To the Editor:--Transcranial Doppler ultrasonography allows continuous noninvasive monitoring of cerebral blood flow velocity and represents an important advance in our ability to monitor intra-cranial hemodynamics. [1]There are practical limitations to its routine intraoperative application, one of which is the constancy of the angle of insonation, i.e., the angle between the direction of the probe and the direction of the artery segment being insonated. Many commercial fixation devices are available, all of which are based on a head-band or head-strap design. Although these devices are functional, they preclude use of the monitor in neurosurgical procedures, which is arguably the area where it can be most useful.
We wish to report our experiences with a custom-designed attachment system (in collaboration with DWL, Electronics, Sipplingen, Germany) using car inserts and a foam-padded nose rest to anchor the system, leaving the head unencumbered (Figure 1and Figure 2). The side-mounted transducers are equipped with swivel locks to fix the position, and the thumb wheel mounted on the nose rest allows alteration of tension to achieve optimal signals. With the exception of neurosurgical procedures using subtemporal incisions, its deployment causes no interference. We have used this system successfully for intraoperative monitoring in 12 cases with good results.
Figure 1. The fixation frame viewed from above. The ear inserts and the foam-padded nose rest are used to anchor the frame without interfering with the potential surgical field. The adjustable Doppler transducers are mounted on the side-arms.
Figure 1. The fixation frame viewed from above. The ear inserts and the foam-padded nose rest are used to anchor the frame without interfering with the potential surgical field. The adjustable Doppler transducers are mounted on the side-arms.
Figure 2. The frame applied to a patient undergoing craniotomy for resection of a frontal-parietal arteriovenous malformation.
Figure 2. The frame applied to a patient undergoing craniotomy for resection of a frontal-parietal arteriovenous malformation.
Arthur M. Lam, M.D.; Professor of Anesthesiology and Neurological Surgery; University of Washington School of Medicine; Department of Anesthesiology; Harborview Medical Center; 325 Ninth Avenue, ZA-14; Seattle, Washington 98104.
(Accepted for publication March 13, 1995.)
