Continuous Measurement of Critical Closing Pressure using Readily Available Blood Pressure Monitors for Treatment of Circulatory Shock in Critically Ill Patients

• Management of circulatory shock requires blood pressure monitoring:
  • Treatment of circulatory shock in critically ill patients requires management of blood pressure using invasive monitoring.
  • Optimal individual blood pressure targets remain uncertain.
• Critical closing pressure provides unique information:
  • Critical closing pressure measures vascular tone in response to disease and therapy.
  • A new method allows continuous measurement of critical closing pressure in the systemic circulation using readily available blood pressure monitors.
  • Tissue perfusion pressure (TPP), the difference between mean arterial pressure and critical closing pressure, provides unique information compared to other hemodynamic parameters.
• TPP predicts risk of mortality and other outcomes:
  • Tissue perfusion pressure (TPP) can predict the risk of mortality, length of hospital stay, and peak blood lactate levels.
  • TPP may provide an additional target for blood pressure optimization in patients with circulatory shock.
• Circulatory shock is a common reason for ICU admission:
  • Circulatory shock is one of the most common reasons for admission to an intensive care unit (ICU).
  • Prompt treatment is required to reverse the cause and prevent severe organ injury and death.
• Pressure drop across circulation depends on inflow arterial pressure and outflow pressure:
  • The pressure drop across the circulation depends on both inflow arterial pressure (mean arterial pressure - MAP) and outflow pressure.
  • The outflow pressure is conventionally taken as central venous pressure (CVP).
  • The systemic circulation has a critical closing pressure (Pcrit) that is the arterial pressure when blood flow stops and circulation collapses.
  • Perfusion pressure driving flow is the difference between MAP and Pcrit.
• Estimation of Pcrit and TPP from arterial blood pressure waveforms:
  • Pcrit can be estimated in a patient with intact circulation by knowing at least two points on a plot of cardiac output (CO) versus mean arterial pressure (MAP).
  • Pcrit can be continuously estimated from available arterial blood pressure (ABP) monitoring devices such as an indwelling arterial catheter.
  • Variability in ABP over short time periods can be used to estimate Pcrit.
  • A linear fit to the scatterplot of PP (pulse pressure) multiplied by HR (heart rate) versus MAP provides the zero-flow intercept as Pcrit.
• Relationship of TPP and Pcrit to conventional hemodynamic measures:
  • Tissue perfusion pressure (TPP) provides unique information compared to mean arterial pressure (MAP) and central venous pressure (CVP).
  • Pcrit and TPP have broader and more complex distributions compared to MAP.
  • TPP shows a modest linear relationship with systemic vascular resistance (SVR) at low SVR and flattens out at higher SVR.
• TPP monitoring can provide unique information in the ICU:
  • Continuous TPP monitoring can provide unique information for individual patients in the intensive care unit (ICU).
  • TPP can help optimize blood pressure management in patients with circulatory shock.
• TPP has a complex relationship with CO and Pcrit intervals.:
  • TPP increases with incrementally lower Pcrit levels.
  • A higher vasoactive inotrope score (VISmax) corresponds to lower mean TPP.
  • VISmax predicts mortality with high significance.
• TPP adds value to MAP for risk prediction.:
  • Optimal TPP threshold of 34 mmHg best separates short stay and long stay/death groups.
  • Differences in mortality, length of stay, and maximum lactate are highly significant based on stratifying patients by MAP and TPP thresholds.
  • TPP provides additional discriminatory information beyond MAP in critically ill patients.
• External validation using the MIMIC III database supports the validity of TPP.:
  • Optimal thresholds for MAP and TPP in the MIMIC cohort are consistent with those derived from the MGH cohort.
  • TPP can separate outcomes with statistical significance.
  • TPP adds value to MAP in the external cohort.
• TPP trajectories and their relationship to outcomes.:
  • Four common TPP trajectories are identified: uniformly low, uniformly high, increasing, and decreasing.
  • Lower TPP correlates with higher lactate values and worse tissue perfusion.
  • Clusters with lower TPP have higher mortality, reoperation rates, prolonged mechanical ventilation, and increased length of stay.
• Continuous TPP monitoring in clinical practice.:
  • Real-time monitoring of Pcrit and TPP along with MAP and other clinical variables is possible.
  • TPP calculation with 1-min resolution allows for individual patient assessment.
  • Hemodynamically unstable patients exhibit high Pcrit and low TPP.
• Measurement of Critical Closing Pressure:
  • Continuous measurement of critical closing pressure (Pcrit) in patients using readily available blood pressure signals without perturbing circulation or cardiovascular function.
  • Serial measurements of Pcrit in thousands of patients and extension of the concept to define the metric of total pressure drop (TPP) across the intact circulation.
• Advantages and Assumptions of the Method:
  • Method takes advantage of intrinsic variability in cardiac output (CO) to estimate Pcrit.
  • Assumptions include constant vascular resistance (Rs) within short time windows and PP × HR as a valid approximation of CO.
  • High-frequency sampling and basic filtering used to remove artifacts and ensure accuracy of linear fit.
• Hemodynamic Information and Clinical Utility:
  • Pcrit provides unique information compared to mean arterial pressure (MAP), cardiac output (CO), and systemic vascular resistance (SVR).
  • Total pressure drop (TPP) may serve as an additional target for blood pressure management in heart failure and circulatory shock.
  • TPP allows individualization of hemodynamic management and optimization of fluid balance.
• Alternative Monitoring Strategies:
  • Pcrit and TPP provide a readily available alternative for advanced hemodynamic monitoring in critically ill patients.
  • Potential application to noninvasive blood pressure monitors and monitoring in standard medical floors or ambulatory settings.