Comparison between intravenous lidocaine and fentanyl on cough reflex and sympathetic response during endotracheal intubation in dogs

ObjectiveTo compare the effects of intravenous (IV) lidocaine and fentanyl on the cough reflex and autonomic response during endotracheal intubation in dogs.Study designRandomized, blinded, superiority clinical trial.AnimalsA total of 46 client-owned dogs undergoing magnetic resonance imaging.MethodsAfter intramuscular methadone (0.2 mg kg^–1), dogs were randomized to be administered either IV lidocaine (2 mg kg^–1; group L) or fentanyl (7 μg kg^–1; group F). After 5 minutes, alfaxalone was administered until endotracheal intubation was possible (1 mg kg^–1 IV over 40 seconds followed by 0.4 mg kg^–1 increments to effect). Total dose of alfaxalone was recorded and cough reflex at endotracheal intubation was scored. Heart rate (HR) was continuously recorded, Doppler systolic arterial blood pressure (SAP) was measured every 20 seconds. Vasovagal tonus index (VVTI) and changes (Δ) in HR, SAP and VVTI between pre-intubation and intubation were calculated. Groups were compared using univariate and multivariate analysis. Statistical significance was set as p < 0.05.ResultsGroup F included 22 dogs and group L 24 dogs. The mean (± standard deviation) alfaxalone dose was 1.1 (± 0.2) and 1.35 (± 0.3) mg kg^–1 in groups F and L, respectively (p = 0.0008). At intubation, cough was more likely in group L (odds ratio = 11.3; 95% confidence intervals, 2.1 – 94.2; p = 0.01) and HR increased in 87.5% and 54.5% of groups L and F, respectively (p = 0.02). The median (range) ΔHR between pre-intubation and intubation was higher (13.1%; – 4.3 to + 55.1) in group L (p = 0.0021). Between groups, SAP and VVTI were similar.Conclusion and clinical relevanceAt the stated doses, whilst reducing the alfaxalone dose, fentanyl is superior to lidocaine in suppressing the cough reflex and blunting the increase in HR at endotracheal intubation in dogs premedicated with methadone.     

Effect of intravenous lidocaine on heart rate, systolic arterial blood pressure and cough responses to endotracheal intubation in propofol-anaesthetized dogs

OBJECTIVE: To evaluate the effect of intravenous lidocaine on coughing and variations in heart rate (HR) and systolic arterial pressure (SAP) at endotracheal intubation in propofol-anaesthetized dogs. STUDY DESIGN: Prospective, randomized, blinded clinical study. ANIMALS: Eighty dogs, ASA grades I/II. METHODS: Dogs were randomly assigned to one of two treatments, with dogs in the lidocaine group receiving 1 mg kg(-1) lidocaine intravenously and those in the saline group receiving 0.05 mL kg(-1) saline intravenously before induction of anaesthesia with up to 6.5 mg kg(-1) propofol intravenously. An electrocardiogram was recorded continuously. Heart rate was calculated and SAP (using Doppler ultrasonic flow detection) was recorded at the following time points: pre-treatment, following lidocaine or saline administration, before and after intubation. The occurrence, number and strength of coughs were recorded. Systolic arterial pressure and HR were compared using one-sample t-tests to examine whether SAP and HR changed with test drug administration or following intubation. The number of coughs was compared between groups using t-tests. A cross tabulation and chi-square or Fisher's exact test was used to compare proportions of dogs that coughed and intensity of coughing in each group. The level of significance was set at p < 0.05. RESULTS: Heart rate did not change in either group. Systolic arterial blood pressure increased following intubation in both the lidocaine (p = 0.003) and saline groups (p = 0.001). There was no difference in the increase in SAP or in the number or intensity of coughs at intubation between groups. CONCLUSIONS AND CLINICAL RELEVANCE: Intravenous lidocaine had no effect on the occurrence or intensity of coughing or on changes in SAP at endotracheal intubation in dogs anaesthetized with propofol. The use of 1 mg kg(-1) lidocaine intravenously before intubation in dogs to attenuate cough and the pressor response was not supported.     

