Postoperative hypertension is a sign before it is a number

Why it matters

A high blood pressure in the PACU is one of the commonest reasons a nurse calls a resident, and the commonest response is to treat the number. The sources on this day say the number has no evidence-based threshold. The POQI statement on perioperative arterial pressure records that, for adult noncardiac surgical patients, there is insufficient evidence to recommend a general upper limit at which therapy should be initiated, although pressures above 160 mmHg have been associated with myocardial injury and infarction sessler-2019-d6. That is the strongest available statement that the number itself is not the treatment target.

The consequence of getting this wrong is a patient whose pain, full bladder or rising carbon dioxide is treated with a vasodilator. The pressure falls and the cause remains.

Mechanism

Blood pressure rises after surgery when the sympathetic nervous system is driven by something. In the PACU the drivers are mostly ordinary and mostly reversible: pain, a distended bladder, hypercarbia from hypoventilation, hypoxaemia, shivering and cold, anxiety, and the abrupt withdrawal of an antihypertensive the patient takes at home. Each raises catecholamine output, heart rate and vascular tone. A vasodilator lowers the pressure by acting on the last step in that chain; it does nothing to the first. The mechanism therefore dictates the sequence: find what is driving the sympathetic response and remove it, and treat the pressure directly only when nothing reversible explains it or the level itself threatens harm.

Evidence

The POQI consensus statement is the primary source. For adult noncardiac surgical patients it finds insufficient evidence to recommend a general upper limit of arterial pressure at which therapy should be initiated, while recording that pressures above 160 mmHg have been associated with myocardial injury and infarction sessler-2019-d6.

The 2013 ASA guideline on postanesthetic care states that the literature continues to be insufficient to evaluate the impact of cardiovascular assessment and monitoring, or of routine electrocardiographic monitoring, on perioperative complications asa-pacu-2013-d6. The same guideline states that assessment of urine output and voiding should be done case by case, which is the bladder limb of this day’s differential asa-pacu-2013-d6.

What this does not show

Neither source tests any treatment of postoperative hypertension against any outcome. The POQI document is a consensus statement and the ASA document is a guideline that describes its own literature as insufficient sessler-2019-d6 asa-pacu-2013-d6. The association above 160 mmHg is an association, and the statement that draws attention to it declines, in the same sentence, to turn it into a threshold sessler-2019-d6.

The differential itself, pain, bladder distension, hypercarbia, hypoxaemia and drug withdrawal, is clinical reasoning that the held sources support only in part: the bladder limb is in the ASA guideline, and the rest is physiology asa-pacu-2013-d6. [TODO_VERIFY: a source for abrupt antihypertensive or clonidine withdrawal as a cause of PACU hypertension, before it appears in a quiz item.]

This day has two ledger rows, both consensus documents, and no primary study. It is the thinnest day with sources on the site, and the topic term it carries was added to the vocabulary for it.

At the bedside

When the pressure is high, examine the patient before you examine the drug chart. Ask about pain and look at the analgesia given. Palpate or scan the bladder. Look at the respiratory rate and depth, the capnograph if there is one, and the saturation. Check the temperature and whether the patient is shivering. Ask what antihypertensives they take at home and when the last dose was.

Treat what you find. A pressure that falls when the pain is treated or the bladder is emptied was never a hypertension problem.

If nothing reversible explains it and the level is one you judge dangerous for this patient, then treat the pressure, knowing that no general threshold has evidence behind it and that the number above which injury has been associated is 160 mmHg sessler-2019-d6. [PRACTICE VARIES: the pressure at which a PACU protocol calls for direct treatment, and the agent used, differ between institutions; follow local protocol and know that the threshold is a local decision, not an evidence-based one.]

Check yourself

Three items. Every option carries an explanation. Progress is not saved.