Acid-base balance

Acid-base balance US Medical PG Question 1: A 27-year-old man with a past medical history of type I diabetes mellitus presents to the emergency department with altered mental status. The patient was noted as becoming more lethargic and confused over the past day, prompting his roommates to bring him in. His temperature is 99.0°F (37.2°C), blood pressure is 107/68 mmHg, pulse is 120/min, respirations are 17/min, and oxygen saturation is 98% on room air. Laboratory values are ordered as seen below. Serum: Na+: 144 mEq/L Cl-: 100 mEq/L K+: 6.3 mEq/L HCO3-: 16 mEq/L BUN: 20 mg/dL Glucose: 599 mg/dL Creatinine: 1.4 mg/dL Ca2+: 10.2 mg/dL Which of the following is the appropriate endpoint of treatment for this patient?

• A. Clinically asymptomatic
• B. Normal anion gap (Correct Answer)
• C. Normal glucose
• D. Vitals stable
• E. Normal potassium

Acid-base balance Explanation: ***Normal anion gap*** - A **normal anion gap** (approximately 8-12 mEq/L) indicates resolution of the **metabolic acidosis** characteristic of diabetic ketoacidosis (DKA). The current anion gap is high (Na - (Cl + HCO3) = 144 - (100 + 16) = 28 mEq/L). - The patient's presentation with **type 1 diabetes** and **altered mental status**, coupled with **hyperglycemia** (599 mg/dL) and **low bicarbonate** (16 mEq/L), is highly suggestive of DKA, for which anion gap normalization is a key treatment endpoint. *Clinically asymptomatic* - While a desirable outcome, resolution of symptoms occurs gradually and is not the primary biochemical endpoint for DKA treatment. - Patients may have residual symptoms even after metabolic derangements have significantly improved. *Normal glucose* - In DKA treatment, glucose is allowed to drop to a level (e.g., <200 mg/dL) but not necessarily to normal range, before initiating **dextrose-containing intravenous fluids** to prevent hypoglycemia while continuing insulin. - **Normal glucose** alone does not guarantee resolution of ketoacidosis, which is the main life-threatening aspect of DKA. *Vitals stable* - **Stable vital signs** indicate hemodynamic stability, which is crucial but does not confirm the resolution of the underlying DKA metabolic derangements. - Vitals can stabilize or worsen independently of acidosis resolution, especially if complications arise. *Normal potassium* - **Potassium levels** are critical to monitor and correct during DKA treatment, as insulin administration drives potassium into cells, potentially causing **hypokalemia**. - While important for patient safety, achieving a normal potassium level is part of supportive care and not the primary endpoint for resolving the ketoacidotic state itself.

Acid-base balance US Medical PG Question 2: A 32-year-old man is brought to the emergency department after he was found unresponsive on the street. Upon admission, he is lethargic and cyanotic with small, symmetrical pinpoint pupils. The following vital signs were registered: blood pressure of 100/60 mm Hg, heart rate of 70/min, respiratory rate of 8/min, and a body temperature of 36.0°C (96.8°F). While being assessed and resuscitated, a sample for arterial blood gas (ABG) analysis was taken, in addition to the following biochemistry tests: Laboratory test Serum Na+ 138 mEq/L Serum Cl- 101 mEq/L Serum K+ 4.0 mEq/L Serum creatinine (SCr) 0.58 mg/dL Which of the following values would you most likely expect to see in this patient’s ABG results?

