Acid Base Balance

Base excess (BE)

A calculated value also known as buffer base capacity. The BE measures substances that can accept or combine with hydrogen ions. It reflects the degree of acid-base imbalance by indicating the status of the body's total buffering capacity. It represents the amount of acid or base that must be added to a blood sample to achieve a pH of 7.4 and is essentially a measure of increased or decreased bicarbonate. The normal is −3 to 13.

Observation and Patient Interview

A complete health history Each specific disorder has different symptoms. It is important to identify any prescribed and over-the-counter medications that the patient is currently taking, as well as any complementary health approaches, such as vitamins and herbal supplements.

PaO2

A measure of the pressure exerted by oxygen that is dissolved in the plasma. Only about 3% of oxygen in the blood is transported in solution; most is combined with hemoglobin. The normal value is 75-100 mmHg. Valuable for evaluating respiratory function, but it is not used as a primary measurement in determining acid-base status.

pH

A measurement of the hydrogen ion concentration of a solution.

Serum bicarbonate (HCO3)

A value that reflects the renal regulation of acid-base balance. The normal HCO3 value is 24-28 mEq/L.

Diagnostic Tests

ABGs VBGs Allen Test

Three Systems that work to maintain pH

Buffer systems, the respiratory system, and the renal system.

Untreated metabolic acidosis

Can lead to myocardial depression, seizures, shock, and multi-organ failure.

Acid-base disorders

Classified as metabolic or respiratory disorders and as primary (simple) and mixed.

Concepts Related to Acid-Base Balance

Cognition Fluids and Electrolytes Oxygenation Perfusion Stress and Coping

Hypoxemia

Decreased oxygen levels in the blood that result when PaO2 falls below 80 mmHg

Respiratory Buffer: Alkalosis

Depresses the respiratory center, decreasing both the rate and depth of respiration and causing carbon dioxide retention. The retained carbon dioxide then combines with water to restore carbonic acid levels and bring the pH back within the normal range.

Nurse's Role with Sodium Bicarbonate Therapy

Monitor the patient's condition and educate the patient and family about the prescribed treatment.

Electrolyte imbalances & Health Promotion

Sodium and potassium, may be caused by certain medications, supplements, or changes in diet.

Bases

Substances that accept hydrogen ions in solution. Also called alkalis.

Buffers

Substances that prevent major changes in pH by releasing hydrogen ions. When excess acid is present in body fluid they bind with hydrogen ions to minimize the change in pH.

Fully Compensated

The pH is restored to normal limits

Metabolic disorders

The primary change is in the concentration of bicarbonate.

Respiratory disorders

The primary change is in the concentration of carbonic acid

Pharmacologic Therapy: Acidosis

The therapeutic goal is to reverse the effects of excess acids in the blood and return the patient to normal pH levels as quickly as possible. The treatment of choice for acute acidosis is sodium bicarbonate infusions, provided that the patient's bicarbonate level is low. Carefully monitor the patient's ABGs during infusions and watch for signs of alkalosis

Primary disorders

Usually have one cause. For example: Respiratory failure often causes respiratory acidosis due to retained carbon dioxide

Two Acids Produced By The Body

Volatile acids and nonvolatile acids

Respiratory Alkalosis Common Causes

• Anxiety-induced hyperventilation • Fever • Early salicylate intoxication • Hyperventilation with mechanical ventilator

Interventions: Metabolic Acidosis

• Monitor ABG values, intake and output, and LOC. • Administer IV sodium bicarbonate carefully as ordered. Treat underlying problem as ordered.

