Acute Respiratory Failure and Mechanical Ventilation


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Acute Respiratory Failure and Mechanical Ventilation


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



  1. A 73‐year‐old woman is admitted to the intensive care unit after undergoing exploratory laparotomy and subtotal colectomy for C. diff colitis. Her past medical history is significant for smoking and clinically severe obesity with BMI 44.6 (height 160 cm, and weight 114 kg). She is hypotensive on a norepinephrine drip and mechanically ventilated on assist control volume mode of ventilation. The most appropriate initial tidal volume setting is:

    1. 1100 mL
    2. 684 mL
    3. 312 mL
    4. 520 mL
    5. 912 mL

    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.


  2. 48‐year‐old man has acute respiratory failure after a motorcycle crash. He is on low tidal volume, high PEEP ventilation with FiO2 100% and his PaO2 is 50 mm Hg. He is started on inhaled nitric oxide (NO). Based on the current evidence, the role of NO in acute respiratory failure is best characterized as:

    1. decreased mortality.
    2. improved oxygenation but not mortality
    3. decreased rate of acute kidney injury
    4. NO has no effect on oxygenation
    5. routine ARDS management

    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.


  3. 27‐year‐old man with ARDS after debridement for necrotizing soft tissue infection of the perineum has worsening hypoxemia with PaO2 90 mm Hg on 90% FiO2 despite optimal low tidal volume ventilator settings and neuromuscular blockade. The next most appropriate step in his management would be:

    1. Inhaled nitric oxide
    2. High dose steroids
    3. ECMO rescue
    4. Prone positioning
    5. Continue current management and start prone positioning if there is no improvement after 72 hours.

    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.


  4. 56‐year‐old woman who was initially admitted with necrotizing pancreatitis develops acute respiratory distress and hypotension. She is intubated and admitted to the intensive care unit. Over the next 24 hours, she is given 10 L of crystalloid for persistent hypotension and oliguria. She is on assist control volume‐cycled ventilation (tidal volume 6 mL/kg, FIO2 30%, PEEP of 5) with an SpO2 of 98%. The ventilator is alarming for high pressure. Measurement of the pressures reveals a high peak airway pressure and a normal plateau pressure. The next step in management would be to:

    1. Decompressive laparotomy for abdominal compartment syndrome
    2. Neuromuscular blockade by continuous infusion
    3. Change to pressure support ventilation mode
    4. Adjust the ventilator alarm settings thresholds
    5. Inhaled bronchodilator therapy

    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.


  5. Non‐invasive ventilation in the critically ill patients is best supported by clinical evidence for this diagnosis:

    1. COPD exacerbation
    2. Acute Respiratory Distress Syndrome
    3. Post‐extubation hypercarbic failure
    4. Hypercarbia due to severe traumatic brain injury
    5. Facilitating secretion clearance for pneumonia

    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.


  6. The criterion that is most predictive of a successful attempt at liberation from mechanical ventilation is:

    1. Glasgow Coma Score of 8T
    2. Minute ventilation of 20 L/min
    3. Rapid Shallow Breathing Index of 40
    4. Maximal inspiratory pressure of −10 cm H2O
    5. Calculated PaO2/FiO2 ratio of 125

    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.


  7. A 67‐year‐old woman with COPD is mechanically ventilated after undergoing cytoreductive surgery for ovarian cancer. She is on volume control ventilation with a decelerating waveform for gas delivery. Which of the following best describes the characteristics of the decelerating gas delivery waveform compared to a square waveform?
    Schematic illustration of the waveform a patient.


    1. Higher peak airway pressure
    2. Higher likelihood of CO2 retention
    3. Lower likelihood of CO2 retention
    4. Shorter inspiratory time
    5. Lower mean airway pressure

    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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Dec 15, 2022 | Posted by in CRITICAL CARE | Comments Off on Acute Respiratory Failure and Mechanical Ventilation

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