Abstract
Objectives
The aim of this study was to report the incidence of anaesthetic complications associated with feline bronchoscopy.
Methods
This was a retrospective analysis of anaesthetic records and electronic case logs of feline bronchoscopies at two university hospitals (centres B and L) between January 2013 and December 2015. A two-tailed Fisher’s exact test was used for comparison of variables and outcomes between centres.
Results
Seventy-nine cases were included. Desaturation (SpO2 <90%) was the most frequently encountered complication, reported in 24 cats (30.3%); centre B reported significantly less desaturation than centre L (22.4% vs 52.4%; P = 0.014). The use of an endotracheal tube or laryngeal mask airway resulted in a lower incidence of desaturation (22.9% vs 22.2%) than the use of a tracheal catheter through which oxygen was insufflated (48.0%). The latter method was associated with an increased incidence of desaturation (P = 0.034). Patients to which terbutaline was administered had a lower incidence of desaturation (27.5%) than those that did not receive it (35.7%), although this was not statistically significant (P = 0.46). Airway management method and the use of terbutaline differed significantly between centres, as did the profile of complications. Pneumothorax was encountered in two cats (2.5%) and cardiac arrest resulting in the death in one of these cats (1.3%).
Conclusions and relevance
Desaturation is a frequently encountered complication during and after bronchoscopy. Airway management method and the use and timing of terbutaline warrant prospective evaluation for their role in decreasing the incidence of desaturation. Bronchoscopy is a high-risk procedure with frequent requirement for post-procedure oxygen supplementation. Pneumothorax and cardiac arrest are potential complications.
Introduction
Bronchoscopy and bronchoalveolar lavage (BAL) are essential diagnostic tools for feline patients with respiratory disease. 1 They are commonly used in both human and veterinary species but are associated with complications, including haemoglobin desaturation, atelectasis, bronchospasm, bradycardia, hypercapnia and pneumothorax.2,3 Balancing ideal anaesthetic management and optimum access for the bronchoscopist is a challenge for both human paediatric and veterinary anaesthetists, with drug choice and airway management being two major considerations in human paediatric anaesthesia. 2
Despite the frequency with which bronchoscopy and BAL are performed in veterinary hospitals, there are limited data related to the incidence and severity of complications encountered. Johnson and Drazenovich reported a complication rate of 38% in cats undergoing flexible bronchoscopy and BAL, with 12% of the study population experiencing moderate-to-severe complications, which included requiring oxygen supplementation overnight, pneumothorax and the inability to restore spontaneous ventilation leading to euthanasia. 1 During this study, the introduction of pretreatment with terbutaline 12–24 h prior to anaesthesia significantly reduced the incidence of complications. 1 Bronchoscopy and BAL have been shown to induce airflow limitation in cats, thought to be due to bronchoconstriction, with this effect being more severe with pre-existing lower airway inflammation. 4 Beta (β)-agonist-mediated bronchodilation may improve airflow and oxygen delivery to alveoli during bronchoscopy and BAL; however, β2-agonists have been shown to also increase oxygen consumption, which can limit their clinical application in some human cases.1,5,6
The primary aim of this multicentre retrospective study was to identify the incidence of desaturation during bronchoscopy. Secondary aims were to characterise the incidence and nature of other anaesthetic complications experienced in the perianaesthetic period of cats undergoing bronchoscopy and BAL, and to investigate the impact of anaesthetic management on the complications seen.
Methods and materials
Electronic patient records and electronic anaesthesia case logs at two university teaching hospitals (centres B and L) were used to identify cats that underwent bronchoscopy between 1 January 2013 and 31 December 2015 after which anaesthetic records were retrieved from physical or electronic storage, as well as an electronic case log, which documented the same information and included a free-form comment section.
Data collected from the anaesthetic records and electronic case logs were collated. This included sex, neuter status, age, breed, weight, American Society of Anesthesiologists’ (ASA) grade, anaesthetic drugs used for premedication, induction and maintenance of general anaesthesia, procedures performed under anaesthesia, airway management method (endotracheal tube [ETT], laryngeal mask [LMA] or an orotracheal oxygen catheter), timing of terbutaline administration if given, miscellaneous drugs administered during anaesthesia, duration of anaesthesia and if recovery from anaesthesia was performed in an intensive care unit (ICU).