Metabolic Alkalosis Common Causes

↑ Acid loss or excretion • Vomiting, gastric suction • Hypokalemia ↑ Bicarbonate • Alkali ingestion (bicarbonate of soda) • Excess bicarbonate administration

Metabolic Acidosis Common Causes

↑ Acid production • Lactic acidosis • Ketoacidosis related to diabetes, starvation, or alcoholism • Salicylate toxicity ↓ Acid excretion • Renal failure ↑ Bicarbonate loss • Diarrhea, ileostomy drainage, intestinal fistula • Biliary or pancreatic fistulas ↑ Chloride • Sodium chloride intravenous (IV) solutions • Renal tubular acidosis •Carbonic anhydrase inhibitors

Sodium bicarbonate Therapy

is used only in patients with a pH less than 7.2 It should be used judiciously in patients with cardiac disease and renal impairment because of the sodium content. Also used to alkalinize the urine and speed the excretion of acidic substances. Is useful in treating overdoses of certain acidic medications such as aspirin and phenobarbital and is useful as adjunctive therapy for certain chemotherapeutic drugs such as methotrexate. Is also used in chronic renal failure to neutralize the metabolic acidosis that occurs when the kidneys cannot excrete hydrogen ion. Intravenous (IV) sodium bicarbonate causes the urine to become more alkaline.

Risk Factors

- Critically Ill Patients Each disorder is treated separately, with the underlying cause considered in the critically ill patients.

Hypercapnia

A condition marked by a PaCO2 level above 45 mmHg. Also known as hypercarbia.

Hypocapnia

A condition that results when PaCO2 falls below 35 mmHg. Also called hypocarbia.

Arterial blood gas (ABG)

A laboratory test primarily used to evaluate oxygen and carbon dioxide exchange and the acid-base balance within the blood. Reflects acid-base balance throughout the entire body better than venous or capillary blood that has dispersed oxygen into the tissues and has collected carbon dioxide.

PaCO2

A measure of the pressure exerted by dissolved carbon dioxide in the blood; it reflects the respiratory component of acid-base regulation and balance because it is regulated by the lungs. The normal value is 35-45 mmHg Less than 35 mmHg is known as hypocapnia Greater than 45 mmHg is known as hypercapnia

Allen test

A measurement of radial or ulnar artery patency; either the radial or ulnar artery is digitally compressed by the examiner after blood has been forced out of the hand by clenching it into a fist. The hand will lose its normal color. Digital pressure is released from one artery while the other remains compressed. The return of color indicates that the hand has good collateral supply of blood and that arterial puncture can safety be performed.

Bicarbonate (HCO3)

A weak base. When an acid is added to the system, the hydrogen ion in the acid combines with bicarbonate, and the pH changes only slightly.

Volatile acid

Acids eliminated from the body as a gas. Carbonic acid (H2CO3) is the only volatile acid produced in the body. It dissociates (separates) into carbon dioxide (CO2) and water (H2O); the lungs eliminate the carbon dioxide.

Respiratory Acidosis Common Causes

Acute respiratory acidosis • Acute respiratory conditions (pulmonary edema, pneumonia, acute asthma) • Opiate overdose • Foreign body aspiration • Chest trauma Chronic respiratory acidosis • Chronic respiratory conditions (COPD, cystic fibrosis) • Multiple sclerosis, other neuromuscular diseases • Stroke

Manifestations: Respiratory acidosis

Acute: • Headache • Irritability, altered mental status • ↓ LOC • Cardiac arrest Chronic: • Dull headache • Impaired memory • Personality changes • Weakness Laboratory findings: • Arterial blood pH less than 7.35 • PaCO2 above 45 mmHg • HCO3 normal or slightly elevated çin acute; above 28 mEq/L in chronic

Reasons for False Pulse Oximeter Readings

Anemia, carbon monoxide poisoning, hypothermia, hypotension, peripheral vasoconstriction, and poor peripheral perfusion

Physical Examination

Assess the patient's vital signs, including pulse oximetry. Assess mentation. Use fall precautions for patients with decreased LOC. Skin color and temperature, rate of respirations, lung sounds, bowel sounds, and urine output

Pharmacologic Therapy

Careful monitoring of ABG levels prevents overtreatment that causes pH to alter in the opposite direction, changing alkalosis to acidosis or acidosis to alkalosis.

