Confounding Variables and Generalizability in EMS Research

Reference: Snyder BD, Van Dyke MR, Walker RG, et al. Association of small adult ventilation bags with return of spontaneous circulation in out of hospital cardiac arrest. Resuscitation 2023. Date: January 11, 2024 Guest Skeptic: Dr. Chris Root is an EMS fellow in the Department of Emergency Medicine at the University of New Mexico Health Sciences Center in Albuquerque, NM. He is also a flight physician with UNM’s aeromedical service, Lifeguard Air Emergency Services. Prior to earning his MD, he worked as a paramedic in the New York City 911 system. Case: You are dispatched to an out-of-hospital cardiac arrest (OHCA). The patient is a 54-year-old man who collapsed in front of his family after complaining of chest pain for several hours. On your arrival, first responders from the fire department are performing high-quality basic cardiac life support. You continue with compressions and defibrillations and your partner places an advanced airway. Your EMS agency has equipped you with small-volume adult bag-valve masks (BVMs), the first responders have been utilizing a standard adult BVM thus far during the resuscitation. Your partner asks you which of the two BVMs you should use to continue the resuscitation. Background: There is continuing debate regarding the appropriate ventilation strategy for OHCAs. Common commercially available BVMs can deliver volumes that exceed normal tidal volumes. Some have argued in favor of using smaller BVMs to avoid hyperventilation. The issue of BVM ventilation in the context of pre-oxygenation for endotracheal intubation was discussed on SGEM#281. Airway management in OHCA has also been covered in SGEM#247 and SGEM#396. We have looked at OHCA more than a dozen times on the SGEM. For a full list of check out the links below to the SGEM blogs:  SGEM#50:Under Pressure Journal Club: Vasopressin, Steroids and Epinephrine in Cardiac Arrest SGEM#54:Baby It’s Cold Outside: Pre-hospital Therapeutic Hypothermia in Out of Hospital Cardiac Arrest SGEM#59:Can I Get a Witness: Family Members Present During CPR SGEM#64:Classic EM Paper: OPALS Study SGEM#107:Can’t Touch This: Hands on Defibrillation SGEM#136:CPR – Man or Machine? SGEM#143:Call Me Maybe for Bystander CPR SGEM#152:Movin’ on Up – Higher Floors, Lower Survival for OHCA SGEM#162:Not Stayin’ Alive More Often with Amiodarone or Lidocaine in OHCA SGEM#189:Bring Me to Life in OHCA SGEM#238:The Epi Don’t Work for OHCA SGEM#247:Supraglottic Airways Gonna Save You for an OHCA? SGEM#275:10th Avenue Freeze Out – Therapeutic Hypothermia after Non-Shockable Cardiac Arrest SGEM#306:Fire Brigade and the Staying Alive APP for OHCAs in Paris SGEM#314:OHCA – Should you Take ‘em on the Run Baby if you Don’t get ROSC? SGEM#329:Will Corticosteroids Help if…I Will Survive a Cardiac Arrest? SGEM#336:You Can’t Always Get What You Want – TTM2 Trial SGEM#344:We Will…We Will Cath You – But should We After an OHCA Without ST Elevations? SGEM#353:At the COCA, COCA for OHCA SGEM#380:OHCAs Happen and you’re head over heels – Head elevated during CPR? SGEM#396: And iGel myself I’m over you, cus I’m the King (tube) of wishful thinking. Clinical Question: Is using a small adult BVM during resuscitation of out of hospital cardiac arrest associated with return of spontaneous circulation? Reference: Snyder BD, Van Dyke MR, Walker RG, et al. Association of small adult ventilation bags with return of spontaneous circulation in out of hospital cardiac arrest. Resuscitation 2023. Population: Adult patients treated with an advanced airway for non-traumatic OHCA in a single urban EMS system in the US between 2015 and 2021 Excluded: "Age <18, received basic life support (BLS) only, termination of resuscitation due to advance directives, ALS interventions prior to EMS arrival, insufficient capnography data, cricothyrotomy, advanced airway placed while patient had spontaneous circulation,