ABG series  ANAS SAHLE , MDDAMASCUSE HOSPITAL
Acid-Base Disorders and the           ABG 6
BREIF PREVIEW
Summary of the Approach to               ABGs1.   Check the pH2.   Check the pCO23.   Select the appropriate compensation ...
EXPECTED CHANGES IN             ACID-BASE DISORDERSPrimary Disorder                       Expected ChangesMetabolic acidos...
PH       PH>7,43          PH:7,37-7,43         PH<7,37                          MIXED VS      ALKALOSIS           NORMAL  ...
PCO2<36,           RES.ALK+                HCO3<21              M.AC                PCO2>44,           RES.AC +PH(7,37-7,4...
Respiratory system includes:1.    CNS (medulla)2.    Peripheral nervous system (phrenic nerve)3.    Respiratory muscles4. ...
Potential causes of Respiratory Failure
RESPIRATORY     ACIDOSIS / ALKALOSISCO2 + H2O    H2CO3     H+ + HCO3-      Respiratory Acidosis      Respiratory Alkalosis...
RESPIRATORY ALKALOSIS
RESPIRATORY ALKALOSIS  Normal 20:1 ratio is increased    pH of blood is above 7.4H2CO3       HCO3-                     = 7...
RESPIRATORY ALKALOSISCause is Hyperventilation  Leads to eliminating excessive amounts of CO2  Increased loss of CO2 from ...
HYPERVENTILATIONHyper = “Over”          Elimination of CO2          H +                 pH        14
RESPIRATORY ALKALOSISCan be the result of:  1) Anxiety, emotional disturbances  2) Respiratory center lesions  3) Fever  4...
RESPIRATORY ALKALOSISAnxiety is an emotional disturbance  The most common cause of hyperventilation, and thus respiratory ...
RESPIRATORY ALKALOSISFever  Rapid shallow breathing blows off too much CO2                           17
RESPIRATORY ALKALOSIS Salicylate poisoning(Aspirin overdose)   Ventilation is  stimulated without  regard to the status of...
RESPIRATORY ALKALOSISAssisted Respiration  Administration of CO2 in the exhaled air of the care - giver                   ...
RESPIRATORY ALKALOSISHigh Altitude  Low concentrations of O2 in the arterial blood reflexly stimulates ventilation in an a...
Causes of Respiratory Alkalosis        CENTRAL RESPIRATORY STIMULATION                    (Direct Stimulation of Resp Cent...
INTRATHORACIC STRUCTURAL CAUSES:1.   Reduced movement of chest wall & diaphragm2.   Reduced compliance of lungs3.   Irrita...
RESPIRATORY ALKALOSISKidneys compensate by:  Retaining hydrogen ions  Increasing bicarbonate excretion                    ...
RESPIRATORY ALKALOSISDecreased CO2 in the lungs willeventually slow the rate of breathing  Will permit a normal amount of ...
RESPIRATORY ALKALOSIS           metabolic balance before onset of -                                     alkalosis         ...
RESPIRATORY ALKALOSIS                         H2CO3 : Carbonic Acid                          HCO3- : Bicarbonate IonH2CO3 ...
RESPIRATORY ALKALOSISCO2  CO2 + H2O                     0.5       :    20                      respiratory alkalosis-     ...
RESPIRATORY ALKALOSIS                                         HCO3-0.5      :     15                               Alkalin...
RESPIRATORY ALKALOSISH2CO3          HCO3-        Cl-                          Chloride                         containing0...
RESPIRATORY ALKALOSIS Usually the only treatment needed is toslow down the rate of breathing Breathing into a paper bag or...
Treatment of Respiratory Alkalosis Resp alkalosis by itself not a cause of resp  failure unless work of increased breathi...
RESPIRATORY ACIDOSIS   39
RESPIRATORY ACIDOSISCaused by hyperkapnia due tohypoventilation   Characterized by a pH decrease  and an increase in CO2  ...
HYPOVENTILATIONHypo = “Under”         Elimination of CO2          H +                pH        41
RESPIRATORY ACIDOSISThe speed and depth of breathing control theamount of CO2 in the bloodNormally when CO2 builds up, the...
RESPIRATORY ACIDOSISRespiratory acidosisdevelops when thelungs dont expel CO2adequatelyThis can happen indiseases that sev...