• A. pH: decreased, HCO3- : increased, Pco2: increased (Correct Answer)
• B. pH: increased, HCO3- : decreased, Pco2: decreased
• C. pH: decreased, HCO3- : decreased, Pco2: decreased
• D. pH: increased, HCO3- : increased, Pco2: increased
• E. pH: normal, HCO3- : increased, Pco2: increased

Acid-base balance Explanation: ***pH: decreased, HCO3- : increased, Pco2: increased*** - The patient's **depressed respiratory rate** (8/min) indicates severe hypoventilation, leading to **CO2 retention** and subsequent **respiratory acidosis** (decreased pH, increased PaCO2). - In **acute respiratory acidosis**, the body initiates immediate buffering, causing a **mild increase in HCO3-** (approximately 1 mEq/L per 10 mmHg rise in PaCO2). Over 3-5 days, renal compensation leads to more significant HCO3- retention, but in this acute presentation, some HCO3- elevation is expected from acute buffering mechanisms. - The **decreased pH** indicates that compensation is incomplete, which is typical in the acute setting. *pH: increased, HCO3- : decreased, Pco2: decreased* - This pattern is characteristic of **respiratory alkalosis** (increased pH, decreased PaCO2) with metabolic compensation (decreased HCO3-), which would occur in hyperventilation, opposite to the patient's presentation. - The patient's **slow respiratory rate** of 8/min directly contradicts the finding of decreased PaCO2. *pH: decreased, HCO3- : decreased, Pco2: decreased* - This suggests a **metabolic acidosis** (decreased pH, decreased HCO3-) with respiratory compensation (decreased PaCO2), typically seen in conditions like DKA or lactic acidosis. - Although the pH is decreased, the patient's severe bradypnea (RR 8/min) indicates increased CO2 retention, not decreased CO2. *pH: increased, HCO3- : increased, Pco2: increased* - This combination of findings is indicative of **metabolic alkalosis** (increased pH, increased HCO3-) with respiratory compensation (increased PaCO2). - This is inconsistent with the patient's pinpoint pupils, cyanosis, and **severe bradypnea**, which are classic signs of opioid overdose causing respiratory depression and acidosis, not alkalosis. *pH: normal, HCO3- : increased, Pco2: increased* - A normal pH despite increased HCO3- and PaCO2 indicates **fully compensated respiratory acidosis**, which requires days of renal compensation to develop. - In this **acute, severe drug overdose** with profound respiratory depression, the body would not have sufficient time to achieve full compensation, thus the pH would remain low.

Acid-base balance US Medical PG Question 3: A 24-year-old woman presents to the emergency department after she was found agitated and screaming for help in the middle of the street. She says she also has dizziness and tingling in the lips and hands. Her past medical history is relevant for general anxiety disorder, managed medically with paroxetine. At admission, her pulse is 125/min, respiratory rate is 25/min, and body temperature is 36.5°C (97.7°F). Physical examination is unremarkable. An arterial blood gas sample is taken. Which of the following results would you most likely expect to see in this patient?

• A. pH: increased, HCO3-: increased, Pco2: increased
• B. pH: decreased, HCO3-: decreased, Pco2: decreased
• C. pH: decreased, HCO3-: increased, Pco2: increased
• D. pH: increased, HCO3-: decreased, Pco2: decreased (Correct Answer)
• E. pH: normal, HCO3-: increased, Pco2: increased

Acid-base balance Explanation: ***pH: increased, HCO3-: decreased, Pco2: decreased*** - The patient's presentation with **agitation**, **dizziness**, **paresthesias** (tingling in lips and hands), and **tachypnea** (respiratory rate 25/min) is highly suggestive of **hyperventilation** due to an anxiety attack. - **Hyperventilation** leads to excessive **CO2 expulsion**, causing a decrease in Pco2, which results in respiratory alkalosis (increased pH) and a compensatory decrease in HCO3-. *pH: increased, HCO3-: increased, Pco2: increased* - An **increased pH** coupled with **increased HCO3-** and **increased Pco2** would suggest a **metabolic alkalosis with respiratory compensation**, which is not consistent with the patient's acute hyperventilation. - While pH is increased, the other values contradict the primary respiratory cause suggested by the symptoms. *pH: decreased, HCO3-: decreased, Pco2: decreased* - This profile describes **metabolic acidosis with respiratory compensation**, which would typically present with **Kussmaul breathing** and other signs of acidosis, not acute hyperventilation and agitation. - Symptoms such as dizziness and tingling are associated with alkalosis, not acidosis. *pH: decreased, HCO3-: increased, Pco2: increased* - This pattern is characteristic of **respiratory acidosis with metabolic compensation**, often seen in conditions like **COPD exacerbation** or **opioid overdose** with hypoventilation. - The patient's rapid breathing and clinical picture are not consistent with respiratory acidosis. *pH: normal, HCO3-: increased, Pco2: increased* - A **normal pH** with **increased HCO3-** and **increased Pco2** would indicate a **compensated metabolic alkalosis**. - Her acute symptoms point to an uncompensated or acutely compensated respiratory disorder, not a compensated metabolic issue.

