ABG - Interpretation

Acid Base disturbance identification steps

1. Dr.C.S.N.Vittal an Reading

2. 3. To determine alveolar ventilation 2. To determine acid-base status 1. To determine oxygenation Systematic Analysis o f ABG Arterial Blood Gases

3. The Anatomy of a Blood Gas Report --- XXX Diagnostics ---- Blood Gas Report 05:36 Jul 22 2009 Pt ID 2570/00 Measured 37.0 C pH 7.463 pCO 2 44.4 mm Hg pO 2 113.2 mm Hg Corrected 38.6 C pH 7.439 pCO 2 47.6 mm Hg pO 2 123.5 mm Hg Calculated Data HCO 3 act 31.1 mmol / L HCO 3 std 30.5 mmol / L BE 6.6 mmol / L O 2 CT 14.7 mL / dl O 2 Sat 98.3 % Ct CO 2 32.4 mmol / L pO 2 (A-a) 32.2 mm Hg pO 2 (a/A) 0.79 Entered Data Temp 38.6 C Ct Hb 10.5 g/dl FiO 2 30.0 % Measured Values Temp Correction ? Any Value Calculated Data Which are the useful ones? Entered Data Derived from other sources

4. Traditional Measurements Additional options include: Co-oximeter; measures O2 saturation Na + , K + , Ca 2+ , Cl - Haematocrit

5. Temperature Correction: A spin-off of microprocessor capability? “ There is no scientific basis ... for applying temperature corrections to blood gas measurements…” Shapiro BA, OTCC, 1999. Uncorrected pH & pCO 2 are reliable reflections of in-vivo acid base status Temperature correction of pH & pCO 2 do not affect calculated bicarbonate pCO 2 reference points at 37 o C are well established as reliable reflectors of alveolar ventilation Reliable data on DO 2 and oxygen demand are unavailable at temperatures other than 37 o C --- XXX Diagnostics ---- Blood Gas Report 05:36 Jul 22 2009 Pt ID 2570/00 Measured 37.0 C pH 7.463 pCO 2 44.4 mm Hg pO 2 113.2 mm Hg Corrected 38.6 C pH 7.439 pCO 2 47.6 mm Hg pO 2 123.5 mm Hg Calculated Data HCO3 act 31.1 mmol / L HCO3 std 30.5 mmol / L BE 6.6 mmol / L O 2 CT 14.7 mL / dl O 2 Sat 98.3 % Ct CO 2 32.4 mmol / L pO 2 (A-a) 32.2 mm Hg pO 2 (a/A) 0.79 Entered Data Temp 38.6 C Ct Hb 10.5 g/dl FiO2 30.0 %

6. ( ) Acid Base Equation Henderson - Hasselbach Equation --- XXX Diagnostics ---- Blood Gas Report 05:36 Jul 22 2009 Pt ID 2570/00 Measured 37.0 C pH 7.463 pCO 2 44.4 mm Hg pO 2 113.2 mm Hg Corrected 38.6 C Calculated Data HCO 3 act 31.1 mmol / L HCO 3 std 30.5 mmol / L BE 6.6 mmol / L O 2 CT 14.7 mL / dl O 2 Sat 98.3 % t CO 2 32.4 mmol / L pO 2 (A-a) 32.2 mm Hg pO 2 (a/A) 0.79 Entered Data Temp 38.6 C Ct Hb 10.5 g/dl FiO 2 30.0 % pH = pKa + log [ Salt ] [Acid]

