Mastering BLS Ventilation: Core Techniques

Continued from Mastering BLS Ventilation: Introduction and Mastering BLS Ventilation: Hardware

Now that we understand the goals and the basic tools, let’s talk about the most important techniques for optimizing airway management and providing BLS ventilation to apneic patients.

 

Hand Technique

How do you hold a BVM to the patient’s face?

As a rule, we’re taught something called the “EC clamp.” It looks like this:

In theory, this lets us press the mask against the patient’s face (using the “C” of our thumb and forefinger) while pulling the jaw forward (using the “E” of our other fingers behind the mandible), and still leaves one hand free to squeeze the bag.

In theory.

In reality, this is tricky at best. Partly it’s because we’re trying to seal the edges of a circle by pressing on only one side, which usually results in a leak from the other side. Partly it’s because pulling the jaw forward like this — a highly necessary action — takes a fair amount of force, and we’re in a poor position to grip from. It also doesn’t help that, if no OPA is present, this method usually squeezes the mouth shut, leaving only the nasal passage for an airway.

One useful tip: positioning the bag directly opposite your EC hand and pulling it downward can help seal off the most common point for leaks.

Does the EC technique work? It can work. And it’s fast and versatile to apply, so it’s a reasonable place to start. However, if you find that it’s not working, don’t be too surprised. You would be wise to practice the hell out of it on mannequins (or ideally in an OR or similar setting), but not everyone has that opportunity. What’s the alternative?

Use two hands. The inelegant nature of the EC clamp has been widely recognized for years, despite the fact that many of us in emergency medicine pretend otherwise. In fact, if you flip open your EMT textbook or the handouts from your last CPR class, you will notice that one-person BVM use is strongly discouraged. (In my Limmer textbook, it’s last in preference after the two-person BVM and even the pocket mask.) In the field, this is ignored, because we adopt the attitude that any EMT should be able to sit at the patient’s head and “handle the airway” without help. But that doesn’t change the fact that it’s a crummy technique, and many of the patients who are “bagged” this way only survive because they didn’t need much help to begin with.

What does work reliably is placing both hands on the mask, thumbs toward the feet and fingers behind the jaw. This way you have a hand on both sides and can easily obtain a seal (and if there is a leak it’s readily located), while also providing a strong bilateral grip to protract the jaw. You can sustain this position for a long time, and as a bonus, it tends to open rather than close the mouth.

Basic two-hand seal

A slightly different version with thumbs wrapped around, resembling a "double EC"

Both methods compared

The downside is that it doesn’t leave a hand to squeeze with. Ideally, another rescuer should squeeze the bag. This lets you focus on maintaining the airway while they focus on bagging slowly, gently, and at an appropriate rate. (But remind them to stop squeezing when they see chest rise; with two hands it’s tempting to try and empty the whole bag, which is far in excess of what’s necessary if you have a good seal.) It can even help to separate the mask from the bag entirely, position it perfectly on the face, clamp down your grip, and then allow the bag to be attached and ventilation begun; this ensures everything is where it ought to be. On scene you often have enough personnel for this; in the back of the ambulance you may or may not. Can you still execute this method alone?

You can, and I highly recommend that you work out the logistics now, with your own unique body type and equipment. For patients in a bed or a high stretcher, you can often stand behind the head, hold the seal with your hands, and squeeze the bag with your elbow against your side. In the patient compartment, you can sit in the tech seat and squeeze the bag against one leg with your elbow, or between your knees if you’re an experienced Thighmaster. A supine patient on the ground can be the trickiest position; you may be able to squeeze the bag against a leg or something similar, but often your best bet will simply be to recruit help. (Again, please experiment with this now, so you’re not improvising while a patient turns blue.) Just remember that using two people to bag isn’t a failure, and has no impact on your sexual adequacy; it’s a legitimate method which is supported by literature and explicitly recommended by the experts we’re supposed to be listening to.

