Adrian A. Maung, MD1 and Lewis J. Kaplan, MD2,3 1 Yale School of Medicine, New Haven, CT, USA 2 Division of Trauma, Surgical Critical Care and Emergency Surgery, Department of Surgery, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA 3 Corporal Michael J. Crescenz VA Medical Center, Philadelphia, PA, USA The patient is at risk for developing acute respiratory distress syndrome based on her clinical condition as well as risk factors of smoking and morbid obesity. Low tidal volume ventilation, as described by ARDSnet, was the first intervention demonstrated to improve mortality in those with ARDS. Initial tidal volumes should be set at 6–8 mL/kg based on predicted (ideal) body weight. Based on the patient’s height 160 cm, her predicted body weight is 52 kg thus answer C is the correct choice. Choice A is based on 10 mL/kg and actual weight. Choice B is 6 mL/kg but based on actual weight. Choice D is based on 10 mL/kg and ideal body weight and Choice E is 8 mL/kg and actual body weight. Answer: C Brower RG, Matthay MA, Morris A, et al. Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med. 2000; 342(18):1301–1308 Khan YA and Ferguson ND . What is the Best Mechanical Ventilation Strategy in ARDS in Evidence‐Based Practice of Critical Care , 3rd Edition Elsevier 2020. Current clinical evidence does not support a role for inhaled NO in the routine management of ARDS. Although inhaled NO may improve oxygenation, it has not been shown to improve mortality (Answer B). NO has also been associated with increased rates of acute kidney injury. Answer: B Gebistorf F, Karam O, Wetterslev J, et al. Inhaled nitric oxide for acute respiratory distress syndrome (ARDS) in children and adults. Cochrane Database Syst Rev. 2016;(6):CD002787. Ruan SY, Huang TM, Wu HY, et al. Inhaled nitric oxide therapy and risk for renal dysfunction: a systematic review and meta‐analysis of randomized trials. Crit Care. 2015; 19:137. Clinical evidence supports the use of early prone positioning in patients with severe ARDS (answer D). The PROSEVA trial published in 2013 demonstrated an improved 28‐day mortality with 16 hours of prone positioning per day (16% in the prone group vs 32.8% in control group). Most of the research has focused on early rather than a rescue role for severe ARDS and therefore waiting for 72 hours (choice E) would not be appropriate. Inhaled nitric oxide (choice A) has not been associated with improved outcomes. ECMO (choice C) has a role in the management of refractory hypoxemia but would not be the next step in the management of this patient. The role of early steroids remains controversial but there is no benefit to late (after 14 days) (choice B) steroid administration Answer: D Guérin C and Reignier J . PROSEVA study group. “Prone positioning in severe acute respiratory distress syndrome”. N Engl J Med. 2013; 368(23):2159–68. PMID: 23688302. Guérin C, Albert RK, Beitler J, et al. Prone position in ARDS patients: why, when, how and for whom. Intensive Care Med. 2020; 46(12):2385–2396. Epub 2020 Nov 10. PMID: 33169218; PMCID: PMC7652705. Elevated airway pressure can occur secondary to different pathologies that affect airway resistance and/or pulmonary compliance. The ventilator in many cases automatically reports the peak airway pressure but it is also important to measure the plateau pressure to distinguish between problems with pulmonary compliance (elevated plateau pressure) vs. problems with airway resistance (difference between peak and plateau pressures). The patient in the clinical vignette is certainly at risk for development of abdominal compartment syndrome but a normal plateau pressure would point away from this diagnosis (choice A). A high peak pressure and normal plateau pressure is most suggestive of increased airway resistance that could be secondary to bronchospasm (Answer E), endotracheal tube occlusion, retained secretions and mucous plugging. Neuromuscular blockade (answer B) or a change to pressure support mode (answer C) would not address increased airway resistance. Ignoring the ventilator alarm (choice D) without further investigation is never a good idea. Answer: E Maung A and Kaplan L . Waveform analysis during mechanical ventilation. Curr Probl Surg. 2013; 50(10): 438–446. PMID: 24156841. Multiple randomized trials have shown that non‐invasive ventilation (NIV) decreases rates of intubation and improves mortality compared to standard therapy in patients with COPD exacerbation. (Answer A). NIV has also been shown to be helpful in acute cardiogenic pulmonary edema. There is currently conflicting (and even evidence that demonstrates deleterious effects) with using NIV in ARDS (choice b) and post‐extubation failure (choice c). Contraindications to NIV include severe altered mental status (choice d) and copious secretions (choice e). Answer: A Plant PK, Owen JL and Elliott MW . Early use of non‐invasive ventilation for acute exacerbations of chronic obstructive pulmonary disease on general respiratory wards: a multicentre randomised controlled trial. Lancet 2000; 355(9219):1931–5. PMID: 10859037 Bourke SC, Piraino T, Pisani L, et al. Beyond the guidelines for non‐invasive ventilation in acute respiratory failure: implications for practice. Lancet Respir Med. 2018; 6(12):935–947. PMID: 30629932. Although there is no single clinical predictor with the sensitivity and specificity to predict 100% successful liberation from mechanical ventilation, certain objective measures have been validated and used in combination as a screening tool. These include the rapid shallow breathing index < 105 breaths/min/L (answer C), minute ventilation < 10 L/min, an alert and appropriately interactive mental status, maximal inspiratory pressure less than −20 to −25 cm H2O and a P/F ratio ≥ 150. Answer: C Baptistella AR, Sarmento FJ, da Silva KR, et al. Predictive factors of weaning from mechanical ventilation and extubation outcome: a systematic review. J Crit Care. 2018; 48:56–62 PMID: 30172034. Two most commonly used gas flow waveforms in adults are square and decelerating. The square waveform is characterized by higher peak airway pressure, shorter inspiratory time (thus longer expiratory time) and lower mean airway pressure compared to the decelerating waveform (Choices: a, d and e). Since the expiratory time is shorter with the decelerating waveform, there is a higher likelihood of CO2 retention (answer b) especially in patients who have preexisting limitation of expiratory flow such as COPD. Answer: B Maung A and Kaplan L Waveform analysis during mechanical ventilation. Curr Probl Surg. 2013; 50(10): 438–446 PMID: 24156841.
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Acute Respiratory Failure and Mechanical Ventilation
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