alterations in arterial blood gases

What is the

Measurement of partial pressure of oxygen (O2), carbon dioxide (CO2), pH (acid/base), and bicarbonate (HCO3) in the bloodstream.

Arterial blood gases (ABGs)

What does Increased H+ ions in the body; pH is < 7.35, mean?

acidosis

What are the acids

H+, H2CO3(carbonic acid)

1. CO2 = a potential acid and normal by-product of metabolism; excess CO2 in the bloodstream combines with H2O to create carbonic acid (H2CO3) 

2. Acids are produced during metabolic processes 

What is a potential acid and normal by-product of metabolism; excess CO2 in the bloodstream combines with H2O to create carbonic acid (H2CO3) 

CO₂

excess CO2 in the bloodstream combines with H2O to create…

carbonic acid (H2CO3) 

Acids are produced during….

metabolic processes

What does decreased H+ ions in the bloodstream; pH is > 7.45, mean?

alkalosis

What is the

Difference between extracellular anions and cations; assists in identification of metabolic acidosis

anion gap

What is the..

Level of excess or insufficient bicarbonate in body

Base excess

What are the bases

HCO₃ (bicarbonate)

What are chemical substances that balance or “buffer” the pH by releasing or binding H+ 

buffer

What is the body’s method of keeping the pH at a controlled level 

Compensatory Mechanisms

What is the

“pressure exerted by a single gas” 

1. When O2 and CO2 are reported on an ABG result, it is the partial pressure that is being reported 

2. pO2, pCO2 

partial pressure

When O2 and CO2 are reported on an ABG result, what is being reported

partial pressure

What is the

number of H+ ions in the bloodstream 

1. Increased H+ = decreased pH (acidosis) 

2. Decreased H+ = Increased pH (alkalosis)

pH

Increased H+ =

decreased pH (acidosis)

Decreased H+ =

increased pH (alkalosis)

REGULATION OF PH 

The body’s number one goal is: KEEP pH within normal limits

Buffers

• Bind or release H+ ions 

• Working all the time 

• Examples: proteins, carbonic acid-bicarbonate, phosphate

Lungs

• elimnates CO₂ when exhaling

• may speed up respiratory rate or slow down, depending on pH level 

• Responds to change in pH in 1-3 minutes and lasts 12-24 hours 

• Cannot eliminate H+ 

Kidneys

• Responsible for producing, excreting, and retaining HCO3(bicarbonate) 

• Excrete H+ 

• Responds to change in pH within ~ 24 hours; lasts until the pH is normalized 

What is the body’s one goal?

keep pH within normal limits

What..

1. Bind or release H+ ions 

2. Working all the time 

3. Examples: proteins, carbonic acid-bicarbonate, phosphat

buffers

What..

1. Eliminates CO2_ when exhaling 

2. May speed up respiratory rate or slow down, depending on pH level 

3. Responds to change in pH in 1-3 minutes and lasts 12-24 hours 

4. Cannot eliminate H+ 

lungs

What..

1. Responsible for producing, excreting, and retaining HCO3(bicarbonate) 

2. Excrete H+ 

3. Responds to change in pH within ~ 24 hours; lasts until the pH is normalized 

kidneys

Normal ranges for ABG results

• pH = 7.35 – 7.45 

• pO2 = 80 – 100 mmHg 

• pCO2 = 35 – 45 mmHg 

• HCO3 = 22-26 mEq/L 

• SaO2 = 95 – 100% 

• Base Excess -2 to +2 mEq/L 

What is the normal pH range for ABG results

7.35 – 7.45 

What is the normal pO2 range for ABG results

80 – 100 mmHg 

What is the normal pCO2 range for ABG results

35 – 45 mmHg

What is the normal HCO3(bicarbonate) range for ABG results

22-26 mEq/L

What is the normal SaO2 range for ABG results

95 – 100%

What is the normal Base excess range for ABG results

-2 to +2 mEq/L

ABG results have three-part names, name them 

_Compensation   Origin   Acidosis/Alkalosis(we start here)  

Six steps to ABG interpretation: 

Pro tip: Draw up(if high), down(if low), or side-ways(if normal) arrows next to values! 

Step 1: Check the pH 

• Is the pH normal?  

• Is the pH low? (Acidosis) 

• Is the pH high? (Alkalosis) 

Step 1 gives us the last name of the ABG: acidosis

Step 2: Check the pCO2 

• Is the pCO2 normal? 

• Is it low? 

• Is it high? 

Step 3: Check the HCO3 

• Is the HCO3 normal? 

• Is it low? 

• Is it high? 

