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Experts Discuss Innovative Approaches to Intubation

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The ability of paramedics to perform endotracheal intubation (ETI), particularly when used in conjunction with rapid sequence intubation (RSI), has become increasingly controversial. The introduction of new products, the use of standalone disposable continuous positive airway pressure (CPAP) masks and a de-emphasis on ETI in cardiac arrest patients reduces the number of patients who receive this low-frequency, high-risk procedure. As the number of intubation opportunities dwindles, paramedics are less likely to gain valuable real-world experience.

Although improvements in products and monitors, such as pulse oximetry and digital end-tidal carbon dioxide (EtCO2), have helped improve tube placement, successful advanced airway programs require adequate and frequent training, rigorous clinical oversight and an active quality improvement program—a trifecta that is rare even in the best of economic times.

Research is providing confirmation that EMS is at a critical juncture with regard to advanced airway management. The San Diego Paramedic RSI Trial, one of the largest studies of prehospital intubation, determined that paramedic RSI protocols to facilitate ETI of head-injured patients were associated with an increase in mortality. (1) Inadvertent hyperventilation, transient hypoxia and longer on-scene times associated with the RSI procedure were specifically noted. A follow-up study two years later documented the same results.(2)

Faced with mounting evidence, some EMS agencies are abandoning the procedure altogether, but is that necessary? A recent review published in the Annals of Emergency Medicine suggests that two simple techniques may make a world of difference in preventing deadly hypoxia, thus dramatically improving patient outcomes.

The review, by Scott D. Weingart, MD, and Richard M. Levitan, MD, focused on hypoxia during RSI.(3) Among their conclusions, the researchers examined two straightforward, inexpensive techniques that EMS crews can use to stave off oxygen desaturation during ETI. The first technique uses a nasal cannula to deliver up to 15 liters per minute (LPM) of oxygen to the patient during intubation. This oxygen is in addition to the preoxygenation the patient typically receives via bag-valve mask (BVM) prior to the procedure. Using the cannula and high flow oxygen slows the rate at which the patient desaturates, extending the window of opportunity for the paramedic to perform what can be a challenging and dangerous skill.

Secondly, the researchers determined that further desaturation could be delayed by repositioning the patient in a 20° head-up position. They determined that saturation goals were not only reached faster in this sitting position, but the patient was also in a better position for the laryngoscopic procedure.

Even though the study was conducted for RSI in the emergency department, Levitan believes the techniques easily translate to the prehospital environment. “I’ve done this now for a year and a half,” he says. “It’s a game-changing, simple concept.”

Avoiding desaturation
Levitan, an emergency medical physician and professor at Thomas Jefferson University Hospital in Philadelphia, states that patients with oxygen levels below 88% can decrease to crucial levels of oxygen saturation (less than 70%) in moments. A patient breathing room air before RSI can desaturate in the 45–60 seconds between administration of the sedative/paralytic and airway placement. Studies show that patients who receive preoxygenation with 100% oxygen desaturate at a significantly slower rate than patients on room air prior to intubation. (4,5)

Although apneic oxygenation will only slightly raise oxygen levels in the bloodstream, Levitan and Weingart found that it significantly increases the reservoir of oxygen in the alveoli. According to a study from 2004, even a single episode of desaturation can worsen a patient’s outcome, particularly among those who have experienced traumatic brain injuries.(6)

Studies that have calculated the time to desaturation found that healthy adults will desaturate in eight minutes on room air; moderately ill adults in five minutes; and obese adults in 2.7 minutes.7 However, given the wide range of variables in prehospital situations, Levitan says it’s impossible to predict the exact duration of safe apnea for these patients. One calculation found desaturation times as short as 23 seconds, making these techniques to slow desaturation even more critical for paramedics attempting RSI.(8)

How it works
Levitan recommends placing a nasal cannula delivering 15 LPM of oxygen in addition to the non-rebreather mask, on a wide awake patient to counteract the apneic period that occurs while the paramedic is inserting the laryngoscope. Obtunded patients should receive 15 LPM via nasal cannula, plus either the non-rebreather or BVM. It should be left on, delivering oxygen to the patient during intubation attempts.

He says the cannula works best out of the available options because it provides the best rate of oxygen. Facemasks and non-rebreather masks are less optimal because they can only provide high oxygen levels to spontaneously breathing patients (depending on flow rates) and are a poor delivery system for apneic patients. BVMs only provide oxygen to apneic patients if manual ventilations are delivered. The cannula delivers more oxygen, in part, because oxygen continuously flows into the nasopharynx, even during exhalation.

