Essay: ARDS: Ventilator Strategies and Risks of Recruitment Maneuvers



Outline

I. Introduction

II. Definition of ARDS

a. The Berlin Definition

i. Timing

1. 1 week

CXR

2. Bilateral opacities

ii. Not heart failure or fluid overload

i. Oxygenation

I. Mild

II. Moderate

III. Severe

b. American-European Consensus Conference

i.  ALI

ii. Oxygenation

iii. CXR Findings

III. Overview of Pathophysiology

a.  Inflammatory response

i. Cytokines

b. Edema

i. Cellular breakdown

c.  V/Q Mismatch

i. Dead Space

ii. Lung Perfusion

iii. Gas Exchange

IV. Definition/Role of Lung Recruitment Maneuvers (6)

a.  Increase Transpulmonary Pressures

b. ARDSnet

I. Effectiveness of Recruitment Maneuvers (RM)

ii. Length of time RM lasted

iii. One hour  

a. Indicated by drop in PaO2 (5-torn page)

B. Open Lung Approach

i. High levels of lung aeration

A. Conducting recruitment maneuvers

ii. Decremental PEEP titration

i. Maximum lung compliance

ii. Set PEEP between over distention and recruitment.

C. ARDSnet

i. Vent Setting Strategy

1. Low VT

2. High RR

3. Minute Ventilation determined auto-PEEP

D. Optimal PEEP

i. Esophageal Pressure

1. Inspiratory hold for 5 second

2. Expiratory hold for 5 second

ii. Esophageal Balloon

iii. Volumetric Capnography

iv. Less Dead Space

E. HFOV

i. Increased PaO2

ii. Increased PaCO2

iii. Reduction of cardiac output

F. Potential Harm of Recruitment Maneuvers

a. Cardiac

A1. Systemic Hypotension

i. Increase Right Ventricular Afterload

1. Decrease Cardiac Output

2. Increased Pulmonary vascular resistance

3. Shock from right ventricular failure.

ii. Left Ventricular Function

1. Intraventricular Septum Shift

2. Impaired Cardiac Compliance

iii. Decreased Venous Return

1. High PEEP

iv.  Pulmonary

1. Over distention/ Barotrauma

v. Over Distention

1. Increased Alveolar-Capillary Permeability

vi. Atelectrauma

1. Alveoli stress caused by collapsing and re-opening

2. VILI

3. Pulmonary inflammation

3. Summary

Abstract

Recruitment maneuvers are a complex and controversial topic within respiratory care, especially with ARDS patients. There are many questions that can arise such as, when to use a recruitment maneuver, is a recruitment maneuver a safe and efficient way to improve oxygenation. Through different studies many of the maneuvers mentioned have posed harmful side effects while briefly increasing oxygenation. Many of the harmful side effects include decreased cardiac output, barotrauma, and cardiac strain. Many of the current protocols establish a widely-accepted ventilator management strategy that requires low tidal volume and higher rates to minimize stress on the alveoli. This is said to reduce the stress and damage to the lungs.  Increasing the respiratory rate without optimal PEEP can be noted to cause damage to the lungs, as well as the tidal volume. When mentioning the disease process, a topic that is turbulent flow versus laminar flow. With lungs that are not properly inflated or a vent that is not set to the optimal settings can cause an issue with barotrauma and increase alveolar stress among certain parts of the lung. With different modes of ventilation that provide a gentler way of ventilating such as, HFOV also has its side effects. Many of them like the recruitment maneuvers, the difference between these is the idea of the lung remaining inflated over a long period of time. While the knowledge of the disease is increasing, management is still a variable when caring for these types of patients. There are protocols such as ARDSnet and open lung approach to managing recruitment maneuvers in ARDS patients, the idea behind these protocols are increasing PEEP and PIP, then slowly returning to baseline.

