So the family went to King’s Dominion the other weekend.  As a teen, between 1975 and 1979  my friends and I went once or ten times every summer.  Roller coasters, flume rides, hideously overpriced food (we thought at the time – how little we knew).  It was fun.  But that was before EMS.

Now-me arrives with the family, and the first ride I get on is the Drop Tower.  Sit in your chair, which raises you to almost 300 feet.  Nice view.  Then it drops you.

During the second or two I fell, I thought, “Well, this is fun.”  But afterwards?  Meh.

The roller coasters teen-me had loved were worse.  Whether it started with a slow climb or shot like a bullet down a barrel, the initial “Whee!” was followed immediately by a feeling of inconvenience as the coaster turned, swiveled, looped and banked.  Each bump, jerk, twist, and abrupt change in direction, which used to elicit a “Wow!’, now annoyed me.  Like a scene in a movie where the main character is not enjoying a show, but is being constantly prodded and bumped by the popcorn eating fat man beside him who points and laughs and can’t get enough.  No, I’m not enjoying it, and you can’t make me.  When will it be over?

I reacted thus to every ride, when suddenly I had the terrifying suspicion that I might be getting old.  Isn’t this how old people react to these rides?  This is terrible.  I don’t want to get old.  Old people take cruises, and leave the ship to visit shoreline gift shops.

The more I considered this dire prospect, however, the more it became clear to me that while my body might be aging, it was not “getting old” that did in these rides for me.  It was physics, law, and mostly EMS.


In my uninformed teen years, when I last enjoyed this sort of thing, it was because I suspected there was an element of danger.  After all, the TV ads played up the speed, the screaming, the terror.  That’s dangerous, right?  Dangerous and exciting, and fun.  One expected reporters and cameramen at the end of each ride. “My God, he made it!”  “Welcome back!”  “How did it feel?”  “Were you ever afraid?”  A teenage male steps from a roller coaster as a warrior steps from a longboat to the shores of a conquered nation.  Plant that flag and on to the next.

The truth was always there, but we chose to ignore it or, more correctly, were in ignorance of it – it’s all physics.  This weight going this fast exerts this force in this direction, plan accordingly.

This visit there was a particular roller coaster which was completely indoors, and mostly dark. Flight of Fear.  Just ahead of me, a determined ride attendant was bravely trying to secure a lap bar onto a woman who hasn’t had a lap in probably 20 years.  While the occupants of the cars around her ratcheted down their restraints with a satisfying tick-tick-tick-tick-tick-tick, the attendant grunted and shifted and struggled.  Finally, a single “tick” was produced, and he pronounced her good to go.

It occurred to me that the system *must* be designed so that the weight of the cars made the additional weight of the passengers negligible in the calculations.  The only way to make a ride safe is to factor in, say, a 10% margin of error and make sure that a 500 lb person is only 5% of the car weight – or whatever numbers the engineers used.  That, or these poor fools were doomed.  (They made it).


I vaguely recall that as a teen, the signs around a ride did nothing more than identify it:  “Rebel Yell”, for instance. Oh boy, here’s the roller coaster, Rebel Yell.

Now, there are multiple signs at each ride, giving one something to read while waiting in line.  Some of these signs I think are there for marketing purposes – there’s some sort of rating system such as ski trails use, the “black diamond” marking this as an Advanced Level Ride or some such.  Following this is another sign warning the usual suspects – the pregnant, heart patients and such – about possible injury.  “May cause dizziness”.

Standard fare, and I’ll be very surprised if sometime soon there isn’t a touch-screen with a camera that requires one to tap “I agree” and takes your photo doing so, to eliminate all liability to the park.  While you’re at it add a little note to the bottom showing calories burned on the ride, and remember to send me my royalty check for the ideas.

Still, where every convenience store aisle is now marked with a “Piso mojado” pylon, or else lawsuit, it is actually the lack of signs which nail home the lack of danger.  Everyone is quick to put up “Caution!”, “Warning!”, “Do Not Enter!” signs for the most trivial reasons.  Non-trivial, but let’s be realistic here, hospitals put “Caution!” signs on the doors of patients who have minor coughs.  It’s a hospital, I expect there to be sick people here, but thank you.

