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NS 7911 > Module 3: Blood Gas Analysis > Flashcards

Module 3: Blood Gas Analysis Flashcards

1
Q

What is ventilation?

A

the act of inhalation and exhalation that allows the process of gas exchange to occur throughout the body via the pulmonary system

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2
Q

What are 3 respiration dependent on?

A

dependent on the pulmonary system to provide
- adequate alveolar ventilation,
- pulmonary perfusion,
- diffusion of gases across the alveolar-capillary membrane
with the help of the circulatory system for transport

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3
Q

Where does alveolar respiration occur? cellular respiration?

A
  • Within the lungs, alveolar respiration occurs.
  • Within cells, cellular respiration occurs.
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4
Q

What is cardiovascular system responsible for?

A

responsible for transport of oxygen and carbon dioxide between these two sites.

**brain partly regulates some of the process.

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5
Q

What is pulmonary ventilation vs alveolar ventilation?

A
  • Pulmonary ventilation is the exchange of air/02 between the atmosphere and the lungs.
  • Alveolar ventilation occurs across the alveolar-capillary membrane and exchanges air/02 between the lungs and cells.
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6
Q

Is alveolar ventilation a key process in gas exchange?

A
  • Although alveolar ventilation has been identified as a key process in gas exchange it is only one part of the larger process of gas exchange.
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7
Q

What is mechanical ventilation aim at?

A
  • Mechanical ventilation is largely aimed at improving alveolar ventilation,
  • but alveolar ventilation is only one part of what happens in the lungs and only one part of the whole process of respiration
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8
Q

What is the entire process of respiration dependent on?

A
  • alveolar ventilation,
  • pulmonary perfusion,
  • cardiac output, etc.

**A dysfunction in any one of these processes will affect gas exchange.

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9
Q

Which parameters of the blood gas are used to assess ventilation? Acid-base balance? Oxygenation?

A
  • Ventilation is assessed by looking at the pCO2.
  • Acid-base balance is assessed by looking at the pH, pCO2, and HCO3.
  • Oxygenation is assessed by looking at the pO2 and the O2 saturation.
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10
Q

Which parameter is used to determine the respiratory component of acid-base abnormalities? Which one determines the metabolic component?

A
  • The pCO2 determines the ventilatory component. An increase in pCO2 creates a decrease in pH which is called “respiratory acidosis” (or ventilatory acidosis). It is due to hypoventilation.
  • The HCO3 determines the metabolic component. A net decrease in HCO3 causes a decrease in pH and is called metabolic acidosis. It is due to many etiologies, such as anaerobic metabolism producing lactic acid, a loss of HCO3 from the kidney or failure of the kidney to eliminate excess H+.
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11
Q

Why is the amount of carbon dioxide in the blood a direct measure of ventilation?

A
  • Because the amount of carbon dioxide in the blood is a reflection of the amount produced by metabolism and the amount exhaled through ventilation, or breathing.
  • As metabolism does not change greatly, pCO2 is an indication of ventilation.
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12
Q

Explain “compensation” using compensated respiratory acidosis as an example.

A
  • When hypoventilation leads to respiratory acidosis (↓ pH, ↑ pCO2, and HCO3), the body will compensate by creating a compensated metabolic alkalosis.
  • The kidneys will retain HCO3 and when the levels elevate, it looks like this:
  • Normal pH, ↑pCO2, and ↑ HCO3.
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13
Q

Whereas elimination of CO2 is only dependent on adequate ventilation, tissue oxygenation is dependent on several processes. What are they?

A
  • Tissue oxygenation is dependent on adequate ventilation.
  • In addition, tissue oxygenation is dependent on: oxygen delivery to the tissues (cold, hypovolemia, cardiac failure can lead to tissue hypoxia) and presence of anemia (reduced oxygen ¬carrying capacity resulting in reduced oxygen content of the blood).
  • When hypoventilation leads to respiratory acidosis (↓ pH, ↑ pCO2, and normal HCO3 ) the body will attempt to bring the pH back to normal by retaining bicarbonate.
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14
Q

How often may a blood gas be ordered when infant is first ventilated?

A
  • ordered quite frequently (sometimes as often as every half hour)
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15
Q

Are blood gases ordered when infant is on CPAP?

A
  • Blood gases can be used to assess whether an infant is also tolerating CPAP.
  • These gases are done less frequently (every 1-2 days).
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16
Q

What are the 5 components of blood gas analysis used to assess efficacy of mechanical ventilation?

A
  • pH
  • pCO2
  • HCO₃
  • pO2
  • BE/BD
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17
Q

What is pO2 affected by? pCO2?

A
  • pO2 is affected by the Mean Airway Pressure (MAP) and the FiO2
  • pCO2 is affected by the Minute Ventilation.

