1
Q
What are the 3 main determinants of oxygen supply?
A
- AMOUNT of oxygen that is present in the arterial blood when it leaves the lungs
- CAPACITY of the blood to transport oxygen to the cells
- EFFECTIVENESS of the pump that circulates the blood throughout the body;
- to ensure adequate cellular oxygenation, it is not sufficient to have great gas exchange and ventilation, or optimal conditions for maximizing oxygen transport—adequate cardiac output is required to move the saturated arterial blood around the body to the cells that need it
2
Q
What are 3 parameters of good indication of determinants of oxygen?
A
- Arterial oxygen saturation (SaO2): which represents the amount of oxygen present in the arterial blood when it leaves the lungs
- Hemoglobin (Hgb): which indicates the capacity of the blood to transport oxygen to the cells
- Cardiac output (CO): which is an indicator of the effectiveness of the pump that circulates the blood throughout the body
3
Q
What is oxygen demand?
A
- Any factors that increase or decrease the amount of oxygen the cells require to function will influence oxygen demand.
- Metabolic factors exert the strongest influence on oxygen demand and include temperature, activity level, and stress.
4
Q
What are 3 metabolic factors exert the strongest influence on oxygen demand?
A
- temperature,
- activity level,
- stress.
5
Q
What are 3 factors that influence arterial oxygen saturation?
A
- Concentration of oxygen in the inspired gas (FiO2)
- Ventilation: the infant’s ability to get air in and out of the lungs
- Alveolar gas exchange: the effectiveness of gas exchange at the alveolar-capillary membrane
6
Q
What is ventilation? What factors influence ventilation (2)?
A
- is the movement of air in and out of the lungs
Factors influence ventilation:
- respiratory rate RR
- tidal volume Vt (the size of each breath)
7
Q
Whats minute ventilation?
A
Respiratory rate x tidal volume = minute ventilation
- influenced by work of breathing
8
Q
What is infants respiratory rate and tidal volume influence by?
A
- influenced by work of breathing.
- Work of breathing, in turn, is influenced by lung development, lung compliance, airway resistance, and respiratory muscle function.
9
Q
What is work of breathing? What are 4 factors that influence work of breathing?
A
- How hard an infant has to work to sustain adequate ventilation will clearly influence their capacity to maintain adequate arterial oxygen saturation and oxygen supply.
Factors influence work of breathing in infants:
- lung development,
- compliance,
- airway resistance, and
- respiratory muscle function.
10
Q
What are the 5 stages that lung development is divided into?
A
- embryonic (3–6 weeks),
- pseudoglandular (6–16 weeks),
- canalicular (16–24 weeks): lung development has progressed to the point where gas exchange may be possible
- saccular (24–40 weeks): important blood-air barrier is established
- alveolar (birth–childhood).
11
Q
What is compliance in regards to work of breathing (ventilation)
A
- is a measure of the distensibility of a tissue
- It considers the relationship between the degree to which the tissue will stretch and the force or pressure required to make that stretch occur.
- In considering the impact of compliance on work of breathing, both compliance of the lung tissue and compliance of the thoracic cage are important.
- Infants, especially preterm infants, have less-compliant lungs and more-compliant rib cages, which can lead to difficulties with ventilation.
12
Q
What is airway resistance in regards to work of breathing (ventilation)?
A
- effectiveness of ventilation: influenced by the ability of air to flow through the conducting airways.
- In the respiratory system, the conducting airways include all anatomical passages from the point of air entry to the respiratory bronchioles and alveoli.
- In the conducting airways, airway resistance is influenced by the diameter of the airway.
- Airway diameter decreases with lower gestational age and smaller size
13
Q
What is respiratory muscle function in regards to work of breathing (ventilation)?
A
- There are many muscles involved in the mechanics of ventilation.
- Infants, especially preterm infants, have weak muscles and tend to tire easily.
14
Q
What is alveolar gas exchange?
A
- exchange of gases across the alveolar-capillary membrane
- Alveolar gas exchange is influenced by several factors, including the process of diffusion of gases across the alveolar-capillary membrane
15
Q
Why premature infants have difficulty with alveolar gas exchange (3)?
A
- due to decreased surfactant production,
- decreased surface area for gas exchange, and
- increased distance between alveoli.
16
Q
What influence diffusion in alveolar gas exchange (2)?