 

The Sniffing Position

We understand now that successful BLS airway management means maximizing the passable upper airway and minimizing obstructions. Bringing the jaw forward will always be helpful, by pulling the tongue and other anterior structures away from the posterior pharyngeal wall. Now let’s look a little closer at the position of the head itself.

We’re taught to rotate the head back in the head-tilt chin-lift maneuver. Why do we do this? In essence, because it helps align the oral and nasal passages with the pharynx.

In other words, in a neutral position there’s an angle that approaches 90 degrees between the oral cavity (through which air initially passes — or the nasal cavity, which is nearly parallel) and the pharynx (the initial portion of the passage down into the lungs). Such a sharp angle increases the resistance to air and increases the likelihood of occlusion. By rotating the head backwards along the atlanto-occipital joint — i.e. where the skull meets the spine — we can straighten out this corner. We can’t make it completely straight, because the head doesn’t rotate that far (if it did you’d be able to directly face the sky without leaning), but we can improve the angle substantially.

The trouble is that when we do this, we change another angle too. The angle between the pharynx and the trachea tends to sharpen in the vicinity of the larynx as we tilt the head backward. Since the pharynx follows the alignment of the upper neck and lower head, and the trachea follows the alignment of the lower neck and thorax — with the larynx and glottis smack in the middle — there’s an additional angle here that should be straightened as much as possible.

Image courtesy of http://tinyurl.com/c6logld

The good news is that with a supine patient lying on a flat surface, such as a bed or stretcher, simply rotating the head back will partially accomplish this. That’s because our occiput — the back of the skull — is somewhat bulbous and protruding, and when you tilt the head back, it rolls over this rounded prominence, elevating the head. Thus, a standard head tilt produces a small amount of neck-to-thorax flexion, which helps improve the angle at the larynx.

Many patients benefit from greater head movement, however. What we’re trying to do is shift the head forward — anteriorly — while maintaining (not increasing or decreasing) atlanto-occipital extension. In combination, this creates what’s known as the sniffing position, as it resembles someone ostentatiously “sniffing the air.” (“Leading with the chin” may be a more intuitive description.) It’s widely taught as the optimal position for intubation, but it can also reduce resistance to BVM ventilation; you may even encounter patients with perilaryngeal swelling (particularly epiglottitis) who assume this position intuitively to maintain their narrowing airway.

To establish the sniffing position, you need to pad behind the head. It’s sensible to treat each patient somewhat individually, but a good starting point is to elevate the head until the ear (that is, the canal or meatus) is horizontally aligned with, or slightly in front of, the notch of the clavicles. This is often only a few inches (average is ~7cm) beyond the elevation you’ll get from the occiput against the bed alone, but you’ll certainly need to put something back there. Pillows are usually too soft unless you fold them gratuitously, but a folded towel or blanket can work well, or really anything flat.

 A few special cases are worth mentioning. First, children. Kids are notorious for having enormous heads compared to their bodies, and the frequent result is that after rotating the cranium, you’ll have created all the anterior movement you need. In fact, it’s possible you’ll need to pad the back and upper shoulders in order to avoid hyperflexion of the neck.

Image courtesy of http://www.narenthorn.or.th/node/77?page=0%2C2

Now consider obese patients. Their general airway challenges make them great candidates for this technique, but because they have extra adipose tissue on their back — which elevates their torso relative to their head — they have the opposite problem as kids: you may need to provide substantially more padding behind the head in order to achieve ear-sternal alignment.

Interestingly, though, in very big patients you may encounter a different situation. Because relatively more adipose tissue collects in the lower back and hips than in the upper back and shoulders, while supine, the morbidly obese patient may actually be “upside down”; their torso is angled uphill, resulting in their head and chest being crunched together even while lying “flat.” To achieve anything like reasonable airway positions, you’ll need to first correct this by elevating (really just leveling) their upper back. This is called ramping, and may require a substantial amount of linen, although you might be able to get part of the way there by raising the back of the stretcher a little (thus preferentially elevating their upper back, since most people slip down a fair amount). Once you’ve achieved body normality, you can create your sniffing position, aligning ear to clavicles in the usual fashion.