Now, to be scary all one has to do is remind people of their mortality.  I have heard that in the early days of air travel the larger airports had notary-publics available to sell you life insurance and notarize a quick last will and testament before boarding.  Add that, and I’ll take it seriously again.

Or not.  When the carnival comes to town, we have a team of inspectors trained to verify the safety of the rides – ferris wheels and teacup rides for the most part – but considering they’re assembled and disassembled every couple of weeks, I appreciate this.  How much safer a standing attraction?


The price of my adrenaline seems to have gone up.  A roller coaster used to afford me a big vicious jolt of epi that had me grinning and shaking for the next twenty minutes.  That same coaster now only buys a moment’s worth of anxiety – is my cell phone safe in its case, or will it go flying off? – before seeing me back to my natural, mellow state.

What I saw as a teen:  Accept the Challenge, Traverse the Danger, Exit Victorious and Immortal.

What I see now:  Wait in Line, Get Tossed About, Get Out.

I explained this to She Who Must Be Obeyed.  “I get tossed around in rides every day, but there’s no guarantee that it’s safe.  I guess my adrenaline has a higher standard now.”  Come to think of it, when I was being tossed around on the first roller coaster of the day, my absolute first instinct was to turn to the right and tell the driver to take it easy – which would have been the correct orientation for a medic on the bench seat.

To underscore this, on returning home, I checked the news as I sometimes do and found that Rescue responded to another park that very day.  Even in failure the ride went from an entertainment to a mere inconvenience.  Every one of those passengers owes a debt to the engineers who designed that ride so well that it could completely fail and STILL not kill them.

In contrast, only a couple of days later we had a unit totalled as it was t-boned, responding through an intersection.  The AIC was injured (we would classify it as minor, but tell that to her) and the driver and patient were for the most part uninjured, thanks in great part to engineering.

That is the sort of ride that might get a little adrenaline flowing, certainly.

I suppose what I learned, at the theme park that day, was that for me, now, Adrenaline =/= Fun.  It’s something I suppress so it doesn’t get in the way of my thinking, and of my job.

Fortunately for me I don’t need to get amped up to have fun.  

Parcheesi anyone?


Did I tell you about the time…?

Our patient, c/c “chest pain”, was sinus tach and sprinkling PVCs like confetti.

We’re applying oxygen, he’s got some morphine on board, and we’re just opening the nitro when he codes, just as we get to the hospital.

We hit the ED doors running, pushing, bagging.

“Code! We need a room!”

“Room 4!” The charge is right on top of things.

We roll into room four. “On Three! onetwothree!”

Our patient is onto the bed, CPR resumes, bagging resumes.

The attending physician is a new guy, I’ve never seen him before.

“What’s the story?”

“68 year old male, chest pain for 1 day, took two aspirin 325 at home and called 911, sinus tach with PVCs on the way in, coded three minutes ago.”


“Full code” Really? Didn’t he see us working the guy? But okay.

The attending says to the nurse, “Get RT down here, let’s tube this guy,”

To us: “Stop CPR. Let’s get a rhythm check.”

We stop CPR. The monitor shows little tremors, minor quakes on the surface of the heart. Some life left, it seems.

“Fine VFib,” the attending says. “Charge and shock”

A nurse grabs paddles, puts her hand on the dial. “What do you want to charge to?” she asks.

The attending seems to consider it.

“Oh, I think he just need about tree-fiddy.”

“I’m sorry?” the nurse said.

“He need about tree-fiddy.”

Well, it was about then that we noticed the attending was a six-story tall crustacean from the Paleolithic era.

“Dammit, monster!” I said. “We ain’t chargin’ to no tree-fiddy! In this ED we *work* our patients! Ain’t no protocol for tree-fiddy! Monophasic, bi-phasic, ain’t none of them call for tree-fiddy!”