Compensation: Metabolic alkalosis

Cause: Bicarbonate excess Compensation: Rate and depth of respirations decrease; CO2 is retained. Effect on ABGs: ↑ pH ↑ HCO3 ↑ PaCO2

Compensation: Respiratory alkalosis

Cause: Loss of CO2and deficient carbonic acid Compensation: Kidneys excrete bicarbonate and conserve H+ to restore carbonic acid: bicarbonate ratio. Effect on ABGs: ↑ pH ↓ PaCO2 ↓ HCO3

Compensation: Respiratory acidosis

Cause: Retained CO2and excess carbonic acid Compensation: Kidneys conserve bicarbonate to restore carbonic acid: bicarbonate ratio of 1:20. Effect on ABGs: ↓ pH ↑ PaCO2 ↑ HCO3

Compensation: Metabolic acidosis

Cause: Excess nonvolatile acids; bicarbonate deficiency Compensation: Rate and depth of respirations increase, eliminating additional CO2. Effect on ABGs: ↓ pH ↓ HCO3 ↓ PaCO2

Alteration: Respiratory acidosis

Caused by an excess of dissolved carbon dioxide, or carbonic acid; it can be acute or chronic.

Alteration: Respiratory alkalosis

Caused by hyperventilation, leading to a carbon dioxide deficit.

Interpreting ABGs: Step 7

Evaluate oxygenation. PaO2 < 80 mmHg = hypoxemia; possible hypoventilation. PaO2 > 100 mmHg = hyperventilation.

Interpreting ABGs: Step 5

Evaluate the pH, HCO3, and BE for a possible metabolic problem. If the pH is < 7.35, the HCO3 is < 24 mEq/L, and the BE is < −3 mEq/L, then low bicarbonate levels and high H+concentrations are causing metabolic acidosis. If the pH is > 7.45, the HCO3 is > 28 MEq/L, and the BE is > +3 mEq/L, then high bicarbonate levels are causing metabolic alkalosis.

Interpreting ABGs: Step 3

Evaluate the pH-PaCO2 relationship for a possible respiratory problem. If the pH is < 7.35 (acidosis) and the PaCO2 is > 45 mmHg (hypercapnia), retained carbon dioxide is causing increased H+ concentration and respiratory acidosis. If the pH is > 7.45 (alkalosis) and the PaCO2 is < 35 mmHg (hypocapnia), low carbon dioxide levels and decreased H+concentration are causing respiratory alkalosis.

Analysis of ABGs

First, evaluate each individual measurement; then, analyze the interrelationships to determine the patient's acid-base status The PaCO2 measures the pressure exerted by dissolved carbon dioxide in the arterial blood and reflects the respiratory component of acid-base regulation and balance because it is regulated by the lungs.

Health Promotion

Focuses on maintaining fluid balance. Both over-hydration and dehydration can result in acid-base imbalances. Nurses focus on patient teaching regarding adequate nutrition, taking medications as prescribed, and following treatment regimens for chronic illnesses.

Carbonic acid

IS a weak acid produced when carbon dioxide dissolves in water. When a base is added to the system, it combines with carbonic acid, and the pH remains within the normal range.

Nursing Assessment

Identifying patients at risk for acid-base disturbances, including those who have a risk for significant electrolyte imbalances, net gain or loss of acids, net gain or loss of bases, ventilation abnormalities, abnormal kidney function, and metabolic malfunction. Consider what the patient's vital signs are telling you. Count the patient's respirations for a full minute. Consider the rate and depth of respirations in your assessment. Decreased LOC

Patient Teaching: Sodium Bicarbonate

Include the following points when teaching patients and their families about sodium bicarbonate: • Immediately contact the primary healthcare provider if gastric discomfort continues or is accompanied by chest pain, dyspnea, or diaphoresis. • Use non-sodium antacids to prevent the absorption of excess sodium or bicarbonate into the systemic circulation. • Do not use any antacid, including sodium bicarbonate, for longer than 2 weeks without consulting your healthcare provider. Should include the goals of therapy, the reasons for obtaining baseline data such as vital signs and electrolyte levels, and possible drug side effects.

