Abstract
Objective
To investigate anaesthesiologists’ attitudes towards endotracheal intubation and the perceived incidence of complications secondary to endotracheal intubation in dogs and cats.
Study design
A cross-sectional online questionnaire-based study.
Methods
Using an online questionnaire distributed via electronic mail, the perceived incidence of complications secondary to endotracheal intubation in dogs and cats was investigated. Attitudes towards endotracheal intubation, average caseload and percentage of animals intubated were examined. The study population consisted of Diplomates, Residents, and residency trained members of the American and European Colleges of Veterinary Anaesthesia and Analgesia. Univariate descriptive statistics were calculated. For each complication, a mean incidence score (MIS) was calculated, ranging from 1 (never) to 5 (always). Additionally, a Wilcoxon signed rank test and binary regression analyses were performed. A p ≤ 0.05 was regarded as significant.
Results
The overall response rate was 35.1%, with a completion rate of 26.6%. Most dogs and cats undergoing general anaesthesia were intubated. Endotracheal intubation was viewed as an integral part of modern anaesthesia. Significant differences were found in the incidence of 16 of the 24 examined complications between dogs and cats (p ≤ 0.001). In dogs, the most frequently perceived complications were reported to be cuff leak (MIS 3.20) and coughing during intubation (MIS 3.10), whereas in cats, the most frequently perceived complications were reported to be coughing and laryngeal spasm during intubation (MIS 3.01 and 2.91, respectively). Socio-demographic and practice-specific aspects did not appear to play a significant role in the reported incidence of complications.
Conclusion
And clinical relevance: Endotracheal intubation was considered a state-of-the-art technique by the respondents. It was associated with a perceived low incidence of major complications and more frequent minor ones. Differences between dogs and cats need to be accounted for. Considering the retrospective and self-reporting nature of this survey, true incidences might differ.
Keywords
Introduction
Veterinary anaesthetists commonly perform endotracheal intubation as part of the airway management of anaesthetized dogs and cats. Benefits of endotracheal intubation include provision of a patent airway, facilitation of mechanical ventilation, protection of lower airways from aspiration of fluids, and prevention of contamination of the work environment with waste anaesthetic gases (
Mosley, 2017
). However, endotracheal intubation in dogs and cats has been associated with complications, which may become evident during the procedure itself, shortly after, or even after days or weeks. Described complications range from minor, such as coughing and soft tissue trauma of the oral cavity and larynx, to major (i.e., potentially life-threatening), such as unnoticed oesophageal intubation, laryngeal oedema, tracheal stenosis and tracheal necrosis (Brown, 2007
; Auckburally and Flaherty, 2017
; Auckburally A, Flaherty D (2017) Airway Management Part 1. https://www.scvetspecialists.co.uk/about-us/news/december-2017/airway-management-part-1 Last accessed 27 April 2022
Sager, 2018
; Dugdale et al., 2020
).Unlike in human medicine, veterinary literature investigating complications secondary to endotracheal intubation is scarce. Endotracheal intubation has been found to increase the risk of complications and the odds of death in cats undergoing general anaesthesia (GA) (
Clarke and Hall, 1990
; Dyson et al., 1998
; Brodbelt et al., 2008
). Additionally, potentially life-threatening complications have been described in several veterinary case reports (Knecht et al., 1972
; Hardie et al., 1999
; Bergadano et al., 2004
; Kästner et al., 2004
; Alderson et al., 2006
; Hofmeister et al., 2007
; Bhandal and Kuzma, 2008
; Thomas and Syring, 2013
). However, specific studies on the type and incidence of complications associated with endotracheal intubation in dogs and cats have not been yet published.During the investigation for this study, no veterinary research analysing the factors influencing the risk of complications secondary to endotracheal intubation could be identified. In human medicine, risk factors such as skill level of the physician, urgency of the procedure, physical status of the patient, and technique-specific factors have been demonstrated to play a role in the incidence of complications (
Divatia and Bohwmick, 2005
; Griesdale 2008; Pacheco-Lopez et al., 2014
). Conversely, in veterinary medicine, this remains to be determined. Likewise, although veterinary anaesthesiologists are trained to perform endotracheal intubation in dogs and cats, research on their knowledge and attitudes towards endotracheal intubation have not yet been published.Therefore, this study aimed to answer (I) what are anaesthesiologists’ attitudes towards endotracheal intubation in dogs and cats, (II) what is the perceived incidence of complications encountered during endotracheal intubation, while animals are intubated and after extubation in dogs and cats, and (III) whether socio-demographic, practice-specific, and technical aspects affect the incidence of these complications.
We hypothesised that veterinary anaesthesiologists perceive endotracheal intubation in dogs and cats as a safe procedure with a low risk of complications, but that minor complications happen frequently. We further hypothesised that there is a significant difference in the perceived incidence of complications secondary to endotracheal intubation between dogs and cats. Finally, we hypothesised that socio-demographic, practice-specific, and technical aspects affect the perceived incidence of these complications.
Materials and methods
A closed, web-based survey was designed using the software Alchemer (Louisville, CO, USA). The target population included Diplomates, Residents, and residency trained members of the American and European Colleges of Veterinary An(a)esthesia and Analgesia (ACVAA and ECVAA, respectively). For the purpose of writing the manuscript, the term 'anaesthesiologist' was applied to all participants.
