Acid Base Balance

Acid Base Balance

Ana Corona, MSN, FNP-C

Nursing Instructor

September 2007

Definitions Acidosis (acidemia) occurs when pH drops below

7.35

Alkalosis (alkalemia) occurs when the pH rises above 7.45

A primary respiratory problem is determined if the PaC02 is less than 35mmHg(alkalosis) or greater than 45 mmHg(acidosis).

A primary metabolic problem is when the HC03 is less than 22mEq/L (acidosis) or greater than 26mEq/L(alkalosis).

Metabolic Acidosis

Clinical Manifestations hyperkalemia: shift of acid to ICF and K+ to

the ECF anorexia, nausea, and vomiting warm, flushed skin cardiac dysrhythmias & CNS dysfunction headache, diarrhea, tremors

Metabolic Acidosis: Etiology

Loss of base: such as in cases of severe diarrhea or Gain of metabolic acids: Anaerobic metabolism; Drug overdose (e.g.salicylates); Renal failure; Diabetic ketoacidosis

Decreased blood pH; decreased HCO3 normal PaCO2 or decreased if compensation is

occurring.

Metabolic Acidosis Nursing Intervention

Assess the clinical symptoms, health history, and lab results.

Identify the underlying cause to intervene appropriately.

When there is severe acidosis (pH < 7.1), sodium bicarbonate is necessary to bring the pH to a safe level.

Correct the sodium and water deficits, as well.

Metabolic Alkalosis

Clinical Manifestations cardiac dysrhythmias; seizures; confusion;

muscle twitching, agitation >pH;>HC03; normal PaCo2 or elevated if

compensation occurs

Metabolic Alkalosis: Etiology

Loss of metabolic acids: such as in cases of prolonged vomiting or gastrointestinal suctioning. Hyperaldosteronism can cause sodium retention and loss of hydrogen ions and potassium. or Gain of Base: an increased intake of bicarbonate. Diuretics (e.g. Lasix) can cause sodium, potassium, and chloride excretion more than bicarbonate excretion.

Metabolic Alkalosis

Increased blood pH increased HCO3 normal PaCO2 or elevated if compensation is

occurring.

Metabolic Alkalosis Nursing Intervention Assess the clinical symptoms, health history, and

lab results. Identify the underlying cause to intervene

appropriately. If potassium levels are decreased administer

potassium as ordered per physician. If acid-base disturbance is due to hypochloremic

alkalosis with volume depletion, administer a sodium chloride IV solution.

If the condition is caused by hyperaldosteronism, administer potassium.

Respiratory Acidosis

Clinical Manifestations > PaCo2; HCO3 is normal or > with renal

compensation vasodilatation; cardiac dysrhythmias,

tachycardia, somnolence, decreased ventilation

Respiratory Acidosis etiology

Carbon dioxide is retained when ventilation is depressed; therefore, leading to acidosis and hypercapnia (excess PaCO2).

Decreased blood pH Increased PaCO2 Normal HCO3 or elevated if compensation is

occurring.

Respiratory Acidosis Nursing Intervention



Restore alveolar ventilation (this will remove excess CO2), and if spontaneous ventilation is compromised (e.g. due to drug overdose or neuromuscular disorders) provide mechanical ventilation.

Respiratory Acidosis Nursing Intervention Monitor the pH, PaCO2, PaO2, and HCO3 very

closely. A rapid decline of the PaCO2 can lead to respiratory

alkalosis with seizures and death. Check for hypoxemia and hypercapnia when

administering oxygen. Oxygen can work as a respiratory depressant when

the person's respiratory center is no longer stimulated by a low pH and elevated PaCO2.

Renal buffering generally corrects an uncomplicated chronic respiratory acidosis.

Respiratory Alkalosis

Clinical Manifestations > pH; < PaC02; HCO3 normal or low due to

compensation nausea, vomiting, tingling of fingers

Respiratory Alkalosis Etiology

Occurs when there is alveolar hyperventilation and a decrease in PaCO2 (hypocapnia).

Hypoxemia (caused by pulmonary disease, high altitudes, or congestive heart failure), hypermetabolic conditions (fever or anemia), gram-negative sepsis, hysteria, or cirrhosis of the liver can stimulate hyperventilation.


Increased blood pH Decreased PaCO2 Normal HCO3 or decreased if compensation

is occurring.

Respiratory Alkalosis Nursing Interventions



Correct the hypoxemia and reverse the hypermetabolic states if present.

