1. Arterial Blood Gas Analysis
Kathleen Guentner, PhD, RN, CNE
Amber Kolesar, MSN, RN
UPMC Shadyside School of Nursing

2. ABG Analysis
Three parameters must be assessed during interpretation of an arterial blood gas result
Oxygenation
Acid – Base status
Degree of Compensation

3. ABG Analysis Oxygenation Evaluate the PaO2 Evaluate the SaO2
PaO2 < 80 mmHg
Consider age related alterations
End result = Hypoxemia
Evaluate the SaO2
SaO2 < 93%
Inadequate amount of oxygen is bound to hemoglobin for transport to tissues.
End result = Hypoxia
Partial pressure of arterial oxygen (PaO2) declines linearly with aging (about 0.3%/yr) until age 75, at which time it stabilizes at about 80 mm Hg in healthy nonsmokers. This gradual decline is mostly attributable to ventilation/perfusion (V/Q) mismatch caused by age-related collapse of peripheral airways, leading to shunting of blood through nonventilated alveoli. PaO2 at any age can be roughly estimated by the equation PaO2 = (0.43 x age).
Altitude!

4. ABG Analysis Acid Base Balance
Evaluate the blood pH (normal, increased or decreased)
Evaluate the PaCO2 (increased, decreased or normal)
Evaluate the HCO3 (normal, increased, or decreased)

5. ABG Analysis Blood pH The optimal blood pH is 7.40
The body tolerates a narrow margin of normal pH of 7.35 – 7.45
A pH lower than 7.35 = Acidosis
A pH greater than 7.45 = Alkalosis

6. ABG Analysis
Blood pH
If the pH is within normal range, it is important to assess which side of 7.40 it falls.
This may indicate that the patient may be acidotic or alkalotic, but compensating.
7.35 – 7.39 = Acidosis
7.41 – 7.45 = Alkalosis

7. ABG Analysis
PaCO2
A PaCO2 less than 35 is indicative of respiratory alkalosis
A PaCO2 greater than 45 is indicative of respiratory acidosis

8. ABG Analysis
HCO3
A HCO3 level less than 22 is indicative of metabolic acidosis
A HCO3 level greater than 26 is indicative of metabolic alkalosis

9. The Arrow Method of ABG Analysis

10. “Remember ROME” Respiratory Opposite Metabolic Equal
(if arrows with PH is opposite= resp.
If same= metabolic)

11. It’s Easy! Assess the pH, PaCO2 and HCO3
If the values are elevated, place the corresponding arrow.
If the values are decreased, place the corresponding arrow.

12. Now “Match Em”
If the pH and PaCO2 arrows are moving in opposite direction, this signifies a RESPIRATORY problem.
pH PaCO = Respiratory Acidosis
pH PaCO = Respiratory Alkalosis
Remember as the pH decreases……..

13. Now “Match Em”
If the pH and HCO3 arrows are moving in the same direction, this signifies a METABOLIC problem.
pH HCO = Metabolic Acidosis
pH HCO = Metabolic Alkalosis

14. EXAMPLE #1 pH: 7.22 PaCO2: 55 HCO3: 25 pH PaCO2 HCO3 Normal
Respiratory
Acidosis
Normal

15. EXAMPLE #2 pH: 7.31 PaCO2: 35 HCO3: 20 pH PaCO2 HCO3 Normal Metabolic
Let’s follow the steps we talked about
Assess the pH. Is it high or low (alkalotic or acidotic), its low, so we have acidosis ( )
Assess the PaCo2. Is it high, low, or normal it is normal (35-45) DRAW ON SCREEN, PUT “N”, or NORMAL
Assess the HCO3, is it low, high or normal, it is low (22-26) moving in the same direction of the pH
Refer to the chart. Acidosis is present (decreased pH) with the PaCO2 being normal, HCO3 being low, so the ph & HCO3 are moving in the same direction, reflecting a metabolic problem.
If this was a patient gas we would have to restore tissue perfusion to the hypoxic tissues pH
PaCO2
HCO3
Metabolic
Acidosis
Normal

16. EXAMPLE #3 pH: 7.49 PaCO2: 30 HCO3: 23 pH PaCO2 HCO3 Normal
Let’s follow the steps we talked about
Assess the pH. Is it high or low (alkalotic or acidotic), its high, so we have alkalosis ( )
Assess the PaCo2. Is it high or low, it is low and in the opposite direction of the pH (35-45)
Assess the HCO3, is it low, high or normal, it remains in the normal range (22-26)……. DRAW ON SCREEN, PUT “N”, or NORMAL
Refer to the chart. Alkalosis is present (increased pH) with the PaCO3 decreasing, they are changing in the opposite direction reflecting a primary respiratory problem.
If this was a patient gas we would have to improve ventilation status by providing 02 therapy, mechanical ventilation, due to muscles becoming exhausted, remember respiratory failure may occur pH
PaCO2
HCO3
Respiratory
Alkalosis
Normal

