Cardiovascular Responses to Nasal Stimulation Under Ethmoidal-Maxillary Nerve Block and Lidocaine Gel in Anesthetized Beagles
ABSTRACT
This study aimed to compare the effect of ethmoidal-maxillary nerve block (EMBLOCK) and topical application of 2% lidocaine gel (LGEL) on cardiovascular variables (heart rate and arterial blood pressure) during mechanical stimulation of the nasal cavity. The working hypothesis was that both techniques (EMBLOCK and LGEL) similarly blunt the cardiovascular responses to the stimulation. Six beagles were anesthetized using alfaxalone and isoflurane on three occasions with each treatment (EMBLOCK, LGEL, and control) in random order. The nasal cavity from the nose tip to the medial canthus was stimulated with a standard-tip cotton swab, and cardiovascular variables were recorded before and after stimulation. The maximum increases in heart rate and blood pressure were significantly smaller in EMBLOCK and LGEL than in the control. There was no significant difference between EMBLOCK and LGEL. Therefore, although further clinical studies are required, EMBLOCK and LGEL can be used because both EMBLOCK and LGEL attenuated the cardiovascular response to mechanical stimulation of the nasal cavity in dogs.
Introduction
The trigeminal nerve is associated with the sensation of the nasal cavity in dogs.1 The nerve is further divided into the ophthalmic, maxillary, and mandibular nerves.1 Among the three nerves, the ophthalmic nerve innervates the medial mucosa of the nasal cavity after dividing into the ethmoidal nerve, and the maxillary nerve innervates the lateral mucosa of the nasal cavity.1 Hence, both nerve blocks are required to ensure desensitization of the nasal cavity. The local block techniques have been suggested for anesthetic stabilization and to reduce the complications of nasal procedures in previous studies performed in dogs, horses, and humans.2–4 Furthermore, the concurrent block of ethmoidal and maxillary nerves (EMBLOCK) achieves optimal peri- and postanalgesia for cleft lip repair with primary rhinoplasty in human medicine.2
During canine nasal procedures, the nasal cavity mucosa is unavoidably stimulated mechanically, and nasal stimulation causes tachycardia, hypertension, and head movement because of nasal sensitivity, despite the procedure being performed under general anesthesia.5 A previous study suggested the application of EMBLOCK for anesthetic stabilization during nasal procedures in dogs.4 In the previous study, for EMBLOCK, the needles were inserted at four sites, which are the most medial points of the eye socket and the bilateral infraorbital foramina, and lidocaine was injected on the bilateral ethmoidal and sphenopalatine foramina (Figure 1).4 Complications, such as neurotoxicity, can occur during local blockade in the facial region, and several such cases have been reported in veterinary and human medicine.6–8 This is caused by direct local anesthetic inflow into the brain due to accidental intra-arterial injection, as explained in previous reports.7,8 Hence, in order to be able to present options to clinicians in situations in which they are concerned about the occurrence of side effects during EMBLOCK, it is necessary to study an interchangeable technique that does not require needle insertion.
Citation: Journal of the American Animal Hospital Association 58, 6; 10.5326/JAAHA-MS-7183
This study used cardiovascular parameters as an indicator of sensation/pain4,5,9 and aimed to compare the effects of EMBLOCK and topical application of 2% lidocaine gel (LGEL) on cardiovascular variables including heart rate (HR) and systolic arterial pressure (SAP), mean arterial pressure (MAP), and diastolic arterial pressure (DAP) during mechanical stimulation of the ventral nasal meatus in anesthetized dogs. The authors hypothesized that both techniques would similarly blunt the cardiovascular responses to stimulation.
Materials and Methods
Animals
This study was approved by the Institutional Animal Care and Use Committee of Seoul National University (SNU-180424-3). Six beagles (four males, two females) with a median (interquartile range) body weight of 10.5 kg (10.2–10.8 kg and aged 1 yr (1–2 yr) were included. The dogs were housed in individual stainless-steel kennels in a temperature-controlled room with a 12-hr light/dark cycle. Before the experimental procedures, all dogs underwent a complete physical examination, complete blood cell count evaluation, blood chemistry analysis, and thoracic radiographs.
