Ventilatory Management of ARDS Alexei Ortiz Milan; MD, MSc 2017
Outline Ventilatory management of ARDS Protected Ventilatory Strategy Use of NMB Selection of PEEP Driving pressure Lung Recruitment Prone positioning Length of Mechanical Ventilation
Ventilatory Management 1. Low Vt ventilation Strict 6ml/kg IBW or less (consider NAHCO3 infusion if to acidotic) Plateau pressure measurement Early use of NMBs if severe ARDS 2. Assess recruitability- improve oxygenation, reduces VILI High PEEP (?Guidance by measuring TPP) Prone positioning Early consideration for ECMO if failing to achieve ventilatory parameters 3. Minimize VILI Reduce duration of ventilation by running negative fluid balance early Reduce duration of ventilation by careful timing of initiation of spontaneous breathing to prevent VIDD
Protected Ventilatory Strategy IBW calculation For male= height in cm - 100 For female= height in cm -110
Am J Respir Crit Care Med Vol 166. pp 1510 1514, 2002 Results: Two trials showed significant increases in the odds ratio for survival of patients treated with low vs control tidal volume (Amato et al, and ARDSNet) The other three trials showed a nonsignificant decrease in the odds ratio for this relationship (Brower et al, Brochard et al, Stewart et al)
Data Synthesis: 4 RCTs tested lower versus higher Vt ventilation at similar PEEP in 1149 patients, 3 RCTs compared lower versus higher PEEP at low Vt ventilation in 2299 patients, and 2 RCTs compared a combination of higher Vt and lower PEEP ventilation versus lower Vt and higher PEEP ventilation in 148 patients Results: Lower Vt ventilation reduced hospital mortality (odds ratio, 0.75 [95% CI, 0.58 to 0.96]; P = 0.02) compared with higher Vt ventilation at similar PEEP Higher PEEP did not reduce hospital mortality (odds ratio, 0.86 [CI, 0.72 to 1.02]; P = 0.08) compared with lower PEEP using low Vt ventilation Higher PEEP reduced the need for rescue therapy to prevent life-threatening hypoxemia (odds ratio, 0.51 [CI, 0.36 to 0.71]; P < 0.001) and death (odds ratio, 0.51 [CI, 0.36 to 0.71]; P < 0.001) in patients receiving rescue therapies
Results: Short-term infusion of cisatracurium besylate was associated with lower hospital mortality (RR, 0.72; 95% CI, 0.58 to 0.91;P= 0.005) Neuromuscular blockade was also associated with lower risk of barotrauma (RR,0.43; 95% CI, 0.20 to 0.90;P= 0.02), but had no effect on the duration of mechanical ventilation among survivors (MD, 0.25 days; 95% CI, 5.48 to 5.99;P= 0.93, or the risk of ICU-acquired weakness (RR, 1.08; 95% CI, 0.83 to 1.41; P= 0.57) Conclusions: Short-term infusion of cisatracurium besylate reduces hospital mortality and barotrauma and does not appear to increase ICU-acquired weakness for critically ill adults with ARDS
Paralysis vs diaphragmatic atrophy NMBs not associated with diaphragmatic atrophy when used for 48 hrs After 48 hrs, pt weaned to PS Only beneficial effect on outcome if PaO2/FIO2 < 120 NMBs also reduced mortality in severe sepsis
Selection of PEEP
JAMA, March 3, 2010 Vol 303, No. 9 Results: Treatment effects varied with the presence or absence of ARDS (PaO2/FiO2 200 mmhg) In pts with ARDS (n=1892), there were 324 hospital deaths (34.1%) in the higher PEEP group and 368 (39.1%) in the lower PEEP group (adjusted RR, 0.90; 95% CI, 0.81-1.00;P=0.049) In pts without ARDS (n=404), there were 50 hospital deaths (27.2%) in the higher PEEP group and 44 (19.4%) in the lower PEEP group (adjusted RR, 1.37; 95% CI, 0.98-1.92;P=0.07) Conclusions: Treatment with higher vs lower levels of PEEP was not associated with improved hospital survival. However, higher levels were associated with improved survival among the subgroup of patients with ARDS
Respir Care 2013;58(9):1416 1423 Endpoints assessed at 28 days Primary endpoint: PaO2/FiO2 Secondary endpoints: mortality, VFDs, ICU and hospital stay, MOD-free days, and respiratory and hemodynamic parameters Groups assignment: 34 pts assigned to Compliance-guided group, and 36 pts assigned to FiO2-guided group Results: There was no significant difference in PaO2/FIO2 There was a trend toward better oxygenation in the compliance-guided group over the first 2 weeks of study. The compliance-guided group had significantly more MOD-free days at day 28 [20.5 (0 26) vs 6 (0 23.75); p= 0.02] as well as more respiratory failure-free days [14.5 (0 22.5) vs 7.5 (0 19); p= 0.03]
Determining optimal PEEP LIP
Tranaspulmonary Pressure Monitoring Ptp= Paw Pesoph Ptpplat 25 cmh2o reduce alveolar overdistension PtpPEEP 0 10 cmh2o reduce cyclic alveolar collapse
(N = 30) (N = 31) Results: PaO2/FiO2 ratio at 72 hours was 88 mm Hg higher in the esophageal-pressure guided group than in the control group (95% CI, 78.1 to 98.3; P = 0.002) This effect was persistent over the entire follow-up time at 24, 48, and 72 hrs; P = 0.001 Respiratory-system compliance was also significantly better at 24, 48, and 72 hrs in the esophageal pressure guided group (P = 0.01) Conclusions: As compared with the current standard of care, a ventilator strategy using esophageal pressures to estimate the transpulmonary pressure significantly improves oxygenation and compliance. Multicenter clinical trials are needed to determine whether this approach should be widely adopted