Evaluation of laryngeal mask as an alternative to endotracheal intubation in cats anesthetized under spontaneous or controlled ventilation

OBJECTIVE: To compare the cardiorespiratory effects and incidence of gastroesophageal reflux with the use of a laryngeal mask airway (LMA) or endotracheal tube (ET) in anesthetized cats during spontaneous (SV) or controlled ventilation (CV). STUDY DESIGN: Prospective randomized experimental trial. ANIMALS: Thirty-two adult crossbred cats, weighing 2.7 +/- 0.4 kg. METHODS: The cats were sedated with intramuscular (IM) methotrimeprazine (0.5 mg kg(-1)) and buprenorphine (0.005 mg kg(-1)), followed 30 minutes later by induction of anesthesia with intravenous (IV) thiopental (12.5-20 mg kg(-1)). An ET was used in 16 cats and an LMA in the remaining 16 animals. Anesthesia was maintained with 0.5 minimum alveolar concentration (0.6%) of halothane in oxygen using a Mapleson D breathing system. Cats in both groups were further divided into two equal groups (n = 8), undergoing either SV or CV. Neuromuscular blockade with pancuronium (0.06 mg kg(-1)) was used to facilitate CV. Heart and respiratory rates, direct arterial blood pressure, capnometry (PE'CO2) and arterial blood gases were measured. Gastric reflux and possible aspiration was investigated by intragastric administration of 5 mL of radiographic contrast immediately after induction of anesthesia. Cervical and thoracic radiographs were taken at the end of anesthesia. Data were analyzed using anova followed by Student-Newman-Keuls, Kruskal-Wallis or Friedman test where appropriate. RESULTS: Values for PaCO2 and PE'CO2 were higher in spontaneously breathing cats with the LMA when compared with other groups. Values of PaO2 and hemoglobin oxygen saturation did not differ between groups. Gastroesophageal reflux occurred in four of eight and two of eight cats undergoing CV with ET or LMA, respectively. There was no tracheal or pulmonary aspiration in any cases. CONCLUSIONS AND CLINICAL RELEVANCE: The use of an LMA may be used as an alternative to endotracheal intubation in anesthetized cats. Although aspiration was not observed, gastric reflux may occur in mechanically ventilated animals.     

Traumatic endotracheal intubation in the cat

BACKGROUND: Orotracheal intubation is a commonly performed procedure in the cat, but it is not without complications. Tracheal rupture has been reported in cats, but trauma to the arytenoids from intubation has not been documented. OBSERVATIONS: An otherwise healthy, 5-year-old male domestic shorthair cat presented for total ear canal ablation to resolve intractable otitis media and externa. The cat was premedicated with glycopyrrolate, hydromorphone, and acepromazine. Anesthesia was induced with diazepam and ketamine, and maintained with isoflurane in oxygen. During orotracheal intubation, the larynx was poorly visualized and excessive force was used to perform intubation. Subsequently, blood was observed in the larynx and laryngoscopy revealed a tear lateral to the patient's right arytenoid which had been created during intubation. The larynx was re-intubated normally and the cat suffered no obvious ill effects from the trauma to the larynx. CONCLUSIONS: Direct observation and proper technique must be employed during orotracheal intubation in cats in an attempt to avoid laryngeal trauma.     