Correct symptoms from hysterical hyperventilation by rebreathing from a paper bag (increases PaCO2).

Basic Questions There are three critical questions to keep in mind

when attempting to interpret arterial blood gases (ABGs).

First Question: Does the patient exhibit acidosis or alkalosis? Second Question: What is the primary problem? Metabolic? or Respiratory? Third Question: Is the patient exhibiting a compensatory state?

In order to understand ABG analysis and remember what is abnormal, you need to review what is normal.

Remember Definitions Acidosis (acidemia) occurs when pH drops below

7.35

Alkalosis (alkalemia) occurs when the pH rises above 7.45

A primary respiratory problem is determined if the PaC02 is less than 35mmHg (alkalosis) or greater than 45 mmHg (acidosis).

A primary metabolic problem is when the HC03 is less than 22mEq/L (acidosis) or greater than 26mEq/L (alkalosis).

Assessment Step 1

Step One: Determine the acid/base status of the arterial blood. Keep in mind what is Normal

If the blood's pH is less than 7.35 this is an acidosis, and if it is greater than 7.45 this is an alkalosis.

You may hear nurses or doctors say: "The patient is 'acidotic' or 'alkalotic'

Assessment Step 2

Once you have determined the pH, you can move on to determine the 'primary' problem, or which system, respiratory or metabolic is the prime messenger.

Respiratory System Carbon Dioxide acts as the ‘acid’ of the human

body, you will be able to determine if the primary acid-base imbalance is respiratory.

Chemically speaking, there is an equilibrium between carbonic acid and bicarbonate.

Therefore, just remember that an increased PaCO2 (>45mmHg) along with an acidosis (pH < 7.35) represents a RESPIRATORY ACIDOSIS.

If you have a situation where there is a decreased PaCO2 (less than 35mmHg) and an alkalosis (pH greater than 7.45) you will have a RESPIRATORY ALKALOSIS! Easy. Right?

Metabolic System

Keep in mind that HCO3 represents a ‘base’ situation, and if there is an increased HCO3 (greater than 26 mEq/L) in an alkalotic environment (pH greater than 7.45) there is a METABOLIC ALKALOSIS.

On the opposite side of the coin, if there is a decreased HCO3 (less than 22 mEq/L) in an acidic environment (pH less than 7.35) this will be representative of METABOLIC ACIDOSIS.

Compensation

Our bodies have compensatory mechanisms that assist us to return to a state of homeostasis (equilibrium).

The body attempts to compensate for whatever the primary problem is in an effort to return the acid-base balance to normal.

An illustration of COMPENSATION is given below:

A newly diagnosed Type 1 diabetic client has a ‘primary’ problem of metabolic acidosis (pH 7.29; HCO3 16 mEq/L) due to an increase in ketone bodies (ketoacidosis).

The nurse notes that the ABGs show a below normal PaCO2 value (27mmHg) and the client is breathing faster in an attempt to ‘blow off’ the carbon dioxide (CO2:’acid’) to create a respiratory alkalosis, the opposite of metabolic acidosis!

Hint! In order to recognize ‘compensation’ look for a change in the buffering system that was not involved in the ‘primary’ problem.

Review the three essential steps of ABG analysis

Number One: Determine if the client is demonstrating an acidotic (remember: pH less than 7.35) or alkalotic (pH greater than 7.45).

Number Two:

What is the 'primary problem?

If the client is acidotic with a PaC02 greater than 45 mmHg it is RESPIRATORY

If the client is acidotic with a HC03 less than 22 mEq/L it is METABOLIC!

If the client is alkalotic with a PaC02 less than 35 mmHg it is RESPIRATORY!

If the client is alkalotic with a HC03 greater than 26 mEq/L it is METABOLIC!

Number Three:Is the client compensating?

Are both components (HCO3 and PaCO2) shifting in the same direction?

Up or down the continuum? Above or below the normal ranges? If this is noted, you know that the client’s buffering

systems are functioning and are trying to bring the acid-base balance back to normal.

Case Study 1 A client recovering from surgery in the post-anesthesia care unit is difficult to arouse two hours following surgery. The nurse in the PACU has been administering Morphine Sulfate intravenously to the client for complaints of post-surgical pain. The client’s respiratory rate is 7 per minute and demonstrates shallow breathing. The patient does not respond to any stimuli! The nurse assesses the ABCs (remember Airway, Breathing, Circulation!) and obtains ABGs STAT! The STAT results come back from the laboratory and show:

pH = 7.15 Pa C02 = 68 mmHg HC03 = 22 mEq/L

1. Compensated Respiratory Acidosis2. Uncompensated Metabolic Acidosis3. Compensated Metabolic Alkalosis4. Uncompensated Respiratory Acidosis

Answer

The answer is #1

uncompensated respiratory acidosis

Case Study 2 An infant, three weeks old, is admitted to the Emergency Room.