17. Evaluate for Compensation
When a patient develops an acid-base imbalance the body will typically attempt to compensate for the abnormality.
If the buffer systems within the body are unable to maintain a normal pH, the lungs & the kidneys will attempt to compensate. (

18. Evaluate for Compensation
If the problem is respiratory in origin, the kidneys will work to correct it.
If the problem is metabolic in origin, the lungs will work to correct it.
It may take as little as 5 to 15 minutes for the lungs to recognize a metabolic problem, and start to correct it. However, the kidneys take a lot longer to correct a respiratory problem, typically up to 1 day.

19. Evaluate for Compensation
Determine the degree of compensation:
Uncompensated (if PH abnormal, and one other abnormal)
Partially compensated (all 3 abnormal)
Fully compensated (pH normal, but others both abnormal)
if PH abnormal, and one other abnormal

21. Consequences: Impaired Cellular and Organ Function
When compensatory mechanisms fail, the following physiologic consequences occur:
Altered cell function, especially in the brain when CO2 crosses the blood–brain barrier
Change in intracellular enzyme activity resulting in cell dysfunction
Acidosis: decreases the level of consciousness (LOC)
Alkalosis: decreases the LOC and has other neurologic manifestations; may cause dysrhythmias

22. Evaluate for Compensation
Uncompensated
pH is abnormal, & either the PaCO2 or HCO3 is also abnormal
There is no indication that the opposite side has tried to correct for the other.

23. Evaluate for Compensation
Partially Compensated
pH is abnormal, & both the PaCO2 and HCO3 are also abnormal
This indicates that one system has attempted to correct for the other but has not been completely successful.
ALL 3 Values are abnormal

24. Evaluate for Compensation
Fully Compensated
pH is normal, & both the PaCO2 & HCO3 are abnormal
The normal pH indicates that one system has been able to compensate for the other.

25. Steps for Evaluating Compensation
Assess the pH, determine acidosis or alkalosis.
Remember, even if the pH is normal, determine whether the pH falls on the acidotic or alkalotic side of 7.40.
Place the corresponding arrow next to the pH
(2nd line) But what happens if the pH and PaCo2 are moving in the same direction, this is not what we would expect to see right?

26. Steps for Evaluating Compensation
Assess the PaCO2 and the HCO3
Place the corresponding arrows next to the values.
Continue the matching game: Which value matches with the pH?
The other component should be moving in the opposite direction, which indicates compensation.

27. Steps for Evaluating Compensation
Example:
pH ; PaCO ; HCO3 30
Which value matches with the pH?
All three values are abnormal

28. EXAMPLE #1 (COPD PTS) pH: 7.31 PaCO2: 55 HCO3: 28 pH PaCO2 HCO3
Partially Compensated
Respiratory Acidosis

29. EXAMPLE #2 (Kidney Issues)
pH: 7.31
PaCO2: 25
HCO3: 20 pH
PaCO2
HCO3
Partially Compensated
Metabolic Acidosis

30. EXAMPLE #3 (Anxiety) pH: 7.48 PaCO2: 25 HCO3: 21 pH PaCO2 HCO3
Partially Compensated
Respiratory Alkalosis

31. EXAMPLE #4 (NG drainage/vomiting)
pH: 7.48
PaCO2: 55
HCO3: 31 pH
PaCO2
HCO3
Partially Compensated
Metabolic Alkalosis

32. EXAMPLE #5 pH: 7.39 Normal PaCO2: 60 HCO3: 30 pH PaCO2 HCO3 N
Fully Compensated
Respiratory Acidosis N

33. Case Study
A 21 year old college student is admitted to the Emergency Department after taking an overdose of Oxycontin. The patient is unconscious & breathing at a rate of 6 to 7 bpm. The patient’s ABG on room air is as follows:
pH: 7.23 (low); PaCO2: 71 (high); PaO2: 64; HCO3: 26 (normal)
Interpretation: (resp. acidosis. Uncompensated)
Possible Cause? Drug overdose
Nursing Interventions: intubation (high resp above 20, high Fio2 40) NARCAN
pH= Low
Paco2= High
HCO3= Normal
Respiratory Acidosis probably caused by over sedation/overdose of Dilaudid
Expected signs & symptoms: respiratory distress, drowsiness, decreased responsiveness
Nursing interventions: Give Narcan & intubate ASAP

