Case summary:

An ALS crew responded to 30s man who overdosed.  While in route, the crew was notified that CPR was in progress.  Per report of bystanders, the patient was found unresponsive, lying in a pile of snow.  They gave the patient intranasal (IN) naloxone given a known history of substance use and called 911.  Law enforcement arrived prior to EMS and administered 8mg of IN naloxone.  When EMS arrived, they found that the patient had agonal respirations, a weak pulse and was very cold to the touch.  The crew immediately began providing bag valve mask (BVM) ventilations while attempting for an IV.  The IV was unsuccessful so they gave additional IN naloxone.  Another attempt at an IV was made which was successful so fluids were started given the weak pulse.  The initial HR was 46 bpm.  The crew loaded the patient into the rig and attempted to begin rewarming with passive measures.  Right after they loaded the patient, he was found to be in ventricular fibrillation so the patient was defibrillated, chest compressions were started, he was given IV epinephrine, and he was intubated.  The crew began treatment to receiving facility with CPR in progress.  Prior to arrival at the hospital, they gave two more doses of epinephrine and defibrillated one more time with the rhythm after the second shock degrading to asystole.  The patient arrived at the receiving facility still in cardiac arrest and received ongoing care there.

Highlights of the case:

Opioid overdose care

The most important intervention in the treatment of suspected opioid overdose is supporting ventilation.  Opioid overdose kills patients by suppressing their respiratory drive at the level of the brain stem.  This causes the patient’s CO2 level to rise and eventually causes their oxygen saturation to drop.  If the CO2 level gets too high or the oxygen saturation gets too low, the patient can go into cardiovascular collapse and die.  Naloxone works by entering the brain and knocking opioids off their receptors in the brain stem which in turn will bring back the patient’s respiratory drive and get the patient to start ventilating and oxygenating again.  However, this takes time to work.  The IN route can take between 3-17 minutes to work with the IV route taking about 2 minutes to work.  The goal of naloxone is restoration of the patient’s respiratory drive, not treating altered mental status or unconsciousness.  Since naloxone does not work immediately (and IN taking up to 17 minutes to work if enough is given), we do not want to rely completely on naloxone.  For this reason, the lifesaving intervention in opioid overdose is BVM since this will immediately support both oxygenation and ventilation.  There really should never be a situation where naloxone is prioritized over BVM or be a time where naloxone is given but BVM is not used.  End-tidal capnography can be very useful in these patients since we can use it to titrate the amount of nalxone we are giving.  If a patient is drowsy or asleep but has a normal respiratory rate and ETCO2, naloxone would not be indicated.  In this situation, we could monitor their ventilation with ETCO2 and if the patient’s respiratory rate drops below 10 and/or the ETCO2 goes above 45, we could then give the lowest dose of naloxone to get these values back to normal.  This way we can support ventilation and oxygenation while also decreasing the risk of naloxone induced pulmonary edema and precipitated opioid withdrawal, both which can harm the patient.

Severe hypothermia can induce sudden cardiac arrest

When patient’s core temperature becomes very low (<32C or 90F), patients can suddenly go into cardiac arrest from hypothermia itself.  The reason for this is that the cardiac myocytes become irritable which can lead to sudden ventricular fibrillation (VF).  The risk of VF goes up as the core temperature drops.  The typical progression is of the rhythm as the temperature drops is sinus bradycardia -> atrial fibrillation with slow ventricular response -> ventricular fibrillation -> asystole.  If a patient feels cold to the touch and has a bradycardic rhythm (especially atrial fibrillation with slow ventricular response), we should have a high index of suspicion for profound hypothermia which can be potentially fatal.  The hypothermic heart is so irritable that simply moving a patient too aggressively can precipitate VF arrest.  This has been seen with things as minor is transferring a patient from a stretcher to a hospital bed.  This might be unavoidable since the process of extrication and transport to a hospital involves multiple patient transfers.  In patients that are known to be profoundly hypothermic or who have a bradyarrhythmia, EMS should have extreme caution to move patients as gently as possible to decrease the chance of precipitating VF arrest.  The patient in this case likely overdosed on an opioid while outside leading him to become profoundly hypothermic.  He likely did not respond to BVM and naloxone because he was now unconscious from being so hypothermic.  The patient was found to be significantly bradycardic prior to extrication which most likely indicated some degree of myocardial irritability from the hypothermia.  Given this irritability, the simply act of extrication was all it took to precipitate VF arrest.  This was likely unavoidable in this particular situation.  Once a patient goes into cardiac arrest from hypothermia, prompt transport to the hospital is almost always indicated since these patients need to be aggressively rewarmed with ongoing resuscitation.  Unless there is a specific reason to terminate resuscitation early, most cases of cardiac arrest with hypothermia should be continued until the patient is warmed to 32C or higher, which is the temperature where the heart should no longer be experiencing myocardial irritability.  Depending on the rewarming techniques used and the initial temperature of the patient, this can take hours to do.