Anaesthesia records were scrutinised for adverse events encountered during or after bronchoscopy, until care of the case was handed from anaesthesia to ICU or ward staff. Recordings were taken every 5 mins. Adverse events are defined here as desaturation (SpO2 <90%) as measured by peripheral pulse oximetry; bradycardia (heart rate <100 beats per min [bpm]); tachycardia (>180 bpm); hypotension (oscillometric mean arterial pressure [MAP] <60 mmHg, Doppler <90 mmHg); hypertension (oscillometric MAP >120 mmHg, Doppler >160 mmHg); hypercapnia (end-tidal concentration of carbon dioxide >60 mmHg). Other adverse events recorded, if they occurred, included pneumothorax (if this developed under anaesthesia or during recovery), cardiopulmonary resuscitation (CPR; if implemented), death and euthanasia.
The record was considered complete if both the anaesthetic record and electronic case logs were retrieved. Both anaesthetic records and electronic case logs were assessed together to gather the maximum amount of data. As both anaesthetic records and electronic case logs provide the same information in different formats, cats that had an incomplete record were included in analysis if the data available were considered sufficiently reliable. Case records from feline anaesthetics performed between 1 January 2013 and 31 December 2015 at centre B and centre L were considered for inclusion.
The bronchoscope used for individual patients was not routinely recorded so could not be used as a variable. During the study period centre B used an Olympus videoendoscope GIF-XP260 with a 6.5 mm external diameter and 1030 mm working length, and videobronchoscopes BF-3C40 and BF-IT240 with 3.6 mm and 6 mm external diameters and 550 mm working length. Centre L used an Olympus videoendoscope GIF-XP260N with a 5.5 mm external diameter and 1100 mm working length, and videobronchoscope BF-P260f with a 4.4 mm outer diameter and 600 mm working length. Not all endoscopes or bronchoscopes were available at each centre for the entire study duration. Primarily, Datex-Ohmeda multiparameter monitors were used at both centres, as well as a Cardell oscillometric blood pressure monitor and multiple portable pulse oximeters and Doppler blood pressure measurement devices The specific monitoring equipment used for each case was not recorded.
Statistical analysis was performed in SPSS statistics Editor Version 23. Outcome measures were dichotomised to presence or absence of a complication, as determined by the previously described parameters. Drugs used for premedication, induction of anaesthesia and maintenance of anaesthesia were also dichotomised as the small data set and varied drug combinations would have resulted in too large a number of categories to analyse reliably. Centre L primarily used medetomidine when alpha (α)2 agonists were used, centre B predominantly used dexmedetomidine. For the purposes of statistical analysis these are grouped together. The method of anaesthesia maintenance was categorised as volatile or total intravenous (IV) anaesthesia ‘TIVA’, within these categories the agent used to maintain anaesthesia was recorded and analysed. The size of ETT or LMA or breathing system used were not analysed. Neither were the type and volume of IV fluid therapy.
Terbutaline use was categorised as three dichotomous variables: ‘terbutaline’, if at least one dose of terbutaline was administered in the perianaesthetic period; ‘pre-emptive’, where terbutaline was administered prior to anaesthesia; and ‘during’, where terbutaline was administered during anaesthesia. Each cat could appear in all three variables.
The bronchoscopist was not routinely recorded so differentiation between novice and experienced practitioners could not be made. The anaesthetist was routinely recorded; however, we did not analyse level of training as a variable.
Descriptive results are reported as absolute number and percentage of the associated population, either pooled, centre B or centre L. Normally distributed continuous data are reported as mean (± 95% SD). Differences between centres with regard to drugs used, airway management methods, terbutaline use and the incidence of complications were analysed using the two-tailed Fisher’s exact technique, with a P value ⩽0.05 accepted as statistically significant for the primary outcome measure (desaturation), and Bonferroni-corrected P value ⩽0.005 for secondary outcome measures. After preliminary analysis of the data by a statistician, further statistical analysis was not undertaken owing to the marked differences in many confounding factors between centres and the small sample size.
