Can Thrills of AVF/AVG Diminish in Cases of Hypotension?
Yes, thrills over an arteriovenous fistula (AVF) or arteriovenous graft (AVG) can diminish during hypotension due to reduced intra-access blood flow, though this is not explicitly detailed in the KDOQI guidelines as a primary clinical indicator.
Understanding the Mechanism
The palpable thrill represents blood flow through the AV access, and any condition that reduces flow through the access circuit can diminish or alter the thrill. While the 2019 KDOQI guidelines 111 extensively describe abnormal thrills as indicators of stenosis, they also acknowledge that "many variables affect their measurements" and specifically note that flows and pressures are related to "patients' response to it (eg, hypotension)" 1.
Clinical Context from Guidelines
The KDOQI guidelines 11 describe normal physical examination findings:
- Normal thrill: Should be palpable at the arterial anastomosis and throughout the entire outflow vein (AVF) or over the entire graft (AVG), and should be "easy to compress"
- Abnormal thrill: Described as "weak and/or discontinuous" with only a systolic component, typically indicating stenosis 1
However, the guidelines note that an AVG with low intra-access blood flow "feels mushy" 11, which directly supports that reduced flow states affect the palpable characteristics of the access.
Hypotension as a Confounding Variable
The KDOQI guidelines 1 explicitly state that surveillance measurements can be affected by "patients' response to it (eg, hypotension)" and that "flows and pressures are related to the hemodialysis procedure, patients' response to it (eg, hypotension), the AV access, and AV access circuit anatomy." This acknowledgment indicates that hypotension is a recognized variable that affects access hemodynamics and, by extension, physical examination findings.
Critical Clinical Pitfall
The major caveat is distinguishing between a diminished thrill from hypotension versus one from stenosis or thrombosis. The ACR Appropriateness Criteria 222 emphasize that changes in access thrill or bruit warrant investigation, with up to 90% of accesses with abnormal physical examinations having an underlying clinically significant finding on imaging 222.
Practical Approach:
- If hypotension is present: Reassess the thrill after blood pressure normalizes
- If thrill remains diminished after BP correction: This suggests underlying stenosis or access dysfunction requiring imaging (fistulography or Doppler ultrasound) 222
- If thrill is completely absent: Consider thrombosis as a primary concern, regardless of blood pressure status
Supporting Evidence
Research data 3 demonstrates that venous pressure correlates with thrill presence—patients with a palpable thrill had mean systolic venous pressures of 35.8 mm Hg, while those without a thrill had pressures of 102.6 mm Hg. This suggests that hemodynamic alterations, including those from systemic hypotension affecting arterial inflow, can impact thrill characteristics.
Bottom Line
While hypotension can transiently diminish the thrill through reduced flow, any persistent change in thrill quality warrants further evaluation to exclude stenosis or thrombosis, as these represent the primary threats to access patency and patient outcomes. The thrill should return to baseline once blood pressure is restored; failure to do so mandates imaging evaluation per KDOQI and ACR guidelines 122.