Discussion
We present our experience after the introduction of a technique using
negative pressure in a housing barrier (NOVID) to reduce the spread of
droplets and aerosol during endonasal skull base and transoral surgery.
We have used this technique both in the sinonasal region for
ethmoidectomy, maxillary antrostomy, transpterygoid nasopharyngectomy,
and transsphenoidal sellar skull base surgery, as well as for endo-oral
palate surgery. This technique is still in evolution, but we found a
minimum of contamination of the surgical field with dye or visible
fluid. While the fluorescein is only a surrogate marker, since it is
applied only intermittently during the case. Notably, we identified dye
at the inlet of the smoke evacuator after the skull base procedures,
indicating it is capturing fluid in the form of droplets or aerosol
under NOVID.
A surgeon routinely places suction in the patient’s nasal
cavity. However, the routine suction is attached to the HEPA filter in
the Neptune suction machine which captures particles down to 0.3
microns. The smoke evacuator ULPA filter attachment on the side of the
Neptune captures particles down to 0.1 microns.11 The
COVID-19 virus is 0.125 microns and in theory should be captured by an
ULPA filter but not the standard suction.9 Viral
particles could theoretically escape from the Neptune system with the
standard filter. We did examine the Neptune machine at the end of the
surgery and found the fluid in the container to brightly fluoresce, and
no dye visible outside the machine.
In general, we found droplet spread where the instruments or cottonoids
were placed. We did find droplets on the surgeon’s abdomen and on the
surgeon’s arm. One droplet was found at the foot of the bed. In the two
cases that generated aerosol we found the droplets under the drape away
from the nares. Whether this occurred due to aerosol from drilling or
due to irrigation and instrument passing over a prolonged time period,
we cannot determine at this time. However, in general we found very
little droplet contamination away from the surgical field. Large
droplets were found at expected locations: the patient’s chest where the
gauze wipe is located, the instrument table, around the epinephrine
cottonoids, and in one case on the nurse’s abdomen. This suggest that
surgical fomites including the instruments, cottonoids and tissue
specimens are a major source of spread of fluid to the surgical field.
We suspect the droplet at the patient’s foot occurred during removal of
an instrument or cottonoid as it was in a linear trajectory and no other
droplets identified outside the surgical field. This suggests that
methods to reduce contamination caused by surgical instruments and
cottonoids may be useful. We suggest, gentle withdrawal of instruments
from the nasal cavity and passage of cottonoids and biopsy specimens off
the field onto a plastic tray similar to the plastic safe sharps passing
tray used for the hands-free transfer or sharps in many operating
rooms.12
There is wide concern within the skull base field regarding aerosol
generation and droplets spread during endoscopic endonasal and upper
aerodigestive tract surgery. The NOVID system combines a fluid resistant
barrier and a negative pressure environment to reduce the spread of
aerosols and droplets. One alternate option is to place a suction into
the nasal cavity to create negative pressure
environment.8 However, this may obstruct access to the
surgical field or become clogged. Surgeons commonly use suctions while
operating and drilling, but they can also become clogged, or be too deep
in the field to catch the aerosol generated anteriorly. NOVID also
allowed for repetitive entry and removal of instruments into and out of
the surgical field and allows the surgeon to operate unencumbered. There
are potential improvements in the instrument port design. We envision
that the ideal surgical port would create a better seal around the
instrument and could wipe off any fluid or droplet contamination from
the scope and instruments as it is removed from the barrier.
NOVID also appears to reduce splash back during irrigation, and the
negative pressure may capture aerosol created by cauterization or
high-speed drilling. Identification of fluorescence at the smoke
evacuator tip suggests it was able to draw aerosolized droplets. It is a
limitation of this study that due to the urgent concerns created during
this pandemic, we do not have control group to compare droplet spread.
Nevertheless, it is encouraging to find in the skull base cases, no
droplets or fluorescence on the outside of the drape or around the
patient’s head other than where the instruments were direct contact.
Also, fluorescein is routinely used on the epinephrine soaked
cottonoids, which could cause false positive findings. However, the
cottonoids after being removed from the patient should be considered
contaminated.
We also found the nursing staff and anesthesia team to be extremely
appreciative of the monitoring of spread of patient’s fluids into the
operating room environment and with the use of a barrier. This
assessment seemed to provide the team some peace of mind to see how,
where, and the minimal amount of contamination that occurred. We now
routinely use the fluorescein during each case as a marker of fluid
spread for quality assurance for all the operating room staff.