ARTERIAL BLOOD GAS ANALYSIS FINAL.pptx

The combined Copenhagen and Physico-chemical approach

1. ARTERIAL BLOOD GAS ANALYSIS Dr Unnikrishnan P MD,DA,PDCC,MBA www.thelaymedicalman.blogspot.in

2. TOUGH QUESTIONS Was demonetization a good step ? Where Virat stands as a captain compared to Dhoni ? What will be Kim Jong Un’s next plan? When will you be able to see Evs dominating Indian roads? Are you an expert in interpreting ABG?

3. Really difficult to contain!

4. ABG HAS THE R IGHT T O I NFORMATION ABOUT OXYGENATION VENTILATION ACID BASE IMBALANCE

5. At the end of the day… Know Copenhagen See PaO2 ,with A-a gradient & PaO2/FiO2 No more strained relations with the Alveolar Gas equation See PaCO2 with a search for CO2 production ,Abnormal Alveolar ventilation and Dead space ventilation Look for AG in Acidosis Chloride: I am here In wide AG acidosis, calculate the Bicarbonate gap

6. REVIEW OF RESPIRATORY PHYSIOLOGY Lets focus on the Oxygenation & Ventilation part of ABG

7. V/Q Mismatch is the commonest cause of hypoxia* V/Q : Ideal -1, Real life: 0.3-2.1 What will be the V/Q in these alveoli ? This dead space adds to apparatus dead space and can pCO2 [dead space causes less hypoxia than shunt] Facebook page: Anesthesia Info from The Lay Medical Man Normal ratio of Dead space ventilation to Vt is 0.3; When >0.5  CO2 will increase

8. The shunt! . Shunt fraction Consequence 2-3% Normal 10% Tolerated by a healthy person 25-45% Life threatening: Requires mechanical ventilation, PEEP, recruitment, positioning, FOB and suctioning

9. Clues to the existence of shunt You are increasing FiO2 and still PaO2 is not coming up? Widened Alveolar arterial gradient Inappropriately low PaO2/FiO2

10. The concept of ‘Mixed Venous Sample’ Venous effluents from different organs have different oxygen content How a single sample can represent the whole body? Pulmonary Artery Catheter (PAC) Mixed Venous PO2 [PvO2]  40 mm of Hg Mixed Venous saturation [SvO2 ]  75% In low CO states with continuing O2 extraction, PvO2 will be low Sample from a CVC [if no PAC] can serve as an alternative Facebook page: Anesthesia Info from The Lay Medical Man

11. Shunt doesn’t affect PaCO2 In spontaneously breathing patient   in PaCO2 or  in PaO2  stimulation of chemo receptors   Mv Oxygen Dissociation Curve is sigmoid CO2 Dissociation Curve is linear Facebook page: Anesthesia Info from The Lay Medical Man

12. PaO2 is the uncle who is there in front of every crowd! The major mode of transport of O2 is by binding to Hb If Hb is 15g/dl and PaO2 is 100 mm Hg, the absolute amount of dissolved O2 is 0.3 ml 70 times less than the that carried with Hb Infact the less accurate pulseoximeter looks at this lions share of oxygen carried; i.e., the % saturation of oxygen with Hb Facebook page: Anesthesia Info from The Lay Medical Man

13. Travel [of O2] and Living [of humans] When air is inhaled, it gets saturated with water vapour . So to find out the alveolar partial pressure of O2, water vapour pressure has to be substracted ..also the mean airway pressure!

14. Travel [of O2] and Living [of humans] Alveolar partial pressure of O2 713 x FiO2 – 1.25 x PaCO2 PAO2 = [(P B – PH2O ) FiO2 ] – (PaCO2 / RQ) Atmospheric pressure is 760 mm Hg at sea level PH2O is vapor pressure of water at 37°C and is equal to 47 mmHg The respiratory quotient or respiratory coefficient (RQ) is the ratio of CO2 produced divided by the O2 consumed, and its value is typically 0.8 (RQ = CO2 eliminated / O2 consumed ). R is taken as ! @FiO2> 0.6 P B – PH2O is known as P i O2  713 Simplified as Facebook page: Anesthesia Info from The Lay Medical Man