RESPIRATORY ACIDOSISRespiratory acidosis can also develop whendiseases of the nerves or muscles of the chestimpair the mec...
RESPIRATORY ACIDOSISThe treatment of respiratory acidosisaims to improve the function of the lungsDrugs to improve breathi...
RESPIRATORY ACIDOSISDecreased CO2 removalcan be the result of:1) Obstruction of air   passages2) Decreased respiration   (...
RESPIRATORY ACIDOSIS1) Obstruction of air passages   Vomit, anaphylaxis, tracheal cancer                                  ...
RESPIRATORY ACIDOSIS2) Decreased Respiration   Shallow, slow breathing   Depression of the respiratory centers in the  bra...
RESPIRATORY ACIDOSIS3) Decreasedgas exchangebetweenpulmonarycapillaries andair sacs of lungs   Emphysema   Bronchitis   Pu...
RESPIRATORY ACIDOSIS4) Collapse of lung   Compression injury, open thoracic wound        Left lung       collapsed        ...
Causes of         Acute Respiratory Acidosis      EXCRETORY COMPONENT PROBLEMS:1.   Perfusion:               Massive PTE  ...
4.   Muscular defects:               Severe hypokalemia               Myasthenic crisis5.   Failure of Mechanical Ventilat...
Causes of        Chronic Respiratory Acidosis      EXCRETORY COMPONENT PROBLEMS:1.   Ventilation:              COPD       ...
CONTROL COMPONENT PROBLEMS:1.   CNS:    Obesity Hypoventilation Syndrome                   Tumours             Brainstem i...
RESPIRATORY ACIDOSIS             metabolic balance before onset of -                                       acidosis       ...
RESPIRATORY ACIDOSIS                        H2CO3 : Carbonic Acid                         HCO3- : Bicarbonate IonH2CO3    ...
RESPIRATORY ACIDOSIS                            CO2         CO2                      CO2                                  ...
RESPIRATORY ACIDOSIS                                         H2CO3                            HCO3-                       ...
RESPIRATORY ACIDOSIS                                               LactateH2CO3           HCO3-       LIVER               ...
TREATMENT OF          RESPIRATORY ACIDOSIS   The goal is to increase the exhalation of    CO2. The treatments are :    – ...
CASE -1 A 28 year old woman was admitted electively to a  HDU (high dependency unit) following a caesarian  section. A d...
• ACIDOSIS PH<7,37                    • RESPIRATORY PCO2>40                    • ∆HCO3=0,1(62- 40)=2,2(+24)               ...
CASE-2A 69 year old patient had a cardiac arrestsoon after return to the ward following anoperation.Resuscitation was comm...
LAB :Anion gap 24,Lactate 12 mmol/l.                     ABG             PH       6,85             PCO2     82            ...
PH<7,37           • ACIDOSIS PCO2>40            • RESPIRATORY                    • ∆HCO3=0,1(82- 40)=4,2 (+24)ACUTE.R.AC  ...
DiscussionCardiac arrest with low cardiac output and tissuehypo-perfusion causing a:– severe lactic acidosis.Ventilation i...
CASE-3A 70 year old man was admitted with severecongestive cardiac failure.He has been unwell for about a week andhas been...
LAB:      BIOCHEMISTRY                                   ABGNA             127                           PH         7,58K ...
PH>7,43            • ALKALOSISPCO2<40            • RESPIRATORY                   • ∆HCO3=0,4(40 -21)=24 – 7,6C,R .ALK     ...
DiscussionThe history suggests the followingpossibilities:    Respiratory alkalosis in response to the dyspnoea    associa...
DiscussionThis patient has a triple acid-basedisorder:    Acute metabolic acidosis probably due to renal    failure (?prer...
