acid base, blood gas interpretation

Question 1

Why look at blood gas levels

Answer 1

not a primary disease: reflects disease state, need to address underlying cause

early indicator of change-pulmonary function, metabolic balance

POC monitors more common now

Question 2

pH

Answer 2

acidemia: <7.35
alkalemia: >7.45

Question 3

PCO₂

Answer 3

normal 35-45 mmHg

Question 4

Partial pressure of O₂

Answer 4

measures oxygen dissolved in plasma

normals vary with percentage of O₂ inspired

Question 5

PaO₂

partial pressure of Oxygen in arteries

Answer 5

reflects ventilation/respiratory function

increased–>hyperoxia

decreased–>hypoxia/hypoxemia

Question 6

hypoxia numbers

Answer 6

<80 mmHg moderate

<60 mmHg severe

Question 7

PvO₂

partial pressure of oxygen in veins

Answer 7

reflects tissue oxygen use

Question 8

HCO₃

Answer 8

bicarbonate level

normal values variable

carnivores: 16 to 24
herbivores: 24 to 30

Question 9

Total CO₂

Answer 9

95% is HCO₃

5% is carbonic acid and dissolved CO₂

normal is within 2 units of HCO₃

Question 10

Base Excess/base deficit

Answer 10

indicates the amount of HCO₃ below or above normal

difference between normal buffer base and actual buffer base

Question 11

What are the buffers in the body?

Answer 11

HCO₃

Hemoglobin

phosphate

ammonium

serum proteins

Question 12

SAT/SaO₂

Answer 12

percent oxygen saturation

same as pulse oximeter reading

Question 13

What is a normal SaO₂ reading? Abnormal?

Answer 13

perfect: 100
normal: >95

serious hypoxemia: <90

severe hypoxemia: <70

lethal hypoxemia: <60

Question 14

Will a patient be cyanotic if their SaO₂ is at 90?

Answer 14

NO!

Question 15

respiratory acidosis

Answer 15

increase in PCO₂ (hypercapnia)

increases denominator causing a decrease in pH

Question 16

rule outs for respiratory acidosis

Answer 16

respiratory depression from general anesthesia or CNS trauma/disease

primary respiratory compromise (pneumonia, pneumothorax, respiratory muscle weakness, restricted chest wall movement related to pain, upper airway obstruction)

malignant hyperthermia (increased CO_² production)

Question 17

respiratory alkalosis

Answer 17

decreased PCO₂ (hypocapnia)

decreases denominator to increase pH

Question 18

rule outs for respiratory alkalosis

Answer 18

excessive manual or mechanical ventilation during general anesthesia

anxiety, directly stimulating respiratory centers

hypoxic stimulation in compromised patient

pain

Question 19

metabolic acidosis

Answer 19

decreased HCO₃

results in an increase in numerator to cause a decrease in pH

Question 20

rule outs for metabolic alkalosis

Answer 20

shock, poor tissue perfusion resulting in anaerobic tissue metabolism

DKA, poisoning

diarrhea, renal tubular acidosis

Question 21

metabolic alkalosis

Answer 21

increase in HCO₃

increase in numerator leads to increase in pH

Question 22

rule outs for metabolic alkalosis

Answer 22

primary gastric vomiting

potassium wasting diuretics, decreased fluid volume/dehydration

excessive endogenous sodium bicarbonate therapy

Question 23

PaO₂ normals

Answer 23

room air: 85 to 105 mmHg

33% O₂: 150 mmHg

nasal O₂: 200 mmHg

pure O_²: 500 mmHg

Question 24

BE normals

Answer 24

-4 to +4