Key Words

Recruitment maneuvers, PEEP, Peak inspiratory pressure, HFOV, Barotrauma, Alveoli, Cardiac output, Stress, ARDS, Cardiac Output.

Introduction

There are many ways to manage a patient with ARDS, but are any of these ventilator strategies more beneficial or harmful then another. While there has been an adoption of management strategies among many caregivers, there are still slight differences among the two most popular. Which include the ARDSnet protocol and the open lung approach, which both have their positives and negatives. ARDSnet leans more on the side of lower tidal volumes and higher rates, while the open lung approach leans more in favor of recruitment maneuvers. While the lower tidal volumes and higher respiratory rates make sense, there is the issue of alveolar stress. This is regarding, the opening and closing of the alveoli, while this can maintain proper ventilation, it can also can cause further damage to the lung. Recruitment maneuvers can also cause complications with cardiac output and cause cardiac strain because of the increase in pressure within the lung and pressure against the heart. Optimal PEEP comes into the equation, with the proper and most effective settings on the ventilator we enter a state of lung recruitment and adequate oxygenation. The purpose of this paper is not to simply discount certain ventilator strategies but, to analyze the harm and benefits of different recruitment maneuvers. Also, there will be comparisons between commonly used management strategies. This is done to analyze the strategies many clinicians used every day and improve care for patients. As clinicians, the management of these patients appropriately is a vital part of our knowledge not only knowing the benefits of certain settings or maneuvers we must explore the risks and harms.  

Definition of ARDS

There are two definitions for ARDS, one is the Berlin definition and the other is the American-European Consensus Conference (AECC) definition. The differences between the two are minimal, for example the Berlin definition is more specific regarding time frame as opposed to acute onset. In the Berlin definition is more specific and has more subgroups. When comparing the Berlin definition “with the AECC definition the final Berlin definition had better predictive validity for mortality.”1 The Berlin definition is shown in detail below in table 1.

Berlin Definition:

Timing

Within one week of a known clinical insult or new or worsening respiratory symptoms.

Chest Imaging

Bilateral opacities – not fully explained by effusions, lobar/lung collapse, or nodules

Origin of Edema

Respiratory failure not fully explained by cardiac failure or fluid overload. Need objective assessment (e.g. Echocardiography) to exclude hydrostatic edema if no risk factor present.

Oxygenation

Mild

200 mm Hg < PaO2/ FiO2 less than or equal to 300 mm Hg with PEEP or CPAP greater than or equal to 5 cm H2O

Moderate

100 mm Hg < PaO2/ FiO2 less than or equal to 200 mm Hg with PEEP or CPAP greater than or equal to 5 cm H2O

Severe

PaO2/ FiO2 less than or equal to 100 mm Hg with PEEP greater than or equal to 5 cm H2O

Table 1: Definition of ARDS according to the berlin definition specific details on subgroups of oxygenation and specific information regarding timing. 1

With the Berlin definition being specific, there is very little room to misinterpret the diagnosis. The Berlin definition has improved the ability to diagnose and correctly manage patients with ARDS.   From a respiratory stand point the specific guidelines involving oxygenation make it easy to determine whether the patient is critical or is the disease is worsening. With an arterial blood gas the starting point and progression can be easily monitored. When mentioning the origin of edema, it is important to note that respiratory failure with ARDS patients is not solely caused by fluid overload.1 It is important because it illustrates that there is another factor, which is a decreased compliance.