The national ethics committee of the Medical University Vienna (Vienna, Austria) deemed no approval was required for this study (Ref: 005_001). Participants' consent for data collection was ensured by a statement in the invitation e-mail and on the first page of the survey. Participation was anonymous, confidential, and voluntary. No incentives were offered to participants. Responses were automatically anonymized and neither internet protocol addresses nor other identifying data were available to the authors.
The survey was developed based on relevant literature for endotracheal intubation and guidelines for the development of online surveys, including the ‘Checklist for Reporting Results of Internet E-Surveys (CHERRIES;
Eysenbach, 2004
; Bennett, 2020
). The survey underwent two stages of pre-testing. In a first stage, cognitive interviews (Presser et al., 2004
; Campanelli, 2008
) with five specialists in veterinary anaesthesiology or emergency and critical care were performed to determine whether wording and content could lead to uncertainties or misunderstandings by the respondents. In a second stage, an online pre-test phase was conducted with 21 anaesthesiologists. Relevant comments that were likely to improve the quality of data were incorporated into the final version of the survey.E-mail invitations containing a link to the online questionnaire were sent by the Executive secretaries of the ACVAA and ECVAA to their members. The ECVAA invited 360 members (179 Diplomates and 181 Residents, or residency trained individuals) on May 26th, 2021, and the ACVAA invited 358 members (278 Diplomates and 80 Residents, or residency trained individuals) on May 16th, 2021. E-mail reminders were sent 2 weeks after the initial invitation. Additionally, the survey was announced on the ECVAA Residents' Facebook group on June 9th, 2021. The survey was closed on June 24th, 2021. The invitation provided information about the background of the study, the participating university, ethical approval, and rights of participants during the reply process.
The survey consisted of four sections focusing on socio-demographic and practice-related factors, general aspects concerning endotracheal intubation, endotracheal tube (ETT) cuff inflation, cuff pressure measurement and complications secondary to endotracheal intubation (Appendix A). The present study comprises a subset of data obtained from the survey. The data presented here focused on the attitudes of anaesthesiologists towards endotracheal intubation and the perceived complications secondary to endotracheal intubation. The following questions were included in this study:
The first section included 12 close-ended questions (1–12) that provided information on socio-demographic and practice-specific factors.
The second section included six single choice questions (14–19) that were focused on the frequency of intubation in dogs and cats undergoing GA, the number of dogs and cats intubated per week by the participant, and the frequency of difficult intubations. Additionally, three single-choice questions (28–30) on the use of a stylet/bougie, lidocaine spray, and lubrication during intubation were included. This section also included eight statements to examine the anaesthesiologists' attitude towards endotracheal intubation in dogs and cats (question 20). Participants were asked to indicate their level of agreement from 1 “strongly disagree” to 5 “strongly agree” and 6 “I don’t know”. Finally, the perceived occurrence of seven specific complications during endotracheal intubation was queried using the responses from 1 “never” to 5 “always” and 6 “I don’t know” (questions 33 and 34).
The third section included two single-choice questions (35 and 38) related to the participants’ attitudes towards cuff pressure measurement and reassessment of cuff pressure during anaesthesia.
The final section included four matrix-style questions (41–44). The first two questions queried seven complications seen while animals were intubated, the second two questions queried 10 complications seen after animals were extubated. Participants were requested to indicate the perceived frequency of occurrence from 1 “never” to 5 “very often” and 6 “I don’t know”.
Questions could be skipped, enabling participants to finish one or more sections without answering all questions. Respondents were able to review/change their answers until submission of the completed survey.
Data analysis
The statistical software IBM SPSS Statistics version 27.0 (IBM Corporation, Armonk, NY, USA) was used to conduct all analyses. Univariate descriptive statistics are presented in Tables or text. Using the results from questions 33, 34 and 41–44, a mean incidence score (MIS) ranging from 1 (never) to 5 (always/very often) was derived by taking the mean value of all answers from the respondents for each specific complication.
For bivariate statistics, Wilcoxon signed rank tests were conducted to identify differences between dogs and cats for several factors. These factors included general attitudes towards endotracheal intubation, the average number of cases undergoing GA in the facility, the percentage of anaesthetised animals that were intubated, number of animals intubated by the participant per week, and the percentage of intubations that were perceived as difficult. In addition, Wilcoxon signed rank tests were used to identify differences between dogs and cats in relation to the specific complications that may have occurred during endotracheal intubation, while the animals were intubated or after extubation.
Binary logistic regression analyses were conducted separately for dogs and cats to examine effects of socio-demographic, practice-specific, and technical aspects of intubation on the perceived incidence of complications: Supplementary Tables S1, S2 and S3 includes information about specific complications (dependent variables), dichotomisation of the dependent variables and the predictor variables included in the survey.
