March 31, 2016

ICM ARTICLE REVIEW

The management of shock is inexorably linked to blood pressure. Targeting specific mean arterial blood pressure (MAP) values in shock elicits considerable debate and has recently been the focus of a number of research articles. Supporting organ perfusion and by extension organ function in the face of circulatory collapse remains uncontested. However, the article “Higher versus lower blood pressure targets for vasopressor therapy in shock: a multi-centre pilot randomised controlled trial” highlights yet again the paucity of evidence in regards to which blood pressure values should be targeted in shock. Conventionally, MAP values greater than 65mmHg have been recommended and manipulation with vasopressor therapy is relatively straightforward. Despite being widely accepted practice the evidence base remains elusive. Thus, the blood pressure value that should be targeted clinically alongside optimal vasopressor therapy remains unknown.

Lamontagne et al. describe a multi-centre open label feasibility study involving 118 adult patients with presumed vasodilatory shock randomly allocated to a target MAP of 60-65mmHg or 75-80mmHg. The primary outcome was to assess whether a measurable difference in mean MAP values between groups could be achieved. In attempt to glean additional information for a future study, mortality and functional outcome data as well as data around vasopressor therapy was collected (complications, duration, fluid therapy etc). Study MAP targets were followed regardless of transfers and surgical interventions. Administration of fluids, inotropes and corticosteroids were at the discretion of the treating critical care teams. There were no differences in baseline characteristics except for a higher proportion of chronic hypertensive patients being in the lower MAP group as compared with the higher MAP group (57% vs 33%).

Results:

  • The primary outcome of the trial was clearly achieved demonstrating a difference in mean MAP values between both groups (9mmHg, 95% CI 7-11).
  • Achieved MAP was frequently above the prescribed dosing range in the lower MAP group (70mmHg) cf higher MAP group (79mmHg).
  • The higher MAP group had longer and higher infusion rates of vasopressor compared to the lower MAP group.
  • The higher MAP group had a greater usage of blood products.
  • A clear distinction in MAP was not achieved in the chronic congestive heart failure subgroup.
  • All further secondary endpoints showed no difference between both groups, including mortality and adverse events.

Take home messages

  • This trial clearly answers its primary objective of being able to achieve a purely numerical distinction between target MAP groups. However, is an average difference of 9mmHg between groups clinically relevant enough? The achieved MAP in both groups was almost exclusively above the prescribed range especially in the lower MAP group. A feature not limited to this paper but one, which could nullify the ability to draw conclusions about the clinical implications of specific MAP targets.
  • The increased blood product use in the higher MAP group implies that the mere introduction of an approach to increase MAP could also increase the intensive use of other therapies. Hence, important confounding factors such as the differential use of inotropes, blood products and corticosteroids need careful consideration in larger studies.
  • Given that achieving distinctive MAP targets in certain cohort of patients (e.g. congestive heart failure) proved difficult, should any larger trial incorporate a composite of physiological targets e.g. MAP, cardiac output and oxygen delivery.

This excellent scoping study by the Canadian Critical Care Trials Group informs the future design of a larger trial. Most importantly, the need to attain the prescribed MAP target in each group and given the multi-factorial management of patients with vasodilatory shock, the potential need to account for multiple confounding variables.

This article review was submitted by Michael Berry and Brijesh Patel on behalf of the ESICM NEXT Committee.

Reference

Lamontagne F et al. Higher versus lower blood pressure targets for vasopressor therapy in shock: a multi-centre pilot randomised controlled trial. Intensive Care Medicine, Original, Volume 42, Issue 4 / April, 2016, Pages 542 – 550

Comment on this news