 x 1.34 = 8.9 ml O2/dl 85 mm Hg, SaO2 Patient B 95%, Hb 7 gm% CaO2 = .85 x 15 x 1.34 = 17.1 ml O2/dl Patient A, with the higher PaO2, is more hypoxemic. ALWAYS CHECK CaO2 CONTENT Patient B: PaO2 55 mm Hg, SaO2 85%, Hb 15 gm% Manisha Sahay

ABG shows SO2 75% Pulse oximeter shows SO2 97% Which would you believe? Explain. ABG is reliable as it measures oxy Hb separately while on pulse oximeter any bound Hb is shown as saturated Hb eg Hb bound to CO will also increase SO2 in pulseox. Manisha Sahay

B. Ventilation PaCO2 important for assessing ventilation • (N= 35-45 mmHg) • > 45 hypoventilation • < 35 hyperventilation Manisha Sahay

Hypoventilation Ventilation failure CO2 , ,O2 Lung dz Oxygenation failure CO2 N,O2 Arterial blood pAO2 Manisha Sahay

C. Oxygenation vs Ventilation failure Alveolar-arterial O2 gradient PAO2-PaO2 PAO2 generally given on ABG pAO2 = piO2 – pCO2 / RQ (respiratory quotient) piO2= (Barometric Pr-Pr H2O) X FiO2 piO2 = (760-45) x . 21 = 150 mmHg  O2  CO2 PAO2= 150 – 40 / 0.8 = 150 – 50 = 100 mm Hg PaO2 = 90 mmHg pAO2 – paO2 = 10 mmHg One click and wait

No click Alveolar- arterial Difference Oxygenation Failure Ventilation Failure WIDE GAP NORMAL GAP piO2 = 150 piO2 = 150 pCO2 = 40 pCO2 = 80 PaO2 = 45 O2 PaO2 = 45 CO2 palvO2= 150 – 40/.8 palvO2= 150-80/.8 =150-50 =150-100 =100 = 50 A-a = 100 - 45 = 55 A-a = 50 - 45 = 5

ABC’s of ABG  1 Acidosis or alkalosis  2 Metabolic or respiratory  3 Compensation Metabolic acidosis: 1.2(∆HCO3 = ∆ PCO2 Metabolic alkalosis: 0.7(∆ HCO3 = ∆ PCO2 Respiratory acidosis AcutC 0.1(ΔPCO2) = ΔHCO3 Respiratory acidosis: Chronic 0.3(ΔPCO2) = ΔHCO3 Respiratory alkalosis Acute 0.2(ΔPCO2) = ΔHCO3 Respiratory alkalosis chronic0.5(ΔPCO2) = ΔHCO3  4 Anion gap  5 Δ anion gap = Δ HCO3- metabolic alkalosis  6 urine AG  7 Oxygenation and ventilation Remember the “golden rule” of acid-base interpretation: always look at a patient’ Manisha Sahay

HANDS ON ABG Manisha Sahay

Case 1 A 16-year-old male with diabetes mellitus presents after having eaten no food and taken no insulin for the last 3 days . He is hypotensive, tachycardic, and markedly tachypneic (respiratory rate 36). He smells strongly of acetone and is dehydrated, and clinical findings are consistent with left lower lobe pneumonia. Results of ABG testing are: • PaO2 = 68 mm Hg • PaCO2 = 17 mm Hg • HCO3- = 6 mEq/L • pH = 7.30. What is the acid-base abnormality? Manisha Sahay

Case 2 A 16-year-old female presents with 24 hours of unremitting emesis. She is dehydrated and hypotensive. Tests of her ABG • PaO2 = 104 mm Hg, • PaCO2 = 46 mm Hg, • HCO3- = 35 mEq/L • pH = 7.49. What is the acid-base disturbance here? Manisha Sahay

Case 3 Blood Gas Report o Measured 37.0 C pH 7.523 PaCO2 30.1 mm Hg PaO2 105.3 mm Hg Calculated Data HCO3 act 22 mmol / L O2 Sat 98.3 % PO2 (A - a) 8 mm Hg DPO2 (a / A) 0.93 FiO2 21.0 %

Case 4 8 year old diabetic with respi. Distress fatigue and loss of appetite. Blood Gas Report o Measured 37.0 C pH 7.23 PaCO2 23 mm Hg PaO2 110.5 mm Hg Calculated Data HCO3 act 14 mmol / L Entered Data FiO2 21.0 % Na = 130, Cl = 90

Case 5 A 16-year-old male presents with anorexia and unremitting emesis for 4 days ABG testing  HCO3 - = 18 mEq/L  PaCO2 = 33 mm Hg  pH = 7.36  Na = 130 meq/L  Cl = 89 meq/L Manisha Sahay

Case 6  A 15 yr old type 1 diabetic presents with following abnormalities after missing insulin  ABG: pH 7.31 PaCO2 26 mmHg HCO3 12 mEq/L Serum Electrolytes: PaO2 92 mm Hg Na 140 mEq/L K 5.0 mEq/L  Evaluate the acid-base Cl 100 mEq/L disturbance(s)?

