N470: Oxygenation (exam 2)

Explain the process of pulmonary gas exchange

inspiration & delivery of O2 from environment > alveoli, diffusion across alveolar-capillary membrane > attaches to Hb, dissolves in blood > left heart

movement of gasses from atmosphere to alveoli (& vice versa)

ventilation

mechanism by which O2 moves across the alveoli & into the pulmonary capillary

diffusion

O2 leaves alveoli to combine with Hgb (HbO2) or dissolve in blood (PaO2) to be carried to left side of heart

perfusion

factors that influence ventilation

1) conducting airways

2) ventilatory muscles

3) thorax (flexibility of rib cage)

4) elasticity of lungs

5) nervous system/regulators

regulators of ventilation

1) controller (CNS)- brainstem, cerebral cortex, neurons of spinal cord

2) group of effectors (the two muscle groups)

3) sensors (chemoreceptors)

what is the role of central chemoreceptors in the medulla in ventilatory regulation?

detect increased H+ and increases ventilation in response

what is the role of peripheral chemoreceptors in the aortic arch and carotids in ventilatory regulation?

sense decreased PaO2, and increased PaCO2 and H+ to increase ventilation

Inadequate ventilation occurs in the presence of... (6)

- minimal/absent chest wall motion

- increased WOB/accessory muscle use

- wheezes

- decreased/absent breath sounds (unilateral or bilateral)

- paradoxical chest wall motion

- respiratory distress

Qualifications for respiratory distress* (3)

1) PaCO2 >/= 50

2) PaO2

The movement of molecules from HI to LOW concentration; the mechanism by which O2 moves across alveoli into blood

diffusion

Which type of alveolar epithelial cells make up 90% of alveolar surface within lungs and are highly susceptible to injury/inflammation?

Type I alveolar epithelial cells

Which type of alveolar epithelial cells produce, store, secrete pulmonary surfactant?

Type II alveolar epithelial cells

phospholipid that lowers surface tension of the lungs, stabilizes alveoli, increases pulmonary compliance, eases WOB

surfactant

What occurs in disease with the disruption of synthesis and storage of surfactant?

alveoli collapse and pulmonary gas exchange is impaired

What is the role of macrophages in alveoli?

phagocytic role; keep alveoli clean and sterile; release hydrogen peroxide enzymes when killing microorganisms

three factors that affect diffusion of gas across alveolar-capillary membrane*

1) pressure gradient (driving pressure)

2) surface area

3) thickness

PAO2 vs PaO2

PAO2 - partial pressure of O2 in the ALVEOLI

PaO2 - partial pressure of O2 in arterial BLOOD

Same idea for PACO2 vs PaCO2

A-a increases to mmHg for every 10% increases in FiO2

A-a increases 5 to 7 mmHg for every 10% increases in FiO2

Interventions to increase surface area for discussion

- IS

- TCDB

- sighs/yawns

- PEEP (including pursed lip breathing)

The thicker the alveolar capillary membrane, the _________ the rate of diffusion

The thicker the alveolar capillary membrane, the slower the rate of diffusion

conditions that increase alveolar capillary membrane thickness

- ARDS

- pulmonary edema

- pulmonary fibrosis

The two ways oxygen is transported in the blood

plasma and hemoglobin

More than ____% of all oxygen transported in hemoglobin

More than 97 % of all oxygen transported in hemoglobin

Which is more important, SaO2 or PaO2?

SaO2

What is measured as SaO2 or SpO2?

oxyhemoglobin (HbO2)

What is PaO2?

The amount of oxygen dissolved in the plasma/blood

Which two provide info on ventilation?

a) pH

b) PaCO2

c) PaO2

d) SaO2

a) pH

b) PaCO2

Which two provide info on oxygenation?

a) pH

b) PaCO2

c) PaO2

d) SaO2

c) PaO2

d) SaO2

Normal pH

7.35-7.45

Normal CO2

35-45

Normal PaO2

80-100

Normal SaO2

95-100%

Normal HCO3

21-28 mEq/L

excessive retention of CO2 d/t hypoventilation, leading to decrease in pH below 7.35

respiratory acidosis

causes of respiratory acidosis

COPD

atelectasis

pna

neuromuscular dz

post-op recovery

narcotics

decreased HCO3 and decrease in pH below 7.35

metabolic acidosis

causes of metabolic acidosis

DKA

starvation

impending shock

ASA OD

diarrhea

Low PCO2 d/t hyperventilation (excessive CO2 exhaled); resulting in a pH above 7.45

respiratory alkalosis

causes of respiratory alkalosis

- hysteria

- fear

- anxiety

- head injury

- pain

- fever

- ventilator

increased HCO3 and an increase in pH above 7.45

metabolic alkalosis

causes of metabolic alkalosis

- diuretics

- prolonged NG suction w/o electrolyte replacement

- excessive vomiting

- overuse of antacids

What occurs in shift to the left?

Hgb increases affinity; its easier for Hgb to pick up O2, but harder for it to be released to the tissues; more O2 will stay bound and return to lungs

Shift to the left can result in tissue hypoxia even though...

there is sufficient O2 in the blood

Causes for a shift to the left

- decreased CO2

- decreased body temp

- decreased 2,3- DPG

- increased pH (alkalosis)

What occurs in shift to the right?