Image courtesy of http://bariatrictimes.com/2012/02/16/airway-management-in-bariatric-surgery-a-challenge-for-anesthesiologists/

Truth be told, there are advantages to sitting up almost any respiratory patient. It reduces the chance of airway occlusion from soft tissues, helps blood and secretions drain, reduces impedance on the chest wall, and prevents the abdominal viscera from compressing the diaphragm. The only reason we don’t manage everyone this way is because it’s hard to do much with a patient sitting high or semi-Fowler’s, such as bagging them or airway insertion. But for the patient who’s still breathing spontaneously, the simplest airway intervention is simply to keep them upright or perhaps in the lateral recovery position.

 

Key Points

  1. The two-hand BVM technique is preferable to the EC technique whenever possible, and it’s far easier to perform with a second person to assist.
  2. Optimal airway diameter and angles can be achieved by protracting the jaw and simultaneously elevating and extending the head into a “sniffing position.”
  3. Pediatric patients may not need additional head elevation to achieve this, or may even need padding of the back.
  4. Obese patients may need substantial head elevation.
  5. Very obese patients may need to be “ramped” to level their torso before attempting other airway maneuvers.
  6. When more aggressive management is not needed, an upright or lateral supine position provides the simplest protection of the airway.

 

Tune in next time for a few extra tricks to increase our airway options, and a comprehensive approach for bringing it all together.

Continued at Mastering BLS Ventilation: Supplemental Methods and finally Mastering BLS Ventilation: Algorithms

Mastering BLS Ventilation: Hardware

 

 

Continued from Mastering BLS Ventilation: Introduction

The basic tool of BLS oxygenation is the bag-valve-mask, aka the bag-mask (as the AHA calls it), aka the Ambu-Bag (as most in-hospital staff call it, after one of the popular manufacturers), aka the self-inflating resuscitator. We’ll talk about techniques for optimizing for BVM success later. For the moment, let’s discuss some of the other auxiliary aids available. As we do, remember our main challenges: if we don’t minimize the resistance to airflow into the trachea, we’ll be prone to inflating the stomach instead of the lungs. And if we don’t minimize obstructions higher in the pharynx, we won’t be able to introduce any air at all.

 

Nasopharyngeal and Oropharyngeal airways

The NPA (or nasal trumpet) and OPA are the mainstays of BLS airway adjuncts. Essentially, they’re just curved pieces of plastic or rubber, designed to be inserted into the upper airway to prevent soft tissue from collapsing and obstructing the lumen.

When I first learned about these, it was just after hearing about the head-tilt chin-lift and jaw thrust, which were purportedly enough to open any self-obstructing airway. Why did we need these tools? “This way,” my instructor advised, “you don’t have to sit there holding their airway open.”

Well, yes and no.

The standard theory behind these devices is this: in a supine, unconscious patient, the tongue (and other soft tissue) wants to collapse into the pharynx. If we can jam something in the way, it will essentially “splint” open the passage — stick a foot in the door — much as if we were holding tissue back with a tongue depressor. Positioning the head and neck in such a way that it widens the relevant gaps would accomplish the same thing.

Under this thinking, we have several redundant tools to accomplish the same purpose. Whether we open the airway by tilting their head and lifting their jaw, or by sticking an OPA in the mouth, or by sticking an NPA in the nose, the result is the same.

But this doesn’t quite reflect reality. Sometimes it will, but in many patients with difficult airways, it’s not so simple to maintain a patent passage for airflow. In an obese patient with challenging upper airway anatomy, the amount of soft tissue standing in your way may be profound, and it can obstruct the lumen in multiple places. Additionally, tone may be so lacking that it easily “molds” around anything you stick in there.

In other words, if you place a BLS airway, the only breathable passage you’re really guaranteed is the lumen enclosed by the device itself: the central hole or grooves. And that’s not very much room. Our goal isn’t to create a tiny breathing tube, it’s to maximize the amount of usable airway — we’d like to be able to ventilate through as large a diameter as possible. That means using everything we can.