Driving Pressure ΔP = Vt/CRS Can be calculated for patients who are not making inspiratory efforts as: On volume-target modes ΔP = Ppl PEEP On pressure-target modes ΔP = Ppeak PEEP
N Engl J Med 2015;372:747-55 Subjects: 336 patients with ARDS Primary Outcome: survival in the hospital at 60 days Secondary Outcome: varying variables such as VT, PEEP, and plateau pressures Results: higher mortality was noted only when higher Pplat were observed in patients with higher ΔPs protective effects of higher PEEP were noted only when there were associated decreases in ΔP at constant levels of Plat was observed that Vt was a strong predictor of survival when normalized to CRS(i.e., ΔP) but not when normalized to PBW strong association between ΔP and survival was found even though all the ventilator settings that were used were lung-protective (RR of death, 1.36; 95% CI, 1.17 to 1.58; P<0.001)
Assess potential for Lung Recruitment Recruitment of partially collapse lung may improve lung compliance Improved compliance translates to a fall in Pplat and also a reduction in TPP, both of which are associated with reduce VILI and improves outcomes Can be done with RMs or prone positioning, and maintained using High PEEP or HFO However, may cause volutrauma if pt unrecruitable No mortality benefit in mild ARDS, only moderate to severe ARDS is heterogeneous hence not surprising that some pts are not recruitable (e.g., pulmonary contusion secondary to chest trauma)
JAMA. 2008;299(6):637-645
Prone positioning JAMA. 2009;302(18):1977-1984 Interventions: Patients were randomized to undergo supine (n=174) or prone (20 hours per day; n=168) positioning during ventilation. Primary outcome: 28-day all-cause mortality. Secondary outcomes: 6-month mortality and mortality at intensive care unit discharge, organ dysfunctions, and the complication rate related to prone positioning. Results: Prone and supine patients from the entire study population had similar 28-day (31.0% vs 32.8%; relative risk [RR], 0.97; 95% confidence interval [CI], 0.84-1.13;P=.72) and 6-month (47.0% vs 52.3%; RR, 0.90; 95% CI, 0.73-1.11;P=.33) mortality rates, despite significantly higher complication rates in the prone group. Conclusion: prone positioning does not provide significant survival benefit in patients with ARDS or in subgroups of patients with moderate and severe hypoxemia.
Reduce duration of ventilation a) Achieve a negative fluid balance ASAP Once pt cardiovascular stable (e.g., minimal vasopressor requirement), aim for - Furosemide - Amiloride - Thiazides - Spironolactone - Aminophylline infusion (beware Tachycardia) -?Nesiritide If the above fail, consider early CVVH to achieve negative fluid balance natriuresis: `Conservative fluid strategy and hypoxia both strongly associated with neurocognitive decline later, as well as poor glycemic control
b) Encourge synchronized spontaneous breathing after first 48 hours Advantages of spontaneous ventilation (e.g., allowing pt to breathe spontaneously): -Improve ventilation to peri-diaphragmatic area, where much dependent blood flow occurs, hence improving V/Q matching -Helps exercises diaphragmatic muscles, preventing resp. muscle atrophy -Allows reduction in sedation Disadvantages of spontaneous ventilation - In diseased lung, develop negative intrathoracic pressure gradient (e.g., -20 cmh2o at dependent lung bases and -5 at open lung apex) - This pressure differential may cause a pendeluft effect with gas moving from non- dependent to dependent lung => minimal net gain in Vt - Negative intrathoracic pressure may also => negative pressure pulmonary oedema - Negative intrathoracic pressure + increase dependent blood flow + lung damage => haemorrhagic lung injury due to increase microvascular pressure gradient - Spontaneous ventilation => increased afterload
Take Home Low tidal volumen ventilation (6 ml/kg IBW) is associated with low mortality in ARDS when Pplat is limited to 30 cmh2o and driving pressure less than 14 cmh2o. The use of NMBs is save and recommended for the first 48 hrs of mechanical ventilation in order to avoid VILI and reduce hospital mortality. PEEP should be tailor according protocolized method (FiO2/PEEP ARDS-Network chart, transpulmonary pressure monitoring, U/S, etc). RMs are not recommended as routine intervention in ARDS, ONLY in refractory hypoxemia as rescue therapy when previously interventions have failed. Prone positioning is not associated with survival benefit, and the risk of complication is significantly higher than supine positioning. Reduce the duration of mechanical ventilation by achieving negative fluid balance once pt is cardiovascular stable and encouraging synchronized spontaneous breathing after 48 hrs on MV.
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