15. ESTIMATING SHUNT FRACTION mm

16. The Alveolar –Arterial Oxygen Gradient As O2 reaches blood by diffusion, the expected PaO2 will be less than PAO2 [ suspect air bubble, in ABG sample, if > 100 in patient breathing room air] Known as Alveolar –Arterial Oxygen Gradient 10-15 mm in young to middle aged PaO2= 109- 0.43 [age in years] It increases with increase in FiO2 [@FiO2 of 1, 110!) If higher than expected for age, shunt fraction is high Patient should receive 100% O2 for 15 mins Ideally PaO2 should be  550; every 20 mm Hg difference is equal to 1% shunt Facebook page: Anesthesia Info from The Lay Medical Man

17. The Alveolar –Arterial Oxygen Gradient Hypoxemic respiratory failure with Normal A-a DO2 Hypoventilation** High altitude Fire Inadvertent use of low O2 containing mixtures during anesthesia Hypoxemic respiratory failure with widened A-a DO2 Increased shunt fraction Increased dead space ventilation Diffusion abnormality Low cardiac output and increased O2 uptake Facebook page: Anesthesia Info from The Lay Medical Man

18. PaO2/ FiO2 Normal  550 Obtained value is substracted from 550 For every difference of 100, the shunt is  5% PaO2 68 mmol of Hg on FiO2 of 0.4 68/0.4=170 , 550-170=380  20% Used to diagnose ARDS (< 200) and ALI (< 300 ) Roughly, shunt %: 5005, 30015, 20020 Facebook page: Anesthesia Info from The Lay Medical Man

19. Real life situation* Patient breathing room air, has PaO2 90 mm of Hg, SpO2 96%, and PaCO2 110 mm of Hg Apply Alveolar Gas Equation [713x0.2]-[1.2x110]= PAO2 is 18 !, but Sp O2 is 96. So one among the value is wrong. Facebook page: Anesthesia Info from The Lay Medical Man

20. CaO2- Oxygen Content Oxygen carried as oxyhemoglobin + dissolved O2 CaO2= [1.39 X Hb ( gm /dl) X Saturation] + 0.003 X PaO2 1.39 is the amount of O2 in ml, that will bind to 1 gm of Hb 0.003 is the solubility coefficient of O2 If Hd =15 g/dl, SaO2 99%, 20.4 ml as oxy Hb + 0.3 ml in plasma 20.7 Facebook page: Anesthesia Info from The Lay Medical Man

21. Abnormal hemoglobins and SpO2 .

22. Abnormal hemoglobins : Carboxy Hb .

23. Abnormal CO2? Abnormality in Production OR Washout

24. Abnormal CO2? ? Increased production

25. Abnormal CO2? ? High or low alveolar ventilation

26. Abnormal CO2? ? Increased dead space ventilation Clues to increased dead space ventilation Persisently high PCO2 despite high minute ventilation PCO2-ETCO2 disparity > 5 mmof Hg Increased dead space Pulmonary vascular disease Pulmonary embolism Hypovolemia Low cardiac output COPD ARDS Pulmonary fibrosis

27. REVIEW OF ACID-BASE PHYSIOLOGY Lets focus on the acid-base part of ABG

28. A great quote! O pKa is the negative logarithm of the dissociation constant pKa ' s value is dependent on the temperature,[H+] and the ionic concentration of the solution. It has a value of 6.1 @ 37  C and pH of 7.4 Facebook page: Anesthesia Info from The Lay Medical Man

29. A few confusing very good approaches! Only measured variable in ABG is pH and PaCO2 All methods rely on PaCO2 to measure respiratory acid base imbalance For measuring metabolic acid base balance, Copenhagen school rely on pH and SBE while Boston school rely on calculated bicarbonate We are following the Copenhagen school here Acids are either Respiratory acids or Metabolic acids Facebook page: Anesthesia Info from The Lay Medical Man

30. Metabolic and Respiratory acids Na, K, Cl are called strong ions LUNGS 2000mM KIDNEYS 70 mM @Tissue level @Pulmonary capillary level

