Acid-Base Balance Regulation and ABG Interpretation

A set of 100 flashcards based on the Chapter 7 lecture on Acid-Base Balance and ABG Analysis.

Normal Arterial $pH$ Range

$$7.35 - 7.45$$

Acidosis

A condition occurring when $pH$ falls below the normal arterial range.

Alkalosis

A condition occurring when $pH$ rises above the normal arterial range.

Normal Venous $pH$ Range

$$7.30 - 7.40$$

Chemical Buffer System

The first system for the regulation of $H^+$ and $HCO_3^-$.

Respiratory System

The second system for the regulation of $H^+$ and $HCO_3^-$.

Renal System

The third system for the regulation of $H^+$ and $HCO_3^-$.

Acids

Substances that release $H^+$.

Examples of Acids

$HCl$ (Hydrochloric acid) and $H_2CO_3$ (Carbonic acid).

Bases

Substances that accept $H^+$.

Examples of Bases

$NaOH$ (Sodium hydroxide) and $HCO_3^-$ (Bicarbonate).

$pH$ of Gastric Juices

$$2$$

$pH$ of Tomato Juice

$$4$$

$pH$ of Human Urine

$$5$$

$pH$ of Pure Water

$7$ (Neutral)

$pH$ of Human Blood

$$7.4$$

$pH$ of Hand Soap

$$10$$

$pH$ of Household Bleach

$$12$$

Carbonic acid-bicarbonate buffer system

One of the three chemical buffer systems in the body.

Phosphate buffer system

One of the three chemical buffer systems in the body.

Protein buffer system

One of the three chemical buffer systems in the body.

Carbonic Acid-Bicarbonate Buffer System Defense

The first line of defense in regulating acid-base balance.

Carbonic Acid-Bicarbonate Equation

$$H_2CO_3 \rightarrow HCO_3^- + H^+$$

Henderson-Hasselbalch Equation

$$pH = pK + \log(\frac{[HCO_3^-]}{[CO_2]})$$

$pK$ of Carbonic Acid

$$6.1$$

Phosphate Buffer System Effectiveness

$1/6$ as effective as the carbonic acid-bicarbonate buffer system.

Phosphate Buffer System Primary Locations

Effective in the urine and intracellular fluid.

Protein Buffer System Locations

Found in plasma and cells.

Buffering Power of Intracellular Proteins

Responsible for $75\%$ of the buffering power of body fluids.

Amphoteric Molecules

Molecules like hemoglobin that can act as both an acid and a base.

Respiratory System Buffering Power

Twice the buffering power of the chemical buffering systems.

Respiratory Acid-Base Reaction

$$H_2O + CO_2 \rightleftharpoons H_2CO_3 \rightleftharpoons HCO_3^- + H^+$$

Normal $CO_2$ Elimination Rate

$$200\,mL/min$$

Normal Alveolar Ventilation ($V_A$)

$$4\,L/min$$

Normal Alveolar $CO_2$ tension ($PACO_2$)

$$40\,mm\,Hg$$

Normal Plasma $PaCO_2$

$$40\,mm\,Hg$$

Molecules in Normal Ventilation (Eucapnia)

$400$ molecules of dissolved $CO_2$, $400$ molecules of $H_2CO_3$, and $1$ molecule of $H^+$.

Hypoventilation Alveolar Ventilation ($V_A$)

$$2\,L/min$$

Hypoventilation Alveolar $CO_2$ tension ($PACO_2$)

$$80\,mm\,Hg$$

Hypercapnia

Clinical condition associated with hypoventilation where $PACO_2$ is high.

Molecules in Hypoventilation

$800$ molecules of dissolved $CO_2$, $800$ molecules of $H_2CO_3$, and $2$ molecules of $H^+$.

Hyperventilation Alveolar Ventilation ($V_A$)

$$8\,L/min$$

Hyperventilation Alveolar $CO_2$ tension ($PACO_2$)

$$20\,mm\,Hg$$

Hypocapnia

Clinical condition associated with hyperventilation where $PACO_2$ is low.

Molecules in Hyperventilation

$200$ molecules of dissolved $CO_2$, $200$ molecules of $H_2CO_3$, and $0.5$ molecules of $H^+$.

Renal System Function (Acids)

Rids the body of fixed acids.

Renal System Function (Alkali)

Regulates alkaline substances in the blood.

Arterial Blood Gas (ABG) Analysis

The most basic test of lung function requiring an anaerobic sample of arterial blood.

$pH$ Units

No units are used for $pH$.

$pH$ of Water

$7$, which is the midpoint of the scale.

