Acid-Base Disorders — MCQs
A 24 year old male presents with altered sensorium and rapid shallow breathing. ABG shows:pH 7.2, sodium 140, bicarbonate 10 and chloride 98. Probable diagnosis is -
Which of the following is a cause of metabolic acidosis with a normal anion gap?
A patient presents with metabolic acidosis and increased anion gap. Which is most consistent with this presentation?
In plasma, if pH is 5, what is the fraction of base to acid?
A patient presents with malignant hyperthermia and metabolic acidosis. Immediate treatment should be started with:
Patient in hospital was given IVF and patient develops hyperchloremic metabolic acidosis. Which fluid will cause this?
All of the following are used to maintain proper oxygen flow to the patient except:
During cardiopulmonary resuscitation in an adult, at what rate are chest compressions given?
What is the maximum concentration of potassium that can be safely delivered via a central line?
The Acute Physiology and Chronic Health Evaluation (APACHE) scoring system is used for what purpose?
Acid-Base Disorders Indian Medical PG Practice Questions and MCQs
Question 1: A 24 year old male presents with altered sensorium and rapid shallow breathing. ABG shows:pH 7.2, sodium 140, bicarbonate 10 and chloride 98. Probable diagnosis is -
- A. Amphetamine toxicity
- B. DKA (Correct Answer)
- C. Renal tubular acidosis
- D. Ethylene glycol poisoning
Explanation: ***DKA*** - The patient presents with **altered sensorium** and **rapid shallow breathing** (Kussmaul breathing), consistent with severe metabolic acidosis [1]. - The ABG results show **pH 7.2** (acidosis), **bicarbonate 10** (metabolic component), and an **elevated anion gap** (Na - (Cl + HCO3) = 140 - (98 + 10) = 32), which are characteristic findings in **diabetic ketoacidosis (DKA)** [1], [2]. *Amphetamine toxicity* - Amphetamine toxicity typically causes **sympathomimetic effects** such as tachycardia, hypertension, hyperthermia, and agitation, rather than directly leading to a high anion gap metabolic acidosis of this severity. - While it can cause some metabolic derangements, the primary acid-base disturbance is usually different or less pronounced in this manner compared to DKA. *Renal tubular acidosis* - Renal tubular acidosis (RTA) typically presents with a **normal anion gap metabolic acidosis** (hyperchloremic metabolic acidosis), where the anion gap would not be significantly elevated. - The calculated anion gap of 32 in this patient rules out RTA as the primary cause of this severe acidosis. *Ethylene glycol poisoning* - Ethylene glycol poisoning also causes a **high anion gap metabolic acidosis** and altered mental status. - However, it is typically associated with additional specific symptoms like **flank pain**, **oliguria**, and detection of **calcium oxalate crystals** in the urine, which are not mentioned in this case.
Question 2: Which of the following is a cause of metabolic acidosis with a normal anion gap?
- A. Diabetic ketoacidosis
- B. Aspirin poisoning
- C. Renal tubular acidosis (Correct Answer)
- D. Lactic acidosis
Explanation: ***Renal tubular acidosis*** - **Renal tubular acidosis (RTA)** is characterized by a defect in renal acid excretion or bicarbonate reabsorption, leading to **metabolic acidosis** with a **normal anion gap** [1]. - The deficiency in net acid excretion results in the retention of chloride ions to maintain electroneutrality, hence it's also known as **hyperchloremic metabolic acidosis** [1]. *Diabetic ketoacidosis* - **Diabetic ketoacidosis (DKA)** is a high anion gap metabolic acidosis caused by the accumulation of **ketoacids** (beta-hydroxybutyrate, acetoacetate). - These unmeasured anions increase the anion gap, distinguishing it from normal anion gap acidosis. *Aspirin poisoning* - **Aspirin (salicylate) poisoning** typically causes a **mixed acid-base disorder** with both metabolic acidosis and respiratory alkalosis [1]. - The metabolic acidosis component is a **high anion gap acidosis** due to the accumulation of salicylates and their metabolites. *Lactic acidosis* - **Lactic acidosis** is a common cause of **high anion gap metabolic acidosis**, resulting from the overproduction or decreased clearance of **lactate** [1]. - The increased concentration of lactate, an unmeasured anion, leads to the widening of the anion gap.
Question 3: A patient presents with metabolic acidosis and increased anion gap. Which is most consistent with this presentation?