The mother reports that the infant has been irritable, difficult to breastfeed and has had diarrhea for the past 4 days. The infant’s respiratory rate is elevated and the fontanels are sunken. The Emergency Room physician orders ABGs after assessing the ABCs.

The results from the ABGs come back from the laboratory and show:


1. Compensated Respiratory Alkalosis2. Uncompensated Metabolic Acidosis3 Compensated Metabolic Acidosis4 Uncompensated Respiratory Acidosis

Answer

Answer is #3 Compensated Metabolic Acidosis

Case Study 3 A client, 5 days post-abdominal surgery, has a nasogastric tube.

The nurse notes that the nasogastric tube (NGT) is draining a large amount (900 cc in 2hours) of coffee ground secretions. The client is not oriented to person, place, or time. The nurse contacts the attending physician and STAT ABGs are ordered.



1. Compensated Respiratory Alkalosis 2. Uncompensated Metabolic Acidosis 3. Compensated Metabolic Acidosis 4. Uncompensated Metabolic Alkalosis

Answer

Answer is #4 Uncompensated Metabolic Alkalosis

Case Study 4 A client is admitted to the hospital and is being prepared for a

craniotomy (brain surgery). The client is very anxious and scared of the impending surgery. He begins to hyperventilate and becomes very dizzy. The client looses consciousness and the STAT ABGs reveal:



1. Compensated Metabolic Acidosis 2. Uncompensated Metabolic Acidosis 3. Uncompensated Respiratory Alkalosis 4. Uncompensated Respiratory Acidosis

Answer

The answer is #3 Uncompensated Respiratory Alkalosis

Case Study 5 A two-year-old is admitted to the hospital with a diagnosis of

asthma and respiratory distress syndrome. The father of the infant reports to the nurse that he has observed slight tremors and behavioral changes in his child over the past three days. The attending physician orders routine ABGs following an assessment of the ABCs. The ABG results are:


1. Compensated Respiratory Alkalosis 2. Uncompensated Metabolic Acidosis 3. Compensated Respiratory Acidosis 4. Uncompensated Respiratory Alkalosis

Answer

Answer is #3 Compensated Respiratory Acidosis

Case Study 6 A young woman, drinking beer at a party, falls and

hits her head on the ground. A friend dials "911" because the young woman is unconscious, depressed ventilation (shallow and slow respirations), rapid heart rate, and is profusely bleeding from both ears.

Which primary acid-base imbalance is this young woman at risk for if medical attention is not provided?

1. metabolic acidosis 2. metabolic alkalosis 3. respiratory acidosis 4. respiratory alkalosis

Answer

Correct answer is #3 Respiratory Acidosis

Case Study 7 An 11-year old boy is admitted to the hospital with

vomiting, nausea and overall weakness. The nurse notes the laboratory results: potassium: 2.9 mEq.

Which primary acid-base imbalance is this boy at risk for if medical attention is not provided?

1. metabolic acidosis

2. metabolic alkalosis

3. respiratory acidosis

4. respiratory alkalosis

Answer

Correct Answer is #2 Metabolic Alkalosis

Case Study 8

An elderly gentleman is seen in the emergency department at a community hospital. He admits to taking many tablets of aspirin (salicylates) over the last 24-hour period because of a severe headache. He complains of an inability to urinate. His vital signs are: Temp = 98.5; apical pulse = 92; respiration = 30 and deep.

Which primary acid-base imbalance is the gentleman at risk for if medical attention is not provided?


Answer

Correct Answer is #1 Metabolic Acidosis

Case Study 9 A young man is found at the scene of an automobile accident in

a state of emotional distress. He tells the paramedics that he feels dizzy, tingling in his fingertips, and does not remember what happened to his car. Respiratory rate is rapid at 34/minute.

Which primary acid-base disturbance is the young man at risk for if medical attention is not provided?


Answer

Correct Answer is #4 Respiratory Alkalosis

ACID BASE PARAMETERS

Respiratory Acidosis

PH PCO2 HCO3


PH PCO2 HCO3

Metabolic Acidosis

PH PCO2 HCO3

Metabolic Alkalosis

PH PCO2 HCO3

Acid Base Balance

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