Vent Management on the Run...
/“Influence of Critical Care Transport Ventilator Management on ICU Care and Opportunities for Improvement.” Air Medical Journal, July-August 2020.
Introduction
This is a great paper recently presented at the Critical Care Transport Medicine Scientific Forum. It covers a subject area I have always been interested in. Over time, our understanding of critical care has evolved to show the importance of a low tidal volume strategy for ventilating patients, particularly those with lung injury/ARDS. However, even patients with normal lungs are potentially harmed by high tidal volume strategies.
In Critical Care Transport, we are often involved during the beginning phases of the patient’s time on the ventilator. This is especially true of patients who we intubate and then initiate mechanical ventilation on. High tidal volumes can be deleterious both acutely and over-time. Acutely – high tidal volumes can cause overt barotrauma such as pneumothorax or pneumomediastinum. They can also decrease venous return and contribute to breath stacking and AutoPEEP, all of which can cause/contribute to hemodynamic instability and potential cardiac arrest. Over the longer timeframe, high tidal volumes can cause disruption at the alveolar level and contribute to progressive and continued lung injury.
This paper explores the association between prehospital/CCT ventilator settings, and in-hospital settings. It was a retrospective cohort study of mechanically ventilated patients transported by the DHART program to the academic medical center at Dartmouth. They assessed the referring location, the mean patient contact time, the mean tidal volume prior to ICU handoff, as well as the initial ICU settings and ventilator settings after 6 hours in the ICU. They also examined in-hospital mortality.
Results
383 patients were included in the study. 81% of the patients were transported from a referring Emergency Department. The mean patient contact time was 77 minutes. The mean tidal volume prior to ICU handoff was 7.5 cc/kg of IBW. 31% of patients received a high tidal volume of greater than 8 cc/kg IBW during transport. Transport tidal volumes strongly influenced initial ICU tidal volumes. If a patient received high tidal volumes during transport, they were more than 3 times as likely to receive high tidal volumes in the ICU. After 6 hours, patients were still twice as likely to be receiving high tidal volumes. Overall in-hospital mortality for these patients was 35%.
Limitations
This study is limited for several reasons. It was based on clinical data from a single CCT service and a single academic medical center. It was a retrospective chart review, rather than the gold standard of a true prospective randomized controlled trial. There is also the possibility of a Hawthorne effect, as they didn’t specify whether there was any blinding done, and it’s possible that the staff may have acted differently knowing they were being studied. Finally, the endpoints were primarily focused on surrogate endpoints such as tidal volumes, and there was no comparison group for the one true endpoint of in-hospital mortality.
Discussion
I was excited to see this come out, as author Dr. Matt Roginski and I had talked about this potential study a few years ago. It confirms one of the most important concepts in HEMS – “what we do matters.”
By that, I mean that many of our interventions have downstream effects that we may not necessarily immediately see. Obvious examples are administration of medications such as TXA and/or Calcium, as these interventions can be time-sensitive and can also be lost in the shuffle of a busy Trauma Bay. I’ll freely admit that this papers nicely ties into a subject I feel very strongly about as well – namely the use of the ventilator and appropriate Ideal Body Weight-based ventilator strategies for mechanically ventilated patients.
Although we often only care for patients for comparatively brief periods of time, the interventions we perform and the treatments we initiate (such as choice of vasopressors) can persist in-hospital for a long-term. Some refer to this as “therapeutic momentum.” This paper shows that this is also true for ventilator settings. Intuitively, I think many of us have suspected this. In the past, I have been as guilty of it as anyone – if the patient is “doing well” at the outside facility, I have often just reproduced their ventilator settings on our ventilator and then moved on. In recent years, I have become much more focused on this area and so now will force myself to deliberately pause and really evaluate their ventilator settings and make appropriate adjustments.
We are starting to see improved technology with our transport ventilators. For instance, the Hamilton T-1 ventilator automatically calculates the cc/kg of IBW if the height and sex of the patient is entered. Many teams will also carry a tape measure or utilize other tools and references to help accurately measure the patient’s height and generate an IBW to use to calculate appropriate tidal volumes.
This paper further highlights the importance of our CCT teams appropriately managing these patients, as the settings we use will likely be carried forward to the in-hospital setting, at least for a period of time. Often, when patients are dropped off in-hospital – their transport settings are initially reproduced on the hospital ventilator at the bedside. If we are not ideally managing these patients, those potentially harmful settings can persist even after the patient leaves our care (as evidenced by this paper). As mentioned above – if a patient was receiving inappropriately high tidal volumes during transport, they were three times as likely to continue receiving those on arrival to hospital, and still twice as likely to be receiving them 6 hours later.
Of course, the in-hospital teams are frequently excellent and can use their skills and resources (i.e.: frequent blood gases, etc), to alter/correct the ventilator settings if necessary. However, our goal should be to deliver patients with “perfect” ventilator settings if possible. If we can deliver a patient as ideally optimized as possible, this frees up the cognitive burden on the receiving team to perform other interventions and treatments. It’s important to remember that “critical care is a concept, not a location”, and so if we have the capability and knowledge to provide optimized ventilator management during transport – it is our obligation to do so.
AUTHORSHIP
Andrew Cathers, MD - Dr. Cathers is an Emergency Medicine Physician as well as Flight Physician, and Assistant Medical Director of University of Wisconsin Med Flight with a focus on Education and Training in their Program. He is kind enough to share recaps of recently published HEMS literature which should be posted quarterly here on TamingtheSRU
Peer Review/Editing/Posting provided by Jeffery Hill, MD MEd