Results
Altogether, 7653 anaesthetics were performed at centre B and 10,016 at centre L. In total, 79 feline cases were identified in which bronchoscopy was performed, with 58 from centre B and 21 from centre L. Six cats underwent two bronchoscopies and two cats underwent three; these were counted in the analysis as separate cases as they were performed under separate anaesthetics. Complete patient records were obtained for 73 (92.4%) cases. Demographic data are presented in Table 1. Through a combination of data from electronic logs and anaesthetic records, two cases had missing data points. One case from centre L had no record of drugs used for the induction and maintenance of anaesthesia and one case from centre B had no record of airway management. These cases were included in statistical analysis, but null values were used for these variables.
Characteristics of cats undergoing bronchoscopy at centre B and centre L
Age and weight are presented as mean value (± 95% SD)
ASA = American Society of Anaesthesiologists’ grade (as attributed by the case anaesthetist); M = male; NM = neutered male; F = female; NF = neutered female
Procedure and management descriptive results
Bronchoscopy and BAL alone was performed in 12 cats. Other procedures performed under the same anaesthetic were CT in 54 cats; rhinoscopy in 14, radiographs in nine, fine-needle aspirates in six cats, ultrasonography in four cats, and upper gastrointestinal endoscopy, myringotomy, chest drain placement, echocardiography and oesophagostomy tube placement in one cat each. Forty-seven cats had two procedures performed under the same anaesthetic, 19 cats had three procedures and one cat had four procedures. Mean anaesthetic duration was 73 ± 36 mins at centre B and 66 ± 25 mins for cats at centre L.
Anaesthetic management characteristics are summarised in Table 2. Premedication was performed with an opioid in 78 cats (98.7%). Opioids were combined with one or more of the following drugs: an α2 agonist in 49 (62.0%) cats, midazolam in six (7.6%), ketamine in five (6.3%), alfaxalone in four (5.1%) and acepromazine in three cats (3.8%). Fourteen (17.7%) cats received an opioid alone for premedication. One cat received ketamine and midazolam without an opioid for premedication. α2 agonists were used more frequently at centre L than centre B (95.2% vs 50% of cases; P <0.001).
Summary of anaesthetic management of cats undergoing bronchoscopy and bronchoalveolar lavage at two referral centres
Reported as absolute numbers and percentages of the pooled and individual centre data. P values taken from two-sided Fisher’s exact test between centres for each drug intervention; significance (*) accepted as P <0.05. One data point is missing from centre L for induction of and maintenance of anaesthesia; one data point is missing from centre B for airway management. Percentages from these categories are still reported as a proportion of the total associated population
TIVA = total intravenous anaesthesia; ETT = endotracheal tube; LMA = laryngeal mask
Propofol was used to induce anaesthesia in 29 cats at centre B (50%) and no cats at centre L; alfaxalone was used to induce anaesthesia in 29 cats at centre B (50%) and 20 cats at centre L (95.2%). Propofol was used to induce anaesthesia significantly more frequently at centre B compared with centre L (P <0.001). Conversely, centre L used alfaxalone more frequently than centre B (P <0.001). Co-induction was performed six times with midazolam and twice with ketamine at centre B; no co-inductions were performed at centre L. There was no statistically significant difference for either midazolam or ketamine (P = 0.329 and P = 1.000, respectively).
Anaesthesia during bronchoscopy was maintained by TIVA in 28 cats (35.4%) and by volatile anaesthesia in 50 cats (63.3%). TIVA was used in 19 cats at centre L (90.5%) and nine cats at centre B (15.5%). TIVA was used more frequently at centre L than centre B (P <0.001). TIVA was performed with either alfaxalone in 19 cats at centre L and seven cats at centre B, or propofol in two cats at centre B and no cats at centre L. Alfaxalone TIVA was used more frequently at centre L than centre B (P <0.001), there was no significant difference between centres in the use of propofol TIVA. Isoflurane was used in 24 cats at centre B (41.4%) and two cats at centre L (9.5%); sevoflurane was used in 26 cats at centre B (44.8%) and no cats at centre L. Sevoflurane was used more frequently at centre B than centre L (P <0.001); there was no significant difference in the use of isoflurane between centres (P = 0.432).