A
- influenced by such factors as the thickness of the alveolar-capillary membrane
- the difference in concentration of gases on either side of the membrane
17
Q
Does CO2 diffused more rapidly than O2?
A
- Carbon dioxide (CO2) diffuses 20 times more rapidly than oxygen [diffusion coefficient]
- This is a critical piece of information in understanding the relationship between gas exchange, oxygenation, and ventilation.
- The ready diffusibility of CO2 makes it easy for it to pass from the pulmonary capillary to the alveoli, even when diffusion is impaired by a pathological process that increases the thickness of the alveolar-capillary membrane,
18
Q
What primarily determined CO2 levels?
A
- CO2 levels are determined primarily by ventilation NOT oxygenation
ventilation is inadequate:
- less CO2 is exhaled from the body and
- so CO2 levels increase in the alveoli.
- The increase in alveolar CO2 concentration results in a decrease in driving pressure for CO2 (that is, the difference between alveolar CO2 concentration and venous CO2 concentration).
- As a result, the movement of CO2 from the pulmonary capillary to the alveoli will decrease, allowing CO2 levels in the arterial blood (PaCO2) to rise.
- Thus, CO2 levels in the arterial blood are influenced primarily by ventilation not by diffusion.
- PaCO2 (measured in arterial blood gas analysis) is the best indicator of ventilation.
19
Q
How does the difference in concentration of O2 in alveoli and in capillary support movement of O2 from alveoli to capillary?
A
- increase the driving pressure of oxygen whenever we administer supplemental oxygen to infants via nasal prongs or through CPAP or a mechanical ventilator.
- The movement of oxygen across the alveolar-capillary membrane is influenced by two processes: ventilation and diffusion
20
Q
What does the ventilatory processes (decreased ventilation) do in regards to movement of oxygen across the alveolar-capillary membrane?
A
- Ventilatory processes bring oxygen into the alveoli and so to the alveolar-capillary interface
- In decreased ventilation, there is less oxygen available in the alveoli to diffuse to the capillary, driving pressure is decreased and so diffusion is reduced, and consequently oxygen levels in the arterial blood fall.
- To put it simply, if the oxygen doesn’t get to the alveolar-capillary membrane, it cannot get into the arterial blood supply.
- Thus, decreased ventilation will reduce arterial oxygen levels, even when the alveolar-capillary membrane is physiologically normal
21
Q
What is the diffusion processes in regards to movement of oxygen across the alveolar-capillary membrane?
A
- Oxygen is significantly less diffusible than CO2.
- This has implications for diffusion of oxygen in the presence of pathophysiological processes.
- When any pathophysiological process is present that impedes diffusion across the alveolar-capillary membrane (for example, RDS, TTN, BPD) or when the alveolar-capillary membrane surface area is decreased (for example, MAS, pneumothorax, prematurity), arterial oxygen levels are much more strongly affected than CO2 levels.
- Diffusion and gas exchange problems, therefore, will primarily influence oxygen levels and create oxygenation problems.
22
Q
What is the relationship between ventilation and perfusion in the lungs?
A
- they both will be greatest in the dependent areas of the lungs.
- In other words, when an infant is upright, airflow (ventilation) and blood flow (perfusion) favour the lower portions of the lungs.
- When we position an infant on their right side, the right lung (especially the part nearest the bed) receives the greatest proportion of the air and blood flow.
23
Q
Infant with pneumonia affecting the lower lobe of their left lung. What happens if nurse position infant in bed with their left lung down?
A
- The largest proportion of the blood supply will go to the dependent or lower lung—that is, the lung that is not being well ventilated because of the lower lobe pneumonia.
- So now all that blood will be flowing past unventilated alveoli.
- Because the perfusion and the ventilation are not matched, gas exchange cannot occur in this area of the lung.
- The end result is impaired gas exchange and decreased arterial oxygenation.
24
Q
What is the definition of compliance?
A
- measure of distensibility of a tissue
25
What is O2 demands? vs O2 supply? O2 consumption?
- O2 demands: the amount of O2 the cells needs
- O2 supply: the amount of O2 available to the cells
- O2 consumption: the amount of oxygen a cell consumes in order to function.
26
What is "reservoir" and "ready to use" oxygen being carried by Hgb?