Comparing AECC vs Berlin definition

The Berlin definition states the minor differences will be easier to discuss. With the timing criteria stated by the Berlin definition, it’s specific to one week as compared to AECC broad criteria of acute onset. There is no clear definition of time regarding onset or when symptoms began. Regarding chest x-rays, the standards are very similar by stating bilateral opacities but the Berlin definition is more specific to state what the opacities are not defined by. There was no mention of edema in the AECC definition so this is a clear addition to the berlin definition. Also, the addition of subgroups to the oxygenation criteria makes it very clear and specific on how to separate the severity of ARDS. The AECC definition did not consider the oxygenation index, or dead space when initially building their definition.2 When dealing with ARDS there are other factors that affect the lung tissue and lung compliance. This will be briefly discussed in the next section. Comparing the two definitions is a vital part of our practice to know the details of each definition and to know how the findings of the disease has progressed. Working as a healthcare provider, these definitions impact how we treat and determine the severity of our patient’s disease. It can help by preventing the disease from worsening if it is not in the severe subcategory. In the next section the pathophysiology of ARDS will be briefly discussed to give some information on what happens with the body when a patient is diagnosed with ARDS.

Overview of Pathophysiology

Inflammatory and Cellular Response

When mentioning ARDS patients the most common pattern identified in these patients is diffuse alveolar damage.3 The epithelium tissue of the alveoli and capillaries become inflamed by cytokines which results increases the permeability.3 Knowing that inflammation is a factor can help not only with a respiratory but also other disciplines within the care team. Not only is inflammation and cellular response a factor in ARDS, but also V/Q mismatch and dead space. These will be discussed in the next section.

V/Q Mismatch

When discussing ARDS, V/Q mismatch and dead space are critical points within the disease process.  A study by Tusman et al. illustrates how ARDS and acute lung injury can affect the distribution of dead space and tidal volume.4 This distribution and ventilation can be monitored by utilizing volumetric capnography. The different phases of the wave form, ranging from SI to SIV, show different pieces of information regarding the lungs and ventilation. More specifically, SIII of the capnography waveform, this was shown to represent the relationship between ventilation and dead space most accurately.4 With ARDS patients or ALI patients there is many dead space or non-functional areas of the lung. With having a brief overview of the effects ARDS has on the lungs, the definition of recruitment maneuvers will be discussed next.

Definition of Lung Recruitment Maneuvers

Lung recruitment maneuvers are attempts to increase the functional areas of the lung. By increasing the functional areas of the lung this will increase gas exchange. This can be done by performing many different strategies. Which include: increasing PEEP, inspiratory hold, and changing ventilator modes. There has been protocol or standards of care regarding ventilator management with ARDS patients. The protocols are named ARDSnet, and the open lung approach. With the ARDSnet protocol the recruitment maneuver effectiveness is determined by the increased functional lung volume. The increased functional lung volume can be measured by increased SPO2 and indicated with volumetric capnography. These lung recruitment maneuvers, excluding the ventilator mode changes, which only a short period of time. To determine the length of time a recruit maneuver was effective was done by studying PaO2. There are several different strategies to perform recruitment maneuvers, several of these strategies will be discussed in the next section.

Recruitment Maneuver Strategies

Recruitment maneuver strategies can be done by using many different techniques but many of them only last up to an hour after completing the maneuver in its entirety. When switching modes from conventional to high frequency oscillatory ventilation, the recruitment part of HFOV is set constant by the mean airway pressure, so the effects are much longer. Many of these strategies are used to find the optimal PEEP, or the PEEP needed to adequately ventilate and oxygenate patients. There are two different protocols when managing the ventilator that are similar with subtle differences. These the open lung approach and the ARDSnet protocol. These two are different meaning that one manages recruiting the lung and the other focuses on management of the ventilator. These topics will be discussed further within the next sections. When comparing different recruitment maneuvers, initially PaO2 decreased but slowly increases over time.5 This can be due to decreased blood flow or impaired cardiac output. There have been multiple studies that show the effects of a patient in the prone position compared to the supine position. When managing ARDS patients, it is important to keep in mind the level of stress and damage caused by the cycling of the ventilator. When mentioning stress on the alveoli, it is referring to the over-distention at the end of inspiration. It is important to note that a “patient can have more than 20,000 cycles a day of recruitment and derecruitment.”6 Lung recruitment strategies are said to increase the number of days free from mechanical ventilation when compared to low PEEP management.7

