ACID-BASE BALANCE

C Washington RN, MSNEd

Acid-Base Balance

Homeostasis & optimal cellular function Hydrogen ion concentration of body

fluids wnl

Hydrogen ion concentration falls pH rises solution become more alkaline or basic

3 Systems that maintenance pHBuffers Moves or release hydrogen ionsRespiratory system Regulate carbonic acid by eliminating or

retaining CO2Renal system Long term regulation of acid-base in body

ABG Interpretation: 1st Step Determine if the pH represents acidosis

or alkalosis or is perfectly normal

Acid-Base Disorders Hydrogen ions (H+) determines acidity of

body fluids

Acids release H+ ions in solution

Bases accepts H+ ions in solution

Acid-Base Disorders H+ ions concentration of a solution is

measured by its pH

Normal pH 7.35-7.45 (pH of 7 is neutral)

Relationship between H+ ions & pH H+ ion concentration increases

pH falls Solution becomes more acid

H+ ions concentration falls pH rises Solution becomes more alkaline

Acidic or Alkalotic pH 7.0 pH 7.9 pH 7.4 pH 7.5 pH 7.3

Note: pH alone is not sufficient to tell us

whether an imbalance is due to a respiratory or metabolic problem

Evaluate other values of ABGs to determine the primary problem

Or whether the body is attempting to compensate for the imbalance

Regulation of Acid-Base Balance Buffer Systems

Protein molecules, phosphate Helps to maintain a stable pH Removes or release H+ ions Excess acid (acidosis) pH <7.35

buffers bind with H+ ions To alkaline (alkaline) pH >7.45

buffers release H+ ions

Most Important Buffer system Bicarbonate-carbonic acid buffer system Controlled by lungs & kidneys Aeorobic metabolism = to forms of acid

respiratory acid (carbonic acid)

metabolic acids

In order to maintain proper pH balance, the

body attempts to maintain a ratio of 20:1 (bicarb to carbonic acid)

Regulation of Acid-Base Balance Respiratory System

Eliminates or retains carbon dioxide ↑ carbon dioxide (acid) stimulate respiration

↑rate & depth of resp ↓ pH to normal range

Alkalosis depresses respiration ↓ rate & depth of resp retains carbon

dioxideNormal PaCO2 = 35- 45 mmHg

ABG Interpretation: 2nd Step Evaluate the pCO2 Determine if it falls within the acceptable range If pCO2 falls below the lower limit (resp alkalosis) Id pCO2 falls above the upper limit (respiratory

acidosis) High pCO2 represents acidosis (retention of CO2) Note: High value in pH represents alkalosis. High CO2 =CO2 retention or hypoventilation CO2 is acidotic in the blood=respiratory acidosis

Interpreting pCO2 values pCO2 of 22 pCO2 of 32 pCO2 of 35 pCO2 of 40

pCO2 of 45 pCO2 of 50 pCO2 of 60

Regulation of Acid-Base Balance

Renal System Normal bicarbonate 22-26 mEq/L

Acidosis Excess H+ ions pH falls kidneys excrete H+ and retain bicarbonate

Alkalosis Kidneys retains H+ ions excrete bicarbonate

Metabolic Components When there is a loss of acid in the body or An excess base HCO3 will be greater than 26 Resulting in metabolic alkalosis When there is an excess of metabolic acid Or not enough base HCO3 will be less than 22 Causing metabolic acidosis

ABG Interpretation: 3rd Step Determine the direction of the the metabolic

component HCO# Whether it is within normal limits High (metabolic alkalosis) Low (metabolic acidosis)

Think of HCO3 as a base

*too much causes metabolic alkalosis

*too little causes metabolic acidosis

Interpreting HCO3 Values HCO3 of 22 HCO3 of 16 HCO3 of 30

HCO3 of 25 HCO3 of 12 HCO3 of 27

Base Excess (BE) Metabolic component Calculation of circulating buffer/base Normal range BE is -2 to +2

BE of -8 represents a deficit of base=metabolic acidosisBE of +10 representsan excess of base=metabolic alkalosis

Acid-Base Imbalances

Metabolic Alkalosis

Excess HCO3

Caused by diarrhea, steroid or diuretic therapy.