New App – Rampart BLS

A new app has been submitted to Google Play and should be appearing shortly.

Rampart-BLS is a BLS  scenario emulator.  PLEASE have one of the many fine, natural-sounding voices (such as IVONA or SVOX) installed on your Android device!

In this app, you are the ED doc or OMD.  Your EMT-B is calling from the scene and requesting medical direction.  Tell him (or her, depending on the Android Voice – installed separately) what to do:  Get vitals, splint, hold c-spine, etc.

The app is designed for EMT-B students, to give practice in acquiring SAMPLE, OPQRST, and DCAP-BTLS information, as well as head-to-toe assessments and vital signs.  There are 29 scenarios by default, and a built-in scenario editor so you can change things or even add your own – no limit.  An optional Debrief mode will provide feedback at the end of the scenario, letting you know how you did.  The app runs in standard phone mode or speakerphone mode.

The full help file (available in-app) is reprinted below.

A simple little scenario operator for EMT-B students.

Quick Start

Start the app right away by pressing the “Play” button on the main screen, OR you can change things around first.

You can pick a scenario by:

  • Tapping the Scenario # box and selecting a scenario;
  • Swiping across the main screen, left (next scenario) or right (previous scenario);
  • Selecting Menu -> Previous or Menu -> Next;
  • Selecting Menu -> Random;

Once you have a scenario selected:

  • Use the sliders on the screen to control how fast the EMT-B speaks, and how many seconds you have until a response is required. You can adjust these at any
    time, and they take effect with the next sentence.
  • Tap “Debrief” in the upper right corner to toggle post-scenario debriefing.

Once you’ve clicked the Start Scenario (Play) button, guide the EMT-B on the phone through his emergency. He’ll explain the situation and ask for orders. Tapping the
“pause” button will pause the scenario after the EMT finishes speaking. Long-press pause to interrupt the EMT and pause immediately.

Your EMT won’t do anything you don’t order. In general:

  • Consider the chief complaint;
  • Order immediate interventions, if necessary;
  • Have the EMT-B get SAMPLE information;
  • For medical situations, have the EMT-B get OPQRST information;
  • For trauma scenarios, request DCAP-BTLS information;
  • Direct the EMT to apply secondary interventions (O2, splint, etc.) as appropriate;
  • Direct the EMT to transport the patient

There are certain criteria common to every scenario:

  • Some patients may have prescriptions (Epi-pen, nitro, etc.) but NO patient will have taken medication prior to the EMTs arrival;
  • If you order activated charcoal, for scenario purposes you have already spoken with Poison Control and that is the correct action;
  • All patients will agree to be transported;
  • Don’t forget Scene Safety and isolation precautions!

Telling the EMT to transport the patient will end the scenario.

This app is meant to reinforce good BLS skills. As such, you are required to do things a bit differently from “real life”. For instance,
if the patient in the scenario is a stabbing victim, you can’t just ask, “Where is he stabbed?” or “Is he bleeding anywhere?”. Instead, you should conduct
a proper head to toe examination of the patient. You can’t ask, “What are his vital signs?” but must instead request BP, heart and respiration rates,
breath sounds, etc.


At the end of a scenario, if Debrief=On, you can press the Play button and get a screen which roughly shows how you did. If there was information
you remembered to check (ostensibly by following SAMPLE, OPQRST, and DCAP-BTLS) it is green; stuff you missed is red, and stuff you didn’t ask about
but was blank anyway will be greyed out. Debriefs are not stored, but you can “long-press” anywhere on it and bring up a share dialog, allowing you to
email it (to yourself, if you like) or send it elsewhere.

I need more time!

After the EMT speaks, a countdown timer appears (controlled by the “Your Reply in…” slider). If you need more time to think for this particular moment,
at the beep tell the EMT to “Wait”. If you continually need more time, adjust the slider to the right or say, “Slower”.

If for a particular exchange you don’t want to wait until
the countdown has elapsed, just tap the timer and the EMT will be ready for your input immediately. You can say “Faster” at the next beep or adjust the
slider to the left, too. You can change the default countdown time in Menu -> Prefs.

