Critical Care in a Submarine

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Mike Tom

EM trained at Cooper and Undersea and Hyperbaric Medicine trained at UPenn. Still manning the ED and chamber with Penn in west Philly. Dog dad and fisherman.

The Pre-brief

Many practitioners have very little exposure and most patients have never heard of hyperbaric oxygen therapy (HBOT) until a patient needs it.  This is by no means to proclaim ignorance of the masses but rather a testament to the Lilliputian size of the niche that is hyperbaric medicine.  While the bankers’ hours treatments are filled with walking and talking patients with diabetic and delayed radiation wounds, the after hours and emergency dives are filled with patients whose disease processes are more fitting for a critical care driven audience.  After a very brief overview of the emergent indications for HBOT approved by the Undersea and Hyperbaric Medical Society (UHMS), let’s discuss some considerations and limitations to critical care in a pressurized steel ward.

Multiplace vs. Monoplace

A basic understanding of the two main types of chambers is important when considering HBOT for your patients.  Multiplace chambers (Class A chambers) by definition can hold multiple people and are pressurized with room air while the patient breathes 100% O2 via a mask or hood.  These are typically large steel chambers, and in the interest of caring for the critically ill, allow a critical care nurse and respiratory therapist to be physically at the bedside and have hands-on the patient if needed during treatments.  Monoplace chambers (Class B chambers), conversely, are typically acrylic cylinders designed to hold a single occupant: the patient.  Being much smaller in volume, these are pressurized with 100% O2 with no mask or hood needed.  Perhaps the most important limiting factor is that providers cannot directly have hands-on access to patients should complications arise during treatments.  Critical care in monoplace chambers is not impossible but can be a conundrum, and few and far between are the monoplace facilities that have both the staff with appropriate training and willingness to treat sick patients.      

 

Vent Management

Most multiplace HBOT facilities are staffed by physicians with either EM or anesthesia training and a background in airway and ventilator management.  A limitation arises, though, in that very few ventilators are FDA approved for HBOT, and those that tend to be older models with very basic capabilities.  The patient with unstable ventilation requirements or who requires advanced ventilation modes can be difficult to manage in the chamber.  Depending on the risks and benefits and urgency of the HBOT indication on a case-by-case basis, the patient with markedly dynamic ventilation requirements may need to stay in the ICU ward to settle in on the vent before initiating HBOT.  Studies are currently underway to investigate the safety and efficacy of newer vents in a pressurized environment.  

Lines and tubes

Multiple continuous infusions can be maintained during HBOT.  Approved infusion pumps can safely accompany patients in the chamber.  Patients can receive HBOT while requiring vasopressor support.  Again, depending on risks and benefits on a case-by-case basis though, the patient on three pressors at or near-maximum rates may be better off to stay in an ICU setting until achieving some hemodynamic improvement prior to initiating HBOT.  

Therapies requiring suction are generally compatible with HBOT.  While an untreated pneumothorax is the only absolute contraindication to HBOT, a chest tube can be maintained and attached to suction if needed during treatments.  Similarly, wound vacs can be maintained during treatments.    

CRRT is generally not compatible with HBOT.  

 

Monitoring

Cardiac telemetry and end-tidal CO2 monitoring can be continued during treatments without issue, and most chambers will have monitors external to the chamber such that the physicians not inside can also keep an eye on these.  Invasive blood pressure monitoring can be maintained during treatments, as long as the A-line is re-calibrated upon reaching treatment depth and again with any changes in depth thereafter.  

Though we routinely check every device, most modern AICD’s and pacemakers are compatible with HBOT.  Many of the newer implantable glucose monitors, however, either do not have data regarding functionality at pressure or are not compatible. 

 

60 ft. “underwater” in a resource desert

While the analogy comparing a submarine to a hyperbaric chamber is not a perfect one, it does go beyond the outward appearance of both being large steel vessels.  Both have limited resources available inside and both are not able to immediately “surface” in the event of extreme circumstances (i.e. patient coding).  Relative to an ICU or ED room, equipment is sparse, and there is usually only physical space for one to two caretakers as opposed to a whole ICU team.  These factors can make caring for an exceptionally unstable patient a challenge.    

To compound matters, there is a requisite delay in decompressing a chamber to a surface pressure (sea level) environment where a full complement of equipment and personnel becomes available.  Most HBOT treatments take place at a pressure equivalent in the range of 30-66 feet of seawater (fsw), meaning that the pressure in the chamber is the same as is felt being underwater at the given treatment depth.  Rapid or immediate decompression from treatment depth is effectively the same as a SCUBA diver shooting to the surface.  This puts the patient and inside tenders at risk for gas embolism and the inside tenders at risk for decompression sickness (the bends).  As such, even in a coding patient, the absolute fastest they can be decompressed in order to exit the chamber is in the 5-10 minute range.  Needless to say, a code in a hyperbaric chamber at depth is something we go to great lengths to avoid.2   

 

On the horizon

Intriguingly, multiple sites are investigating the compatibility of handheld ultrasound devices with HBOT.  Major considerations in this arena are twofold

  • Fire hazard: In general, modern batteries (lithium) are forbidden in hyperbaric chambers given the fire hazard.  Workarounds to mitigate the fire risk are being developed.    
  • Device reliability at pressure: From the standpoint of the ultrasound device manufacturers, little to nothing is known as to how the devices function or if they can be reliable in a pressurized environment.  Preliminary studies suggest that these devices can function reliably at pressure.  

POCUS may soon be available to help guide the management of critically ill HBOT patients even at pressure! 

The Debrief

  • Given hands on access to the critically ill patient, multiplace hyperbaric chambers are preferred and arguably required for the critically ill patient.  
  • Most multiplace hyperbaric chambers are staffed by EM or anesthesia trained physicians and can accommodate patients on the ventilator, with vasopressor requirements, and with invasive blood pressure monitoring.  
  • Risks and benefits need to be carefully considered in those requiring extreme levels of ventilatory or vasopressor support as a code in a chamber can be very difficult to manage.

References

  1. Moon, R. E. (Ed.). (2019). Undersea and Hyperbaric Medical Society: Hyperbaric Oxygen Therapy Indications (14th ed.). North Palm Beach, FL: Best Publishing Company.
  2. Wright KT, Praske SP, Bhatt NA, Magalhaes RM, Quast TM. Treatment of cardiac arrest in the hyperbaric environment: key steps on the sequence of care–case reports. Undersea Hyperb Med. 2016 Jan-Feb;43(1):71-8. PMID: 27000016.
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