Instellen van beademingsparameters bij de obese pa3ent MDO 19-1- 2015 Nynke Postma
1. Altered respiratory mechanics in obese pa@ents 2. Transpulmonary pressure 3. Titra@ng PEEP 4. Titra@ng @dal volume 5. Effects of pa@ent posi@oning 6. Key messages
Obesity & respiratory mechanics Baseline altera@ons in respiratory mechanics of the obese pa@ent: Decrease in TLC Decrease in FRC and VC Increase in pleural pressure Increase of upper and lower airway resistance.
Obesity: Increased weight of the chest wall Increased abdominal pressure } decrease in respir. system compliance
Obesity & respiratory mechanics Dysfunc@on of the small airways & expiratory flow limita@on PEEP i at rest Air trapping during exercise Intrinsic mechanical loading of inspiratory muscles Work of breathing & VO 2
Obesity & gas exchange Atelectasis with shun@ng V/Q mismatch due to airway narrowing and varia@ons in lung perfusion Arterial hypoxemia Elevated A- a gradient
Transpulmonary pressure (P L ) Distending pressure across the lung P L =P A - P pl Obesity: P pl - - > P L - - > collapsing pressure - - > ATELECTASIS impaired gas exchange decreased lung compliance
Transpulmonary pressure (P L ) Hogere P pl ó lagere P L
Transpulmonary pressure (P L ) Safe upper limit: 25 cm H2O
Obesity & ARDS Obesity Heterogenic lung ARDS Heterogenic lung Obesity + ARDS Heterogenic lung +++
Obesity & ARDS Atelectasis & ARDS VALI Shear stresses at the intersec@on of open and closed alveoli
Open lung strategy Agempts to create parenchymal homogeneity by: 1. Recruitment maneuvers 2. PEEP @tra@on to op@mize respiratory mechanics 3. Minimize airway pressures
New focus: Reducing transpulmonary pressure Obese pa@ent: P pl à PEEP to overcome collapse and prevent derecruitment. High P peak ( 30 cmh2o) can be applied without lung overdisten@on P L <25 cmh2o at end inspira@on is considered safe (Mead J, Takishima T, Leith D. Stress distribu7on in lungs: a model of pulmonary elas7city. J Appl Physiol. 1970 ; 28 ( 5 ):596-608 )
PEEP level? Under@tra@on of PEEP: Collapse of alveoli during expira@on Atelectrauma lung injury. Over@tra@on of PEEP: Hemodynamic compromise Increased dead space ven@la@on Overdistension of the lungs at end- infla@on.
Methods of @tra@ng PEEPlevel 1. Using transpulmonary pressure by measuring P es 2. Using the airway pressure- @me curve profile (stress index) 3. Using @dal compliance
Titra@ng PEEP level: esophageal pressure (P es ) P esophageal (P es ) es@mates P pl P L can be es@mated PEEP can be individually @trated to achieve a posi@ve P L at end- exhala@on. Talmor et al. N Engl J Med. 2008 : improvement of gas exchange and trend to improved 28- day mortality a primarily surgical ARDS popula7on
Obesity and Pes
Measurement of P es Lower 1/3 of oesofagus In sedated, paralyzed mechanically ven@lated pa@ents: 35-45 cm distance from the nares transmission of the heartbeat
Effects of pa@ent posi@on P es (supine) > P es (upright) (~5cmH2O) Medias@nal weight Much more fluctua@on in P es from cardiac ac@vity in supine posi@on compared with upright posi@on
Titra@ng PEEP with use of P es Technique: Increase PEEP un@l P L (end- expira@on) > 0 Goal: Preven@on of atelectrauma by preven@ng lung collapse Talmor et al. N Engl J Med. 2008 : improvement of gas exchange and trend to improved 28- day mortality a primarily surgical ARDS popula7on
Titra@ng PEEP with use of P es Assump@ons: P es approximates P pl Expiratory airway collapse is not occurring in the lung regions in which local P pl < P es measured Risk: Severe overdistension in lung regions where P es overes@mates P pl (ventral regions) Talmor et al. N Engl J Med. 2008 : improvement of gas exchange and trend to improved 28- day mortality a primarily surgical ARDS popula7on
Piralls Inter- individual variable contribu@on of medias@nal weight to P es Increasing PEEP to a target may cause injurious overdistension of other lung regions
Titra@ng PEEP level: @dal compliance Pa@ent receiving a set V t, P plat is measured as PEEP is increased. 1. Pplat increase in PEEP : improved lung compliance and an element of recruitable lung. 2. Pplat increase in PEEP : no recruitment; areas of overdisten@on or hyperinfla@on
Tidal volume Based on ideal body weight 6 ml/kg IBW Hypercapnia Acute illness Chronic hypoven@la@on
Pa@ent posi@oning: prone posi@on Pro Allows the weight of medias@nal @ssue to be supported by the sternum Decrease of lung collapse Improvement of V/Q matching Decrease of shunt. Con Futher increase abdominal pressure Pressure ulcera Further studies in obese pa@ents needed
Prone posi@on
Pa@ent posi@on: reverse trendelenburg Facilita@on of weaning from the ven@lator. Gravita@onal unloading: Reduc@on in trans - diaphragma@c pressure Decreased atelectasis, Improved gas exchange
Key messages Obese pa@ent Altered respiratory mechanics Increased heterogeneity of the lung Ven@lator strategies that focus on P L as a measure of lung stress show promise in pilot studies
Literature