An 89-year-old bedridden man with a history of dementia, non– insulin-dependent diabetes, hip fracture (treated conservatively), diastolic heart failure, and chronic kidney disease was admitted to the medicine service for confusion and possible UTI. The patient had a one week hospital admission for UTI one month ago. While he was waiting for bed assignment, he starts to desaturate in the emergency department. His vital signs are heart rate 115 beats/min, blood pressure 100/60 mm Hg, respiratory rate 26 breaths/min, SpO2 86% on room air. Lung auscultation was unrevealing. You were consulted by the medicine team to evaluate the patient for possible ICU admission for hypoxic repository failure. Portable x-ray was negative for any acute process per radiology official read. Your bedside lung ultrasound images show the following:
Besides placing the patient on oxygen, what would be the BEST next step in management?
Correct Answer: A
Based on the ultrasound images, this patient likely has pneumonia (answer A). The negative auscultation findings and negative chest x-ray cannot rule out pneumonia due to their low accuracy and negative predictive values. Moreover, chest x-ray diagnostic accuracy for pneumonia has been questioned. Bourcier et al. showed that chest x-ray has low sensitivity in diagnosing pneumonia when compared to lung ultrasound (95 vs. 60%).
Multiple sonographic signs were described in the literature to assist in the diagnosis of pneumonia. These signs include b-lines, air bronchograms, subpleural consolidations “hepatization,” pleural line abnormalities, and pleural effusions. Air bronchograms and subpleural consolidations “hepatization” are the most specific sonographic signs. Air bronchograms are thought to be caused by air trapped in small airways within a consolidated lung. On ultrasound, it will look like hyperechoic dots and lines (air) within a hypoechoic (fluid) area (Figure 1). Subpleural consolidations, which also known as “hepatization,” is a sonographic sign of consolidated lung. Typically, the lung parenchyma is not visible on ultrasound since air does not conduct sound waves, but when small airways and alveoli get filled by purulent fluid, sound waves will be able to go through the lung parenchyma. Sonographically, consolidated lungs will have the echotexture of the liver, hence the name hepatization of lungs.
Answers C and D are both incorrect because the patient does not have sonographic signs suggesting pleural edema or effusion. Pulmonary embolism can cause peripheral lung parenchyma infarction, which sonographically appears like consolidation. The presence of air bronchograms, on the other hand, is pathognomonic of pneumonia.
A 65-year-old female patient presents with acute respiratory failure to the ICU. She is intubated and placed on pressure support ventilation. The driving pressure is set at 10 cm H2O. The PEEP is set at 10 cm H2O. Esophageal balloon is placed, and a pressure of negative 12 cm H2O is obtained at end inspiration.
Given these measurements please estimate transpulmonary pressure.
Correct Answer: C
Transpulmonary pressure is defined as the difference between alveolar pressure and pleural pressure.
Alveolar pressure (at end inspiration) is the driving pressure plus PEEP (here, 10 cm H2O + 10 cm H2O = 20 cm H2O).
The pressure measured by the esophageal balloon is a surrogate for the intrapleural pressure and is measured at −12 cm H2O for this patient. Therefore, the estimated transpulmonary pressure is 32 cm H2O. Elevated transpulmonary pressures increase the strain on the lung and worsened lung injury. It is important for clinicians to consider the impact of the pleural pressure on the transpulmonary pressures to identify patients at risk for worsening lung injury and to institute better ventilation strategies.
A 48-year-male patient with a BMI of 48 kg/m2 is undergoing a spontaneous breathing trial in anticipation of extubation.
What is the best position to optimize his respiratory mechanics?
Correct Answer: D
Morbid obese patients have a marked reduction in functional residual capacity mainly due to a reduction in expiratory reserve volume. The diaphragm is displaced upward decreasing lung and chest wall compliance. In contrast to supine position, both beach chair and reversed Trendelenburg positions increase functional residual capacity as well as spontaneous tidal volume. However, there is a larger increase seen in reversed Trendelenburg position. This is potentially because the lower leg position exerts less upward pressure on the abdomen and diaphragm. Hence, in morbidly obese individuals, it is recommended to perform spontaneous breathing trial, extubation, and preoxygenation in reverse Trendelenburg position.
A 47-year-old male patient (BMI 55 kg/m2 ) with methicillin-resistant Staphylococcus aureus pneumonia suffers an aspiration event. His oxygen saturation on a nonrebreather face mask is 72%. His previous endotracheal intubation was described as “straightforward.”
What is the best initial approach for airway management?
Correct Answer: B
The patient is acutely hypoxic, and invasive mechanical ventilation seems to be the safest option. While noninvasive ventilation has a role in management of respiratory failure in the morbid obese population its use in acute hypoxic respiratory failure is limited. Given that the patient is already hypoxemic, an awake fiberoptic intubation would be not easily tolerated and likely result in further potentially dangerous hypoxemia. Morbid obese critically ill patients desaturate quickly during airway manipulation due to limited reserve. Rapid-sequence induction followed by intubation via direct laryngoscopy is the fastest way to secure the airway and hence the safest. In this patient, previous record of intubation without difficulty is further reassuring. However, fiberoptic intubation and video laryngoscopy are important backup options in this patient, if direct laryngoscopy fails.
A 67-year-old patient (BMI 40 kg/m2 ) is admitted to the ICU in acute respiratory failure.
What is the best way to optimize the patient’s end expiratory lung volume?
Generally, clinicians set a lower PEEP than what was used during a recruitment maneuver. This becomes more important in obese individuals where the transpulmonary pressure is higher. It has been shown that measurement of transpulmonary pressures by esophageal balloon following a recruitment maneuver lead to same PEEP settings as after a decremental PEEP trial. In obese patients, the latter strategies had no negative hemodynamic effects but improved lung mechanics as well as oxygenation significantly.
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