Acid-base balance US Medical PG Question 4: A 66-year-old man is brought to the emergency department by his daughter because of 3 days of fever, chills, cough, and shortness of breath. The cough is productive of yellow sputum. His symptoms have not improved with rest and guaifenesin. His past medical history is significant for hypertension, for which he takes hydrochlorothiazide. He has a 30-pack-year history of smoking. His temperature is 38.9 C (102.0 F), blood pressure 88/56 mm Hg, and heart rate 105/min. Following resuscitation with normal saline, his blood pressure improves to 110/70 mm Hg. His arterial blood gas is as follows: Blood pH 7.52, PaO2 74 mm Hg, PaCO2 28 mm Hg, and HCO3- 21 mEq/L. Which of the following acid-base disturbances best characterizes this patient's condition?

• A. Metabolic acidosis
• B. Respiratory acidosis
• C. Respiratory alkalosis (Correct Answer)
• D. Normal acid-base status
• E. Metabolic alkalosis

Acid-base balance Explanation: ***Respiratory alkalosis*** - The patient's pH of **7.52** indicates alkalemia. A **PaCO2 of 28 mm Hg** (normal range 35-45 mm Hg) is low, indicating a respiratory component. - The **primary disturbance is respiratory alkalosis** due to hyperventilation from pneumonia/sepsis causing tachypnea and increased CO2 elimination. - The HCO3- of 21 mEq/L (normal range 22-26 mEq/L) is at the lower limit of normal. In acute respiratory alkalosis, bicarbonate remains near normal since **metabolic compensation takes 2-3 days** to develop significantly. - With a 3-day history, minimal renal compensation is expected, consistent with the near-normal bicarbonate. *Metabolic acidosis* - Metabolic acidosis would present with a **low pH** and a **low HCO3-**, which is not seen here. - The patient's pH is **alkaline (7.52)**, not acidic, ruling out this diagnosis. *Respiratory acidosis* - Respiratory acidosis would be characterized by a **low pH** and a **high PaCO2**, indicating hypoventilation. - The patient's **PaCO2 is low (28 mm Hg)** and the **pH is high**, directly contradicting respiratory acidosis. *Normal acid-base status* - A normal acid-base status would have a **pH between 7.35 and 7.45** and PaCO2 between 35-45 mm Hg. - The patient's **pH of 7.52** and **PaCO2 of 28 mm Hg** are both abnormal, specifically indicating alkalemia and hypocapnia. *Metabolic alkalosis* - Metabolic alkalosis would feature a **high pH** and a **high HCO3-** (typically >26 mEq/L), often resulting from conditions like vomiting or diuretic use. - While the patient is on hydrochlorothiazide, his **HCO3- is 21 mEq/L** (low-normal, not elevated), indicating this is not a primary metabolic alkalosis.

Acid-base balance US Medical PG Question 5: A 50-year-old woman presents to the ED 6 hours after ingesting three bottles of baby aspirin. She complains of nausea, vomiting, dizziness, and tinnitus. Her blood pressure is 135/80 mmHg, pulse is 110/min, respirations are 32/min, temperature is 100.1 deg F (37.8 deg C), and oxygen saturation is 99% on room air. Arterial blood gas at room air shows, PCO2 11 mmHg, and PO2 129 mmHg. Blood salicylate level is 55 mg/dL. Management should involve which of the following acid-base principles?