MAP and FiO2 → pO2

Blood oxygen levels, or pO2, are affected by ventilator FiO2 and MAP.

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18
Q

How is hypoxemia treated by?

A
  • ↑ FiO2
  • ↑ MAP

**since pO2 is dependent on MAP and FiO2

19
Q

What is mean airway pressure (MAP)?

A
  • refers to the average pressure in the lungs during one complete breath, including inspiration and expiration.
20
Q

How can Mean Airway Pressure (MAP) be increased by?

A
  • ↑ PIP
  • ↑ PEEP
  • ↑ flow
  • ↑ I time
21
Q

How can hypoxemia be treated by? hyperoxia treated by?

A

Hypoxemia may be treated by:
↑ FiO2
↑ PEEP
↑ PIP
↑ flow
↑ I time

Hyperoxia may be treated by:
↓ FiO2
↓ PEEP
↓ PIP
↓ flow
↓ I time

22
Q

What does minute ventilation refers to?

A
  • refers to the volume of gas moved in and out of the lungs in one minute.
  • Minute ventilation = tidal volume × rate.

**Minute ventilation can be increased by increasing either the tidal volume or the rate or both.

23
Q

What is tidal volume?

A
  • the volume of gas moved in and out of the lungs with each breath.
  • On a time cycled, pressure limited ventilator (a typical infant ventilator) the tidal volume depends on lung compliance and resistance.
  • Lung compliance cannot necessarily be controlled by clinicians, however the PIP can.

**tidal volume can be increased by increasing the PIP.

24
Q

How can hypercapnia be treated? hypocapnia be treated?

A

Hypercapnia may be treated by:
↑ PIP
↑ rate
↑ tidal volume

Hypocapnia may be treated by:
↓ PIP
↓ rate
↓ tidal volume

25
Q

What are 3 non-invasive technique used to monitor blood gases?

A
  • pulse oximeter or
  • a transcutaneous CO2 monitor.
  • CO2 can also be measured from the expiratory hose of the ventilator and is referred to as End Tidal CO2 (only used in term infants and is not commonly seen in the NICU)
26
Q

How is CO2 measure from expiratory hose?

A
  • CO2 can also be measured from the expiratory hose of the ventilator and is referred to as End Tidal CO2.
  • In order to measure the End Tidal CO2 a module is added to the expiratory limb of the ventilator, creating more deadspace.
  • Due to this deadspace, End Tidal CO2 is only used in term infants and is not commonly seen in the NICU
27
Q

What is the use of having continuous information about O2 saturation, pO2 or pCO2 in regard to assessing infant (4)?

A

be used to assess an infant’s response to:
- care (e.g., suctioning),
- ventilator setting changes, and
- handling; to detect trends over time;
- to wean an infant from the ventilator and
- assess their tolerance of CPAP;
- to plan care;
- to detect hypo/hyperoxemia and hypo/hypercapnia early,
- allowing for early intervention,
- often before physical responses such as color change or bradycardia are apparent.

28
Q

Explain, in your own words, respiratory acidosis.

Include in your explanation: the common causes and the resulting blood gas picture.

A
  • Respiratory acidosis is excess acid in the blood as a result of respiratory problems.
  • The problems that can cause respiratory acidosis arise from ventilatory insufficiency and failure to eliminate CO2.
  • For example, pneumonia, RDS, meconium aspiration, pulmonary hypoplasia, BPD - all of these conditions can be accompanied by insufficient ventilation and hypercapnia (↑ pCO2).
  • The blood gas picture is characterized by ↑ pCO2, ↓ pH, and & HCO3−.
    For example: pCO2 50, pH 7.29, HCO3- 21
29
Q

Explain, in your own words, compensated respiratory acidosis.

Why does it happen, how does it happen, and what is the resulting blood gas picture?

A
  • Compensated respiratory acidosis occurs when respiratory acidosis is not corrected.
  • If left uncorrected, the body will attempt to compensate for the ↓ pH.
  • This is done by retaining HCO3−, a base which will increase the pH.
  • Increasing an acidotic, low pH will normalize it.
  • The blood gas picture changes from what was described above to one that is characterized by ↑ pCO2, ±, ↑ pH and ↑ HCO3−.
  • For example, a typical compensated respiratory acidosis looks like: pCO2 50, pH 7.35, HCO3− 27.

**This is such a common blood gas picture that the normal range of pH for infants with long-term respiratory problems is 7.30-7.45.

30
Q

Explain, in your own words, respiratory alkalosis. Why is this generally an iatrogenic problem?

A
  • Respiratory alkalosis occurs because of too little CO2 and is generally the result of hyperventilation.