Use of neuromuscular blockade with rocuronium bromide for intubation in cats

ObjectiveTo determine whether neuromuscular blockade with rocuronium bromide (RB) would improve endotracheal intubation (EI) conditions in comparison with topical lidocaine hydrochloride (LH).Study designRandomized prospective study.AnimalsForty seven healthy cats of unspecified breed, aged 17 ± 11 months and weighing 2.8 ± 0.8 kg, undergoing elective procedures.MethodsAnesthesia was induced with xylazine (XZ) (1.1 mg kg^?1 IM) and tiletamine‐zolazepam (XTZ) (7 mg kg^?1 IM) and EI was attempted. Cats which could not be intubated at the first attempt (n = 34), were randomly medicated with either 0.1 mL LH 10% spray on the laryngeal mucosa (n = 17) or 0.6 mg kg^?1 intravenous RB (n = 17). Sixty seconds later, a second attempt at EI was performed. The effect of both drugs was assessed using a previously published scale (Sandor Agoston). EI conditions associated with laryngoscopy, vocal cord position and movement, cough, patient movement, time and attempts needed in order to perform EI were recorded. Heart rate and end‐expired CO₂ concentration were monitored.ResultsGroups were comparable in age, weight, gender and hematological parameters. Clinically acceptable EI conditions were not significantly different between RB and LH assisted groups (p = 0.31). However, there was a significant difference in cough, vocal cord movement and position between the RB and the LH groups. The group intubated at the first attempt and receiving neither RB nor LH coughed persistently (11/13). The cats receiving RB had to be ventilated for 10–28 minutes.Conclusions and clinical relevanceThe present study shows that, when used in cats anesthetized with XTZ, RB paralyzes the internal laryngeal muscles keeping the vocal cords in an intermediate position (paramedial) 60 seconds after being administered. RB is an effective alternative to LH to overcome the airway protective reflexes when performing EI but requires ventilatory support until the paralysis wears off.     

A low-cost portable simulator of a domestic cat larynx for teaching endotracheal intubation

ObjectiveTo design and construct an affordable simulator of the cat larynx for training intubation maneuvers and to share the designs for its fabrication.Study designResearch and development study.AnimalsA domestic cat.MethodsThe cadaver of a cat, dead by natural causes, was frozen in sternal recumbency with the neck extended and the mouth wide open. A computed tomography image was acquired and used to construct a digital three-dimensional (3D) model of the pharynx and trachea. A digitally adapted model was 3D-printed and used to generate a silicone model of these structures, which was placed within a wooden container. The quality of the simulator was assessed by 46 veterinary anesthesiologists and veterinarians with experience in tracheal intubation maneuvers, and their opinions were obtained through an anonymous questionnaire.ResultsSeveral preliminary prototypes were assessed regarding stability, texture and cost. Finally, a silicone model of a cat larynx (LaryngoCUBE) was produced and encased in a wooden container. Results from the questionnaire showed high scores regarding anatomy, tissue texture and intubation maneuver realism, compared with the real procedure.Conclusionsand clinical relevance Use of LaryngoCUBE as a training tool may improve the skills of students and reduce the use of animals for teaching endotracheal intubation. Blueprints and computational models are provided online so that the simulator can be fully reproduced.     

Laryngeal mask airway insertion requires less propofol than endotracheal intubation in dogs

OBJECTIVE: To compare the doses of propofol required for insertion of the laryngeal mask airway (LMA) with those for endotracheal intubation in sedated dogs. STUDY DESIGN: Randomized prospective clinical study. Animals Sixty healthy dogs aged 0.33-8.5 (3.0 +/- 2.3, mean +/- SD) years, weighing 2.2-59.0 (23.4 +/- 13.6, mean +/- SD) kg, presented for elective surgery requiring inhalation anaesthesia. METHODS: Animals were randomly assigned to receive either a LMA or an endotracheal tube. Pre-anaesthetic medication was intravenous (IV) glycopyrrolate (0.01 mg kg(-1)) medetomidine (10 microg kg(-1)) and butorphanol (0.2 mg kg(-1)). Repeated IV propofol injections (1 mg kg(-1) in 30 seconds) were given until LMA insertion or endotracheal intubation was achieved, when the presence or absence of laryngospasm, the respiratory rate (fr) and the total dose of propofol used were recorded. RESULTS: The total propofol dose (mean +/- SD) required for LMA insertion (0.53 +/- 0.51 mg kg(-1)) was significantly lower than for endotracheal intubation (1.43 +/- 0.57 mg kg(-1)). The LMA could be inserted without propofol in 47% of dogs; the remainder needed a single 1 mg kg(-1) bolus (n = 30). Endotracheal intubation was possible without propofol in 3.3% of the dogs, 47% needed one bolus and 50% required two injections (n = 30). The f(r) (mean +/- SD) was 18 +/- 6 and 15 +/- 7 minute(-1) after LMA insertion and intubation, respectively. CONCLUSION AND CLINICAL RELEVANCE: Laryngeal mask airway insertion requires less propofol than endotracheal intubation in sedated dogs therefore propofol-induced cardiorespiratory depression is likely to be less severe. The LMA is well tolerated and offers a less invasive means of securing the upper airway.     

