Discussion:
The yew tree is a common, native poisonous evergreen with bright
red-berries that could be appealing to young children (1). If searching
through graveyards and harvesting the tree is unappealing, the seeds can
be purchased easily online, as happened in this case. Once ingested (and
particularly if chewed during ingestion) the taxine alkaloids are
absorbed where their main action is on cardiac myocytes, where they
primarily antagonise the Ca2+ channels causing heart block and
eventually cardiac arrest (2). It is estimated that 1g of yew leaves
contain 5mg of taxines, and the lethal dose can be as low as 3.0mg/kg in
humans (2).
Previous case studies on Yew Tree poisoning in adults generally outline
lethal cardiotoxicity, and provide pessimistic reading whilst awaiting
the arrival of a similar patient in the emergency department. With no
prior experience in treating taxine alkaloid toxicity, and with a
relatively junior on-call night staff in a district general hospital,
this case had a more positive outcome. Guidance from Toxbase (6)
previously published case reports and the experience of a cardiothoracic
nurse working on the critical care outreach team overnight were
pertinent to this outcome.
The decision to use Dobutamine (a B1-agonist) and Isoprenaline (a
non-selective beta agonist) over Atropine (an antimuscarinic alkaloid)
and Adrenaline (a non-selective alpha and beta agonist) meant the drug
administered were more cardio-specific than what may otherwise be used
and the aforementioned hypotension as a result of the non-specific
actions of adrenaline was not noted. However with hindsight, and having
received no ill effects on switching to an adrenaline infusion in the
ICU, we would have a lower threshold for using adrenaline in future
similar cases. External, and then later internal, pacing allowed for a
reduction in doses of both medications (and the total cessation of
Isoprenaline).
Without the pacing the underlying rhythm was asystole. Several previous
case studies have described successful outcomes after prolonged cardiac
arrests, and a review of 43 cases of Yew Tree poisoning found CPR was
required in 26 (60%) of cases (4). With this in mind, it may be
beneficial to have a Lucas or similar device available, if possible, to
save on staff resources, shall the patient deteriorate to cardiac
arrest. Replacing the fast patches the paramedics apply with hospital
parches may also be a consideration, as though they may be compatible
with hospital defibrillators you are not always able to pace through the
patches paramedics use.
The accidentally triggered emesis on the ICU admission covid-19 throat
swab may also have helped in this case. This episode occurred about 9
hours post ingestion of the seeds, and the regurgitation of whole and
partially digested seeds in the vomit may well have reduced subsequent
plasma levels of the taxine alkaloids and prevented any further
deterioration over the following days. Toxbase does suggest initiating
vomiting or using activated charcoal, but it was not deemed appropriate
in the initial management due to the fluctuating GCS and possible
aspiration risk. In future, earlier consideration of gastric emptying
could be considered.
Poisoning from Yew Tree seeds may become more prevalent, due to the easy
access to the toxic substance from online shops. We were lucky our
patient informed us of what he took, allowing the team to prepare for
his arrival adequately. Many patients who attempt suicide through
ingestion of substances may not share this information, and so
supportive therapy and treating symptoms may be the best option. In this
case, there was no direct antidote and so supportive therapy was also
all that was available. A successful outcome was obtained without the
need for ECMO by following the valuable guidelines of Toxbase, verbal
conversations with UK NPIS and the experience of the multi-disciplinary
acute care team. Whilst this case was managed successfully in a district
general hospital we would still recommend early discussion with UK NPIS
and the local ECMO centre, as early transfer to a more appropriate
centre may be required.