31. Unity in Diversity; concept of SBE HCO3 may be the primary mover in metabolic imbalance But there are other Non carbonic buffer systems The concept of SBE makes this multi-buffer system into a hypothetical system, where the entire body behaves like a bicarbonate solution BE [actual] = BE of whole blood SBE = BE of ECF Facebook page: Anesthesia Info from The Lay Medical Man

32. This is how I did it! Hmm tasty Facebook page: Anesthesia Info from The Lay Medical Man ECF is the fluid through which acid base changes are mediated. Create a hypothetical ECF compartment by diluting the arterial Blood 3 fold by its own plasma. Now report BE of this compartment: Your delicious dish is ready : SBE is the best measure of assessing metabolic acid base changes; Reported in mM /L Normal: ± 2 mM /L

33. Scribble pad  pCO2 12 mm Hg = 0.1 pH =  BE 6 mEq /L Rosenthal correction factor: Change in pH = 0.015 pH units per degree C change in temperature CO2 crosses cell membranes easily so changes in pCO2 affect intracellular pH rapidly and in a predictable direction Net production of the non volatile or fixed acids are about 70-100 mmoles of H+ per day in an adult Facebook page: Anesthesia Info from The Lay Medical Man

34. Helmoholz’s Daven port nomogram . Facebook page: Anesthesia Info from The Lay Medical Man

35. pH and [H+] 

36. So when we arrange it in order, in response to an acid base change First defense: Buffering Second: Respiratory : alteration in arterial pCO2 Third defense: Renal : alteration in HCO3 excretion Facebook page: Anesthesia Info from The Lay Medical Man

37. T he buffers . Facebook page: Anesthesia Info from The Lay Medical Man

38. Salute our buffers! In the ICF proteins (mainly imidazole group of Histidine and phosphates) is responsible for 97-99% of body's total buffering of respiratory acid base disorders, 60% for metabolic acidosis and 30% for metabolic alkalosis Protein buffers in blood: hb-150 g/L plasma proteins 70g/l Hb contains about 3 times the number of histidine residues per molecule, and present in twice the conc , so quantitatively its 6 times more importa nt than plasma proteins Facebook page: Anesthesia Info from The Lay Medical Man

39. Salute our buffers! Deoxy hemoglobin is a better buffer than oxyhemoglobin Respiratory disorders are predominantly buffered in the intracellular compartment Conversely ecf buffers 40% for a metabolic acidosis and 70% for a metabolic alkalosis In ECF bicarbonate system is the most important In blood, Hb is the most important for CO2 Facebook page: Anesthesia Info from The Lay Medical Man

40. Salute our buffers! Bicarbonate buffer system is the major buffer system in the ECF. Responsible for about 80% of extracellular buffering. It can't buffer respiratory acid base disorders [Bicarbonate system cannot buffer changes in H+ produced by the reaction between CO2 and H2O] Facebook page: Anesthesia Info from The Lay Medical Man

41. Where is the dustbin? Standard pH Standard bicarbonate Buffer base Total CO2 Facebook page: Anesthesia Info from The Lay Medical Man

42. THESE GAPS ARE REALLY HURTING .

43. ANION GAP When all the commonly measured anions are substracted from the cations , the result is a positive value of 12±4 mEq /L Due to unmeasured anions Corrected AG = Calculated AG + 2.5 [4.5-measured albumin in g/dl] Facebook page: Anesthesia Info from The Lay Medical Man

44. WIDE & NORMAL AG GAP ACIDOSIS If AG > 20  suspect ; if > 25 confirmed Some conditions generate anions these are neutralized by bicarbonatebicarbonate falls   AG widens Some conditions lead to loss of bicarbonate this is counterbalanced by gain in chloride gain in chloride exactly matches loss of bicarbonate  AG is normal Facebook page: Anesthesia Info from The Lay Medical Man

45. WIDE & NORMAL AG GAP ACIDOSIS . Facebook page: Anesthesia Info from The Lay Medical Man

46. Negative AG Hypoalbuminemia Lithium toxicity Multiple myeloma Facebook page: Anesthesia Info from The Lay Medical Man

