Acid-Base ImbalanceMetropolitan Community College

Fall 2013

Acid Base Balance Hydrogen ions - Low concentrations

but highly reactive Concentration affects physiological

functions Alters protein and enzyme functioning Can cause cardiac, renal, pulmonary

abnormalities Alters blood clotting, Metabolization of meds

Acid and Bases Acids – compounds that form hydrogen

ion in a solution Proton donors Strong acids give up their hydrogen ion easily Weak acids hold on to their hydrogen ion more tightly

Bases – compounds that combine with hydrogen ion in a solution Proton acceptors Neutralizes

20:1 ratio (20 parts bicarbonate to one part carbonic acid)

What is pH?

pH is a measurement of the acidity or alkalinity of the blood.

It is inversely proportional to the number of hydrogen ions (H+) in the blood. The more H+ present, the lower the pH will be. The fewer H+ present, the higher the pH will be.

Homeostasis keeps pH in a very narrow range 7.35-7.45 for optimum functioning 6.8-7.8 compatible with life

Blood pH

Blood pH < 7.40 acidosis

Blood pH > 7.40 alkalosis

Body Acids

Respiratory Acid - CO2 – eliminated by lungs (288 L/day)

Metabolic acids: Lactic acids Pyruvic acid Ketoacids (DKA) Acetoatic acids Beta-hydrobutyric acids Very little metabolic acid is produced on a daily basis Metabolized by the liver or eliminated by the kidneys

Four Basic Categories of Abnormalities Respiratory acidosis

Excess of carbon dioxide leading to an acid pH Respiratory alkalosis

Lower than normal level of carbon dioxide leading to an alkaline pH

Metabolic acidosis Excess of hydrogen ion or a deficiency in

bicarbonate leading to an acid pH Metabolic alkalosis

Excess of bicarbonate leading to an alkaline pH

Buffer Systems Like a sponge

Soaks up extra ions Squeezed when there’s not enough

Extracellular Buffers Carbonic acid: controlled by respiration Bicarbonate: controlled by excretion

Intracellular Buffers Phosphate Buffer System

Dihydrogen phosphate (H2PO4) – hydrogen donor or acid

Hydrogen phosphate (HPO4) – hydrogen acceptor or base

Buffer Systems Protein Buffers

In the blood Plasma Proteins Hemoglobin: deoxygenated is better than

oxygenated at buffering Bones

Carbonate and phosphate salts in bone provide a long term supply of buffer.

In acute metabolic acidosis bone takes up hydrogen in exchange for calcium, sodium, and potassium.

Role of the Lungs Regulate plasma pH minute to minute

by regulating the level of Carbon Dioxide (CO2)

Carbon Dioxide is measured as a partial pressure of carbon dioxide in arterial blood PaCO2 35-45mmHg

Lungs alter rate and depth of ventilations in order to retain or excrete CO2

Minute Volume – Tidal Volume Ventilation is measured by how much air

the lungs move in one minute (minute ventilation)

Minute Ventilation is the product of respiratory rate and depth and is referred to as the TIDAL VOLUME (Vt)

Normal depth tidal volume is about 500ml Normal respiratory rate is 12 breaths per

min12 breaths x 500 ml = 6000 ml or 6 liters

Anatomic Dead Space The volume of air that doesn’t reach the

alveolar airspace Trachea & Bronchi Doesn’t take part in gas exchange

Estimated at 1ml/lb of ideal body weight 150lb of ideal body weight = 150ml of dead

space Tidal volume – dead space = alveolar

volume 500ml – 150ml = 350ml

RR x alveolar volume = minute alveolar ventilation 12 x 350ml = 4200ml or 4.2 L/min

Hypercarbic Drive Respiratory center in the medulla controls the rate and

depth of ventilation Responds to levels of arterial CO2, denoted as PaCO2

Chemoreceptors in the medulla come into contact with CSF

As PaCO2 rises the arterial PaCO2 reaches equilibrium with the CO2 in the CSF

The CO2 in the CSF dissociates into hydrogen ions The hydrogen ions stimulate the chemoreceptors in the

medulla which in turn stimulates the diaphragm and intercostal muscles

Respiratory rate and depth increase and CO2 is blown off

Hypoxic Drive There are also peripheral chemoreceptors

Carotid arteries Bifurcation of the common carotid and arch of

aorta Respond to levels of

Oxygen in the blood or PaO2 Hydrogen ions or pH Carbon dioxide in the blood or PaCO2

As PaO2 falls below 60 mmHg the respiratory center is stimulated to increase rate and depth

The role of the Kidneys Two main functions to maintain acid/base

Secrete hydrogen ions Restore or reclaim bicarbonate (HCO3)

In high metabolic acidosis, the kidneys can excrete ammonia as a urinary buffer.