• A. Serum neutralization, urine alkalization
• B. Serum alkalization, urine alkalization (Correct Answer)
• C. Serum neutralization, urine acidification
• D. Serum acidification, urine acidification
• E. Serum acidification, urine alkalization

Acid-base balance Explanation: ***Serum alkalization, urine alkalization*** - Managing **aspirin overdose** involves **aggressive serum alkalization** to promote the shift of salicylic acid from the cells into the bloodstream, where it remains ionized and cannot freely diffuse into the CNS. This also reduces its toxicity by increasing the proportion of the ionized form. - Subsequently, **urine alkalization** with **sodium bicarbonate** is used to trap the ionized salicylate in the renal tubules, preventing reabsorption and enhancing its excretion. *Serum neutralization, urine alkalization* - This option is flawed because the goal is not to "neutralize" the serum pH to a neutral 7.0 but rather to raise it above normal towards an alkaline state (typically pH 7.45-7.55) to enhance salicylate elimination. - While urine alkalization is correct, the idea of serum neutralization is incorrect and could lead to inadequate treatment. *Serum neutralization, urine acidification* - This approach is entirely incorrect for **salicylate toxicity** as **acidifying the urine** would promote the reabsorption of salicylic acid from the renal tubules, worsening toxicity. - Serum neutralization, as mentioned, is not the correct term or goal for managing **aspirin overdose**. *Serum acidification, urine acidification* - This strategy would be **dangerous** in the context of **salicylate overdose** as it would significantly increase the proportion of **non-ionized salicylic acid**, allowing it to more readily cross cell membranes, including the blood-brain barrier, thereby increasing systemic and central nervous system toxicity. - It would also drastically reduce elimination. *Serum acidification, urine alkalization* - **Serum acidification** is contraindicated in **salicylate poisoning** as it drives salicylate into the tissues, exacerbating its toxicity, particularly in the central nervous system. - While urine alkalization is correct for enhancing elimination, combining it with serum acidification would counteract its benefits and worsen patient outcomes.

Acid-base balance US Medical PG Question 6: A 55-year-old man presents with an unremitting cough and swelling of the lower limbs for the past 2 weeks. He says he has had a chronic cough for years, however, he feels it is getting worse. He reports a 30-pack-year smoking history. Physical examination reveals mild central cyanosis and expiratory wheezes throughout the chest. Oxygen therapy is ordered immediately but, soon after administering it, his respiratory rate starts to slow down and he becomes drowsy. Dysfunction of which of the following receptors most likely led to this patient’s current condition?

• A. Pleural pain receptors
• B. Central chemoreceptors
• C. Airway stretch receptors
• D. Pulmonary stretch receptors
• E. Peripheral chemoreceptors (Correct Answer)

Acid-base balance Explanation: ***Peripheral chemoreceptors*** - In patients with chronic obstructive pulmonary disease (COPD) like this patient, the **central chemoreceptors** become desensitized to chronically elevated CO2 levels. Their primary respiratory drive then shifts to the **peripheral chemoreceptors** (carotid and aortic bodies), which are sensitive to **hypoxia**. - Administering high-flow oxygen **eliminates the hypoxic stimulus** sensed by these normally functioning peripheral chemoreceptors, removing the hypoxic drive to breathe and leading to **hypoventilation, CO2 retention, respiratory acidosis**, and drowsiness (CO2 narcosis). *Pleural pain receptors* - These receptors are primarily involved in sensing pain associated with **pleural inflammation** or injury, contributing to the sensation of pain with breathing. - They do not play a role in regulating the primary ventilatory drive in response to blood gas changes. *Central chemoreceptors* - These receptors are located in the **medulla** and are primarily sensitive to changes in **arterial PCO2** and pH (via H+ ions in CSF). - In chronic respiratory diseases with CO2 retention, they become **desensitized** to elevated CO2, shifting the main respiratory drive to the peripheral chemoreceptors' response to hypoxia. *Airway stretch receptors* - These receptors, including **slowly adapting stretch receptors** and **rapidly adapting irritant receptors**, are located in the airways and respond to lung inflation and irritants. - They are involved in the Hering-Breuer reflex and cough reflex but are not the primary drivers of ventilation in response to hypoxemia. *Pulmonary stretch receptors* - These receptors are located in the **bronchial smooth muscle** and respond to lung distension, contributing to the **Hering-Breuer reflex** which inhibits inspiration to prevent overinflation. - While important for lung mechanics, they do not directly sense blood gas levels to drive ventilation in the context of hypoxia or hypercapnia.

