6 The criterion that is most predictive of a successful attempt at liberation from mechanical ventilation is:Glasgow Coma Score of 8TMinute ventilation of 20 L/minRapid Shallow Breathing Index of 40Maximal inspiratory pressure of −10 cm H2OCalculated 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: CBaptistella 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?Higher peak airway pressureHigher likelihood of CO2 retentionLower likelihood of CO2 retentionShorter inspiratory timeLower mean airway pressureTwo 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: BMaung A and Kaplan L Waveform analysis during mechanical ventilation. Curr Probl Surg. 2013; 50(10): 438–446 PMID: 24156841.
8 19‐year‐old woman has worsening respiratory failure over the past 48 hours. She is ten days after a motor vehicle collision resulting in multiple rib fractures, pulmonary contusions, and a grade 1 liver laceration. She is on low tidal volume ventilation, 100% FiO2 with PaO2/FiO2 ratio of 71. She is being proned and was started on neuromuscular blockade. She is not on vasopressors and has a hemoglobin of 9 mg/dL The next most appropriate intervention would be:High frequency oscillation ventilationVeno‐arterial ECMOVeno‐venous ECMORib fracture fixationHelium‐oxygen mixtureExtracorporeal membrane oxygenation (ECMO) should be considered as salvage therapy in patients with refractory hypoxemia despite receiving standard care. In general, veno‐venous ECMO (answer C) is utilized in patients who do not have severe cardiac dysfunction such as this patient and veno‐arterial (choice b) is used in patients with hemodynamic compromise. Besides the inability to anticoagulated a patient, there are no specific absolute contraindications to ECMO. High frequency oscillatory ventilation (choice a) has been shown to have no benefit and possibly cause harm. Rib fracture fixation (choice d) remains an evolving therapy that is of optimal use in specific patient population but would not be appropriate in this patient due to severe ARDS. Helium‐oxygenation mixture is sometimes utilized in cases with airflow resistance but would be contraindicated in this patient due to her high oxygen requirement.Answer: CTillman BW, Klingel ML, Iansavichene AE, et al. Extracorporeal membrane oxygenation (ECMO) as a treatment strategy for severe acute respiratory distress syndrome (ARDS) in the low tidal volume era: a systematic review J Crit Care. 2017; 41:64–71 PMID: 28499130.Goligher EC, Munshi L, Adhikari NK, et al. High‐frequency oscillation for adult patients with acute respiratory distress syndrome. a systematic review and meta‐analysis. Ann Am Thorac Soc. 2017; 14(Suppl. 4):S289–S296 PMID: 29043832.
9 Causes of postoperative respiratory failure in the immediate post‐anesthesia period include which of the following:Inadequate reversal of neuromuscular blockadeOpioid‐induced respiratory depressionIatrogenic or negative pressure pulmonary edemaReduction in functional reserve capacityAll of the above Early postoperative respiratory complications are common and may arise from multiple etiologies (answer e). General anesthesia and mechanical ventilation can lead to atelectasis and reduction in the functional reserve capacity of up to 50%, even in healthy individuals, especially if no PEEP is used during the procedure. Residual neuromuscular blockade can lead to impaired respiratory muscle strength and upper airway obstruction. Hypoxemia can be due to pulmonary edema, whether due to fluid resuscitation or negative pressure (identified more commonly in young, healthy, and muscular patients). Opioids, which are commonly administered both intraoperatively and postoperatively, can cause decreased respiratory drive, decreased level of consciousness, and upper airway obstruction due to a decrease in the supraglottic airway tone.Answer: EKarcz M and Papadakos PJ Respiratory complications in the postanesthesia care unit: a review of pathophysiological mechanisms Can J Respir Ther Winter. 2013; 49(4): 21–9 PMID: 26078599.Gupta K, Prasad A, Nagappa M, et al. Risk factors for opioid‐induced respiratory depression and failure to rescue, a review. Curr Opin Anaesthesiol. 2018; 31 1:110–119 PMID: 29120929.
10 A 46‐year‐old woman is invasively mechanically ventilated after developing pneumonia following a motorcycle crash. She is on assist control ventilation with oxygen saturations in the low 80s. Which of the following maneuvers would be most likely to improve her oxygenation.Increase in tidal volumeIncrease in respiratory rateChange from square to decelerating waveformIncrease in expiratory timeDecrease in inspiratory timeOxygenation most closely correlates with mean airway pressure and reflects the area under the curve described by the gas‐flow waveform. Change to a decelerating waveform (choice C) extends the inspiratory time and the area under the curve thus increasing the mean airway pressure. Increases in tidal volume (choice A) and respiratory rate (choice B) both increase the minute ventilation and likely CO2 clearance but not oxygenation. Increase in expiratory time (choice D) increases the CO2 clearance and maybe helpful in patients with significant airway resistance (e.g. asthma and COPD). This may however lead to poorer oxygenation due to decreased mean airway pressure. Decrease in inspiratory time (choice E) would lead to a lower mean airway pressure and possibly worse oxygenation.Answer: CMaung A and Kaplan L . Waveform analysis during mechanical ventilation. Curr Probl Surg. 2013; 50(10): 438–446 PMID: 24156841.
11 A 52‐year‐old man is 6 days status‐post orthotopic liver transplantation and is evaluated by the rapid response team on the general floor for acute hypercarbic and hypoxemic respiratory failure as well as fever (T = 101.8° F) and hyponatremia (Na = 128 mEq/L). Which of the following modalities is the most appropriate for acute, pre‐ICU management?Diuretic administrationOral endotracheal intubationHigh‐flow nasal cannula (HFNC)Full face‐mask BiPAPNasal mask CPAPThis patient demonstrates acute respiratory failure in the setting of presumed volume overload. However, diuretic therapy will require some time to clear excess fluid in order to support oxygenation and CO2 clearance. HFNC therapy and CPAP are much better at supporting oxygenation than CO2 clearance ‐ and the patient requires both. BiPAP may work but is less effective at immediate rescue in a patient who is anticipated to need higher PEEP, and a longer inspiratory time to support an increased mean airway pressure to correct hypoxemia. Also, BiPAP does not allow one to precisely control minute ventilation as does oral endotracheal intubation and mechanical ventilation regardless of patient location. This patient is expected to have an elevated CO2 production based on fever and will therefore have a higher than usual minute ventilation requirement that is able to be met much better with invasive mechanical ventilation than with a non‐invasive modality.Answer: BMoore S, Weiss B, Pascual JL, et al. Management of acute respiratory failure in the patient with sepsis or septic shock. Surg Infect. 2018; 19(2): 191–201; https://doi.org/10.1089/sur.2017.297.
12 A 43‐year‐old woman is involved in a MVC.