Hgb loses its affinity; its harder for Hgb to bind to O2, but easier for Hgb to release O2; more O2 is released to cells; less O2 will be carried from lungs

Causes for a shift to the right

- increased CO2

- increased body temp

- increased 2,3- DPG

- decreased pH (acidosis)

normal alveolar ventilation

4 L/min

normal pulmonary capillary perfusion

5 L/min

Normal V/Q (ventilation/perfusion)

4:5 or 0.8

When V/Q is >0.8, this means...

ventilation exceeds perfusion

When V/Q is <0.8, this means there is...

poor ventilation

Causes for impaired perfusion in V/Q matching

- decreased Hgb (anemia, CO poisoning)

- decreased flow (hemorrhage, PE)

- physiologic shunt (true shunt) (anatomic L to R cardiac shunt)

in diseased states when alveoli are ventilated but not perfused (only in PE)

alveolar dead space

Two types of pulmonary shunts

1) pulmonary anatomic

2) intrapulmonary

the combined amount of anatomic shunt and intrapulmonary shunt is called an...

an absolute shunt

refers to blood that moves from the R heart into the L heart w/o coming into contact w/ alveoli (normally 2-5%)

anatomic shunt

normal flow of blood past completely unventilated alveoli; R to L shunt

pulmonary shunt

shunts >20-30% usually requires...

mechanical ventilation

when there is an excess of perfusion in relation to alveolar ventilation (alveolar ventilation reduced but not absent)

shunt-like effect

pulmonary shunts go ___ to ___, whereas cardiac shunts go ___to ___

pulmonary shunts go R to L , whereas cardiac shunts go L to R

people with this kind of disease cannot fully fill their lungs with air; most often result from a conditions that stiffen the lungs

restrictive lung disease

Examples of restricted lung disease-

- interstitial lung disease (idiopathic pulmonary, psychosis

Signs of impaired gas exchange

- tachypnea

- restlessness, anxiety, confusion,

- crackles

- ABG impaired oxygenation= decreased PaO2, decreased SaO2

- ABG impaired ventilation= increased PaCO2, decreased PH

- intrapulmonary shunt

- infiltrates by CXR

Causes of ARDS

- trauma

- pulmonary infection, aspiration

- prolonged cardiopulmonary bypass

- shock

- fat emboli

- sepsis

s/s of ARDS

tachypnea, dyspnea, retractions, hypoxia, tachycardia, decreased pulmonary compliance

inflammatory syndrome marked by disruption of alveolar-capillary membrane

ARDS

ARDS clinical definition

- acute onset

- bilateral infiltrates on CXR

- PAWP <18 mmHg, or no clinical evidence of left ventricular failure

- hypoxemia refractory to O2 tx

what is ALI?

acute lung injury

PaO2/FiO2 ratio below 300 is considered*

ALI

PaO2/FiO2 ratio below 200 is considered*

ARDS

s/s or ARDS

1) air hunger

2) labored/rapid breathing (dyspnea)

3) low O2 levels in blood

4) cough/fever

5) low BP

6) confusion

7) extreme tiredness

three courses of patho for ARDS*

1) increased alveolar flooding

2) change in small airway diameter

3) injury to pulmonary vasculature

these lead to increased WOB and eventually hypoxemia refractory to oxygen therapy

Imaging for ARDS

- CXR

- CT

- bronchoscopy

LAB tests for ARDS

1) ABG

2) BMP

3) CBC

4) blood/urine/sputum cx

heart tests for ARDS

1) ECG

2) echo

ARDS collaborative management

- treat underlying cause

- promote pulmonary gas exchange

- fluids

- medications

How to promote pulmonary gas exchange in ARDs (6)

- supplemental O2

- intubation and mechanical vent

- lowest possible FiO2 to maintain SaO2>90%

- PEEP

- high RR w/ low TV to prevent barotrauma

- pressure ventilation reverse I:E ratio

Fluids for ARDS

NS and LR

purpose for medication in ARDS (5)

- prevent and tx infections

- vasoactive medications

- relieve pain/discomfort

- prevent clots in legs/lungs

- minimize gastric reflux

In severe respiratory failure, ______ can be used temporarily to give the lungs a rest

In severe respiratory failure, ECMO can be used temporarily to give the lungs a rest

Which position is helpful for ARDS?

prone

corticosteroids benefit in late ARDS because they promote breakdown and inhibit ________ as well as decrease ________

corticosteroids benefit in late ARDS because they promote breakdown and inhibit fibrosis as well as decrease edema

Possible complications for ARDS (9)

1) pulmonary fibrosis

2) barotrauma

3) PE

4) VAP

5) pneumothorax

6) cardiac dysfunction

7) blood clots

8) acute renal failure

9) memory/cognitive/ emotional problems

What do people with ARDS die from?

sepsis or MODS

mortality for ARDS

40-60%

When there is an excess of hydrogen (acidosis), how does it affect potassium levels?

increases potassium

a substance that reacts rapidly with acids and bases to maintain a neutral environment of stable pH such as Hgb, phosphate, or serum proteins

buffer

carbonic acid is converted to ___ in the lungs and is excreted from the body

CO2

non-volatile acids that must be excreted in the kidney

lactic acid and ketones

the slowest but most powerful compensatory mechanism is the ______ system

renal