Interpreting ABGs: Step 4

Look at the bicarbonate. If the HCO3 is < 24 mEq/L, bicarbonate levels are lower than normal. If the HCO3 is > 28 mEq/L, bicarbonate levels are higher than normal.

Interpreting ABGs: Step 1

Look at the pH. • pH < 7.35 = acidosis • pH > 7.45 = alkalosis

Interpreting ABGs: Step 6

Look for compensation. Renal compensation 1. In respiratory acidosis (pH < 7.35, PaCO2 > 45 mmHg), the kidneys retain HCO3 to buffer the excess acid, so the HCO3 is > 28 mEq/L. 2. In respiratory alkalosis (pH > 7.45, PaCO2 < 35 mmHg), the kidneys excrete HCO3 to minimize the alkalosis, so the HCO3 is < 24 mEq/L. Respiratory compensation 1. In metabolic acidosis (pH < 7.35, HCO3 < 24 mEq/L), the rate and depth of respirations increase, increasing carbon dioxide elimination, so the PaCO2 is < 35 mmHg. 2. In metabolic alkalosis (pH > 7.45, HCO3 > 28 mEq/L), respirations slow and carbon dioxide is retained, so the PaCO2 is > 45 mmHg.

Symptoms of alkalosis

Irritability, confusion, cyanosis, slow respirations, irregular pulse, and muscle weakness. If these symptoms occur, withhold the medication and notify the healthcare provider.

Carbon dioxide

Is a potential acid; when combined with water, it forms carbonic acid, a volatile acid.

Relationship between hydrogen ion concentration and pH

Is inverse: As hydrogen ion concentration increases, the pH falls, and the solution becomes more acidic; As hydrogen ion concentration falls, the pH rises, and the solution becomes more alkaline or basic.

Renal System

Is responsible for the long-term regulation of acid-base balance.

The normal pH of body fluids

Is slightly basic, ranging from 7.35 to 7.45. (A pH of 7 is neutral.) Normal pH indicates acid-base balance.

Baking Soda

Is used as a home remedy to neutralize gastric acid, relieving heartburn and sour stomach. Although occasional use is acceptable, nurses should be aware that patients may misinterpret cardiac symptoms as heartburn, and overuse of sodium bicarbonate may lead to systemic alkalosis.

Considerations when drawing blood for ABGs

It is important to apply pressure to the puncture site for 10 minutes (more than 10-15 minutes if the patient is receiving anticoagulant therapy) after the procedure to reduce the risk of bleeding or bruising.

Ion Trapping

Less acid is reabsorbed in the renal tubules, so more acid and acidic medicine is excreted. Monitor the patient's acid-base status closely and report symptoms of imbalance. Provide care directed toward supporting critical body functions such as cardiovascular, respiratory, and neurologic status, which may be impaired secondary to the drug overdose.

Interpreting ABGs: Step 2

Look at the PaCO2. PaCO2 < 35 mmHg = hypocapnia; more carbon dioxide is being exhaled than normal. PaCO2 > 45 mmHg = hypercapnia; carbon dioxide is being retained.

Bilevel positive airway pressure

May be an option for certain patients who are not in immediate need of intubation and who meet certain criteria that include severe respiratory distress and acute respiratory acidosis, especially if intubation is contraindicated. Monitor patients receiving bipap therapy for pneumothorax and hypotension secondary to decreased venous return

Alteration: Metabolic acidosis

May be caused by excess acid in the body or loss of bicarbonate from the body.

Alteration: Metabolic alkalosis

May be caused by loss of acid or excess bicarbonate in the body.