47. If you are still not confused, The Bicarbonate Gap can do that When there is a wide AG acidosis, the the rise in AG is matched by the fall in HCO3 BG= AG-HCO3=0 ; If its NOT ‘0’ BG>+6= Metabolic alkalosis per se / compensatory BG <-6 = Hyperchloremic acidosis / HCO3 deficit as part of respiratory alkalosis BG= Na-Cl-39 Facebook page: Anesthesia Info from The Lay Medical Man

48. Delta Ratio Increase in AG /decrease in Bicarbonate Facebook page: Anesthesia Info from The Lay Medical Man Delta ratio <0.4 Hyperchloremic normal AG acidosis 0.4-0.8 Combined high AG & normal AG acidosis 1-2 High AG acidosis Lactic acidosis 1.6 DKA; close to 1 >2 Concurrent metabolic alkalosis Pre existing compensated respiratory acidosis

49. The concept of normality; who is normal? . “ Do not fear to be eccentric in opinion, for every opinion now accepted was once eccentric.”  ―   Bertrand Russell Facebook page: Anesthesia Info from The Lay Medical Man

50. NORMAL VALUES . Facebook page: Anesthesia Info from The Lay Medical Man

51. ARTERIAL Vs VENOUS BLOOD . Facebook page: Anesthesia Info from The Lay Medical Man

52. INDIVIDUAL ACID BASE ABNORMALITIES AND ‘COMPENSATION’ mm

53. Two watch guards! . Facebook page: Anesthesia Info from The Lay Medical Man

54. ACUTE RESPIRATORY ACID BASE CHANGES Facebook page: Anesthesia Info from The Lay Medical Man

55. CHRONIC RESPIRATORY ACID BASE CHANGES compensated by renal handling of bicarbonate; hence SBE changes pH return to 2/3 rd of normal W/F Acute on Chronic Facebook page: Anesthesia Info from The Lay Medical Man

56. Respiratory Acidosis :Causes E.g. if PaCO2 is 60 mm of Hg and cause is chronic respiratory acidosis, then the expected SBE is 0.4 X 20 = 8 mM /L Facebook page: Anesthesia Info from The Lay Medical Man CAUSES Upper airway obstruction Status asthmaticus Pneumonia Pulmonary edema CNS depression Neuro muscular impairment Ventilatory restriction

57. Respiratory Acidosis . Facebook page: Anesthesia Info from The Lay Medical Man

58. Respiratory Acidosis . Facebook page: Anesthesia Info from The Lay Medical Man

59. Respiratory Acidosis: effects  CBF and ICP Arrhythmia Hyperventilation Patients with marked elevations of PCO2 may be comatose; but several OTHER factors contribute to this and screen for those: Anesthetic effects of very high PCO2 Hypoxemia Raised ICP [in patients breathing room air, PCO2 > 90 mm of Hg is not compatible with life If you acutely reduce CO2: accumulated HCO3 will r emain Facebook page: Anesthesia Info from The Lay Medical Man

60. Respiratory Alkalosis Normal in mountain dwellers and pregnant women Generally a poor prognostic sign, when present in critically ill Facebook page: Anesthesia Info from The Lay Medical Man CAUSES Hypoxemia Pulmonary disorders CNS disorders Hepatic failure Sepsis Salicylate toxicity Anxiety- hyperventilation

61. RESPIRATORY ALKALOSIS-COMPENSATION compensated by renal handling of bicarbonate; hence SBE changes pH return to 2/3 rd of normal Facebook page: Anesthesia Info from The Lay Medical Man

62. Respiratory Alkalosis: Causes . Facebook page: Anesthesia Info from The Lay Medical Man

63. Respiratory Alkalosis : Effects Increased neuromuscular irritability Cerebral vasoconstriction Decreased ICP Increased cerebral excitability Inhibition of respiratory drive Hypokalemia Respiratory alkalosis + abnormal respiratory muscle activity ? High ventilatory demand cautious decision making regarding extubation Pre intubation respiratory acidosis Ventilator therapy titrated to a PaCO2 of 40 mm Hg extubation  respiratory acid osis  over days HCO3 accumulate and correct it Facebook page: Anesthesia Info from The Lay Medical Man

