Page 650 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 52: Acute Lung Injury and the Acute Respiratory Distress Syndrome 469

results of surfactant therapy in infants with the RDS of prematurity. therapy (sedation, therapeutic paralysis, and PEEP), are at risk of sudden
Surfactant therapy of RDS improves gas exchange and lung mechan- and life-threatening deterioration. Changes in intrapulmonary shunt, oxy-
ics, decreases the requirement for CPAP, and lessens barotrauma. 372-374 gen consumption, and systemic perfusion are frequent, making arterial sat-
Anzueto and associates reported the first large prospective RCT of uration and oxygen delivery volatile. Accordingly, careful monitoring for
6
surfactant in ARDS. Their results were disappointing: There was no hypoxemia and the adequacy of oxygen delivery is advisable. Continuous
benefit associated with the exogenous surfactant delivered by inhalation. pulse oximetry is generally reliable (barring gross hypoperfusion) and
Because there were concerns about the appropriate dose, alternative should be used routinely. In addition, frequent sampling of arterial blood
modes of delivery, timing of therapy, and the precise surfactant formula- gases is advisable throughout the first day of management, as well as fol-
tion studied, investigators did not view this study as definitive evidence lowing major interventions or changes in clinical appearance of the patient.
against the use of exogenous surfactant. Since then a number of RCTs, Monitoring the patient’s airway, ventilator function, and the ventilator-
large and small, have been carried out without demonstrating clinical patient interface are equally important, as is assessment for liberation
benefit, including a recent large, multinational RCT of recombinant sur- from assisted ventilation, and if needed, weaning (see Chap. 60).
factant protein C-based surfactant. 375-379 Like perflubron, currently exog- Finally, hemodynamic monitoring, including use of a PAC, has been dis-
enous surfactant for adults is available only as an experimental agent. cussed earlier in this chapter and elsewhere in more detail (see Chap. 28).
Long-Term Sequelae of ARDS Over the past two decades, as treatment for ARDS
Supportive Care and Monitoring Patients With ALI and ARDS has decreased hospital mortality, clinicians and clinical investigators
386
Supportive Therapy Current management of ARDS does not benefit from have become more interested in the long-term health problems of ARDS
proven pharmacologic interventions to prevent, limit ALI, or restore survivors. Pulmonary function is usually mildly impaired after hospital
physiologic function. Based on animal data suggesting a role of platelet discharge from ARDS and improves slightly over the next year. 387,388
activation in the development of ALI and two observational studies that Thus survivors with worsening dyspnea may have another superimposed
380
suggested that prehospitalization antiplatelet therapy was associated with respiratory lesion, such as tracheal stenosis, and should be evaluated
a decreased risk of ALI, 381,382 a multicenter trial is enrolling patients at risk as such. Despite their young age, ARDS survivors score well below the
of ALI development to receive aspirin or placebo. Separately, based on reference standards and other critical care controls on quality-of-life
the anti-inflammatory properties of 3-hydroxy-3-methyl-glutaryl-CoA measures, 30,388-391 and many have evidence of cognitive dysfunction, 28,392
reductase inhibitors (statins), the NIH NHLBI ARDSNet conducted a posttraumatic stress disorder, and physical disability, 27,393,394 long after
390
trial of rosuvastatin versus placebo in subjects with sepsis-associated ALI. hospital discharge. The long-term sequelae of critical illness and ARDS,
This trial showed no survival benefit with the use of rosuvastatin; rosuv- recently termed the post-intensive care syndrome, are an active area of
astatin was associated with more renal and hepatic failure. 383 ongoing research and are covered in detail in Chap. 15.
To date, the largest strides in the recent management of ARDS have
come from therapies aimed at the delivery of mechanical ventilation.
