Date Published: January 30, 2019
Publisher: Public Library of Science
Author(s): N. Patrick Mayr, Gunther Wiesner, Angela Kretschmer, Johannes Brönner, Herbert Hoedlmoser, Oliver Husser, Albert M. Kasel, Rüdiger Lange, Peter Tassani-Prell, Wisit Cheungpasitporn.
Transfemoral Transcatheter Aortic Valve Implantation (TAVI) has become a standard therapy for patients with aortic valve stenosis. Fluoroscopic imaging is essential for TAVI with the anesthesiologist’s workplace close to patient’s head side. While the use of lead-caps has been shown to be useful for interventional cardiologists, data are lacking for anesthesiologists.
A protective cap with a 0.35 lead-equivalent was worn on 15 working days by one anesthesiologist. Six detectors (three outside, three inside) were analyzed to determine the reduction of radiation. Literature search was conducted between April and October 2018.
In the observational period, 32 TAVI procedures were conducted. A maximum radiation dose of 0.55 mSv was detected by the dosimeters at the outside of the cap. The dosimeters inside the cap, in contrast, displayed a constant radiation dose of 0.08 mSv.
The anesthesiologist’s head is exposed to significant radiation during TAVI and it can be protected by wearing a lead-cap.
To date about 350.000 transfemoral Transcatheter Aortic Valve Implantations (TAVI) have been performed  with more than 13.000 in Germany in 2015 alone . As periprocedural fluoroscopic imaging is essential, this procedure is done in cardiologic catheterization laboratories (CathLabs)  or specially designed Hybrid-ORs. As several steps of the procedure, may be painful to the patient or haemodynamically impairing, anesthesia managed care is mandatory for these patients. Thereby, the anesthesiologist’s workplace is close to the patient’s head side. Periprocedural pain and unrest, or cases of emergency may demand a close contact of the anesthesiologist to the patient. Furthermore, the X-ray protection, attached to the CathLab-table, is often deficient at the head-side and a head-sided position of the C-arm may further impede stationary X-ray protection. In recent years, radiation protection has become an important topic for the interventional cardiologists  and reports of an increased incidence of left sided brain tumors have been published [5, 6]. It has been shown that the use of lead caps and glasses could reduce the radiation exposure of the brain in this group [7–9]. Further data suggest that the occupational radiation exposure of the medical staff during TAVI is highly dependent on the access site used (e.g. transapical vs. transfemoral), protection shields, angulation of the C-arm and beam projection [10–13]. Such data is lacking for the anesthesiologist positioned at the head-side of the patient during TAVI. Therefore, this study was designed as a pilot and it was hypothesized that, despite the presence of a protective shield, the head of the anesthesiologist is exposed to radiation during TAVI procedures. Furthermore, it was investigated whether the use of a lead cap could reduce the radiation exposure of the head.
This trial was a single-center observational pilot-study performed at the Institut für Anästhesiologie, Deutsches Herzzentrum München, a university-hospital specialized in cardiovascular diseases, between February and March 2016. The decision for TAVI and the type of transcatheter valve was at the discretion of the institution´s heart team. All cases were conducted in the same catheterization laboratory using a Philips ALLURA XPER FD 10 X-ray system (Philips Medical Systems Nederland B.V., Best, Nederlands). Informed consent and ethical approval was waived by the ethical committee of the Technische Universität München, as the measurements were done during routine procedures.
During the observational period a total of 32 transfemoral TAVI procedures was conducted in the cardiologic CathLab within 15 working days. Patient´s baseline and procedural data are shown in Table 1.
Despite the presence of a radiation protection shield, the anesthesiologist´s head was exposed to radiation. This is due to the fact that the top height of the protective shield was at 145 cm while the anesthesiologist was 182 cm in height Furthermore, it could be shown for the first time in this real-life setting that the use of a particular protective cap facilitates a significant reduction of radiation, the acting anesthesiologist may be exposed to. Different other radiation protection caps are available, partially also covering the oral mucosa and parotis glands. All clinically evaluated models have shown the ability to reduce the radiation exposure significantly between 62% and 90% [7, 8, 20, 21] in interventional cardiologists. Our measurements showed a reduction of 83–85%. Therefore, the protective potential for the anesthesiologist appears to be comparable with those for interventional cardiologists.
The data obtained in this trial apply only for this specific equipment and setting and might not be generally applied. One limitation of this study is that the measured dose values in terms of Hp(3) exhibit somewhat large uncertainties due to the use of non-enclosed detectors and their placement inside and outside the lead cap. The uncertainties of the measurements were estimated by means of data from the uncertainty analysis of the HMGU extremity dosimeters  and by means of additional calibration measurements with the detectors and the lead cap on the ISO cylinder phantom  (head phantom) at the calibration facilities of the HMGU. All uncertainties in the following are given as expanded uncertainties  with a coverage factor of k = 2, i.e the 95% confidentiality level. The largest dose value outside the lead cap was 0.55±0.2 mSv, with the dominating uncertainty contributions arising from the energy response of the detector and statistical uncertainty. However, in the calibration measurements with the lead cap and a head phantom it was shown, that the presence of the lead cap shields the detector from backscattered radiation from the head phantom, therefore the actual value of the eye lens dose for a person not wearing a lead cap would be about 15%-25% higher depending on the radiation quality. The measured values inside the lead cap are in the order of 0.08±0.03 mSv. In this case the detector is used near the detection limit, which increases the uncertainties mostly due to background subtraction, however this effect could be alleviated by means of dedicated background dosimeters. Even though the measurement uncertainties are pronounced at these small dose values, the relative measurement between the outside and inside levels, i.e. the determined decrease of 85% exhibits a comparatively smaller uncertainty of approximately 11% due to the laws of error propagation. Therefore, the conclusion of the effectiveness of the shielding capability of the lead cap is valid.
In this pilot study, we hypotized that the head of the anesthesiologist is exposed to radiation during TAVI. Furthermore, we evaluated the use of a lead cap to reduce the radiation exposure. In 32 uneventful TAVI procedures, the head was exposed to significant radiation. This primary due to the fact, that the protective shield was lower than the head of the anesthesiologist during routine care. As the anesthesia equipment and monitoring was placed on the right head side of the patient, the radiation exposure of the anesthesiologist´s head was highest on the left side. By wearing the lead cap during these procedures, a reduction of the heads radiation exposure of about 85% was achieved. Despite these findings, structural radiation protection, like protection shields, still remains of high importance.