Lack of reproducibility in pregnancy of Korotkoff phase IV as measured by mercury sphygmomanometry

Background Since hypertensive disorders of pregnancy are common, blood pressure is frequently measured in all pregnant women. Many authorities recommend that Korotkoff phase IV (K4, muffling of sound) is taken as the diastolic identification point measured on mercury sphygomanometry in pregnancy because of reports that phase V (K5, disappearance of sound) is at or near to zero cuff pressure in some pregnant women, We compared the identification and reproducibility of K4 and K5 by observers unaware of each other's results. Methods In the first part of the study, two pairs of observers each took 340 measurements in 85 pregnant women. The second part of the study consisted of 1120 measurements in 80 pregnant and 80 non-pregnant women by five pairs of observers. Measurements were taken simultaneously by sphygmomanometry with a shared cuff and diaphragm; the observers were in separate booths. Findings K5 was identified in all measurements by both observers and never approached zero. K4 was heard in only 52% of measurements; in 33% of cases it was heard by only one of the pair of observers, so the pair agreed on its detection in only 19% of readings. Visual analogue scores used to assess Korotkoff sound quality indicated that systolic blood pressure was perceived significantly more clearly than diastolic blood pressure (K4 or K5). Even when K4 was heard by both observers, agreement an its value was poor (78% within 5 mm Hg vs 86% for K5, p<0.05). K4 was heard significantly less often in non-pregnant women (32% of measurements). There was also no consistency in the identification of K4 within individual women. Interpretation K4 has little value in clinical management because it cannot be reproduced accurately. We recommend that K4 should be replaced by K5 as the measure of diastolic blood pressure in pregnancy.