Tapping the “Pause” button or saying “Stop” will put the EMT on hold, without a timer. Take your time and consider your next move. Tapping “Play” again resumes the scenario.
If only a minute or two has gone by, the EMT will immediately listen for your next command. If it’s been longer than that the EMT will repeat the
scene size-up as a refresher.

Saying “Restart” will clear everything you’ve done and restart the scenario from scratch. This is useful if you pause the scenario, make changes,
and want to test them out.

If you’re using this as a group to augment training with a manikin, you can easily control the volume with voice commands. Saying “Louder” will raise
the volume; the command “Softer” will lower the volume. The command “Shout” will set the volume to your device’s maximum (this might be too much on
some devices – use cautiously). Your normal hardware controls will also adjust the volume.

Everybody’s Staring

Tap the Speaker icon to the left of the Play button to toggle between speakerphone and regular phone mode. That is, you can run the app
with your device laying on the table, or you can hold it to your ear for more privacy. Sometimes, especially in noisy environments, using phone
mode results in better speech comprehension.


On the American TV show Emergency! (1972-1979), the intrepid paramedics Roy and Johnny would be toned out for a call.
Arriving on scene, they would invariably remove their
trusty BioPhone and call up Rampart Hospital, where the on-call doc would guide them through the process of starting an IV
D5W and transporting the patient.

This app is for the budding EMT-B. It places you in the position
of the Rampart docs. Your EMT-B is calling from the scene and asking for instruction.

Your EMT can be ordered to:

  • Confirm scene safety;
  • Assess the patient (area-by-area);
  • Take vital signs (BP, pulse, etc.);
  • Check blood sugar;
  • Start CPR;
  • Provide oxygen;
  • insert OPAs or NPAs as needed;
  • Use an AED;
  • Ventilate with BVM;
  • Control C-spine;
  • Immobilize extremities (splint) or patient (backboard);
  • Assist the patient with Nitro, Epi-pen, or MDI;
  • Administer oral glucose;
  • Administer activated charcoal;
  • Control bleeding;
  • Transport the patient

Note that this app assumes a rather strict list of interventions appropriate to the EMT-B level – your protocols may allow you to do things this app will not,
out of the box. You can add stuff, though – we’ll get to that later.

Hearing Voices

Your EMT’s sex and age is dependent on the voices installed on your Android device, and which voice is “default”.

Complete instructions for adding, removing, updating or changing your device voices is beyond the scope of this app or help file, and varies
with the version of Android your device is using. Consult expert web assistance to add or change voices.

The app was developed and tested using SVOX Victoria UK English, SVOX Grace US English, and IVONA Amy UK English, but other voices are out there and should
work as well.

Them’s Fightin’ Words!

One of the permissions required by the app is Network permission, so the voice recognition in Android can communicate with Google. It is
Google which returns what you said (or what it thinks you said).

If the app doesn’t understand something, it may sometimes ask, “Sorry did you just say…” and read back what Google supplied.
What Google supplies is sometimes WAY off the mark, and can at times be offensive. Just puttin’ that out there, it wasn’t us, honest.

Sample Play Dialogue

(Player hits the PLAY button)

  • Medic 52 here. We’re at a household where a mother suspects her toddler of eating cleaning agents. What are your orders?
  • Hold old is the patient?
  • The patient is 3 years old.
  • Is this patient male or female?
  • The patient is male.
  • Is the patient awake or alert?
  • He’s alert and oriented times 3.
  • What’s his pressure like?
  • BP 120/80
  • How about breath rate?
  • He’s breathing 30 times a minute
  • Okay. Put him on oxygen using a non-rebreather at 10 liters per minute.
  • Okay, he’s on oxygen. What next?
  • Check the patient’s heart rate, please.
  • Pulse is 80
  • Is he allergic to anything?
  • He has no known allergies.
  • Does he take any medications?
  • He was taking Tylenol last week for a fever, but no current medications.
  • Listen to his lung sounds, please.
  • Breath sounds are clear.
  • Check the patient’s abdomen
  • His abdomen is unremarkable
  • Okay. Well, go ahead and bring him to the hospital.
  • Okay, see you in 10 minutes.