7. Standard Bicarbonate: Plasma HCO 3 after equilibration to a PCO 2 of 40 mm Hg : Reflects non-respiratory acid base change : Does not quantify the extent of the buffer base abnormality : does not consider actual buffering capacity of blood Base Excess: Base to normalise HCO 3 (to 24) with PCO 2 at 40 mm Hg ( Sigaard -Andersen) : Reflects metabolic part of acid base D : No info. over that derived from pH, pCO 2 and HCO 3 : Misinterpreted in chronic or mixed disorders --- XXX Diagnostics ---- Blood Gas Report 05:36 Jul 22 2009 Pt ID 2570/00 Measured 37.0 C pH 7.463 pCO 2 44.4 mm Hg pO 2 113.2 mm Hg Corrected 38.60 C Calculated Data HCO 3 act 31.1 mmol / L HCO 3 std 30.5 mmol / L BE 6.6 mmol / L O 2 CT 14.7 mL / dl O 2 Sat 98.3 % t CO 2 32.4 mmol / L pO 2 (A-a) 32.2 mm Hg pO 2 (a/A) 0.79 Entered Data Temp 38.6 C Ct Hb 10.5 g/dl FiO2 30.0 %

8. Oxygenation Parameters: O 2 Content of blood: Hb x O 2 Sat x Const. + Dissolved O 2 --- XXX Diagnostics ---- Blood Gas Report 05:36 Jul 22 2009 Pt ID 2570/00 Measured 37.0 C pH 7.463 pCO 2 44.4 mm Hg pO 2 113.2 mm Hg Corrected 38.60 C Calculated Data HCO 3 act 31.1 mmol / L HCO 3 std 30.5 mmol / L BE 6.6 mmol / L O 2 CT 14.7 mL / dl O 2 Sat 98.3 % t CO 2 32.4 mmol / L pO 2 (A-a) 32.2 mm Hg pO 2 (a/A) 0.79 Entered Data Temp 38.6 C Ct Hb 10.5 g/dl FiO 2 30.0 % Oxygen Saturation Hb x O 2 Sat x Const. + Dissolved O 2 Alveolar / arterial gradient Arterial / alveolar ratio At sea level :- Normal PaO 2 = 75 to 100 mm Hg Normal PvO 2 = 30 – 40 mm Hg

9. Oxygen Saturation Most blood gas machines estimate saturation from an idealized dissociation curve Gold standard is co-oximetry Errors may occur with abnormal haemoglobins. Oxygen content is calculated from this.

10. Alveolar-arterial Difference ( Age and FiO 2 dependent derivative) It predicts the degree of shunt by comparing the partial pressure of  O 2  in the ( A ) alveoli to that in the ( a ) artery. The difference between them gives us an idea how well the oxygen is moving from the alveoli to the arterial blood. The  PaO 2   is obtained from the ABG (PAO 2   -  PaO 2 ) Calculation of the A-a Gradient helps distinguish basic pathogenic causes of hypoxemia. In general, diffusion defects, ventilation-perfusion defects, and right-left shunts result in a widened A-a Gradient whereas hypoventilation and residence at high altitudes do not.

11. Alveolar-arterial Difference Inspired O 2 = 21%= p i O 2 = (760 - 45) x 0.21=150 mm Hg p alv O 2 = p i O 2 - pCO 2 / RQ = 150 - 40/0.8 = 150 – 50 = 100 mm Hg P alv O 2 - p art O 2 = 10 mm Hg p art O 2 = 90 mm Hg O 2 CO 2 Normal = < [(age in yrs /4)+4] RQ = CO 2 produced/O 2 consumed

12. Computation of Alveolar-arterial Difference A-a (O 2 ) = (Fi O2 %/100) * ( P atm  - 47 mmHg) - (Pa CO2 /0.8) - Pa O2 Where:      Fi O2  Room Air = 21 %      Atmospheric Pressure= 760 mm Hg at sea level      Water vapor pressure pH2O (mmHg) = 47 mm Hg at 37 degrees Celsius      Respiratory quotient RQ (VCO2/VO2) = 0.8 (usual) Normal range increases with age.  5 to 20 is normal up to middle age Hypoxemia with a normal gradient suggests : Hypoventilation (decreased respiratory drive or neuromuscular disease) Low FiO2 Hypoxemia with an increased gradient suggests : Ventilation-perfusion imbalance -also known as V/Q mismatch (asthma, COPD) Shunt : Cardiac right to left shunt such as patent foramen ovale , alveolar collapse, (atelectasis), intraalveolar filling (pneumonia, pulmonary edema ), or intrapulmonary shunt. Supplemental O2 will help to correct  the hypoxemia in hypoventilation and V/Q mismatch but not hypoxemia resulting from a shunt. Normal oxygenation for age can be estimated pao2 = 104.2 - (0.27 x age) or More crudely, normal oxygenation for age is roughly 1/3 of the patient's age subtracted from 100. Estimated normal gradient= (Age/4) + 4