During bronchoscopy 35 cats (44.3%) were managed with an ETT, 18 (22.8%) with an LMA and 25 (31.6%) with an oxygen catheter. ETT was used in 33 cats at centre B (56.9%) and two cats at centre L (9.5%). An LMA was used in 18 cats in centre B (31.0%) and was not used in centre L. Both an ETT and an LMA were used more frequently at centre B than at centre L (P <0.001 and P = 0.002, respectively). Oxygen catheters were used in six cats at centre B (10.3%) and 19 cats at centre L (90.5%). Oxygen catheters were used more frequently at centre L than centre B (P <0.001).
Terbutaline was administered to 51 cats (65%) in the perianaesthetic period. Pre-emptive terbutaline was administered to 35 cats (44%), during the anaesthetic in 25 cats (32%) and prior to and during the anaesthetic in nine cats (11%). At centre B, 47 cats (81%) received terbutaline at least once vs four cats at centre L (19%). Terbutaline was used significantly more at centre B than centre L overall, pre-emptively and during bronchoscopy (P <0.001, P = 0.001 and P = 0.013, respectively).
Other drugs administered under anaesthesia varied. Atipamezole was the most commonly administered drug, with 12 cats (15%) receiving it. Other drugs given included atropine, buprenorphine, butorphanol, dexamethasone, dexmedetomidine, ephedrine, fentanyl, furosemide, glycopyrrolate, hydrocortisone and meloxicam; statistical analysis involving these drugs was not undertaken.
Complications descriptive results
Complications encountered during bronchoscopy and recovery, and the 95% confidence intervals, are summarised in Table 3. During bronchoscopy and recovery, desaturation was the most commonly encountered complication, with 24 cats (30.4%) experiencing at least one episode. Desaturation was the most common complication at centre L and was significantly more frequent at centre L, where 11 cats (52.4%) desaturated than centre B, where 13 (22.4%) desaturated (P = 0.014).
Proportions of perianaesthetic complications as recorded by the case anaesthetist
Data are presented as mean (± 95% confidence interval). Significant differences in incidence between centres are marked by an asterisk (*). P values are derived from two-tailed Fisher’s exact test. P ⩽0.05 significant for primary outcome (desaturation) and P ⩽0.005 significant for others following Bonferroni correction. Desaturation if haemoglobin saturation, as measured by peripheral pulse oximetry, was <90%; hypercapnia if end-tidal CO2 >60 mmHg; hypotension if mean arterial pressure (MAP) <60 mmHg (oscillometric) or <90 mmHg (Doppler); hypertension if MAP >120 mmHg (oscillometric) or >160 mmHg (Doppler); bradycardia if heart rate <100 beats per min (bpm); tachycardia if heart rate >180 bpm; pneumothorax; cardiopulmonary resuscitation (CPR); death if animal died or was euthanased; intensive care unit (ICU) if recovery from anaesthesia was performed in an ICU
Cats managed with an ETT or LMA had an incidence of desaturation of 22.9% (8/35) and 22.2% (4/18), respectively. Those managed with an oxygen catheter had an incidence of desaturation of 48.0% (12/25). The use of an oxygen catheter was associated with significantly higher incidence of desaturation when compared with the use of an ETT (P = 0.036) or an LMA (P = 0.043). There was no significant difference in the incidence of desaturation detected between ETT and LMA (P = 0.561).
No statistically significant difference in desaturation in cats that received any terbutaline compared with those that did not receive terbutaline was detected (P = 0.456). Similarly, no statistical significance was found in a separate analysis of terbutaline given pre-emptively (P = 0.089) or intraoperatively (P = 0.600) when compared with no terbutaline.
Tachycardia was the complication with the second highest incidence, reported in 17 cats (21.5%). Tachycardia was seen more frequently at centre B than centre L: 15 cats (25.9%) vs 2 (9.5%); this difference was not significant (P = 0.135).
The incidences of tachycardia in cats given terbutaline and those not given terbutaline were 27.5% (14/51) and 10.7% (3/28), respectively (P = 0.096). Terbutaline use overall and pre-emptive terbutaline were not shown to be associated with the incidence of tachycardia. The use of intra-anaesthetic terbutaline was significantly associated with tachycardia (P = 0.016). Airway management method was not shown to be significantly associated with the incidence of tachycardia.
