Acid Base Balance for EMS

Acid-Base Balance for EMS Anne Clouatre, MHS, EMT-P EMS Regional Program Director Centura Health Porter, Littleton and Parker Adventist Hospitals Emergency Medical Services 303-765-6367

Objectives

Describe pH, acid, base, and buffer.

Compare and contrast the three buffer systems.

Arrange the normal blood gas values.

Differentiate blood gas values for respiratory

and metabolic acidosis and alkalosis.

Evaluate common conditions that may cause acidosis and/or alkalosis.

Porter, Littleton and Parker EMS 303-765-6EMS

pH

What does it mean?

pH stands for the p otential for H ydrogen

pH Scale

The pH scale represents the concentration of hydrogen ions (H + ) and hydroxyl ions (OH - ) in fluids.

pH Scale

The scale ranges from 0-14

What is the neutral point on this scale?

What number is maximum acidity?

What number is maximum alkalinity?

pH Scale

Each unit on the scale represents a logarithm: pH = 1

log[H+]

Therefore, pH = -log[H+]

Definition of logarithm

A logarithm is a mathematical concept that eases the calculation of large numbers. The log of a number is the exponent of the power to which a given base must be raised to equal that number.

T he log of 100 is 2 (100=10 2 )

T he log of 1,000 is 3 (1,000 = 10 3 )

Brady Paramedic Emergency Care, p. 284

pH Scale

What is the pH of a 0.0020 M solution of HCl?

Answer:

pH = -log[H+]

pH = -log (2.0 x 10 -3 )

= -(log 2.0 + log 10 -3 )

= -[0.30 + (-3)]

=-(-2.70)

Therefore, pH = 2.70

General Chemistry, 4e; pp. 551, A-6

pH Scale

Because of the logarithmic nature of the pH scale, there is a 10-fold difference between each unit on the scale.

Therefore, multiply by 10 for every 1 point of increase or decrease on the scale.

A pH of 5.0 is 10x as acidic as a pH of 6.0

pH Scale

A pH of 4.0 is how many times as acid as a pH of 6.0?

Answer: 100 times (10x10 = 100)

A pH of 11.0 is how many times as alkaline as a pH of 7.0?

Answer: 10,000 times (10x10x10x10 = 10,000)

Acids

What is an acid?

It is neither LSD nor crud on your battery terminals!

It is a substance that increases H + ions in water. Increasing acidity is expressed as a number LESS than 7.

What is a base?

a. A substance, which in water, is equal to increasing the concentration of OH - ions

b. What you slide into after a good hit in baseball

c. A substance that decreases the concentration of H + ions

d. Somewhere you can call for medical consultation

Human Beings

Extraordinarily sensitive to pH changes

Most material within cells = 6.8

Blood plasma = 7.35-7.45

Fluids around cells = 7.2-7.3

What are the maximum acid and alkaline pH values that are still conducive to (barely) maintaining life?:

6.9 on the acidotic side

7.8 on the alkalotic side

Let’s draw a pH scale!

Need: paper and a writing utensil

Activity:

1. Draw the pH scale with a straight, horizontal line. Label it with numbers from 0 to 14

0 on the far left and 14 on the far right

Add these to your pH scale (There is one for each number.)

Oven cleaner

Tomatoes

Stomach acid

Baking soda

Black coffee

Urine

Lemon juice

Beer

Sea water

Household ammonia

Bicarbonate of soda

Great Salt Lake

Hydrochloric acid

Distilled water

Sodium hydroxide

Answers…How many do you have correct?

pH 0-hydrochloric acid

pH 1-stomach acid

pH 2-lemon juice

pH 3-ice cold beer (also, cola and vinegar)

pH 4-tomatoes

pH 5-hot, black coffee

pH 6-urine (saliva is 6.5)

pH 7-distilled water (blood is 7.4)

pH 8-sea water

pH 9-baking soda

pH 10-Great Salt Lake

pH 11-household ammonia

pH 12-bicarbonate of soda

pH 13-oven cleaner

pH 14-sodium hydroxide (NaOH) Paramedic Field Care, p. 116

Buffers

“ A substance, especially a salt of the blood, tending to preserve original hydrogen-ion concentration of its solution, upon adding an acid or base.