Alkalosis

The condition that results when hydrogen ion concentration falls below normal and the pH level rises above 7.45.

Acidosis

The condition that results when hydrogen ion concentration increases above normal, causing the pH to drop below 7.35.

Elimination of nonvolatile acids

Must be metabolized or excreted in fluid. Examples are lactic acid, hydrochloric acid, phosphoric acid, and sulfuric acid.

Serum carbonic acid

Normal level is 1.2 mEq/L

Venous Blood Gases

Occasionally ordered when frequent ABGs have resulted in damage to normal arterial gas sampling sites. And when a patient has chronic retention of serum carbon dioxide (CO2), it is reflected in a metabolic panel. If the history of long-standing chronic lung disease is unknown, it is often helpful to look at serum CO2 to see a trend. Healthcare providers often look at venous CO2 when chronic CO2 retention occurs.

Mixed disorders

Occur from combinations of respiratory and metabolic disturbances. For example: A patient in cardiac arrest develops a mixed respiratory and metabolic acidosis due to lack of ventilation (and retained CO2) and hypoxia of body tissues that leads to anaerobic metabolism and acid by-products (excess nonvolatile acids).

Respiratory acidosis

Occurs when carbon dioxide is retained, increasing the amount of carbonic acid in the body. As a result, the pH falls to less than 7.35, and the PaCO2 (pressure exerted by dissolved carbon dioxide in the blood) is greater than 45 mmHg.

Metabolic alkalosis

Occurs when there is an excess of bicarbonate in relation to the amount of hydrogen ion.The pH is above 7.45, and the bicarbonate concentration is greater than 28 mEq/L.

Airway Management

Patients experiencing respiratory distress may require intubation. Although there is no specific rule for when to intubate, generally intubation is indicated if the patient has a PaCO2 greater than 77 mmHg, a PaO2 less than 60 mmHg, and a pH less than 7.20.

Patients with chronic hypercarbia

Require care to correct their status slowly, as correcting PaCO2 too quickly may result in metabolic alkalosis due to excessive retention of bicarbonate

Patients with hypoxemia

Require supplemental oxygen, which has been shown to improve outcomes and reduce mortality rates.

Blood gases may be drawn by

Respiratory therapists, healthcare providers, or nurses with specialized skills (intensive care-trained).

Acids

Substances that release hydrogen ions in solution.

Independent Interventions

Taking vital signs and obtaining a thorough patient history, which includes risk factors: cardiac, renal, pulmonary symptoms; current medications; medical conditions; and other symptoms. For patients in severe distress, family members may need to be consulted for critical information, including recent eating habits and history of vomiting. When taking the patient's health history, the nurse should consider conditions potentially related to culture and developmental stages.

Chronic Condition & Health Promotion

That can easily cause a change in fluid status and subsequent acid-base imbalances include diabetes, Crohn disease, chronic kidney disease, and chronic lung diseases such as COPD.

Respiratory System Buffers

The Respiratory System and the Brain's respiratory center Regulates carbonic acid by eliminating or retaining carbon dioxide. Compensations occur within minutes but because less effective over time

Metabolic acidosis

The amount of bicarbonate decreases in relation to the amount of acid in the body This condition can develop from abnormal bicarbonate losses or from excess nonvolatile acids in the body. The pH falls below 7.35, and the bicarbonate concentration is less than 24 mEq/L.

Compensation

The change in pH affects the rate and depth of respirations, which, in turn, affects carbon dioxide elimination and the PaCO2 and helps restore the ratio of carbonic acid to bicarbonate. The kidneys compensate for simple respiratory imbalances. The change in pH affects both bicarbonate conservation and hydrogen ion elimination.

Pulse Oximeter & ABGs

When perfusion is low, your pulse oximetry reading does not correlate to arterial oxygenation When pulse oximetry is reading a low percentage, it may not correlate to the accurate number in the arterial sample.