Plasma fentanyl concentrations in awake cats and cats undergoing anesthesia and ovariohysterectomy using transdermal administration

Objective To measure the plasma fentanyl concentrations achieved over time with transdermal fentanyl patches in awake cats and cats undergoing anesthesia and ovariohysterectomy. Study design Randomized prospective experimental study. Animals Twenty‐four purpose‐bred cats. Methods Cats were randomly assigned to three groups for Part I of a larger concurrent study. Group P received only a 25 μg hour^?1 transdermal fentanyl patch. Group P/A received the patch and anesthesia. Group A received only anesthesia. After a minimum 1‐week washout period, the cats were randomly reassigned to two groups for Part II of the larger study. Group P/A/O received the patch, anesthesia and ovariohysterectomy. Group A/O received anesthesia and ovariohysterectomy. Patches were left in place for 72 hours and plasma samples were obtained for fentanyl analysis while the patches were in place, and for 8 hours after patch removal for cats in Group P, P/A, and P/A/O. Results The 25 μg hour^?1 transdermal fentanyl patches were well tolerated by the cats in this study (mean body weight of 3.0 kg) and no overt adverse effects were noted. Mean plasma fentanyl concentrations over time, mean plasma fentanyl concentrations at specific times (8, 25, 49, and 73 hours after patch placement), time to first detectable plasma fentanyl concentration, time to reach maximum plasma fentanyl concentration, maximum plasma fentanyl concentration, mean plasma fentanyl concentration from 8 to 73 hours, elimination half‐life, and total area under concentration (AUC) were not statistically different among the groups. Conclusions Halothane anesthesia and anesthesia/ovariohysterectomy did not significantly alter the plasma fentanyl concentrations achieved or pharmacokinetic parameters measured, when compared with awake cats. There was a high degree of individual variability observed both within and between groups of cats in parameters measured. Clinical significance The high degree of variability observed suggests that careful observation of cats with fentanyl patches in place is required to assess efficacy and any potential adverse effects. Anesthesia and anesthesia/ovariohysterectomy do not appear to alter plasma fentanyl concentrations achieved by placement of a 25 μg hour^?1 transdermal fentanyl patch when compared to cats not undergoing these procedures.     

Evaluation of the endotracheal tube cuff pressure resulting from four different methods of inflation in dogs

Objective To evaluate the endotracheal tube cuff pressure achieved by four different inflation methods. Study design Prospective clinical study. Animals Eighty client owned dogs. Methods After anaesthesia induction, endotracheal intubation was performed using plastic or silicone tubes. A clinician unaware of tube type inflated the cuff by simple digital palpation (method A), thereafter the cuff was deflated and inflated again by a second clinician who tried to reproduce a previously learned cuff pressure of between 19 and 24 mmHg (method B). During method C the cuff was inflated to the minimum occlusive volume at an airway pressure of 20 cm H₂O, and in method D the cuff was incrementally deflated until an audible air leak could be heard from the oral cavity at an airway pressure of 25 cm H₂O. For all the methods, an operator recorded the actual cuff pressure obtained using a manometer. Heart rate, respiratory rate and mean arterial pressure were monitored throughout the procedure. Results The mean inflation pressure for plastic tubes was 56 ± 28 mmHg for method A, 20 ± 9 mmHg for method B, 35 ± 32 mmHg for method C and 46 ± 39 mmHg for method D. Pressures using silicone tubes were significantly higher than for plastic tubes, the mean registered pressures being 79 ± 39, 33 ± 16, 77 ± 50 and 92 ± 56 mmHg for methods A, B, C and D. Conclusions and Clinical Relevance None of the methods evaluated in this study can be considered effective for inflating the endotracheal tube cuff to within the optimal range when using silicone tubes. Direct measurement of the cuff pressure with a manometer is therefore recommended.     