Menu stuff

Newer devices are moving away from
actual keys. If your device has a menu button, it should work, or you can use
the icon. Here you have alternate ways to go to the next or
previous scenario (you can also do this by swiping left/right on the main screen), select a random scenario, or edit the current scenario.

Doing Things Your Way

This app will work “right out of the box”, with about 30 scenarios ready to go.

The Edit area allows you to add new scenarios or change existing; you cannot delete scenarios from here. If you really don’t like a particular scenario,
just overwrite it. Make as many changes as you like. Go nuts.

Pressing Menu -> Edit brings up the current scenario for editing.
On the left are the key values. Since real-life scenes can get weird, very little data validation is done during data entry. For instance, no
attempt is made to validate a blood pressure. You can set it to “120/80”, “50 over palp”, or “He’s dead, Jim.” It’s all good.

All changes are made
to a “sandbox”. When you’re done editing, you need to press Menu -> Save to actually save the changes. If you wish, you can exit the Edit menu
and run through the scenario with your changes first to see if you like them.
Most items on the edit screen are self-explanatory, except perhaps BGS (background sounds, and now it’s clear.)

So, you’ve got scenario #1, female abdominal pain. She’s 36 years old, but you want to make her 99. Menu -> Edit, tap the age, enter your
desired number, click OK. This puts your change into a sandbox. Back out and hit PLAY to try it out, or not. Menu -> Save to keep the change.

If you leave heart rate blank, your EMT will report “no pulse found”. A blank BP will get you some variant of “blood pressure is unobtainable.” Take
a moment to look through any scenarios you edit or it could get confusing when your alert-and-oriented patient has no heartbeat. That being said, most
items can be left blank, and the app will fill in a suitable answer.

Revealing Patient Problems

When editing certain fields you’ll find a button near the bottom of the screen, “Reveal…”. Clicking this presents you with a list of problems the patient
might have. You can add one or more of these to any field, such that the problem is revealed, and can be dealt with only after the user gets information from
this item.

For example, if you have an assault victim, perhaps he’s bleeding. Bloody clothes, etc. However, it would be “cheating” for the player to just tell the
EMT to “control the bleeding” as soon as he knows it’s an assault. You haven’t found the bleeding yet. In Edit mode, let’s say you tap EXAM_HEAD.
Tap the “Reveal…” button and select “BLEEDING”. Now, the player has to explicitly check the patient’s head before he’s allowed to “find”
the bleeding. Trying to control bleeding before finding it won’t work.

For those situations where a problem is fairly obvious, put the Reveal item in the scene size-up field, SCENE, which is automatically
spoken at the beginning of each scenario. That is, if the SCENE field tells the player that this is a car-crash, put “SPINAL” right there,
so that taking c-spine precautions is allowed right off the bat. Follow good EMT-B rules of judgement when disclosing Reveal items in the SCENE field.
Rule of thumb: If an intervention would be obvious when you roll up or walk in the door, it should go in SCENE.

Background Sounds

The BGS field allows you to place background sounds in a scenario. Editing this field will bring up a file selection dialog. You can select any sound
on your device. The background sounds available from the app are:

airport nightclub
construction site office cubicle
department store opera intermission
grocery store restaurant, crowded
gym/indoor pool shopping mall
highway, dry sports event
highway, wet train station
hotel lobby TV on, cartoons
nature trail TV on, gameshow

Look, Ma, I’m a programmer!

The built-in editor gives you a handy way to make modifications to each of the scenarios, or to create your own from the ground up.

The Prefs menu item allows you to set certain things to a default startup value of your choice.

If you’re feeling adventurous, you can do more. You’ll need one of the many fine, free SQL editors available in the Play store.