34. Case Study
A woman with a history of panic disorder arrives at the Emergency Department complaining of not being able to “catch her breath”. The woman is crying, shaking and breathing rapidly. An ABG is obtained:
pH: 7.52 (high); PaCO2: 28 (norm); HCO3: 22 (norm); SaO2: 90%
Interpretation: Respiratory Alkalosis uncompensated, hypoxia
Possible Cause? Hyperventilating
Nursing Interventions: Calm down, paper bag, pain
pH= High
Paco2= Normal
HCO3= Normal
Respiratory Alkalosis
Is the patient really in resp distress? NO
She is hyperventilating, we need to calm her anxiety; treat the anxiety attach!! May even use a paper bag to restore PCO2.

35. Case Study
A teenager is being evaluated at the emergency room for complaints of muscle weakness and twitching. Her mother reports “she is always on a dieting” The patient is 5’6 and weighs 102lbs. Among the teenager’s lab results are the following ABG values:
pH: 7.50 (high); PaCO2: 45 (normal); HCO3: 30 (low); SaO2 94%
Interpretation? Metabolic alkalosis uncompensated (difficult to treat)
Possible Cause?
Nursing Interventions? Deep breaths, positioning, 2L NC O2, nutrition education, replace electrolytes, MONITOR
pH= High
Paco2= Normal
HCO3= Low
Metabolic Alkalosis
Very difficult to treat!
The patient probably has an eating disorder, maybe Bulimia (prolonged induced emesis)
Hydrogen retention and bicarbonate excretion may be promoted by administering
Can give K, Ca glucanate
Bicarbonate excretion through the kidneys can be stimulated with drugs such as Diamox (Acetazolamide) → but resolution will be slow
A diuretic that acts as a carbonic anhydrase inhibitor

36. Case Study
A patient has been mechanically ventilated for the past two days in the ICU. The ventilator settings are as follows: AC, rate of 16, FIO2 50%, and TV The patient’s 6am ABG results are as follows:
pH: 7.49 (high); PaCO2: 29 (low); PaO2: 70; HCO3: 25 (normal):
Interpretation? Respiratory alkalosis uncompensated
Possible Cause? Hyperventilation, slow rate/tidal volume
Nursing Interventions? Pain control, increase PEEP,
AC usually initiated as initial mode of ventilation
Respiratory Alkalosis
Ph= High
PaCO2= Low
HCO3= Normal
Common causes: anxiety, fear, hyperventilation
Nursing interventions: Pain control, sedation, decrease rate; patient breathing with vent
Patient at risk for developing cardiac dysrhythmias

37. Case Study
A 53 year old patient presents to the Emergency Department with complaints of weakness, nausea, and shortness of breath. The patient’s STAT ABG results are as follows:
pH: 7.29 (low); PaCO2: 32 (normal); HCO3: 18 (normal); PaO2 80
Interpretation:partially compensated metabolic acidosis
Possible Cause?
Nursing Interventions?
Metabolic Acidosis
pH= Low
PaCO2= Normal
HCO3= Normal
Management
Life Threatening
Treat underlying cause and replace bicarbonate
Insulin/glucose  uncontrolled diabetes
Improvement of oxygenation in lactic acidosis some aerobic metabolism can resume
IV Sodium Bicarbonate administration

38. Case Study
The nurse is caring for a patient 2 days post-abdominal surgery The nurse notes 500cc of coffee ground drainage over the last four hours. The patient is neurologically intact. ABG results are ordered with the following results.
pH: 7.29 (low); PaCO2: 65(high); PaO2: 60; HCO3: 26 (normal)
Interpretation? Respiratory acidosis, uncompensated
Possible Cause?
Nursing Interventions?
Respiratory Acidosis
pH= Low
PaCO2= High
HCO3= Normal
Not text book scenario; Would expect patient to demonstrate Metabolic Alkalosis due to vomiting, NG suctioning; coffee ground emesis
paCO2 74; should be
What else do we need to know here????
COPD
Heart Failure
Pulmonary infection
Atelectasis
Pulmonary Edema
Pulmonary Embolus
Is the patient coughing & deep breathing- Post op abdominal surgery necessity
What are is the patients respiratory rate? Patient probably display dyspnea which could lead to respiratory distress
What is heart rate? Patient probably tachycardic, may have dysrhythmias
Give antibiotics

39. Thank you for your participation