Partially Compensated

When these changes are reflected in arterial blood gas (ABG) values but the pH remains outside normal limits

Respiratory alkalosis

When too much carbon dioxide is lost, carbonic acid levels fall. The pH rises to above 7.45, and the PaCO2 is less than 35 mmHg.

Major Buffers

bicarbonate-carbonic acid buffer system, the phosphate buffer system, and protein buffers

Acid-base balance is critical for

homeostasis and optimal cellular function

Kidney's Role in Acid Base Balance

normally eliminate the excess nonvolatile acids produced during metabolism. also regulate bicarbonate levels in ECF by regenerating or reabsorbing bicarbonate ions in the renal tubules. respond more slowly to changes in pH (over hours to days), they can generate bicarbonate and selectively excrete or retain hydrogen ions as needed. Acidosis: When excess hydrogen ions are present and the pH falls, this organ excrete hydrogen ions and retain bicarbonate Alkalosis: Retain hydrogen ions and excrete bicarbonate to restore acid-base balance.

Manifestations: Metabolic alkalosis

• Confusion • ↓ LOC • Hypotension • Tetany • Seizures • Respiratory failure Laboratory findings: • Arterial blood pH above 7.45 • Serum bicarbonate greater than 28 mEq/L • PaCO2 higher than 45 mmHg with respiratory compensation

Interventions: Respiratory Acidosis

• Frequently assess respiratory status and lung sounds. • Monitor airway and ventilation; assist with insertion of artificial airway and prepare for mechanical ventilation as necessary. • Administer pulmonary therapy measures such as inhalation therapy, percussion and postural drainage, bronchodilators, and antibiotics as ordered. • Monitor fluid intake and output, vital signs, and ABGs. • Administer narcotic antagonists as indicated. • Maintain adequate hydration (2-3 L of fluid per day unless contraindicated by other health conditions).

Manifestations: Respiratory alkalosis

• Hyperventilation • Dizziness • Palpitations • Anxiety-panic • Tetany • ↓ LOC Laboratory findings (in uncompensated respiratory alkalosis): • Arterial blood pH above 7.45 • PaCO2 less than 35 mmHg Laboratory findings (in chronic hyperventilation): • Serum bicarbonate less than 24 mEq/L Arterial blood pH near normal

Interventions: Metabolic Alkalosis

• Monitor intake and output closely. • Monitor vital signs, especially respirations, and LOC. • Administer ordered IV fluids carefully. Treat underlying problem as ordered.

Interventions: Respiratory Alkalosis

• Monitor vital signs and ABGs. • Teach patient to breathe more slowly. • Reduce stimuli in environment and speak in calm, quiet voice.

Manifestations: Metabolic acidosis

• Nausea and vomiting • Weakness • Fatigue • Headache • ↓ Level of consciousness (LOC) • Hyperventilation Laboratory findings: • Arterial blood pH below 7.35 • Serum bicarbonate less than 24 mEq/L • PaCO2 less than 38 mmHg with respiratory compensation

Other Independent Interventions

• Taking weight daily • Monitoring intake and output • Assessing respiratory and renal function • Maintaining a patent airway • Monitoring oxygen saturation • Taking vital signs • Assessing LOC and neurologic function • Prompt reporting of changes in patient condition.

Metabolic Acidosis Values

• pH < 7.35 • HCO3 < 24 mEq/L • Critical values • pH < 7.20 •HCO3 < 10 mEq/L

Respiratory Acidosis Values

• pH < 7.35 • PaCO2 > 45 mmHg • Critical values • pH < 7.20 • PaCO2 > 77 mmHg

Metabolic Alkalosis Values

• pH > 7.45 • HCO3 > 28 mEq/L • Critical values • pH > 7.60 • HCO3 > 40 mEq/L

Respiratory Alkalosis Values

• pH > 7.45 • PaCO2 < 35 mmHg • Critical values • pH > 7.60 • PaCO2 < 20 mmHg