So proper positioning is helpful. So is an OPA. And perhaps an NPA. Or two.

In fact, if at all possible, it’s always worth trying to insert multiple airways. This is typically not taught to EMTs (since textbooks subscribe to the the “splinting” rather than the “protected lumen” theory), but it’s widely practiced in the ED and by experienced paramedics. If you’re having any difficulty at all bagging, shoot for an OPA with bilateral NPAs; filling all the available holes with patent airways is always a good idea.

 

 

Remember what you’re actually doing with each airway. With an NPA, you’re separating the soft palate from the superior and posterior nasopharynx, and if it’s properly sized, it should be long enough to create a passage through the laryngopharynx, nearly to the epiglottis. (If it’s too long, it can stimulate the gag reflex, or jam into the vallecula or epiglottis, actually obstructing the larynx; if it’s too short, it may not protect the laryngopharnyx, or even may not fully span the nasopharynx, allowing the soft palate to shut.) With an OPA, you’re separating the lips, depressing the tongue to prevent it from obstructing the oral cavity, and more importantly protecting the laryngopharynx in the same way the NPA does — keeping the tongue or other anterior structures clear.

So if you only insert an NPA, the nose is your only guaranteed airway. If the mouth itself is shut — and we typically squeeze it shut when we bag using the “EC clamp” technique — nothing will flow through the oropharynx. Conversely, if we only insert an OPA, there is no guarantee that the nasopharynx will remain patent, particularly where the soft palate wants to meet the posterior pharynx.

So use both, because we want it all.

 

OPAs are more widely used, but it’s a shame to neglect the NPA. The advantage, of course, is that patients with an intact gag reflex can still tolerate an NPA, whereas the OPA may stimulate vomiting. It’s unwise to use the “try and see” approach with the OPA, because there’s nothing quite like copious emesis to make a difficult airway more difficult. Kyle David Bates teaches the helpful tip of inspecting for saliva and secretions collecting in the mouth; if there are none, the patient likely has an intact gag reflex. If they are present, an OPA is probably safe. But suction is always worth keeping on-hand and prepared.

It’s taught that NPAs are contraindicated in patients with significant facial or cranial trauma, on the theory that you may pass the device through a basal skull fracture right into the brain. This is probably a negligible risk; the entire concept seems to be based on two (yes, that’s the number before three) case reports in the literature. If your suspicion is quite high (blood from the nose with a positive halo test, for instance), you may want to steer clear, but with a truly difficult airway, remember that oxygenation is more important than an extremely remote risk of poking the patient’s noodle.

NPA placement can be facilitated by ensuring you lubricate the device first (water-based jelly should be available, although traditionally the patient’s saliva can be used as a last resort), aiming “in” (posteriorly) rather than “up” (superiorly), and lifting the nose to facilitate this angle. Also, remember that each nasal fossa has erectile tissue which takes turns engorging and partially obstructing airflow (allowing cyclical “resting” of the mucosa), so at any given time, one nare will likely allow easier NPA passage than the other; if you’re having difficulty, just switch sides. (Stripping part of this tissue away from the concha will occasionally cause post-insertion bleeding, but it’s rarely significant.)

As for the OPA, we usually teach insertion with the tip pointing up, followed by a 180-degree rotation once it’s fully inserted. Just remember that it’s also acceptable and sometimes easier to insert it tip-down while holding back the tongue with a tongue depressor or finger.

Another somewhat prosaic benefit to the OPA is that it may help provide structure to edentulous [toothless] patients when you’re trying to bag them, although simply leaving dentures in place can also work.

 

Apneic Oxygenation

You may not think that the lowly nasal cannula and non-rebreather mask really qualify as useful airway tools in an apneic patient. But oh, you would be wrong.

Pop quiz: is it possible to oxygenate the blood without actively moving any air? In other words, can you breathe without breathing?

