Overview of Acute Respiratory Disease Syndrome (ARDS) and Respiratory Mechanics.

ECMO New Era

Abstract
Cases of patients not receiving adequate ventilation through conventional methods have recently been increasing and intensive care has been suggested following respiratory illnesses induced by the H1N1 virus. It follows, therefore, that the use of high-intensity interventions is considerably influenced by the popularity of ARDS and especially in younger patients. Health professionals have noted ARDS to be the most severe variety of ALI and defined it by the ration of partial arterial blood oxygen pressure (PaO2) to the oxygen fraction in inspired air (FIO2). Respectively, ALI and ARDS are defined by a ratio of PaO2/FIO2 of less than 300 and 200. Further, it is also acknowledged that increased volumes of oxygen and pressure under conventional methods dispose patients to increased lung injury and therefore the significance of the high-intensity interventions. The two strategies to be discussed in this study are ECMO and HFOV, which are both unconventional mechanical methods. It is recommended that HFOV be used as a practical option for refractory ARDS rather than as a habitual component of managing ARDS patients when ECMO is not available. Additionally, when patients fail to improve when using HFOV, ECMO should be the immediate alternative. The two variations of ECMO are VV and VA and both have characteristic advantages and disadvantages. While both ECMO and HFOV have their own advantages and disadvantages, findings have proven that both are beneficial depending on the individual circumstance. A key limitation of the study was that it was non-experimental but it served to fulfill ethical considerations. However, the general provisions of the study suggest that the popularity of ARDS has given rise to increased use of both ECMO and HFOV only after determining that conventional methods have failed. Essentially, both strategies significantly improve the exchange of gas not only rapidly but sustainability.

Keywords Acute respiratory distress syndrome (ARDS) . Extracorporeal Membrane Oxygenation (ECMO) . High-frequency oscillation ventilation ( HVO ).

ECMO New Era
Introduction
In the medical profession, there are rising cases in which patients cannot be ventilated adequately even with the use of sophisticated conventional ventilation (Betit & Craig, 2010). Further, many reports, following the respiratory illness resulting from the H1N1 virus, have suggested the significance of intensive care in affected patients and especially the young. In that perception, respiratory insufficiency is an important issue as it continues being a key cause of neonatal mortality. Further, when conventional ventilation with higher airway pressures and rates is increased, it potentially results in more barotrauma incidents. More, specifically, the high shearing forces that are a result of large amplitudes of pressure can damage lung tissue. Therefore, it becomes critical to explore and better understand alternatives to the conventional methods that can bring down the incidents of mortality and this paper will focus on extracorporeal membrane oxygenation (ECMO) and high frequency oscillatory ventilation (HFOV). On one hand, HFOV is an unconventional type of mechanical ventilation used to maintain lung recruitment by constant distending pressure. HFOV’s efficiency is basically due to the improved exchange in pulmonary gas. The pressure variations oscillate around the mean airway pressure (MAP) at rates as high as 900 cycles every minute creating small tidal volumes typically in the range of 1 – 4mL/kg (Hayes, Black & Tobias, 2015). Its key aim is to avoid lung injury that results from over-distention or the loss of recruitment also referred to as atelectrauma. On the other hand, ECMO uses a pump to provide respiratory (and also cardiac) support to individuals whose lungs (and also heart) are not able to adequately provide gaseous exchange for life sustenance (Wang, Zhou & Lynch, 2010). Essentially, the pump is used outside the body for the circulation of blood through an artificial lung and back into the patient’s bloodstream. By providing a lung-heart bypass support, ECMO supplies enough oxygen while the lungs and heart are allowed sufficient time to rest and heal. Conditions that commonly require ECMO include congenital diaphragmatic hernia, severe pulmonary hypertension, heart malfunctions, severe air leak complications, severe pneumonia and meconium aspiration syndrome as well as the recovery period following heart surgery (Malhotra & Drazen, 2013). With ventilation and oxygenation as the key focus, this paper will discuss how ECMO and HFOV have an impact on respiratory failure among the affected population, which in this case are often the young and healthy. To facilitate the research, a comparison of HFOV and ECMO will also be a key feature of the paper.
