Round-up Review of PEEP Dr. J.B. Elsberry Prof. J.M. Newberry Special Thanks Gregory A. Schmidt, MD Professor, University of Chicago Peter C. Rimensberger Pediatric and Neonatal ICU University Hospital of Geneva Switzerland

A 23 yo woman is admitted to the ICU with status asthmaticus. She is ventilated with: Vt 600cc; RR20; FiO and has PO 2 135; PCO 2 73; pH What do you do next (assume therapy is maximal)?

The following changes are made: Vt 600 to 800; RR 20 to 32 PO 2 105; PCO 2 66; pH 7.09; HR 136. Meanwhile, the airway pressure begins to alarm: flow is changed from square to decelerating (the alarm stops). The heart rate rises to 160, blood pressure falls to 88/68, the ventilator begins alarming again and, while the patient is being moved for a CXR, she arrests.

Two Aspects of MV l 1. To control PO 2 (oxygenation) –When mask therapy is insufficient –Adjust: FiO 2, PEEP l 2. To control PCO 2 (ventilation) –When the patient can’t –When we’d rather the patient not –Adjust: Mode, rate, tidal volume Intubation differs from MV. ETT may be needed when MV isn’t.

What is PEEP?

ZEEP/PEEP Surgery by T.Whitehead Video by G.Volgyesi Producer A. S. Slutsky

Setting the PEEP l PEEP recruits alveoli, raising PO 2 –Some lesions are not PEEP-responsive l PEEP may protect the lung l PEEP makes the lung bigger –Pneumothorax, but only if Vt is excessive –Hypotension, but only if critically dry l Range: 5-30, average ~10 cmH 2 O l Use enough to get the SpO 2 >0.88 and FiO 2 < 0.60 l Major error: PEEP too low

AutoPEEP l Lungs don’t empty at end-expiration l Usually associated with airflow obstruction l Problems: –Increased WOB and difficulty triggering –Barotrauma, hypotension l You have to look for it l Also called intrinsic PEEP

AUTOPEEP: Ventilator Changes TIME VOLUME

Measuring AutoPEEP

Reducing AutoPEEP l Reduce V E –Lower Vt –Lower RR l Raise inspiratory flow (square) l Treat airflow obstruction l Use HeO 2 l Accept hypercapnia

Pressure – Flow – Time - Volume. V or V P or V Loops V / P / V. t Curves on the ventilator display - to assess patient-ventilator synchrony - to get some information on respiratory mechanics under dynamic conditions (!) - to detect erroneus ventilator settings - to guide in the search for optimal ventilator settings

When is Auto PEEP a good thing l APRV l Increased MAP

Ventilation: Control of PCO 2 V 1. Ventilator produces a constant pressure of gas: PCV,PSV 2. Ventilator produces a constant flow of gas: ACV, IMV

PCV: Flow, Pressure, Vol

Volume Assist-Control Pao Vol Flow I E TIME

Rrs vs Crs 1. Low shoulder 2. Elevated Pplat- PEEP 3. Normal expiratory flow

After Initial Stabilization l 1. Use the airway pressure and waveform displays to determine the physiology and to follow changes with time and treatment l 2. Ascertain your goals, eg. rest, lung protection, exercise l 3. Adjust the ventilator in accord with the patient’s physiology and comfort and with your goals

ARDSNet: V T and Mortality ARDSNetwork. NEJM 342:1301, 2000

Subsequent Adjustments l ARDS –Adjust PEEP to least PEEP c/w SpO 2 > 0.87 with FiO 2 <0.6 –Lower FiO 2 to 0.6 –Reduce V T below 6mL/kg IBW, if needed, to keep Pplat < 30cmH 2 O

What is the best P/F ratio? l 1: PaO 2 = 90 & FiO 2 = 1.0 l 2: PaO 2 = 60 & FiO 2 = 0.50 l 3: PaO 2 = 70 & FiO 2 =.21

Answers l 1: PaO 2 = 90 & FiO 2 = 1.0 P/F = 90 l 2: PaO 2 = 60 & FiO 2 = 0.50 P/F = 120 l 3: PaO 2 = 70 & FiO 2 =.21 P/F = 333

Lichtwarck-Aschoff M AJRCCM 2000; 182: The oxygen response (limitations) P/F-ratio, oxygen delivery and Crs during PEEP steps

Lung Injury, AutoPEEP PCO 2

Permissive Hypercapnia l Sacrifice PCO 2 /pH for lung protection l Well-tolerated and standard therapy for status asthmaticus, ARDS

Use of Stress Index constant-flow inflation. < 1downward concavity, suggesting a continuous decrease in elastance (or increase in compliance) further recruitment of alveoli is likely.. 29 ) 29 Pao = airway pressure. (Reprinted with permission from the American Thoracic Society

Pao TIME 80 PRESSURE ALARM V. x Ti Te Flow Rate and Flow Profile

The oxygenation response: Can it be used? PEEP and Vt effects in ALI "static" compliance: static PIP (Pplat) - PEEP tidal volume Cst = Recruitment Overdistension Burns D J Trauma 2001;51:

Constant V T : Plateau - PEEP [  ] Prevalent recruitment Balance Prevalent overdistention PEEP [cm H 2 O] Airway pressure [cmH 2 O] PEEP Plateau L. Gattinoni, 2003

Constant V T : PaCO 2 and PaO 2 Prevalent recruitment Balance Prevalent overdistention PEEP [cmH 2 O] [mmHg] PaCO 2 PaO 2 L. Gattinoni, 2003