Using the nasal cannula set at a flow rate to 15 LPM, high-fraction inspired oxygen (FiO2) rates can reach near 100%. “Oxygen flows into the upper airway. You can passively oxygenate incredibly well with no movement of the diaphragm,” he says. The patient isn’t bothered by the high flow rate because they’re sedated. Levitan reports that the short time the patient is on hon-humidified oxygen
represents a minimal risk for bleeding and irritation.

All patients must be monitored using a finger probe pulse oximeter. Levitan says that it’s important to note that the reading on the finger probe lags behind actual arterial circulation by as much as 60 seconds, especially for critically ill patients with poor cardiac output.

Re-positioning the patient
Multiple studies show that elevating the patient’s head helps prevent or delay desaturation.9 Levitan says repositioning a patient into a head-elevated position is even more critical for obese patients, a group prone to rapid desaturation. A further study that specifically looked at positioning of obese patients prior to preoxygenation, found that patients in the supine position desaturated in 162 seconds vs. 214 seconds for sitting patients.(10)

The elevated position is also helpful in preventing passive regurgitation, which can help prevent aspiration pneumonia. It also places the patient in the proper position for intubation. The reverse Trendelenburg position has been found to be useful for patients who couldn’t bend at the waist due to immobilization for a possible spinal injury.

Summary
Historically, the focus of ETI has been on success rates. Levitan believes the goal needs to shift to providing adequate oxygenation and ventilation to the patient. “The problem in EMS is not failing to intubate. The problem is failing to oxygenate,” he says. With two easy steps, ETI can be a safer procedure, allowing critical seconds for the paramedic to successfully intubate the patient. This improves the risk/benefit for the paramedic and provides a positive outcome for the patient.

Levitan admits that there are certainly situations in which hyper-oxygenation can damage the brain and heart, such as severe hypoxia. However, using high-flow oxygen in that critical time when people aren’t breathing during RSI can significantly improve the outcome of a high-risk procedure.

He says others seem to think so, too. Since he began teaching people to “crank up the nasal O2 and don’t de-sat,” the idea has been catching on like wildfire.“It’s a simple technique that expands the margin of safety dramatically,” he says.

Resources
1. Davis DP, Hoyt DB, Ochs M, et al. The effect of paramedic rapid sequence intubation on outcome in patients with severe traumatic brain injury. J Trauma. 2003;54(3):444–453.
2. Davis DP, Stern J, Sise M, et al. A follow-up analysis of factors associated with head-injury mortality after paramedic rapid sequence intubation. J Trauma. 2005;59(2):486–490.
3. Weingart SD, Levitan RM. Preoxygenation and prevention of desaturation during emergency airway management. Ann Emerg Med. 2012;59(3):165–175. Epub 2011 Nov 3.
4. Heller ML, Watson TR Jr. Polarographic study of arterial oxygenation during apnea in man. N Engl J Med. 1961;264(2):326–330.
5. Heller M, Watson T Jr., Imredy D, et al. Apneic oxygenation in man: Polarographic arterial oxygen tension study. Anesthsiology. 1964;25(1):25–30.
6. Davis DP, Dunford JV, Poste JC, et al. The impact of hypoxia and hyperventilation on outcome after paramedic rapid sequence intubation of severely head injured patients. J Trauma. 2004;57(1):1–10.
7. Benumof J, Dagg R, Benumof R. Critical hemoglobin desaturation will occur before return to an unparalyzed state following 1 mg/kg intravenous succinylcholine. Anesthesiology. 1997;87(4):979–982.
8. Farmery A, Roe P. A model to describe the rate of oxyhaemoglobin desaturation during apnoea. Br J Anaesth.1996;76(2):284–291.
9. Lane S, Saunders D, Schofield A, et al. A prospective, randomized controlled trial comparing the efficacy of preoxygenation in the 20 degrees head-up vs. supine position. Anesthesia. 2005;60(11):1064–1067.
10. Ramkumar V, Umesh G, Philip F. Preoxygenation with 20° head-up tilt provides longer duration of non-hypoxic apnea than conventional preoxygenation in non-obese healthy adults. J Anaesth. 011;25(2):180–194.
11. Altermatt FR, Muñoz HR, Delfino AE, et al. Pre-oxygenation in the obese patient: Effects of position on tolerance to apnoea. Br J
Anaesth
. 2005;95(5):706–709.
 

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