- A. Renal tubular acidosis
- B. Lactic acidosis (Correct Answer)
- C. Hyperaldosteronism
- D. Diarrhea
Explanation: ***Lactic acidosis*** - **Lactic acidosis** is a common cause of **high anion gap metabolic acidosis**, resulting from increased lactate production or decreased lactate clearance [1]. - Conditions like **sepsis**, **shock**, and severe hypoxia can lead to increased anaerobic metabolism and subsequent lactic acid accumulation [1]. *Renal tubular acidosis* - This condition is characterized by **metabolic acidosis** but typically presents with a **normal anion gap** (non-anion gap metabolic acidosis) [1]. - It involves impaired acid excretion or bicarbonate reabsorption by the renal tubules, not an accumulation of unmeasured anions [1]. *Hyperaldosteronism* - **Hyperaldosteronism** typically causes **hypokalemia** and **metabolic alkalosis**, not metabolic acidosis [2]. - Excess aldosterone leads to increased sodium reabsorption and potassium/hydrogen ion excretion [2]. *Diarrhea* - Severe **diarrhea** leads to a loss of bicarbonate from the gastrointestinal tract, causing a **normal anion gap metabolic acidosis** [1]. - It does not involve the accumulation of unmeasured acids that would increase the anion gap.
Question 4: In plasma, if pH is 5, what is the fraction of base to acid?
- A. 0.01
- B. 0.1 (Correct Answer)
- C. 1
- D. 10
Explanation: ***0.1*** - This question applies the **Henderson-Hasselbalch equation**: pH = pKa + log([base]/[acid]). For the **bicarbonate buffer system** (the primary plasma buffer), pKa ≈ 6.1. - Substituting the given values: $5 = 6.1 + \log([HCO_3^-] / [H_2CO_3])$ - Rearranging: $\log([HCO_3^-] / [H_2CO_3]) = 5 - 6.1 = -1.1$ - Therefore: $[HCO_3^-] / [H_2CO_3] = 10^{-1.1} ≈ 0.079$ - Among the given options, **0.079 is closest to 0.1**, making this the correct answer. - Note: pH 5 in plasma is physiologically impossible (incompatible with life), but this tests theoretical understanding of the buffer equation. *0.01* - This ratio would correspond to an even **more acidic** condition with $\log([base]/[acid]) = -2$. - Using Henderson-Hasselbalch: pH = 6.1 + (-2) = 4.1, which is lower than the given pH of 5. - The calculated ratio of 0.079 is much closer to 0.1 than to 0.01. *1* - A ratio of 1 means **equal concentrations** of base and acid, which occurs when pH = pKa. - This would give pH = 6.1, not the given pH of 5. - This represents a **neutral buffer condition**, not the acidic state described. *10* - This ratio indicates an **alkaline** solution with 10 times more base than acid. - Using Henderson-Hasselbalch: pH = 6.1 + log(10) = 6.1 + 1 = 7.1 (physiological alkalosis). - This contradicts the given acidic pH of 5.
Question 5: A patient presents with malignant hyperthermia and metabolic acidosis. Immediate treatment should be started with:
- A. Intravenous fluids
- B. Sodium bicarbonate
- C. Paracetamol
- D. Intravenous Dantrolene (Correct Answer)
Explanation: ***Intravenous Dantrolene*** - **Dantrolene** is the specific and primary treatment for **malignant hyperthermia** as it acts directly on the **ryanodine receptor** to inhibit calcium release from the sarcoplasmic reticulum, relaxing skeletal muscle. - Its prompt administration is crucial in reversing the life-threatening metabolic and physiological derangements associated with this condition, including **hyperthermia** and **metabolic acidosis**. *Intravenous fluids* - While **intravenous fluids** are important for maintaining hydration and supporting renal function in patients with **malignant hyperthermia**, they are a supportive measure, not the definitive treatment. - They primarily address complications like **dehydration** and **rhabdomyolysis**, but do not directly treat the underlying pathophysiology of excessive calcium release. *Sodium bicarbonate* - **Sodium bicarbonate** may be used to correct severe **metabolic acidosis**, which can be a consequence of **malignant hyperthermia**. - However, treating the acidosis without addressing the primary cause (malignant hyperthermia) by administering dantrolene is insufficient and will not stop the progression of the syndrome. *Paracetamol* - **Paracetamol (acetaminophen)** is an antipyretic often used for fever reduction, but it is entirely ineffective in treating the rapid and severe hyperthermia of **malignant hyperthermia**. - The temperature dysregulation in malignant hyperthermia is caused by uncontrolled muscle metabolism, not a response to typical antipyretics, and thus paracetamol would provide no therapeutic benefit.
Question 6: Patient in hospital was given IVF and patient develops hyperchloremic metabolic acidosis. Which fluid will cause this?
