Intraoperative imaging is a ubiquitous tool in neurosurgery, cranial and spinal procedures.
Mobius Airo TruCT (Shirley, Massachusetts, United States) is the largest inner bore,
mobile intraoperative computed tomography (CT) imaging system that seamlessly integrates
into an operating room (OR) setup.[1] In transport mode, the ring is aligned with the base, and the scanner moves on the
ramp to the desired location for scanning of the operative site. An intraoperative
imaging system that gives high-quality images and a wide field of vision in both two-
and three dimensions is provided by this device. There are few reports on use of intraoperative
CT in neurosurgery and spine surgeries.[2]
[3]
[4] There is a paucity of literature on the ergonomics of CT scanner location, anesthetic
workstation placement, and patient alignment for CT-guided neuronavigation, or scanning
from an anesthesiologist point of view; we found it worthwhile to share our limited
experience.
Using a navigation system, accurate, minimally invasive imaging-guided treatments
can be performed. As a result, it is less time-consuming, more cost-effective, and
less disruptive to the surgical workflow. Anesthesiologists and their workstation
environment are intertwined in the OR and the science of ergonomics is the study of
this relationship to improve safety, performance, and patient well-being.[5] Patient, equipment, and monitors should be positioned in such a way that an anesthesiologist
can access the patient in a catastrophic situation and allow smooth functioning of
the OR.
During routine surgical procedures requiring the need of a mobile CT scanner, all
basic standard anesthesia monitors are attached to the patient. The patient is intubated
under controlled conditions and maintained under general anesthesia. Intravenous fluids
and infusions necessary for maintaining the adequate depth of anesthesia are securely
connected. Positioning should be performed according to lesion localization, with
supine, lateral decubitus, modified semiprone, or semisupine positions being all suitable.
The scanning of the head or the desired surgery part is done after induction of anesthesia
and before the incision, for brain mapping, after removal of the tumor, and intraoperatively
during dissection of the tumor when required. CT-compatible surgical table with surgical
head clamp is a vital part of the system that is optimized for neurosurgical workflow
and intraoperative imaging. During cranial surgery, the head of the patient is positioned
away from the scanner, to allow the use of standard surgical instruments ([Fig. 1]). During CT imaging, the table is rotated 180 degrees and the patient's head is
positioned in the center of the scanner. At the end of scanning, the operating table
swings back in its original place. This setup besides being safe also minimizes movement
of anesthetic equipment and has a short transit time to and from the CT imaging scanner.
The monitoring cables and ventilation tubing must be of considerable length to allow
for this rotational movement and vigilance is required during movement to avoid disconnections.
Importantly, the anesthesia workstation pipelines must always be assembled and aligned
within the edge of the table to avoid entanglement with the system.
Fig. 1 The scanner is at the tail end of the patient.
The Association of Anesthetists has released the ergonomic standards for tracheal
intubation, which state that the patient's forehead should be at the level of the
anesthetist's xiphoid process or nipple while the patient lying on an operating table
or trolley for tracheal intubation. With the increased height of the mobile CT scanner
and its inability to be lowered to accommodate patients in need of emergency airway
intervention or placement of central lines, the operating table presents several ergonomic
issues. To avoid difficulty, the intubation should be done before the table is set
up for a mobile CT scanner. This limitation particularly makes a difficult extubation
challenging.
For imaging purposes, it may be necessary to detach the extensions of monitors and
lines. Tube dislodgement, inadequate depth of anesthetic, and patient awakening are
all possible consequences of this process. The duration of imaging may take 5 to 10 minutes
and to avoid light anesthesia, propofol aliquots in the dose of 0.4 to 0.6 mg/kg can
be given. The patient is monitored by the main anesthesiologist and a junior resident.
We prefer to have the arterial line in place with an extension. Any arrythmia or hypotension
can be monitored with an arterial line in place. If an arterial line is not in place,
then the anesthesiologist wearing a lead apron can feel the radial pulse during the
imaging. The capnography can help us to detect any disconnection or misplacement of
the endotracheal tube. One of the main concerns is the effects of radiation on the
anesthesiologist and other healthcare workers. Zhang et al demonstrated that ∼50%
of the radiation dose is delivered by a routine 64 slice CT scanner.[6] This is avoided by using the lead aprons during scanning while monitoring the patient.
A comprehensive approach to patient monitoring under anesthesia called closed-loop
monitoring has been suggested by Manohar et al.[7] We applied closed-loop monitoring during intraoperative scanning to prevent disastrous
consequences. It includes a closed-loop visual inspection of the patient, anesthesia
machine, standard monitors, and surgical field in a definitive sequence to ensure
none of the clinical parameters are missed ([Fig. 2]). Also, the alarm limits should be set appropriately to detect any subtle changes
as early as possible. This approach will prevent adverse events as well as improve
the safe provision of anesthesia and reduce anesthesia-related morbidity/mortality.
Fig. 2 Closed-loop monitoring includes the following steps: (A) Taking care of intravenous cannula, arterial lines, and infusions; (B) monitoring;
(C) drugs; (D) during the rotation of the table; (E) completion of scan. ECG, electrocardiogram, ETCO2, end-tidal carbon dioxide; ETT, endotracheal tube; NIBP, noninvasive blood pressure;
SpO2, peripheral oxygen saturation.
The placement of a mobile CT scanner at the tail end was preferred by neurosurgeons
owing to optimum surgical space for them to work. The disadvantages include the following:
(1) It requires frequent disconnection of the circuits and lines; (2) there may be
an accidental breach in the sterility at the surgical site during rotation of table;
(3) if the patient is undergoing neuromonitoring, the leads need to be disconnected
and there can be damage while moving. In our practical experience, the optimal placement
of the mobile CT scanner should be at the head end during surgical procedures away
from the surgical area ([Fig. 3]). The advantages include the following: (1) It eliminates the need to rotate the
table; (2) disconnection of the circuits and lines is not necessary; (3) the depth
of anesthesia and hemodynamics of the patient will not be disrupted, while the disadvantages
are: (1) The surgical space will be restricted; (2) the sterility of the surgical
field will be compromised as the mobile CT scanner occupies the space.
Fig. 3 The scanner is at the head end of the patient.
During the logistics, it is of utmost importance to maintain the sterility of the
surgical field. We should make sure that the headpin holder applied for neurosurgical
procedures is not touching the scanner while imaging or neuronavigation. To maintain
sterility, a large transparent surgical drape permitting full coverage of the mobile
CT scanner should be used to separate the OR into a sterile and nonsterile part.
Intraoperative mobile CT scanner provides a major benefit to the surgeon in providing
real-time imaging and in technically difficult cases and has a smooth workflow. It
also avoids patient transport to the radiology department in the immediate postoperative
period.
Conclusion
Intraoperative usage of CT scanning is becoming more common. Safety of patient and
smooth workflow is of utmost importance. Constant communication with the staff and
the surgeons is very essential. Workflows must be established, as they are important
to prevent errors during patient movement that requires constant vigilance with no
compromise regarding safety and clinical standards.
