2. Considerations and indications for ICU admission following poisoning
Commonly used severity of illness models such as the Acute Physiology and Chronic Health Evaluation (APACHE) scoring system are not validated for poisoned patients. Caution should therefore be exercised when thinking about applying them to predict who may require ICU admission following poisoning.
Several factors must be considered when thinking about an ICU admission for poisoning. These include:
i) Poison-induced end-organ toxicity
ii) Poison characteristics (pharmacodynamics)
iii) Patient characteristics (pharmacokinetics)
iv) What an ICU can offer the poisoned patient over other departments
These are discussed in more detail below. Before considering any of the above though, the initial assessment of the patient with possible poisoning should always assume the traditional ABCDE approach (see the assessment of the critically ill patient module).
Above all, when you are assessing a critically ill patient with poisoning and you are wondering whether they would benefit from intensive care nothing is more useful than both experience (your seniors!) and good clinical judgement.
Poison-induced end-organ toxicity
Regardless of what poison has been taken, when there is profound derangement of physiology it may be necessary to, at least initially, treat this rather than the poison itself. Think “treat the patient, not the poison”. This may be especially true in the case of poly-agent poisoning.
The following is a list of system based end-organ toxicities that may be seen in acute poisoning, all of which may benefit from ICU intervention:
a) Respiratory: refractory hypoventilation, hypoxia, acute lung injury
b) Cardiovascular: hypertension, hypotension, tissue ischaemia, arrhythmia
c) Neurological: depressed conscious level, delirium, status epilepticus
d) Gastrointestinal: acute hepatic failure, vomiting and aspiration risk
e) Genitourinary: acute kidney injury
f) Metabolic: metabolic acidosis, electrolyte disturbance
When presented with a critically ill patient displaying any of the above but with no other diagnosis one must always think about poisoning as a potential cause and investigate and treat accordingly. This is especially true in elderly patients, and those with unexplained acute hepatic failure.
Poison characteristics (pharmacodynamics)
a) Predictable side effects:
Sometimes when the poison is known, there may be predictable complications such as those listed above that may warrant ICU admission, for example, cardioactive drugs.
b) Sustained-release preparations:
Even when ICU admission is not warranted immediately, if sustained release preparations have been ingested patients may predictably deteriorate later.
Patient characteristics (pharmacokinetics)
a) Older patients with less physiological reserve
b) Pre-existing renal impairment
c) Pre-existing hepatic impairment
These patients may suffer significant compromise due to poisoning as they are less able to metabolise and eliminate poisons effectively. As a result they may suffer either prolonged toxicity, or toxicity at lower doses.
What an ICU can offer the poisoned patient over other departments
More often than not in critically ill poisoned patients, supportive care measures rather than poison specific antidotes offer the greatest chance of reducing morbidity and mortality. The ICU is therefore ideally placed to offer this, including:
a) Mechanical ventilation
b) Continuous invasive monitoring (arterial, central venous and cardiac output)
c) Vasopressor, inotropic, chronotropic drug support
d) Temporary transvenous cardiac pacing
e) Ability for seizure control including the use of thiopentone coma
f) Temporary renal replacement therapy
g) 1-to-1 Nurse to patient ratio
h) Regular medical review
i) All the above in addition to a safe environment for suicidal patients