Study Design
This study was conducted as a placebo-controlled, blinded, randomized, and repeated crossover study design. Each dog was anesthetized on three occasions, with each instance separated by more than 7 days, as follows: (1) EMBLOCK by injections of 2% lidocainea bilaterally at ethmoidal and maxillary foramina; (2) LGEL by topical application of 2% lidocaine gelb bilaterally in the nasal cavity; and (3) control. The treatment order for each dog was determined by drawing lots for randomization.
Anesthesia and Physiologic Variable Measurement
Before each anesthetic procedure, food was withheld for at least 8 hr with free access to water. IV catheterization was performed with a 22 G catheterc in the cephalic vein. Hartmann’s (sodium lactate) solutiond was infused at 5 mL/kg/hr, and acepromazinee (0.01 mg/kg) was injected IV. After 5 min, anesthesia was induced using IV alfaxalonef (2 mg/kg). General anesthesia was maintained with isofluraneg in oxygen (2 L/min) using a rebreathing circuit systemh, and the vaporizer was adjusted with a target of 1.5% end-tidal isoflurane concentration (FEIso). To maintain an end-tidal carbon dioxide concentration (PECO2) of 40 mm Hg, the dogs were ventilated using a volume-controlled ventilatori with the following ventilator settings: tidal volume of 10–13 mL/kg, a peak inspiratory pressure of 10–12 cm H2O, and an inspiration time of 1 s. A warm-water blanketj was used to keep the body temperature at a target of 37.5°C. Arterial catheterization was achieved with a 22 G catheter in the dorsal pedal artery to measure arterial blood pressure. The arterial catheter was connected to heparinized saline-filled noncompliant tubing, and the tubing was connected to a disposable pressure transducerk placed at the level of the heart. The transducer was zeroed to atmospheric pressure before measuring arterial blood pressure. After preparing for vital sign monitoring, the dogs were left in sternal recumbency for 30 min to stabilize the physiologic variables. During anesthesia, HR, SAP, MAP, DAP, FEIso, PECO2, oxygen saturation, and rectal temperature were continuously monitored using a multiparameter monitorl.
Nasal Cavity Local Anesthesia
Local anesthesia of the nasal cavity was performed by the same investigator in all dogs. For the EMBLOCK, four syringes were readied to use at each site, and the short bevel needlesm were connected to 3 mL syringes filled with 2% lidocaine solution. During the ethmoidal nerve block, the hair dorsal to the medial canthus was clipped, and the needle was inserted at the angularis oculi vein groove after disinfection of the skin with alcohol-soaked gauze (Figure 1).4 The needle was advanced in a 45° angle to the dorsal plane while maintaining contact with the medial part of the orbit, and the needle tip was placed at the target point, which was identified using the frontal process of the zygomatic arch in a lateral view (Figure 1).4 During the maxillary nerve block, the needle was inserted at the infraorbital foramen after disinfection of the oral mucosa with 0.2% chlorhexidine-soaked gauze (Figure 1).4 In addition, the needle was advanced along the infraorbital canal, and the needle tip was placed at the target point, which was identified using the lateral canthus (Figure 1).4 To avoid intravascular administration, negative pressure was applied to the syringe plunger before the injections, and 1 mL of lidocaine was injected at each site (total 4 mL per dog), which was within the range of the maximum safe dose (10 mg/kg).10 During lidocaine administration, injection pressure was assessed manually to avoid intraneural injection, and the needle was reinserted if high injection pressure was felt.
For LGEL, two syringes were readied to use at each nostril, and 8 Fr feeding tubesn were connected to 3 mL syringeso filled with 2% lidocaine gel. The depth of the nasal cavity, from the nose tip to the level of the medial canthus, was quartered, and 0.5 mL of lidocaine gel was applied at each depth level (total 4 mL per dog), which was within the range of the maximum safe dose (10 mg/kg).10 In addition, the lidocaine gel was gently spread on the nasal cavity mucosa with a cotton swabp, and to minimize irritation, the nasal insertion of a cotton swab was limited to one time.