Acid-base balance US Medical PG Question 7: A 72-year-old man being treated for benign prostatic hyperplasia (BPH) is admitted to the emergency department for 1 week of dysuria, nocturia, urge incontinence, and difficulty initiating micturition. His medical history is relevant for hypertension, active tobacco use, chronic obstructive pulmonary disease, and BPH with multiple urinary tract infections. Upon admission, he is found with a heart rate of 130/min, respiratory rate of 19/min, body temperature of 39.0°C (102.2°F), and blood pressure of 80/50 mm Hg. Additional findings during the physical examination include decreased breath sounds, wheezes, crackles at the lung bases, and intense right flank pain. A complete blood count shows leukocytosis and neutrophilia with a left shift. A sample for arterial blood gas analysis (ABG) was taken, which is shown below. Laboratory test Serum Na+ 140 mEq/L Serum Cl- 102 mEq/L Serum K+ 4.8 mEq/L Serum creatinine (SCr) 2.3 mg/dL Arterial blood gas pH 7.12 Po2 82 mm Hg Pco2 60 mm Hg SO2% 92% HCO3- 12.0 mEq/L Which of the following best explains the patient’s condition?

• A. Metabolic acidosis complicated by respiratory alkalosis
• B. Non-anion gap metabolic acidosis
• C. Respiratory alkalosis complicated by metabolic acidosis
• D. Respiratory acidosis complicated by metabolic alkalosis
• E. Metabolic acidosis complicated by respiratory acidosis (Correct Answer)

Acid-base balance Explanation: ***Metabolic acidosis complicated by respiratory acidosis*** - The patient's pH is significantly low (7.12), indicating **acidemia**. The **HCO3- is markedly low (12 mEq/L)**, and PCO2 is elevated (60 mm Hg), suggesting both a metabolic and a respiratory component to the acidosis. - The severe infection (fever, elevated heart rate, hypotension, flank pain, leukocytosis, elevated creatinine) and the signs of hypoperfusion contribute to **lactic acidosis (metabolic acidosis)**, while his history of COPD and lung findings (decreased breath sounds, wheezes, crackles) explain the impaired ventilation leading to **respiratory acidosis**. *Metabolic acidosis complicated by respiratory alkalosis* - While a **metabolic acidosis** is clearly present due to the low pH and HCO3-, the PCO2 is elevated, indicating **respiratory acidosis**, not alkalosis. - Respiratory alkalosis would be characterized by a **low PCO2** due to hyperventilation. *Non-anion gap metabolic acidosis* - To determine the anion gap, we use the formula: **Na+ - (Cl- + HCO3-)**. In this case, 140 - (102 + 12) = 140 - 114 = **26 mEq/L**. - An anion gap of 26 mEq/L, which is significantly elevated (normal range is typically 8-12 mEq/L), indicates an **anion gap metabolic acidosis**, not a non-anion gap one. *Respiratory alkalosis complicated by metabolic acidosis* - The low pH and HCO3- confirm **metabolic acidosis**, but the elevated PCO2 (60 mm Hg) indicates **respiratory acidosis**, not alkalosis, as the respiratory component is also acidotic. - Respiratory alkalosis would result from **hyperventilation and a low PCO2**. *Respiratory acidosis complicated by metabolic alkalosis* - While the elevated PCO2 indicates **respiratory acidosis**, the HCO3- is significantly low (12 mEq/L), which points to a **metabolic acidosis**, not metabolic alkalosis. - **Metabolic alkalosis** would be characterized by an **elevated HCO3-**.