NEXT LECTURE1. Approche to hypoxiemic patient2. Cases
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ABG 6 Series

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ABG 6 Series

  1. 1. ABG series ANAS SAHLE , MDDAMASCUSE HOSPITAL
  2. 2. Acid-Base Disorders and the ABG 6
  3. 3. BREIF PREVIEW
  4. 4. Summary of the Approach to ABGs1. Check the pH2. Check the pCO23. Select the appropriate compensation formula4. Determine if compensation is appropriate5. Check the anion gap AG=NA – (HCO3 + CL):12 46. If the anion gap is elevated, check the delta-delta G:G Ratio =Δ AG (12-AG) Δ HCO3 (24-HCO3)7. If a metabolic acidosis is present, check urine pH8. Generate a differential diagnosis
  5. 5. EXPECTED CHANGES IN ACID-BASE DISORDERSPrimary Disorder Expected ChangesMetabolic acidosis PCO2 = 1.5 × HCO3 + (8 ± 2)Metabolic alkalosis PCO2 = 0.7 × HCO3 + (21 ± 2) PCO2= 0.9 * HCO3 +16Acute respiratory acidosis delta pH = 0.008 × (PCO2 - 40) ΔHCO3 = 0.1 × (PCO2-40)Chronic respiratory acidosis delta pH = 0.003 × (PCO2 - 40) ΔHCO3 = 0.35 × (PCO2-40)Acute respiratory alkalosis delta pH = 0.008 × (40 - PCO2) ΔHCO3 = 0.2 × (40 – PCO2 )Chronic respiratory alkalosis delta pH = 0.003 × (40 - PCO2) ΔHCO3 2nd × (40 – PCO2) From: THE ICU BOOK - = 0.4 Ed. (1998) [Corrected]
  6. 6. PH PH>7,43 PH:7,37-7,43 PH<7,37 MIXED VS ALKALOSIS NORMAL ACIDOSISPCO2>40 PCO2<40 PCO2<40 PCO2>40 M.AL R.AL M.AC R.AC
  7. 7. PCO2<36, RES.ALK+ HCO3<21 M.AC PCO2>44, RES.AC +PH(7,37-7,43) HCO3>27 M.ALK PCO2(nor), M.AC +M.ALK HCO3(nor) AG
  8. 8. Respiratory system includes:1. CNS (medulla)2. Peripheral nervous system (phrenic nerve)3. Respiratory muscles4. Chest wall5. Lung6. Upper airway7. Bronchial tree8. Alveoli9. Pulmonary vasculature
  9. 9. Potential causes of Respiratory Failure
  10. 10. RESPIRATORY ACIDOSIS / ALKALOSISCO2 + H2O H2CO3 H+ + HCO3- Respiratory Acidosis Respiratory Alkalosis 10
  11. 11. RESPIRATORY ALKALOSIS
  12. 12. RESPIRATORY ALKALOSIS Normal 20:1 ratio is increased pH of blood is above 7.4H2CO3 HCO3- = 7.4 =0.5 1 : 20 12
  13. 13. RESPIRATORY ALKALOSISCause is Hyperventilation Leads to eliminating excessive amounts of CO2 Increased loss of CO2 from the lungs at a rate faster than it is produced Decrease in H+ CO2 CO2 CO2 CO2 CO2 CO2 CO2CO2 CO2 CO2 CO2 CO2 13
  14. 14. HYPERVENTILATIONHyper = “Over” Elimination of CO2 H + pH 14
  15. 15. RESPIRATORY ALKALOSISCan be the result of: 1) Anxiety, emotional disturbances 2) Respiratory center lesions 3) Fever 4) Salicylate poisoning (overdose) 5) Assisted respiration 6) High altitude (low PO2) 15
  16. 16. RESPIRATORY ALKALOSISAnxiety is an emotional disturbance The most common cause of hyperventilation, and thus respiratory alkalosis, is anxietyRespiratory center lesions Damage to brain centers responsible for monitoring breathing rates Tumors Strokes 16
  17. 17. RESPIRATORY ALKALOSISFever Rapid shallow breathing blows off too much CO2 17
  18. 18. RESPIRATORY ALKALOSIS Salicylate poisoning(Aspirin overdose) Ventilation is stimulated without regard to the status of O2, CO2 or H+ in the body fluids 18