You might say no. But why not? Gas exchange in the alveoli is not an active process; you’re not forcing the O2 molecules across the membrane by any chemical or muscular exertion. They simply diffuse passively, like gin dispersing into your tonic. All you’re doing when you breathe (either spontaneously or via positive-pressure ventilation) is providing a fresh supply of air to ensure that the concentration of oxygen in the alveoli remains higher than the concentration in the blood (thus allowing diffusion to occur). If we can keep the alveolar oxygen levels high without breathing, that’s just fine.

Suppose, for instance, that we place the apneic patient on a nasal cannula at relatively high flow. This should fill the pharynx with near-100% O2. Even without breathing, gas exchange is occurring in the alveoli; oxygen is diffusing across the membrane into the blood where it binds hemoglobin, and carbon dioxide is diffusing the opposite direction. Far less CO2 is moving out than oxygen is moving in, however (due to differences in solubility and hemoglobin affinity), so there’s actually a net “loss” of gas. This creates some “suction” or a partial vacuum in the alveoli, which will draw in whatever gas is waiting in the upper airway to fill it. Since we’ve flushed that space with pure O2, oxygen will move down that gradient, enter the alveoli, and continue diffusing into the blood, creating a continuous flow. Using this method, patients have been demonstrated to maintain reasonable sats for ridiculously long periods (up to 100 minutes in ideal circumstances).

This is a technique called apneic oxygenation. Although referred to by different names, it’s not new (among other things, it’s a traditional component of most brain-death evaluations), but it’s recently been getting more publicity. In particular, Scott Weingart of EMcrit and Richard Levitan recently published a paper comprehensively describing its use in difficult intubations. They advise placing a cannula at 15 L/min in order to suffuse the pharynx with near-100% O2, and this recommendation has some support in the literature. (Interestingly, whether the patient has their mouth open or closed may not matter.) We’re usually taught that nasal cannulae shouldn’t be used at flows this high, since it’ll dry and irritate the mucosa of the nose, and this is true; however, for short periods in critical patients, a dry nose is not the foremost concern.

How could this be useful for our purposes? Our main challenge with the BVM is ensuring that positive pressure goes where we want it to. This is obviously essential. But if bagging is initially challenging, could we potentially buy time? As long as the airway down to the glottis is open to flow, at least partially, it takes no skill at all to place a cannula (probably already present) and run up the flow to 15 L/min. Even if we’re totally unable to ventilate effectively, this will help keep the patient oxygenated and saturated while we work on a more definitive solution.

A couple of caveats: first, there must actually be a somewhat patent (if not totally secure) airway for this to work. If upper airway structures (or even a foreign body) have totally occluded the nasopharynx or laryngopharynx, no oxygen will reach the trachea. Second, this is a short-term temporizing measure only, because although it may help oxygenate, it will not help to “ventilate,” meaning to remove waste carbon dioxide; as discussed, CO2 is much less capable of passively diffusing without actual tidal movement to clear the alveolar space. Sustained apnea will therefore lead to continually increasing hypercapnia. Finally, this is really intended for patients with largely normal V/Q ratios; it will probably be of limited use for patients with significant shunt (e.g. bronchoconstriction, pulmonary edema, etc.) or dead space (e.g. pulmonary embolism). In other words, it’s of little help to your respiratory patients, whose problem is that their lungs aren’t working properly; if they’re moving air at all, they’re most likely suffusing their alveoli with high-concentration O2, it’s just that they’re just unable to exchange it. They need something like CPAP to help recruit more usable alveoli. Apneic oxygenation is for patients with working lungs who merely aren’t breathing spontaneously or adequately protecting their airway.

Can’t you just use a mask for this? Eh. Studies suggest that O2 from a non-rebreather tends to remain outside the face (in the bag and mask itself) unless the patient actually breathes, since it’s easier for the gas to simply overflow from the exhalation ports than to penetrate their airway; this is distinguished from the cannula, which actually shoots pressurized oxygen directly into the nasopharynx.