Overview of Acute Respiratory Disease Syndrome (ARDS) and Respiratory Mechanics
Prior to the exploration and discussion of the topic, it is important to have an understanding of lung injury and respiratory mechanics in the state of oxygenation and ventilation. ARDS, a condition represented by severe hypoxemia and bilateral pulmonary infiltrates, has been recognized by health professionals as the most severe type of acute lung injury (ALI) (Marco & Ranieri, 2012). Vlaar, Binnekade and Prins (2010) defined the necessary severity of hypoxemia for the diagnosis of ARDS by the ration of partial arterial blood oxygen pressure (PaO2) to the oxygen fraction in inspired air (FIO2). Essentially ALI and ARDS are defined respectively by a ratio of PaO2/FIO2 of less than 300 and 200. The Berlin definition of ARDS was arrived at by timing radiographic changes, origin of edema and the severity basing on the PaO2/FIO2 ratio within a week of the onset of respiratory symptoms on 5cm of CPAP (continuous positive airway pressure) (Marco & Ranieri, 2012). There are three regions of interest in lung tissue in cases of ALI and the first region that is severely diseased is characterized by a limited ability to recruit safely. Then there are the uninvolved regions that still show regular compliance and aeration, over-distension is possible when increased ventilatory support is provided. Thirdly, there are the intermediate regions characterized by edema and reversible alveolar collapse. From the perspective of respiratory mechanics, ALI is generally associated with decreasing lung compliance whereby for the same delivery pressure, less volume of air is delivered compared to conditions in which ALI is absent. As discussed in this study, for both ECMO and HFOV, there are blood transfusion and clotting factors to be considered since there are always risks of blood reaction as in any other blood transfusion case.
Review of the Literature
According to Wang, Zhou and Lynch (2010), ECMO refers to the use of external (extracorporeal) artificial lungs (membranes) to provide blood with oxygen (oxygenation) and circulate it around the body continuously. Concurring with the description, Betit and Craig (2010) contribute that it is best suited for newborn babies and children suffering from severe respiratory and cardiac failure. From their experience, Cianchi et al (2011) established that early ECMO was consistently safe when used as an intervention acute respiratory distress syndrome (ARDS) induced by H1N1. As Hayes, Black and Tobias (2015) reported, mortality statistics related to patients placed under ECMO treatment has stabilized since 2005 although the rate is still high in infants born with a birth weight of less than 2kgs. Berkel et al (2013) noted that persistent pulmonary hypertension (PPHN) in newborns has conventionally been treated with mechanical ventilation, muscle relaxants, oxygen, non-selective vasodilators and sedation for the purpose of reversing acidosis. Riscili et al (2011) also noted that there were significant increases in the use of healthcare globally as a result of pandemic influenza and ECMO and HFOV were the common high-intensity rescue interventions. Hayes, Black and Tobias (2015) addressed ventilation from the perspective of age. They studied whether infants with ARDS in whom the predefined settings of ventilation did not maintain adequate oxygenation and removal of carbon dioxide could be transitioned safely to HFOV. Their study found that the use of HFOV is efficacious but they supported earlier findings by Ferguson and Slutsky (2009) that ECMO should be used as an emergency in infants who did not show improvement when using HFOV. According to Carlo (2011), who disagreed with Cianchi et al (2011) that ECMO should fundamentally be considered as a safe therapeutic option, ECMO must be used as a rescue solution in infants with ARDS. The same views supporting the use of ECMO in emergencies among infants were expressed by Malhotra and Drazen (2013). From the literature review, it may be assumed that neither ECMO nor HFOV can be argued to be superior to the other in terms of functionality and achieving results. Rather, they are appropriately suited for different situations since ECMO is preferred in emergencies. However and more importantly, the ARDS has influenced the expanding utilization of high-intensity rescue therapies (Riscili et al, 2011).
Method
This paper uses both qualitative and quantitative research methods although the emphasis is on qualitative method. The combination was adopted in such a way that quantitative tools address the weaknesses of the qualitative model specifically in cases where there is a need for the primacy of evidence or when quantitative findings is more authoritative. This is supported with mixed models of research where the methods are merged so that the research framework can give priority to one over the other.
This researcher also underscores that this study is non-experimental, a strategy that eliminates the need to manipulate human subjects as independent variable, since it is unethical. As stated by Johnson and Christensen (2008) this type of research can lead to the possibility of mental and physical harm to subjects. With the mixed-method identified, the ultimate aim is to ensure that the research strategy allows the greatest level of control over the qualities that can potentially interfere with the validity and reliability of the research findings.
Since this study emphasizes the qualitative method, both literature review and interviews will be conducted. Specifically, the review of literature is aimed at obtaining background knowledge about ARDS and respiratory mechanics in order to establish concepts such as professionals’ opinion. In addition, it informed the development of interview and survey questionnaire. Previous studies in the review of literature will also be used in the analysis of the collected data.