Nasal Cavity Stimulation and Cardiovascular Responses
Stimulation of the nasal cavity was started 10 min after local anesthesia treatment to ensure the peak effect of lidocaine had been achieved.10 Two standard-tip cotton swabs were inserted into the bilateral ventral nasal meatuses concurrently to stimulate the nasal cavity mucosa. The insertion depth was at the level of the medial canthus, and the cotton swab was inserted and extracted five times by the anonymized investigator (DK) within 10 s. To obtain the values of cardiovascular parameters such as HR, SAP, MAP, and DAP, the multiparameter monitor was video-recordedq from immediately before stimulation (baseline) until any increased values returned to the baseline or recorded for 5 min when the values did not change. After recording, the fluid infusion and isoflurane vaporizer were terminated. During the anesthesia recovery period, the dog was visually monitored for 1 hr after extubation to check for complications associated with local blockade.
Statistical Analyses
Stimulation-induced changes (Δ) of the cardiovascular variables (ΔHR, ΔSAP, ΔMAP, and ΔDAP) were calculated as the difference between the peak value after stimulation and the baseline for each variable in each dog. Baseline values of the cardiovascular variables were compared using the Kruskal-Wallis test among the treatments. Differences among EMBLOCK, LGEL, and control were analyzed using the Kruskal-Wallis test. Furthermore, post hoc comparison was performed with the Bonferroni-corrected Mann-Whitney U test. All analyses were performed using SPSS version 25r, and the differences were considered significant when P ≤ .05.
Results
Preanesthesia examinations showed that all dogs were clinically healthy based on physical examinations, laboratory tests, and thoracic radiographs. At baseline, the FEIso and PECO2 were established at 1.5% and 40 mm Hg, respectively, in all treatments. In addition, the median (interquartile range) of oxygen saturation and rectal temperature were 98% (97–98%) and 37.5°C (37.4–37.6°C), respectively, during the 18 anesthetic occasions in six dogs.
Baseline values for HR, SAP, MAP, and DAP did not differ among EMBLOCK, LGEL, and control treatments (Table 1). Significant differences of Δ cardiovascular variables were noted among EMBLOCK, LGEL, and control treatments. In post hoc analyses, signifi-cant differences were identified in EMBLOCK and LGEL compared with the control (Table 2). Relative to the control treatments, the increases in cardiovascular parameters were smaller in the EMBLOCK and the LGEL treatment (Table 2). There was no significant difference between EMBLOCK and LGEL.
During recovery from anesthesia, mydriasis was observed in 3 of 12 eyes (25.0%) with EMBLOCK, and the mydriasis disappeared within 1 hr after lidocaine injection, whereas mydriasis was not observed in LGEL.
Discussion
The results of this study showed that EMBLOCK can significantly attenuate the cardiovascular responses studied during nasal cavity stimulation, and the application of LGEL on the nasal cavity has the same effect as the EMBLOCK, which was consistent with the authors’ hypotheses. Nerve signal transmission initiated by nasal cavity stimulation is blocked by the EMBLOCK treatment, and the activation of mechanoreceptors in the nasal cavity mucosa is blocked in the LGEL treatment.4,9 Although the mechanisms of the two treatments are different, equal desensitization effect of the nasal cavity by both methods was identified in this study.
Immediately after irritation of the nasal cavity mucosa, sudden changes in patient parameters can occur. When the reaction is more severe, involuntary movements can occur, which may interfere with the procedure and can cause nasal mechanical injury.5,11 To suppress the responses of nasal passage stimulation, options such as deepening the level of anesthesia, administration of additional sedatives, or application of local anesthesia can be selected.