Hypotension was reported in 14 cats (17.7%): 12 at centre B (20.7%) and two at centre L (9.5%). Hypertension was reported in six cats (7.6%): three each at centre B and centre L (5.2% and 14.3%, respectively). Hypercapnia was reported in three cats (3.8%): two at centre B and one at centre L (3.4% and 4.8%, respectively). Bradycardia was documented in two cats (2.5%), both at centre L (9.5%). The incidence of these complications did not differ significantly between centres. Fifteen cats (19.0%) required intensive care during recovery: 12 at centre B (20.7%) and three at centre L (14.3%).
There was no association between duration of anaesthesia and incidence of any complications. As cats that underwent multiple procedures were likely to have a longer duration of anaesthesia, we did not investigate the relationship between number of procedures and complications.
Pneumothorax was documented in two cats, one at each centre. The case at centre L was the only fatality during the perianaesthetic period in the study. The cat was pre-medicated with medetomidine and methadone, anaesthesia was induced with alfaxalone and anaesthesia was maintained with isoflurane vaporised in oxygen during CT and alfaxalone variable-rate infusion during bronchoscopy. An ETT was used during CT and an oxygen catheter for bronchoscopy. The cat was spontaneously ventilating throughout: it was bradycardic (90–100 bpm) and normotensive during CT. Bradycardia was not treated by the case anaesthetist. Desaturation was documented during bronchoscopy but resolved when the bronchoscope was withdrawn. Minutes after the end of the procedure and cessation of TIVA, while monitored by the case anaesthetist, rapid development of desaturation, absent femoral pulses and lack of spontaneous ventilation prompted CPR, including intubation of the trachea, manual intermittent positive pressure ventilation, chest compressions and administration of adrenaline, atipamezole and atropine. CPR was unsuccessful.
Post-mortem radiography identified a pneumothorax, pneumo-mediastinum and pneumo-retro-peritoneum. Post-mortem bronchoscopy did not identify a tracheal or bronchial perforation. Owing to the order of clinical events it is not certain if the radiographic findings were the cause of cardiac arrest or a result of CPR. Unfortunately, a full post-mortem examination was not performed in this case. Despite this, it was considered likely by the case clinicians and anaesthetist that cardiac arrest was, at least in part, due to bronchoscopy and BAL. Because of this, and other complications experienced under anaesthesia the case was included in the statistical analysis.
Discussion
This retrospective multi-centre study documents the incidence of various complications encountered during feline bronchoscopy; haemoglobin desaturation and tachycardia were the two most commonly identified complications. Perianaesthetic technique differed markedly between centres, as did the incidence of desaturation and tachycardia. The data presented here suggest that anaesthetic technique may alter the type and incidence of complications seen during bronchoscopy. Death occurred in 1.3% (–1.2 to 3.8%), more frequently than that reported in the general feline anaesthetised population (0.24% [0.20–0.27%]) and comparable to that reported in ASA 3–5 cats (1.4%), despite cats in the population in this study being categorised as ASA 2–3. 7 Similarly, Johnson and Drazenovich reported incidences of pneumothorax (3%) and euthanasia (5.8%) in 68 cats undergoing bronchoscopy. 1 Pneumothorax, cardiorespiratory arrest and death are major complications, with a probable greater risk of occurring during these procedures than in the general population. Anaesthetists and bronchoscopists must remain alert to these risks through the procedure and recovery period.
Haemoglobin desaturation is an expected complication of feline bronchoscopy. 1 The incidence of desaturation in this study is higher than that previously reported by Johnson, 8 where 16/68 (24%) cats had mild complications, which were primarily haemoglobin desaturation. In contrast, desaturation is a relatively uncommon complication of feline anaesthesia in general, with an incidence of 3.8%. 8
Desaturation could arise from both patient and mechanical factors; patients undergoing bronchoscopy typically have pulmonary disease, which may impair gas exchange; also, the bronchoscope inevitably occupies a significant portion of the airway, which may decrease global or regional ventilation. Finally, pulmonary function may be impaired further during the procedure by bronchospasm following BAL. 4 The type or severity of pulmonary disease of these cases was not characterised in this study, so the influence of disease type or severity on complication incidence cannot be discerned here.
Bronchoscope size, relative to patient airway size, may significantly contribute to desaturation. In smaller airways, the bronchoscope occupies a larger cross-sectional area of the airways, increasing resistance and thus reducing airflow. Relatively large bronchoscopes can wedge in small airways and can also preclude examination of lower segmental bronchi in small patients.9–11 Centre B had access to smaller external diameter bronchoscopes than centre L throughout the study period, which may have resulted in a lesser impact on airflow. The larger diameter bronchoscopes at centre L also precluded the use of ETT in most cases.