Acid-base balance US Medical PG Question 8: A 17-year-old boy is brought to the physician by his father because of a 7-month history of fatigue, recurrent leg cramps, and increased urinary frequency. His pulse is 94/min and blood pressure is 118/85 mm Hg. Physical examination shows dry mucous membranes. Laboratory studies show: Serum Na+ 130 mEq/L K+ 2.8 mEq/L Cl- 92 mEq/L Mg2+ 1.1 mEq/L Ca2+ 10.6 mg/dL Albumin 5.2 g/dL Urine Ca2+ 70 mg/24 h Cl- 375 mEq/24h (N = 110–250) Arterial blood gas analysis on room air shows a pH of 7.55 and an HCO3- concentration of 45 mEq/L. Impaired function of which of the following structures is the most likely cause of this patient's condition?

• A. Ascending loop of Henle
• B. Collecting duct
• C. Distal convoluted tubule (Correct Answer)
• D. Descending loop of Henle
• E. Proximal convoluted tubule

Acid-base balance Explanation: ***Distal convoluted tubule*** - The patient presents with **hypokalemia**, **metabolic alkalosis**, **hypomagnesemia**, and **hypocalciuria** (24-hour urine Ca2+ 70 mg, normal up to 250 mg), which are characteristic findings of **Gitelman syndrome**. - **Gitelman syndrome** is caused by a loss-of-function mutation in the **thiazide-sensitive Na-Cl cotransporter (NCC)**, located in the **distal convoluted tubule**, leading to impaired reabsorption of Na+ and Cl- at this segment. *Ascending loop of Henle* - Impaired function of the **Na-K-2Cl cotransporter (NKCC2)** in the **thick ascending limb of the loop of Henle** causes **Bartter syndrome**. - Bartter syndrome typically presents with **hypercalciuria**, in contrast to the hypocalciuria seen in this patient. *Collecting duct* - Dysfunction of the **collecting duct** can lead to various conditions, such as **renal tubular acidosis** or **diabetes insipidus**, depending on which channels or receptors are affected. - However, the specific combination of **hypokalemia**, **metabolic alkalosis**, **hypomagnesemia**, and **hypocalciuria** points away from primary collecting duct dysfunction. *Descending loop of Henle* - The **descending loop of Henle** is primarily permeable to **water** and has a limited role in electrolyte reabsorption. - Impairment here would primarily affect **urine concentration** and dilution but would not account for the specific electrolyte imbalances observed. *Proximal convoluted tubule* - The **proximal convoluted tubule** is responsible for reabsorbing a large fraction of filtered electrolytes, glucose, and amino acids. - Dysfunction here (e.g., **Fanconi syndrome**) would typically present with **generalized aminoaciduria**, **glycosuria**, **phosphaturia**, and **proximal renal tubular acidosis**, which are not seen in this patient.

Acid-base balance US Medical PG Question 9: A 32-year-old woman is admitted to the emergency department for 36 hours of intense left-sided back pain that extends into her left groin. She reports that the pain started a day after a charitable 5 km (3.1 mi) marathon. The past medical history is relevant for multiple complaints of eye dryness and dry mouth. Physical examination is unremarkable, except for intense left-sided costovertebral pain. The results from laboratory tests are shown. Laboratory test Result Serum Na+ 137 Serum Cl- 110 Serum K+ 3.0 Serum creatinine (SCr) 0.82 Arterial blood gas Result pH 7.28 pO2 98 mm Hg pCO2 28.5 mm Hg SaO2% 98% HCO3- 15 mm Hg Which of the following explains this patient’s condition?