13. Alveolar-arterial Difference Oxygenation Failure p i O 2 = 150 p i CO 2 = 40 P alv O 2 = 150 – 40/0.8 = 150 – 50 = 100 p O 2 = 45 O 2 CO 2 Ventilation Failure p i O 2 = 150 p i CO 2 = 80 P alv O 2 = 150 – 80/0.8 = 150 – 100 = 50 p O 2 = 45 D = 100 -45 = 55 D = 50 -45 = 5 760 – 45 = 715 (atm) -- (Wat vapour pressure) 21% of 715 =150

14. PaO 2 / FiO 2 Ratio or "P/F" Ratio (Carrico index ) Another much friendlier method ( because it doesn't use the alveolar gas equation) used to predict shunt. Just like the name says, PaO 2 is divided by FiO 2 Normal PaO2/FiO2 is >400 mmHg Recent Berlin criteria defines mild ARDS at a ratio of <300

15. Oxygenation: Limitations of Parameters O 2 Content of blood: Useful in oxygen transport calculations --- XXX Diagnostics ---- Blood Gas Report 05:36 Jul 22 2009 Pt ID 2570/00 Measured 37.0 C pH 7.463 pCO 2 44.4 mm Hg pO 2 113.2 mm Hg Corrected 38.60 C Calculated Data HCO3 act 31.1 mmol / L HCO3 std 30.5 mmol / L BE 6.6 mmol / L O 2 CT 14.7 mL / dl O 2 Sat 98.3 % t CO 2 32.4 mmol / L pO 2 (A-a) 32.2 mm Hg pO 2 (a/A) 0.79 Entered Data Temp 38.6 C Ct Hb 10.5 g/dl FiO2 30.0 % Alveolar / arterial gradient Reflects O 2 exchange with fixed F i O 2 Impractical Differentiates hypoventilation as cause O 2 saturation Ideally measured by co-oximetry Calculated values my be error prone Alveolar / arterial ratio Proposed to be less variable Same limitation as A-a gradient Never comment on the oxygenation status without knowing the corresponding FiO 2 . Calculate the expected paO 2  (generally five times the FiO 2 )

16. The Blood Gas Report: The Essentials pH 7.40 + 0.05 PCO 2 40 + 5 mm Hg PO 2 80 - 100 mm Hg HCO 3 24 + 4 mmol /L O 2 Sat > 95 A-a D 2.5 + (0.21 x Age) mm Hg --- XXX Diagnostics ---- Blood Gas Report Measured 37.0 C pH 7.463 pCO 2 44.4 mm Hg pO 2 113.2 mm Hg Calculated Data HCO 3 act 31.1 mmol / L O 2 Sat 98.3 % pO 2 (A - a) 32.2 mm Hg Entered Data FiO2 30.0 %

17. Technical Errors Avoid Insufficient sample Hemolysis of the specimen General Recommendations Do not cool Analyze within 30 min. For samples with high paO2 e.g. shunt or with high leucocyte or platelet count – analyse within 5 mon When analysis is delayed for more than 30 min, use glass syringes and ice slurry Inspect sample for clots Mix blood thoroughly by inverting syringe 10 times Only 0.05 ml of heparin required to anticoagulated 1 ml of blood

18. Technical Errors Correct method of mixing of the arterial sample with the anticoagulant in two dimensions to prevent stacking of red blood cells.