  19. 19. RESPIRATORY ALKALOSISAssisted Respiration Administration of CO2 in the exhaled air of the care - giver Your insurance won’t cover a ventilator any longer, so Bob here will be giving you mouth to mouth for the next several days 19
  20. 20. RESPIRATORY ALKALOSISHigh Altitude Low concentrations of O2 in the arterial blood reflexly stimulates ventilation in an attempt to obtain more O2 Too much CO2 is “blown off” in the process 20
  21. 21. Causes of Respiratory Alkalosis CENTRAL RESPIRATORY STIMULATION (Direct Stimulation of Resp Center):Structural Causes Non Structural Causes• Head trauma Pain• Brain tumor Anxiety• CVA Fever• Voluntary PERIPHERAL RESPIRATORY STIMULATION (Hypoxemia  Reflex Stimulation of Resp Center via Peripheral Chemoreceptors)• Pul V/Q imbalance• Pul Diffusion Defects Hypotension• Pul Shunts High Altitude
  22. 22. INTRATHORACIC STRUCTURAL CAUSES:1. Reduced movement of chest wall & diaphragm2. Reduced compliance of lungs3. Irritative lesions of conducting airways MIXED/UNKNOWN MECHANISMS:1. Drugs – Salicylates Nicotine Progesterone Thyroid hormone Catecholamines Xanthines (Aminophylline & related compounds)2. Cirrhosis3. Gram –ve Sepsis4. Pregnancy5. Heat exposure6. Mechanical Ventilation
  23. 23. RESPIRATORY ALKALOSISKidneys compensate by: Retaining hydrogen ions Increasing bicarbonate excretion HCO3- HCO3- H + H+ HCO3 - HCO3- H + H+ H+ HCO3- HCO - H + 3 H+ HCO3- HCO3- H+ HCO3- H + HCO3- H + H+ 26
  24. 24. RESPIRATORY ALKALOSISDecreased CO2 in the lungs willeventually slow the rate of breathing Will permit a normal amount of CO2 to be retained in the lung 27
  25. 25. RESPIRATORY ALKALOSIS metabolic balance before onset of - alkalosis pH = 7.4- respiratory alkalosis- pH = 7.7- - hyperactive breathing “ blows off ” CO2 - body’s compensation - kidneys conserve H+ ions and eliminate HCO3- in alkaline urine - therapy required to restore metabolic balance - HCO3- ions replaced by Cl- ions 28
  26. 26. RESPIRATORY ALKALOSIS H2CO3 : Carbonic Acid HCO3- : Bicarbonate IonH2CO3 HCO3- (Na+) HCO3- (K+) HCO3- 1 : 20 (Mg++) HCO3- (Ca++) HCO3-metabolic balance before onset of alkalosis- pH = 7.4- 29
  27. 27. RESPIRATORY ALKALOSISCO2 CO2 + H2O 0.5 : 20 respiratory alkalosis- pH = 7.7- hyperactive breathing “ blows off ” CO2- 30
  28. 28. RESPIRATORY ALKALOSIS HCO3-0.5 : 15 Alkaline Urine BODY’S COMPENSATION - kidneys conserve H+ ions and eliminate HCO3- in alkaline urine31
  29. 29. RESPIRATORY ALKALOSISH2CO3 HCO3- Cl- Chloride containing0.5 : 10 solution - therapy required to restore metabolic balance - HCO3- ions replaced by Cl- ions 32
  30. 30. RESPIRATORY ALKALOSIS Usually the only treatment needed is toslow down the rate of breathing Breathing into a paper bag or holdingthe breath as long as possible may helpraise the blood CO2 content as theperson breathes carbon dioxideback in after breathing it out 33
  31. 31. Treatment of Respiratory Alkalosis Resp alkalosis by itself not a cause of resp failure unless work of increased breathing not sustained by resp muscles Rx underlying cause Usually extent of alkalemia produced not dangerous. Admn of O2 if hypoxaemia If pH>7.55 pt may be sedated/anesthetised/ paralysed and/or put on MV.