Results
A total of 61 partial and 191 complete responses to the survey were collected. Overall response rate was 35.1%, with a completion rate of 26.6%. After review of the data, 59 responses were excluded due to missing answers to questions analysed in this study. Thus, 193 responses were included for statistical analysis, representing 21.8% of all ACVAA and 29.7% of all ECVAA respondents. Detailed information about specific socio-demographic as well as practice-specific data for the whole study population are listed in Supplementary Table S4
Attitudes of anaesthesiologists towards endotracheal intubation in dogs and cats
More than 95% of the participants agreed that intubation is a key element of state-of-the-art anaesthesia. Agreement with the statement that ‘intubation should be performed in every patient undergoing general anaesthesia’ was significantly higher for dogs (90.7%) compared to cats (75.6%; p < 0.001). Similarly, more respondents agreed with the statement that ‘intubation reduces mortality’ in dogs (88%) compared to cats (76.6%; p < 0.001). The same species difference was found regarding the statement that intubation carries ‘a low incidence of complications’, which was found to be 94.3% in dogs versus 71.0% in cats (p < 0.001).
Caseload, frequency of endotracheal intubation and difficulties with endotracheal intubation in dogs and cats
An average caseload of more than 20 cases per week was indicated by 81.4% of the respondents when referring to dogs and 21.0% of the respondents when referring to cats (p < 0.001). Subsequently, participants reported that significantly more dogs were intubated per week compared with cats (p < 0.001). Most respondents indicated that endotracheal intubation was performed in 91-100% of their cases undergoing GA, but dogs were significantly more likely to be intubated during GA compared to cats (95.3% versus 88.0% respectively, p < 0.001). Difficult intubation was reported in less than 10% of cases by 83.3%, i.e., most participants, when referring to dogs, whereas 62.0% of participants indicated the same when referring to cats. Similarly, difficult intubation was reported in greater than 10% of cases significantly more often in cats than dogs (36.2% versus 16.1%, p < 0.001).
Residents and residency trained participants intubated on average more dogs (p < 0.001) and cats (p = 0.039) per week compared to Diplomates. However, no significant differences between the groups were identified for the perceived incidence of difficult intubations.
Complications secondary to endotracheal intubation in dogs and cats
In the following sections, results are provided to a greater level of detail regarding complications during endotracheal intubation, while animals were intubated and after extubation. All queried complications with their respective MIS were ranked from highest to lowest for dogs and cats (Table 1).
Table 1Complications secondary to endotracheal intubation in dogs and cats ranked from highest to lowest incidence. Data were obtained via an anonymous online survey distributed to Diplomates, Residents and residency trained members of the American and European Colleges of Veterinary An(a)esthesia and Analgesia.
| Dogs | Cats | |||
|---|---|---|---|---|
| Rank | Complication | MIS ± SD | Complication | MIS ± SD |
| 1 | Cuff leak | 3.20 ± 0.71 | Coughing during intubation | 3.01 ± 0.67 |
| 2 | Coughing during intubation | 3.10 ± 0.56 | Laryngeal spasm during intubation | 2.91 ± 0.87 |
| 3 | Coughing after extubation | 2.53 ± 0.67 | Cuff leak | 2.77 ± 0.77 |
| 4 | Accidental oesophageal intubation | 2.45 ± 0.64 | Endotracheal tube occlusion | 2.69 ± 0.63 |
| 5 | Difficulties visualising the larynx | 2.43 ± 0.57 | Accidental extubation | 2.39 ± 0.67 |
| 6 | Accidental extubation | 2.37 ± 0.60 | Coughing after extubation | 2.38 ± 0.76 |
| 7 | Endotracheal tube displacement | 2.29 ± 0.64 | Accidental oesophageal intubation | 2.31 ± 0.71 |
| 8 | Endotracheal tube occlusion | 2.27 ± 0.57 | Endotracheal tube displacement | 2.30 ± 0.66 |
| 9 | Blood on the tube after extubation | 2.21 ± 0.53 | Difficulties visualising larynx during intubation | 2.17 ± 0.68 |
| 10 | Bronchial intubation or accidental one-lung-intubation | 2.13 ± 0.54 | Blood on the tube after extubation | 2.08 ± 0.57 |
| 11 | Difficulties breathing after extubation | 1.92 ± 0.68 | Bronchial intubation or accidental one-lung-intubation | 1.99 ± 0.66 |
| 12 | Laryngeal oedema after extubation | 1.89 ± 0.56 | Laryngeal oedema after extubation | 1.93 ± 0.66 |
| 13 | Bronchitis or pneumonia after extubation | 1.88 ± 0.61 | Difficulties breathing after extubation | 1.75 ± 0.62 |
| 14 | Laryngeal spasm during intubation | 1.64 ± 0.59 | Laryngeal laceration or trauma during intubation | 1.68 ± 0.69 |
| 15 | Ruptured cuff | 1.62 ± 0.62 | Bronchitis or pneumonia after extubation | 1.67 ± 0.57 |
| 16 | Cuff herniation | 1.54 ± 0.61 | Ruptured cuff | 1.45 ± 0.60 |
| 17 | Change of voice after extubation | 1.51 ± 0.63 | Tracheal necrosis or rupture after extubation | 1.42 ± 0.53 |
| 18 | Laryngeal laceration or trauma during intubation | 1.48 ± 0.61 | Difficulties swallowing after extubation | 1.41 ± 0.53 |
| 19 | Difficulties swallowing after extubation | 1.47 ± 0.55 | Cuff herniation | 1.36 ± 0.55 |
| 20 | Cuff not deflatable | 1.42 ± 0.52 | Change of voice after extubation | 1.35 ± 0.55 |
| 21 | Dental damage during intubation | 1.32 ± 0.58 | Cuff not deflatable | 1.30 ± 0.47 |
| 22 | Tracheal stenosis after extubation | 1.26 ± 0.44 | Dental damage during intubation | 1.29 ± 0.58 |
| 23 | Tracheal necrosis or rupture after extubation | 1.22 ± 0.42 | Tracheal stenosis after extubation | 1.27 ± 0.48 |
| 24 | Loss of voice after extubation | 1.22 ± 0.42 | Loss of voice after extubation | 1.20 ± 0.43 |
MIS = mean incidence score ranging from 1 (never) to 5 (always/very often); SD = standard deviation.