- A. RL
- B. 5 % dextrose
- C. NS (Correct Answer)
- D. DNS
Explanation: ***NS*** - **Normal Saline (0.9% NaCl)** contains a **chloride concentration of 154 mEq/L**, which is unphysiologically high (supranormal) compared to plasma (approx. 100 mEq/L). - Rapid infusion leads to the retention of excess chloride and dilution of serum bicarbonate, resulting in a **non-anion gap (hyperchloremic) metabolic acidosis**. *RL* - Ringer's Lactate (RL) is a **buffered solution** because it contains **lactate (28 mEq/L)**, which is metabolized by the liver into bicarbonate. - Because of the bicarbonate precursor (lactate) and a near-physiologic chloride concentration (109 mEq/L), RL tends to **prevent or correct** acidosis, rather than causing it. *DNS* - Dextrose Normal Saline (DNS) still contains the **supranormal chloride concentration** (154 mEq/L) from the normal saline component, posing a similar theoretical risk. - However, it is typically less associated with severe acidosis than pure NS in large volumes, and often the primary differentiating fluid in this context is the **buffered RL**. *5 % dextrose* - **5% Dextrose in Water (D5W)** contains no electrolytes (salt) and is only used to provide free water and small amounts of calories. - Rapid infusion of D5W results in dilution and can cause **hyponatremia** and free water excess, but it cannot precipitate hyperchloremic acidosis.
Question 7: All of the following are used to maintain proper oxygen flow to the patient except:
- A. Different pin index for nitrogen and oxygen (Correct Answer)
- B. A proportioner between N₂ and O₂ control valves
- C. Calibrated oxygen concentration analyzers
- D. Placement of oxygen flowmeter downstream of the nitrogen flowmeter
Explanation: ***Different pin index for nitrogen and oxygen*** - Oxygen and nitrogen *do not* use pin index safety systems; the **Pin Index Safety System (PISS)** is used for small gas cylinders to prevent wrong gas connection, but nitrogen is a non-medical gas. - While medical gases have specific pin index patterns, this system is for preventing inadvertent connection of gas cylinders to the wrong yoke, not for *maintaining proper oxygen flow to the patient* from the anesthesia machine's internal system. *A proportioner between N₂ and O₂ control valves* - This device, such as the **Ohio proportioner** or **Link 25 system**, mechanically or pneumatically links the **nitrous oxide (N₂O)** and **oxygen (O₂)** flow controls. - It ensures that the inspired oxygen concentration never falls below a preset safe level, typically 25%, thereby **preventing hypoxic gas mixtures**. *Calibrated oxygen concentration analyzers* - **Oxygen analyzers** continuously monitor the inspired oxygen concentration and provide an audible and visual alarm if the level deviates from the set range. - This serves as a critical safety measure to detect and alert anesthesia providers to **hypoxic gas delivery** or machine malfunctions. *Placement of oxygen flowmeter downstream of the nitrogen flowmeter* - Positioning the **oxygen flowmeter downstream** (closest to the patient) of all other gas flowmeters (e.g., nitrous oxide, air) is a crucial safety feature. - This design ensures that **any leak occurring upstream** of the oxygen flow tube will primarily affect other gases, reducing the risk of an **undetected hypoxic mixture** reaching the patient.
Question 8: During cardiopulmonary resuscitation in an adult, at what rate are chest compressions given?
- A. 72 compressions/min
- B. 90 compressions/min
- C. 100 compressions/min (Correct Answer)
- D. 120 compressions/min
Explanation: **Explanation:** The correct answer is **C. 100 compressions/min**. **Medical Concept:** According to the latest American Heart Association (AHA) and ERC guidelines for Basic Life Support (BLS) and Advanced Cardiovascular Life Support (ACLS), the recommended rate for chest compressions in adults is **100 to 120 compressions per minute**. High-quality CPR is essential to maintain coronary and cerebral perfusion. A rate of at least 100 bpm ensures sufficient cardiac output, while exceeding 120 bpm is discouraged as it reduces the time for ventricular filling and decreases the quality of recoil. **Analysis of Options:** * **A (72/min) & B (90/min):** These rates are too slow. Inadequate compression frequency fails to generate the necessary intrathoracic pressure and arterial perfusion pressure required to restart the heart or protect the brain. * **D (120/min):** While 120 is the upper limit of the recommended range, standard medical examinations (like NEET-PG) traditionally prioritize the baseline "at least 100/min" as the gold standard answer when a range is not provided. **High-Yield Clinical Pearls for NEET-PG:** * **Compression Depth:** 2 to 2.4 inches (5 to 6 cm) in adults. * **Compression-to-Ventilation Ratio:** 30:2 for adults (single or dual rescuer). * **Recoil:** Allow complete chest recoil after each compression to allow the heart to fill. * **Minimize Interruptions:** Keep pauses in compressions to less than 10 seconds. * **EtCO2 Monitoring:** A capnography reading of <10 mmHg during CPR indicates poor quality compressions.