With an SQL editor you can customize this app. The scenarios, the recognized words, the commands your EMT can follow, almost everything is located
in an SQL database, “dtsemt_emtb.db”. You don’t need a lot of skill to make changes.

Depending on your device, your memory card, and permissions it could be in one of several places, but
a likely location is on the external card, in /Android/data/com.dtsemt.rampartb/files. You do not need root access to change this file.

Opening this file with an SQL editor gives you access to almost everything, and a little look-around in it should show you how. Sort the records
alphabetically by key and the instructions for making changes precede each section.

If you completely trash the file, no worries – just uninstall the app and reinstall from Google Play.


Disclaimers and all that jazz is on the Menu -> About page.

Comments made on the app Ratings area are NOT automatically forwarded to the author!

This is Betterware; if you can think of any way to make it better, please send suggestions to DTsEMT@gmail.com.

Clicking an ad link once in a while helps to keep this app free.


New App – Parkland

Available on the link to the left, or in the Google Play store: https://play.google.com/store/apps/details?id=com.dtsemt.parkland

As usual, completely free, and ad-free.  Calculates fluid resuscitation requirements based on the Parkland formula.


New App

… in the Google Play store.  DTsEMT Menu allows you to remove any shortcuts you might have to other DTs (Medics of Anarchy) titles and replace them with a single shortcut to the Menu app, freeing up screen space.

The app scans your device on launch and creates a menu of all DTsEMT titles – building, well, a menu.

It does NOT check the Play store for new DTsEMT titles.

Absolutely free, like all MoA apps.

who is… The Most Interesting Medic In The World…?

To him, anything less than a 14 gauge in the Circle of Willis is a peripheral line;

When he marks “transporting”,  the hospital pages a “Code Awesome, ETA 5 minutes”;
When he brings in a patient, the ED docs gather around – to learn;
When he was dispatched to the wrong address, the occupant faked illness to become his patient;
Just sitting at his table at lunch is worth one hour CE credit
 He needs no siren; he just smiles at the rear view mirrors of the cars in front of him
Any more?

Of course, Scotch is a colloid

In discussing blood pressures, and fluid resuscitation, my current precept asked a simple question, “When would you use crystalloids over colloids, assuming both were available?”.  Further discussion led to a narrowing of the question to, “When would you use crystalloids and pressors, rather than simply switching to colloids?”

Since there are a variety of reasons to use any fluid resuscitation, let’s make this a trauma patient.  Mr. Smith was using his chainsaw to remove a fallen tree on his property when – whoops! – chainsaw slips and he has a deep cut on his anterior thigh.  EMS arrives, bleeding is controlled to an oozing wound.  Mr. Smith is ashen, tachycardic and hypotensive.  The nearest ED is a 20-minute response.

Now, to understand why the precept posed this question, you need to know that it takes far less of a colloid solution to produce the same effect on blood pressure as lots of crystalloid.  Generally, 250ml of colloid has the same BP effect as 4 liters of crystalloid.  That is, 1/16th the amount of colloids does the work of crystalloids.

“What!”  you exclaim.  “DTs, this means that…  hmmm, 4/4 = 1 liter, therefore 250/4 = 62.5… this means that instead of hanging a liter of saline wide open to raise a blood pressure, I can draw up a 50ml syringe of this ‘colloid’ of which you speak and bolus a nice big systolic BP almost immediately!  Why, this revolutionizes EMS!  A guaranteed systolic in my pocket!”

Not so fast!  There is, as you have probably guessed, quite a bit more to it, and as you might also have guessed, we’ll start at the very beginning of the subject.

We first need to discuss pressures.  Any fluid, in any container, exerts hydrostatic pressure.  This is the pressure the fluid (hydro) exerts on the container walls due to gravity, when the fluid is at rest (static).

If we were dumping fluid into a metal bucket, or a Styrofoam cup, we’d pretty much know all we needed to.  Since we’re putting fluid into living things (patients), we need to first explore a couple of concepts.