Respiratory Alkalosis

Deficit HCO3

Caused by hyperventilation

Metabolic Acidosis

Deficit HCO3

Common in cases of kidney disease and diabetes

Respiratory Acidosis

Excess HCO3

Caused by hypoventilation

Acid-Base Imbalances Metabolic Acidosis

Ph < 7.35 HCO3- < 22 mEq/L

Respiratory Acidosis pH <7.35 PaCO2 > 45 mmHg

Acid Base Imbalances

Metabolic Alkalosis pH > 7.45 HCO3- > 26 mEq/L

Respiratory Alkalosis pH >7.45 PaCO2 <35 mmHg

Acid Base Imbalance

pH pCO2 HCO3-Respiratory Acidosis

↓ ↑ Normal or ↑

Respiratory Alkalosis

↑ ↓ Normal or ↓

Metabolic Acidosis

↓ ↓ ↓

MetabolicAlkalosis

↑ ↑ ↑

Practice: Analyzing ABGspH pCO2 HCO3 Answer

1 7.41 40 24

2 7.5 42 35

3 6.72 40 5

4 7.26 63 25

5 7.52 18 25

Compensation When there is an imbalance in one

parameter of the buffer system (bicarbonate-kidneys) – carbonic acid (lungs) the other tries to compensate for it by causing the opposite imbalance

Goal: Restore the 20:1 ratio & return the pH back to the acceptable range 7.35-7.45

ABG Interpretation: Final Step Determine if compensation is present

and to what extent When compensation is present, you will

see two imbalances The question-Which is the primary

problem & which imbalance is due to compensation

Compensation The Clue: pH

If the pH is leaning toward acidosis or alkalosis then the parameter with the matching imbalance is the primary problem & the other is due to compensation

Compensation: Example Pt has chronic pulmonary problems & is

in a chronic respiratory acidosis. His kidneys will compensate by retaining

bicarbonate Creating a metabolic alkalosis to balance

his chronic respiratory acidosis

Compensation pH 7.30 acidosis PCO2 70 respiratory acidosis HCO3 30 mild metabolic alkalosis Interpretation

Respiratory acidosis with partial compensation by the kidneys.

The kidneys have only begun to compensate, because the pH is not back to acceptable limits yet

Supplementary Resources Handout:

“Interpreting Arterial Blood Gases”

Nursing Article”Perfecting your acid-base balancing act: How to detect and correct acid-base disorders”

The nursing caring for a patient undergoing several days of gastric decompression recognizes that the patient is at risk for which of the following acid-base imbalances? Metabolic acidosis Metabolic alkalosis Respiratory acidosis Respiratory alkalosis

A patient is admitted with suspected heroin overdose & a resp rate of 5 to 6 per minute. Which of the following assessment data would the nurse anticipate? (select all that apply) pH 7.29 Alert & oriented PaCO2- 54 mmHg HCO3- 32 mEq/L Skin warm & flushed

Client diagnosis: bacterial pneumoniaABGs: pH 7.24, PCO2 65 mmHg & HCO3- 24 mEq/L Antibiotics and O2 started. What is a priority nursing intervention?

Mrs. Mendoza

75-years-old H/O emphysema Adm with Pneumonia Decreased urine

output Lethargy Decreased chest

excursion hypotension

Which assessment data indicate that this client has impaired gas exchange?

Mrs. Mendoza

Which of the following

ABG values indicates that

this client is a CO2retainer?