However, when it comes to patients who do still have some spontaneous respirations, a non-rebreather can certainly be useful, and here’s a way to supercharge it. Contrary to popular belief, you’re not actually delivering 100% oxygen with a typical mask at 15 L/min — more like 60–70% in most cases. This is due both to the poor seal it generally forms with the face and to the fact that at least one external port is usually left open to room air, so that if the oxygen supply is interrupted or becomes inadequate the patient won’t be suffocated. However, you can get closer to 100% FiO2 by simply cranking up the flow. Once you hit around 30–60 L/min, enough surplus oxygen is overflowing through the mask that the patient should be breathing nearly pure O2. Your portable oxygen tank probably won’t allow a flow this high (and it’d quickly run empty if it did), but most wall- or ambulance-mounted regulators should, although it may be near their maximum flood. Just crank the regulator up to 15 and keep turning until it won’t turn anymore; the indicator won’t change, but the flow will keep increasing. (Although I won’t be the one to recommend it due to the [likely overstated] safety concerns, you could probably also get good results by taping over any valveless ports in the mask, and holding it tightly sealed to their face — or better yet, letting them hold it.)

It may seem convenient, incidentally, to simply press a BVM against their face. Although this may — may — produce an effective seal, it provides poor O2 flow for spontaneous respirations; often times patient-initiated breaths simply bypass the reservoir and draw room air.

 

Key Points

  1. When it comes to BLS airway adjuncts, the more the better. Two NPAs and an OPA is ideal.
  2. NPAs are generally safe; the risk of penetrating the cranial vault is probably negligible.
  3. Don’t go poking around with the OPA in already-difficult airways; make an effort to determine whether a gag reflex is present before stimulating it.
  4. If an open airway to the lungs exists, but ventilations are difficult, a nasal cannula at 15 L/min is an excellent way to provide apneic oxygenation as a temporizing measure to maintain saturation.
  5. The only “high-flow” oxygen device on your ambulance for a spontaneously-breathing patient is a non-rebreather with flow of 30+ L/min.

A general reminder: although we are cavalier with failing to include in-line or footnoted citations, these are all evidence-based recommendations, and readers are encouraged to inquire for the literature behind anything that seems surprising or dubious.

 

Continued at Mastering BLS Ventilation: Core Techniques, then Mastering BLS Ventilation: Supplemental Methods, and finally Mastering BLS Ventilation: Algorithms

Mastering BLS Ventilation: Introduction

Sometimes, patients can’t breathe. When that happens, we need to breathe for them.

Simple enough. This is life support at its most fundamental, and many of the interventions classified as “BLS” are found here — techniques and devices for artificially supporting the body’s airway and breathing.

And it doesn’t seem so hard. When they taught it in class, it only took a day or two, and a few pages in the textbook encompassed the subject. How to size an OPA, how to hold the BVM, something about jaw thrusts, and you’re through. Spend a few minutes playing with a mannequin and now you’re an expert.

In the real world, though, this is not child’s play. Managing the airway of a sick, apneic patient is, at best, a high priority; at worst, it’s an unqualified catastrophe. Case reports and horror stories of airways gone wrong can be found under every roof: the failed intubation, the disastrous cricothyrotomy, the foreign body obstruction that couldn’t be cleared. These are emergencies because as we all know, without an airway, you cannot survive. It’s simple stuff.

And then there’s the BVM — aka the bag-valve-mask or “Ambubag.” Ask a room full of novice EMTs and they’ll all agree it’s about as straightforward as tying your shoes: slap it on, squeeze, any idiot could do it. But ask the senior medic in the corner, and he may paint a grimmer picture. Jeff Guy has described it as a more difficult skill than endotracheal intubation, yet one of the hot topics today in prehospital medicine is whether paramedics should remove intubation from their scope of practice because it’s too hard. But nobody’s going to take away the BVM. It’s irreplaceable; it’s the first and last line, the means of ventilation that any patient starts with, and the fallback if your next move fails. The only problem is that doing it well, and for really tough patients, doing it at all, is a purely skill-based exercise. It’s the Jedi’s lightsaber: simple, versatile, but designed for an expert.