It is an usually iatrogenic problem among infants because hyperventilation rarely occurs naturally.
Rather, hyperventilation often occurs as a result of too high a rate being set on the ventilator.

The blood gas picture for respiratory alkalosis is characterized by: ↓ pCO2, ↑ pH, & HCO3−.

For example, pCO2 28, pH 7.41, HCO3−22.

31
Q

Normal range value for blood gas anaylsis

A

pH: 7.35-7.45
pCO2: 35-45
PaO2: 50-80 (arterial)
HCO3-: 20-26
BE: -4 to +4

**pO2 (capillary): 40-60 (less accurate)

32
Q

Blood gas analysis assess what three interrelated but separate processes?

A
  • oxygenation,
  • ventilation, and
  • acid-base homeostasis
33
Q

How is oxygenation assess by?

A
  • assessed by how much oxygen the lungs are delivering to the bloodstream, told by the pO2 and oxygen saturation.
  • pO2 measures dissolved oxygen (3% of total oxygen)
  • O2 sat measures oxygen carried on hemoglobin (97% of total oxygen)

**Arterial pO2 values are much more accurate than capillary pO2 values

34
Q

What is alveolar ventilation determined by?

A
  • determined by the pCO2 level.
  • Carbon dioxide is very sensitive to minute ventilation, which is the volume of air inspired and exhaled in a minute.
  • Minute ventilation (tidal volume x rate), and in particular, tidal volume (volume of air moved with each breath) is affected by the functioning of the pulmonary system.

**Normal values for pCO2 are 35–45 mmHg

35
Q

What does hypoventilation leads to? hyperventilation leads to?

A

Hypoventilation leads to a buildup of CO2
- A high amount of CO2 in the bloodstream, such as when ventilation is impaired, decreases the pH as excess carbon dioxide combines with water to form carbonic acid, creating respiratory acidosis *

Hyperventilation leads to a decrease in CO2
- A low amount of CO2 in the bloodstream, usually caused by over ventilation, will cause a respiratory alkalosis

36
Q

What is the acid-base balance on infants blood reflected by?

A
  • reflected by the pH
  • Normal range for pH is 7.35–7.45
  • A pH less than 7.35 indicates acidosis
  • A pH more than 7.45 indicates alkalosis
37
Q

What is respiratory acidosis?

A
  • caused by too much CO2, which combines with water to form carbonic acid, which in turn drops the pH
  • commonly caused by hypoventilation

Respiratory acidosis
pH — 7.22 low
pCO2 — 57 elevated
HCO3– — 21 normal

38
Q

What is metabolic acidosis?

A
  • caused by too much lactic acid
  • occurs with hypoxia and/or poor perfusion
  • anaerobic metabolism produces a lot of lactic acid as a byproduct, which lowers the pH
  • caused by failure of the kidneys to eliminate the hydrogen ions they normally eliminate from the body via urine
  • caused by failure of the kidneys to reabsorb the bicarbonate they normally recycle back into the body.

Metabolic acidosis
pH — 7.22 low
pCO2 — 40 normal
HCO3– — 17 low

39
Q

What is respiratory alkalosis?

A
  • Alkalosis (state of too much base or too little acid) is caused by too little carbon dioxide
  • occurs with hyperventilation

Respiratory alkalosis
pH — 7.51 elevated
pCO2 — 30 low
HCO3– — 21 normal

** respiratory alkalosis is seen in an infant who is hyperventilating, either spontaneously or by a mechanical ventilator set with too high of a rate.

40
Q

What is metabolic alkalosis?

A
  • caused by loss of acid through gastric suctioning

Metabolic alkalosis
pH — 7.51 elevated
pCO2 — 40 normal
HCO3– — 28 elevated

41
Q

What is hypoxemia vs hypoxia?

A

hypoxemia:
- low O2 in blood (PaO2 level)
hypoxia:
- low O2 in tissue

42
Q

What are the 5 common causes of hypoxemia in neonatal period?

A
  • ventilation/perfusion (V/Q) mismatch
  • alveolar hypoventilation
  • right-to-left shunt
  • diffusion: impaired O2 pathway
  • areas of high altitude yields low O2 concentration
43
Q

What is the Oxygen Hemoglobin Dissociation Curve?

A
  • main function of the circulating blood to deliver O2 to tissue and remove CO2
  • graphs that plots proportion of heh Hgb in its saturated form on vertical axis against prevailing O2 tension on horizontal axis
  • a left shift: high O2 affinity: alkalosis, fetal hgb, hypothermia, hypocarbia,
  • a right shift: low O2 affinity: acidosis, hypercarbia, hyperthermia, exercise

NS 7911 (6 decks)

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