- oxygen that is transported in bound form acts as a “reservoir” or bulk supply of oxygen for the body,
- while the oxygen in solution is “ready for use.”
27
What is the oxyhemoglobin dissociation curve?
- reflects the relationship between oxygen and hemoglobin
- oxygen that remains bound to hemoglobin cannot participate in cellular metabolism
- and so, oxygen and hemoglobin need to dissociate from each other in order to be useful in the body
28
What does the efficiency of oxygen transport system depends on?
- depends on the ability of the hemoglobin molecule to bind oxygen as it passes through the lung and to release it at the tissue level on demand.
- The ease with which hemoglobin will bind and release oxygen is influenced by the “affinity” between these molecules:
- when affinity is increased, hemoglobin binds oxygen readily but is slower to release it;
- when affinity is decreased, it does not bind oxygen as readily but it releases it easily.
- Thus, as affinity changes, the relationship between oxygen and hemoglobin changes
29
What is Oxyhemoglobin Dissociation Curve Shifts when curve shifts to the right?
Curve shifts to the right: "Right Releases"
- PaO2 is greater for any given level of SaO2
- more bound oxygen is released into solution
- as the curve moves to the right, the affinity of hemoglobin for oxygen is reduced, favouring release of oxygen into solution
Common conditions that cause the curve to shift to the right (and a decrease in affinity):
-fever,
- acidosis (decreased pH), or
- an increase in PaCO2
30
What is Oxyhemoglobin Dissociation Curve Shifts when curve shifts to the left?
curve shifts to the left: "left shift has all the Ls” (Low temperature, aLkalosis, Low PaCO2)"
- the PaO2 is lower for any given level of SaO2
- as the curve moves left, proportionally less bound oxygen is released into solution.
- A shift of the oxyhemoglobin dissociation curve to the left represents an increased affinity of hemoglobin for oxygen and occurs in situations associated with a decrease in tissue metabolism and, therefore, lower cellular oxygen need.
Common conditions associated with a shift to the left include:
- decreased temperature,
- alkalosis (increased pH), and
- decreased PaCO2 levels.
31
What is the difference in fetal and adult hemoglobin?
- fetal hemoglobin differs most from adult hemoglobin in that it is able to bind oxygen with greater affinity than the adult form, giving the developing fetus better access to oxygen from the mother's bloodstream.
- This means that the neonate’s oxyhemoglobin dissociation curve is shifted to the left,
- meaning that the PaO2 is lower than adults with similar oxygen saturations; therefore, a neonate’s normal Pa02 level (50–80) is lower than an adult (> 80).
32
What happens to oxygen demand and oxygen consumption when theres adequate oxygen supply? when oxygen supply is limited?
- oxygen supply is adequate: then oxygen demand and oxygen consumption will be the same.
- oxygen supply is limited: oxygen consumption may be less than real oxygen demand of the cell
33
What are 3 effect/ problems of hyperoxia in preterm infants?
- development of severe retinopathy of prematurity (ROP),
- chronic lung disease, and
- brain injury
** recommendation is to maintain preterm infants’ oxygen saturations at 87%–94% until vascular maturation of the retina, and adjust upward as the infants nears term
34
A left shift of the oxyhemoglobin curve means that hemoglobin’s affinity for 02 is?
- increased/ improved
35
A right shift of the oxyhemoglobin dissociation curve means that hemoglobins affinity of 02 is?
- decreased/ reduced
36
What are some developmentally supportive caring measures by nurses for infants while in NICU?
- supported positioning,
- protecting sleep,
- limiting noise and light,
- minimizing unnecessary handling, and
- managing pain and
- manage stress
*** are invaluable in decreasing unnecessary oxygen consumption.
37
What are the components of acid-base balance?
- pH: measures the bloods acidity
- PaO2: The partial pressure of oxygen dissolved in the blood. Indicates how well the lungs are transferring oxygen to the blood
- pCO2 (respiratory component): partial pressure of carbon dioxide dissolved in the blood. Indicates how well the lung is removing CO2 from the blood
- HCO3 (metabolic component): amount of bicarbonate in blood (buffer for pH) --> controlled by kidneys
- base excess: amount of excess or deficit of base present in blood
38
What does blood gases reveal?
