The Hamilton T1 is quickly becoming one of the most prominent ventilators in the transport environment. While initially, all the bells and whistles can be intimidating, some high points make the learning curve slightly less steep. My goal for this blog is to highlight some "hacks" that are actually just strategies you should know and common misconceptions. Hacks just sounds cooler and provides just enough clickbait to reel you away for a few minutes.
Strictly Pressure Ventilator
The first concept you should understand about the T1 is that it is strictly a pressure-driven ventilator. Even though you will see a “volume” mode, it is not a volume mode. In a proper volume mode, the ventilator will shove whatever tidal volume the provider sets into the patient, and the pressure it generates will vary.
The volume mode on the T1 is more of a pressure-regulated volume control. This means the provider may enter a goal tidal volume for the ventilator to target, but it is not guaranteed. The ventilator will slowly increase or decrease the inspiratory pressure with each breath to try and aim for the tidal volume you selected. The only thing that will prevent the ventilator from being able to hit the targeted tidal volume is if it requires an inspiratory pressure that is too close to your pressure alarm limit (within 10cmh2O, to be exact).
I do not like to wait for the ventilator to titrate up the inspiratory pressure before it hits my goal tidal volume. Instead, I like to use pressure control ventilation (PCV) and titrate the pressure myself.
You Rarely Need SIMV
SIMV is an add-on to the two previous modes I discussed (CMV or PCV), allowing you to add pressure support to a patient-triggered breath. Pressure support is excellent because if a patient tries to take a breath, sucking air through an ETT is uncomfortable. Pressure support provides a little boost at the beginning of the breath to help them overcome breathing through a tube.
The majority of the patients I transport are acutely intubated and likely still paralyzed. This means they will not be taking any of their own breaths, so pressure support is unnecessary. There was a thought at one point that in the transport environment, the ventilator may be unnecessarily triggered by bouncing down the road or turbulence in the air. I am not sure where this started, but it was always recommended to transport in SIMV so that each triggered breath was not a full ventilator-administered breath. It may seem obvious, but if your ventilator is triggered by turbulence or bumps, you need to adjust the trigger and not just switch it to SIMV.
Monitoring, PAGE 3!
Say this in your head three times: Monitoring, Page 3… Monitoring, Page 3… Monitoring, Page 3
The menu section of the T1 has many values we can use to understand better what the patient’s lungs are doing with the air we are inflating them with. One of my go-to values is on page 3 of the menu. This page contains something called a Rinsp & Cstat, and the information it provides will help solidify your strategy. Let’s take a closer look at what these values mean.
Cstat
Cstat measures your lungs' compliance and is measured in milliliters per cmh2O. How much volume will I recruit for every one cmH2O of positive pressure I supply to the lungs? An intubated patient typically has a Cstat between 50-100 ml/cmh2O. If lung compliance is poor, the Cstat will fall below those values, and the provider will target a lung protective strategy in correlation to clinical presentation.
This picture shows a Cstat of 38 ml/cmH2O and indicates for pulmonary compliance.
Rinsp
This value reflects the inspiratory resistance as the air flows into the patient. The value you are reading is cmh2O/L/sec, which shows how much pressure you lose as you blow air through the ETT and airways. This means that the higher the Rinsp, the higher the resistance. Just the inherent resistance of ventilating through an ETT will provide most patients with a Rinsp somewhere between 8-15 cmH2O/L/sec. However, the higher this number gets, the less your Cstat tells you anything useful.
For example, the picture above shows a Rinsp of 35 and Cstat of 24. Because the Rinsp is so high, I know a lot of the pressure I’m trying to supply to the lungs is getting lost through the airways and, therefore, not participating in alveolar recruitment. This means I need to consider that either something is obstructing my ETT or the patient has an obstructive pathology.
FOAMfrat T1 Reference Card
The above graphic is taken from the FOAMfrat T1 reference card and outlines how C stat and Rinsp can help guide your ventilator strategy.
VTE > Pressure
I commonly ask new flight clinicians what they expect to see if the pressure-driven intubated patient we are flying develops a tension pneumothorax. What do you think they say? Yes, nearly everyone says they expect to see the PIPs increase. You probably can see where I am going with this.
With the T1 being a pressure-driven ventilator and me being in a mode where I set the inspiratory pressure, the only thing that will change is the exhaled tidal volumes dropping. One could argue that if they are in the T1’s CMV (pressure-regulated volume control) mode, the ventilator would slowly titrate up the inspiratory pressure as the VTE drops from the pneumo. Still, even that will soon meet the pressure alarm limit, and VTEs will drop.
Understand The Flow Waveform
Depending on the ventilators you have used in the past, this may be the first time you are exposed to ventilator waveforms and loops. The T1 provides fantastic visuals of patient/ventilator interactions. The relationship between your flow and pressure waveform is beneficial and arguably one of the first things a provider should commit time to understand.
When transporting a ventilated patient, I keep the flow and pressure waves on my screen by default to continuously monitor how the lungs receive and send each breath. Here is an infographic to explain what I am looking at.
The baseline of the flow waveform is the point at which air is neither going in nor coming out of the lungs. In the graphic above, you can see we spend a lot of time between the inspiratory and expiratory phases. If your goal is to increase mean airway pressure and optimize oxygenation, this strategy works and allows time for alveolar recruitment. However, suppose your goal is to optimize minute ventilation for a metabolic acidosis patient. In that case, this long breath hold is suboptimal because it does not increase tidal volume and is just taking up space where we could add a few more breaths to increase minute volume. My buddy Bryan Winchell calls the time we ride that zero flow baseline "time on the table." We can dedicate this time to mean airway pressure or minute ventilation.
Summary
My goal with this blog was not an all-encompassing manual on mechanical ventilation but rather a quick resource for providers to "cut their teeth" when starting a new relationship with the T1 transport ventilator. I have included a link to the Hamilton T1 reference card below.
Check Out The FOAMfrat 12-Hour Ventilator Course included in the Studio Membership.