  32. 32. RESPIRATORY ACIDOSIS 39
  33. 33. RESPIRATORY ACIDOSISCaused by hyperkapnia due tohypoventilation Characterized by a pH decrease and an increase in CO2 pH CO2 CO CO2 CO2 CO CO2 2 CO2 COCO2 2 CO2 CO2 pH CO2 CO2 40
  34. 34. HYPOVENTILATIONHypo = “Under” Elimination of CO2 H + pH 41
  35. 35. RESPIRATORY ACIDOSISThe speed and depth of breathing control theamount of CO2 in the bloodNormally when CO2 builds up, the pH of theblood falls and the blood becomes acidicHigh levels of CO2 in the blood stimulate theparts of the brain that regulate breathing,which in turn stimulate faster and deeperbreathing 44
  36. 36. RESPIRATORY ACIDOSISRespiratory acidosisdevelops when thelungs dont expel CO2adequatelyThis can happen indiseases that severelyaffect the lungs, suchas emphysema, chronicbronchitis, severepneumonia, pulmonaryedema, and asthma 45
  37. 37. RESPIRATORY ACIDOSISRespiratory acidosis can also develop whendiseases of the nerves or muscles of the chestimpair the mechanics of breathingIn addition, a person can develop respiratoryacidosis if overly sedated from narcotics andstrong sleeping medications that slowrespiration 46
  38. 38. RESPIRATORY ACIDOSISThe treatment of respiratory acidosisaims to improve the function of the lungsDrugs to improve breathing may helppeople who have lung diseases such asasthma and emphysema 47
  39. 39. RESPIRATORY ACIDOSISDecreased CO2 removalcan be the result of:1) Obstruction of air passages2) Decreased respiration (depression of respiratory centers)3) Decreased gas exchange between pulmonary capillaries and air spacs of lungs4) Collapse of lung 48
  40. 40. RESPIRATORY ACIDOSIS1) Obstruction of air passages Vomit, anaphylaxis, tracheal cancer 49
  41. 41. RESPIRATORY ACIDOSIS2) Decreased Respiration Shallow, slow breathing Depression of the respiratory centers in the brain which control breathing rates Drug overdose 50
  42. 42. RESPIRATORY ACIDOSIS3) Decreasedgas exchangebetweenpulmonarycapillaries andair sacs of lungs Emphysema Bronchitis Pulmonary edema 51
  43. 43. RESPIRATORY ACIDOSIS4) Collapse of lung Compression injury, open thoracic wound Left lung collapsed 52
  44. 44. Causes of Acute Respiratory Acidosis EXCRETORY COMPONENT PROBLEMS:1. Perfusion: Massive PTE Cardiac Arrest2. Ventilation: Severe pul edema Severe pneumonia ARDS Airway obstruction3. Restriction of lung/thorax: Flail chest Pneumothorax Hemothorax
  45. 45. 4. Muscular defects: Severe hypokalemia Myasthenic crisis5. Failure of Mechanical Ventilator CONTROL COMPONENT PROBLEMS:1. CNS: CSA Drugs (Anesthetics, Sedatives) Trauma Stroke2. Spinal Cord & Peripheral Nerves: Cervical Cord injury LGBS Neurotoxins (Botulism, Tetanus, OPC) Drugs causing Sk. m.paralysis (SCh, Curare, Pancuronium & allied drugs, aminoglycosides)
  46. 46. Causes of Chronic Respiratory Acidosis EXCRETORY COMPONENT PROBLEMS:1. Ventilation: COPD Advanced ILD Restriction of thorax/chest wall: Kyphoscoliosis, Arthritis Fibrothorax Hydrothorax Muscular dystrophy Polymyositis
  47. 47. CONTROL COMPONENT PROBLEMS:1. CNS: Obesity Hypoventilation Syndrome Tumours Brainstem infarcts Myxedema Ch sedative abuse Bulbar Poliomyelitis2. Spinal Cord & Peripheral Nerves: Poliomyelitis Multiple Sclerosis ALS Diaphragmatic paralysis
  48. 48. RESPIRATORY ACIDOSIS metabolic balance before onset of - acidosis pH = 7.4- respiratory acidosis- pH = 7.1- breathing is suppressed holding CO2 in - body body’s compensation- kidneys conserve HCO3- ions to restore - the normal 40:2 ratio kidneys eliminate H+ ion in acidic urine- - therapy required to restore metabolic balance - lactate solution used in therapy is 40 converted to bicarbonate ions in the liver 59
  49. 49. RESPIRATORY ACIDOSIS H2CO3 : Carbonic Acid HCO3- : Bicarbonate IonH2CO3 HCO3- (Na+) HCO3- (K+) HCO3- 1 : 20 (Mg++) HCO3- (Ca++) HCO3-- metabolic balance before onset of acidosis - pH = 7.4 60
  50. 50. RESPIRATORY ACIDOSIS CO2 CO2 CO2 CO22 : 20breathing is suppressed holding CO2 in body- pH = 7.1- 61