19. Before you Begin Reading an ABG First: Initial Clinical Assessment From history, clinical examination and initial investigations, - most likely A-B disorder ? Second: Acid-Base Diagnosis Perform a systematic evaluation of the blood gas and other results and make A-B diagnosis Finally: Clinical Diagnosis Synthesize the information to make an overall clinical diagnosis Structured Approach to Assessment

20. Before you Begin Reading an ABG Never comment on the ABG without obtaining a relevant clinical history of the patient because History gives a clue to the etiology of the given acid–base disorder. Importance of Clinical History / Examination Hypotension, renal failure, uncontrolled diabetic status, of treatment with drugs such as metformin is likely to have Metabolic acidosis History of diuretic use, bicarbonate administration, high-nasogastric aspirate, and vomiting Metabolic alkalosis COPD, muscular weakness, postoperative cases, and opioid overdose Respiratory acidosis Sepsis, hepatic coma, and pregnancy Respiratory alkalosis

21. Acid Base Evaluation 'Acid-base physiology ' by Kerry Brandis –from http:// www.anaesthesiaMCQ.com Stepwise Approach

22. The Boston Approach : Present method – uses Six bicarbonate based bedside rules to assess compensation Copenhagen Approach - uses Four SBE-based bedside rules to assess compensation Standard bicarbonate Buffer Base Base Excess Stewart Method : Physicochemical approach superior to the physiologic approach, but it requires multiple calculations and additional laboratory values and is thus more challenging to use in the clinical setting. The Great Atlantic Acid Base Debate

23. "The traditional measurements of pH, pCO 2 and plasma bicarbonate concentration continue to be the most reliable biochemical guides in the analysis of acid-base disturbances. These measurements, when considered in the light of the appropriate clinical information and a knowledge of the expected response of the intact patient to primary respiratory or metabolic disturbance, allow rational evaluation of even the most complicated acid-base disorders.” -  Schwartz and Relman in 1963 (Boston)

24. Steps in Acid-Base Analysis Step 1 . Consider the clinical settings! Anticipate the disorder! Step 2 . Look at the pH? Step 3. Who is the culprit for changing pH?...Metabolic / Respiratory process Step 4. If respiratory…… acute and /or chronic? Step 5 . If compensations appropriate? Step 6. If metabolic, Anion gap increased and/or normal or both? Step 7. Is more than one disorder present? Mixed one? Arterial Blood Gases: A Simplified Bedside Approach; Vishram Buche, J Neonatal Biol. 2014, 3:4 Boston method

25. First : Check the Consistency of Report Assess the internal consistency of the values using the Henderseon-Hasselbach equation: [H + ] =   24 (PaCO 2 )             [HCO 3 -] If the pH and the [H + ] are inconsistent, the ABG is probably not valid. pH Approx H + ( mmol /l) 7.0 100 7.05 89 7.10 79 7.15 71 7.20 63 7.25 56 7.3 50 pH Approx H + ( mmol /l) 7.35 45 7.40 40 7.45 35 7.50 32 7.55 28 7.60 25 7.65 22 The hydrogen ion is calculated by subtracting the two digits after the decimal point of pH from 80, e.g., if the pH is 7.23 then [H + ] = 80 - 23 = 57

26. Step 2: pH Look at the pH Is the patient acidemic pH < 7.35 (acidosis +) or alkalemic pH > 7.45 (alkalosis +) A normal pH does not rule out acid base disorder Interpretation of arterial blood gas ; Pramod Sood, Gunchan Paul, and Sandeep Puri I ndian J Crit Care Med. 2010 Apr-Jun; 14(2): 57–64 .

