Notes from the Chair: Plan Now To Attend the AARC Congress
Michael Hewitt, RRT-NPS, FAARC, FCCM
As I write this column, we are only a short time away from this year’s AARC International Respiratory Congress, Dec. 6-9 in Las Vegas, NV.
The Advance Program has been up on the AARC website for awhile now, but if you’ve yet to take a look, please click on the link to see what the Program Committee has planned for us this year.
I think you’ll see the meeting is a must attend for everyone in our specialty section. Topics range from “A Practical Approach to Acute Respiratory Failure: A Case-Based Discussion” to “Stopping the Revolving Door for COPD” to “Hospital Acquired Infections: How Are We Doing?” to “Putting Best Evidence into Practice for Optimum Patient Benefit.” Both the Donald F. Egan Lecture and the New Horizons Symposium are especially geared to our area—Robert M. Kacmarek will address “The Mechanical Ventilator—Past, Present, and Future” in the former, and the latter features an “ARDS Update.” The Phil Kittredge Memorial Lecture was developed with us in mind too—Stephen I. Rennard, MD, will talk about “COPD Heterogenetiy: What This Will Mean in Practice.”
These topics just scratch the surface of what’s available, so again, take a few moments to review the Advance Program, and then consider joining us this December. We’ll also be hosting a section meeting at the Congress, and we invite everyone to attend. It’s a great way to meet your colleagues in the section face-to-face and find out what the section will be doing next year, and how you can get more actively involved.
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Managing the Difficult ARDS Patient
Keith D. Lamb, RRT, Christiana Care Health System
A couple of weeks ago I was searching for a decent article to send out as our departments’ monthly journal club topic. Since most of my interests lie within the management of ARDS, the following article caught my attention: “Therapeutic Strategies for Severe Acute Lung Injury” in the August issue of Critical Care Medicine.1 After reading the article, I thought I would jot down a couple of thoughts I had on the topic and how they impact the way we practice as RTs.
ARDS has been studied in the literature since the early 1820s and was initially described as “pulmonary edema not caused by heart failure.” In the early 1960s it was most often described in association with its etiologies (DaNang lung, shock lung, post-traumatic lung). By the late 1960s what we now call ARDS was finally recognized as pulmonary abnormalities having common presentations but vast etiologies. Finally, in 1992 the American European Consensus Conference developed the definition of ARDS/ALI that we recognize today.
Many strategies have been developed and studied to assist clinicians in their quest to achieve better outcomes in the ARDS patient. Despite these strategies, mortality in ARDS has remained at around 40%. A landmark paper written in 2004 and published in the New England Journal of Medicine described the ARDSnet data regarding the “low tidal volume” approach to managing ARDS. The data showed that mortality could be reduced by almost 10%.
Since this paper was published, the low tidal volume approach has become the gold standard, and protocols around the world have been written reflecting the data. There is no doubt that this strategy has merit, and should be followed when at all possible. However, one of the major obstacles encountered by those following protocols based on the ARDSnet data is that some patients simply cannot maintain acceptable gas exchange, forcing the clinician to manage the patient via other modalities or adjunct therapies.
I have broken down the modalities used in ARDS into six categories: conventional ventilation, non-conventional ventilation, pharmacological support, ECLS/ECMO, acid base buffering, and prone positioning. Here’s a description of each, including pros and cons related to its use—
Conventional ventilation
Conventional ventilation refers to the positive pressure modes that are used in our everyday practice. Although some institutions may be a bit more progressive and use lesser known modes a little more frequently, conventional ventilation most often includes volume assist control, pressure assist control, volume and pressure SIMV, pressure support ventilation, Bilevel/APRV, and the hybrid modes like auto-flow and pressure regulated volume control.
As mentioned above, using lower volumes and distending pressures has been associated with better survival rates. When using volume modes, take care to use volumes that are 6–8 ml/kg/predicted body weight while ensuring that plateau or static pressures remain <30 cmH2O. If alveolar pressures climb, drop tidal volume and increase frequency. When using pressure modes, attempt to utilize pressures that are <30 cmH2O if possible. This is one of the best strategies available given that there is clear evidence that following it decreases death rates associated with ARDS. Studies have compared volume controlled ventilation, pressure controlled ventilation, and APRV/Bilevel, but there is no strong evidence supporting any mode over volume controlled ventilation. When acceptable gas exchange cannot be maintained, you may need to rely on other methods.
PROS: Easy to manage. Equipment is readily available since most modern microprocessor controlled ventilators can provide any of the above conventional modes, or at least something similar. Most RTs are trained to use conventional ventilation modes. Data show lower mortality when conventional ventilation is used in ARDS (volume assist control).
CONS: Some patients may not be able to achieve acceptable gas exchange no matter what mode you use.
RESOURCE: NHLBI ARDS Network
Nonconventional ventilation
HFOV: High frequency oscillatory ventilation has been around for some time, but most of the studies on its use have been conducted in neonates. In the last few years, however, we have seen promising developments in the adult arena. Ventilators have been manufactured that are specifically made for adults, and data has been reported comparing the use of HFOV with conventional modes of ventilation, some of which has shown a slight trend in increasing survival. There is currently a large multicenter, randomized controlled trial in the UK comparing HFOV with volume controlled ventilation. HFOV uses small sub-dead space tidal volumes at very high rates, up to 900 breaths per minute via the Sensormedics 3100B. Oxygenation and ventilation are managed independent of each other, which is clinically convenient in that making changes to Paw to improve oxygenation may not negatively impact ventilation.
