Tissue perfusion pressure a potential target to guide clinical care of circulatory shock
Key takeaways:
- Tissue perfusion pressure may be a new target for BP optimization in circulatory shock.
- TPP was significantly associated with mortality, hospital stay and blood lactate value.
Continuous hemodynamic evaluation of tissue perfusion pressure may provide unique insights to guide clinical care of patients with circulatory shock and predict adverse in-hospital outcomes, researchers reported.
Aaron D. Aguirre, MD, PhD, cardiologist and critical care physician and assistant professor of medicine at Harvard Medical School, and colleagues at Massachusetts General Hospital and the Massachusetts Institute of Technology developed a novel assessment to improve hemodynamic monitoring in patients admitted to the cardiac ICU with circulatory shock.
“Current approaches to managing patients with circulatory shock from causes such as sepsis or HF rely on the average BP as the primary target for optimizing treatment strategies. This mean arterial pressure, or MAP, has proven to be an inadequate single measure of the state of blood flow or perfusion to vital organs,” Aguirre told Healio. “We sought to develop a new metric based on the underlying physiology of the circulation that could provide additional guidance to physicians managing patients with advanced HF and shock.”
TPP for hemodynamic evaluation in circulatory shock
For this study, Aguirre and colleagues tested the prognostic value of tissue perfusion pressure (TPP) — defined as the difference between MAP and critical closing pressure — in an analysis of 5,988 cardiac ICU admissions at Massachusetts General Hospital and an external validation cohort of 864 admissions culled from the Medical Information Mart for Intensive Care III database.
“Our approach revisits a fundamental property of the circulation known as the critical closing pressure, which is the arterial pressure at which small vessels collapse and blood flow stops,” Aguirre told Healio. “This parameter was studied decades ago by physiologists but has been historically difficult to measure in patients where blood flow cannot be readily stopped. We used engineering principles to develop a simplified circuit model of the circulation and to estimate the critical closing pressure from the natural variation in blood flow and BP with respiration. This then allowed us to define a new measure of perfusion, the tissue perfusion pressure or TPP, as the MAP minus the critical closing pressure.”
Patients with a short hospital stay — less than 14 days — were compared with those with a longer composite of long stay or death during hospitalization based on MAP and TPP values during the first 24 hours of their postoperative ICU stay.
MAP and TPP were significantly different between the patients with a short compared with longer hospital stay (P < .0005), according to the study, with the optimal thresholds for separating outcome groups deemed to be 34mm Hg for TPP and 74 mm Hg for MAP.
Based on these thresholds, the researchers reported that increased TPP was significantly associated with reduced mortality rate (P < .00005), mean length of stay (P < .0005) and maximum lactate value (P < .00005).
Moreover, the external validation cohort reinforced prognostic value of TPP when added to MAP.
‘TPP correlates strongly with important outcomes’
“The main takeaways are that critical closing pressure and tissue perfusion pressure can now be measured from standard arterial BP waveforms used routinely in the ICU,” Aguirre told Healio. “The TPP correlates strongly with important outcomes in cardiac intensive care patients, including the mortality, length of hospital stay and peak blood lactate levels. TPP may therefore provide a new target for optimizing therapies in patients with circulatory shock.
“This study was a collaboration between engineers and physicians at the Massachusetts General Hospital and the Massachusetts Institute of Technology. The work represents an exciting example of how engineering methods applied to outstanding clinical problems can advance our understanding of complex physiology and inform new approaches to diagnosis and treatment,” Aguirre said.
For more information:
Aaron D. Aguirre, MD, PhD, can be reached at aguirre.aaron@mgh.harvard.edu.
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