A blood pressure reading that is consistently lower than 90/60 mmHg is termed as low blood pressure or hypotension, while a reading over 140/90 mmHg is termed as high blood pressure or hypertension. A new study by Puja Myles and Sudhir Venkatesan from the University of Nottingham in Britain and colleagues has revealed that patients with low blood pressure before an operation are at an increased risk of death during or after the surgery than those with preoperative high blood pressure.
The study said, "While high blood pressure control is important for long-term health, high blood pressure itself does not impose a significant risk of postoperative death."
Researchers used data from 252,278 patients from the United Kingdom Clinical Practice Research Datalink to perform their analysis. A number of models of varying complexities were used to account for 29 perioperative risk factors including age, gender, race, co-morbidities, medications and surgical risk score. Perioperative refers to the three phases of surgery- preoperative, intraoperative and postoperative.
After adjustment for the risk factors, the effect of high blood pressure was not found to be associated with increased odds of post-surgery mortality. However, preoperative low blood pressure was associated with statistically significant increases in the odds of perioperative mortality rate. For patients with a systolic blood pressure (the bottom number) of below 100 mmHg, the likelihood of death increased by 40%. For those with a diastolic blood pressure (the bottom number) of under 40 mmHg, the likelihood of death increased by 2.5 times. While the risk from low BP was present in patients with low systolic or low diastolic pressure, values below 100/40 were of the greatest risk. Hence, the likelihood of death further increased as either or both systolic or diastolic blood pressure decreased further.
The researchers said, "Preoperative low blood pressure is under-recognized as a risk factor for perioperative mortality. Future studies will need to identify how this risk can be modified to improve patient outcomes."
This study was presented at Euroanaesthesia 2015, the European Anesthesiology Congress, in Berlin, Germany.