Question

A patient is admitted to the ICU with severe necrotizing pancreatitis. A few hours after admission, he developed increasing oxygen requirements and was intubated for hypoxemic respiratory failure. Intially, his oxygen saturation improved to the mid-90% range on an FiO2 of 0.5, but in the past 2 hours, the nurse has had to increase the FiO2 back to 0.7 and his SaO2 is still in the lower 90% range. The patient remains on a PEEP of 5 cmH2O. The respiratory therapist drew an ABG which shows pH 7.35, PCO2 38, PO2 60, HCO3 - 22 on an FiO2 of 0.8. The patient's repeat chest x-ray is shown a "ground glass appearance". An echocardiogram performed earlier in the day revealed normal left ventricular function. How do you explain his worsening oxygenation status? What can you do to improve his oxygenation? What other changes should you consider making in the ventilator settings? If his oxygen saturation fails to improve despite being on high levels of support (i.e., FiO2 of 1.0 and 20 cmH2O of PEEP), what other options do you have for improving his oxygenation?

Answer 1

ANSWERS:-

1) How do you explain his worsening oxygenation status?  

* His worsening oxygenation is due to Acute Respiratory Distress Syndrome( ARDS).

* ARDS is a clinical syndrome characterized by a sudden and progressive pulmonary edema, increasing bilateral infiltrates on chest x-ray, hypoxaemia refractory to oxygen supplementation and reduced lung compliance.

* One cause of ARDS is metabolic disorders like pancreatitis.

* In Pancreatitis a lot of inflammatory chemicals are secreted in to the blood and this will affect the lung function causing the oxygen level to fall dangerously low.

* The inflammatory triggers initiates the release of cellular and chemical mediators, causing injury to the alveolar capillary membrane. This results in leakage of fluid into alveolar interstitial space and alterations in capillary bed.

* Alveoli collapse because of inflammatory infiltrates, blood and fluid and results in hypoxaemia.

2) Changes in the ventilator settings :-

* increase the rate ( respiratory ) and

*increase PEEP( positive end expiratory pressure ) to prevent alveolar collapse.

PEEP is the positive pressure that will remain in the airway at the end of the respiratory cycle, that is greater than the atmospheric pressure in mechanically ventilated patient.

* Increased PEEP in ARDS helps to protect alveoli and improve arterial oxygenation.

* *Increase FiO2.

3) Other options to improve oxygenation :-

* Nebulization, chest physiotherapy and positioning can be used.