27. Step 3: Who is the Culprit - Pattern In a normal ABG pH and paCO 2  move in opposite directions. HCO 3 - and paCO 2  move in same direction. ? Primary Disturbance Acidemia : With HCO 3 < 20 mmol/L = metabolic With PCO 2 > 45 mm hg = respiratory Alkalemia : With HCO 3 > 28 mmol/L = metabolic With PCO 2 < 35 mm Hg = respiratory When the pH and paCO 2  change in the same direction (which normally should not), the primary problem is metabolic; When pH and paCO 2  move in opposite directions and paCO 2  is normal, then the primary problem is respiratory. If [HCO 3 ] and PCO 2 move in opposite directions THEN a mixed disorder must be present

28. Step 3 contd … The exception : When the metabolic component is also acid [ both are contributing to the acid pH. Mixed Disorder – if HCO 3 -  and paCO 2  change in opposite direction (which they normally should not), then it is a mixed disorder: pH may be normal with abnormal paCO 2  or abnormal pH and normal paCO 2 ) Here, we should look at the % difference and decide which is the dominant disturbance? If the pH is below normal and the pCO 2 is elevated, the primary disorder is respiratory acidosis

29. Step 4 : Acute or Chronic? Ratio of rate of change in H + to change in paCO 2 -- - --helps in guiding us to conclude whether the respiratory disorder is acute, chronic, or acute on chronic If Respiratory, is it Acute or Chronic? Respiratory Acidosis H + / D PaCO 2 (per 10 mmHg increase in PaCO 2 (up to a PaCO2 of 70 ) Fall in pH ACUTE < 0.08 = 0.08 X (PaCO 2 - 40) CHRONIC > 0.03 = 0.03 X (PaCO 2 - 40) ACUTE on CHRONIC 0.03 to 0.08

30. Step 5: – Compensations Rules of Compensations: D epends upon the proper functioning of the organ system involved in the response (lungs or kidneys) and on the severity of acid–base disturbance. Acute compensation occurs within 6–24 h and chronic within 1–4 days. Respiratory compensation occurs faster than metabolic compensation. In clinical practice, it is rare to see complete compensation. The maximum compensatory response in most cases is associated with only 50–75% return of pH to normal. However, in chronic respiratory alkalosis, the pH may actually completely return to normalcy in some cases

31. Appropriate Compensation During Simple Acid-Base Disorders DISORDER EXPECTED COMPENSATION Metabolic METABOLIC ACIDOSIS  PCO 2   = 1.5 × [HCO 3 −  ] + (8 ± 2) METABOLIC ALKALOSIS  PCO 2   increases by 7 mm Hg for each 10 mEq /L increase in serum [HCO 3 −  ]  Respiratory Acidosis ACUTE [HCO 3 −] increases by 1 for each 10 mm Hg increase in PCO 2 CHRONIC [HCO 3 − ] increases by 3.5 for each 10 mm Hg increase in PCO 2   Respiratory Alkalosis ACUTE [HCO 3 −] falls by 2 for each 10 mm Hg decrease in PCO 2 CHRONIC  [HCO 3 −] falls by 4 for each 10 mm Hg decrease in PCO 2 Nelson, Textbook of Pediatrics, 21 e Step 5: – Compensation adequate?

32. Step 5 : If Respiratory – Compensation adequate? Respiratory Acidosis: Acute (< 24 hrs ): “ The 1 - for 10 rule of Acute Respiratory Acidosis” [HCO 3 - ] h by 1 mEq /L for every 10 mm Hg h in paCO 2  > 40 D [HCO 3 ] = 1/10 D PCO 2 Chronic (> 24 hrs ): “The 4 for 10 rule of Chronic Respiratory Acidosis” [HCO 3 - ] h by 4 mEq /L for every 10 mmHg h in paCO 2  > 40 D [HCO 3 ] = 4/10 D PCO 2 Expected HCO 3 = 24 + [(Actual pCO 2 -40)/10] Expected HCO 3 = 24 +[4*(Actual pCO 2 -40)/10] Rule 1 Rule 2