Pharmacokinetics of intravenous and transdermal fentanyl in alpacas

The purpose of the study was to determine pharmacokinetics of fentanyl after intravenous (i.v.) and transdermal (t.d.) administration to six adult alpacas. Fentanyl was administered i.v. (2 μg/kg) or t.d. (nominal dose: 2 μg kg^?1 hr^?1). Plasma concentrations were determined using liquid chromatography–mass spectrometry. Heart rate and respiratory rate were assessed. Extrapolated, zero‐time plasma fentanyl concentrations were 6.0 ng/ml (1.7–14.6 ng/ml) after i.v. administration, total plasma clearance was 1.10 L hr^?1 kg^?1 (0.75–1.40 L hr^?1 kg^?1), volumes of distribution were 0.30 L/kg (0.10–0.99 L/kg), 1.10 L/kg (0.70–2.96 L/kg) and 1.5 L/kg (0.8–3.5 L/kg) for V₁, V₂, and V_ss, respectively. Elimination half‐life was 1.2 hr (0.5–4.3 hr). Mean residence time (range) after i.v. dosing was 1.30 hr (0.65–4.00 hr). After t.d. fentanyl administration, maximum plasma fentanyl concentration was 1.20 ng/ml (0.72–3.00 ng/ml), which occurred at 25 hr (8–48 hr) after patch placement. The area under the plasma fentanyl concentration‐vs‐time curve (extrapolated to infinity) after t.d. fentanyl was 61 ng*hr/ml (49–93 ng*hr/ml). The dose‐normalized bioavailability of fentanyl from t.d. fentanyl in alpacas was 35.5% (27–64%). Fentanyl absorption from the t.d. fentanyl patch into the central compartment occurred at a rate of approximately 50 μg/hr (29–81 μg/hr) between 8 and 72 hr after patch placement.     

Effect of transdermally administered fentanyl on the minimum alveolar concentration of isoflurane in cats

OBJECTIVE: To determine the effect of two doses of fentanyl, administered transdermally, on the minimum alveolar concentration (MAC) of isoflurane in cats. STUDY DESIGN: Prospective, randomized study. ANIMALS: Five healthy, spayed, female cats. METHODS: Each cat was studied thrice with at least 2 weeks between each study. In study 1, the baseline isoflurane MAC was determined in triplicate for each cat. In studies 2 and 3, isoflurane MAC was determined 24 hours after placement of either a 25 or 50 microg hour(-1) fentanyl patch. In each MAC study, cats were instrumented to allow collection of arterial blood and measurement of arterial blood pressure. Twenty-four hours prior to studies 2 and 3, a catheter was placed and secured in the jugular vein and either a 25 or 50 microg hour(-1) fentanyl patch was placed in random order on the left thorax. Blood samples for plasma fentanyl determination were collected prior to patch placement and at regular intervals up to 144 hours. After determination of MAC in studies 2 and 3, naloxone was administered as a bolus dose (0.1 mg kg(-1)) followed by an infusion (1 mg kg(-1) hour(-1)) and MAC redetermined. RESULTS: The baseline isoflurane MAC was 1.51 +/- 0.21% (mean +/- SD). Fentanyl (25 and 50 micro g hour(-1)) administered transdermally significantly reduced MAC to 1.25 +/- 0.26 and 1.22 +/- 0.16%, respectively. These MAC reductions were not significantly different from each other. Isoflurane MAC determined during administration of fentanyl 25 micro g hour(-1) and naloxone (1.44 +/- 0.16%) and fentanyl 50 micro g hour(-1) and naloxone (1.51 +/- 0.19%) was not significantly different from baseline MAC (1.51 +/- 0.21%). CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl patches are placed to provide long-lasting analgesia. In order to be effective postoperatively, fentanyl patches must be placed prior to surgery. Plasma fentanyl concentrations achieved intraoperatively decrease the need for potent inhalant anesthetics in cats.     

