Critical Care & Adv Nephrology Final - Lecture 1 Acid/Base disorders

Dr. Smithburger: Slide Sledge Hammer Approach

What is the normal range of arterial blood pH?

7.35–7.45

At what pH levels is a patient generally considered "dead"?

≤ 6.7 or ≥ 7.7

Which of the following is NOT a way the body regulates pH?

Sweating (skin)

pH affects all of the following EXCEPT:

Hair color

pH is defined as:

The negative log of [H⁺] (the inverse of how much acid)

A lower pH indicates:

More acidic (more H⁺)

What is an acid?

An H⁺ donor (e.g., HCl, lactic acid, CO₂)

What is a base?

An H⁺ acceptor (e.g., Cl⁻, HCO₃⁻)

Which of the following is an example of an ACID?

CO₂

A buffer is best described as:

The ability of a weak acid + anion (base) conjugate pair to RESIST pH changes after addition of a strong acid or base

Buffers are MOST efficient at a pH:

Close to their pK

Which of the following is NOT an example of a physiologic buffer?

Sodium chloride

Which enzyme catalyzes the conversion of CO₂ + H₂O ↔ H⁺ + HCO₃⁻?

Carbonic anhydrase

The bicarbonate buffer system is summarized as:

CO₂ + H₂O ↔ H⁺ + HCO₃⁻

Carbonic anhydrase is a therapeutic target for which drug class used in acid-base/altitude management?

Carbonic anhydrase inhibitors (e.g., acetazolamide)

The Henderson-Hasselbalch equation for the bicarbonate buffer is:

pH = 6.1 + log [HCO₃⁻]/(0.03 × PaCO₂)

In the Henderson-Hasselbalch equation for the bicarbonate buffer, the BASE is:

HCO₃⁻

In the Henderson-Hasselbalch equation, the ACID is represented by:

H₂CO₃ (or 0.03 × PaCO₂)

The suffix "-EMIA" refers to:

An OBJECTIVE sign in the blood (refers to abnormal pH being too high or too low)

The suffix "-OSIS" refers to:

The disease process (the metabolic or respiratory process that led to the abnormal pH)

A patient with a pH of 7.2 has:

Acidemia (low pH); they are also said to have acidosis (the underlying process)

What is the normal range for PaCO₂ in arterial blood?

35–45 mmHg

What is the normal range for HCO₃⁻ in arterial blood?

22–26 mEq/L

What is the normal range for arterial PO₂?

80–100 mmHg

What is the normal arterial O₂ saturation?

95%

A blood gas is documented in which order?

pH/PaCO₂/PO₂/HCO₃/SaO₂

A pH < 7.35 is termed:

Acidemia

A pH > 7.45 is termed:

Alkalemia

A PaCO₂ of < 35 mmHg as a primary disorder indicates:

Respiratory alkalosis

A PaCO₂ of > 45 mmHg as a primary disorder indicates:

Respiratory acidosis

An HCO₃⁻ of < 22 mEq/L as a primary disorder indicates:

Metabolic acidosis

An HCO₃⁻ of > 26 mEq/L as a primary disorder indicates:

Metabolic alkalosis

Which set of values represents respiratory acidosis?

↓ pH, ↑ PaCO₂

Which set of values represents respiratory alkalosis?

↑ pH, ↓ PaCO₂

Which set of values represents metabolic acidosis?

↓ pH, ↓ HCO₃⁻

Which set of values represents metabolic alkalosis?

↑ pH, ↑ HCO₃⁻

Which form of pH regulation acts immediately but has very limited capacity?

Buffers (bicarbonate and CO₂)

How does respiration regulate pH?

By "blowing off" or retaining CO₂ (the acid) through altered minute ventilation

Respiratory pH regulation is controlled by:

H⁺ chemoreceptors in the carotid body and brainstem

How quickly can respiratory compensation occur?

Very rapidly (minutes)

How does the kidney regulate pH (metabolic compensation)?

Increases or decreases reabsorption of HCO₃⁻ (the base)

What is the timeline for renal (metabolic) compensation?

Partial in 6–12 hours, complete in ~48 hours

Compensation in acid-base disorders refers to:

Changes the BODY makes to correct a pH problem (usually NOT complete)

Is compensation usually complete (returns pH fully to normal)?

NO — usually not complete

In a metabolic problem, who compensates?

The lungs

In a respiratory problem, who compensates?

The kidneys

In metabolic ALKALOSIS (too much HCO₃⁻), the body compensates by:

RETAINING CO₂ (decreasing minute ventilation) to ↓pH

In metabolic ACIDOSIS (too little HCO₃⁻), the body compensates by:

Getting rid of CO₂ (INCREASING minute ventilation, i.e., hyperventilation) to ↑pH

In respiratory ALKALOSIS (too little CO₂), the body compensates by:

Reabsorbing LESS bicarb to ↓pH

In respiratory ACIDOSIS (too much CO₂), the body compensates by:

RETAINING bicarb (more reabsorption) to ↑pH

What is a "mixed" acid-base disorder?

Two acid-base processes occurring at once (e.g., ↓pH, ↑PaCO₂, ↓HCO₃⁻ = mixed respiratory and metabolic acidosis)

How are mixed disorders treated?

Treat each disorder separately

A change in PaCO₂ of 10 mmHg causes approximately what change in pH?

