Respiratory failure

Question 1

Define respiratory failure

Answer 1

• failure of respiratory system to maintain normal blood gases
• hypoxemic (PaO2 50 mmHg)

• acute vs. chronic (compensatory mechanisms activated)

Question 2

Px of hypoxemia

Answer 2

restlessness, confusion, cyanosis, coma, cor pulmonale

Question 3

Px of hypercapnia

Answer 3

headache, dyspnea, drowsiness, asterixis, warm periphery, plethora, increased ICP (secondary to vasodilatation)

Question 4

Define type 1 & type 2 RF

Answer 4

Type 1: hypoxaemic
PaO2 decreased, PaCO2 normal or decreased
V/Q mismatch problem & involves hyperventilation (hence normal/low CO2)

Type 2: hypercapnic
• PaCO2 increased, PaO2 decreased
Fatigue, lack of respiration problem. (hence low O2, high CO2)

Question 5

Describe relationship b/w H+ & K+

Answer 5

Acidosis = hyperkalaemia
Alkalosis = hypokalaemia

H+ and K+ swap places (H+ into cell, K+ out of cell if too much H+. hence more K+ detected)

Question 6

Rx of T1 RF

Answer 6

• reverse the underlying pathology
• oxygen therapy: maintain oxygenation (if shunt present, supplemental O2 is less effective)
• ventilation, BiPAP and PEEP/CPAP: positive pressure can recruit alveoli and redistribute lung fluid

• improve cardiac output: ± hemodynamic support (fluids, vasopressors, inotropes), reduction of O2 requirements

Question 7

Should you give O2 in RF?

Answer 7

Yes - T1 RF

No but Yes - T2 RF (decrease hypoxic drive to breathe but still need to give O2 if hypoxic)

Question 8

Should you give O2 in COPD?

Answer 8

Yes - provide suppl O2 to achieve target SaO2 from 88-92%

Question 9

Causes of hypercapnia

Answer 9

• high inspired CO2
• low total vent (e.g. brainstem stroke, myasthenia gravis, Guillain-Barre, muscle fatigue)
• high deadspace vent
• high CO2 production (e.g. fever, sepsis, seizure, acidosis)

Question 10

Rx of T2 RF

Answer 10

• reverse the underlying pathology
• if PaCO2 >50 mmHg and pH is acidemic consider noninvasive or mechanical ventilation
• correct exacerbating factors
- NTT/ETT suction: clearance of secretions
- bronchodilators: reduction of airway resistance
- antibiotics: treatment of infections
• maintain oxygenation (see above)
• diet: increased carbohydrate can increase PaCO2 in those with mechanical or limited alveolar ventilation; high lipids decrease PaCO2

Question 11

Define ARDS

Answer 11

clinical syndrome characterized by severe respiratory distress, hypoxemia, and noncardiogenic pulmonary edema

Defined by:
• Hypoxaemia PaO2/FiO2

Question 12

What criteria do you use for ARDS and what does it consist of?

Answer 12

The Berlin criteria

    - acute onset
- within 7 d of a defined event, such as sepsis, pneumonia, or patient noticing worsening of respiratory symptoms – usually occurs within 72 h of presumed trigger
- bilateral opacities consistent with pulmonary edema on either CT or CXR
- not fully explained by cardiac failure/fluid overload, but patient may have concurrent heart failure
- an objective assessment (e.g. echocardiogram) should be performed if no clear risk factors

Question 13

What are the risk factors for ARDS?

Answer 13

• direct lung injury:

- airway: aspiration (gastric contents, drowning), pneumonia, inhalation injury (oxygen toxicity, nitrogen dioxide, smoke)
- circulation: embolism (fat, amniotic fluid), reperfusion injury

• indirect lung injury

- circulation: sepsis, shock, trauma, blood transfusion, pancreatitis
- neurogenic: head trauma, intracranial hemorrhage, drug overdose (narcotics, sedatives, TCAs)

Question 14

What is the pathophysiology of ARDS?

Answer 14

• disruption of alveolar capillary membranes -> leaky capillaries -> interstitial and alveolar pulmonary edema -> reduced compliance, V/Q mismatch, shunt, hypoxemia, pulmonary HTN

Question 15

Cx of ARDS

Answer 15

Fibrotic lung changes
• sequelae of ARDS include residual pulmonary impairment, severe debilitation, polyneuropathy and psychologic difficulties, which gradually improve over time

Question 16

Rx of ARDS

Answer 16

• treat underlying disorder (e.g. antibiotics if infection present)
• mechanical ventilation using low tidal volumes (