EMBLOCK and LGEL can both be considered for local anesthesia of the nasal cavity, which was documented in this study. Each of these methods has advantages and disadvantages. For EMBLOCK, in the case of neoplastic lesions at the site of local anesthetic drug administration, there is a possibility of causing metastasis from drawing neoplastic cells along the needle tract. In addition, systemic side-effects can be caused by accidental intravascular or intraneural injection. For LGEL, if the nasal cavity is obstructed it may not be possible to apply the gel appropriately. In addition, intranasal lidocaine gel can interfere with visualization during rhinoscopy or intranasal surgery per the author’s experience. In human medicine, according to the judgment of the clinician, EMBLOCK or LGEL is used to implement effective analgesic treatment during nasal procedures.2,12,13 Because the effects of EMBLOCK and LGEL were equivalent in this study, either technique can be proposed equally during canine nasal procedures.
Before the application of EMBLOCK and LGEL, the volume of local anesthetic should be discussed. Depending on the size of the dog, the required dose of local anesthetic may differ. Furthermore, in EMBLOCK, because the diameter of the ethmoidal and maxillary nerves are different, appropriate volume division of local anesthetic drugs at four injection sites should be ensured for effective nerve blockade. Because the maxillary nerve is thicker in diameter than the ethmoidal nerve, a relatively higher volume of local anesthetic is likely to be required for maxillary nerve blockade. In LGEL, because of the rapid absorption rate of the respiratory mucosa,14 local anesthetic agents may be absorbed before the onset of local anesthesia if a small amount of local anesthetic is applied. The volume of the gel that can contact the nerves until the onset of local anesthesia should be studied.
As a temporary complication, mydriasis was observed during anesthetic recovery in EMBLOCK. Mydriasis is caused by the blockade of the oculomotor nerve, which is a parasympathetic nerve located near the ethmoidal nerve.15,16 However, temporary complications resolved within 1 hr, and by analogy from this result, lidocaine injected in this study might be also effective for about 1 hr of nasal local anesthesia.10
The cardiovascular system is influenced by hypercarbia and hypothermia. Hypercarbia increases blood pressure,17 and hypothermia initially induces tachycardia and elevation of blood pressure but induces bradycardia and a decrease of blood pressure as it worsens.18 For the response evaluation using the cardiovascular variables, all dogs were ventilated, and the PECO2 was maintained at 40 mm Hg. In addition, body temperature was maintained within the range of 37.4–37.6°C. Hence neither of these factors should have had any impact on the results of this study.
Based on the result of a pilot experiment (unpublished data), the anesthetic protocol in this study was selected. Under a light plane of anesthesia, nasal stimulation in control dogs induced not only changes in cardiovascular variables but also head and limb movements. These movements interrupted accurate cardiovascular monitoring and identical stimulation among interventions. In this study, an anesthetic protocol that restrained movements but permitted cardiovascular responses was achieved using administration of acepromazine and isoflurane at FEIso of 1.5%.19,20 In addition, general anesthesia was induced using short-duration alfaxalone to minimize the effect of the induction agent during nasal stimulation.21 The sedatives and anesthetics administered in this study may have had a suppressive effect on the cardiovascular system, but the effect would be same in all dogs because the same anesthetic protocol was used in all subjects.
The limitations of this study are the small sample size and the lack of saline injection or topical administration of saline in control subjects. In addition, the systemic action of lidocaine such as analgesic effect or cardiovascular suppression could not be excluded. However, in the previous study, the lidocaine used for local blockade did not have a major systemic effect.9
Conclusion
In conclusion, the EMBLOCK and LGEL attenuated the cardiovascular response, specifically HR and blood pressure, to mechanical stimulation of the nasal cavity in dogs. Therefore, although additional clinical studies are required to determine the usefulness of the two techniques, EMBLOCK and LGEL can be applied alone or in combination to provide significant desensitization of the nasal cavity for nasal procedures.
Canine skull views: lateral (A), oblique (B), and rostral (C), including anatomical landmarks for the ethmoidal-maxillary nerve block such as angularis oculi vein groove (a), infraorbital foramen (b), ethmoidal foramen (c), sphenopalatine foramen (d), and frontal process of zygomatic arch (e).
Contributor Notes
M. Jang’s present affiliation is Department of Veterinary Clinical Sciences, College of Veterinary Medicine, Kyungpook National University, Daegu, Republic of Korea.