… principal blood buffers include carbonic acid, carbonates, bicarbonates, monobasic and dibasic phosphates, and proteins. Hemoglobin is an important protein buffer.”

Taber’s Cyclopedic Medical Dictionary, 18th ed, p. 275

Buffers and pH Balance

pH balance is carefully regulated by three bodily systems:

blood chemicals

lungs

kidneys

Bicarbonate-Carbonic Acid Buffer

This is the first and quickest way of maintaining acid-base balance.

This buffer is dependent upon the lung and kidney buffers:

Respiratory Renal

CO 2 + H 2 O H 2 CO 3 H + + HCO 3 -

Carbonic Acid

Blood Buffer

Bicarbonate-Carbonic Acid Buffer

Reaction occurs mostly in erythrocytes

About 80% of extracellular fluid buffering occurs by way of this buffer system

There are 20 parts of HCO 3 - (bicarbonate)

to every 1 part of H 2 CO 3 (carbonic acid).

What do each of these represent?

CO 2

H 2 O

H 2 CO 3

H +

HCO 3 -

O 2

Bonus: CO

carbon dioxide

water

carbonic acid

hydrogen

bicarbonate

oxygen

carbon monoxide

Respiratory Buffer System

Second fastest; reacts in 1-3 minutes

“ Triggered by the action of chemoreceptors in the respiratory centers of the brain stem that detect pH in cerebrospinal fluid” Paramedic Field Care, p. 115

Respiratory Buffer System

Example:

Patient with diabetic ketoacidosis (DKA)

What type of respirations will this person have and why?

Rapid and deep respirations…They indicate that the respiratory system is blowing off CO 2 and H 2 O to rid the body of excess acid by producing a RESPIRATORY ALKALOSIS.

This is how the body tries to compensate for the METABOLIC ACIDOSIS brought on by the DKA.

Paramedic Field Care, p. 115-116

Renal (Kidneys) Buffer System

Slowest; takes hours to days but provides long-term acid-base balance maintenance

Kicks in when blood buffers and respiratory buffers are slacking off!

Kidneys regulate pH by excreting excess H + or HCO 3 - ions

Renal (Kidneys) Buffer System

What will the kidneys eliminate if the pH of the extracellular fluid is decreasing?

H + ions

What will the kidneys eliminate if the pH of the extracellular fluid is increasing?

HCO 3 - ions

Normal Arterial Blood Gas Values

pH

PaO 2

PaCO 2

HCO 3

7.35 - 7.45

90%-100%

35 - 45

22 - 26 mEq/l

Normal Arterial Blood Gas Values

Normal PaO 2 depends

on altitude…therefore, the “full range”

of normal PaO 2 is 70%-100%. Paramedic Field Care, p. 117

Arrange the blood gas values

1. Normal range for pH

2. Normal range for PaO 2

3. Acidotic range for pH

4. Normal range for PaCO 2

5. Alkalotic range for pH

6. Normal range for HCO 3 -

7. Acidotic range for PaCO 2

8. Alkalotic range for PaCO 2

22 - 26 mEq/l

7.35 - 7.45

Over 45

70%-100%

35 - 45

Below 35

Over 7.45

Below 7.35

Respiratory Derangements

Respiratory

Acidosis_________

Caused by retention of CO 2

pH is decreased

CO 2 level is increased

Respiratory Alkalosis________

Caused by excessive elimination of CO2

pH is increased

CO2 level is decreased

Respiratory Derangements

Respiratory

Acidosis_________

What are some causes for the retained CO 2 ?

What is the treatment?

Respiratory Alkalosis________

What are some causes for the loss of CO 2 ?