64. Metabolic Acidosis Produced by increase in titratable hydrogen ion concentration Respiratory compensation return pH to one third to half way normal Facebook page: Anesthesia Info from The Lay Medical Man

65. Metabolic Acidosis : Causes Respiratory Facebook page: Anesthesia Info from The Lay Medical Man

66. Metabolic Acidosis : Causes . Facebook page: Anesthesia Info from The Lay Medical Man

67. Metabolic Acidosis : effects Decreased strength of respiratory muscles Hyperventilation Myocardial depression Sympathetic over activity Decreased arrhythmia threshold Resistance to catecholamines Hyperkalemia Increased metabolic demand [N:5%of VO2; in distress 25%] Insulin resistance Facebook page: Anesthesia Info from The Lay Medical Man

68. Urinary Anion Gap [UAG] =UA-UC=[Na]+[K]-[ Cl ] If acidosis is due to loss of base via bowel, kidneys will try to increase [H+] loss with NH4+ & Cl - in urine  UAG So in a patient with hyperchloremic metabolic acidosis: Negative UAG  GIT loss of [HCO3-] Positive UAG Loss of base via kidney (problem is with kidney and it cant increase ammonium excretion) “ neGUTive ” Facebook page: Anesthesia Info from The Lay Medical Man

69. Metabolic Acidosis and Mechanical ventilation Respiratory effect is hyper ventilation  may not be tolerated by patients with compromised cardiac or respiratory reserve mechanical ventilation may be required in such patients , till underlying metabolic acidosis is addressed When on ventilator, try to mimic the natural compensation; but don’t go < 30 mmof Hg of PaCO2 Facebook page: Anesthesia Info from The Lay Medical Man

70. Metabolic Alkalosis Produced by decrease in titratable hydrogen ion concentration Depress ventilation Facebook page: Anesthesia Info from The Lay Medical Man weaning

71. Metabolic Alkalosis Generally pCO2 wont go > 55; if > 55, indicates severe alkalosis OR combined metabolic alkalosis + respiratory acidosis Usually [HCO3-]   prompt [HCO3-] excretion by kidney; persistence requires additional process to impair [HCO3-] excretion

72. Metabolic Alkalosis: Causes .

73. Additional points- Metabolic alkalosis Depresses respiration  hypoxemia & hypercarbia Effects on PaCO2 are seen only when HCO3> 35 Mm/L Chloride responsive [Urinary Cl - < 15 mEq /L]: Rx is chloride-volume-potassium repletion [ If severe infusion of 0.1N HCl Chloride resistant [Urinary Cl - >25 mEq /L]: Rx is correction of the cause of mineralocorticoid excess and potassium depletion Selective HCO3 excreting diuretic Acetazolamide Facebook page: Anesthesia Info from The Lay Medical Man

74. Curious facts Hepatic metabolism of citrate, lactate, acetate--. Brief alkalosis Chloride and bicarbonate are the only anions present in appreciable amounts in ECF: so a defiency in one must lead to an increase in the other to maintain electroneutrality Vomiting and diuretics cause chloride depletion Mineralocorticoid excess [in Cushings , the excess corticosteroids have some mineralocorticoid effects] K+ & H+ loss matched by [HCO3-] Facebook page: Anesthesia Info from The Lay Medical Man

75. You cant exist alone man; who is behind you? Reduced GFR Chloride depletion Potassium depletion ECF volume depletion Because kidney has a large capacity to excrete bicarbonate and return the plasma level to normal Facebook page: Anesthesia Info from The Lay Medical Man

76. Urinary Chloride ,

77. Effects of Metabolic Alkalosis: Reduced cerebral blood flow Seizures Tetany Reduction in coronary blood flow Predisposistion to refractory arrhythmias Decreased contractility Hypoventilation Hypokalemia , Hypomagnesemia Reduced ionized calcium Promote anaerobic glycolysis  lactate Weaning failure, especially if HCO3 is >35

78. Impaired arterial oxygen content Hypoventilation Micro atelectasis V-P mismatch So assess for the requirement of supplemental oxygen in metabolic alkalosis

