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Respiratory regulation of Acid-Base Balance DR. SUMREENA MANSOOR ASSISTANT PROF OF BIOCHEMISTRY DEPT OF BIOCHEMISTRY & MOLECULAR BIOLOGY Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Arterial Blood Gas (ABG) pH, pCO2, pO2 – Measured directly HCO3-, O2 saturation (usually) – Calculated from pH, pCO2, and pO2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Normal Arterial Blood Gas Values pH 7.35 - 7.45 PaCO2 35-45 mmHg(4.7-6.0kpa) PaO2 70-100mmHg(11.3-12.6kpa) SaO2 93 - 98% HCO3¯ 22 - 26 mmol/L Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Arterial Blood Gases Condition State of PaCO2 in blood alveolar ventilation > 45 mm Hg Hypercapnia Hypoventilation 35 - 45 mm Hg Eucapnia Normal ventilation < 35 mm Hg Hypocapnia Hyperventilation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Practical Approach 1. Check the pH If the pH < 7.35 acidemia is present. If the pH > 7.45 alkalemia is present. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Practical Approach 2. Check the pCO2 pH < 7.35 and pCO2 > 40 respiratory acidosis pH > 7.45 and pCO2 < 40 respiratory alkalosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17 year-old female patient while hyperventilating (frequent, deep, sighing respiration to sustained, obvious, rapid, deep breathing) fell unconscious to the floor. An attending Physician diagnosed her condition as "hyperventilation syndrome" caused by her anxiety and mental stress. He successfully treated her by rebreathing expired CO2 from a paper bag and she completely recovered. What happened to the acid-base balance in her body? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiratory alkalosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 54 year-old man becomes critically unwell with confusion and hypotension Test Results Normal Range PaO2 7.9 kPa 11.3-12.6 PaCO2 12.8 kPa 4.7-6.0 pH 7.16 7.36-7.44 HCO-3 42 mmol/l 20-28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiratory acidosis with renal compensation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A 25 year-old patient has acute exacerbation of bronchial asthma. Which abnormality on the arterial blood gas evaluation does this patient most likely have? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. High pH suggesting low Hydrogen *[H+] ions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 17 year old w/severe kyphoscoliosis, admitted for pneumonia pH: 7.47 pCO2: 25 mmHg pO2: 60 mmHg HCO3: 14 mmol/L Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Compensated respiratory alkalosis due to chronic hyperventilation secondary to hypoxia Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 9 year old with H/O asthma, audibly wheezing x 1 week, has not slept in 2 nights; presents sitting up and using accessory muscles to breath with audible wheezes Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. pH: 7.51 pCO2: 25 mmHg pO2 35 mmHg HCO3: 22 mEq/L Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Uncompensated respiratory alkalosis with severe hypoxia due to asthma exacerbation Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 57-year-old male with COPD, home oxygen dependence, daily chronic sputum production, is treated with several types of metered dose inhalers. No other medications. He is in his usual state. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chronic respiratory acidosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The patient described in above problem develops increasing shortness of breath, purulent sputum production, and increased weakness requiring emergency room visit. He appears to be in moderate respiratory distress peripheral cyanosis. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acute respiratory acidosis and chronic respiratory acidosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MALE, AGED 70 YEARS, WITH RESPIRATORY AND METABOLIC FAILURE DUE TO COPD. HE WAS ADMITTED TO ICU AND MECHANICALLY VENTILATED Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. ON ADMISSION THIS PATIENT HAD A PARTIALLY COMPENSATED RESPIRATORY ACIDOSIS, i. e PCO2 AND [HCO-3]. VENTILATION WAS OVER-ENTHUSIASTIC AND PRODUCED A RESPIRATORY ALKALOSIS (P CO2 <35). Copyright © The McGraw-Hill Companies, Inc. 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