∗ significant difference between the species.
Complications during endotracheal intubation in dogs and cats
The complication with the highest MIS during endotracheal intubation was reported to be coughing in both species (MIS 3.10 and 3.01 for dogs and cats, respectively). Second-ranked complications were laryngeal spasm in cats (MIS 2.91) and difficulties visualising the larynx in dogs (MIS 2.43), followed by accidental oesophageal intubation for both species (MIS 2.45 and 2.31 for dogs and cats, respectively). Anaesthesiologists who performed fewer endotracheal intubations in dogs per week indicated a higher perceived incidence of oesophageal intubation (p = 0.010) and coughing during endotracheal intubation compared to respondents that intubated dogs more frequently (p = 0.023; Supplementary Table S1). Likewise, younger anaesthesiologists stated a significantly higher perceived incidence of coughing observed during endotracheal intubation compared to older respondents (p = 0.003). With a MIS of 1.64 versus 2.91, laryngeal spasm was significantly less often reported in dogs compared to cats (p < 0.001; Table 2). Laryngeal spasm in dogs was positively associated with a greater number of dogs receiving GA per week (p = 0.014). Additionally, a positive association between the use of a stylet and reported occurrence of laryngeal spasm in cats was identified (p < 0.001) (Supplementary Table S2). While less frequently reported than laryngeal spasm, laryngeal laceration or trauma was also perceived to be seen significantly more often in cats (MIS 1.68) than in dogs (MIS 1.48; p < 0.001). Difficulty visualising the larynx (p < 0.001), accidental oesophageal intubation (p = 0.001), accidental bronchial or one-lung intubation (p = 0.001), and coughing (p = 0.037) were complications during endotracheal intubation that were reported significantly more often in dogs compared to cats (Table 2).
Table 2“How often do you see the following complications during intubation of dogs and cats?”. Relative frequencies and mean incidence scores of complications during intubation in dogs and cats. Data were obtained via an anonymous online survey distributed to Diplomates, Residents and residency trained members of the American and European Colleges of Veterinary An(a)esthesia and Analgesia.
| Dogs (n = 191-193) | Cats (n = 190-193) | p | |||
|---|---|---|---|---|---|
| n | % | n | % | ||
| Laryngeal spasm | < 0.001 | ||||
| Never | 80 | 41.7 | 9 | 4.7 | |
| Rarely | 101 | 52.6 | 53 | 27.5 | |
| Sometimes | 11 | 5.7 | 79 | 40.9 | |
| Often | - | 50 | 25.9 | ||
| Always | - | 2 | 1.0 | ||
| I don’t know | - | - | |||
| Difficulties visualising the larynx | < 0.001 | ||||
| Never | 5 | 2.6 | 25 | 13.1 | |
| Rarely | 103 | 53.6 | 113 | 59.2 | |
| Sometimes | 81 | 42.2 | 48 | 25.1 | |
| Often | 3 | 1.6 | 5 | 2.6 | |
| Always | - | - | |||
| I don’t know | - | - | |||
| Dental damage | 0.353 | ||||
| Never | 139 | 72.8 | 142 | 74.3 | |
| Rarely | 45 | 23.6 | 42 | 22.0 | |
| Sometimes | 3 | 1.6 | 5 | 2.6 | |
| Often | 3 | 1.6 | 1 | 0.5 | |
| Always | - | - | |||
| I don’t know | 1 | 0.5 | 1 | 0.5 | |
| Laryngeal laceration or trauma | < 0.001 | ||||
| Never | 108 | 56.3 | 83 | 43.5 | |
| Rarely | 73 | 38.0 | 83 | 43.5 | |
| Sometimes | 8 | 4.2 | 21 | 11.0 | |
| Often | 1 | 0.5 | 1 | 0.5 | |
| Always | - | - | |||
| I don’t know | 2 | 1.0 | 3 | 1.6 | |
| Accidental oesophageal intubation | 0.001 | ||||
| Never | 11 | 5.7 | 23 | 12.0 | |
| Rarely | 88 | 45.6 | 91 | 47.4 | |
| Sometimes | 90 | 46.6 | 74 | 38.5 | |
| Often | 4 | 2.1 | 4 | 2.1 | |
| Always | - | - | |||
| I don’t know | - | - | |||
| Coughing | 0.037 | ||||
| Never | 1 | 0.5 | 1 | 0.5 | |
| Rarely | 18 | 9.4 | 38 | 19.8 | |
| Sometimes | 133 | 69.3 | 113 | 58.9 | |
| Often | 40 | 20.8 | 39 | 20.3 | |
| Always | - | 1 | 0.5 | ||
| I don’t know | - | - | |||
| Bronchial intubation or accidental one-lung-intubation | 0.001 | ||||
| Never | 16 | 8.3 | 40 | 21.1 | |
| Rarely | 134 | 69.8 | 110 | 57.9 | |
| Sometimes | 39 | 20.3 | 37 | 19.5 | |
| Often | 1 | 0.5 | 1 | 0.5 | |
| Always | - | - | |||
| I don’t know | 2 | 1.0 | 2 | 1.1 | |
“Never”= 1, “Rarely”= 2, “Sometimes”= 3, “Often”= 4, “Always”= 5, “I don’t know” =6.