PROS: May get you out of a jam. Likely to improve oxygenation, but may or may not effectively ventilate. Because of a “lack” of large pressure swings it may be useful in managing those with large air leaks such as BP fistulae. Is probably protective, although data is somewhat lacking. Data relating to survival improvement is promising.
CONS: No overwhelming data supporting survival improvement. Staff competency may be difficult to obtain and maintain. Difficult to transport due to lack of battery. No backup ventilation. Must use long acting neuromuscular blockade such as cisatracurium, which has been associated with an increased incidence of neuropathy.
RESOURCE: Respiratory Therapy On-Line: HFOV
Pharmacological support
Exogenous inhaled nitric oxide: This is another therapy that got its start in neonatal critical care. A potent pulmonary vasodilator, NO may improve V/Q matching by dilating pulmonary vasculature that articulates with functioning alveoli. It may also improve blood flow and oxygenation. It may help those with right heart failure, but may be detrimental to those with left heart failure. It may decrease significant right to left shunt via PFO by decreasing pulmonary vasculature resistance and right heart pressures. NO will improve oxygenation in most patients, but it has not been shown to improve survival in ARDS patients and it may increase incidence of renal failure.
PROS: Fairly easy to use the new machines. Will improve oxygenation in the majority of cases.
CONS: No data to support survival improvement. Expensive. May increase renal failure. Staff competency may be difficult to achieve and maintain. Nitric dioxide levels and methemoglobinemia must be monitored closely.
RESOURCE: Effect of Nitric Oxide on Oxygenation and Mortality in Acute Lung Injury: Systematic Review and Meta-Analysis
Steroids: The idea behind steroid use is to decrease the anti-inflammatory response in ARDS. There is no clear evidence supporting the use of glucocorticoids in ARDS. There is data, however, suggesting that its use, especially late (>14 days into course of ARDS) may actually decrease survival. A higher rate of infection has been associated with the use of steroids.
PROS: May help attenuate lethal inflammatory response of ARDS.
CONS: May increase the incidence of death, neuropathy, and infection.
ECLS/ECMO
Extra corporeal life support (ECLS) and extra corporeal membrane oxygenation (ECMO) have had dismal outcomes when used for rescue from profound refractory gas exchange problems in ARDS. It is hypothesized that, for the most part, these adverse outcomes can be attributed to the very late initiation of these therapies. Recent studies have shown an improvement in mortality among patient sent to special referral sites that specialize in ECMO. ECMO is usually done venovenous in adults. There are plenty of potential complications.
PROS: Takes lungs out of the equation when there is a completely refractory gas exchange problem.
CONS: Weak data supporting its use in ARDS. Requires highly specialized equipment and personnel trained in its use. Requires anticoagulation, which excludes many patient populations. Difficult to transport.
RESOURCE: Efficacy and Economic Assessment of Conventional Ventilatory Support versus Extracorporeal Membrane Oxygenation for Severe Adult Respiratory Failure (CESAR): a Multicentre Randomised Controlled Trial
Acid base buffering
Today’s management strategies allow for permissive hypercarbia and acidemia. Most clinicians are willing to allow a plasma pH of ≥ 7.20. However, complications associated with profound acidemia have to be considered. Enzyme function can be attenuated in the face of acidemia, and for those patients on vasopressor support this can mean a need for higher levels of infused drug. This can lead to higher lactic acid levels, metabolic acidemia, and so on. At times there may be a need for acid base buffering in order to avoid using injurious ventilator settings like increasing tidal volumes. NaHCO3-, and Tromethamine (trishydroxymethyl aminomethane) have been successfully used to buffer profound acidemia. Sodium bicarb releases CO2, which can be counterproductive in the difficult-to-ventilate patient. Tromethamine does not release CO2, but is contraindicated in patients with renal failure, a common co-morbidity in ICU patients. Dialysis has also been proven effective in buffering acidemia, but needs cannulation and intense management.
PROS: Can be used to allow for permissive hypercarbia and a more protective ventilator strategy. Can allow less vasopressor support and potentially help improve cyclic metabolic acidemia.
CONS: Dialysis can be difficult to manage at times, requires more invasive venous access, and has the potential for infection. Sodium bicarbonate produces CO2 and may be counterproductive.
RESOURCE: The Treatment of Acidosis in Acute Lung Injury with Tris-Hydroxymethyl Aminomethane (THAM)
Prone positioning
Prone positioning changes V/Q matching, reduces compressive atelectasis, and will most likely improve oxygenation. It is cheap, but is logistically difficult at times depending on body habitus and specific injuries. It also increases the risk of losing central lines airways and chest tubes, as well as the incidence of facial edema and pressure ulcerations on the face and upper torso. Newer data shows some trend toward improved survival in ARDS, especially in those patients left in the prone position for longer uninterrupted periods of time.
PROS: Cheap. Improves oxygenation and may improve survival.
CONS: Potential complications, including airway loss. Can be difficult depending on patient’s body habitus.
RESOURCE: Prone Position in Acute Respiratory Distress Syndrome
It’s our job
In conclusion, today’s clinicians should be aware of the current data and make their recommendations accordingly. It is our job as RTs to ensure that those around us are making their decisions based on sound science and supported data.
Reference
- Diaz JV, Brower R, Calfee CS, Matthay MA. Therapeutic strategies for severe acute lung injury. Crit Care Med 2010;38(8):1644-1650.
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