ARDS

Question 1

How do you define respiratory failure? (include number values)

Answer 1

• PaO2 < 50 (nl:80) on 50% oxygen
• PaCo2 > 50 (nl:40)
• acute resp failure: pH <7.25 (nl:7.4)
• chornic resp failure: pH approaching 7.4 (compensatory)

Question 2

Type 1 respiratory failure

Answer 2

• hypoxemia
• alveolar flooding –> shunting
• ex: pulm edema (cardiogenic with CHF, or non-cardiogenic), pneumonia, alveolar hemorrhage,

Question 3

Type 2 Respiratory failure

Answer 3

• hypercapnic (cant get rid of CO2)
• due to alveolar hypoventilation
• treat underlying cause

Question 4

3 “sources” of alveolar hypoventilation

Answer 4

1. CNS (drugs, hypothyroidism, metabolic alkalosis, CNS lesion, idiopathic alveolar hypoventilation)
2. Chest wall, neuromuscular system (kyphoscoliosis, Myasthenia Gravis, Guillain-Barre, ALS, Muscular dystrophy, Obesity, diaphragmatic fatigue, polymyositis, cervical cord injury)
3. **Lung **(COPD, CHF, ARDS, Severe Asthma)

Question 5

Type 3 Respiratory Failure

Answer 5

• from atelectasis, “perioperative respiratory failure”
• decreased FRC (after general anesthesia)

Question 6

Type 4 Respiratory Failure

Answer 6

• hypo-perfusion of respiratory muscles
• occurs durign shock, multi organ system failure

Question 7

Pulmonary Rules of Arterial Blood Gases

Answer 7

PaCo2:

ACUTE: for every 10 unit change in PaCO2, you have a 0.08 pH change

CHRONIC: for every 10 unit change in PaCO2, you have a 0.03 pH change (note: overcompensation never occurs)

PaO2:

AaDo2<25 normal lung/gas exchange unit

Question 8

What is ARDS, how does it present

Answer 8

sudden onset of severe dyspnea from some diffuse lung injury

• severe dyspnea
• reapid onset
• diffuse infiltrates in imaging
• hypoxemia
• leads to resp failure

Question 9

Etiology of ARDS

Answer 9

Divided into direct and indirect lung injury

direct: pneumonia, aspiration of something, pulmonary contusion (bruise), drowning, toxic inhalation

indirect: sepsis, severe trauma (bone fractures, rail chest, head trauma, burns), multiple transfusions, drug OD, pancreatitis, postcardiopulmonary bypass

Question 10

Pathophysiology of ARDS (4 steps)

Answer 10

key is to remember that inflammation takes place

1. insunlt
2. inflammation
3. cytokine storm
4. acute lung injury (increase capillary leak, lungs fill with fluid-interstitium first then alveoli) note: leakage causes proteins to leave vessel, and fluid follows. n ormally osmotic pressure keeps the fluid in the blood vessels, but you lose this with leakage

Question 11

Clinical course of ARDS

Answer 11

Exudative stage:

1. edema
2. hyaline membrane (lung trying to repair itself)

Proliferative stage:

1. interstitial inflammation
2. interstitial fibrosis

Question 12

Key cells and features in the pathophysiology of ARDS

Answer 12

• shunting AND V/Q mismatch
• secondary alterations in surfactant function
• increased pulmonary vascular resistance
• decreased pulmonary compliance
• decreased FRC (lungs collapsing)

Question 13

how do you rule out heart failure in ARDS?

Answer 13

wedge pressure (LAP) must be <18

if it were high, that would imply you have LHF and back up of blood and thus increased pressure in the LA

seeing a normal LAP tells us that its an isolated lung problem

Question 14

treatment

Answer 14

ventilation to control RR,Tidal Vol, FiO2,

PEEP (to pop/stent open those collapsing alveoli)

Question 15

Qualitative distinction between acute lung injury and ARDS

Answer 15

ALI: P/F less than or equal to 300

ARDS: P/F less than or equal to 200

P:F ratio is the ratio of arterial oxygen concentration to the fraction of inspired oxygen. It reflects how well the lungs absorb oxygen from expired air.