A surgical instrument comprising: (a) an ultrasonic transducer; (b) a shaft extending distally relative to the ultrasonic transducer along a longitudinal shaft axis; (c) a waveguide acoustically coupled with the ultrasonic transducer and extending distally through the shaft; (d) an end effector arranged at a distal end of the shaft, wherein the end effector includes an ultrasonic blade acoustically coupled with the waveguide, wherein the ultrasonic transducer is operable to drive the waveguide and the ultrasonic blade with ultrasonic energy; and (e) a nodal support element arranged within a distal portion of the shaft, wherein the nodal support element encircles the waveguide at a distal-most acoustic node thereof, wherein the nodal support element comprises: (i) a support portion aligned with the distal-most acoustic node, wherein the support portion is configured to engage an inner surface of the shaft and thereby support the waveguide in coaxial alignment with the shaft axis, wherein the support portion includes a plurality of deformable elements spaced circumferentially about an exterior thereof, wherein the deformable elements are configured to deform against the inner surface of the shaft; and (ii) a sealing portion extending axially from the support portion, wherein the sealing portion is configured to sealingly engage the inner surface of the shaft and thereby prevent proximal ingress of fluid through the shaft. (a) an ultrasonic transducer; (b) a shaft extending distally relative to the ultrasonic transducer along a longitudinal shaft axis; (c) a waveguide acoustically coupled with the ultrasonic transducer and extending distally through the shaft; (d) an end effector arranged at a distal end of the shaft, wherein the end effector includes an ultrasonic blade acoustically coupled with the waveguide, wherein the ultrasonic transducer is operable to drive the waveguide and the ultrasonic blade with ultrasonic energy; and (e) a nodal support element arranged within a distal portion of the shaft, wherein the nodal support element encircles the waveguide at a distal-most acoustic node thereof, wherein the nodal support element comprises: (i) a support portion aligned with the distal-most acoustic node, wherein the support portion is configured to engage an inner surface of the shaft and thereby support the waveguide in coaxial alignment with the shaft axis, wherein the support portion includes a plurality of deformable elements spaced circumferentially about an exterior thereof, wherein the deformable elements are configured to deform against the inner surface of the shaft; and (ii) a sealing portion extending axially from the support portion, wherein the sealing portion is configured to sealingly engage the inner surface of the shaft and thereby prevent proximal ingress of fluid through the shaft. (i) a support portion aligned with the distal-most acoustic node, wherein the support portion is configured to engage an inner surface of the shaft and thereby support the waveguide in coaxial alignment with the shaft axis, wherein the support portion includes a plurality of deformable elements spaced circumferentially about an exterior thereof, wherein the deformable elements are configured to deform against the inner surface of the shaft; and (ii) a sealing portion extending axially from the support portion, wherein the sealing portion is configured to sealingly engage the inner surface of the shaft and thereby prevent proximal ingress of fluid through the shaft.