Topical irrigation against gravity may lead to better sinus penetration

INTRODUCTION

Nasal sinus irrigation serves as an effective topical therapy for treatment of different nasal sinus diseases as well as postoperative care^1,4–6. Given its wide utility, active research using endoscopy of live patients or cadavers with dye laden irrigant or using computed tomography (CT) of contrast agents or radioactive tracers^1–3 have examined various factors (head positions, degree of surgery, etc.) that may improve nasal irrigation distribution⁷. However, one factor is largely overlooked - patients are routinely instructed to deliver the irrigation solution through the upper nostril while the head is tilted to one side (e.g. see FDA implicit recommendation⁹). Intuitively, this would allow the flow of fluid through the upper nostril, driven by gravity, to fill the paranasal cavity and then exit out the lower nostril. However, there has been little objective evidence to suggest that this is the optimal technique for nasal irrigation. Here, we investigate how irrigations behave when fluid reversely enters through the lower and exits the upper nostril against gravity (the backfill technique).

METHODS

Computational fluid dynamic (CFD) simulated irrigations of 240 mL saline at 12 mL/s (typical of neti-pot or Sinugator®) through the upper (conventional) or the lower (backfill) nostril based on one post-operative patient in three head positions: tilting 45° to-the-left, 90° to-the-left, and 45° to-the-left and 45° forward (Fig. 1) was utilized. This postoperative model, as well as the CFD technique, has been previously published and validated^8,10. The patient was a 47-year-old male with chronic rhinosinusitis, who underwent bilateral wide maxillary antrostomies, total ethmoidectomies, sphenoidotomies, and a Draf III frontal sinusotomy. In brief, the 3D model was generated based on patients’ CT scans using a series of software: AMIRA (Thermo Fisher Scientific, Waltham, MA) and ICEM CFD software (Ansys Inc., Canonsburg, PA), with the final nasal airway volume filled with 3.7 million tiny elements or mesh (Fig.1). Irrigation simulation was carried out based on these elements with the commercial software CFX (Ansys Inc., Canonsburg, PA), using a multiphase free surface method, simulating the interaction between the fluid solution (saline in this case) and air. A 4mm in diameter circular opening was created on the appropriate nostril plane, mimicking the inlet for a common irrigation device. The contralateral nostril would serve as the mass flow outlet. The nasopharyngeal opening was assumed to be closed off by the soft palate (velopharyngeal closure), reflecting breath holding during irrigation. A k-ε turbulence model was used to simulate the air and fluid movement, along with a transient scheme with second order backward Euler to capture fluid movement throughout the simulation time.

Figure 1:

Nasal irrigation outcomes using backfill vs conventional techniques with varying head positions at 12 mL/s for 20s. A) Head tilt 45° to the left: backfill irrigation resulted in faster filling of the left maxillary sinus (completely filled at 6s) when compared to conventional filling at 20s and better filling of the ethmoid sinus. B) Head tilt 45° to the left and 45° forward: backfill irrigation resulted in faster and greater filling of the left maxillary sinus as well as other sinuses (left frontal, ethmoid) than conventional irrigation. The latter failed to achieve a full fill of the maxillary sinus. C) Head tilt 90° to the left: both filling methods allowed for a full fill of the left maxillary sinus. However, the backfill technique allowed for greater filling of other sinuses (ethmoid, frontal, etc.). D) The 3D model of the nasal airway was created using patient specific CT scans. The mucosal interface and inner volume of the nasal airway was populated with 3.7 million tetrahedral and triangle elements, with a denser element count at the boundaries.

This study has received the appropriate Institutional Review Board (IRB) approval and all identifying images included in the figures have been taken with proper consent.

RESULTS

In all head positions, the backfill technique had significantly better penetration and faster filling than the conventional technique (Fig. 1). For 45° left and 45° forward, 6s was required for full maxillary sinus filling during lower-nostril-entry (backfill), vs. a full 20s for only half maxillary filling during upper-nostril-entry (conventional). For 45° left, backfill again required 6s for full-fill vs. 11.5s for nearly full-fill during upper-entry. Penetration into other sinuses (ethmoid, sphenoid, frontal) was also better with back-fill than with conventional. For the 90° left, both backfill and conventional techniques reached 100% fill of the left maxillary sinus, however, the backfill technique also achieved a 60–70% fill of the frontal and ethmoid sinuses, versus conventional technique only reaching ~50% for these sinuses. We believe the different outcomes between the two techniques could be due to orientation of the narrow sinus ostium and main nasal airway. By filling through the upper nostril, the fluid flow path may miss the ostium that results in low penetration. Even in the case where the fluid path did reach the ostium, the fluid flow may rush across the ostium and exit out the lower nostril before it has enough time to penetrate into the ostium opening. However, by filling through the backfill technique, fluid will be pushed against gravity and be pooled against the ostium. This may allow for more time and fluid pressure to facilitate greater fluid penetration before it is allowed to spill out to the upper nostrils. This effect is demonstrated in supplementary video 1, where as a demo, two holes were drilled in an acrylic box. The acrylic box represents the main nasal airway, and the two holes (one 2.4 mm and the other 4.8 mm in diameter) represent typical pre-surgery and post-surgery ostium size, respectively. Fluid was then poured into the box above the hole with gravity (conventional technique) vs below the holes against gravity (backfill technique). For both sizes of holes, conventional irrigation showed limited fluid penetration through the “ostium”, even when both holes are completely exposed to the fast-moving fluid flow path. However, by pushing fluid through using the backfill technique against gravity, the fluid would pool and submerge the openings and resulted in strong fluid penetration through both ostium openings.

CONCLUSION

Contrary to conventional wisdom, pushing irrigant against gravity through the lower nostril can allow the irrigrant to pool around the ostium for improved penetration into the paranasal cavity. Limitations of the study include that this is a modeling study with limited data. Nevertheless, future large-scale clinical study should investigate whether this novel paradigm may generally improve the outcome of irrigation methodologies (squeeze bottle, etc.) that involve head-side-tilt.

Supplementary Material

alr22711-sup-0001-videoS1

Video 1: Irrigation videos of the simulated head positions and irrigation techniques on the created nasal model through computational fluid dynamic simulation using ANSYS CFX, as well as the acrylic box demo which shows conventional and backfill filling of the two openings representing ostium openings.