A 22-year-old man with a history of severe reactive airway disease and polysubstance abuse is brought to the emergency department following a motor vehicle collision. Endotracheal intubation is performed and placement confirmed by continuous capnography. Peak inspiratory pressure on the ventilator is 45 cm H2O.
Which of the following describes the MOST LIKELY appearance of his capnogram?
Correct Answer: C
A timed capnograph has 4 segments with phase 0 representing inspiration. In a mechanically ventilated patient, a “normal” capnograph takes a relatively box-shaped appearance with a relatively flat phase III (A, Normal Capnogram figure).
The clinical scenario in the question suggests obstructive lung pathology which manifests as an up-sloped phase III which some have described as “shark-finned” appearance (C, Obstructive Lung Disease figure). Any airway obstruction, including obstruction of the endotracheal tube, can result in this waveform. A biphasic capnograph has been previously described but is not specific for endobronchial intubation (B). Regardless, its presence should prompt further investigation.
Capnography has additional utility as a noninvasive cardiac output monitor. Current American Heart Association/ Advanced Cardiac Life Support guidelines recommend the use of continuous capnography during cardiopulmonary resuscitation as an assessment for adequacy of cardiopulmonary resuscitation and a sensitive detector for return of spontaneous circulation. A flat capnograph should alert the physician to possible esophageal intubation or inadvertent extubation, as adequate ventilation should produce a waveform (D).
A 72-year-old female (body mass index of 27 kg/m2 ), admitted for exacerbation of chronic obstructive pulmonary disease (COPD), is started on noninvasive ventilation on the floor. She is claustrophobic, and the intern orders lorazepam for mask tolerance. Soon after, the patient is found to be obtunded and a code is called. During laryngoscopy, particulate gastric contents are noted in the posterior pharynx. Her postintubation vitals are:
Despite adjustment of ventilatory parameters and maximal bronchodilator therapy, airway inspiratory pressures remain high.
Which of the following actions would be BEST next step in the management of this patient?
Correct Answer: D
High-quality randomized control trials support the use of noninvasive ventilation as a first-line intervention for patients with acute hypercapnic respiratory failure due to exacerbation of COPD. It is associated with decreased mortality and a lower likelihood of invasive ventilation. However, vigilance is required, particularly as failure necessitates intubation. Furthermore, as this is a “nonsecure” ventilation modality, there is a potential risk for gastric aspiration.
For this patient, diagnostic studies such as surface ultrasonography, ABG, chest x-ray (answers A, B, and C) are all reasonable management steps that should be taken, as they can be helpful in narrowing the differential diagnosis. The presence of gastric contents in the pharynx on laryngoscopy does not guarantee aspiration but should raise suspicion. Most aspirated gastric content is liquid and quickly disperses, but in the event of particulate aspiration, bronchoscopy (answer D) could be both diagnostic and therapeutic and should be the next step in management.
A 68-year-old man in stable atrial fibrillation with rapid ventricular response undergoes transesophageal echocardiogram and successful synchronized cardioversion under conscious sedation in the medical intensive care unit (ICU). Topical 20% benzocaine spray is used for oropharyngeal anesthesia prior to transesophageal probe insertion. His starting SpO2 is 99% on 6 L/min oxygen via nasal cannula. Within a few minutes, the patient appears blue-gray and SpO2 decreases to 84%. His saturation fails to improve on 10 L/min oxygen via simple face mask. The rest of the vital signs remain stable.
Which of the following findings would be LEAST consistent with the patient’s clinical condition?
Correct Answer: A
Conventional pulse oximeter determines the ratio of light absorbance at two wavelengths (660 nm-red and 940 nm-infrared) and plots this against direct measurements (arterial oxygen saturation, SaO2 ) to determine the peripheral oxygen saturation (SpO2 ). SpO2 generally correlates well with arterial SaO2 ; however, this relationship can be inaccurate when local tissue perfusion is impaired.
The given clinical context of recent benzocaine use and presence of normal vital signs except SpO2 suggest benzocaine-induced methemoglobinemia. This patient needs to be further evaluated by cooximetry. In this case, PaO2 will remain normal (answer C) since it measures the oxygen dissolved in blood and methemoglobin affects the oxygen carrying capacity of hemoglobin. However, if the PaO2 were lower, causes for an elevated A-a gradient should be explored (ie, aspiration, bronchospasm, etc.). Mild hypercarbia due to hypoventilation is likely during procedural sedation (answer D). Since this patient’s vital signs are stable (after cardioversion), it is reasonable to expect a normal SpO2 waveform, as compared to the poor waveforms seen in low perfusion states (answer B).
An 88-year-old woman with an acute GI bleed undergoes endoscopic evaluation and subsequently remains intubated in the ICU in anticipation of further intervention the following day. She is 5′6″ and has her ideal body weight of 60 kg throughout her life. Her arterial blood gas (ABG) shows:
She is hemodynamically stable, and her airway pressures are low.
Which of the following is the MOST appropriate next step in her management?
Correct Answer: B
This patient has a minute ventilation of ∼4.5 L, which is inadequate, as the ABG indicates a respiratory acidosis. Since physiologic and anatomic dead space both increase with age, this is not entirely surprising. The patient has an additional issue—her oxygenation is adequate but suboptimal. A PaO2 of 68 on 50% FiO2 indicates a large A-a gradient. The patient’s relatively low Tv (5.3 mL/kg) should raise suspicion of atelectasis from hypoventilation. This could be combated with frequent recruitment maneuvers and increasing PEEP (answers C and D).
However, increasing the tidal volume would increase the minute ventilation and improve atelectasis and is a reasonable first step in management of this patient (answer B). For instance, increasing tidal volume to 400 mL (7 mL/kg ideal body weight) would still be well within the lung protective paradigm while increasing the patient’s minute ventilation by 25%.
You are the sole intensivist at a rural hospital, and the overnight hospitalist asked you to evaluate a patient with a left-sided malignant pleural effusion who is experiencing dyspnea. You determine that the patient has a very large pleural effusion, and you decide that a thoracentesis will be needed. Under ultrasound guidance, you place a chest tube and begin to aspirate the pleural effusion.
At what point should you stop your thoracentesis to maximize your drainage and minimize complication(s)?
Re-expansion pulmonary edema (RPE) can be a life-threatening complication during thoracentesis for pleural effusion. Some evidence suggests that RPE occurs due to the sudden decrease in pleural pressure. It had been recommended to stop thoracentesis when pleural pressure dropped below −20 cm H2O (answer C) or when more than 1 L of fluid was removed (answer A). However, various studies have shown that large volume thoracentesis (more than 1 L) can be performed without adverse events, even if the final pleural pressure is below −20 cm H2O. In addition, further investigation show that there is little change in pleural pressure when the patient coughs, so coughing should not be an end point for thoracentesis (answer D). However, chest discomfort is recommended as the point at which thoracentesis would be stopped, due to the potential of development of unsafe negative pressure (answer B).
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