Examination of laryngeal function of healthy dogs by using sedation protocols with dexmedetomidine

Multiple uses of dexmedetomidine in small animals: a mini review

Dexmedetomidine is an alpha-2 adrenergic agonist, which use had an exponential increase in human and veterinary medicine in the last 10 years. The aim of this mini review is to summarize the various uses of dexmedetomidine underlining its new applications and capabilities in the small animals' clinical activity. While this drug was born as sedative in veterinary medicine, some studies demonstrated to be effective as an analgesic both in single administration and in continuous infusion. Recent studies have also shown the role of dexmedetomidine as an adjuvant during locoregional anesthesia, increasing the duration of the sensitive block and consequently decreasing the demand for systemic analgesics. The various analgesic properties make dexmedetomidine an interesting drug for opioid-free analgesia. Some studies highlighted a potential neuroprotective, cardioprotective and vasculoprotective role of dexmedetomidine, thus conferring it a place in critical care medicine, such as trauma and septic patients. Dexmedetomidine has demonstrated to be a multitasking molecule and it is ready to face new challenges.

Elective cricothyrotomy in a dog with transient laryngeal paralysis secondary to Australian paralysis tick (Ixodes holocyclus) envenomation

The tube cricothyrotomy (CTT) has recently been introduced to small animal medicine as a viable surgical airway access procedure; however, there are no reports documenting its clinical use. The author's objective is to describe the clinical application, complications, and management of an elective CTT in a dog. Furthermore, the characteristics of CTT that may be clinically advantageous over temporary tube tracheostomy (TT) will be discussed. A 2‐year‐old female spayed German shepherd dog required mechanical ventilation (MV) due to unsustainable work of breathing as a result of tick paralysis and aspiration pneumonia. After successful weaning from MV, the dog was diagnosed with laryngeal paralysis. A surgical airway was performed using CTT to allow extubation and patient management whilst conscious. Complications included frequent tube suctioning due to accumulation of airway secretions in the tube and a single dislodgement event. The dog made an uneventful recovery with complete stoma healing by the second intention within 15 days. To the authors' knowledge, this is the first clinical report of an elective CTT performed to successfully manage upper airway obstruction in the dog. Its efficacy, clinical management and patient outcome are described.

Minimizing Motion Artifacts in Intravital Microscopy Using the Sedative Effect of Dexmedetomidine

Among intravital imaging instruments, the intravital two-photon fluorescence excitation microscope has the advantage of enabling real-time 3D fluorescence imaging deep into cells and tissues, with reduced photobleaching and photodamage compared with conventional intravital confocal microscopes. However, excessive motion of organs due to involuntary movement such as breathing may result in out-of-focus images and severe fluorescence intensity fluctuations, which hinder meaningful imaging and analysis. The clinically approved alpha-2 adrenergic receptor agonist dexmedetomidine was administered to mice during two-photon fluorescence intravital imaging to alleviate this problem. As dexmedetomidine blocks the release of the neurotransmitter norepinephrine, pain is suppressed, blood pressure is reduced, and a sedation effect is observed. By tracking the quality of focus and stability of detected fluorescence in two-photon fluorescence images of fluorescein isothiocyanate-sensitized liver vasculature in vivo, we demonstrated that intravascular dexmedetomidine can reduce fluorescence fluctuations caused by respiration on a timescale of minutes in mice, improving image quality and resolution. The results indicate that short-term dexmedetomidine treatment is suitable for reducing involuntary motion in preclinical intravital imaging studies. This method may be applicable to other animal models.

Comparison of immediate and short-term outcomes of cricoarytenoid and thyroarytenoid lateralization in dogs with idiopathic laryngeal paralysis

OBJECTIVE

To compare the immediate and short-term outcomes of thyroarytenoid lateralization (TAL) and cricoarytenoid lateralization (CAL) for the treatment of canine laryngeal paralysis in dogs.

STUDY DESIGN

A prospective, clinical trial.

ANIMALS

Fourteen client-owned dogs referred to our hospital because of bilateral laryngeal paralysis.

METHODS

Dogs with confirmed laryngeal paralysis were randomly assigned to the CAL or TAL group. Video images of the rima glottidis obtained preoperatively, immediately postoperatively (t0), and 15 days postoperatively (t1) were digitized. The rima glottidis area was measured using image-analysis software. An increase in the rima glottidis area was expressed as a percentage of the preoperative area.

RESULTS

The rima glottidis area increased by a mean of 152% at t0 and 127% at t1 for the TAL group and 205% at t0 and 199% at t1 for the CAL group compared with preoperative values. The increase in the rima glottidis area differed (P < .05) between the 2 groups at all postoperative time points. A reduction of the area occurred at t1 in both groups. There was no difference between t0 and t1 (P > .05) in the CAL group but there was a large difference (P < .05) in the TAL group.