Metabolic Derangements

Metabolic

Acidosis_________

Caused by production of metabolic acids

pH is decreased

CO 2 level is normal

Metabolic Alkalosis________

Caused by excessive diuretics, prolonged emesis, or too much bicarb administration

pH is increased

CO 2 level is normal

Metabolic Derangements

Metabolic

Acidosis_________

What are some causes for the production of metabolic acids?

Metabolic Alkalosis________

What are some causes for the alkalosis?

Respiratory Acidosis

What is it?

What are the lab values?

Numerous causes:

Central - narcotic, sedative, alcohol overdose; CNS lesions

Neuromuscular - hypokalemia, botulism

Thoracic-pulmonary - pneumonia, smoke inhalation, pneumothorax

Airway obstruction - foreign body

Adapted from Haddad’s Poisoning and Drug Overdose , p. 141

Respiratory Alkalosis

What is it?

Numerous causes:

General - anxiety, pain, fever, encephalitis, meningitis sedative

Peripheral - hypotension, hypoxemia, CHF, pulmonary embolism

Miscellaneous - mechanical ventilation, sepsis, cirrhosis

Metabolic Acidosis

What is it?

Numerous causes:

Renal failure, diabetic ketoacidosis, ibuprofen overdose, antifreeze ingestion (ethylene glycol intoxication)

Diarrhea, parenteral alimentation, hydrochloric acid ingestion

Adapted from Haddad’s Poisoning and Drug Overdose , p. 122, 133

Metabolic Alkalosis

What is it?

Numerous causes:

Sodium chloride-responsive - diuretics, cystic fibrosis

Sodium chloride-resistant - licorice ingestion, chewing tobacco

Miscellaneous - bicarbonate administration, penicillin, milk-alkali syndrome

What’s the matter?

pH: 7.20, PCO 2 : 30, HCO 3 - : 16

Respiratory alkalosis, metabolic acidosis

POTENTIAL CAUSE? Shock

pH: 7.60, PCO 2 : 27, HCO 3 - : 23

Respiratory alkalosis

POTENTIAL CAUSE? hyperventilation

What’s the matter?

pH: 7.12, PCO 2 : 68, HCO 3 - : 29

Respiratory acidosis, metabolic alkalosis

POTENTIAL CAUSE? Long-term COPD’er

pH: 7.2, PCO 2 : 60, HCO 3 - : 14

Respiratory acidosis, metabolic acidosis

POTENTIAL CAUSE? Cardiac arrest

Clinical Features

RESPIRATORY

ACIDOSIS

Altered LOC

Tachycardia

Cardiac dysrhythmias

Diaphoresis

Visual disturbances

Headache

Abnormal breathing

Clinical Features

RESPIRATORY

ALKALOSIS

Circumoral paresthesia

Digital paresthesia

Carpopedal spasm

Altered LOC

Seizures

Tetany

(All are related to neuromuscular irritability.)

Clinical Features

METABOLIC

ACIDOSIS

Tachycardia

Pulmonary edema

Decreased cardiac output

Tachypnea

Deep breathing

Confusion - coma

Clinical Features

METABOLIC

ALKALOSIS

Neuromuscular irritability

Seizures

Tetany

Delirium

Hyperreflexia

Headache

Abnormal breathing

Super Mind Tank Scenarios

1. Break into groups of 2-3 people

2. Design a scenario to share with the class. Create it so that you can ask the audience at least 2 questions about your patient.

3. Include the following in your scenario:

Patient chief complaint

Physical exam findings

Vital signs

Patient pH, PaCO 2 , and HCO 3 -

Objectives Assessment

Can you describe pH, acid, base, and buffer?

Are you able to compare and contrast the three buffer systems?

Can you arrange the normal blood gas values?

Are you able to differentiate blood gas values for respiratory and metabolic acidosis and alkalosis?

Can you evaluate common conditions that

may cause acidosis and/or alkalosis?

THANK YOU Feel free to contact me or the rest of our team if you have any questions or comments: Anne - 303.765.6367 Porter, Littleton and Parker EMS 303-765-6EMS