Physiologic $pH$ Range

$$6.90 - 7.80$$

$PaCO_2$ Units

$$mm\,Hg$$

Normal $PaCO_2$ Range

$$35 - 45\,mm\,Hg$$

Mixed Venous $PaCO_2$ Range

$$40 - 46\,mm\,Hg$$

$PaO_2$ Units

$$mm\,Hg$$

Normal $PaO_2$ Range

$$80 - 100\,mm\,Hg$$

Mixed Venous $PaO_2$ Range

$$40\,mm\,Hg$$

Impaired Oxygenation Marker

Indicated by the severity of $PaO_2$ at rest.

Alveolar Gas Equation ($PAO_2$)

$$PAO_2 = (Pb - PH_2O) \times FIO_2 - (PaCO_2 \times 1.25)$$

Normal A-a Gradient

Usually less than $20\,mm\,Hg$ in healthy persons.

Condition for matched A-a Gradient

If ventilation matches perfusion, the blood leaving the capillaries has an oxygen tension very close to the alveoli.

Tissue Oxygen Delivery ($DO_2$) Equation

$$DO_2 = CaO_2 \times CO \times 10$$

Arterial Oxygen Content ($CaO_2$) Equation

$$CaO_2 = (Hb \times 1.34 \times SaO_2) + (PaO_2 \times 0.003)$$

Bicarbonate ($HCO_3^-$) Units

$$mEq/L$$

Normal Bicarbonate Range

$$22 - 26\,mEq/L$$

Base Excess ($BE$) Units

$$mEq/L$$

Normal Base Excess Range

$$+/- 2\,mEq/L$$

Acute Ventilatory Failure

Also known as Respiratory Acidosis.

Acute Alveolar Hyperventilation

Also known as Respiratory Alkalosis.

Disturbance: Chronic Ventilatory Failure

Failure characterized by complete renal compensation.

Disturbance: Metabolic Acidosis

A metabolic disturbance where the base is low or fixed acid is high.

Disturbance: Combined metabolic and respiratory acidosis

A condition where both metabolic and respiratory systems cause acidity.

Acute Ventilatory Failure Examples

COPD exacerbation, Drug overdose, General anesthesia, Head trauma, and Neurologic disorders.

Acute Alveolar Hyperventilation Examples

Hypoxia, Pain, anxiety, and fever, Brain inflammation, and Stimulant drugs.

Metabolic Acidosis Examples

Lactic acidosis, Ketoacidosis, Salicylate intoxication, Renal failure, and Uncontrolled diarrhea.

Anion Gap Purpose

Determines if metabolic acidosis is due to fixed acid accumulation or excessive loss of bicarbonate ions.

Law of Electroneutrality (Cations)

$$Na^+$$

Law of Electroneutrality (Anions)

$Cl^-$ and $HCO_3^-$

Metabolic Alkalosis Examples

Hypokalemia, Hypochloremia, Gastric suction, Vomiting, Excessive corticosteroids, Sodium bicarbonate administration, Diuretic therapy, and Hypovolemia.

Common ABG Specimen Sites

Radial and Brachial arteries.

Alternative ABG Specimen Sites

Femoral, Dorsalis pedis, Posterior tibial, and Umbilical.

Warmed Capillary Sample

A specialized type of specimen collection for gas analysis.

Modified Allen's Test Step 1

Instruct the patient to make a tight fist.

Modified Allen's Test Step 2

Apply pressure to both the radial and ulnar arteries.

Modified Allen's Test Step 3

Open the fist; a blanched palm/fingers should be observed.

Modified Allen's Test Step 4

Release pressure off the ulnar artery only.

Positive Modified Allen's Test

Flushing of the palm occurs within $15$ seconds.

Lesion Puncture Prohibition

Do not puncture through a lesion.

Surgical Shunt Consideration

Do not puncture distal to a surgical shunt.

Arterial Puncture Precautions

Peripheral Vascular Disease (PVD) and infection are indications to find another site.

Patient Drug History Query

Query patients specifically about anticoagulant drugs before puncture.

Standard Precautions

Always use standard precautions during specimen collection.

ABG Sample Mixing

After collection and air expulsion, gently roll the syringe to mix the sample.

Eucapnia (Molecules)

Molecules of dissolved $CO_2$ and $H_2CO_3$ are both at $400$.

Hypercapnia (Molecules)

Molecules of dissolved $CO_2$ and $H_2CO_3$ are both at $800$, and molecules of $H^+$ are at $2$.

Hypocapnia (Molecules)

Molecules of dissolved $CO_2$ and $H_2CO_3$ are both at $200$, and molecules of $H^+$ are at $0.5$.

Lactic Acidosis

A specific clinical example of metabolic acidosis.

Salicylate Intoxication

A clinical cause of metabolic acidosis due to aspirin-like drugs.

Hypovolemia

A clinical example/cause that leads to metabolic alkalosis.

Mixed Venous Normal $O_2$ Tension

$$40\,mm\,Hg$$