Rationale and Background
protective mechanisms (hypoxic pulmonary vasoconstriction) by use of deep sedation in these patients o Hypoxia due to significant shunt responds very poorly to increases in FiO2 -with a potential paradoxical fall in PaO2 o Pulmonary vasodilators such as iNO improve V/Q matching and thereby reduce shunt and improve oxygenation irrespective of FiO2 o If hypoxia is considered to be the main driver behind MOF and death in ARDS then improving oxygenation should lead to improved morbidity and mortality. On the other-hand effects of iNO are short-lived and do not treat underlying pathology, -so on its own as a treatment, other than buying time (short-lived: tachyphylaxis) it may not improve outcomes
afterload (which we know already to be acutely elevated as part of ARDS pathophysiology) o This is individual, as the effect of increased intrathoracic pressure on RV afterload may be offset/balanced by the beneficial effect on the RV of improved oxygenation / CO2 clearance o iNO shown to be effective in treatment of pulmonary hypertension and reducing RV afterload (especially in neonates) Advantages and Disadvantages
are a problem in ARDS and which may contribute to M&M and reduced ventilatorfree days o Cheap, readily accessible in most ICUs, minimal additional training required to use
NO2 levels, dedicated inserts increase dead space of circuit o Physiological: May cause systemic hypotension, associated AKI, pulmonary oedema (if LV dysfunction), platelet inhibition may increase bleeding, methaemoglobinaemia, if complications cannot rapidly wean/discontinue (rebound PHtn and hypoxia), increase ICP o Other: not all patients are responsive, dose-response unclear, tachyphylaxis occurs (short-term treatment) Evidence
identification of responders and use of differing dosing regimens (low dose to high dose tried)
o No effect on 28d mortality or ventilator free days o Improved P/F (and/or oxygenation index) at 24h o Increase in renal failure in iNO group o Cannot recommend as a treatment in this group Summary (my practice)
with a better evidence-base of benefit e.g. proning, ECMO
increasing beyond this and am likely to experience marked worsening in systemic hypotension etc., I am vigilant for other anticipated complications
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![]() About the AuthorIdunn Morris is the Nepean ICU provisional fellow (research). The information provided in these summaries is subject to personal interpretation of the studies touched on. Certainly, the summary 'my practice' section does not correspond to recommended clinical practice, rather 'an approach' based on the information presented. Categories
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January 2021
About WTETIntensive care medicine is full of unanswered questions, controversies and subtle variations in practice. 'What's the evidence Tuesdays' aims to provide a brief 10-minute oral overview of the rationale and evidence behind an investigation, intervention or approach to management. Whilst based on the fellowship 'critically evaluate' style exam questions it is an MDT forum designed to encourage all clinical staff to know and keep up-to-date with the evidence (or at times lack of!) that guides our day-to-day decisions and where applicable understand why debate amongst the critical care community may still exist. Each week a two-sided written summary of the session is created for those who were unable to attend. Similarly, this summary provides a written resource for fellowship exam candidates to refer to with the understanding these are not model exam answers.
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