The method of oxygen delivery differs depending on how the airway is managed. Delivery through an ETT or LMA is dependent on spontaneous or positive pressure ventilation to deliver oxygen to the alveoli. Use of an oxygen catheter provides constant flow into the trachea, which may provide oxygen delivery during periods of apnoea. The position of the catheter may limit distribution of oxygen to both lungs, particularly if the catheter is advanced past the carina. Constant gas delivery may be beneficial in some circumstances but may promote gas trapping and increase the risk of barotrauma to alveoli if insufficient space around the bronchoscope is available for gas to escape. Gas trapping is also a risk if air is insufflated through the biopsy channel of the bronchoscope and carries the disadvantage of reducing the area of lung to which oxygen is delivered as the bronchoscope is advanced into smaller airways. This technique was not used at either centre during the study. The fraction of inspired oxygen was not routinely recorded but could be lower when oxygen catheters are used instead of ETTs or LMAs, which may contribute to the higher incidence of desaturation seen when oxygen catheters were used.
LMAs can provide advantages over ETTs for feline bronchoscopy; they have a larger internal diameter than an appropriately sized ETTs so that this is no longer a limiting factor for passage of a bronchoscope. LMAs can provide an adequate seal around the larynx for both spontaneous and positive pressure ventilation. 12 LMAs are commonly used in human paediatric bronchoscopy for similar reasons. 13 Our data showed no difference in the incidence of desaturation between utilising an ETT or LMA. It has recently been suggested that cats should not be intubated routinely for bronchoscopy. 11 Our data appear to suggest that with an ETT or LMA and suitable bronchoscope sizes, feline bronchoscopy can be carried out in a patient with a secured airway. This may be advantageous when compared with insufflation of oxygen. Use of an ETT or LMA throughout anaesthesia will likely also mitigate any environmental pollution with inhaled agents when a patient would otherwise be transferred from volatile to TIVA anaesthesia and extubated. In our opinion, LMAs are beneficial in feline bronchoscopy as they allow similar management of anaesthesia to that obtained with an ETT, but in patients too small to allow tracheal intubation with an ETT of sufficient diameter to allow passage of a bronchoscope.
There was no significant difference in any complication incidence between TIVA and volatile maintenance of anaesthesia. There was a strong centre effect on the use of TIVA or volatile maintenance of anaesthesia along with terbutaline use and airway management, potentially masking any effect of maintenance technique on complications.
Pulse oximetry was used to monitor haemoglobin saturation routinely. The site of probe placement could not be identified from the retrospective data, but common clinical practice was to use the lingual site. Bronchoscopy inevitably involves movement around the head, which can easily disturb a lingual probe. Accidental movement of the probe during the procedure and vasoconstriction from the widespread use of α2 agonists can both cause artefactual readings and be a source of inaccuracy of pulse oximeters, which could affect our reported incidence of desaturation. 14
In this study, we did not differentiate between desaturation occurring during the procedure and during the recovery phase. The transition to lower inspired oxygen tension, which typically occurs at this point, may be a high-risk time for the development of hypoxaemia. It is possible that anaesthetic drug choice can affect the speed of recovery from anaesthesia and so, potentially, the incidence of post-anaesthetic hypoxaemia. This should be examined in future studies.
Perianaesthetic administration of terbutaline has been thought to decrease the incidence of desaturation during bronchoscopy and BAL, probably as the resultant bronchodilation counteracts bronchospasm in response to BAL.1,15 Terbutaline use, in general, was not shown to significantly reduce the incidence of desaturation in this study; however, it was used significantly more frequently at centre B, which had a significantly lower incidence of desaturation. The small data set and multiple, confounding differences in general anaesthetic management between the centres may mask an effect of pre-emptive terbutaline in decreasing the incidence of desaturation. Intraoperative terbutaline was given reactively to the development of desaturation, which may further mask any overall beneficial effect of treatment with terbutaline. A prospective study evaluating the effect of pretreatment with terbutaline on the incidence of desaturation during feline bronchoscopy is required to properly evaluate its value.