The point is that establishing a patent airway in a sick person who can’t do it themselves, and ventilating them using that airway, is such an important task that it generally mandates a large toolbox. Airways are often managed via complex flowcharts or algorithms, where one method can yield to another if it fails, and then to another and another. Countless different devices and methods are available, so that even when obstacles are present, any moron can stumble onto something that works before the patient crashes altogether.

And then there’s us. The Basic EMT stands at the bottom of the spectrum in terms of training, yet is expected to oxygenate any patient using nothing but the meager BLS jump-kit. He has the BVM, a couple of basic airways, masks, cannulas, suction, positioning — and beyond that, just his wits and skills. And as for those, he probably spent little to no time actually practicing them in class, and may perform them only rarely in the field.

This won’t do. When it comes to psychomotor skills, these are the most essential, because we don’t have a Plan B. If BLS techniques fail, our only recourse is to sprint for the hospital or ALS, and hope nobody dies along the way.

So let’s talk about all the principles and tricks of creating a BLS airway and ventilating with the BVM. First, we’ll need to understand why it’s hard.

 

Basic Physiology

Ordinarily, we suck at breathing.

I mean we literally suck. We drop the diaphragm and widen the ribs, expanding the area inside our chest. This expands the lungs, forcing them to suck air into the only opening available — through the mouth and nose, down the pharynx, through the trachea, and into the bronchial tree.

That’s assuming that the airway is open, of course.

Now, what if I whack you over the head, and your body loses the ability to spontaneously breathe? We’ll want to breathe for you. Can we pull down your diaphragm and expand your chest? Not very easily, unless we stick a plunger on your sternum, or put you in an iron lung. Instead, we reverse this process: rather than creating negative pressure inside the chest, we force positive pressure in from the outside. Rather than sucking, we blow.

Blowing is a little tricky, though. One of the main problems is that there’s more than one place for air to go. Consider the pharynx, the working area of your upper airway. We can get there via two paths: the oropharynx (via the mouth and over the tongue), or the nasopharynx (via the nostrils), but they arrive at the same place, the laryngopharynx (or hypopharynx). What happens next?

If we peered into your hypopharyngeal space, we would see that two openings emerge below. One leads to a tube which lies posterior (toward your back): your esophagus, which conveys cheeseburgers and beer into your stomach. One leads to a tube which lies anterior (toward your front): your trachea, which brings air into the lungs for gas exchange. Remember these relative positions — the trachea is in front, and you can palpate it at the neck (the “Adam’s apple” is part of it). The esophagus lies behind this, and is not usually externally palpable.

Given that food and air both enter via the pharynx, how do we ensure that cheeseburgers ends up in the esophagus and air ends up in the trachea? Well, the gatehouse to the trachea is the larynx (the “voicebox,” where vocalization occurs), and the opening to this chamber is called the glottis. The glottis is normally open, but when you swallow, a couple of drape-like vestibular folds and a little flap, the epiglottis, are pulled in to cover the larynx. The result is that food is forced into the esophagus.

What about the other direction? The esophagus is formed from rings of muscles called esophageal sphincters, which help “milk” food downward when you swallow. The bottommost ring is the lower esophageal sphincter, which opens during swallowing, but otherwise is mostly constricted, sealing off the esophagus from the stomach itself. This prevents air from passing down and gastric contents from coming up (something we know as heartburn).

To summarize, as you sit here reading this, your esophagus is clamped off by your lower esophageal sphincter, and your trachea is open, allowing you to breathe. But if you take a bite of your coffee-cake, your epiglottis and vestibular folds will block off your airway, your esophageal sphincter will open, and the food bolus will be directed into your stomach.

 

Down the wrong pipe

The trouble with blowing instead of sucking is that we have no way of aiming where we blow.

I know what you’re thinking. If we force air down the pharynx, the esophageal sphincter should block off the stomach, ensuring that it flows into the larynx and down the trachea. Right?