3
While it is possible that further explication of the mechanisms of lung CONCLUSION
injury will provide new avenues for pharmacologic intervention, at Standardization of the criteria that define ARDS has aided in iden-
present, management of these patients relies on application of proven tification of specific at-risk groups. This in turn has spurred further
mechanical ventilation strategies, combined with meticulous supportive research into the underlying reasons why certain risk groups (such as
therapy. Appropriate management includes timely diagnosis and treat- alcoholics 395,396 ) are at greater risk for ARDS. A recent NHLBI consensus
ment of underlying diseases, nosocomial infections, and other problems. statement summarized the important directions for future research,
Indeed, even if new pharmacologic agents become available, the same including functional response to injury and interaction between bio-
supportive therapy will be necessary to maintain a viable patient to ben- chemical pathways and different cell types. The completion of the
397
efit from treatment. For a detailed description of elements of supportive human genome project has led to characterization of many of the genes
care, please refer to the relevant other chapters in this text. encoding mediators of lung injury. The effect of variation in these
398
Reducing PEEP, even for short periods of time, is often associated genes on predisposition to ARDS in at-risk groups, such as sepsis, pneu-
with alveolar derecruitment and hence rapid arterial hemoglobin monia, and trauma, may help identify subgroups whose genotypes place
desaturation. Thus once endotracheal tube suctioning has been accom- them at unusually high risk or low risk for developing ARDS. Identifying
plished for diagnostic purposes, nursing and respiratory therapy staff these putative enabling and protective polymorphisms for developing
should be instructed to keep airway disconnections to a minimum or ALI will provide hypotheses for interventions for prevention and for
to use an in-line suctioning system that maintains sterility and positive treatment of patients with ARDS in the future.
pressure, usually via the suctioning catheter residing in a sterile sheath However, while waiting for those new genetically tailored therapies,
and entering the endotracheal tube via a tight-sealing diaphragm. These much can be done in the present. The landmark ARDSNet low-tidal-
suctioning systems generally are effective for lesser levels of PEEP volume ventilation strategy trial proved that ventilator therapy can be pro-
(<15 cm H O) but often leak if higher levels are attempted. tocolized to reduce VILI. Arguably this simple and inexpensive strategy
3
2
Recognizing the importance of nutritional support in the critically ill, the can save thousands of lives of ARDS patients if widely accepted and utilized.
ARDSNet recently published research studies: (1) EDEN—whether lower- Unfortunately, studies since the publication of the ARDSNet study in 2000
volume (trophic) enteral feeding would improve outcomes in patients with have indicated that that there are challenges to the widespread and timely
ALI compared to full enteral feeding and (2) OMEGA—whether dietary acceptance and implementation of this low-tidal-volume strategy. 399-403
supplementation with omega-3 (n-3) fatty acids and antioxidants would Thus the present challenges include not only improving on this therapy,
improve outcomes. 384,385 In EDEN, trophic enteral feeding was not associ- but also overcoming the obstacles so that clinicians can consistently make
384
ated with improved outcomes. However, because trophic enteral feeding a diagnosis of ARDS early, and then begin appropriate ventilatory support.
was associated with significantly less gastrointestinal intolerance (vomiting,
384
constipation, and increased gastric residual volumes), a reasonable
approach would be to slowly escalate enteral feeding volume toward caloric KEY REFERENCES
goal to avoid gastrointestinal side effects. In OMEGA, dietary supplementa- • ARDS Definition Task Force, Ranieri VM, Rubenfeld GD, et al.
tion with omega-3 fatty acids and antioxidants was not associated with a Acute respiratory distress syndrome: the Berlin definition. JAMA.
survival benefit; in fact, supplementation was associated with a trend toward 2012;307:2526.
harm and was associated with gastrointestinal side effects (diarrhea). 385
• ARDSNet Investigators. Ventilation with lower tidal volumes as
Monitoring Patients with ARDS, by virtue of their serious gas exchange compared with traditional tidal volumes for acute lung injury
(and sometimes hemodynamic) impairment, combined with the effects of

section04.indd 469 1/23/2015 2:19:49 PM