Respiratory Failure: A Case Study

Now we switch gears to look at a case:

Key findings: High Respiratory rate, high pulse, bilateral crackles, blood pH of 7.45, pO2 at 60, worsening to 40 2 hours later, oxygen gradient at 56, worsening to 67 two hours later.

Also, another way to show lung function is to get the arterial oxygen tension and divide by the % of oxygen in inspired air.  The goal should be 500, our patient is at 286 at admission, then goes down to 190.

 And the lung x-ray

 See the bilateral diffuse infiltrates, consistent with acute lung injury or acute respiratory distress syndrome, which cause respiratory failure.  It is often caused by inhalation of damaging chemicals, causing lung damage and infiltration into the lungs.

So what are acute respiratory damage and respiratory distress symdrome?  Check out the handy chart.

So we are looking for a decreased ratio of arterial oxygen to inspired oxygen, bilateral infiltrates on chest x-ray, and no evidence of pulmonary edema. 

·         The big differentiating factor is the arteriolar pressure divided by the fraction of oxygen in inspired air. 

·         Below 300-acute lung injury, below 200, acute respiratory distress syndrome. 

·         So acute respiratory distress syndrome is an extreme form of acute lung injury.

PEEP stands for positive end expiratory pressure, a strategy used in a ventilator to open airways.

 As mentioned before, we need to rule out pulmonary edema, since it presents on an x-ray like ALI and ARDS.  This can be ruled out by measuring pulmonary artery wedge pressure, which would be increased in pulmonary edema, but is normal (less than or equal to 18 mm Hg) in ALI and ARDS 

So our patient had gone from ALI upon admission to ARDS 2 hours after admission.
 

 So what can cause ALI and ARDS?

• Anything that causes damage to the alveolar endothelium, which will then result in increased permeability of capillaries, which causes fluid to fill the alveoli, a non-cardiogenic pulmonary edema. 
• This decreases gas exchange.
• There can be direct lung injury to the lungs. 
  • Like our patient, who inhaled toxic fumes. 
  • Or you could have acid aspiration, which can occur in labor if a patient does not fast for 12 hours before delivery and they vomit and then inhale the vomit. 
  • Or there can be a lung infection.
• Another option is inflammatory mediators released during sepsis.

Back to the Respiratory System Index