NURSING 115 – ACID BASE BALANCE
DEFINITIONS: ACID & BASE:
-Acid: a molecule that can release an hydrogen ion (H+)
-Base: a molecule that can accept or combine with an hydrogen ion (H+)
ACID, BASE, AND pH:
What is pH?
-Represents hydrogen ion concentration
-More hydrogen ion we have the more acidic we become
-The less hydrogen ion we have we become alkalotic
-When pH is higher you get more basic
-When pH is lower you get more acidic – EX: ketoacidosis
NORMAL RANGE:
pH 7.35 – 7.45
Acidosis pH < 7.35
Alkalosis pH > 7.45
ARTERIAL BLOOD GAS (ABG) LEVELS – DEFINITION & NORMALS:
-PaO2 – the amount of dissolved oxygen in the blood
Normal Values: 80 – 100 mmHg
-PaCO2 – the amount of dissolved carbon dioxide in the blood
Normal Values: 34-45 mmHg
-HCO3 – the bicarbonate io
Normal Values: 22 – 28 mEq/L
NORMAL ABG LEVELS
PaO2 80 – 100 mmHg
PaCO2 34 – 45 mmHg
HCO3 22 – 26 mEq/L
BASE EXCESS/DEFICIT & ANION GAP:
- Base Excess/Deficit : measurements of bicarbonate excess or deficit
- Anion Gap: difference between cations and anions in the extracellular space
BASICS
FACTOR MEAN RANGE
pH 7.40 7.35 -7.45
PaO2 (mmHg) 90 80 -100
PaCO2 (mmHg) 41 35 -45
HCO3 (mEq/L) 24 22 -26
BE/BD -2 to +2
SO2:
- SO2 – oxygen saturation measured in the arterial blood (SaO2) or pulse (SpO2)
- Pulse Oximetry – transcutaneous measurement with external finger probe
-Normal Value: 92% or greater
SPECIFIC ISSUES
CONDITION VALUES
ACIDOSIS pH < 7.35
ALKALOSIS pH > 7.45
HYPOXIA PaO2 < 60
HYPEROXIA PaO2 > 100
ALVEOLAR HYPERVENTILATION PaCO2 < 35
VENTILATORY FAILURE PaCO2 > 50
CARBONIC ACID EQUATION:
-This equation expresses the biologic acid-base relationship between the respiratory
system (CO2) and the metabolic system (HCO3)
CO2 + H2O H2CO3 H+ + HCO3-
LUNGS KIDNEYS
pH REGULATION – 2 CONTROL SYSTEMS:
1. Respiratory System: respiratory mechanisms eliminate CO2
•Excess CO2 or excess H+ ions in the blood act directly on the respiratory
center in the brain to control ventilation
•This is a quick response -> within minutes
2. Renal System: renal mechanisms conserve HCO3 ions and eliminate hydrogen ions
•The kidneys regulate acid-base balance by excreting an acidic urine or an
alkaline urine. They excrete excess H+ ions and reabsorb or regenerate HCO3
ions
•Takes longer to affect pH -> days
RESPIRATORY ACIDOSIS: DECREAED pH/ INCREASED PCO2
Signs & Symptoms:
-ABG values
-Blood pressure changes
-Headache
-Hypoventilation
-Restlessness, confusion
-Tachycardia
Cause:
-Ventilatory failure
-Acute airway obstruction
-Severe pneumonia
-Pulmonary edema
-Neuromuscular disorders
-CNS depression (drugs, CNS event)
-Compensated – chronic lung disease
RESPIRATORY ALKALOSIS: INCREASED pH/DECREASED PCO2:
Signs & Symptoms:
•ABG values
•Dizziness
•Hyperventilation
•Light – headedness
•Muscle cramps and spasm
•Parathesis
•Palpitations
•Anxious females
•Increased Ph Decreased PaCO2
•pH- >7.35
•PCO2 < 35
•Parathesias lips and fingers
Cause:
•Acute alveolar hyperventilation:
•Anxiety
•Hypoxia
•Drugs (OD or bicarb base)
•Sepsis
•Hepatic encephalopathy
•Increased Ph Decreased PaCO2
•Parathesias lips and fingers
•OTC meds = pH changes
METABOLIC ACIDOSIS: DECREASED PH/DECREASED HCO3
Signs and Symptoms:
•ABG Values
•Arrythmias
•Hyperventilation (secondary to compensation)
•Hypotension
•Lethargy, coma
•Signs and symptoms related to underlying cause
•Decreased PH decreased HCo3
•pH < 7.34
•HCO3 < 22
Cause:
•Ketoacidosis (diabetic/alcoholic)
•Renal failure
•Lactic acidosis
•Diarrhea
•Toxins (methanol)
•Decreased PH decreased HCo3
•Common cause DKA – type I DM
•increase RR – Kuzzmaul resp
•pH < 7.35 HCO3 < 22
METABOLIC ALKALOSIS: INCREASED pH/increased HCO3
Signs and Symptoms:
•ABG values
•Arrhythmias
•Confusion
•Apathy, stupor
•Hypoventilation (secondary to compensation)
•Muscle weakness (hypokalemia)
•Increased PH-- increased HCO3
•pH > 7.45
•HCO3 < 28
REVIEW - ACIDOSIS
CONDITION pH: 7.35 – 7.45 PaCO2: 35 – 45 HCO3: 22 – 26 BE/BD: -2 to
+2
RESPIRATORY
ACIDOSIS
7.25
A
65
A
26
N
+2
N
RESPIRATORY
ACIDOSIS WITH
COMPENSATION
7.3
A
64
A
32
B
+8
B
REVIEW - ALKALOSIS
CONDITION pH: 7.35 – 7.45 PaCO2 35 – 45 HCO: 22 – 26 BE/BD: -2 to +2
RESPIRATORY
ALKALOSIS
7.6
B
25
B
24
N
0
N
RESPIRATORY
ALKALOSIS WITH
COMPENSATION
7.49
B
25
B
19
A
-5
A
REVIEW - ACIDOSIS
CONDITION pH: 7.35 – 7.45 PaCO2: 35 - 45 HCO3: 22 - 26 BE/BD: -2 to +2
METABOLIC
ACIDOSIS
7.2
A
40
N
15
A
-9
A
METABOLIC
AIDOSIS WITH
7.3
A
30
B
15
A
-9
A
COMPENSATION
REVIEW - ALKALOSIS
CONDITION pH: 7.35 – 7.45 PaCO2: 35 – 45 HCO3: 22 – 26 BE/BD: -2 to +2
METABOLIC
ALKALOSIS
7.51
B
40
N
32
B
+8
B
METABOLIC
ALKALOSIS WITH
COMPENSATION
7.46
B
46
A
32
B
+8
B
Uncompensated Resp Alkalosis hyperventilation
Compensated respiratory compensation chronic alveolar hyperventilation
Alkalosis with compensation.
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