CONCLUSION

Cricoarytenoid lateralization and TAL were both effective for surgical abduction of the arytenoid cartilage. Although a reduction (P < .05) in the rima glottidis area occurred in the TAL group at t1, we observed no associated clinical signs.

CLINICAL SIGNIFICANCE

Cricoarytenoid lateralization and TAL result in good short-term outcomes in dogs with laryngeal paralysis.

Efficacy and Safety of Dexmedetomidine Premedication in Balanced Anesthesia: A Systematic Review and Meta-Analysis in Dogs

Simple Summary

Dexmedetomidine, on account of its potent sedative and analgesic properties, is commonly used in balanced anesthesia of small animal anesthesia; however, concerns regarding its cardiovascular effects prevent its full adoption into veterinary clinical practice. We conducted this meta-analysis to determine the effects of dexmedetomidine on sedation, analgesia, cardiovascular and adverse reactions in dogs compared to other premedications. The outcomes included sedation score, pain score, heart rate, systolic arterial blood pressure, mean arterial blood pressure and the incidence of adverse effects. Thirteen studies were included in this meta-analysis. The results showed that dexmedetomidine provides a satisfactory sedative and analgesic effect in balanced anesthesia of dogs. After dexmedetomidine premedication, dogs experienced lower heart rate and higher blood pressure within an acceptable range. The combinations in balanced anesthesia and routes of delivering drugs would affect heart rate, systolic arterial blood pressure, and mean arterial blood pressure of dogs. Before using dexmedetomidine, an animal’s cardiovascular status should be fully considered.

Abstract

Dexmedetomidine is commonly used in small animal anesthesia for its potent sedative and analgesic properties; however, concerns regarding its cardiovascular effects prevent its full adoption into veterinary clinical practice. This meta-analysis was to determine the effects of dexmedetomidine on sedation, analgesia, cardiovascular and adverse reactions in dogs compared to other premedications. Following the study protocol based on the Cochrane Review Methods, thirteen studies were included in this meta-analysis ultimately, involving a total of 576 dogs. Dexmedetomidine administration probably improved in sedation and analgesia in comparison to acepromazine, ketamine and lidocaine (MD: 1.96, 95% CI: [−0.08, 4.00], p = 0.06; MD: −0.95, 95% CI: [−1.52, −0.37] p = 0.001; respectively). Hemodynamic outcomes showed that dogs probably experienced lower heart rate and higher systolic arterial blood pressure and mean arterial blood pressure with dexmedetomidine at 30 min after premedication (MD: −13.25, 95% CI: [−19.67, −6.81], p < 0.0001; MD: 7.78, 95% CI: [1.83, 13.74], p = 0.01; MD: 8.32, 95% CI: [3.95, 12.70], p = 0.0002; respectively). The incidence of adverse effects was comparable between dexmedetomidine and other premedications (RR = 0.86, 95% CI [0.58, 1.29], p = 0.47). In summary, dexmedetomidine provides satisfactory sedative and analgesic effects, and its safety is proved despite its significant hemodynamic effects as part of balanced anesthesia of dogs.

Influence of doxapram and intermittent 10% carbon dioxide inspiration on cardiovascular and laryngeal functions in anesthetized dogs

OBJECTIVE

To compare the effects of two doses of doxapram intravenous injection and carbon dioxide inhalation on the cardiovascular and laryngeal functions of anesthetized hounds.

STUDY DESIGN

Experimental study.

ANIMALS

Six healthy adult dogs.

METHODS

In a Latin-square design, the mean arterial blood pressure (MABP) and heart rate (HR) were recorded continuously. The inspiratory normalized glottic gap areas (iNGGA) were measured before and after each stimulation with 0.55 mg/kg of doxapram (L-DOX), 2.2 mg/kg of doxapram (H-DOX), or 90 s of inhalation of 10% carbon dioxide in oxygen (I-CO₂ ). The stimulations were tested in duplicate or triplicate. Video clips of the laryngeal movement were scored by board-certified surgeons masked to the treatment.

RESULTS

The MABP increased with L-DOX and H-DOX up to 81% (both p < .001 compared to I-CO₂ ), and persisted during the other stimulations (both p < .001). An intermittent tachycardic effect of up to 79% increase in HR was observed with doxapram. The HR following H-DOX was higher than L-DOX and I-CO₂ (both p < .016). Neither hypertension nor tachycardia was observed with I-CO₂ . The iNGGA increased with all treatments (p < .001). The iNGGA was greater with H-DOX than L-DOX and I-CO₂ (both p < .007). All treatments received higher scores (all p < .001) with acceptable inter- and intra-observers Krippendorff's alphas.

