VNERi and the vascular tone

Case report: An 85 YO female with a history of HF with preserved EF came in for respiratory distress with labile blood pressure resulting in the initiation of norepinephrine after a small bolus of 500 ml LR. VS: HR 110, BP 84/36 (MAP 52),RR 29, Saturation 91% on 10 L. POCUS revealed IVC <50% collapsible, hypodynamic heart, and B-lines to L3. An arterial line placement and a central line were initiated. She was placed on the Edwards Hemosphere after the initiation of NorEpi with the following reading: CO 7.8, SV 70, SVR 500. BP 150/49, vasopressin was then added. What is going on here?

Introduction

Bedside tools assess vascular tone (DAP and DSI) and response to norepinephrine (NE), crucial for managing patients in septic shock through personalized vasopressor management. They provide real-time data to optimize NE initiation and guide additional vasopressor use if target mean arterial pressure (MAP) is not met. Continuous VNERi evaluation enhances fluid resuscitation and tailored interventions, ultimately improving patient outcomes in septic shock.

DAP: diastolic arterial pressure DSI: DIastolic shock index

DSI and the initiation for first line vasopressor

The diastolic shock index (DSI = HR/DAP) is suggested as a better way to estimate vascular tone than DAP alone and is a stronger predictor for septic shock. Values above 3.3 were linked to higher mortality. This might have suggested a trigger for NE initiation. Hence the initiation of norepi.

Why are we not titrating the NE when the SBP is in the 150’s?

Low DAP (diastolic arterial pressure) typically results from arterial stiffening in older adults, with increased systolic aortic pressure and decreased diastolic pressure due to reduced elastic recoil. This patient’s DAP remained low reflecting an SVR of 500.

Quick pathophysiology

Vascular dysfunction involves lower vascular tone, causing arterial hypotension and multiple organ dysfunction syndrome (MODS) even with high cardiac output. Patients who increase their cardiac output with fluid therapy show reduced systemic vascular resistance after infusion. Norepinephrine is the primary vasopressor for septic shock, but a second vasopressor may be needed if norepinephrine does not reach target levels. Diastolic arterial pressure (DAP) and heart rate (HR) are useful tools for determining this. Studies indicate that a DAP below 44 mmHg is associated with higher mortality rates in septic shock, making this threshold important for initiating vasopressor treatment.

The role of VNERi in determining second line vasopressor

Recently, a vascular norepinephrine responsiveness index (VNERi) has been proposed to identify vascular hyporesponsiveness to NE by combining DAP, HR, and NE dose. Impaired vasomotor tone responsiveness results from mechanisms such as alpha-adrenergic receptor downregulation and excessive cytokine production, leading to inadequate arteriolar constriction in response to norepinephrine (NE) and persistent hypotension. Adding another vasopressor can mitigate the need for higher NE doses and minimize adverse effects.

VNERi = DAP/(HR × NE dose) (NE dose expressed in µg/(kg·min)), This index was evaluated in the ANDROMEDA-SHOCK database.

The patient was eventually titrated off her 02 requirements, decreased norepi dose from 20mcg/min to 5 with vasopressin at 0.04 u/min and an SVR maintained at >800.

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