∗ Related-Samples Wilcoxon Signed Rank Test – “I don’t know” answer option excluded from analyses.
Complications while animals were intubated
Leakage of the ETT cuff was the most commonly reported complication in both species while animals were intubated, with a MIS of 3.20 and 2.77 in dogs and cats, respectively. This complication was perceived to be seen significantly more often in dogs than in cats (p < 0.001; Table 3). Regression analysis revealed no significant association of socio-demographic or practice-specific factors with leakage of the ETT cuff (Supplementary Table S2). In cats, the second most commonly reported complication was occlusion of the ETT (MIS 2.69), which was perceived to be seen significantly more frequently than in dogs (p < 0.001) (Table 3). Further significant differences between the species were found for cuff herniation (p < 0.001) and rupture of the cuff (p < 0.01) (Table 3). For cuff herniation, no significant association with socio-demographic or practice-specific factors could be found (Supplementary Table S2).
Table 3“How often do you see the following complications in dogs and cats while they are intubated?”. Relative frequencies and mean incidence scores of complications in dogs and cats while intubated. Data were obtained via an anonymous online survey distributed to Diplomates, Residents and residency trained members of the American and European Colleges of Veterinary An(a)esthesia and Analgesia.
| Dogs (n = 181-183) | Cats (n = 182) | p | |||
|---|---|---|---|---|---|
| n | % | n | % | ||
| Endotracheal tube displacement | 0.647 | ||||
| Never | 13 | 7.1 | 15 | 8.2 | |
| Rarely | 109 | 59.9 | 102 | 56.0 | |
| Sometimes | 55 | 30.2 | 60 | 33.0 | |
| Often | 5 | 2.7 | 5 | 2.7 | |
| Very often | - | - | |||
| I don’t know | - | - | |||
| Cuff herniation | < 0.001 | ||||
| Never | 93 | 51.4 | 120 | 65.9 | |
| Rarely | 73 | 40.3 | 53 | 29.1 | |
| Sometimes | 11 | 6.1 | 6 | 3.3 | |
| Often | - | - | |||
| Very often | - | - | |||
| I don’t know | 4 | 2.2 | 3 | 1.6 | |
| Endotracheal tube occlusion (e.g., due to mucus, kinked tube, etc.) | < 0.001 | ||||
| Never | 9 | 4.9 | 2 | 1.1 | |
| Rarely | 116 | 63.7 | 67 | 36.8 | |
| Sometimes | 55 | 30.2 | 98 | 53.8 | |
| Often | 2 | 1.1 | 15 | 8.2 | |
| Very often | - | - | |||
| I don’t know | - | - | |||
| Accidental extubation | 0.688 | ||||
| Never | 8 | 4.4 | 12 | 6.6 | |
| Rarely | 102 | 55.7 | 93 | 51.1 | |
| Sometimes | 70 | 38.3 | 72 | 39.6 | |
| Often | 3 | 1.6 | 4 | 2.2 | |
| Very often | - | 1 | 0.5 | ||
| I don’t know | - | - | |||
| Cuff leak | < 0.001 | ||||
| Never | 1 | 0.5 | 8 | 4.4 | |
| Rarely | 23 | 12.6 | 52 | 28.6 | |
| Sometimes | 102 | 55.7 | 99 | 54.4 | |
| Often | 52 | 28.4 | 20 | 11.0 | |
| Very often | 5 | 2.7 | 3 | 1.6 | |
| I don’t know | - | - | |||
| Ruptured cuff | < 0.001 | ||||
| Never | 83 | 45.6 | 110 | 60.4 | |
| Rarely | 86 | 47.3 | 63 | 34.6 | |
| Sometimes | 13 | 7.1 | 9 | 4.9 | |
| Often | - | - | |||
| Very often | - | - | |||
| I don’t know | - | - | |||
| Cuff cannot be deflated (i.e., before extubation) | < 0.001 | ||||
| Never | 108 | 59.3 | 128 | 70.3 | |
| Rarely | 72 | 39.6 | 53 | 29.1 | |
| Sometimes | 2 | 1.1 | 1 | 0.5 | |
| Often | - | - | |||
| Very often | - | - | |||
| I don’t know | - | - | |||
“Never”= 1, “Rarely”= 2, “Sometimes”= 3, “Often”= 4, “Always”= 5, “I don’t know” =6.
