P-on-U Phenomenon in Hypokalæmia

Report:

Sinus rhythm

Non-specific ST/T changes

Prominent U waves consistent with hypokalæmia

Comment:

The patient was in fact hypokalæmic at 2.9 mEq/L - a frequent finding in sick alcoholics, especially after prolonged vomiting with attendant alkalosis. The ECG normalised with potassium replacement ( Fig 202a below).

T waves are flat, with prominent U waves; P waves fall on the descending limb of the U wave. The P-on-U pun is of course Schamroth’s145.

202a.

203. Ventilated 26 year old man with pulmonary œdema of the right lung and hypoplasia of the left pulmonary artery

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