Adult Invasive Mechanical Ventilation

2018 Year in Review: Adult Invasive Mechanical VentilationKarsten J RobertsIntroductionVentilatory SupportPatients Without ARDSCOPDHyperoxiaVentilator-Associated EventsEffects in Prolonged WeaningPrevention of EventsVentilator AsynchronySedationFrequency of AsynchronyVentilator LiberationSBT and Sedation Protocol in ARDS30-min Versus 120-min SBTExtubation to Noninvasive VentilationSummaryResearch in the area of adult invasive mechanical ventilation is rich and diverse. With more than3,200 articles on mechanical ventilation published in 2018, isolating the most relevant literature isa challenge. Separated into 5 themes (ie, ventilatory support, hyperoxia, ventilator-associated events,prevention of events, and ventilator liberation), this article will describe the most important paperspublished on adult invasive mechanical ventilation in 2018.Key words: mechanical ventilation;ventilatory support; hyperoxia; ventilator asynchrony; ventilator-associated events; ventilator liberation.[Respir Care 2019;64(5):604–609. © 2019 Daedalus Enterprises]IntroductionPatients receiving invasive mechanical ventilation re-port feelings of pain, loneliness, discomfort, terror, andanxiety.1,2Mitigation of these adverse events are commonchallenges for the ICU team. Improving synchrony, opti-mizing sedation, early mobility, and prevention of com-plications are all goals in the evidence based managementof the ventilated patient.There are 5 prevalent themes in recently published lit-erature on mechanical ventilation. As they relate to animagined wish list for mechanical ventilation, the themesare ventilator support and hyperoxia (with the aim to pre-Mr Roberts is affiliated with the Hospital of the University of Penn-sylvania, Department of Respiratory Care Services, Philadelphia, Penn-sylvania.Mr Roberts presented a version of this paper at the Year in Review of theAARC Congress 2018, held December 4-7, 2018, in Las Vegas, Nevada.The author has disclosed no conflicts of interest.Correspondence: Karsten J Roberts MSc RRT, Hospital of the Universityof Pennsylvania, Department of Respiratory Care Services, 3400 SpruceStreet, Ground Floor, Founders Building, Philadelphia, PA 19104.E-mail: karsten.j.roberts@gmail.com.DOI: 10.4187/respcare.06927604RESPIRATORYCARE•MAY2019 VOL64 NO5

vent injury), ventilator-associated events and ventilatorasynchrony (with the aim to prevent iatrogenic complica-tions), and ventilator liberation (with the aim to liberatethe patient from the ventilator as soon as possible). Re-search in the area of adult invasive mechanical ventilationis rich and diverse. With more than 3,200 articles pub-lished in 2018, it is a challenge to isolate the most relevantliterature published in the last calendar year. With thesethemes in mind, this article will review the pertinent lit-erature published on adult invasive mechanical ventilationin 2018.Ventilatory SupportPatients Without ARDSThe last 2 decades have provided a plethora of datasupporting low tidal volume (VT) in patients with ARDS.3-6Plausible benefits of using low VTin patients withoutARDS are fewer complications and decreased ventilatordays.7To investigate the potential effectiveness of low VTversus intermediate VTon ventilator-free days, the Protec-tive Ventilation in Patients Without ARDS (PReVENT)trial was conducted.7Designed as a randomized control trial, the primary out-come of the PReVENT trial was ventilator-free days atday 28 in subjects without ARDS.7A low-VTstrategy wasinitiated in 475 subjects and defined as 6 mL/kg of pre-dicted body weight. Comparatively, 480 individuals wereassigned to a group with an “intermediate” VTof 10 mL/kgpredicted body weight. Both groups had 21 (mean) venti-lator free days with no significant differences in ICU lengthof stay (mean 6 vs 6 d) or hospital length of stay (14 vs15 d). Other high-value outcomes of 28-d and 90-d mor-tality showed no significant differences between groups.There were no significant differences in adverse events(eg, development of ARDS, pneumonia, severe atelectasis,or pneumothorax) between groups.7RecentposthocobservationalanalysisofpreviousARDStrials completed found that decreased driving pressure (P)is associated with increased survival.8Schmidt et al9shiftedthe focus onP toward subjects without ARDS. A retro-spective study of 622 subjects was conducted to determineassociation ofP with mortality on the first day of me-chanical ventilation. Classification of non-ARDS versusARDS was tested using the same model as Amato et al.8Similarly, to confirm the accuracy of their analysismodel, Schmidt et al9validated data in 543 subjects.The study confirmed an association betweenP andmortality in ARDS. However, an independent associa-tion betweenP and mortality in subjects without ARDSwas not established. This was further confirmed by alack of association with secondary outcomes of hospi-tal, ICU, and 6-month mortality.9COPDDuetoreportedlyhighermortalityinsubjectswithCOPDexacerbations, clinicians avoid invasive mechanical ven-tilation and opt for noninvasive ventilation. A retrospec-tive study by Gadre et al10included subjects with severeCOPD and respiratory failure and sought to describe char-acteristics and outcomes in subjects with COPD who re-ceived invasive mechanical ventilation. Baseline diagnosisof COPD according to the Global Initiative for ObstructiveLung Diseases standard was confirmed using pre-hospitalpulmonary function tests. A total of 670 subjects with apre-morbid diagnosis of COPD were included in the study,88% of whom were intubated for other etiologies, mostcommonly pneumonia.Overall hospital mortality was 25%, with mortality be-ing significantly lower in subjects with COPD exacerba-tions without additional comorbidities. Subjects with pri-mary COPD exacerbations were more likely to be admitteddirectly to the ICU from the emergency department. Me-dian duration of mechanical ventilation was 3 d, medianICU length of stay was 5 d, and median hospital length ofstay was 12 d. ICU mortality and hospital mortality werelower in subjects with COPD exacerbations. Twenty-sixpercent of the subjects were readmitted and mechanicallyventilated within the 4-y study period. Shorter durations ofmechanical ventilation and discharges to home were moreprevalent in subjects without comorbidities. Discharges tohomewerealsoassociatedwithoverallimprovedsurvival.10The application of mechanical ventilation in any diseaseprocess is complicated and unique. The fact that patientswithout ARDS had no significant differences in clinicaloutcomes raises new questions about what variables mayinfluence duration of mechanical ventilation when using alow-VTstrategy. As our understanding of a low-VTstrat-egy continues to evolve, more research will be needed, notonly in subjects with or without ARDS, but also in patientswithotheretiologies.Theuseoflow-VTstrategiesinCOPD,for example, may lead to improved outcomes in a patientpopulation that continues to increase. Similarly, future re-search may elucidate the role ofP in subjects with eti-ologies other than ARDS.HyperoxiaThe detrimental effects of oxygen on the lungs has beenknown for more than a century.11Harm caused by hyper-oxia may not only resemble ARDS, but it may also domore lung damage in patients with ARDS.11,12Two recentstudies have reported hyperoxia to be common in mechan-ically ventilated subjects.12,13Aggarwal et al12extracted data from several ARDSNetstudies and reviewed cases with a PaO280 mm Hg.Hyperoxia, or above-goal oxygen exposure, was defined2018 YEAR INREVIEW:ADULTINVASIVEMECHANICALVENTILATIONRESPIRATORYCARE•MAY2019 VOL64 NO5605