- acid base balance
- oxygenation status (arterial gases only)
- abnormalities of ventilation
- pH and pCO2 MATCH = RESPIRATORY
- pH and HCO3 MATCH = METABOLIC
39
Whats respiratory acidosis? vs metabolic acidosis?
respiratory acidosis:
- Results from an accumulation of carbon dioxide which combines with water in the body to produce carbonic acid (which lowers pH)
- Any condition that results in hypoventilation
- high PCO2 + low pH + normal HCO3
metabolic acidosis:
- Caused by either a deficit of base in the bloodstream or an excess of acids (other than CO2)
- The presence of metabolic acidosis should lead to the search for hypoxia
- Hypoxia in any tissue bed will produce metabolic acids as a result of anaerobic metabolism
- high HCO3 + low pH + normal PCO2
40
What does Hypoventilation lead to? hyperventilation?
- hypoventilation: hypoxia and hypercapnia (high CO2)
- hyperventilation: Hypocarbia, also known as hypocapnia (low pCO2)
41
Whats mixed acidosis?
- Mixed acid base disorders occur when there is more than one primary acid base disturbance present simultaneously
42
Whats respiratory alkalosis? metabolic alkalosis?
respiratory alkalosis:
- Results from alveolar hyperventilation which elevates the pH
- Any condition that causes hyperventilation
- low PCO2 + high pH + normal HCO3
metabolic alkalosis:
- Caused by either an excess of base or a loss of acid can cause metabolic alkalosis
- high HCO3 + high pH + normal PCO2
43
Why are preterm infants particularly at risk for infection/sepsis (3)?
- Miss out on maternal transfer of immunoglobulin in the 3rd trimester
- cellular immune system is immature (decreased phagocytotic ability to ingest microorganisms)
- Cannot localize infections
- Decreased ability to manage stress (decreased habituation and consoling behaviors).
44
What is neonatal sepsis? what are 2 types?
- Neonatal sepsis: is defined as a blood infection in the first 28 days of life, or up to 4 weeks after the expected due date for preterm infants
- 2 types: early onset and late onset
45
What is the difference between early onset vs late onset sepsis?
early onset sepsis:
- Defined by positive bacterial, viral or fungal culture in blood and/or CSF in the first 2 days after birth
- Usually results from organisms acquired intrapartum
- Most infants have symptoms within 6 h of birth, and almost all cases occur within 72 h.
- Group B streptococcus (GBS) and gram-negative enteric organisms (predominantly Escherichia coli) account for most cases of early-onset sepsis.
late onset sepsis:
- Late-onset neonatal sepsis defined as any positive blood and/or CSF culture for bacteria, viral or fungi after 2 days of age
- Late-onset sepsis is usually acquired from the environment
- Staphylococci account for 30 to 60% of lateonset cases and are most frequently due to intravascular devices
- Staphylococcus aureus and S. epidermidis, and Pseudomonas aeruginosa (normal human flora) are usually associated with late-onset disease
46
Whats MRSA?
- MRSA is a type of staphylococcus or "staph" bacterium that is resistant to many antibiotics
- Normally lives on your skin and in your nose
- can be spread from one person to another through casual contact or through contaminated objects.
- It is commonly spread from the hands of someone who has MRSA.
47
Whats CPO?
- Carbapenemase-Producing Organisms (CPO) are multidrugresistant gram-negative bacteria,
such as Klebsiella and Escherichia coli (E.coli), Acinetobacter and Pseudomonas.
- CPO can colonize in the gastrointestinal (GI) tract & patients may be asymptomatic, but can cause serious infections if it spreads
- Often spread through healthcare exposures
48
What are signs & symptoms of infection (3)?
- Temperature instability
- Tone (hyper/hypotonic)
- CNS status change
- CBC & Differential: Thrombocytopenia, anemic, Elevated CRP
- Color (pale)
- Perfusion
- Hypotension
- Respiratory distress
- Apnea
- Bradycardia/Tachycardia
- Poor feeding
- Feeding intolerance
- Decreased urine output
- Blood sugar: Hypoglycemia, Hyperglycemia
- Acidosis
- Electrolytes disturbance
49
What are the management of sepsis?
- CBC, CRP
- septic work up
- antibiotics
- clinical monitoring
50
What is c-reactive protein (CRP)
serum CRP:
- Marker of inflammation
- Normal: < 10 mg/dL
- Increases at 8 to 12 hours and peaks at 24 to 48 hours