∗ Related-Samples Wilcoxon Signed Rank Test – “I don’t know” answer option excluded from analyses.
Complications after extubation
These were reported to be infrequent (Table 4). The complication with the highest MIS after extubation was coughing in both species (MIS 2.52 and 2.38 for dogs and cats, respectively). With a MIS of 2.21 for dogs and 2.08 for cats, blood on the tube after extubation was the only other complication with a MIS greater than 2, suggesting a relative frequency more often than “rarely”. Tracheal necrosis or rupture was significantly more often reported in cats than in dogs (p < 0.001; Table 4). A positive association between reassessment of cuff pressure after initial inflation and tracheal necrosis and rupture in cats was found (p = 0.008; Supplementary Table S2). Blood on the tube (p = 0.001), change of voice (p = 0.001), difficulty breathing (p < 0.001) and bronchitis or pneumonia (p < 0.001) after extubation were reported more often in dogs than in cats (Table 4). Regression analyses indicated that members of the ACVAA reported a significantly higher incidence of bronchitis or pneumonia after extubation in dogs compared to members of the ECVAA (p = 0.027; Supplementary Table S3).
Table 4“How often do you see the following complications in dogs and cats after being extubated?” Relative frequencies and mean incidence scores of complications after extubation in dogs and cats. Data were obtained via an anonymous online survey distributed to Diplomates, Residents and residency trained members of the American and European Colleges of Veterinary An(a)esthesia and Analgesia.
| Dogs (n = 182-184) | Cats (n = 182-183) | p | |||
|---|---|---|---|---|---|
| n | % | n | % | ||
| Coughing | 0.130 | ||||
| Never | 5 | 2.7 | 20 | 10.9 | |
| Rarely | 87 | 47.5 | 83 | 45.4 | |
| Sometimes | 73 | 39.9 | 66 | 36.1 | |
| Often | 13 | 7.1 | 11 | 6.0 | |
| Very often | - | - | |||
| I don’t know | 5 | 2.7 | 3 | 1.6 | |
| Blood on the tube | 0.001 | ||||
| Never | 10 | 5.4 | 22 | 12.0 | |
| Rarely | 124 | 67.4 | 125 | 68.3 | |
| Sometimes | 49 | 26.6 | 34 | 18.6 | |
| Often | - | 1 | 0.5 | ||
| Very often | - | - | |||
| I don’t know | 1 | 0.5 | 1 | 0.5 | |
| Laryngeal oedema | 0.515 | ||||
| Never | 35 | 19.2 | 43 | 23.6 | |
| Rarely | 117 | 63.9 | 95 | 52.2 | |
| Sometimes | 15 | 8.2 | 31 | 17.0 | |
| Often | 1 | 0.5 | - | ||
| Very often | - | - | |||
| I don’t know | 15 | 8.2 | 13 | 7.1 | |
| Tracheal necrosis or rupture | < 0.001 | ||||
| Never | 139 | 76.0 | 107 | 58.5 | |
| Rarely | 40 | 21.9 | 70 | 38.3 | |
| Sometimes | - | 3 | 1.6 | ||
| Often | - | - | |||
| Very often | - | - | |||
| I don’t know | 4 | 2.2 | 3 | 1.6 | |
| Change of voice | 0.001 | ||||
| Never | 79 | 43.2 | 96 | 52.5 | |
| Rarely | 55 | 30.1 | 38 | 20.8 | |
| Sometimes | 7 | 3.8 | 5 | 2.7 | |
| Often | 1 | 0.5 | - | ||
| Very often | - | - | |||
| I don’t know | 41 | 22.4 | 44 | 24.0 | |
| Loss of voice | 0.439 | ||||
| Never | 117 | 63.9 | 120 | 65.6 | |
| Rarely | 33 | 18.0 | 25 | 13.7 | |
| Sometimes | - | 2 | 1.1 | ||
| Often | - | - | |||
| Very often | - | - | |||
| I don’t know | 33 | 18.0 | 36 | 19.7 | |
| Difficulties with breathing | < 0.001 | ||||
| Never | 48 | 26.2 | 63 | 34.4 | |
| Rarely | 99 | 54.1 | 100 | 54.6 | |
| Sometimes | 31 | 16.9 | 18 | 9.8 | |
| Often | 1 | 0.5 | - | ||
| Very often | - | - | |||
| I don’t know | 4 | 2.2 | 2 | 1.1 | |
| Difficulties with swallowing | 0.124 | ||||
| Never | 93 | 51.1 | 102 | 56.0 | |
| Rarely | 71 | 39.0 | 62 | 43.1 | |
| Sometimes | 4 | 2.2 | 3 | 1.6 | |
| Often | - | ||||
| Very often | - | ||||
| I don’t know | 14 | 7.7 | 15 | 8.2 | |
| Tracheal stenosis | 0.670 | ||||
| Never | 125 | 68.7 | 126 | 69.2 | |
| Rarely | 43 | 23.6 | 39 | 21.4 | |
| Sometimes | - | 3 | 1.6 | ||
| Often | - | - | |||
| Very often | - | - | |||
| I don’t know | 14 | 7.7 | 14 | 7.7 | |
| Bronchitis or pneumonia | < 0.001 | ||||
| Never | 43 | 23.6 | 66 | 36.3 | |
| Rarely | 105 | 57.7 | 96 | 52.7 | |
| Sometimes | 23 | 12.6 | 9 | 4.9 | |
| Often | - | - | |||
| Very often | - | - | |||
| I don’t know | 11 | 6.0 | 11 | 6.0 | |
“Never”= 1, “Rarely”= 2, “Sometimes”= 3, “Often”= 4, “Always”= 5, “I don’t know” =6.
