Arterial Blood Gasses

1
Arterial Blood Gasses

• At the end of this self study the participant
  will
• 1. Correctly identify the following
• Respiratory acidosis
• Respiratory alkalosis
• Metabolic acidosis
• Metabolic alkalosis
• See BJH Policy Arterial Blood Gas Sampling
• Physician alert levels per BJC Laboratory
  (http//www.testcatalog.org/nrr/catalogs/bjc/catal
  og/)

2
pH

• Normal pH 7.35 to 7.45
• For normal metabolism to occur pH must be
  maintained in the normal range
• When the pH is below 7.35, blood is acidic.
• When the pH is above 7.45, blood is alkalotic.
• Physician alert values for blood pH are below 7.2
  OR above 7.6
• Values outside of that range may interfere with
  cellular functioning, and if uncorrected, will
  lead to death.

3
PaCO2 - partial pressure of CO2

• Definition the amount of carbon dioxide gas
  dissolved in the blood
• Normal PaCO2 35-45 mmHg (torr)
• Physician alert value at BJH is 75 mmHg or
  greater
• Carbon Dioxide is acidic
• as PaCO2 ?, pH levels ?, (acidic)
• as PaCO2 ? , pH levels ?, (alkaline)
• Blood carries CO2 to the lungs, where excess CO2
  combines with H2O to form carbonic acid (H2CO3).
• The level of H2CO3 in blood determines blood pH
• H2CO3 triggers the lungs to adjust the rate and
  depth of ventilation to stabilize CO2 .

4
HCO3 (Bicarb) (Base)

• Normal HCO3 22-26 mEq/L
• Kidneys excrete or retain bicarbonate (HCO3)
  according to pH level.
• HCO3 ?, pH levels ? alkaline
• HCO3 ? , pH levels ? acidic
• Kidneys may take from hours to days to correct an
  imbalance.
• Remember the lungs and kidneys work together.
• Goal maintain blood pH by balancing 1 part acid
  to 20 parts base.

5
PaO2 partial pressure of O2

• Normal PaO2 - 80-105 mmHg
• Physician alert value 40 or less
• PaO2 (Partial Pressure of Oxygen) amount of
  oxygen dissolved in the blood. (The other 97 of
  oxygen is attached to the hemoglobin)
• It primarily measures the effectiveness of the
  lungs in pulling oxygen into the blood stream
  from the atmosphere.
• Critical Threshold lt60 mmHg

6
PaO2

• Elevated PaO2 levels are associated with
• Increased oxygen levels in the inhaled air
• Polycythemia
• Decreased PaO2 levels are associated with
• Decreased oxygen levels in the inhaled air
• Anemia
• Heart decompensation
• Chronic obstructive pulmonary disease
• Restrictive pulmonary disease
• Hypoventilation

7
SaO2 Arterial Oxygen Saturation

• Definition of hemoglobin combined with O2 
• Normal SaO2 on room air is in excess of 95.
• deep or rapid breathing can ?to 98-99.
• Oxygen-enriched air (40 - 100), can push SaO2
  to 100.
• Oxygen Saturation will fall if ? O2 available
• increased altitudes.
• Airway obstruction (e.g. asthmatic attack)
• Alveolar lung disease.
• Oxygen Saturation will rise if
• Deep or rapid breathing occurs
• ? oxygen levels (supplemental O2)

8
Summary of ABG Acid/Base
Respiratory Acidosis Respiratory Alkalosis Metabolic Acidosis Metabolic Alkalosis
pH 7.35-7.45 lt7.35 gt7.45 lt7.35 gt7.45
CO2 35-45 gt45 lt35 35-45 35-45
HCO3 22-26 22-26 22-26 lt22 gt26

9
Indications for ABG

• Inadequate Ventilation?
• Not awake or breathing too fast, (concern about
  respiratory muscle fatigue)
• Are there concerns about oxygenation that cant
  be addressed with pulse ox?
• Carbon Monoxide (carboxyhemoglobinemia)
• Methemoglobinemia (e.g., benzocaine intoxication)
• Are there concerns about acid-base balance?
• Sepsis, DKA, Poly-drug overdose
• Chronic CO2 retention
• Miscellaneous
• After intubation
• Monitor vent settings
• Pre-op baseline

10
Potential Electrolyte Changes

• Goal serum electoneutrality
• Acidemia pH below 7.35
• H ions enter cells to correct low plasma pH
• K ions leave cells
• Result possible hyperkalemia
• Alkalosis pH above 7.45
• ? HCO3 will lower H
• K ions enter cell
• Result possible hypokalemia

pH lt 7.35
H
Cell
K
pH gt 7.45
Cell
K

11
ABG Interpretation

• First, pH
• Normal, 7.35-7.45
• If normal, quit here
• Second pH
• pH lt 7.35 Acidosis
• pH gt7.45 Alkalosis
• Third, Cause
• If CO2 is abnormal, respiratory cause
• If HCO3 is abnormal, metabolic cause

12
Respiratory Alkalosis

• pH gt7.45
• pCO2 lt35
• Always due to blowing off carbon dioxide
• hypoxemia
• psychogenic
• compensation for metabolic acidosis
• stimulation of CNS
• inappropriate mechanical ventilation

13
Respiratory Alkalosis Physical Assessment

• Dizziness
• Tingling
• Lightheadedness
• Numbness
• Hypocalcemia
• Hypokalemia (K enters cell for
  electroneutrality)
• Hyperventilation

