ACID-BASE BALANCE

Med-Surg Nursing I

Acid-Base Balance Homeostasis is the of equilibrium in the internal

environment of the body, naturally maintained by adaptive responses that promote healthy survival.

During normal metabolism the body produces many acids; these acid alter the internal environment of the body, including fluid and electrolyte balances. Therefore, it must be regulated to maintain homeostasis.

Acid-Base Balances Many health problems may leads to acid-

base imbalances in additional to fluid and electrolyte imbalances.

E.g. patient with Diabetes mellitus, chronic obstructive pulmonary disease and kidney disease frequently develop acid-base imbalances.

Others like vomiting and diarrhoea may cause loss of acid base in addition to fluids and electrolytes.

Cont…Acid-Base Balances Acid-base balance required maintenance of

hydrogen ion (H+) concentration within narrow range (0.0004 mEq/L).

The acidity or alkalinity of a solution depends on its H+ concentrations.

An increase in H+ leads to acidity. A decrease in H+ leads to alkalinity. The H+ concentration is measured as pH. As H+ falls, pH rise, solution become alkaline. As H+ rise, pH falls, solution become acidic.

Cont…Acid-Base Balances The pH of a chemical solution may range

from 1 – 14. A solution with pH 7 is considered neutral. An acid solution has a pH < 7. An alkaline solution has a pH > 7. The normal pH of the body fluid is 7.35

– 7.45. If pH drops < 7.35, the person has acidosis. If pH greater > 7.45, the person has alkalosis.

Regulation of Acid-Base Balance Metabolic process in the body continuously

produce acids in 2 forms: volatile acids and nonvolatile acids.

Volatile acids can be eliminate from the body as a gas.

Carbonic acid (H2CO3) is the only volatile acid produced in the body.

H2CO3 CO2 + H2O CO2 and H2O is then eliminated from the

body through the lungs.

Cont…. Regulation of Acid-Base Balance Nonvolatile acids include all other acids

produced in the body. E.g. lactic acid, hydrochloric acid, phosphoric

acid, sulfuric acid. There are 3 system work together to maintain

the pH: - Buffers- Respiratory system- Renal system

Cont…. Regulation of Acid-Base Balance Buffers react immediately. The respiratory system responds in minutes

and reaches maximum effectiveness in hours.

The renal response takes 2 to 3 days to respond maximally but the kidney can maintain balance for a long period of time.

Buffer System Buffers are substances that prevent major

changes in pH by removing or releasing H+. Buffers act chemically to change strong acids

into weaker acids or to bind acids to neutralize their effect.

Example of buffers, bicarbonate-carbonic acid, monohydrogen-dihydrogen phosphate, intracellular and plasma protein and hemoglobin buffers.

When excess acid is present in body fluid, buffers bind with H+ to minimize the change in pH.

Cont….Buffer System If body fluids become too alkaline, buffers

release H+, to restore the pH. Although buffers act immediately but their

capacity to maintain pH is limited.

Cont….Buffer System

E.g. bicarbonate-carbonic acid buffer system.

CO2 + H2O H2CO3 H+ + HCO3¯

Bicarbonate (HCO3¯) is a weak base; when an acid added to the system, the H+ in the acid combines with carbonic acid (HCO3¯) become weak acid, H2CO3, the pH changes only slightly.

H2CO3 is produced when CO2 dissolve in the water.

Cont….Buffer System The normal serum bicarbonate level is 24

mEq/L. Normal level of carbonic acid is 1.2 mEq/L. The ratio of bicarbonate to carbonic acid is

20:1, in order to maintain the pH within the normal range.

Adding strong acid to extracellular fluid depletes bicarbonate, causing the pH drops < 7.35. This known as acidosis.

Adding strong base depletes carbonic acid as it combines with the base. The pH rise > 7.45. This known as alkalosis.

Respiratory System The respiratory system regulates carbonic

acid in the body by eliminating or retaining carbon dioxide.

CO2 is a potential acid. When CO2 combined with water, it form

carbonic acid, a volatile acid. In acute increases in carbonic acid or H+ in

the blood stimulate the respiratory center in the brain.

