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Chapter 25. Ventilation and Pulmonary Mechanics

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A 50-year-old man underwent a craniotomy for subdural hematoma evacuation. Muscle relaxants were used throughout the case but were not pharmacologically reversed. He was brought to the intensive care unit (ICU) intubated. He had spontaneous breathing efforts shortly after ICU admission and is now being assessed for extubation. Which is the best indicator of return of neuromuscular function prior to extubation?

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A. Ability to follow commands with a strong handgrip

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B. Spontaneous breathing trial showing adequate gas exchange with normal tidal volumes and a respiratory rate of 20 breaths/min

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C. A quantitative train-of-4 ratio of 0.9

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D. Inspiratory force of –20 cm H2O

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C. Residual neuromuscular blockade puts patients at risk for respiratory complications and is a common occurrence in the postanesthesia care unit and ICU. Clinically significant residual paralysis cannot be excluded by any combination of clinical criteria, and a quantitative assessment of the response to nerve stimulation should be assessed. The most common method to accomplish this is train-of-4 (TOF) stimulation of the ulnar nerve at the wrist; this consists of a series of 4 supramaximal stimuli given every 0.5 seconds. Each stimulus in the sequence causes the muscle to contract, and the “fade” provides the basis for evaluation; that is, dividing the amplitude of the fourth response by the amplitude of the first response provides the TOF ratio. It is difficult to exclude residual block using subjective evaluation of the tactile or visual TOF ratio (qualitative monitoring). Objective (quantitative) neuromuscular monitoring devices must be used to reliably detect clinically significant residual neuromuscular blockade. A quantitative train-of-4 ratio of 0.9 is the best indicator of return of neuromuscular function prior to extubation.

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Reproduced with permission from Hanson C, III. Procedures in Critical Care. New York, NY: McGraw-Hill, 2009.

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After placement of a subclavian central venous catheter in a mechanically ventilated patient, you obtain the following ultrasonographic image along the anterior and lateral chest walls. What is the arrow emphasizing?

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Ultrasound (axial image) of the thoracic cavity.

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A. Normal lung parenchyma

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B. Pneumothorax

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C. Pleural effusion

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D. Lung infiltrates

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A. Evaluation of the lung parenchyma is based on the presence of different artifact patterns, all of which emanate from the pleural line. The arrow indicates A-lines, which are present in normal lung and represent reverberation artifacts at parallel intervals underlying the highly echogenic pleural line. B-lines are vertical, laser-like reverberation artifacts that arise ...

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