Step 4: Determine if it is a respiratory (CO2) or metabolic (HCO3) problem 

	pH	pCO2	HCO3
Respiratory Acidosis	Low	High	Normal
Respiratory Alkalosis	High	Low	Normal
Metabolic Acidosis	Low	Normal	Low
Metabolic Alkalosis	High	Normal	High

Step 4 gives us the middle name of the ABG: ____respiratory_________ 

Step 5: Assess for compensation (has the body started compensating in order to fix the pH) 

• Uncompensated 

  • pH and one other value (pCO2 or HCO3) are out of range 

• Partially Compensated 

  • pH, pCO2, and HCO3 are all out of range 

• Fully Compensated 

  • pH is normal 

  • pCO2 and HCO3 are both out of range 

• Is the pH closer to acidosis or alkalosis? 

• pH < 7.40 = acidosis 

• pH > 7.40 = alkalosis 

Step 5 gives us the first name of the ABG: uncompensated

Name: uncompensated respiratory acidosis  

Step 6: Analyze the pO2 and SaO2: Are these values normal, low (hypoxemia!), or high?

What is step 1 of ABG interpretation??

• Is the pH normal?  

• Is the pH low? (Acidosis) 

• Is the pH high? (Alkalosis) 

Step 1 gives us the last name of the ABG:

What is step 2 of abg interpretation

• Is the pCO2 normal? 

• Is it low? 

• Is it high? 

What is step 3 of abg interpretation

• Is the HCO3 normal? 

• Is it low? 

• Is it high? 

step 4 of abg interpretation

Determine if it is a respiratory (CO2) or metabolic (HCO3) problem 

	pH	pCO2	HCO3
Respiratory Acidosis	Low	High	Normal
Respiratory Alkalosis	High	Low	Normal
Metabolic Acidosis	Low	Normal	Low
Metabolic Alkalosis	High	Normal	High

Step 4 gives us the middle name of the ABG:

step 5 of abg interpretation

Assess for compensation (has the body started compensating in order to fix the pH) 

• Uncompensated 

  • pH and one other value (pCO2 or HCO3) are out of range 

• Partially Compensated 

  • pH, pCO2, and HCO3 are all out of range 

• Fully Compensated 

  • pH is normal 

  • pCO2 and HCO3 are both out of range 

    • Is the pH closer to acidosis or alkalosis? 

    • pH < 7.40 = acidosis 

    • pH > 7.40 = alkalosis 

What compensation is this

• pH and one other value (pCO2 or HCO3) are out of range 

uncompensated

What compensation is this

• pH, pCO2, and HCO3 are all out of range 

partially compensated

What compensation is this

• pH is normal 

• pCO2 and HCO3 are both out of range 

  • Is the pH closer to acidosis or alkalosis? 

  • pH < 7.40 = acidosis 

  • pH > 7.40 = alkalosis 

fully compensated

step 6 of abg interpretation

Analyze the pO2 and SaO2: Are these values normal, low (hypoxemia!), or high? 

ABG practice problem:

pH: 7.60 pCO2: 43 HCO3: 32

uncompensated     metabolic      alkalosis   

  first name               middle               last 

ABG practice problem:

 pH: 7.32 pCO2: 71 HCO3: 30

partially compensated      respiratory            acidosis   

  first name                          middle                       last 

ABG PRACTICE

 pH: 7.35    pCO2: 32 HCO3: 19

  fully compensated         metabolic            acidosis  

  first name                          middle                   last 

RESPIRATORY ACIDOSIS (Low pH, Co2 high) 

Lungs do not rid the body of excess CO2; excess CO2 binds with H20 forming H2CO3 

Causes:​ 

Inadequate ventilation due to 

• CNS depression 

• Breathing center in brain so if something suppressing it its going to tell you not to breathe as much, less we breathe= more CO2 we retain 

• Narcotics, sedatives, analgesia 

• Impaired respiratory function due to trauma 

• Pneumonia, atelectasis, pulmonary edema 

Manifestations: 

• Headache, behavioral changes/confusion 

• Weakness 

• Tremors 

• Paralysis 

• Stupor —> coma 

• Warm/flushed skin 

Compensation(is in the kidneys): The kidneys compensate by producing more HCO3. 

What are causes of  

RESPIRATORY ACIDOSIS (Low pH, Co2 high) 

Inadequate ventilation due to 

• CNS depression 

• Breathing center in brain so if something suppressing it its going to tell you not to breathe as much, less we breathe= more CO2 we retain 

• Narcotics, sedatives, analgesia 

• Impaired respiratory function due to trauma 

• Pneumonia, atelectasis, pulmonary edema 

What are manefestations of RESPIRATORY ACIDOSIS (Low pH, Co2 high) 

• Headache, behavioral changes/confusion 

• Weakness 

• Tremors 

• Paralysis 

• Stupor—> coma 

• Warm/flushed skin 

What is the compensation of RESPIRATORY ACIDOSIS (Low pH, Co2 high) 

Compensation(is in the kidneys): The kidneys compensate by producing more HCO3. 