The high rate of tachycardia in cats could initially be thought to be accounted for by the high rate of desaturation, with the tachycardia representing an attempt by the patient to increase oxygen delivery via an increase in cardiac output. However, at centre B the incidence of hypoxaemia in cats was lower than at centre L, whereas the incidence of tachycardia was higher. α2 Agonists were more commonly administered to cats at centre L (95%) than B (50%), and this may have resulted in a tendency to limit the incidence of tachycardia The widespread use of terbutaline in cats at centre B may have resulted in the higher heart rates observed, as terbutaline administration can increase heart rate through β2 adrenergic receptor antagonism. 15 There was a significant association between the administration of intra-anaesthetic, but not pre-anaesthetic, terbutaline with tachycardia in this study. If terbutaline is responsible for the observed increased incidence of tachycardia, then its use in patients with concurrent hypertrophic cardiomyopathy could be questioned. 16
In this study hypercapnia had similar incidence rates between centres. The reported rates here are considerably lower than those reported by McMillan and Darcy, 8 with cats requiring intervention for hypoventilation in 9.7% of cases. The incidence of hypercapnia reported here may not be representative of the actual incidence, as capnography was not possible when using oxygen catheters and can be falsely lowered by leaks created in the breathing system during bronchoscopy when an ETT or LMA are used. If the difference is real it may stem from differences in anaesthetic management and potentially more rapid intervention in cats with known respiratory compromise as are presented for bronchoscopy, impaired gas exchange or other physiological reason. Arterial blood gas measurement was not routine for the cases in this study, so partial pressure of arterial carbon dioxide cannot be commented on.
Several cats required intensive care during recovery, most commonly owing to an ongoing requirement for oxygen supplementation. Criteria for admission to an ICU for recovery, as well as patient characteristics, may vary between centres, and this could account for the differences in reported ICU admission. Significant complications of bronchoscopy should be considered and communicated between staff and clients. Pneumothorax was diagnosed in two cases (2.5%) during this study period, and one of these cats died (1.3%). This highlights the need for close monitoring of these patients both during and after anaesthesia. The authors recommend ensuring that sufficient staff are available to perform the procedure, monitor the patient and that all staff are aware of the risks posed to the patient. Easy access to emergency drugs and thoracocentesis equipment allows rapid treatment of likely complications. Availability of long-term oxygen supplementation, such as oxygen cages, and continual monitoring of patients during recovery of anaesthesia is advisable.
Perianaesthetic technique, including terbutaline administration, drug choices and airway management differed significantly between centres, as did the profile of complications associated with each centre. It is apparent that some of these choices, or combination of choices, may alter the expected likelihood of desaturation and tachycardia seen during bronchoscopy and recovery. However, as the differences in anaesthetic management between centres was so marked, it is impossible in this retrospective study to determine which intervention is significant. Prospective studies are needed to characterise the effect of individual interventions on the incidence of complications encountered during bronchoscopy.
There are several limitations to this study; primarily, it is retrospective and, as such, the quality and fidelity of the data cannot be verified. We tried to mitigate this by using two sources of data for each case where available – the anaesthetic record and electronic logs. Collecting data from two centres allowed a larger number of cases to be analysed. As both centres managed these anaesthetics in consistently different ways, meaningful statistical analysis was difficult for perform, especially considering the low incidence of some complications. It may be better to gather data from multiple centres to diminish this problem. Variability between centres with regard to criteria needed to perform bronchoscopy, different disease types and severity could also affect comparisons between the two centres. The majority of these limitations would be mitigated by performing a prospective multicentre study to better characterise the incidence of complications during feline bronchoscopy and search for potential prognostic factors. Similarly, we cannot account for the influence of different bronchoscopic techniques or levels of bronchoscopist and anaesthetist experience on the incidence of complications.
Conclusions
This study supports others in identifying that feline bronchoscopy is a high-risk procedure, and identifies that airway management technique, administration of terbutaline and anaesthetic drug choice can influence the likelihood of different perianaesthetic complications and require prospective analysis. Clinicians should consider the anticipated benefit of bronchoscopy in the light of the complication rate established here and clinical teams involved in bronchoscopy should be aware of anticipated complications and be prepared to treat them rapidly.
Footnotes
Conflict of interest
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
