What is hypoxemic respiratory failure? Give 4 things that cause this.
Any process that limits diffusion or V/Q mismatching to the point that oxygen saturation is less than 87% or PaO2 is less than 55.
- Ventilation/perfusion mismatch
- Impaired gas diffusion (something going on between airspace and capillaries e.g. interstitial lung disease, alveolar filling processes, interstitial edema, anything that thickens the area)
- Alveolar hypoventilation (hypercapnia. hypoxemia is from excess CO2 so there is no room for O2--look at the alveolar gas equation)
- High altitude (lower barometric pressure)
What is hypercapneic respiratory failure? What are the two general categories?
Any process that impairs ventilation.
Cant breathe: Asthma, COPD, upper airway obstruction, severe burn (chest wall restriction), trauma, neuromuscular.
Wont breathe: respiratory drive issues, central hypoventilation, oversedation, brain injury, seizure.
Cant breathe - lung and associated structures
Wont breathe - brainstem
About ___ % of a normal tidal volume breath (1L) is deadspace
What is deadspace ventilation?
Any process that reduces perfusion to ventilated alveoli increases physiologic dead space.
- Decreased cardiac output
- Pulmonary embolus
- High airway pressures
What 3 things are done for evaluating respiratory failure?
1. Physical exam
3. Arterial blood gas
Do this in every patient, every time
According to this lecturer, what is a normal A-a gradient?
What does a normal A-a gradient reflect?
Normal gas exchange
What is acute-on-chronic respiratory failure?
A patient that has chronic respiratory failure that has an acute episode.
What is the basic approach for classifying respiratory failure?
1. You want to determine which of the two groups the patient's hypoxemia falls under:
A. from a primary diffusion, V/Q, or shunt abnormality (abnormal A-a)
B. Hypercapnia (normal A-a)
because treatment will be different.
2. Use clinical context to determine acute vs chronic
3. Determine if respiratory acidosis is present. If so, there is a component of hypercapneic respiratory failure.
4. Determine acute vs chronic with compensation rules
If a patient with respiratory acidosis has a change of pH of 0.22 and a change of pCO2 of 40, is it chronic or acute or somewhere in between?
0.22/40 = 0.0055 = somewhere in between (acute on chronic)
0.008 = acute (to remember, acute = 8cute)
0.003 = chronic
What is PEEP for?
Positive end-expiratory pressure is used to maintain surface area by keeping airways open. Without PEEP, alveolar units can collapse and be de-recruited.
A patient with asthma has an attack and presents with acute hypercapneic respiratory failure with this arterial blood gas on these ventilator settings. What should be adjusted on the ventilator?
Decrease FIO2 and increase RR and treat asthma with standard therapies (steroids, bronchodilators with or without antibiotics)
A patient with chronic systolic heart failure presents with respiratory failure and an A-a gradient of 450. Why is it so high?
The patient is on a ventilator with VT 500, RR 20, Fio2 90%, PEEP 5 and the blood gas is 7.5/23/45. What should be done on to the ventilator?
Increase Fio2, Increase PEEP.
What is ARDS?
Acute respiratory distress syndrome.
- Occurs within 1 week of known clinical insult or worsening respiratory symptoms
- Diffuse bilateral pulmonary infiltrates
- Not fully explained by cardiac failure or fluid overload
- Severity is classified by PaO2:FIO2 with greater than 5 cmH2O PEEP
What is the pathogenesis of ARDS?
Some sort of insult fires up innate immune system which starts attacking the lung. You get breakdown of alveolar capillary barrier, influx of macrophages, neutrophils, cytokines, capillary leak, protein leak, organization, fibrosis, loss of surfactant, loss of alveolar/capillary barrier function
How does ARDS look in histology?
- Alveolar filling process with proteinaceous edema
- Denuded basement membrane
- "Hyaline membrane" formation (protein deposition
- Neutrophilic infiltrate
- Type 2 cell hyperplasia
What are the associated conditions for ARDS?
Sepsis (most common)
Direct inhalational or aspiration injury
How do we treat ARDS?
Treat the underlying cause of ARDS.
What is ventilatory induced lung injury?
High tidal volume ventilation can worsen lung injury and systemic inflammation
True or False: Prone position in patients with P/F ratio less than 150 reduces mortality rate.
True or False: Ventilator strategy is the only thing that improves ARDS survival
However, it's still necessary to treat the underlying cause in order for the patients to get better
In patients that are on ventilators that need increased ventilation, you may want to increase either the RR or TV. What should you ask yourself?
Ask yourself if this patient might have ARDS. If they have ARDS, increase respiratory rate, not tidal volume or else you will hurt the patient.