RESPIRATORY ALKALOSIS (high pH >7.45, Low CO2 <35) 

Causes: 

Hyperventilation secondary to 

• Pain 

• Anxiety 

• Fear 

• Fever 

• Sepsis 

• CNS lesions 

Manifestations: 

• Constriction of cerebral vessels 

• Dizziness/Panic 

• Light-headedness 

• Tetany 

• Numbness/tingling of digits 

• Seizures 

• Cardiac dysrhythmias 

Compensation: The kidneys compensate by decreasing the production of HCO3. 

What are causes of RESPIRATORY ALKALOSIS (high pH >7.45, Low CO2 <35) 

Hyperventilation secondary to 

• Pain 

• Anxiety 

• Fear 

• Fever 

• Sepsis 

• CNS lesions

What are manefestations of RESPIRATORY ALKALOSIS (high pH >7.45, Low CO2 <35) 

• Constriction of cerebral vessels 

• Dizziness/Panic 

• Light-headedness 

• Tetany (involuntary muscle cramp or spasm)

• Numbness/tingling of digits 

• Seizures 

• Cardiac dysrhythmias 

What compensation does repiratory alkalosis have

The kidneys compensate by decreasing the production of HCO3. 

METABOLIC ACIDOSIS (low pH < 7.35, low HCO3 <22) 

Usually secondary to significant health problems such as DKA and CKD 

Causes: 

• Decreased HCO3 production 

• Excess HCO3 loss 

• Decreased acid excretion by kidneys 

• Increased acid production 

• Aspirin toxicity 

• Starvation 

• Anaerobic metabolism 

Manifestations: 

• HYPERkalemia 

  • high potassium

• Anorexia, N/V, abdominal pain 

• Weakness 

• Confusion, stupor, or coma 

• Peripheral vasodilation 

• Dysrhythmias 

• Warm/flushed skin 

• Bone disease 

Compensation(IN THE LUNGS): The lungs compensate by increasing the rate and depth of breathing (exhaling more CO2). Called “Kussmaul’s Respirations” 

What are causes of METABOLIC ACIDOSIS (low pH < 7.35, low HCO3 <22)

• Decreased HCO3 production 

• Excess HCO3 loss 

• Decreased acid excretion by kidneys 

• Increased acid production 

• Aspirin toxicity 

• Starvation 

• anaerobic metabolism

What are manefestations of METABOLIC ACIDOSIS (low pH < 7.35, low HCO3 <22) 

• HYPERkalemia 

• Anorexia, N/V, abdominal pain 

• Weakness 

• Confusion, stupor, or coma 

• Peripheral vasodilation 

• Dysrhythmias 

• Warm/flushed skin 

• Bone disease 

What is the compensation for METABOLIC ACIDOSIS (low pH < 7.35, low HCO3 <22) 

(IN THE LUNGS): The lungs compensate by increasing the rate and depth of breathing (exhaling more CO2). Called “Kussmaul’s Respirations” 

What is “Kussmaul’s Respirations” 

The lungs compensate by increasing the rate and depth of breathing (exhaling more CO2)

METABOLIC ALKALOSIS (ph > 7.45, HCO3 > 26) 

Causes: 

• Increased renal production of HCO3 

• Excess ingestion of alkali substances 

  • Ex: baking soda  

• GI suctioning, vomiting, bulimia nervosa 

• Diuretic therapy 

• Excess adrenocorticosteroid hormones 

Manifestations: 

• HYPOkalemia 

• Hyperactive reflexes 

• Tetany 

• Confusion, seizures 

• Hypotension 

• Dysrhythmias 

Compensation(IN THE LUNGS): The lungs compensate by decreasing the respiratory rate (retaining CO2). 

What are causes of METABOLIC ALKALOSIS (ph > 7.45, HCO3 > 26) 

• Increased renal production of HCO3 

• Excess ingestion of alkali substances 

• Ex: baking soda  

• GI suctioning, vomiting, bulimia nervosa 

• Diuretic therapy 

• Excess adrenocorticosteroid hormones 

What are manefestations of METABOLIC ALKALOSIS (ph > 7.45, HCO3 > 26) 

• HYPOkalemia 

• Hyperactive reflexes 

• Tetany 

• Confusion, seizures 

• Hypotension 

• Dysrhythmias 

What is the compenstation for METABOLIC ALKALOSIS (ph > 7.45, HCO3 > 26) 

(IN THE LUNGS): The lungs compensate by decreasing the respiratory rate (retaining CO2).