33. Respiratory Alkalosis: Acute (1 – 2 hrs ): “The 2 for 10 rule of Acute Respiratory Alkalosis” [HCO 3 - ] i by 2 mEq /L for every 10 mmHg i in paCO 2  < 40. D [HCO 3 ] = 2/10 D PCO 2 Chronic (> 2 days): “The 5 for 10 rule of Chronic Respiratory Alkalosis” [HCO 3 - ] i by 5 mEq /L for every 10 mmHg i in paCO 2  < 40. D [HCO 3 ] = 5/10 D PCO 2 Step 5 : If Respiratory – Compensation adequate? A Critique of the Parameters Used in the Evaluation of Acid Base Disorders -- Whole blood Buffer Base and Standard Bicarbonate Compared with Blood pH and Plasma Bicarbonate William B. Schwartz and Arnold S. Relman , NEJM 1963,;268:1382-1388 Rule 3 Expected HCO 3 = 24 – [2 (40 - Actual pCO 2 )/10] Expected HCO 3 = 24 - [5*(40 - Actual pCO 2 )/10] (range: +/- 2) Rule 4

34. Step 5: If Metabolic – Compensation adequate? Metabolic Acidosis : – Winter’s Equation : “The One & a Half plus 8 Rule - for a Metabolic Acidosis” Expected paCO 2  = (1.5 x HCO 3 + 8) + 2 ) Metabolic Alkalosis: “The Point Seven plus Twenty Rule - for a Metabolic Alkalosis” Expected pCO 2  = (0.7 x[ HCO 3 + 20] + 5) OR 40 + [0.7 Δ HCO 3 ]  If not: actual PCO 2 > expected : hidden respiratory acidosis actual PCO 2 < expected : hidden respiratory alkalosis If HCO 3 10, PaCO 2 should be 21 – 25 If PaCO 2 is < 21, additional respiratory acidosis If PaCO 2 is > 25, additional respiratory alkalosis Rule 5 Rule 6

35. Step 6: If Metabolic – Anion gap? Anion gap = Na – (Cl + HCO 3 -- ) Usually < 12 # Exception : Severe hypoalbuminemia If AG > 12 Anion gap Met. Acidosis (AGMA) [CAT MUDPILES] If AG < 12 Non Anion gap Met. Acidosis (NAGMA) [USED CAR] C yanide, CO A rsenic T olune M ethanol U remia D iabetic K etoacidosis P araldehyde I nfection L actic acid E thylene Glycol S alicylate poisoning U retero -Sigmoid diversions S aline administration E ndocrinopathies ( Addisons , Prim hyperparathyroid ) D iarrhea C arbonic Anhydrase inhibitors A limentation, hyper R enal Tubular Acidosis

36. Step 6: If Metabolic – Anion gap? Anion gap = Na – (Cl + HCO 3 -- ) Usually < 12 NEW Mnemonics If AG > 12 Anion gap Met. Acidosis (AGMA) DULSI If AG < 12 Non Anion gap Met. Acidosis (NAGMA) RAGE D iabetic Ketoacidosis U remia L actic acidosis S alicylate poisoning I ntoxicants Methanol, Ethanol, Ethylene glycol R enal Tubular Acidosis A cetazolamide, ammonium chloride G I Diarrhea, Enterienteric Fistula, Ureterosigmoidostomy E ndocrinopathies Addisons , Primary Hyperparathyroidism Spiranolactone Triamterene Amiloride

37. Step 7: Does the anion gap explain the change in bicarbonate ? Corrected HCO 3 -- = HCO 3 -- + (AG - 12) anion gap (Anion gap -12) ~ D [HCO 3 ] If D anion gap is greater; consider additional metabolic alkalosis If D anion gap is less ; consider a non-anion gap metabolic acidosis

38. Step 7: contd … Corrected HCO 3 - = HCO 3 - + (AG - 12) Does the anion gap explain the change in bicarbonate ? Example 1 HCO 3 10, AG 26 Corrected HCO 3 = 10 + (26 -12) = 24 No additional disturbance Example 2 HCO 3 15, AG 26 Corrected HCO 3 = 15 + (26 -12) = 29 Additional metabolic alkalosis

