Acute respiratory distress syndrome: Clinical sciences

respiratory distress syndrome or ARDS For short is a life threatening condition associated with acute lung injury that results in progressive respiratory dysfunction And hypoxia S is caused by inflammatory alveolar damage and capillary endothelial injury which ultimately leads to decreased lung compliance and pulmonary arterial vasoconstriction Based on arterial oxygenation patients are grouped into mild moderate and severe ARDS Now if you suspect ARDS you should first perform an ABCD E assessment Patients with ARDS are usually unstable So begin acute management immediately stabilize the airway breathing and circulation which means you will likely need to intubate the patient and place them on mechanical ventilation Next obtain IV access put your patient on cardiac telemetry and begin continuous vital sign monitoring including BP heart rate and pulse oximetry Once you stabilize the patient obtain a focused history and physical examination your patient will report progressive shortness of breath and may have a history of trauma sepsis pneumonia pancreatitis or drug toxicity Physical exam often reveals features of hypoxia like cyanosis tachypnea accessory respiratory muscle use and diffuse pulmonary crackles In addition pulse oximetry will reveal low oxygen saturation levels at this point You should suspect s next order an arterial blood gas or ABG and chest X ray In addition you should estimate the fraction of oxygen in the patient's inspired air or F IO two F IO two is typically 0.21 when breathing room air For patients on supplemental oxygen it varies depending on the mode of oxygen delivery and the amount of oxygen being delivered Now here's a high yield fact to rule out cardiac dysfunction as the cause of lung infiltrates Look for absence of jugular venous distension On examination normal troponin or B type natriuretic peptide levels A normal ECG and a normal echocardiogram Your next step is to measure the PA O2 F IO two ratio by dividing the patient's arterial oxygen level or PA O2 by the estimated F IO two For example if a patient's ABG shows a PA O2 of 90 millimeters of mercury in their breathing room air which has an F IO two of 0.21 Then their PA O2 F IO two ratio is 429 millimeters of mercury Normal pa O2 F IO two ratio is between 405 100 millimeters of mercury Next assess whether your patient meets criteria These include that the respiratory condition starts within a week of an inciting medical event like trauma sepsis pneumonia pancreatitis or drug toxicity Chest X ray showing bilateral lung opacities of noncardiac origin and A PA O2 to F IO two ratio of 300 millimeters of mercury or less measured while receiving positive end expiratory pressure or continuous positive airway pressure of at least five centimeters of water If these criteria are not met consider an alternative diagnosis On the other hand if s criteria are met then diagnose ARDS and assess the PA O2 F IO two ratio Here's a clinical pearl several pulmonary conditions can mimic arts such as cardiogenic pulmonary edema bilateral pneumonia and alveolar hemorrhage So always include these conditions in your differential diagnosis Now if the PA O2 F IO two ratio is greater than 200 less than or equal to 300 millimeters of mercury diagnose mild S the management of mild ARDS involves treating the underlying condition For example if your patient has sepsis you should immediately start appropriate antibiotics Next optimize ventilator management The first step here is to set the ventilator to low tidal volumes starting with 8 mL per kilogram of predicted body weight then titrated to 6 mL per kilogram with a goal of achieving low plateau pressures of 30 centimeters of water or less These settings aim to decrease the risk of alveolar over distention and developing ventilation induced lung injury or V II Tidal volume is the total volume of air the ventilator delivers per breath Whereas plateau pressure is the pressure applied to the small airways and alveoli by the ventilator Next set the peep high enough to keep alveoli open but not too high that it causes over distention that may result in damage and V II the appropriate level of peep is usually decided at the bedside However lower levels of peep starting at a minimum of five centimeters of water are used in patients with mild ARDS and titrated to maintain maximal oxygenation Here's a high yield fact keep in mind that the more dependent lower lobes area of the lungs are affected more than the upper lobes and s so while ventilator settings may improve oxygenation in the affected areas mechanical ventilation can cause trauma to the unaffected areas So it's important to provide adequate oxygenation while avoiding ventilation induced lung injury Moreover ventilation induced lung injury is usually caused by overdistension of the unaffected alveoli leading to edema hemorrhage hyaline formation and alveolar collapse You may also attempt pharmacologic management which involves diuretics to reduce intravascular volume to help reduce pulmonary edema and improve oxygenation And here's another clinical pearl in ours neutrophils inactivated suricate and dead tissue debris fill alveolar spaces and reduce the area available for oxygen exchange So you'll see ventilation perfusion mismatch since the alveoli still receive blood supply but oxygen exchange is compromised This results in hypoxia that does not improve with increased F IO two Finally there's general ICU supportive care which includes enteral feeding DVT prophylaxis and gi ulcer prevention care bundles A set of evidence based practices commonly used for ICU Patients are used to reduce nosocomial infections which is very common in patients A ventilator bundle includes practices like daily oral care with chlorhexidine and raising the head of the bed between 30 to 45 degrees All practices to prevent ventilator acquired pneumonia If your patient has a central line be sure they have a central line bundle to prevent central line associated bloodstream infections which includes antiseptic dressing changes daily assessment of the need for ongoing central line access and removal of the catheter as soon as it's no longer needed Now let's go back and take a look at individuals who have a PA O2 F IO two ratio greater than 100 but less than or equal to 200 millimeters of mercury In this case diagnose moderate ARDS Management will include the same therapy as for mild ARDS and you may add higher peak levels to improve hypoxemia You may also consider prone positioning which is accomplished by placing the patient face down on their abdomen for at least eight hours a day This adjustment may improve ventilation in the unaffected areas of the lung leading to reduced intrapulmonary shunting improvement in oxygen exchange and prevention of V II Finally if the PA O2 F IO two ratio is 100 millimeters of mercury or less diagnose severe ARDS and treat the patient as you would for moderate ARDS In addition consider neuromuscular agents to induce paralysis improving pulmonary compliance and ventilation Finally you should consider extracorporeal membrane oxygenation or ECMO in patients with severe refractory ARDS ECMO is performed by pumping blood from the body to a heart lung machine where a special membrane oxygenates the blood and removes carbon dioxide Then the blood is warmed before returning the blood to the circulation In the setting of severe ARDS This may be the only effective way to maintain oxygen saturation All right as a quick recap if you suspect acute respiratory distress syndrome order ABG chest X ray and calculate the PA O2 F IO two ratio Next use ARDS criteria to rule out or confirm the diagnosis Once you confirm the diagnosis assess the PA O2 F IO two ratio in order to guide your management which primarily relies on treating the underlying cause and optimizing ventilator management Additional treatment options to keep in mind include diuretic use and general icu supportive care such as enteral feeding DVT and gi ulcer prophylaxis and care bundles Finally consider higher levels of peep prone positioning and use the neuromuscular agents and ECMO based on severity