• A. Carbonic acid accumulation
• B. Decreased bicarbonate renal absorption
• C. Decreased renal excretion of hydrogen ions (H+) (Correct Answer)
• D. Decreased synthesis of ammonia (NH3)
• E. Decreased excretion of nonvolatile acids

Acid-base balance Explanation: ***Decreased renal excretion of hydrogen ions (H+)*** - The patient presents with **metabolic acidosis** (pH 7.28, HCO3- 15 mEq/L) with **respiratory compensation** (pCO2 28.5 mm Hg). The anion gap is **normal** (Na+ - (Cl- + HCO3-) = 137 - (110 + 15) = **12 mEq/L**), indicating a **non-anion gap metabolic acidosis**. - The history of **dry eyes and dry mouth** strongly suggests **Sjögren syndrome**, which is commonly associated with **Type 1 (distal) renal tubular acidosis**. - In **Type 1 RTA**, the distal tubule alpha-intercalated cells cannot adequately secrete H+ ions, leading to metabolic acidosis with **inability to acidify urine** (urine pH > 5.5). Associated findings include **hypokalemia** (K+ 3.0), **nephrolithiasis** (calcium phosphate stones due to alkaline urine), and hypercalciuria. - The left-sided flank pain radiating to the groin is consistent with **nephrolithiasis**, a common complication of Type 1 RTA. *Carbonic acid accumulation* - **Carbonic acid accumulation** indicates **respiratory acidosis** with elevated pCO2, which is not present here. - The patient has a **low pCO2 (28.5 mm Hg)**, representing appropriate **respiratory compensation** for the primary metabolic acidosis. *Decreased bicarbonate renal absorption* - **Decreased bicarbonate renal absorption** characterizes **Type 2 (proximal) RTA**. - While Type 2 RTA also causes non-anion gap metabolic acidosis, it is **not typically associated with Sjögren syndrome** and would present with different features (glycosuria, aminoaciduria, phosphaturia as part of Fanconi syndrome). - Type 2 RTA can acidify urine to pH < 5.5 when serum HCO3- is low, unlike Type 1 RTA. *Decreased synthesis of ammonia (NH3)* - **Decreased ammonia synthesis** is characteristic of **Type 4 RTA** or severe chronic kidney disease. - Type 4 RTA presents with **hyperkalemia** (due to hypoaldosteronism), not the hypokalemia seen in this patient. - The normal serum creatinine (0.82 mg/dL) rules out significant renal failure. *Decreased excretion of nonvolatile acids* - **Decreased excretion of nonvolatile acids** would cause **elevated anion gap metabolic acidosis** (e.g., lactic acidosis, ketoacidosis, or advanced renal failure with accumulation of organic acids). - This patient has a **normal anion gap (12 mEq/L)** and **normal renal function** (creatinine 0.82 mg/dL), making this mechanism unlikely. - The clinical context of Sjögren syndrome with dry eyes/mouth points specifically to distal RTA.

Acid-base balance US Medical PG Question 10: A 24-year-old male is brought in by ambulance to the emergency department after he was found unresponsive at home for an unknown length of time. Upon arrival, he is found to be severely altered and unable to answer questions about his medical history. Based on clinical suspicion, a panel of basic blood tests are obtained including an arterial blood gas, which shows a pH of 7.32, a pCO2 of 70, and a bicarbonate level of 30 mEq/L. Which of the following is most likely the primary disturbance leading to the values found in the ABG?

• A. Respiratory acidosis (Correct Answer)
• B. Metabolic alkalosis
• C. Respiratory alkalosis
• D. Metabolic acidosis
• E. Mixed alkalosis

