Skip to main content

"Positive ventilation....not always positive


Injury
Mechanism
Minimisation Strategy
Volutrauma
Non-homogenous lung injury
Over-distension of normal alveolar units to trans- pulmonary pressures above ~30 cm H2O (that corresponds to approximate total lung volume) causes basement membrane stretch and stress on intracellular junctions.
Avoid over-distending the “baby lung” of ARDS:
(a) Maintain Plateau Airway pressure under 30 cm H20
(b) Use Tidal volumes 6ml/kg (4- 8ml/kg)
Good evidence to support this strategy (ARDSNet)
Barotrauma
Increasing the trans-pulmonary pressures above 50 cm H2O will cause disruption of the basement membranes with classical barotrauma
Biotrauma
Mechanotransduction and tissue disruption leads to upregulation and release of chemokines and cytokines with subsequent WBC attraction and activation resulting in pulmonary and systemic inflammatory response and multi-organ dysfunction
Protective lung ventilation strategies
?Use of neuromuscular blockers may ameliorate
page19image12404
Recruitment / Derecruitment Injury
The weight of the oedematous lung in ARDS contributes to collapse of the dependant portions of the lung
Repetitive opening and closing of these alveoli with tidal ventilation will contribute to lung injury.
page19image14900
Consider recruiting collapsed lung +/- employing an open lung ventilation strategy.
This may be achieved by:
(a) Ventilation strategies: Sigh / APRV / “Higher PEEP”
(b) A recruitment manoeuvres: e.g. CPAP 40/40, or stepwise PCV
(c) Prone Positioning (gravitational recruitment manoeuvre)
Good theoretical support and case series / few trials inconclusive outcomes
Shearing injury
This occurs at junction of the collapsed lung and ventilated lung. The ventilated alveoli move against the relatively fixed collapsed lung with high shearing force and subsequent injury.
page19image19132
Oxygen toxicity
page19image19680
Higher than necessary FiO2 overcomes the ability of the cells to deal with free oxygen free radicals and leads to oxygen related free radical related lung injury.
High FiO2 may contribute to collapse through absorption atelectasis.
Limit FiO2 through the use of recruitment, higher PEEP and accepting SaO2 / PaO2 that correspond the the “shoulder” of the oxyhaemoglobin dissociation curve (SaO2 88-94)
Labels:

Comments

Post a Comment

Popular posts from this blog

Driving Pressure in ARDS: A new concept!

Driving Pressure and Survival in the Acute Respiratory Distress Syndrome Marcelo B.P. Amato, M.D., Maureen O. Meade, M.D., Arthur S. Slutsky, M.D., Laurent Brochard, M.D., Eduardo L.V. Costa, M.D., David A. Schoenfeld, Ph.D., Thomas E. Stewart, M.D., Matthias Briel, M.D., Daniel Talmor, M.D., M.P.H., Alain Mercat, M.D., Jean-Christophe M. Richard, M.D., Carlos R.R. Carvalho, M.D., and Roy G. Brower, M.D. N Engl J Med 2015; 372:747-755 February 19, 2015 DOI: 10.1056/NEJMsa1410639 BACKGROUND Mechanical-ventilation strategies that use lower end-inspiratory (plateau) airway pressures, lower tidal volumes (V T ), and higher positive end-expiratory pressures (PEEPs) can improve survival in patients with the acute respiratory distress syndrome (ARDS), but the relative importance of each of these components is uncertain. Because respiratory-system compliance (C RS ) is strongly related to the volume of aerated remaining functional lung during disease (termed functional lung size)...
5 comments
Read more

Steroids In Perioperative period...The Multi-purpose Drugs

1-Steroids are not Bronchodilator ,but have well established usefulness in hyper-reactive airway. They are also said to have a permissive role for bronchodilator medication. They can be administered orally, parenterally or in aerosol form 2- Steroids have been commonly used in chemotherapy for prevention of nausea along with other anti-emetic agents . Dexamethasone was found to be highly effective when given immediately before induction rather than at the end of anesthesia . 3- Steroids do exert analgesic effects. Various routes of administration of steroids include parentral, local infiltration at operated site , as an adjuvant in nerve blocks and central-neuraxial blockade. 4 - Steroids cannot be the mainstay of therapy in anaphylaxis because of the delayed onset of action, so they are used as adjunct after initial treatment with epinephrine. 5- Steroids (Dexamethsone) are of value in reduction or prevention of cerebral edema associated with parasitic infections and neopla...
1 comment
Read more

Anaphylaxis updates part 2- Empty Ventricle Syndrome

Patients with anaphylaxis should not suddenly sit, stand, or be placed in the upright position. Instead, they should be placed on the back with their lower extremities elevated or, if they are experiencing respiratory distress or vomiting, they should be placed in a position of comfort with their lower extremities elevated. This accomplishes 2 therapeutic goals: 1) preservation of fluid in the circulation (the central vascular compartment), an important step in managing distributive shock; and 2) prevention of the empty vena cava/empty ventricle syndrome, which can occur within seconds when patients with anaphylaxis suddenly assume or are placed in an upright position. Patients with this syndrome are at high risk for sudden death. They are unlikely to respond to epinephrine regardless of route of administration, because it does not reach the heart and therefore cannot be circulated throughout the body
Post a Comment
Read more