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.