The sudden increase causing acidosis.

Cont…Respiratory System As a result, both the rate and dept of

respiration increase. The increase rate and dept of lung ventilation

eliminate CO2 from the body, and carbonic acid level falls, bringing the pH to a more normal range.

Although this compensation occurs within minutes, it becomes less effective over time.

Cont…Respiratory System Alkalosis, will depress the respiratory center. Both the rate and dept of respiration

decreases. Carbon dioxide is retained. The retained CO2 combines with water to

restore carbonic acid levels and bringing the pH back within normal range.

Renal System The renal system is responsible for the long-

term regulation of acid-base balance in the body.

Excess nonvolatile acids produced during metabolism normally are eliminated by the kidneys.

The kidneys also regulate bicarbonate levels in extracellular fluid by reabsorbing them in the renal tubules.

Cont….Renal System In acidosis, when excess H+ is present and

the pH falls, the kidneys excrete H+ and retain bicarbonate.

In alkalosis, the kidneys retain H+ and excrete bicarbonate to restore acid-base balance.

Assessment of acid-base balance Acid-base balance is evaluated by

measuring arterial blood gases. Arterial blood is used because it reflects

acid-base balance throughout the entire body better than venous blood.

Arterial blood provides information about the blood oxygenation.

The elements to measure ABG are pH, PaCO2, PaO2, and bicarbonate level.

Cont….Assessment of acid-base balancePaCO2

PaCO2 measures the pressure exerted by dissolved carbon dioxide in the blood.

PaCO2 is regulated by the lungs. The normal values is 35 – 45 mmHg. PaCO2 < 35 mmHg known as hypocapnia. PaCO2 > 45 mmHg known as hypercapnia.

Cont….Assessment of acid-base balancePaO2 PaO2 is a measure of the pressure exerted

by oxygen that is dissolved in the plasma. The normal value for PaO2 is 80 – 100

mmHg. PaO2 < 80 mmHg is indicative of hypoxemia. PaO2 is valuable for evaluating respiratory

function, but not to determine acid-base balance.

Cont….Assessment of acid-base balanceSerum Bicarbonate Reflects the renal reregulation of acid-base

balance. The normal bicarbonate value is 22 – 26

mEq/L.

Base excess (BE) BE reflects the degree of acid-base

imbalance by indicating the status of the body’s total buffering capacity.

The normal value is – 2 to + 2.

Normal Values for ABGParameter Arterial Blood

pH 7.35 – 7.45

PaCO2 35 – 45 mmHg

PaO2 80 – 100 mmHg

HCO3¯ 22 – 26 mEq/L

Base Excess ± 2 mEq/L

Oxygen saturation > 94%

Acid-Base Imbalance Divided into two main categories: acidosis

and alkalosis. Further classified as metabolic or respiratory. Metabolic disorders, the primary change is in

the concentration of bicarbonate. Respiratory disorders, the primary changes is

in the concentration of carbonic acid and CO2.

These classified into: respiratory acidosis, respiratory alkalosis, metabolic acidosis and metabolic alkalosis.

Acid-Base Disturbances and Compensation

Disorder Initial event Compensation

Respiratory acidosis ↓ pH, ↑or normal HCO3¯, ↑PaCO2

↑Renal acid excretion and ↑serum HCO3¯

Respiratory alkalosis ↑pH, ↓or normal HCO3¯, ↓PaCO2

↓Renal acid excretion and ↓serum HCO3¯

Metabolic acidosis ↓pH, ↓HCO3¯, ↓or normal PaCO2

Hyperventilation with resulting ↓PaCO2

Metabolic alkalosis ↑pH, ↑HCO3¯, ↑or normal PaCO2

Hypoventilation with resulting ↑PaCO2

↑/↓ indicate partial compensation in progress

Respiratory acidosis Is caused by an excess of dissolved CO2. Characterized by pH < 7.35, PaCO2 > 45

mmHg. Can be acute or chronic. Causes: acute or chronic lung disease (e.g.

pneumonia, COAD). Other conditions that depress with ventilation,

e.g. excess narcotic analgesic, airway obstruction, neuromuscular disease

Cont…. Respiratory acidosis….Manifestations Increase pulse, respiration rate, BP Headache Warm, flushed skin Blurred vision due to papilledema and dilated

conjuctival blood vessels Irritability, altered mental status Decreasing level of consciousness Hyperkalaemia Cardiac arrest Chronic: weakness, sleep disturbances,

impaired memory, personality changes.