79. Give Cl , K and volume! Chloride deficit = 0.3 X weight X (100- Plasma chloride) Volume of isotonic saline in L = Chloride deficit / 154 Rarely ancillary measures used: One or two dose of Acetazolamide Problems: renal loss of Na and water, raise K, slower and difficult to titrate

80. THE APPROACH .

81. Don’t satisfy the criteria for OCD Even stable patients on ventilator can show variability in PaO2 in the range of 2-37 mm of Hg and in PCO2 in the range of 1-12 mm of Hg … should be considered as normal Unnecessary repeating of ABGs will create confusion Facebook page: Anesthesia Info from The Lay Medical Man

82. Find… primary acid-base disturbances should be detected first by inspection of the pH and PaCO2 After scanning for primary processes, SBE can then be combined with the PaCO2/ SBE rules Facebook page: Anesthesia Info from The Lay Medical Man

83. Scan…. Check : 1. The in vivo metabolic component of any acid-base disturbance. 2 . The appropriateness of the metabolic response to any respiratory acid-base derangement. 3 . The appropriateness of the respiratory response to any metabolic acid-base derangement . For example, if the pH, PaCO2 and SBE are all elevated, the primary process is a metabolic alkalosis Facebook page: Anesthesia Info from The Lay Medical Man

84. Analyse After scanning for primary processes, SBE can then be combined with the PaCO2/ SBE rules, to quantify: Facebook page: Anesthesia Info from The Lay Medical Man

85. ? Compensation; I don’t want.. After scanning for primary processes, SBE can then be combined with the PaCO2/ SBE rules, to quantify: Facebook page: Anesthesia Info from The Lay Medical Man

86. Are you single or married? The next step is to quantify the severity of the metabolic alkalosis by determining the elevation of SBE above the normal range . ? whether the accompanying respiratory acidosis is purely compensatory . If this is not so, there are two primary acid-base disturbances (metabolic and respiratory). Facebook page: Anesthesia Info from The Lay Medical Man

87. Example:1,2 pH = 7.35, PCO2 = 60 mmHg, SBE = 7 mM /L   acidosis Respiratory   SBE =0.4 X PaCO2= 0.4x 20= 8mM/L - therefore compensatory.  Partially compensated respiratory acidosis   pH = 7.15, PCO2 = 60 mmHg, SBE = - 6 mEq /L acidosis   ?Respiratory acidosis .  ?Metabolic acidosis .  The components are pulling in same direction - neither can be compensating for the other  combined respiratory +Metabolic acidosis   Facebook page: Anesthesia Info from The Lay Medical Man

88. Example:3 pH = 7.30, PCO2 = 30 mmHg, SBE = -10 mEq /L  acidosis   Respiratory change is alkaline   Metabolic acidosis .  Compensation?   PaCO2=SBE=10 marked metabolic acidosis with mild respiratory compensation. Facebook page: Anesthesia Info from The Lay Medical Man

89. Example:4 pH = 7.30, PCO2 = 30 mmHg, SBE = -10 mEq /L  acidosis   Respiratory change is alkaline   Metabolic acidosis .  Compensation?   PaCO2=SBE=10 marked metabolic acidosis with mild respiratory compensation. Facebook page: Anesthesia Info from The Lay Medical Man

90. Example:5 . ?alkalosis, ?respiratory, expected= 0.4x 16[40-24]=6 Compensated respiratory alkalosis Facebook page: Anesthesia Info from The Lay Medical Man pH :  PaCO2 :  HCO 3:   BE: 7.44 24 16 -6

91. Example 6 pH Acidosis?, respiratory?, 36x 0.4=14 Compensated respiratory acidosis Facebook page: Anesthesia Info from The Lay Medical Man pH :  PaCO2 :  HCO 3:   BE: 7.38 76 42 +14

92. Example 7 pH .alkalosis, metabolic?, any associated respiratory acidosis? 0.6 x sbe = 0.6x 14=8.4, so Uncompensated metabolic alkalosis Facebook page: Anesthesia Info from The Lay Medical Man pH :  PaCO2 :  HCO 3:   BE: 7.56 44 38 +14