∗ Related-Samples Wilcoxon Signed Rank Test – “I don’t know” answer option excluded from analyses.
Discussion
This study aimed to examine the attitude of veterinary anaesthesiologists towards endotracheal intubation, the perceived incidence of complications secondary to endotracheal intubation in dogs and cats, and if socio-demographic, practice-specific and technical aspects affect the incidence of these complications.
Respondents stated that the majority of dogs and cats undergoing GA at their facilities were intubated. Anaesthesiologists surveyed in this study considered endotracheal intubation as an integral part of modern anaesthesia and, despite significant differences between dogs and cats, reported a low perceived rate of complications associated with it. Respondents also reported that severe complications secondary to endotracheal intubation were infrequent, with minor complications, such as cuff leakage, being more common. Socio-demographic and practice-specific aspects were not shown to influence most complications occurring secondary to endotracheal intubation, and they did not appear to play a significant role in their occurrence in the surveyed group of anaesthesiologists.
Although endotracheal intubation was viewed as a key element in state-of-the-art anaesthesia regardless of species, cats were less likely to be intubated compared to dogs. This finding is in agreement with other studies (
Wagner and Hellyer, 2000
; Nicholson and Watson, 2001
). Endotracheal intubation was found to increase the risk of complications and the odds of death in cats undergoing GA (Clarke and Hall, 1990
; Dyson et al., 1998
; Brodbelt et al., 2008
). The reason for this might be a significantly higher percentage of difficult intubations in cats, as reported in this and other studies (Taylor, 1994
; Wagner and Hellyer, 2000
; Nicholson and Watson, 2001
). Besides the fact that the feline airway is small and delicate, a contributing factor to difficult intubation might be the lower number of cats being intubated by anaesthesiologists resulting in a lack of routine practice compared to dogs. Nonetheless, the reported frequency of difficult intubations in cats was similar between Diplomates and Residents, despite the latter intubating more cats on a weekly basis.Coughing was found to be the most frequently reported complication during intubation for both dogs and cats. Coughing during endotracheal intubation can be a result of insufficient anaesthetic depth. Younger respondents, as well as those who intubate fewer animals per week, reported coughing during endotracheal intubation in dogs and cats more often compared to older respondents or respondents performing endotracheal intubation more frequently. A possible explanation for this could be less experience, and/or routine in endotracheal intubation. This assumption may be supported by the fact that respondents who intubate fewer dogs per week have reported a significantly higher occurrence of coughing compared to participants with a higher weekly caseload.
Accidental oesophageal intubation was identified as the second and third highest-ranked reported complication during intubation in dogs and cats, respectively. This is in agreement with the results obtained in a study on anaesthesia safety incidents, in which oesophageal intubation was one of the most documented incidents (21.6%;
Hofmeister et al., 2014
).Laryngeal spasm was found to be the second most frequently reported complication during endotracheal intubation in cats. It is well known that cats are prone to laryngeal spasm after mechanical stimulation of the soft palate, pharynx, or anterior larynx (
Rex, 1971
). Contrary to our expectations, results of the present study showed a positive association between the use of a stylet or bougie to aid endotracheal intubation and the reported incidence of laryngeal spasm in cats. It is possible that due to mechanical stimulation of the larynx, the use of a stylet could present a primary cause for laryngeal spasm. However, it is also possible that respondents experiencing a high incidence of laryngeal spasm might just be more likely to routinely use these tools to aid endotracheal intubation in cats.While laryngeal spasm was considered a rare event in dogs, there was a substantially higher reported incidence of difficulties visualising the larynx in dogs compared to cats. Although this might be explained by the increasing prevalence of brachycephalic dog breeds, it is not possible to draw this conclusion as our study did not address the percentage of brachycephalic dog and cats receiving GA. Therefore, further studies focused on brachycephalic breeds and the associated risk of complications secondary to endotracheal intubation are warranted.
A leak of the ETT cuff was the most frequently reported complication while the trachea was intubated, and the perceived frequency was significantly higher in dogs than in cats. The significant difference in cuff leakage between dogs and cats could be explained by the difference in the size of the cuffs. As the inner diameter of a high-volume, low-pressure cuffed ETT increases, the size of the cuff increases exponentially. Additionally, larger cuffs have a higher surface area, which causes more longitudinal folds and therefore a higher chance for leaks (
Hwang et al., 2011
).In cats, occlusion of the ETT was the second most frequently reported complication while the trachea was intubated, and it was reported to occur significantly more often in cats than in dogs. An explanation for this might be that smaller sized ETTs are more prone to occlusion by biological material (e.g., mucus, blood, or pus) or by mechanical means (e.g., kinking, compression, or cuff herniation).