O 2 -improvement = Shunt improvement = PaO 2 VA PaCO 2 a) recruitment PaO 2 PaCO 2 VA b) flow diversion L. Gattinoni, 2003

Methods for Selecting PEEP MethodDescription Incremental PEEP 3,27,39 This approach uses combinations of PEEP and FIO 2 to achieve the desired level of oxygenation or the highest compliance. Decremental PEEP 44,45 This approach begins with a high level of PEEP (eg, 20 cm H 2 O), after which PEEP is decreased in a stepwise fashion until derecruitment occurs, typically with a decrease in PaO 2 and decrease in compliance. Stress index measurement 29 The pressure-time curve is observed during constant-flow inhalation for signs of tidal recruitment and overdistension. Esophageal pressure measurement 30,46 This method estimates the intrapleural pressure by using an esophageal balloon to measure the esophageal pressure and subsequently determine the optimal level of PEEP required. Pressure-volume curve guidance 51 PEEP is set slighty below lower inflection pt.

Different Lung Recruitment Maneuvers Recruitment ManeuverMethod Sustained high- pressure inflation 51,56 Sustained inflation delivered by increasing PEEP to cm H 2 O for s Intermittent sigh 59 Three consecutive sighs/min with the tidal volume reaching a Pplat of 45 cm H 2 O Extended sigh 60 Stepwise increase in PEEP by 5 cm H 2 O above baseline with a simultaneous stepwise decrease in tidal volume over 2 min leading to implementing a CPAP level of 30 cm H 2 O for 30 s Intermittent PEEP increase 55 Intermittent increase in PEEP from baseline to set level for 2 consecutive breaths/min Pressure control + PEEP 57 Pressure control ventilation of cm H 2 O with PEEP of cm H 2 O to reach a peak inspiratory pressure of cm H 2 O for 2 min —

Alternate Management Strategy

l We recommend that lung-protective ventilation (volume and pressure limitation with moderate levels of PEEP) be instituted in patients with ALI and ARDS requiring mechanical ventilation. Rescue therapies may be considered in patients who develop refractory hypoxemia… Severe Hypoxemic Respiratory Failure l Part 1—Ventilatory Strategies CHEST May 2010 vol. 137 no

Rescue Strategies l Rescue strategies are aimed at improving alveolar recruitment (high PEEP, recruitment maneuvers, APRV, HFOV) l Nonventilatory rescue strategies, such as inhaled vasodilators, prone positioning, and extracorporeal life support, may be considered in conjunction with the ventilatory strategies… CHEST May 2010 vol. 137 no

NBRC Serial Best PEEP Concepts l Best Cardiac Output l Highest PvO2 l Best Static Compliance l Best Hemodynamics l Best DO 2 (C.O. x CaO 2 ) l Least FiO 2 – See Cairo Pilbeam Summary P 288

Weaning: Liberation l The spontaneous breathing trial greatly assists judgment regarding extubation l Most patients don’t need to be weaned l Respiratory failure is in the patient, not the ventilator l IMV delays weaning

Spontaneous Breathing Trial l 100 ICU patients considered ready for weaning after 8.2 ± 1.1 days of MV l Compared V E, MIP, f/V T, CROP l Best predictor of weaning: f/V T  105 –T-piece; CPAP; or PSV  5 l Example: rate = 28, V T =.300, f/V T = 93 l This RSBI has become the standard Yang KL, Tobin MJ: N Engl J Med 324:1445, 1991

Effect of SBT l 300 ICU patients; screened daily –PaO 2 /FiO 2 > 200; PEEP  5 –Adequate cough; no sedatives or vasoactive drugs –f/V T  105 on CPAP for 1 minute l Randomized to 2 hour SBT or not l Result communicated verbally and with pre- printed message: –“Your patient has successfully completed a 2-hour trial of spontaneous breathing and has an 85% chance of successfully staying off mechanical ventilation for 48 hours.” Ely EW, et.al: N Engl J Med 335:1864, 1996

Effect of SBT l Duration of MV –SBT group: 4.5 d –No SBT: 6 d l Complications (self-extubation; tracheostomy; reintubation; 21+ days MV) –SBT group: 20 % –No SBT: 41 % l Costs: Reduced in SBT group Ely EW, et.al: N Engl J Med 335:1864, 1996

Weaning Modes Tested l IMV: Initial rate = 10; reduced, if possible, at least 2x/d, by 2-4 breaths/min l PSV: Initial PSV = 18cmH 2 O; reduced, if possible, at least 2x/d, by 2-4 cmH 2 O l SBT 1 : T-piece up to 2h/d l SBT 2 : T-piece (or CPAP  5) gradually up to 2h/d, at least 2x/d Esteban A et.al: NEJM 332: 345, 1995

Extubation Criteria l IMV: Tolerate 5 breaths/min for 2h l PSV: Tolerate PSV 5 for 2h l SBT 1 : Tolerate 2h unassisted breathing l SBT 2 : Tolerate 2h unassisted breathing Esteban A et.al: NEJM 332: 345, 1995

Modes and Weaning Esteban A et.al: NEJM 332: 345, 1995

Conclusions l PO 2 is controlled by FiO 2 and PEEP l Don’t be afraid of PEEP l AutoPEEP must be sought and sometimes reduced l Ventilator settings should take into account what’s wrong with the lung l Waveforms can provide useful information l Liberate, don’t wean: use the SBT