To get fluids into our patient, we generally introduce the fluids via the vascular bed – which includes the veins, arteries, and capillaries.  That’s usually where we want it to stay, too, if we’re trying to raise the BP.  And we also know that the vascular bed is made up of cells, which have cell walls.  If these walls just allowed anything in to or out of the cell, they’d be pretty worthless.  To work well, they need to be semi-permeable, and to selectively allow the admission or expulsion of fluids or chemicals.

Another important pressure is osmotic pressure.  It’s called “osmotic pressure” because it deals with osmoles, which is the number of osmotically active particles in a kg of solution (there can be non-osmotically active particles in a solution, but we don’t care about those right now).  By osmosis, fluids move from one side of a semi-permeable membrane to the other,  based on which side has the most solutes.   Imagine a solute as acting like a small sponge;  if cell A has a sponge inside, and the blood vessel outside the cell has a fluid which has 20 times the number of solutes (sponges), fluid will flow out of the cell and into the vessel.

Osmotic pressure is used in a lot of different fields, but in the medical field, we’re talking about cell membranes (and no other kind), and usually as it relates to existing blood plasma (your patient wasn’t completely empty, was he?) so we get to have our own term for it – tonicity – which completely ignores a lot of other ugly stuff about osmolality, osmolarity, and other junk that biologists have to worry about.

Our fluids are either hypotonic – containing fewer solutes than surrounding tissue; isotonic – containing the same number of solutes; or hypertonic – containing more solutes.

There are dozens if not hundreds of different IV solutions in existence.  We are ignoring here whole blood, blood plasma, packed red cells, and other mainstays of ED life, and concerned only with crystalloids and colloids.

What is a crystalloid?

A crystalloid is a fluid in which the solutes are dissolved.   If the particles in a fluid do not dissolve, then that fluid is not a crystalloid.  Two very common crystals also happen to make up our two most common crystalloid solutions.  Salt crystals are added to water to make Normal Saline.  Sugar crystals are added to water to make D5W.

Isotonic ( from the Greek isos, meaning “equal”) crystalloids are those fluids which have roughly the same tonicity as blood plasma.  These include:

  • Normal Saline 0.9%.  This fluid is the most widely used in EMS for volume expansion.  It has no red blood cells, hence no oxygen carrying capability, and includes no electrolytes.  Its administration is purely to increase the hydrostatic pressure in the vessels.  However, it has been noted that about 75% of a saline bolus leaves the vascular bed almost immediately, leaving 25% in circulation.  That 75% can contribute to edema and wet lung sounds if the patient is over-hydrated;
  • Lactated ringers.  This fluid contains a bit more dissolved in it – sodium, chloride, lactate, potassium, and calcium.  It is useful in resuscitation because, as the liver metabolizes lactate, the by-products of that metabolism help to counteract acidosis.  For resuscitation the usual dosing is 20-30ml/kg of body weight.  Ringers is not, however, used for long-term drips since the electrolytes sodium (130 mEq/L) and potassium (4 mEq/L) are respectively too high and too low for homeostasis.  That is, while the tonicity of the fluid is the same as the body, the electrolyte balance is not;
  • D5W.  This fluid is not used in resuscitation.   Dextrose (the D in D5W) is metabolized by the body and leaves plain water (the W in D5W) behind.  Plain water is hypotonic, containing fewer solutes than blood plasma.  Remembering the “solutes = sponges” concept, if the vascular bed has plain water (fewer solutes) and the surrounding cells have more solutes, fluid will shift OUT of the vascular bed and INTO the cells, resulting in a drop in BP.   Since this is occurring wherever a cell contacts the vascular bed, e.g. everywhere, it happens with all cells.  A common complication is that brain cells may swell, causing headache, weakness, nervousness, vomiting, tremors, convulsions, coma, and dilated pupils.  These are not good things.

