Drugs and defibrillation: how to perform advanced life support
Advanced life support is the name given to a number of techniques used alongside basic life support techniques. Whilst basic life support concentrates on chest compressions and ventilation, advanced life support uses equipment and medications to improve patient outcomes in CPR.
Today we’re talking all about a few key concepts in advanced life support - intravenous access, medications and electrical defibrillation. If you want more information on the use of monitoring equipment in cardiopulmonary resuscitation, be sure to check out this post.
Intravenous access
Securing IV access is vital during cardiopulmonary resuscitation. This ensures that emergency medications can be administered reliably, via the most effective route.
Preparation
Preparation is always key in emergency medicine, and we can prepare for emergency situations by ensuring IV access is secured in all patients admitted to the clinic.
This is particularly important in patients undergoing general anaesthesia (even healthy patients can arrest under GA!) and in unwell patients.
In addition to placing IVs in appropriate patients, any catheters should be checked regularly. This minimises the risk of a patient arresting and the team finding out the IV catheter isn’t working mid-CPR!
In all patients, IV catheters should be unbandaged, flushed and checked regularly and then flushed before any IV medications are given. If any concerns arise when the catheter is flushed, it should be thoroughly checked and replaced as needed.
Which vein?
In cardiopulmonary resuscitation, the vein nearest the heart should be used to administer medications. For example, if your patient has a cephalic and saphenous catheter in, all medications should be given via the cephalic vein.
This is because the patient’s circulation won’t be as effective as normal (because they are relying on us to generate it!), so we want to give those medications as much help to get to the heart as possible.
How much flush?
As well as considering the catheter site, we also need to think about how much flush we use after each IV injection. We want to push that medication to the heart, so we’re not leaving it sitting in a peripheral vessel where the blood flow will be poor (or absent!) and the medication won’t work.
Because of this, our flush volumes will be larger in CPR patients than when we routinely give IV medications (I typically use 5ml in cats and small dogs, 10ml in medium dogs, and 15ml in large-giant dogs).
For this reason, it is worth having larger syringes of saline flush in your crash box/crash trolley.
What if I can’t get an IV in?
CPR patients can be very hard to cannulate. Luckily there are a few ways we can make medication administration easier. These include:
Performing a surgical cut-down to visualise the vein, and insert a catheter that way. It is important to note that this is different to a ‘traditional’ cut-down where only the skin is nicked to ease catheter insertion.
Placing an intraosseous catheter. These are inserted into the medullary cavity of a long bone, and can be used to administer fluids and medications, just like an IV.
Administering intra-tracheal medications. If no alternative exists, medications can be given via the intra-tracheal route. This is performed by loading the patient’s medication dose into a rigid dog urinary catheter, which is then placed down the patient’s ET tube before the medications are flushed into the patient.
The use of medications in advanced life support
There are often a lot of different medications in our crash boxes - and each has specific uses. Some medications are administered ASAP after the onset of CPR, and others are administered based on the patient’s ECG assessment, which takes place after the first cycle of basic life support. Common medications include reversal agents, vasopressor agents and anti-arrhythmic medications.
Reversal agents
Reversal agents are generally the first medications we will administer during cardiopulmonary resuscitation. If a patient has had a reversible medication recently (within the duration of effect for that drug) we want to reverse that agent.
Our reversible medications are generally analgesic or sedative agents, such as opioids, alpha-2 adrenergic receptor agonists, and benzodiazepines. These medications cause varying degrees of respiratory and/or cardiovascular depression, which will make our CPR less effective, potentially resulting in poorer patient outcomes.
Common reversal agents include:
Naloxone for opioids, such as fentanyl, buprenorphine or methadone
Atipamezole for alpha-2’s, such as dexmedetomidine or medetomidine
Flumazenil for benzodiazepines, such as midazolam or diazepam
Vasopressors
Vasopressors are medications which cause vasoconstriction, resulting in an increased systemic vascular resistance, and therefore increasing blood pressure. In CPR, they are used to keep blood flow to our vital organs.
The most common vasopressor used is adrenaline; this is used to treat non-shockable ECG rhythms and is administered at a low dose every 4 minutes throughout CPR (every other basic life support cycle). This dose is associated with a higher rate of survival to discharge.
Higher doses of adrenaline may also be used, but only after prolonged CPR. This dose is associated with a higher rate of ROSC, but a lower rate of survival to discharge, and so its use is reserved for much later in CPR.
Parasympatholytics
Atropine is a parasympatholytic agent which is used in CPR when a vagal event (such as vomiting, gastrointestinal disease, ileus or respiratory disease) is suspected to have triggered the arrest. Like adrenaline, it can be given up to every other cycle of basic life support.
Anti-arrhythmics
Anti-arrhythmic agents are not used routinely in CPR but may be used to manage non-shockable rhythms which are not responsive to electrical defibrillation. Lidocaine is the most commonly used anti-arrhythmic medication; alternatives include amiodarone, but this is associated with complications following return of spontaneous circulation.
NB. All medications should be administered only under the direction of a veterinary surgeon.
Electrical Defibrillation
Electrical defibrillation is used to treat shockable ECG rhythms. This aims to covert a patient to a normal rhythm by temporarily pausing the electrical activity of the heart, and allowing the conduction pathways to ‘reset’.
There are two different types of defibrillator used in practice - monophasic and biphasic. A monophasic defibrillator sends the current from one paddle to the other, i.e. across the heart in one direction only.
Conversely, a biphasic defibrillator sends the current from one paddle to the other and back again, so the current flows across the heart twice. Knowing which defibrillator type you have is important, as a biphasic defibrillator needs a lower dose of energy.
Defibrillation Safety
Electrical defibrillation is not without risk and must be performed very carefully by the CPR team. Electrocution, fire and explosion are concerns, particularly if staff are in contact with the patient or table as the shock is administered; if alcohol is present on the patient, or if oxygen is attached to the patient.
In order to defibrillate safely, there are a few key things the team need to follow
Do not use surgical spirit or alcohol on your patient, as this is a fire risk
Disconnect the oxygen source and hold it away from the patient whilst the shock is administered
Ensure that the whole team are away from the patient when the shock is administered, to prevent electrocution. The person administering the shock should say ‘CLEAR’ and confirm all personnel are away from the patient, and no part of them is touching the table or patient at all.
Defibrillating a patient
To defibrillate a patient:
The team continues basic life support as an assistant prepares the defibrillator.
An appropriate energy dose is selected (using the RECOVER medication chart)
Electrode gel is applied to the defibrillator paddles
The defibrillator is charged
Whilst the defibrillator is charging, the patient is moved on to their back
The paddles are positioned either side of the patient, across the heart
The person administering the charge clears the site, confirms everyone is away from the patient and administers the shock
Another full cycle of basic life support is immediately resumed, and the ECG is assessed after the end of that cycle.
So that’s advanced life support in a nutshell. Do you use electrical defibrillation in practice? Let me know your experiences below!
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References
Fletcher, D. et al. 2012. RECOVER evidence and knowledge gap analysis on veterinary CPR part 7: Clinical guidelines. Journal of Veterinary Emergency and Critical Care, 22 (S1), S102-S131.
Yagi, K. 2017. Critical Components to Successful CPR. Today’s Veterinary Nurse, available from: https://todaysveterinarynurse.com/articles/critical-components-to-successful-cpr-the-recover-guidelines-preparedness-and-team/