Blood on the ETT and coughing after extubation are commonly observed complications in human medicine (
Pacheco-Lopez et al., 2014
). Likewise, these were also the most commonly reported complications in this survey for both dogs and cats. Even when using an appropriate and careful technique, endotracheal intubation consists of the introduction of a foreign body into the trachea and as such, it can lead to irritation of the upper respiratory tract. This damage might result in blood on the ETT and might lead to coughing. In addition, over-inflation of the endotracheal cuff or lack of monitoring of ETT cuff pressure might further exacerbate these complications (Liu et al., 2010
; Hockey et al., 2016
).Difficulty breathing after extubation was reported in 16% of dogs and 9% of cats. The incidence of respiratory distress in dogs being almost twice that compared to cats after extubation could be explained by a higher prevalence of brachycephalic dog breeds, but it is not possible to draw this conclusion as our survey did not study the association between this complication and brachycephalic animals.
In this study, the perceived incidence of tracheal necrosis or rupture in cats was reported to be very low (MIS 1.42). However, a significant association between reassessment of ETT cuff pressure and the perceived incidence of tracheal necrosis or rupture was observed (p = 0.008). The authors believe that this finding does not provide evidence that cuff pressure reassessment increases the risk for tracheal necrosis, but rather that respondents that experienced tracheal necrosis or rupture in their practice are more likely to implement regular cuff pressure reassessment, as a means of preventing this complication. Similarly, awareness of the literature could also lead to preventative action by the respondents. Further studies are necessary to determine if a causal relation between reassessment of ETT cuff pressure and incidence of tracheal damage exists.
Although our findings provide the first insights into complications secondary to endotracheal intubation in dogs and cats, this study has limitations. First, the study population was limited to Diplomates, Residents, and residency trained members of the ACVAA or ECVAA in order to investigate a more defined population with a high frequency of endotracheal intubation. However, the assumed high standard of care, knowledge, and technical skill may have resulted in a potential bias. Second, most participants reported to work in a university setting. Conclusions regarding the perceived incidence of complications for the general population of veterinarians in other work settings could therefore not be drawn from this study. Future studies surveying general practitioners about their attitudes towards endotracheal intubation in dogs and cats and perceived complications secondary to endotracheal intubation are warranted. Third, survey responses are subjective and rely on self-awareness and re-collection of events. A respondent’s attitude towards endotracheal intubation might bias how they answer specific questions due to possible (socially) desirable responding (
Paulhus, 1991
), yea-saying (Baumgartner and Steenkamp, 2005
) or nay-saying (Baumgartner and Steenkamp, 2001
). While precise quantification can only be reached with a prospective design, the understanding of the survey’s questions was assessed using interviews and written feedback. Despite this, interpretation of some answers might not have been the same for every respondent. Third, in relation to the binary regression analyses, dichotomization of the ordinal scaled variables may have led to a certain loss of information. However, based on data obtained and the distribution of responses, conducting ordinal regression analyses would have resulted in questionable findings (Bender and Grouven, 1998
). Hence, binary regression analyses seemed to be the preferable model, leading to more valid results. Lastly, it is important to note that the incidence of complications after extubation might be misrepresented as some are only noticed several hours or even days after GA, e.g., tracheal necrosis. These variables were not included in the survey, and it is likely that most of the respondents were not involved in the follow-up of the animals. Further studies investigating long-term complications secondary to endotracheal intubation are warranted.Conclusion
Veterinary anaesthetists that responded to the survey considered endotracheal intubation as a state-of-the-art technique during GA in dogs and cats. Benefits were perceived to be greater in dogs compared to cats, while the incidence of complications was perceived to be lower in dogs compared to cats. Based on the results presented, major complications were reported infrequently in both dogs and cats. Differences in complications between dogs and cats should be considered to improve anaesthesia safety. Further prospective studies are needed to quantify and qualify the relevance of complications secondary to endotracheal intubation in dogs and cats, including the potential impact of brachycephalic breeds on the incidence of these complications.
Uncited reference
Griesdale et al., 2008
.Author’s contributions
MK Investigation, methodology, statistical analysis, visualisation, original draft of manuscript
SvS Investigation, methodology, statistical analysis, data curation, critical revision of manuscript
CB Supervision and critical revision of manuscript
All authors contributed substantially to the conceptualisation of the study, study design and data interpretation. All authors approved the final version.
No funding was received for this study
Declaration of interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The authors thank the anaesthesiologists who participated in the study and the veterinarians who participated in the cognitive and online pre-test. Further thanks goes to the American and European College of Veterinary Anaesthesia and Analgesia for their support in distributing the survey among members.
Appendix A. Supplementary data
The following are the Supplementary data to this article:
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Article info
Publication history
Accepted:
February 9,
2023
Received in revised form:
January 9,
2023
Received:
May 13,
2022
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In Press Journal Pre-ProofIdentification
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