Open Lung Approach

The open lung approach focuses on recruitment of the lung and determining the optimal PEEP for the patient. The strategy consists of increasing the peak inspiratory pressures and PEEP to levels that are not normally set for these patients. This is done to increase functional areas of the lung. Once the patient is stabilized and tolerating the pressures set, and the healthcare provider will begin to slowly bring down the PEEP every twenty minutes until ventilation and oxygenation is at its best. Based on a study that evaluated the side effects that could be associated with the open lung approach, such as, decreased cardiac output, and other hemodynamic variables. “The study emphasized that greater PEEP with open lung ventilation does not significantly affect hemodynamic variables.”7 The idea behind the open lung approach to managing ARDS patients is simply to avoid the cyclic alveolar derecruitment. This minimizes stress on the alveoli by increasing the end expiratory volume.8 There was no evidence that showed increased risk of barotrauma with increased PEEP vs lower tidal volume.9 When the patient was on the open lung approach there was not influence on lung inflammation or edema.10 This study was done to address these issues when previously found during studies using the ARDSnet protocol.

ARDSnet

The ARDSnet protocol is information on how to manage the ventilator while treating a patient with ARDS. It breaks down the respiratory rate and tidal volume aspects of ventilation. The details of this technique require increased respiratory rates with lower tidal volumes. The idea behind ARDSnet is to not push too much pressure or tidal volume into the lungs due to decreased compliance. While making up the difference in tidal volume with increased respiratory rates.

Optimal PEEP

Optimal PEEP is the goal of most strategies and there are many ways to find, and determine exactly what is optimal and what is not. “Conventional ventilation with optimal PEEP is the widely-accepted practice for managing ARDS patients.”8 Many of these recruitment maneuvers drop the PEEP after the maneuver is complete but, it is crucial to maintain a higher level of PEEP at which both oxygenation and ventilation is achieved. It is important to maintain optimal PEEP after the recruitment maneuver to maintain the effects.11 When dealing with recruitment maneuvers and optimal PEEP, the goal is to be accurate and perform these maneuvers safely. One study illustrates how a slower moderate recruitment maneuver, when compared to a vital capacity is more effective. Vital capacity recruitment maneuvers gave the patient similar results with improved oxygenation but, will cause more stress to the alveoli. A slower moderate pressure maneuver yielded the same results but with less stress caused to the lungs.12 When PEEP is adjusted to a higher level that optimal PEEP there is no further recruitment at this point.13 This is because, it starts affecting blood flow which can cause a negative affect towards ventilation and oxygenation. “PEEP could promote further tidal volume reductions by decreasing shunt and alveolar dead space.”14

HFOV

HFOV has been recommended when the tidal volume in ARDS patients can be low to prevent stress on the alveoli from opening and closing. With HFOV the rate is set with hertz which means, for one hertz that is set, it cycles sixty times. With HFOV, the pressure is set high which can cause side effects on the right ventricle.14 There has been discussion comparing HFOV vs. moderately high frequency ventilation while on conventional ventilators. This meaning, high respiratory rates and tidal volumes lower than 6 mL/kg.15 With this idea of moderately high frequency ventilation, there are things to consider such as, how high the respiratory rate is because, at a certain point the reductions in tidal volume are not significant.14 With increasing respiratory rates the best way to effectively ventilate is to minimize dead space so the tidal volume and dead space are not equal.14 ARDS is not exclusive to adult population, but it is very common in the neonatal and pediatric population. “With HFOV using increased pressures, the risk of hyperinflation and air leaks is minimal when applied to premature infants with RDS”.16 With several different recruitment maneuvers listed, it is important to discuss the potential harms and risks that comes along with these maneuvers. These risks and potential harms will be discussed further in the next section.

