In the article by Lichtenstein et al (July 2008),1 the authors describe the use of lung ultrasound in evaluating patients with acute respiratory failure. The algorithmic approach Bedside Lung Ultrasound in Emergency, the BLUE protocol, is described with a diagnostic accuracy of 90.5%. Three hundred and one consecutive patients with acute respiratory failure were assessed; 260 were included (cardiogenic pulmonary edema, 64; pneumonia, 83; decompensated COPD, 49; acute asthma, 34; pulmonary embolism, 21; and pneumothorax, 9) and 41 were excluded from the study (rare causes, 9; no final diagnosis, 16; and several final diagnoses, 16). Among all the patients with a final diagnosis, there was not a single patient with diaphragm paralysis. This could be because of the design of the BLUE protocol, as it does not have assessment of diaphragm function as a step in the algorithm. Diaphragm paralysis, although not a common cause of acute respiratory failure, is likely underdiagnosed, and it is not unusual for an intensivist to come across such a case. Diaphragm paralysis can be diagnosed with the use of bedside ultrasound.2,3 Unilateral diaphragm dysfunction is easier to diagnose than bilateral and, in the presence of comorbid conditions, can be a cause of acute respiratory failure. Trauma (surgical or nonsurgical) and malignancy involving the phrenic nerve are common causes of diaphragm paralysis.4 The assessment of diaphragm function in patients with these conditions and respiratory distress is important. I came across two cases with acute hypercapnic respiratory failure who had unilateral diaphragm paralysis (one left and one right), as seen on ultrasound and fluoroscopy examination. In both cases, unilateral diaphragm paralysis was considered to be the main reason for respiratory failure, but comorbid conditions were believed to be contributory. I have been using the BLUE protocol in my clinical practice and have found it be helpful in bedside evaluation of patients with acute respiratory distress. I suggest that the addition of diaphragm function assessment, a simple technique, as a step in the BLUE protocol will enhance its diagnostic accuracy.