PaCO2 = 40 mm Hg

PaCO2 = 60 mm Hg

Bicarbonate = 42 PaO2 = 60 mm Hg

Mrs. Mendoza

Baseline ABG’spH 7.36PaCO2 60 mm HgPa02 52 mmHgBicarbonate 42

mEq/L

Which of the following ABGs most likely indicate that she is having a negative response to the administration of oxygen. (next slide)

Mrs. Mendoza pH 7.35 PaCO2 64 mm Hg Pa02 60 mmHg Bicarbonate 42 mEq/L

pH 7.36 PaCO2 60 mm Hg Pa02 60 mmHg Bicarbonate 42 mEq/L

pH 7.36 PaCO2 60 mm Hg Pa02 58 mmHg Bicarbonate 38 mEq/L

pH 7.33 PaCO2 66 mm Hg Pa02 66 mmHg Bicarbonate 42 mEq/L

Mrs Mendoza Based on your answer from the last

slide, is the client’s respiratory acidosis compensated or uncompensated? Explain your answer.

Which immediate interventions are needed for this client.

Mrs Mendoza Later in the shift, you note that his

oxygen is set at 5 L/minute. The client says that he asked the nursing

assistant to turn up his oxygen because he was havng trouble breathing.

What actions, if any, should you take at this time

Mr. Henderson: H/O Cellulites

T 101 F 90/60 SOB Diarrhea 2 days pH 7.30 pCO2 28 Pa02 88 HCO3 17

What is the patients acid

base imbalance?

Mr Williams HCO3 level of 17 mEq/L is a result

of: Respiratory hypoventilation Overelimination of bicarbonate Respiratory compromise Underelimination of hydrogen ions

Mr. Williams

Which of the following symptoms wouldindicate a worsening of the acidotic

condition? Increased blood pressure Anxiety Rising PaCO2 Increased urinary output

Mr. Williams Which of the following

interventions would be critical in reversing the client’s condition?

Explain whether or not bicarbonate would be given to this client to correct her condition

IVFs O2 HCO3 K+

Mr. Williams What other lab

values would be important to monitor at this time? Explain

A patient’s blood pH is decreasing. The nurse realizes that this patient’s

hydrogen ion concentration is:

1. Increasing2. Decreasing3. Being affected by oxygen concentration4. Stabilizing

A patient is admitted with the diagnosis of diabetic ketoacidosis.

The nurse realizes that this patient’s body will attempt to attain acid-base balance by:

1. Decreasing its respiratory rate. 2. Increasing the reabsorption of hydrogen

ions.3. Increasing the secretion of hydrogen

ions.4. Decreasing the reabsorption of

bicarbonate.

A patient has a respiratory rate of 20.

The nurse calculates this patient’s minute ventilation to be:

1. 1 L/min2. 2 L/min3. 5 L/min4. 10 L/min

The nurse, admitting a patient with diabetes, believes the patient is attempting to correct an acidotic condition.

Which of the following did this nurse most likely observe while assessing this patient?

1. Slow methodical respirations2. Deep rapid respirations3. Change in level of consciousness4. Intact extraocular movements

The nurse is caring for a patient with metabolic acidosis.

The nurse realizes that which of the following laboratory values might be altered for this patient?

1. Ammonia2. Blood-urea-nitrogen3. Creatinine4. Prothrombin

The nurse is reviewing a patient’s arterial blood gas results.

Which of the following values should the nurse study first?

1. PaCO2

2. HCO3

3. Compensation4. pH

The nurse is caring for a patient with pneumonia who has arterial blood gas values of: pH 7.20, PaCO2 75, HCO3

- 28, PaO2 44.

Which of the following would be a

priority for this patient?

1. Assisting the patient to breathe into a paper bag.

2. Preparing to administer Sodium Bicarbonate IV.

3. Placement of the patient in high Fowler’s position.

4. Administration of the prn sedative available.

A patient is admitted in respiratory acidosis secondary to barbiturate overdose.

Which of the following will the nurse most likely assess in this patient?

1. Kussmaul’s respirations 2. Seizures3. Slow, shallow respirations4. Increased deep tendon reflexes

The nurse is providing discharge instructions to a patient with respiratory alkalosis.

Which of the following statements indicates the patient understands the instructions?

1. “I will not take my Lasix without a potassium supplement.”

2. “I will not use Mylanta 5-6 times a day like I used to.”

3. “I will take a stress management class or seek counseling.”

4. “I will call my MD the next time I have diarrhea for a few days.”