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A 65 -year-old man with chronic obstructive lung disease has been using low-flow oxygen therapy. He has recently developed a severe respiratory tract infection and has trouble breathing. He is admitted to the emergency room because his wife is having trouble arousing him. She relates that he had "turned his oxygen way up" because of difficulty breathing. His respirations are 12 breaths/minute. Arterial blood gases, drawn on admission to the emergency room, indicated a $\mathrm{PO}_2$ of $85 \mathrm{~mm} \mathrm{Hg}$ (normal, 90 to $95 \mathrm{mmHg}$ ) and a $\mathrm{PCO}_2$ of $90 \mathrm{~mm} \mathrm{Hg}$ (normal, $40 \mathrm{~mm} \mathrm{Hg}$ ). His serum $\mathrm{HCO}_3^{-}$was $34 \mathrm{mEq} / \mathrm{L}$ (normal, 24 to $48 \mathrm{mEq} / \mathrm{L})$. What is his $\mathrm{pH}$ ? A. What is the most likely cause of this man's problem? B. How would you explain the lethargy and difficulty in arousal? C. What would be the main goal of treatment for this man in terms of acid-base balance? D. Explain the concurrent respiratory and metabolic acidosis that often occurs in persons with chronic respiratory acidosis. 

   A 65 -year-old man with chronic obstructive lung disease has been using low-flow oxygen therapy. He has recently developed a severe respiratory tract infection and has trouble breathing. He is admitted to the emergency room because his wife is having trouble arousing him. She relates that he had "turned his oxygen way up" because of difficulty breathing. His respirations are 12 breaths/minute. Arterial blood gases, drawn on admission to the emergency room, indicated a $\mathrm{PO}_2$ of $85 \mathrm{~mm} \mathrm{Hg}$ (normal, 90 to $95 \mathrm{mmHg}$ ) and a $\mathrm{PCO}_2$ of $90 \mathrm{~mm} \mathrm{Hg}$ (normal, $40 \mathrm{~mm} \mathrm{Hg}$ ). His serum $\mathrm{HCO}_3^{-}$was $34 \mathrm{mEq} / \mathrm{L}$ (normal, 24 to $48 \mathrm{mEq} / \mathrm{L})$. What is his $\mathrm{pH}$ ?
A. What is the most likely cause of this man's problem?
B. How would you explain the lethargy and difficulty in arousal?
C. What would be the main goal of treatment for this man in terms of acid-base balance?
D. Explain the concurrent respiratory and metabolic acidosis that often occurs in persons with chronic respiratory acidosis.
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Essentials of Pathophysiology: Concepts of Altered States
Essentials of Pathophysiology: Concepts of Altered States
Carol Porth 4th Edition
Chapter 8, Problem 6 ↓

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The Henderson-Hasselbalch equation is pH = pKa + log([HCO3-]/[CO2]). In this case, the pKa is 6.1 (from the Henderson-Hasselbalch equation for bicarbonate buffer system). [HCO3-] = 34 mEq/L [CO2] = 90 mmHg pH = 6.1 + log(34/90) pH = 6.1 + log(0.3778) pH = 6.1 -  Show more…

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A 65 -year-old man with chronic obstructive lung disease has been using low-flow oxygen therapy. He has recently developed a severe respiratory tract infection and has trouble breathing. He is admitted to the emergency room because his wife is having trouble arousing him. She relates that he had "turned his oxygen way up" because of difficulty breathing. His respirations are 12 breaths/minute. Arterial blood gases, drawn on admission to the emergency room, indicated a $\mathrm{PO}_2$ of $85 \mathrm{~mm} \mathrm{Hg}$ (normal, 90 to $95 \mathrm{mmHg}$ ) and a $\mathrm{PCO}_2$ of $90 \mathrm{~mm} \mathrm{Hg}$ (normal, $40 \mathrm{~mm} \mathrm{Hg}$ ). His serum $\mathrm{HCO}_3^{-}$was $34 \mathrm{mEq} / \mathrm{L}$ (normal, 24 to $48 \mathrm{mEq} / \mathrm{L})$. What is his $\mathrm{pH}$ ? A. What is the most likely cause of this man's problem? B. How would you explain the lethargy and difficulty in arousal? C. What would be the main goal of treatment for this man in terms of acid-base balance? D. Explain the concurrent respiratory and metabolic acidosis that often occurs in persons with chronic respiratory acidosis.
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Key Concepts

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Mixed Acid-Base Disorders
Mixed acid-base disorders occur when more than one primary disturbance is present, such as a combination of respiratory acidosis and concurrent metabolic acidosis or compensation. This concept is important in understanding how chronic conditions can become decompensated, and how additional insults like infections can upset previously compensated states.
Chronic Respiratory Acidosis with Renal Compensation
This concept involves understanding how chronic retention of carbon dioxide, as seen in conditions like COPD, leads to respiratory acidosis. Over time, the kidneys adapt by increasing bicarbonate reabsorption, thereby compensating and partially correcting the pH. This compensation distinguishes chronic respiratory acidosis from its acute form, where metabolic compensation has not yet occurred.
Oxygen Therapy and Its Impact on Respiratory Drive
In patients with chronic lung disease, oxygen therapy must be carefully managed because their respiratory drive is often more reliant on hypoxic stimuli rather than elevated CO2 levels. Excessive oxygen administration can diminish this hypoxic drive, leading to hypoventilation and exacerbated carbon dioxide retention, which in turn worsens respiratory acidosis.
CO2 Narcosis and Central Nervous System Depression
Elevated levels of CO2 can lead to CO2 narcosis, a condition where central nervous system function is depressed. This manifests clinically as lethargy, confusion, and difficulty in arousal, because high CO2 concentrations affect neuronal activity and reduce responsiveness.
Acid-Base Balance and pH Calculation
Acid-base balance is governed by the interplay between respiratory and metabolic systems, often analyzed using the Henderson-Hasselbalch equation. Calculating the pH in acid-base disturbances involves understanding how changes in CO2 and bicarbonate levels affect the overall acid-base status, a crucial skill when evaluating conditions like respiratory acidosis.
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Mr. Worried is a 52-year-old widow. He is retired and living alone. He enters the ED complaining of shortness of breath and tingling in fingers. His breathing is shallow and rapid. He denies diabetes; blood sugar is normal. There are no EKG changes. He has no significant respiratory or cardiac history. He takes several antianxiety medications. He says he has had anxiety attacks before. While being worked up for chest pain an arterial blood gas (ABG) analysis is done. The ABG results are: pH= 7.48 PCO2= 28 HCO3= 22 PO2= 85 Problem: pH is _____________ (high or low) PCO2 is _____________ (high or low) He is in respiratory _____________ (alkalosis or acidosis) Solution: 1- What breathing pattern is the patient exhibiting? 2- Mr. Worried is probably suffering from a(n) ___________________. 3- The simplest solution to treat his immediate respiratory issue (shortness of breath, rapid, shallow breathing) is to do what? 4- Why does the simple treatment listed in #3 above work? * Please note this will not work on a person with chronic CO2 retention, such as a COPD patient. These people develop a hypoxic drive, and do not respond to CO2 changes.

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