  51. 51. RESPIRATORY ACIDOSIS H2CO3 HCO3- HCO3- + H+2 : 30 acidic urine BODY’S COMPENSATIONkidneys conserve HCO3- ions to restore the - normal 40:2 ratio (20:1) kidneys eliminate H+ ion in acidic urine- 62
  52. 52. RESPIRATORY ACIDOSIS LactateH2CO3 HCO3- LIVER Lactate HCO3- 2 : 40 - therapy required to restore metabolic balance - lactate solution used in therapy is converted to bicarbonate ions in the liver 63
  53. 53. TREATMENT OF RESPIRATORY ACIDOSIS The goal is to increase the exhalation of CO2. The treatments are : – Based on the underlying causes – By providing ventilation therapy – Intravenous administration of HCO3- – Reversal of sedation or neuromuscular relaxants – Intubation and artificial ventilation (in severe cases)
  54. 54. CASE -1 A 28 year old woman was admitted electively to a HDU (high dependency unit) following a caesarian section. A diagnosis of fatty liver of pregnancy had been made preoperatively. She was commenced on a continuous morphine infusion at 5 mg/hr and received oxygen by mask. This was continued overnight and she was noted to be quite drowsy the next day. ABG Arterial blood gases were PH 7,16 PCO2 61,9 PO2 115 HCO3 21,2
  55. 55. • ACIDOSIS PH<7,37 • RESPIRATORY PCO2>40 • ∆HCO3=0,1(62- 40)=2,2(+24) • 26,2 ≠21ACUTE.R.AC • concomitant M.AC COMP AG=? • ??? Normal AG (12 4)
  56. 56. CASE-2A 69 year old patient had a cardiac arrestsoon after return to the ward following anoperation.Resuscitation was commenced andincluded intubation and ventilation.Femoral arterial blood gases werecollected about five minutes after thearrest.
  57. 57. LAB :Anion gap 24,Lactate 12 mmol/l. ABG PH 6,85 PCO2 82 PO2 214 HCO3 14
  58. 58. PH<7,37 • ACIDOSIS PCO2>40 • RESPIRATORY • ∆HCO3=0,1(82- 40)=4,2 (+24)ACUTE.R.AC • 28,2 ≠14 • concomitant M.AC COMP AG=24 • High AG M.AC Normal AG (12 4) • NO other metabolic disordersGAP:gap=1,2
  59. 59. DiscussionCardiac arrest with low cardiac output and tissuehypo-perfusion causing a:– severe lactic acidosis.Ventilation is depressed causing a:– respiratory acidosis.Inadequate ventilation in this pre-arrest phase mayhave been related to several factors, in particular :– inadequate reversal of neuromuscular paralysis,– airway obstruction in a supine sedated patient or– acute pulmonary oedema.
  60. 60. CASE-3A 70 year old man was admitted with severecongestive cardiac failure.He has been unwell for about a week andhas been vomiting for the previous 5 days.He was on no medication.He was hyperventilating and was verydistressed. Admission biochemistry is listed below.He was on high concentration oxygen bymask.
  61. 61. LAB: BIOCHEMISTRY ABGNA 127 PH 7,58K 5,2 PCO2 21CL 79 PO2 154HCO3 20 HCO3 19UREA 50,5 mmollCREAT 0,38 mmollGLUCO 9,5 mmollAG 33Creat = 5 mgdl (0,075) Urea =141,4 (0,357)cNA=128 Glucose =171 (*18) Corrected Sodium = Measured sodium + 0.016 * (Serum glucose - 100)
  62. 62. PH>7,43 • ALKALOSISPCO2<40 • RESPIRATORY • ∆HCO3=0,4(40 -21)=24 – 7,6C,R .ALK • 16,4 ≠19 • concomitant M.ALK COMP AG=28 • HIGH AG M.ACNormal AG (12 4) GAP:gap • concomitant M.ALK (=4 >2)
  63. 63. DiscussionThe history suggests the followingpossibilities: Respiratory alkalosis in response to the dyspnoea associate with the congestive heart failure A lactic acidosis is possible if cardiac output is low and tissue perfusion is poor Vomiting suggests metabolic alkalosisThe renal failure could be associated witha high anion gap acidosis
  64. 64. DiscussionThis patient has a triple acid-basedisorder: Acute metabolic acidosis probably due to renal failure (?prerenal failure) and possibly to lactic acidosis (hypoperfusion due heart failure and hypovolaemia) Metabolic alkalosis due to severe vomiting Respiratory alkalosis due to dyspnoea from congestive heart failure.The pO2 is elevated due to administrationof a high inspired oxygen concentration
  65. 65. NEXT LECTURE1. Approche to hypoxiemic patient2. Cases

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