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The first thing to ask is: is this genuine
hypotension? By this I mean – what is this patient’s normal blood
pressure. Remember that the principle objective of targeted therapy is to
return the patient to the physiological range: the patient’s vital organs
perform optimally within certain perfusion pressure limits, below which
ischemia may result.
Step 1: if the patient is awake, communicating and
urinating, then he is probably not hypotensive.
In intensive care, patients are often sedated and cannot interact with
you, and the urinary output may be the only clinical sign of tissue
perfusion. If the patient is being treated with diuretics, then this is
lost. The other blunt measure of end organ perfusion is acid base balance:
look at the base excess (is it negative and by how much?); does the
patient have a lactic acidosis?
Step 2: is this measurement
error?
When addressing the information on arterial lines and non-
invasive cuffs, it is the mean pressure that is likely to be accurate. The
systolic pressure may over-read with a tight cuff, or under-read with a
damped arterial line trace. Often there is a considerable difference
between what is being read by the arterial line and the cuff. Care givers
tend to believe the measurement that is closest to the physiologic range.
This is illogical. If the patient’s arterial line is reading low, and
there is no objective evidence of good end-organ perfusion (mentation,
urine output), then the patient is hypotensive until otherwise proven.
Step 3: go to the notes / obtain a history.
You need to establish the patient’s baseline blood pressure. Look for a
measurement made at an outpatient appointment or on admission. Is the
patient on antihypertensive medications? If so – has his pressure been
controlled: is there evidence of end organ damage – left ventricular
hypertrophy with strain on the ECG? If you do not know what the patient’s
baseline blood pressure is, then assume a mean arterial pressure of
80mmHg. If you know that the patient has a history of hypertension, then
it is wise to aim higher, 90mmHg at least. Regardless of the predetermined
target, you must have an endpoint: i.e. drive the blood pressure upwards
until the patient starts urinating.
If you have confirmed
that the patient is indeed hypotensive then:
Step 4: look for an iatrogenic cause.
If the patient is being treated with agents that lower the blood pressure
– propofol, midazolam, morphine, nitroprusside etc, then stop these drugs,
and, if necessary, reverse their effects with phenylephrine (a specific
vasoconstrictor).
Step 5: Move on an look for a cause and
therapeutic strategy.
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