Question 9: What is the maximum concentration of potassium that can be safely delivered via a central line?
- A. 20 mmol/L (Correct Answer)
- B. 40 mmol/L
- C. 60 mmol/L
- D. 80 mmol/L
Explanation: **Explanation:** The management of hypokalemia requires careful titration to avoid life-threatening arrhythmias and phlebitis. The concentration of potassium replacement is strictly governed by the route of administration and the urgency of the clinical situation. **Why 20 mmol/L is the correct answer:** While textbooks often cite different "maximums" based on clinical urgency, standard safety guidelines (such as those from the NHS and various critical care societies) recommend a standard concentration of **20 mmol/L** for routine replacement. Although higher concentrations (up to 40 mmol/L) can be infused via a central line in ICU settings under continuous ECG monitoring, 20 mmol/L is considered the safest standard concentration to prevent accidental bolus-induced cardiac arrest and to minimize the risk of hyperkalemia. **Analysis of Incorrect Options:** * **40 mmol/L:** This is typically the maximum concentration allowed for **peripheral** administration (though 10–20 mmol/L is preferred to avoid pain and phlebitis). While it can be given centrally, it is not the "standard" safe limit for routine replacement. * **60 mmol/L & 80 mmol/L:** These are highly concentrated solutions. They are reserved only for extreme, life-threatening hypokalemia in an ICU setting with a dedicated central venous catheter and constant cardiac monitoring. They are never used for routine safety protocols. **High-Yield Clinical Pearls for NEET-PG:** 1. **Rate of Infusion:** The standard rate of potassium replacement should not exceed **10 mmol/hour**. In emergency cases (e.g., paralysis or arrhythmias), it may be increased to **20 mmol/hour** with continuous ECG monitoring. 2. **Peripheral vs. Central:** Peripheral veins are sensitive; concentrations >40 mmol/L cause severe pain and chemical phlebitis. Central lines are preferred for higher concentrations due to rapid dilution in a high-flow vessel. 3. **The "Magnesium" Rule:** If hypokalemia is refractory to treatment, always check and correct **Magnesium** levels. Low magnesium inhibits potassium reabsorption in the kidneys. 4. **ECG Changes:** Remember the sequence—U waves and flattened T waves in hypokalemia; Tall peaked T waves and widened QRS in hyperkalemia.
Question 10: The Acute Physiology and Chronic Health Evaluation (APACHE) scoring system is used for what purpose?
- A. Predicting postoperative cardiac risk
- B. Predicting postoperative pulmonary complications
- C. Evaluating prognosis in critical care settings (Correct Answer)
- D. Evaluating prognosis after acute myocardial infarction
Explanation: ### Explanation **1. Why Option C is Correct:** The **APACHE (Acute Physiology and Chronic Health Evaluation)** score is the most widely used severity-of-illness scoring system in Intensive Care Units (ICUs). It is designed to predict **hospital mortality** and evaluate prognosis by assessing the severity of a patient's physiological derangement. The score is calculated based on three components: * **Acute Physiology Score:** Based on the worst values of 12 physiological variables (e.g., heart rate, MAP, temperature, GCS, oxygenation) recorded during the first 24 hours of ICU admission. * **Age points:** Increasing age correlates with higher mortality. * **Chronic Health points:** Accounts for pre-existing organ dysfunction or immunocompromised states. A higher APACHE score correlates with a higher risk of hospital death. **2. Why Other Options are Incorrect:** * **Option A:** Postoperative cardiac risk is typically assessed using the **Revised Cardiac Risk Index (Lee’s Criteria)** or the **Goldman Index**. * **Option B:** Postoperative pulmonary complications are predicted using tools like the **ARISCAT (Canet) score** or the **STOP-BANG** questionnaire (for OSA). * **Option D:** Prognosis after acute myocardial infarction is specifically evaluated using the **Killip Classification** or the **TIMI Risk Score**. **3. High-Yield Clinical Pearls for NEET-PG:** * **APACHE II** is the most commonly used version in clinical practice and exams. * **Timing:** It is calculated using the **worst** physiological parameters within the **first 24 hours** of ICU admission. * **Other ICU Scores:** * **SOFA (Sequential Organ Failure Assessment):** Used to track organ dysfunction over time (unlike APACHE, which is a one-time snapshot). * **qSOFA:** Used for rapid bedside screening of sepsis (RR ≥22, Altered Mentation, SBP ≤100). * **Glasgow Coma Scale (GCS):** A component of the APACHE score used to assess neurological status.
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