Acid-base balance Explanation: ***Respiratory acidosis*** - The **pH (7.32)** is acidic (normal 7.35-7.45), and the **pCO2 (70 mmHg)** is significantly elevated (normal 35-45 mmHg), indicating **primary respiratory acidosis** due to hypoventilation. - The **bicarbonate (30 mEq/L)** is elevated above normal (22-26 mEq/L), indicating **partial metabolic compensation** by the kidneys retaining bicarbonate to buffer the acidosis. - This pattern suggests **chronic respiratory acidosis** (e.g., from COPD, CNS depression, neuromuscular disease) with renal compensation. *Metabolic alkalosis* - This would present with **elevated pH** (>7.45) and **elevated bicarbonate** as the primary disturbance, often with compensatory elevation in pCO2. - The patient's **pH is acidic (7.32)**, not alkalotic, ruling out metabolic alkalosis as the primary process. *Respiratory alkalosis* - This would present with **elevated pH** (>7.45) and **decreased pCO2** (<35 mmHg) due to hyperventilation. - The patient has the opposite: **acidic pH and elevated pCO2**, ruling out respiratory alkalosis. *Metabolic acidosis* - This would present with **decreased pH** and **decreased bicarbonate** (<22 mEq/L) as the primary disturbance. - While the pH is low, the **bicarbonate is elevated (30 mEq/L)**, not decreased, ruling out metabolic acidosis as the primary disorder. *Mixed alkalosis* - A mixed alkalosis would involve simultaneous respiratory and metabolic processes causing **elevated pH**. - The patient's **pH is acidic (7.32)**, making any form of alkalosis impossible as the primary disturbance.

Acid-base balance Flashcard 1 of 10

Question: Respiratory compensation in response to metabolic acidosis or alkalosis is _____ (timing)

Answer: immediate

Acid-base balance Flashcard 2 of 10

Question: Hyperventilation as a respiratory compensation for metabolic acidosis is known as _____ breathing

Answer: Kussmaul

Acid-base balance Flashcard 3 of 10

Question: Winters formula is used to calculate the predicted respiratory compensation for a simple _____

Answer: metabolic acidosis

Acid-base balance Flashcard 4 of 10

Question: Renal compensation of respiratory alkalosis includes _____ excretion of fixed H+ as titratable acid and NH4+

Answer: decreased

Acid-base balance Flashcard 5 of 10

Question: Patients with diabetic ketoacidosis have _____ bicarbonate reuptake

Answer: increased

Acid-base balance Flashcard 6 of 10

Question: Acid-base disturbances may affect serum K+ levels via altering activity and directionality of the _____ exchanger

Answer: H+-K+

Extra Information:   Watch Potassium Disorders [https://dashboard.sketchy.com/study/medical/courses/medical-pathophysiology/units/medical-pathophysiology-renal/videos/medical-pathophysiology-renal-volume-electrolyte-and-acidbase-disorders-potassium-disorders?utm_source=anki&utm_medium=partnership&utm_campaign=february_update&utm_content=medical]Watch associated Bootcamp video [https://app.bootcamp.com/med-school/nephrology/videos/electrolytes?index=4] https://onlinemeded.org/spa/renal?ref=anki 

Acid-base balance Flashcard 7 of 10

Question: In _____ cells (in plasma), CO2 is combined with H2O via the enzyme carbonic anhydrase, forming H2CO3

Answer: red blood

Extra Information:   https://onlinemeded.org?ref=anki 

Acid-base balance Flashcard 8 of 10

Question: The delta cells of the islets of Langerhans compose 10% of the islet and secrete _____

Answer: somatostatin

Extra Information:  Watch associated Bootcamp video [https://app.bootcamp.com/med-school/histology/videos/endocrine-system?index=3] https://onlinemeded.org/spa/surgery-general/pancreas/acquire?ref=anki Atlas: 

Acid-base balance Flashcard 9 of 10

Question: What acid-base disturbance is associated with hypokalemia? _____

Answer: Alkalosis

Extra Information:   Watch Potassium Disorders [https://dashboard.sketchy.com/study/medical/courses/medical-pathophysiology/units/medical-pathophysiology-renal/videos/medical-pathophysiology-renal-volume-electrolyte-and-acidbase-disorders-potassium-disorders?utm_source=anki&utm_medium=partnership&utm_campaign=february_update&utm_content=medical]Watch associated Bootcamp video [https://app.bootcamp.com/med-school/nephrology/videos/electrolytes?index=4] https://onlinemeded.org/spa/renal?ref=anki 

Acid-base balance Flashcard 10 of 10

Question: The osmotic diuresis in diabetic ketoacidosis may lead to fatal arrhythmias by causing _____ depletion

Answer: total body K+

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