Here’s the problem. Even ordinarily, your esophageal sphincter only clamps down with a small amount of force — say around 30 cmH2O (centimeters of water, a unit of pressure). This is plenty to prevent air from flowing in during regular respiration. But if air were to be pushed in with greater than 30 cmH2O of force, it will squeeze past the sphincter and enter the stomach. And if we clamp a BVM over your face and squish the bag, we can easily exceed that much pressure.

It gets worse. In order for the esophageal sphincter to work even that well, it requires muscular tone (constant stimulation), just like your postural muscles need tone to keep you from falling over. What happens when you’re unconscious? Sphincter tone decreases. So in the people we’ll actually be bagging, opening pressure may be 20–25 cmH2O or even less. Thus it’s even easier for positive pressure ventilations to force their way into the stomach.

The result? When squeezing the BVM, air often enters the stomach along with (or instead of) entering the lungs. Not only is this pointless, it makes it even harder to inflate the lungs (a bigger abdomen creates pressure on the diaphragm), decreases cardiac preload, and increases the risk of vomiting — which will further obstruct the airway.

The easiest solution is to put a tube into the trachea and seal it off — i.e. endotracheal intubation (or variations on that theme, such as a blind airway). Then we can blow air directly into the lungs without any chance that it’ll enter the wrong pipe. Unfortunately, those are tools we often lack as BLS providers.

 

Angles and Tissues

All of those structures we’ve been describing? They’re soft.

Soft and squishy. And it’s not just the esophageal sphincter that loses tone when you become unconscious.

In ordinary circumstances, the airway is a supple but structured arrangement of tissues that maintains its form. This is important, because there’s not very much space in there. So in the unresponsive patient, it’s no surprise that some of those tissues might collapse together, blocking off the lumen between them. (Check out this fluoroscopic video.)

The tongue is the worst. Tongues are basically big blobby muscles, attached at only one end, and if you remove all firming tone, they just flop wherever gravity takes them. So put an unconscious person supine, and gravity pulls the tongue back into the pharynx, blocking all airflow.

Or the larynx and supralaryngeal tissues run into the posterior pharyngeal wall. Or the soft palate does. Either way, anterior structures end up touching posterior structures, leaving no room in between. Our airway involves a tight 90 degree turn, and this is not a design that remains open without active maintenance. So if we want to breathe for these people, we need to find a way to unblock everything. (Like the jaw thrust — check out this airway cam.)

 

Mask Madness

Trying to push air into someone’s lungs by holding a mask over their face is like trying to blow up a tire by… well, holding a mask over the valve.

I teach CPR, and I can count on one hand the number of times I’ve handed the BVM to somebody and watched them achieve chest rise on the mannequin the first time. Heck, I demo the things and I don’t always pull it off.

Effectively sealing an air-filled plastic mask to someone’s face and then squeezing the bag is a task meant for more hands than any human possesses. Doing it on somebody who’s dying is exponentially more difficult. Add in the fact that they’re probably obese, toothless, vomiting, crumpled in a corner or bouncing around an ambulance, and enshrouded in a thick ZZ Top beard. Now try to get it all done without losing your cool or breaking your proper ventilatory rate. Having fun yet?

 

Key points

  1. BLS ventilation using basic airways, positioning, and the BVM is a difficult, complex, and undertrained skillset for the EMT-B. Yet since we often lack rescue devices or alternate ventilation methods, it is critical that we learn to master it.
  2. Preventing gastric inflation would be difficult even in healthy people, and is extremely difficult in the apneic and unresponsive patient.
  3. Loss of tone in unconscious patients lying supine reliably produces soft tissue airway obstruction which must be cleared.
  4. Obtaining a proper mask seal is a necessary prerequisite for BVM use, but is often difficult or impossible for a single rescuer.

Tune in next time to see some solutions to these challenges.

Continued at Mastering BLS Ventilation: Hardware, then Mastering BLS Ventilation: Core Techniques, then Mastering BLS Ventilation: Supplemental Methods, then finally Mastering BLS Ventilation: Algorithms