Case 7  A 14 yr old boy presents with continuous vomiting of 3 days duration and drowsiness and appears dehydrated  ABG pH 7.50 PaCO2 48 HCO3 32 PaO2 90 Na 139 K 3.9 Cl 85  Evaluate the acid-base disturbance(s)?

Case 8  A 15 yr girl admitted with renal failure on furosemide now in respiratory failure and is on ventilator  ABG • PaCO2 30 mm Hg • PaO2 62 mm Hg • Na+ 145 mEq/L • K+ 2.9 mEq/L • Cl- 98 mEq/L • HCO3- 21 mEq/L • pH 7.52

Case 9  A 12-year-old girl has been mechanically ventilated for two days following a drug overdose. Her arterial blood gas values and electrolytes show:  ABG • pH 7.45 • PaCO2 25 mm Hg • Na + 142 mEq/L • K+ 4.0 mEq/L • Cl- 100 mEq/L • HCO3- 18 mEq/L

Case 10  A 10 year old boy with renal  insufficiency admitted with following values  ABG  pH 7.20  PaCO2 24 mm Hg  Na + 140 mEq/L  K+ 5.6 mEq/L  Cl- 110 mEq/L  HCO3- 10 mEq/L

Types of metabolic acidosis Patient A B C ECF volume Low Low Normal Glucose 600 120 120 pH 7.20 7.20 7.20 Na 140 140 140 Cl 103 118 118 - HCO3 10 10 10 AG 27 12 12 Ketones 4+ 0 0

Urine electrolytes in Metabolic Acidosis Patient A B C U. Na 10 50 U. K 14 47 U. Cl 74 28 Urine AG –50 +69 Dx: Urine Anion Gap = (U. Na + U. K – U. Cl) In Normal anion gap Metabolic Acidosis, Positive Urine AG suggests distal Renal Tubular Acidosis Negative Urine AG suggests non-renal cause for Metabolic Acidosis.

6 year old male with progressive respiratory distress Muscular dystrophy . Blood Gas Report Measured 37.0 C o Case 11 pH 7.301 PaCO2 76.2 mm Hg PaO2 45.5 mm Hg Calculated Data HCO3 act 35.1 mmol / L O2 Sat 78 % PO2 (A - a) 9.5 mm Hg PO2 (a / A) 0.83 Entered Data FiO2 21%

8-year-old male asthmatic with resp. distress Case 12 Blood Gas Report o 8-year-old male asthmatic; Measured 37.0 C 3 days of cough, dyspnea pH 7. 24 and orthopnea not PaCO2 49.1 mm Hg responding to usual PaO2 66.3 mm Hg bronchodilators. Calculated Data HCO3 act18.0 mmol / L O/E: Respiratory distress; O2 Sat 92 % suprasternal and PO2 (A – a) mm Hg intercostal retraction; tired looking; on 4 L NC. Entered Data FiO2 30 %

ABC’s of ABG  1 Acidosis or alkalosis  2 Metabolic or respiratory  3 Compensation Metabolic acidosis: 1.2(∆HCO3 = ∆ PCO2 Metabolic alkalosis: 0.7(∆ HCO3 = ∆ PCO2 Respiratory acidosis AcutC 0.1(ΔPCO2) = ΔHCO3 Respiratory acidosis: Chronic 0.3(ΔPCO2) = ΔHCO3 Respiratory alkalosis Acute 0.2(ΔPCO2) = ΔHCO3 Respiratory alkalosis chronic0.5(ΔPCO2) = ΔHCO3  4 Anion gap  5 Δ anion gap = Δ HCO3- metabolic alkalosis  6 urine AG  7 oxygenation and ventilation Remember the “golden rule” of acid-base interpretation: always look Sahay a patient’ Manisha at

Practice makes a man perfect!! Manisha Sahay

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CME - ABG

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