Management of respiratory acidosis

Treat the underlying cause. Use of bronchodilator drugs to reduce

bronchial spasm. Use of antibiotic to treat respiratory infections. Perform of suction to remove excessive

secretions. Adequate hydration to keep the mucus

membrane moist and facilitate the removal of secretions.

Cont….Management of respiratory acidosis Supplement of O2 as necessary. Mechanical ventilation for patient with severe

respiratory acidosis.

Nursing management of respiratory acidosis

Monitor vital signs and respiratory status (including SPO2) every 15 minutes for the first hour, then every hour.

Monitor ABGs for any changes or improvement.

Assess skin colour, nail beds, and oral mucous membranes.

Assess mental status and orientation every hour.

Cont….. Nursing management of respiratory acidosis

Monitor anxiety levels as evidenced by restlessness and agitation.

Keep side rails in place, and place call bell within reach.

Place in semi Fowler’s or Fowler’s position as tolerated to promotes lung expansion and gas exchange.

Administer oxygen as ordered, carefully monitor response as oxygen can suppress the respiratory drive in patient with chronic respiratory acidosis.

Cont….. Nursing management of respiratory acidosis

Encourage patient with chronic respiratory acidosis to use pursed-lip breathing to maintain open airways through exhalations, and promoting CO2 excretion.

Encourage fluid intake up to 3000 ml /day (if no contraindication) as tolerated to liquefy secretions and hydrate respiratory mucus membrane.

Administer medications such as bronchodilators as orders to relieve bronchial spasm, and dilating airways.

Cont….. Nursing management of respiratory acidosis

Provide chest physiotherapy as ordered to loosen secretions so that patients can cough out of airways.

Respiratory Alkalosis Is characterized by pH > 7.45, PaCO2 < 35

mmHg. It always caused by hyperventilation leading

to CO2 deficit. Causes: anxiety with hyperventilation is the

most common cause. If hyperventilation continues, the kidneys

compensate by eliminating bicarbonate, then the pH may be close to the normal range.

Cont….respiratory

alkalosis…..Manifestations Dizziness Numbness and tingling around mouth, hands

and feet Palpitations Dyspnea Chest tightness Anxiety/panic Tremors Tetany Seizures, loss of consciousness

Management of Respiratory Alkalosis Treat the underlying causes. If the cause is anxiety, instruct patient to

breath more slowly to allow CO2 to accumulate or breath into a closed system (such as paper bag).

A sedative or antianxiety to relieve hyperventilation and restore normal breathing pattern.

Nursing management of respiratory alkalosis Monitor vital signs especially respiratory rate,

dept and ease; including skin colour. These help to identify the underlying cause, such as fever or hypoxia.

Obtain subjective data such as factors leading up to the current situation, current health and recent illnesses or medication use.

Cont….Nursing management of respiratory alkalosis

Reassure the patient that he or she is not experiencing a heart attack and that symptoms will resolve when breathing return to normal.

Instruct patient to maintain eye contact and breath with you to slow the respiratory rate. These help to make the patient aware of respirations and provide a sense of support and control

Cont….Nursing management of respiratory alkalosis Have the patient breath into a paper bag.

This allow the patient to rebreath exhaled CO2, increasing PaCO2 and decreasing pH.

Maintain patient safety due to hyperventilation.

If the patient has experienced repeated episodes of hyperventilation or has a chronic anxiety disorder, refer for counseling. Counseling can help the patient develop alternative strategies for dealing with anxiety.