0.08

A change in HCO₃⁻ of 10 mEq/L causes approximately what change in pH?

0.15

In a primary metabolic ACIDOSIS, the expected respiratory compensation is:

↓ HCO₃⁻ of 1 mEq/L = ↓ PaCO₂ by 1.3 mmHg

In a primary metabolic ALKALOSIS, the expected respiratory compensation is:

↑ HCO₃⁻ of 1 mEq/L = ↑ PaCO₂ by 0.6 mmHg

For ACUTE respiratory acidosis, the expected metabolic compensation is:

HCO₃⁻ ↑ ~1 mEq/L for every 10 mmHg ↑ PCO₂ (or 0.1 × Δ PCO₂)

For CHRONIC respiratory acidosis, the expected metabolic compensation is:

HCO₃⁻ ↑ 4 mEq/L for every 10 mmHg ↑ PCO₂ (or 0.25 × Δ PCO₂)

For ACUTE respiratory alkalosis, the expected metabolic compensation is:

HCO₃⁻ ↓ 1–3 mEq/L for every 10 mmHg ↓ PCO₂ (or 0.2 × Δ PCO₂)

For CHRONIC respiratory alkalosis, the expected metabolic compensation is:

HCO₃⁻ ↓ 3–5 mEq/L for every 10 mmHg ↓ PCO₂ (or 0.4 × Δ PCO₂)

Compensation rules are used to:

Determine if there is a single disorder or a mixed disorder

The anion gap is calculated by:

Na⁺ – (HCO₃⁻ + Cl⁻)

What is the normal range of the anion gap?

4–12 mEq/L

The "normal" anion gap exists due to:

Unmeasured ions — anions (~2–3 mEq/L: protein/albumin, lactate, phosphates, sulfates) and cations (~11 mEq/L: Ca²⁺, Mg²⁺, K⁺)

When albumin is low, how is the anion gap adjusted?

ADD 2.5 to the gap for every 1 g/dL of albumin BELOW 4 g/dL

An anion gap > 12 mEq/L suggests:

Unmeasured anions in extracellular fluid (typically endogenous acids or ingested toxins)

When evaluating metabolic acidosis, calculating the anion gap helps to:

Find the cause of metabolic acidosis (gap vs. non-gap)

The mnemonic MUDPILES is used for:

Causes of HIGH ANION GAP metabolic acidosis

In MUDPILES, "M" stands for:

Methanol

In MUDPILES, "U" stands for:

Urea / Uremia

In MUDPILES, "D" stands for:

Diabetic ketoacidosis (DKA)

In MUDPILES, "P" stands for:

Propylene glycol

In MUDPILES, "I" stands for:

Ingestion (e.g., ecstasy, cocaine, isoniazid)

In MUDPILES, "L" stands for:

Lactic acidosis (e.g., anaerobic metabolism from sepsis/hypoperfusion, metformin)

In MUDPILES, "E" stands for:

Ethylene glycol

In MUDPILES, "S" stands for:

Salicylates

Causes of LACTIC ACIDOSIS include all EXCEPT:

Excess HCO₃⁻ administration

Which medication is a well-known iatrogenic cause of lactic acidosis?

Metformin

The mnemonic USEDCAR is used for:

Causes of NORMAL ANION GAP metabolic acidosis

In USEDCAR, "U" stands for:

Ureteral diversion

In USEDCAR, "S" stands for:

Saline infusion

In USEDCAR, "E" stands for:

Exogenous acid

In USEDCAR, "D" stands for:

Diarrhea

In USEDCAR, "C" stands for:

Carbonic anhydrase inhibitors

In USEDCAR, "A" stands for:

Adrenal insufficiency

In USEDCAR, "R" stands for:

Renal tubular acidosis

Respiratory acidosis is defined by:

pH < 7.35 and PaCO₂ > 45 mmHg

Subjective symptoms of respiratory acidosis may include:

Altered mental status and headache

Objective signs of respiratory acidosis include:

↓RR and tachycardia (along with low pH and high PaCO₂)

Causes of respiratory acidosis (HYPOventilation) include all EXCEPT:

High altitude

Treatment of respiratory acidosis includes all EXCEPT:

Sodium bicarbonate as the FIRST-LINE therapy

Respiratory alkalosis is defined by:

pH > 7.45 and PaCO₂ < 35 mmHg

Subjective symptoms of respiratory alkalosis may include:

Lightheadedness, confusion, seizures, nausea/vomiting

Causes of respiratory alkalosis (HYPERventilation) include all EXCEPT:

Severe COPD with CO₂ retention

Treatments for respiratory alkalosis include all EXCEPT:

Sodium bicarbonate

What medication is used to PREVENT altitude sickness, and what is the mechanism?

Acetazolamide (Diamox) — inhibits bicarb reabsorption in the proximal tubule, essentially creating compensation

What is the typical regimen for acetazolamide for altitude sickness prevention?

Acetazolamide SR 500 mg daily–BID, starting 1–2 days BEFORE ascent and continuing 2 days after arrival at altitude

Subjective symptoms of metabolic acidosis include:

Lethargy, confusion, coma

Objective signs of metabolic acidosis may include:

Hypotension, tachycardia, HYPERventilation (compensation)

Metabolic acidosis can be classified into:

Anion gap (gap > ~20–25, MUDPILES) vs. non-gap (USEDCAR)