Hypertonic (from the Greek prefix hyper-, “over, or excessive”) crystalloids are those whose tonicity exceeds that of plasma.  Again, if the solutes can be thought of as little sponges, this means there are more little sponges going in to the vascular bed than currently exist in the cells.  This results in water being drawn out of the cells and into the vasculature.  The cells shrink, which is called crenation, and this cell-shrinkage is exactly what is sometimes needed:

  • 7% hypertonic saline is considered “mucoactive” and is used to hydrate thick secretions to assist in expectoration;
  • 7% can be administered via central line for traumatic brain injury;
  • 3% hypertonic saline can be used for hemorrhagic shock (drawing water into the vasculature to increase BP), but no other kinds of shock;
  • 3% may be used for acute intracranial pressure (this lowers ICP by shrinking the brain cells);
  • 3% may be used for severe hyponatremia, but this is controversial

Hypotonic (from the Greek prefix hypo-, “under”) crystalloids are those where tonicity is below that of plasma.  Since surrounding cells will contain more solutes, the fluid is drawn immediately into the cells.  This is, in part, why you get so wrinkly in the bathtub – cells contain more solutes than the surrounding fresh water.   We’ve mentioned what happens with over-zealous administration of D5W.  When cells swell to bursting (which they can), the process is known as osmotic lysis or  cytolysis.  There is currently no out-of-hospital use that I know of for hypotonic fluids.

What is a colloid?

A colloid is a fluid which has something in it which is not dissolved.   The particles in colloids are larger, and do not fit through the vascular pores, and so they tend to stay in the vascular bed.  None of the particles in a colloid are osmotically active, and so we don’t have “hypotonic colloids” or “isotonic colloids”.

Colloids are used mainly for fluid expansion, and since it doesn’t leak as readily from the vascular bed smaller amounts (1/16 by volume) can be used to achieve the same results as crystalloids.  However, as hydrostatic pressure increases, the vascular pores “stretch” and allow the larger colloid particles to migrate out of the vascular bed, into cells and interstitial spaces.  When the hydrostatic pressure lowers, those pores “snap shut” and the colloidal particles are trapped outside of the vascular bed.  Therefore, edema caused by colloid administration takes much longer to resolve than edema caused by over-hydrating with crystalloids.

Examples of colloid fluids include:

  • Human albumin, used for trauma, burns, surgeries, and liver disease with ascites;
  • Hetastarch, a synthetic starch used for hemorrhage, burns, surgery, sepsis, and trauma.  Hetastarch has no O2 carrying capabilities or plasma proteins, and a couple of important contraindications

So there we have it, crystalloids and colloids, and completely ignoring Hartmann’s solution, blood plasma, PRBC, and about 99 other IV fluids that a patient can receive.  And we can probably, at this point, answer the initial question:  “What is best for our Mr. Smith?”

Of course, Answer #1 is, “always follow your local protocols”.  But presuming we had, say, normal saline 0.9%; D5W; Lactated Ringer’s solution, and for some reason human albumin on hand, which would be better?

Mr. Smith exhibits ashen skin and tachycardia, and a wound that bled heavily prior to EMS arrival.  He clearly needs fluids.

  • Hypotonic fluids are right out – they would, as we’ve seen, speed in through our IV and straight into cells and just make everything worse;
  • Hypertonic fluids *might* make some sense – they would draw fluid from the cells and interstitial spaces and into the vasculature.  But Mr. Smith has an overall deficit of fluid and needs more added, not just what he has shifted around

Isotonic or colloid it is.  Of the isotonic, D5W is right out – the dextrose will be metabolized and the water will enter cellular space, not stay in vascular space to help with BP.  Of the two remaining, Lactated Ringer’s solution might do well for a bolus, and may correct some of the acidosis we might expect from his initial trauma, but Ringers might not work well as an ongoing drip (due to electrolyte imbalance)

So, we’re down to Normal Saline, and a colloid (we’re pretending we have albumin).  And there, sorry to wuss out on you, is where the jury is still out.  Studies are being done all the time, coming to one conclusion (“Yay Saline!”) or another (“Yay Colloids!”), and the next study claims to shoot that idea down.  We just don’t know which is better.  We do know that colloids are much more expensive than crystalloids.  It would seem that Mr. Smith is getting saline today.

But at least we know why, right?