The data obtained from the qualitative analytical and data collection process, particularly the information gathered from observations, primary sources and qualitative interviews will complement the statistical data derived from the quantitative research. Both qualitative and quantitative data, will be evaluated using qualitative analytical tool called the thematic method, which arrange the information in a logical sequence, which leads to the visual demonstration of causes and effects (Reese, 2002, p. 105) . The outcome is expected to provide accurate description of the research phenomena being investigated.
The study followed a logical progression of research beginning with the identification of the problem, the review of related literature, the collection of qualitative and quantitative data, and, finally, the discussion and analysis. The research population includes individuals, organizations, events from which data could be collected with a focus on young persons. The inclusion criteria included registered nurses, home managers and healthcare assistants working in nursing homes. Through the random sampling method, a specific list of participants will be identified using “by reference to a table of random numbers or generated by a computer using a random number generator” (Poggie, DeWalt and Dressler, 1992)
Ethical considerations relating to moral standards were ensured by obtaining permission from the institutions involved as well as consent from parents in the case of minors. The ethical considerations of the research were guided by the principles of respect for human dignity, beneficence and justice and the key instrument of data collection was the researcher.

ECMO and HFOV
ARDS associated with pandemic influenza has significantly impacted the use of both ECMO and HFOV and the observed illness severity is increasingly straining healthcare resources (Roch et al, 2010). Looking at the two strategies individually, ECMO is a term that was initially used in reference to the continuing extracorporeal support with a focus on oxygenation’s role. The cardiopulmonary bypass technology is used in ECMO to assist the exchange of gas in ARDS patients and allow the reduction of ventilator settings and provide time for both treatment and recovery (Roch et al, 2010). With time, the emphasis subsequently shifted in the case of some patients to the removal of carbon dioxide and was referred to as extracorporeal carbon dioxide removal. However, regardless of the variations of its capabilities, it remains a key tool in organ and life support strategies among clinicians and the two most commonly used are the veno-venous and veno-arterial, denoted as VV and VA respectively (Zhou & Lynch, 2010). Basically, the blood flow rate controls oxygenation while the countercurrent fresh gas flow controls removal of carbon dioxide. Between VV and VA, VA is the standard procedure commonly used in majority of neonatal intensive care units (ICUs). Through VA, a clinician places a cannula in the right atrium via the right jugular vein to drain blood to a venous reservoir (Ferguson & Slutsky, 2009). A pump forces the blood through an oxygenator in which gaseous exchange takes place facilitated by the gas’s and blood’s countercurrent flow. Prior to returning the blood to the body, a heat exchanger raised its temperature to body temperature. The clinicians administer systemic anticoagulation therapy using heparin over the entire bypass circuit and monitor frequently the activated clotting time, which they maintain at between 180 and 240 seconds (Betit & Craig, 2010). On the other hand, the VV technique also places a double-lumen cannula in the right atrium via the right jugular vein. However, unlike VA in which pulmonary circulation is bypassed, pulmonary blood flow is maintained in VV. Further, no cardiac support is provided in VV to facilitate systemic circulation (Zhou & Lynch, 2010). The advantages of VA include the provision of comprehensive cardiovascular support, which makes it appropriate for patients suffering extremely poor cardiac function. However, on the other hand, a key drawback of VA is large-bore arterial puncture and while VV features fewer issues with regards to vascular access, it is only indicated among patients with optimum myocardial function (Berkel et al, 2013).
Indications for ECMO entail various diagnoses such as primary diagnoses related to ARDS, primary pulmonary hypertension (PPHN), asphyxia, meconium aspiration syndrome and group B streptococcal sepsis (Betit & Craig, 2010). Patients are usually sedated with continuous neuromuscular blockade and volume-controlled ventilation with tidal volume of 5 -7cc/kg used before they can be considered for ECMO. If the PaO2 to FIO2 ratio is less than 70mmHg for 2h in conditions of FIO2 of 1, ECMO was indicated (Roch et al, 2010). Other significant indications include cardiac arrest, cardiogenic shock, hypercapneic and respiratory failure. A key benefit of ECMO is that a constant oxygen supply is maintained while the lungs are rested. As acknowledged by most literature, the high oxygen and pressure levels in ventilators in themselves can cause further damage in patients with ARDS (Zhou & Lynch, 2010). However, ECMO is designed to break down the cycle and facilitates the lungs to rest as the damage is healed. Apart from the artificial lung or oxygenator, the ECMO circuit also depends on a motor for the pumping of blood around the body. The implication is that the ECMO machine’s pumping ability can also support when needed in reversible cardiac disorders (Malhotra & Drazen, 2013). On the other hand, the main risk associated with ECMO is the bleeding that takes place during the treatment. The reason is because Heparin, which is a blood-thinning drug, is used to prevent blood from clotting as it flows through the plastic tubing and the undesired result is that bleeding will take pace. Such bleeding can be in any part of the patient’s body but is critical if it occurs in the brain. There are more bleeding risks involved if there is need for surgical procedure while ECMO treatment is ongoing.