39. Summary Remember by heart: (CO 2 is a respiratory acid) pH and HCO 3 : Moves in same direction pH and PCO 2 : Moves in opposite direction When the pH and paCO2 change in the same direction (which normally should not), the primary problem is metabolic ; HCO 3 and PCO 2 : Moves in same direction (simple disorder) HCO 3 and PCO 2 : Moves in opposite directions (Mixed disorder)

40. Aids to Interpretation of Acid-Base Disorders Clue Significance High Anion Gap Always strongly suggest metabolic acidosis Hyperglycemia If ketone bodies are present in urine – diabetic ketoacidosis Hypokalemia and/or hypochloremia Suggest metabolic alkalosis Hyperchloremia Common with normal anion gap metabolic acidosis Elevated creatinine and urea Suggest uremic acidosis or hypovolemia (prerenal renal failure) Elevated creatinine Consider ketoacidosis: ketones interfere in the laboratory method ( Jeffe reaction) used for creatinine measurement & give falsely elevated result; typically urea will be normal Elevated glucose Consider ketoacidosis or hyperosmolar non- ketotic syndrome Urine dipstick tests for glucose and ketone Glucose detected if hyperglycemia, ketone detected if ketoacidosis

41. Exercises:

42. Case 1 --- XXX Diagnostics ---- Blood Gas Report Measured 37.0 C pH 7.30 pCO 2 76.2 mm Hg pO 2 45.5 mm Hg Calculated Data HCO 3 act 38.1 mmol / L O 2 Sat 78 % pO 2 (A - a) 9.5 mm Hg pO 2 ( a / A ) 0.83 Entered Data FiO 2 21 % pH < 7.35; acidemic pCO 2 > 45; respiratory acidemia CO 2 = 76- 40=36; Expected D pH = 36/10 x 0.08 = 0.29 Expected pH = 7.40 – 0.29 = 7.11 Chronic resp. acidosis Limits: D HCO 3 = 4/10 of D pCO 2 = 4/10 x 36 = 10.8 Limits of HCO 3 =24+11=35 Pure Resp Acidosis Hypoxia: Normal A-a gradient Due to hypoventilation

43. Case 2 --- XXX Diagnostics ---- Blood Gas Report Measured 37.0 C pH 7. 24 pCO 2 49.1 mm Hg pO 2 66.3 mm Hg Calculated Data HCO 3 act 18.0 mmol / L O 2 Sat 92 % pO 2 (A - a) 9.5 mm Hg pO 2 ( a / A ) 0.83 Entered Data FiO 2 30 % pH < 7.35; acidemic pCO 2 > 45; respiratory acidemia CO 2 = 49 - 40= 9; Expected D pH = 9/10 x 0.08 = 0.072 Expected pH = 7.40 – 0.072 = 7.328 Acute resp. acidosis Limits: D HCO 3 = 1/10 of D pCO 2 = 1/10 x 9 = 0.9 Limits of HCO 3 =24+1=25 Resp Acidosis + Metabolic Acidosis Hypoxia: piO 2 =715x0.3=214.5 / P alv O 2 =214 - 49/0.8=153 153-66=87

44. Case 3 --- XXX Diagnostics ---- Blood Gas Report Measured 37.0 C pH 7. 23 pCO 2 23 mm Hg pO 2 110.5 mm Hg Calculated Data HCO 3 act 14.0 mmol / L O 2 Sat % pO 2 (A - a) mm Hg pO 2 ( a / A ) Entered Data FiO 2 21.0 % pH < 7.35; acidemic Limits: Expected pCO 2 = (1.5 x HCO 3 ) +8 + 2 = (1.5 x 14)+8 + 2 = 29 + 2 = 27 to 31 Met. acidosis + Resp. alkalosis HCO 3 < 22; Metabolic acidemia If Na = 130, Cl = 100 Anion Gap = 130 – (100+14) = 130 – 114 = 16 Normal AG = 12; D Gap = 16-12 = 4 HCO 3 = 24 -14 = 10, 2.5 accounted for by resp. alkalosis D / D 3.5 indicates additional non-gap acidosis