93. Example 8 Alkalosis, respiratory?, ?metabolic compensation 0.4x 14= 5.6 [ direction: same as CO2] Facebook page: Anesthesia Info from The Lay Medical Man pH :  PaCO2 :  HCO 3:   BE: 7.44 26 18 -4

94. Example 9 compensated ?respiratory ,0.4x16= 6.4, compensated respiratory alkalosis Facebook page: Anesthesia Info from The Lay Medical Man pH :  PaCO2 :  HCO 3:   BE: 7.40 56 34 +7

95. Example 10 A 24 year-old woman is found down in Pioneer Square by some bystanders. The medics are called and, upon arrival, find her with an oxygen saturation of 88% on room air and pinpoint pupils on exam. She is brought into the Harborview ER where a room air arterial blood gas is performed and reveals: pH 7.25, PCO 60, PO 65, HCO - 26, Base Excess 1.223O ; his chemistry panel shows her sodium is 137, chloride 100, bicarbonate 27 Acid-base status:• The patient has a low pH ( acidemia )• The PCO2 is high (respiratory acidosis) and the SBE is normal . The low pH and high PCO2 imply that the respiratory acidosisis the primary process PaO2/FiO2= 325 , 550-325= 225=10% PAO2=713x0.2-1.25x60=68 pAO2-paO2=8 mm of Hg.. Normal, which tells us that her hypoxemia is entirely due to hypoventilation Facebook page: Anesthesia Info from The Lay Medical Man

96. Sorry.. Foreign ABG There is no compensation happening The anion gap is 10 and is, therefore, normal . The respiratory acidosis implies that the patient is hypoventilating . This fact, in combination with the pinpoint pupils suggests the patient is suffering from an acute narcotic overdose. In this case, the narcotic is most likely heroin. Facebook page: Anesthesia Info from The Lay Medical Man

97. Example 11 A 68 year-old man with a history of very severe COPD and chronic carbon dioxide retention (Baseline PCO2 58) presents to the emergency room complaining of worsening dyspnea and an increase in the frequency and purulence of his sputum production over the past 2 days. His oxygen saturation is 78% on room air. Before he is place on supplemental oxygen, a room air arterial blood gas is drawn and reveals: pH 7.25, PCO 68, PO 48, HCO 31, SBE 6 Pao2/fio2=240, shunt fraction 15%, PAO2-PaO2=13 SBE=0.4 X paCO2=11.2 Acute on chronic respiratory failure with respiratory acidosis Facebook page: Anesthesia Info from The Lay Medical Man

98. Example 12 A 65 year-old man is brought into the hospital with complaints of severe nausea and weakness. He has had problems with peptic ulcer disease in the past and has been having similar pain for the past two weeks. Rather than see a physician about this, he opted to deal with the problem on his own and, over the past week, has been drinking significant quantities of milk and consuming large quantities of TUMS (calcium carbonate). On his initial laboratory studies, he is found to have a calcium level of 11.5 mg/ dL,a creatinine of 1.4 and bicarbonate of 35. The resident working in the ER decides to draw a room air arterial blood gas, which reveals: pH 7.45, PCO249, PO 68, HCO - 34. SBE=11 On his chemistry panel, the sodium is 139, chloride 95 , HCO 34 Facebook page: Anesthesia Info from The Lay Medical Man

99. Example 12 paO2/FiO2=340—shunt fraction-10% A-a gradient= 14  PaCO2 = 0.6 x SBE=0.6 x 11=47..compensatory AG 10 normal Partially compensated Metabolic alkalosis Facebook page: Anesthesia Info from The Lay Medical Man

100. References : Dr Suneel P.R., SCTIMST, Arterial blood gas before, during and after mechanical ventilation, Respiratory Care Update 2007 Arterial blood gases made easy, Ian A M Hennessey, Alan G Japp Lawrence Martin, All you really need to know to interpret arterial blood gases, 2 nd edition Simple as ABG, Ted &Larry’s A. Hasan , Handbook of Blood Gas/Acid-Base Interpretation, 2013 Standard Base Excess, T. J. MORGAN, Australasian anesthesia 2003

101. THANK YOU Facebook page: Anesthesia Info from The Lay Medical Man Blog : The Lay Medical Man www.thelaymedicalman.blogspot.in