gms | German Medical Science

Objective: The function of gravitational (g)-valves is strictly dependent on the angle of vertical alignment. Therefore they require an orientation strictly parallel to the longitudinal body axis. Despite its decisive role only 1 out of 166 g-valve-papers (incl. running studies) systematically investigated g-valve-deviation from body axis (= flaw angles). Furthermore, the implantation site on the lateral head has not been compared to the thoracic site.

Methods: From our medical record of about 650 g-valve-implanted patients with retroauricular and thoracic gravitational devices, each 50 consecutive patients were extracted and randomized. On scout-scans / x-rays the deviations against the body axis were measured. The impact on g-valve-function and the additional effect of 30° head elevation were calculated.

Results: Only 22% of retroauricular vs. 28% of thoracic implantations were correctly placed (flaw angle <10°). Cranially placed valves showed anteversion in 84% and retroversion in 16%. The mean deviation was 21° implying a valve-offset of 72mm H₂O in a 200mm H₂O-g-valve, the maximum was 43° (valve-offset: 136mm H₂O). A nocturnal head elevation of 30° may result in a mean valve-offset of 156mm H₂O calculated with the mean deviation angle, and 191mm H₂O in the worst case. In thoracic position the mean deviation was 10° in lateral and 16° in antero-posterior direction implying a valve-offset of 55mm H₂O in a 200mm H₂O-valve. Maximal deviation was 52° resulting in valve-offset of 158mm H₂O.

Conclusions: Positioning failures are common in our series and may indicate malfunction of g-valves. The thoracic implantation site is clearly superior to the head position and should therefore be preferred in adults.