45. Case 4 --- XXX Diagnostics ---- Blood Gas Report Measured 37.0 C pH 7. 48 pCO 2 33 mm Hg pO 2 100.5 mm Hg Calculated Data HCO 3 act 24.0 mmol / L O 2 Sat % pO 2 (A - a) mm Hg pO 2 ( a / A ) Entered Data FiO2 21.0 % pH > 7.35; alkalemia pCO 2 = 33 , Resp. alkalosis HCO 3 – normal No compensation, yet

46. Case 5 --- XXX Diagnostics ---- Blood Gas Report Measured 37.0 C pH 7. 18 pCO 2 41 mm Hg pO 2 100 mm Hg Calculated Data HCO 3 act 14.0 mmol / L O 2 Sat % pO 2 (A - a) mm Hg pO 2 ( a / A ) Entered Data FiO2 21.0 % pH < 7.35; acidemic pCO 2 = Normal, No compensation, yet HCO 3 < 24 Metabolic acidosis

47. Problem Studies Gleson , C., & Devaskar , S. (2011). Avery’s Diseases of the Newborn (9th Ed.). Philadelphia: W.B. Saunders. ISBN: 978-1437701340. Gomella, T.L. (2009). Neonatology: Management, Procedures, On-Call Problems, Diseases and Drugs (6th Edition). Norwalk, Conn.: Appleton & Lang. ISBN: 9780071544313 Karlsen , K.A. (2012). The S.T.A.B.L.E. Program. Park City: The S.T.A. B.L.E. Program.

48. Practice Problem #1 A 31 week old infant is one hour old. CXR shows diffuse atelectasis with air bronchograms . CBG – 7.29/59/42/26

49. Practice Problem #1 Acidosis pCO 2 is high indicating a respiratory problem leading to the acidosis Capillary specimen No compensation Uncompensated respiratory acidosis Treatment: NCPAP or MV

50. Practice Problem #2 A 33 week infant is receiving mechanical ventilation for severe TTN. Settings: IMV 25, PIP 18, PEEP 4, .30. ABG: 7.49/26/95/22

51. Practice Problem #2 Alkalemia The PaCO 2 is low indicating a respiratory alkalosis Pa0 2 is high No compensation Uncompensated Respiratory Alkalosis Treatment: wean the PIP or rate along with Fi0 2

52. Practice Problem #3 26 week infant has been on the ventilator for 2 weeks for RDS. PIE is present. CBG: 7.37/55/65/29

53. Practice Problem #3 pH normal pCO2 is high indicating a respiratory problem, which could lead to acidosis Capillary specimen Compensation present – pH normal with abnormal HCO3 and pC02. pH closer to acidosis Compensated respiratory acidosis Treatment: no action needed. Further increases in the pCO2 could result in decompensation.

54. Practice Problem #4 26 week old infant on the ventilator for RDS. Settings: IMV 30, 19/5, and .40. Infant has lost 30 gms in the past 12 hours with a Na of 148. ABG: 7.29/53/55/17

55. Practice Problem #4 Acidemia The PaCO 2 is high indicating a respiratory acidosis and the HCO 3 is low indicating a metabolic acidosis. Oxygen level adequate. No compensation – pH not normal Uncompensated mixed acidosis. Treatment: increase alveolar ventilation and consider giving volume to correct the hypovolemia

56. Practice Problem #5 Term infant with tight nuchal cord. Infant pale, grunting, with cap refill of 8 seconds. ABG: 7.15/40/75/15/-15

57. Practice Problem #5 Acidosis Metabolic in origin – decreased HCO 3 with normal pCO 2 Oxygen level adequate No compensation – pCO 2 normal Uncompensated Metabolic Acidosis Treatment: consider volume or HCO 3 depending on respiratory assessment.

58. Dr.C.S.N.Vittal Thank You