14
Respiratory Alkalosis Treatment

• Treat cause
• based on pH
• emergent treatment not indicated until pH gt7.55
• Decrease ventilation
• change vent settings, sedation, pain control
• Supportive measures
• Emotional support, relieve stress

15
Respiratory Acidosis

• pH lt7.35
• PCO2 gt45
• Always due to inadequate excretion of carbon
  dioxide.
• Root of problem is Inadequate Alveolar
  Ventilation
• pH term is acidosis
• PCO2 term is hypercarbia

16
Respiratory Acidosis Physical Assessment

• Hypoventilation/Dyspnea
• Mental status changes
• Lethargy
• Headache
• Cough/Wheezing
• Acute Respiratory Acidosis Indicates Sudden
  Failure To Breathe and Requires Immediate
  Investigation

17
Causes of Respiratory Acidosis

• Depressed respiratory drive
• CNS depression
• CNS depressants
• head injury
• respiratory diseases
• Respiratory muscle fatigue / dysfunction
• ARDS
• neuromuscular diseases
• chest trauma

• Increased dead space
• pulmonary emboli
• chronic bronchitis/ emphysema
• Increased CO2 production
• elevated temperature
• high carbohydrate diet

18
Respiratory Acidosis Treatment

• Treat cause
• based on pH
• Bronchodilators if warranted by underlying
  condition
• Supportive Measures
• Airway
• Artificial Ventilation
• Consider Bag/Valve
• Consider intubation (laryngeal
  mask airway (LMA) shown)
• Oxygen Supplementation

19
Metabolic Alkalosis

• pH gt7.45
• HCO3 gt26
• Too much alkalinity
• excess bicarb administration
• antacid overuse
• alkaline drugs
• Lactated Ringers administration
• Metabolic acid loss
• vomiting
• NG suctioning
• diuretics
• steroids

20
Metabolic Alkalosis Physical Presentation

• Hypoventilation
• Electrolyte Disturbances
• Cardiac Dysrythmias
• Alkalosis ionizes calcium, so may exhibit SS
  hypocalcemia
• tetany, Chvostek/Trousseaus signs, seizures

Chvosteks sign
Trousseaus sign
21
Metabolic Alkalosis Treatment

• Lungs can provide limited compensation
• Treat underlying cause
• Correct electrolytes
• Diamox (carbonic anhydrase inhibitor)
• Inhibition reduces reabsorption of NaHCO3
• Ammonium chloride
• metabolized into urea and HCL

22
Metabolic Acidosis

• pH lt7.35
• HCO3 lt22
• Increased HCO3 loss
• Diarrhea (GI preps)
• GI fistula
• Increased H production
• lactic acidosis
• ketoacidosis
• renal failure

• External influences
• Salicylate intoxication
• Ethanol, methanol or isopropyl alcohol
  intoxication

23
Metabolic Acidosis Physical Assessment

• Hyperventilation
• Kussmaul respiratory pattern
• Headache
• Mental Status Changes
• Hyperkalemia
• acidosis draws K out of the cells
• Hypercalcemia
• Increased parathyroid hormone causes
  hypercalcemia and increased bicarb excretion

24
Metabolic Acidosis Treatment

• Treat underlying condition
• based on pH if pH lt7.2 may need IV bicarbonate
  until cause is controlled
• Lactic acidosis, ketoacidosis
• If kidney disease is cause, may require
  hemodialysis
• Acute metabolic acidosis may indicate tissue
  hypoxia
• requires further assessment
• consider oxygen therapy

25
ABG Practice

• pH 7.55
• PaCO2 28
• HCO3 24
• PaO2 84
• Interpretation?

1. Normal
2. Respiratory Acidosis
3. Respiratory Alkalosis
4. Metabolic Acidosis
5. Metabolic Alkalosis

Answer Respiratory Alkalosis pH is above 7.45,
PaCO2 is below 35
26
ABG Practice

1. Normal
2. Respiratory Acidosis
3. Respiratory Alkalosis
4. Metabolic Acidosis
5. Metabolic Alkalosis

• pH 7.28
• PaCO2 54
• HCO3 24
• PaO2 59
• Interpretation?

Answer Respiratory Acidosis pH is below 7.35,
PaCO2 is above 45
27
ABG Practice

• pH 7.42
• PaCO2 38
• HCO3 24
• PaO2 89
• Interpretation?

1. Normal
2. Respiratory Acidosis
3. Respiratory Alkalosis
4. Metabolic Acidosis
5. Metabolic Alkalosis

Answer Normal ABG
28
ABG Practice

• pH 7.31
• PaCO2 38
• HCO3 19
• PaO2 89
• Interpretation?

1. Normal
2. Respiratory Acidosis
3. Respiratory Alkalosis
4. Metabolic Acidosis
5. Metabolic Alkalosis

Answer Metabolic Acidosis pH is below 7.35,
HCO3 is below 22
29
ABG Practice

• pH 7.50
• PaCO2 42
• HCO3 31
• PaO2 82
• Interpretation?

1. Normal
2. Respiratory Acidosis
3. Respiratory Alkalosis
4. Metabolic Acidosis
5. Metabolic Alkalosis

Answer Metabolic Alkalosis pH is above 7.45,
HCO3 is above 26
30
Next moduleABG - Compensation
pH 7.35-7.45
CO2
HCO3