CONCLUSION

All treatments were effective respiratory stimulants in anesthetized dogs; however, doxapram caused hypertension and tachycardia.

CLINICAL SIGNIFICANCE

Carbon dioxide inhalation might improve arytenoid motion without cardiovascular effects in dogs during clinical airway examinations.

Laryngeal function in normal dogs administered isoflurane following partial clearance of alfaxalone or propofol

OBJECTIVE

To assess laryngeal function in normal dogs administered isoflurane following partial clearance of alfaxalone or propofol.

STUDY DESIGN

Randomized experimental crossover study.

ANIMALS

A group of 12 purpose-bred, male Beagle dogs.

METHODS

Dogs were randomly assigned to one of two treatments: alfaxalone-isoflurane (ALF-ISO) or propofol-isoflurane (PRO-ISO) and anesthetized for three video laryngoscopy examinations. The alternate treatment occurred after ≥ 14 days interval. Examinations were performed after induction of anesthesia (LS-A), after 20 minutes of breathing isoflurane via a facemask (LS-B) and after a further 20 minutes of isoflurane (LS-C). Parameters of objective laryngeal function included inspiratory rima glottidis surface area (RGSA-I), expiratory rima glottidis surface area (RGSA-E) and % RGSA increase, calculated from three consecutive respiratory cycles in the final 15 seconds of each video laryngoscopy examination. The % RGSA increase was calculated using [(RGSA-I - RGSA-E)/RGSA-E] × 100. Subjective laryngeal function was evaluated independently by two experienced surgeons blinded to treatment.

RESULTS

The % RGSA increase within each treatment was greater for LS-B and LS-C than for LS-A (ALF-ISO: p = 0.03, PRO-ISO: p = < 0.001). There was no difference within each treatment from LS-B compared with LS-C. RGSA-I increased within each treatment from LS-A to both LS-B and LS-C (ALF-ISO: p = 0.002) and to LS-C (PRO-ISO: p = 0.006). Subjective laryngeal function scores improved from LS-A to LS-C.

CONCLUSIONS AND CLINICAL RELEVANCE

Laryngeal function improved from postinduction examination following either 20 or 40 minutes of anesthesia with isoflurane via facemask. This study demonstrates that isoflurane may have a lesser effect on arytenoid abduction activity compared with more commonly used intravenous induction anesthetics (alfaxalone and propofol).

The Influence of Anaesthetic Drugs on the Laryngeal Motion in Dogs: A Systematic Review

Simple Summary

Laryngeal paralysis is secondary to a loss of normal function of the larynx. Older dogs are particularly affected, with normal breathing becoming difficult. A successful diagnosis typically relies on the visualisation of either, complete, or partially absent, laryngeal movements. The use of anaesthesia drugs to provide sedation and stress relief is most commonly necessary during the diagnosis of laryngeal paralysis. While, the excessive administration of anaesthesia drugs may result in absent movements, the ideal anaesthesia regime remains unknown, and the use of sedation is questionable, given the potential for absent laryngeal movements, even in healthy dogs. In this systematic review, we found a potential benefit from using sedation during the evaluation of laryngeal function when compared to injectable anaesthetics only. The respiratory stimulant doxapram was effective in differentiating normal dogs from dogs with laryngeal paralysis but has associated safety hazards.

Abstract

Anaesthetic drugs are commonly used during the evaluation of laryngeal function in dogs. The aim of this review was to systematically analyse the literature describing the effects of anaesthetic drugs and doxapram on laryngeal motion in dogs and to determine which drug regime provides the best conditions for laryngeal examination. PubMed, Google Scholar, and EMBASE databases were used for the literature search up to November 2019. Relevant search terms included laryngeal motion, anaesthetic drugs and dogs. Studies were scored based on their level of evidence (LoE), according to the Oxford Centre for Evidence-based Medicine, and the quality was assessed using the risk-of-bias tool and SIGN-checklist. In healthy dogs, premedication before laryngeal examination provided better examination conditions and maintained overall adequate laryngeal motion in 83% of the studies. No difference in laryngeal motion between induction drugs was found in 73% of the studies but the effects in dogs with laryngeal paralysis remain largely unknown. Doxapram increased laryngeal motion in healthy dogs without serious side effects, but intubation was necessary for some dogs with laryngeal paralysis. Methodological characteristics varied considerably between studies, including the technique and timing of evaluation, number of assessors, study design, drug dose, combinations, route and speed of administration.