In alkalosis - the kidneys retain hydrogen ion and excrete bicarbonate to correct the pH.

In acidosis - the kidneys excrete hydrogen ions and conserve bicarbonate to correct the pH.

Very slow process

Assessment of ACID BASE

Arterial Blood Gases (ABG) most often and the most accurate to assess acid base balances.

Serum Electrolytes can help fine tune acid base analysis

NORMAL ABG VALUES: pH = 7.35 to 7.45 PaCO2 = 35 – 45 mEq/L HCO3 = 22 – 28 mEq/L

Steps to Interpret ABG’s1. Assess the pH2. Assess the respiratory component – PaCO23. Assess the metabolic component – HCO3,

base excess4. Evaluate compensation

Compensation Once the primary cause is identified look at

the other value If the value is abnormal but moving in the right direction

to bring pH back to normal compensation is occuring If the pH value is normal than compensation is complete

Because renal compensation is slower you can infer whether respiratory abnormalities are acute or chronic If kidneys have had time to compensate is chronic If the kidneys have not had time to compensate its

acute

Respiratory Acidosis Respiratory system fails to keep up

with the body’s CO2 production Causes (pg. 442)

Acute: drug overdose, head trauma, spinal cord injury, upper airway obstruction, pneumothorax

Chronic: obesity, MS, emphysema, spinal cord injury

Clinical Manifestations Anxiety, irritability, confusion, lethargy, increased

heart rate, warm flushed skin Mainly seen with acute causes because chronic

patients have compensated

Respiratory Acidosis Medical treatment

Treat the underlying problem Increase ventilation BiPAP Intubation Supplemental oxygen (care must be taken with chronic

pts) Nursing care

Assess PaCO2 levels and pH. Observe for signs of respiratory distress: restlessness,

anxiety, confusion, tachycardia Encourage fluid intake Position patients with head elevated 30 degrees Administer oxygen with care

Respiratory Alkalosis Most common cause is hyperventilation

caused by anxiety, panic, or pain Stroke Meningitis Head trauma

Clinical Manifestations Anxious Tachycardia Tachypnea Vertigo Forgetfulness

Respiratory Alkalosis Medical treatment

Treat underlying cause of condition Sedation may be needed

Nursing care Administer sedatives or pain medications Provide emotional support Encourage patient to breathe slowly, which will

retain carbon dioxide in the body Breath into a paper bag

Metabolic Acidosis Increase in total body acid Causes (pg. 442)

Starvation Diarrhea Renal failure Diabetic ketoacidosis

Signs and symptoms Kussmaul respirations Altered LOC Headache V tach

Metabolic Acidosis Medical treatment

Treat the underlying disorder Nursing care

Monitor VS & ECG Assess neurological status Provide emotional support

Metabolic Alkalosis An accumulation of base or a loss of

acid in the ECF Causes (pg. 442)

Prolonged nasogastric suctioning or excessive vomiting

Diuretics Electrolyte disturbances Large volume blood transfusions, increased citrate

Clinical Manifestations Lethargy Altered LOC Tetany ECG changes

Metabolic Alkalosis Medical Treatment

Treat the underlying disorder Nursing care

Monitor VS & ECG Monitor labs Accurate I&O including the amount of fluid

removed by suction Provide emotional support Use isotonic saline solutions rather than water

for irrigating NG tubes because the use of water can result in a loss of electrolytes

A client’s blood gas results are pH 7.36, PaCO2 50, HCO3 30. What do these results indicate to the nurse?

A. Respiratory acidosis, compensatedB. Metabolic acidosis, compensatedC. Metabolic acidosis, uncompensatedD. Respiratory acidosis, uncompensated

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Reference Osborn, Wraa, & Watson chapter 19