Effects of two fentanyl constant rate infusions on thermal thresholds and plasma fentanyl concentrations in awake cats

Objective

To determine the pharmacokinetics and effects on thermal thresholds (TT) of two fentanyl constant rate infusions in awake cats.

The effects of two endotracheal tube cuff inflation pressures on liquid aspiration and tracheal wall damage in horses

OBJECTIVE: To investigate the effect of endotracheal tube cuff inflation pressure on the occurrence of liquid aspiration and tracheal wall damage. STUDY DESIGN: Prospective, randomized experimental study. ANIMALS: Ten healthy horses, weighing 535 +/- 55 kg. METHODS: Horses were anesthetized, orotracheally intubated, placed in dorsal recumbency, and maintained on isoflurane in oxygen with controlled ventilation for 175 +/- 15 minutes. The horses were randomly assigned to an endotracheal cuff pressure of 80-100 or 120 cm H2O. The cuff pressure was continuously monitored and maintained at a constant pressure. Methylene blue in saline was instilled proximal to the cuff. After euthanasia, the trachea was opened distal to the endotracheal tube tip to check for evidence of dye leaking past the cuff. The cervical trachea was then resected and opened longitudinally for gross and histologic examinations. RESULTS: No blue staining was found distal to the cuff in any horse. Visual examination of the tracheal mucosa revealed hyperemic and hemorrhagic lesions at the site of the cuff contact. Histologic changes included epithelium attenuation or erosion, submucosal neutrophilic infiltration, and submucosal hemorrhages. Lesions were absent or less extensive in the lower cuff pressure group as compared to the high cuff pressure group. CONCLUSIONS: The endotracheal tube cuff produced a seal sufficient to prevent leakage in both groups. Tracheal wall damage was more severe and occurred more frequently in the higher cuff pressure group. CLINICAL RELEVANCE: Tracheal mucosal damage induced by cuff inflation is pressure-dependent. Cuff pressure monitoring is recommended.     

A comparison between the v‐gel supraglottic airway device and the cuffed endotracheal tube for airway management in spontaneously breathing cats during isoflurane anaesthesia

ObjectiveTo compare airway management using the v-gel supraglottic airway device (v-gel SGAD) to that using an endotracheal tube (ETT), with respect to practicability, leakage of volatile anaesthetics and upper airway discomfort in cats.Study designProspective, randomized clinical trial.AnimalsTwenty European Shorthair cats (9 males, 11 females), weighing 3.3 ± 0.7 kg.MethodsCats were randomly allocated to one of two groups, in which the airway was managed by either the v-gel SGAD or a cuffed ETT, and anaesthetized for neutering procedures. The dose of propofol necessary to insert the ETT or v-gel SGAD; time from the first injection of propofol to the first clinically acceptable reading on the capnograph; leakage of isoflurane around the airway device; and upper airway discomfort scores during recovery and during the first 24 hours after anaesthesia were recorded. Continuous and discrete variables were analyzed with the Mann–Whitney U-test and the Pearson chi-squared test, respectively. Results were considered statistically significant if p < 0.05.ResultsTime from the first injection of propofol to the first clinically acceptable reading on the capnograph was significantly shorter in the v-gel group. The ETT group showed significantly more stridor during recovery. No other significant differences were found.Conclusions and clinical relevanceAirway management with the v-gel SGAD is a sound and practicable alternative to endotracheal intubation with an ETT. However, larger prospective trials will be needed to draw firm conclusions on the benefits and/or drawbacks of the use of v-gel SGAD for airway management in cats.     

The effect of user experience and inflation technique on endotracheal tube cuff pressure using a feline airway simulator

Objective

The effect of user experience and inflation technique on endotracheal tube cuff pressure using a feline airway simulator.