Metabolic Acidosis Is characterized by low pH (<7.35) and low

bicarbonate (<22 mEq/L). It may caused by excess acid in the body or

loss of bicarbonate from the body. When metabolic acid develops, the

respiratory system attempts to return the pH to normal by increasing the rate and dept of respirations.

As a result, CO2 eliminated, PaCO2 falls (< 35mmHg)

Cont…..metabolic acidosis Risk factors: - Acute lactic acidosis results from tissue

hypoxia due to shock or cardiac arrest.- Patients with type I diabetes mellitus are at

risk for developing diabetic ketoacidosis.- Acute or chronic renal failure impairs the

excretion of metabolic acidosis.- Diarrhoea, intestinal suction, or abdominal

fistula increase the risk for excess bicarbonate loss.

Cont…..metabolic acidosis….

Manifestations Weakness Fatigue Headache General malaise Anorexia Nausea and

vomiting Abdominal pain

Decreasing levels of consciousness, then stupor and coma

Dysrhythmias Bradycardia Warm, flushed skin Hyperventilation

(Kussmaul’s ventilation)

Management of Metabolic Acidosis

Treat the underlying causes. Infusion of sodium bicarbonate if the pH <7.1

and serum bicarbonate level is < 10 mEq/L to reduce effects of acidosis on cardiac functions.

Nursing management of metabolic acidosis

Monitors vital signs, including peripheral pulses and capillary refill.

Monitor the ECG pattern for dysrhythmias and changes characteristic of hyperkalaemia.

Monitor laboratory values, ABGs, serum electrolytes, and renal function studies to evaluate the effectiveness of treatment and early identification of potential problems.

Cont…. Nursing management of metabolic acidosis

Monitor and maintain accurate intake and output .

Assess urine output hourly. Note urine less than 30 ml/h or a positive balance on 24 hours total intake and output calculations.

Obtain daily weight using consistent conditions.

Administer medications as ordered, such as diuretic, monitor patient’s response to the therapy.

Cont…. Nursing management of metabolic acidosis Monitor neurologic functions, including

mental status, level of consciousness, and muscle strength.

Ensure patient safety: keep the bed in its lowest position, side rail raised.

Keep clocks, calendars, and familiar objects at bedside. Orientate time, place and circumstances as needed.

Keep patient near to nursing stations and significant others to remain with the patient as much as possible for safety purposes.

Metabolic Alkalosis Is characterized by high pH (>7.45) and high

bicarbonate (>26 mEq/L). It may be caused by loss of acid or excess

bicarbonate in the body. When metabolic alkalosis develops, the

respiratory system attempts to return the pH to normal by slowing the respiratory rate.

CO2 is retained, and PaCO2 increase (>45 mmHg).

Cont….Metabolic Alkalosis

Common cause: vomiting, gastric suction , external drainage of gastric fluid.

The loss of gastric fluid with highly acidic increases the alkalinity of body fluids.

Other cause such as diuretic therapy that promotes excretion of K+; excessive ingestion of antacids containing bicarbonate or use of sodium bicarbonate during cardiopulmonary resuscitation.

Cont….metabolic

alkalosis….Manifestations Confusion Decreasing level of consciousness Tingling of fingers and toes Dizziness Hypertonic muscles Dysrhythmias Hypotension Seizures Respiratory failure (due to compensation

actions)

Management of metabolic alkalosis

Treat the underlying causes. Restore back the normal fluid volume with

sodium chloride. In patient with hypokalaemia, administer KCL

to replace K+.

Nursing management of metabolic alkalosis

Assess vital signs, oxygen saturations, CVP, peripheral pulse volume at least every 4 hours or less.

Monitor mental status and level of consciousness. Report any behaviour changes such as restless, agitation or confusion.

Place in semi Fowler’s or Fowler’s position to facilitate ventilation and gas exchange.

Cont….Nursing management of metabolic alkalosis

Administer oxygen as ordered to maintain oxygen saturation levels.

Schedule care activities to allow rest periods. Record all intake and output. Weigh daily. Administer intravenous fluids as ordered.

Monitor risk of fluid overload if rapid replacement is ordered.

Monitor serum electrolytes, osmolality and ABGs values.

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