Acid-Base Balance
and Imbalance
James Barnett, RN, MSN
Clinical Educator – Neuroscience PCC
Vanderbilt University Medical Center
May 2007
Definitions

pH
Measurement of how alkaline or acid a substance is
 Chemistry

Neutral ph = 7
 pH < 7 is acid
 pH > 7 is alkaline


Normal human blood pH is slightly alkaline at
7.35 – 7.45
Definitions

An Acid is…
A molecule that can donate a H+ ion
 Examples:

H2O  H+ + OH H2CO3  H+ + HCO3

An acid can be weak, moderate, or strong depending
on its pH
Weaker acids are closer to 7
 Stronger acids are closer to 1

Definitions

A Base or alkali is…
A molecule that can accept a H+ ion
 Examples:

H+ + OH-  H2O
 H+ + HCO3-  H2CO3


A base can be weak, moderate, or strong depending
on its pH
Weaker bases are closer to pH 7
 Stronger bases are closer to pH 14

An Important Equilibrium Equation
H2O + CO2  H2CO3  H+ + HCO3-
Water plus carbon dioxide equals carbonic acid which is broken down by
carbonic anhydrase into a hydrogen ion and bicarbonate.
Types of Acids

Volatile acids
Easily move from liquid to gas state
 Within the body

Lung can remove
 H2CO3 + renal enzyme  H2O + CO2 (both of which
are exhaled)


Carbon dioxide is therefore considered an acid
KEY CONCEPT: As CO2 rises, there is more acid  respiratory acidosis
KEY CONCEPT: As CO2 drops, there is less acid  respiratory alkalosis
Types of Acids

Nonvolatile acids
Cannot be changed to gas state
 Within the body

Must be removed by the kidneys (metabolic)
 Examples



Keto acids
Lactic acids
Acid-Base Imbalance
Acid Imbalance

Too much CO2 leads to decreased pH and an acid
condition

Too little CO2 leads to increased pH and an alkaline
condition

PaCO2


Amount of CO2 dissolved in the blood
Good indicator of respiratory and ventilatory function
Base Imbalance

Major base in body is bicarbonate (HCO3-)

Regulated by the kidneys (metabolic)

Too little HCO3- causes decrease in pH and acid
conditions

Too much HCO3- causes increase in pH and
alkaline conditions
More definitions

Acidemia – condition where blood is more acid than
normal (pH < 7.35)

Alkalemia – condition where blood is more alkaline
than normal (pH > 7.45)

Acidosis – the process causing acidemia

Alkalosis – the process causing alkalemia
Respiratory Imbalances

Respiratory mechanisms involve either
Retention of excess carbon dioxide
 Retention of insufficient carbon dioxide


Over- or Under-ventilation or respiration
abnormalities are the main causes of this
imbalance
Metabolic Imbalances

Metabolic mechanisms involve

Renal function alteration

Production of acidic metabolic products

Loss of acid from the body
The Normal’s

pH

7.35 – 7.45

PaCO2

35 – 45 mmHg

HCO3-

22 – 26 mEq/L

PaO2

80 – 100 mmHg
The Abnormal’s

Respiratory Acidosis

Respiratory Alkalosis

Metabolic Acidosis

Metabolic Alkalosis
Respiratory Acidosis

pH < 7.35

PaCO2 > 45
Alveolar Hypoventilation
 CNS depression or disease
 Ventilatory/respiratory
dysfunction
 Acute infections
Signs and Symptoms
 Dyspnea
 Restlessness
 Confusion/lethargy
 Dysrhythmias
 Headache
Treatment
 Increase ventilation
 Treat the cause
Respiratory Alkalosis


pH > 7.45
PaCO2 < 35
Alveolar Hyperventilation







Anxiety
Pain
Fever
Thyrotoxicosis
CNS lesions
Improper vent management,
hypoxia
Pulmonary embolus
Signs and Symptoms







Light headedness
Confusion
Muscle spasm / parasthesias
Dysrhythmias / palpitations
Sweating
Dry mouth
Blurred vision
Treatment



Slow down breathing
Paper bag breathing if anxiety or
fear is cause
Treat the cause!
Metabolic Acidosis


pH < 7.35
HCO3- < 22 mEq/L
Causes

Increased acids from





Anaerobic metabolism
Abn metabolic process (DKA,
lactic acidosis)
Starvation
ASA or other acid ingestion
Excess HCO3- loss



Diarrhea
Renal Failure
Intestinal Fistulae
Signs and Symptoms








Headache
Confusion/lethargy
Stupor/coma
Weakness
Kussmaul respiration
N/V
Dysrhythmias
Flushing
Treatment



Treat the cause!!!
Give Bicarbonate
Dialysis for renal failure
Metabolic Alkalosis
pH > 7.45
 HCO3- > 28
Cause



Increased base
 Excessive use of bicarb
 Lactate from dialysis
 Excessive antacid ingestion
Acid loss
 Vomiting/Gastric suctioning
 Hypo- chloremia -kalemia
 Diuretics
 Large volume blood
transfusion
Signs and Symptoms






Muscle spasms/tetany/seizure
Dizziness
Disorientation/lethargy/coma
Weakness
N/V
Depressed respiratory drive
Treatments


Treat the cause!!!!
Increase respirations
Finished

You have finished this in-service on Acid-Base
Balance and Imbalance.

Continue with the next lesson titled:

Compensated and Uncompensated Blood Gas
Analysis