Potential Harm with Recruitment Maneuvers

While recruitment maneuvers are beneficial for a short period of time, there are also many side effects that come along with them. Such as, decreased systemic blood pressure. Which is caused by an increase in stress when the heart is pumping blood away from the heart. Which decreases cardiac output, increases pulmonary vascular resistance, and can eventually lead to right ventricular failure. There are many others which will be discussed in detail. In the first part of this section the pulmonary side effects will be discussed in detail.

Pulmonary Side effects

Regarding pulmonary side effects, specifically mentioning the open lung approach to recruitment maneuvers, this technique requires increased peak inspiratory pressures and increased PEEP levels. The increased inspiratory pressures are a sure way to cause barotrauma and cause an increase with alveolar stress this is caused by the opening and collapsing of the alveoli, this stress is combatted by the increase of PEEP which makes opening and closing of the lung very minimal. An argument for this technique is simply the decreasing of peak inspiratory pressures and PEEP will cause the lungs to continue the stress after the recruitment maneuver is completed. As stated previously, the final step of the open lung approach for ARDS patients is to get the PEEP to zero then increase to optimal PEEP where ventilation and oxygenation occurs. While considering the ARDSnet protocol, the idea is to maintain low tidal volume and increase respiratory rates. Which can cause stress to the alveoli, while barotrauma was heavily considered while putting together this strategy. The stress can come from the increased amount of opening and closing of the alveoli. One study mentioned, once the PEEP has passed the limit of opening in the lung, it is not helping with oxygenation but, aiding in over distention.11 While many healthcare providers lean towards increase PEEP, according to Kamuf et al, if PEEP is increased higher than optimal PEEP it can cause damage by hyper inflating the healthy tissue.13 According to Ko, with periodic recruitment maneuvers insufficient PEEP level can cause further lung tissue damage.17  Now that the pulmonary aspect of ARDS has been discussed, the cardiac harms and risks will be briefly discussed.

Cardiac Side Effects

Initial studies of PEEP in mechanical ventilation showed a negative impact on cardiac output and venous return.18 This decrease in venous return is all attributed to the increase in intrathoracic pressure.15 It was said that open lung ventilation caused a shift of the intraventricular septum, which was debated. When the lung is inflated with increased peak inspiratory pressures the lung tissue can activate a vagal response causing a decrease in heart rate.19 Systemic hypotension is often seen with recruitment maneuvers due to the sustained inflation pressures that are used.20 The cardiac aspect of ARDS is important to note when discussing recruitment maneuvers because these can easily impact the blood pressure, cardiac output, among other things. These things can cause harm or pose risks for the outcomes of patients.

Summary

Many healthcare providers perform recruitment maneuvers to manage patients with ARDS. Without a proper knowledge of what exactly is happening with the lung these recruitment maneuvers are not beneficial. Not only can these maneuvers be done incorrectly but they can also be dangerous. The potential for risks in these patients while performing these recruitment maneuvers is high which is caused by the decreased lung compliance. There are many areas of research that need to be done, such as comparing different techniques, which techniques are more harmful than others. These comparisons are essential to healthcare providers so we can treat our patients with the safest and most effective care. While more research is required, the information on new technology and equipment is growing. This equipment can make healthcare providers determine the proper settings for patients more efficiently and with more accuracy. Equipment such as, volumetric capnography, esophageal pressures, modes on ventilators that help determine optimal PEEP.  We are headed in the right direction with managing these patients, with different techniques and protocols in places. With these protocols, it gives a base of information that allows healthcare providers with standards and not having to guess what’s best for the patient. While it is important to note the side effects and benefits of these recruitment maneuvers, healthcare providers must understand that all patients are different and tolerate different techniques better or worse than other patients. When dealing with recruitment maneuvers there are many different issues that healthcare providers must consider. Such as, possible damage to the lungs, effectiveness of the recruitment maneuvers, and will it benefit the patient in the long run? While many of the recruitment maneuvers tend to have no long-term effects, the benefits are also short lived.