The increasing understanding of lung recruitment and its physiology, as well as the undesirable consequences of ventilator induced lung injury (VILI), improved strategies in ventilation such as HFOV are aimed at reducing mortality and morbidity associated with VILI. HFOV is one of the several modes of high frequency ventilation in which every mode has unique pros and cons. However, all the modes share a common breathing frequency, which is equal to or greater than 60 breaths per minute or 1Hz and extremely low tidal volumes typically 1 – 3cc/kg, which is lower than dead space (conducting airways’ volume) (Sud et al, 2013). The indications of HFOV usually include the failure of oxygenation that require FIO2 greater than 0.7 (Henderson-Smart, De Paoli & Clark, 2009). HFOV is a form of lung-protective mechanical ventilation in which a respiratory rate more than four times above the normal value is used and during volume and pressure swings, the entire cycle will still operate within the safe window to avoid the injury regions. As air flows towards the alveolar level, pressure is attenuated and, in turn, alveolar stretching is minimized which results in less exposure to trauma (Riscili et al, 2011). Outcomes are generally improved by HFOV especially in open lung strategies because the shear forces are greatly reduced. Essentially, the shear forces are related to the cyclical opening of the collapsed alveoli (Malhotra & Drazen, 2013). The improvement in the exchange of pulmonary gas exchange basically defines the effectiveness of HFOV although practice has shown that favorable influences can also be drawn on respiratory hemodynamics and mechanics. Pulmonary gas exchange is accomplished by direct alveolar ventilation in conventional ventilation. However, while conventional models do not explain gas exchange at tidal volumes lower than the anatomical dead space, HFOV effectively ventilates lungs at extremely low tidal volumes by considerably mixing exhaled and fresh gas in the airways.
A key advantage of HFOV is the reduction in VILI and the dissociation between the clearance of carbon dioxide and oxygenation as it mobilizes secretions. However, it also has disadvantages because it not only requires heavy paralysis and sedation but derecruitment is also most likely to recur once the procedure is ceased (Hayes, Black & Tobias, 2015). Further, the high airway mean pressure exposes younger patients to hemodynamic instability risks and at the same time, active humidification is required throughout the procedure. A summary of findings by a number of researchers has also failed to provide evidence of benefit in numerous cases of important RCT but reported harm and higher mortality (Hayes, Black & Tobias, 2015).
Conclusions and Recommendations
It has been shown that there are increasing cases in which conventional ventilation strategies cannot be used to adequately ventilate patients suffering from ARDS. Therefore, the introduction and use of sophisticated methods such as ECMO and HFOV should be considered. Respiratory illness resulting from the H1N1 virus has called for the need of intensive care in affected patients, especially the young, making respiratory insufficiency a key issue, as it remains a cause of mortality. On the other hand, when conventional ventilation with higher airway pressures and rates is increased, there are increased risks of barotrauma incidents. When conventional ventilation fails in patients with ARDS, HFOV has the potential to improve the exchange of gas rapidly and sustainably. Although neither of the two interventions can conclusively be declared superior, it is acknowledged that they both have advantages and disadvantages and depending on the situation, one may be more suited than the other. However, there is need for more randomized controlled trials so as to establish the benefits it has over conventional mechanical modes of ventilation. It is recommended that rather than using HFOV as a habitual component of managing ARDS patients, it should be considered as a practical option for patients of refractory ARDS when ECMO is not available. However, ECMO should be the immediate option in emergency cases in which infants do not show signs of improvement when using HFOV (Henderson-Smart, De Paoli & Clark, 2009). There are certain warnings, however, issued before a patient is subjected to ECMO. It is imperative that one is satisfied that conventional methods such as recruitment maneuvers, diuresis, prone positioning and fluid resuscitation have failed.
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