Physiological parameter changes during field anaesthesia of bandicoots

Abstract

Introduction

Physiological responses to anaesthesia are described for the first time in eastern barred bandicoot (EBB; Perameles gunnii) and southern brown bandicoot (SBB; Isoodon obesulus).

Method

Two hundred and six field anaesthetics were carried out on free‐ranging bandicoots (82 EBB and 66 SBB) in North West Tasmania. Animals were induced and maintained under general anaesthesia using isoflurane administered via a face mask.

Results

On average, animals required 3% isoflurane for anaesthesia maintenance and recovered within 2–3 min of isoflurane being discontinued. SBB had higher respiratory rates than EBB. Otherwise, we found no significant differences in anaesthetic parameters between the bandicoot species, between sexes or for females with pouch young. Hypothermia was the only anaesthetic‐associated adverse event during this study, occurring in 26 anaesthetics (12.6%). At the start of anaesthesia, bandicoots had a mean body temperature of 35.0°C (SEM 0.8, SD 1.2), and 95% of animals lost temperature during anaesthesia. Bandicoots with an initial body temperature of less than 34.5°C had 20 times greater risk (odds ratio 20.52, 95% CI 5.58–77.19) of developing hypothermia (defined as T _b < 33°C). Heart rates ranged from 100 to >300 beats per minute, and respiratory rates ranged from 8 to 64 breaths per minute. Data support a heart rate reference interval of 140–285 (mean 208, SD 42.72) and a respiratory rate interval of 10–34 for SBB (mean 21, SD 8.89) and 8–20 for EBB (mean 12, SD 4.72) during maintenance of inhalant anaesthesia.

Conclusions

With hypothermia the only anaesthesia‐related adverse event during this study, results support the safety of this form of chemical restraint in the field and provide empirical data that may be used to guide anaesthesia for bandicoots. Results suggest that standard inhalational anaesthetic protocols are suitable for bandicoots irrespective of weight, sex and reproductive status.

ABBREVIATIONS

EBB

Eastern barred bandicoot (Perameles gunnii)

HR

Heart rate

RR

Respiratory rate

SBB

Southern brown bandicoot (Isoodon obesulus)

SpO₂

Blood oxygen saturation

T _b

Body temperature

Bandicoots are medium‐sized omnivorous marsupials of the order Peramelemorphia. ¹ There are two species free‐ranging in Tasmania: the long‐nosed eastern barred bandicoot (Perameles gunnii) and the short‐nosed southern brown bandicoot (Isoodon obesulus). ² Tasmanian eastern barred bandicoot (EBB) are recognised as a subspecies, commonly referred to as Perameles gunnii gunnii, ³ , ⁴ and are 5–10% larger than those found on the mainland. ⁵ Although southern brown bandicoot (SBB) in Tasmania are not recognised as a separate subspecies, they too are generally larger than those on the mainland. ⁶ SBB are slightly heavier than EBB, having a more compact body structure. ² Both species show sexual dimorphism, with males larger and heavier than females. ⁵ , ⁶ Tasmanian female SBB weigh up to 1 kg and males 1.2 kg⁶, whereas female EBB weigh approximately 900 grams and males 1.1 kg. ⁷ Bandicoots are predominantly insectivorous but also feed on a range of plant and fungal resources determined by what is locally abundant. ⁷ , ⁸ , ⁹ , ¹⁰ Like other marsupials, females have a pouch in which young suckle and are raised, and as digging animals, the pouch faces backwards to prevent dirt from entering whilst digging. ² In Australian ecosystems, they increase soil turnover ¹¹ which increases the hydration and nutrient density of soil ¹² , ¹³ , ¹⁴ and promotes fungal dispersal, ¹⁵ providing a service characterised as “ecosystem engineering”. ¹³

Whilst some clinical examination can be done in conscious bandicoots, this should be limited to noninvasive procedures to minimise pain and stress experienced. ¹⁶ Bandicoots can be easily stressed, and although their small size makes manual restraint possible, they may injure themselves or the handler if they struggle. ¹⁷ , ¹⁸ They are also susceptible to capture myopathy, ¹⁹ with stress from prolonged handling a potential trigger. ²⁰ Inhalant anaesthesia using isoflurane has been widely recommended as the chemical restraint of choice for bandicoots due to both its simplicity and safety. ¹ , ¹⁶ , ¹⁷ , ¹⁸ Isoflurane has been shown to have a wide safety margin in small marsupials and can be easily administered via a face mask. ¹⁷ , ²¹ Its dosage can be adjusted throughout procedures to match required anaesthesia depth and duration and may be quickly discontinued in cases of adverse reactions. ²² , ²³ , ²⁴ Recovery from isoflurane anaesthesia is rapid (within a few minutes), without prolonged drug effects ²⁴ or drug residue concerns in wildlife being released back into the ecosystem. ²⁵ Other practical considerations that favour isoflurane usage are that it is economic, is easily accessible and does not require specialised record keeping like scheduled drugs (i.e. opioids). ²⁴ Its usage does, however, require specialised equipment such as vaporisers, and although portable, this equipment's function can be adversely affected by climatic conditions including ambient temperature, altitude and humidity. ²⁶ Isoflurane alone does not provide any analgesia, and so for invasive procedures, additional analgesic drugs must be administered. ²⁷ Inhalant anaesthesia in marsupials poses similar risks to traditional general anaesthesia in small animals. Expected cardiopulmonary effects of isoflurane include a reduction in blood pressure and cardiac output, ²⁷ and with increasing anaesthetic depth animals may develop bradycardia, hypoventilation, hypothermia and/or cardiopulmonary arrest resulting in death. ²⁸ Marsupials have lower metabolic rates than eutherian mammals, ¹⁷ , ²⁹ resulting in lower core body temperatures ³⁰ and also greater daily variations in body temperature. ³¹ With their small size and hence relatively large body area‐to‐volume ratio, bandicoots are particularly susceptible to temperature loss and hence development of hypothermia. ³¹ Anaesthesia in the field poses its own set of challenges, including but not limited to increased exposure to climatic conditions and the unknown health status of animals before the administration of anaesthetic drugs. ²¹ , ²³

Previous studies that have utilised isoflurane inhalant anaesthesia for bandicoots have not described observations of physiological parameters, and current literature on normal heart and respiratory rates (RRs) is limited to that available in wildlife textbooks ¹ , ²⁸ or derived from physiological experiments with limited numbers. ³¹ , ³² , ³³ , ³⁴ In this study, we aimed to record the physiological parameters of free‐ranging SBB and EBB of mixed age and sex whilst under inhalant general anaesthesia using isoflurane, and to produce evidence‐based reference intervals for these parameters to allow practitioners to better monitor and manage bandicoots during general anaesthesia (GA). We also aimed to demonstrate the safety of isoflurane inhalant anaesthesia in the field.

Methods

Trapping sessions

Bandicoots were anaesthetised in the field throughout 2020–2024 as part of a research project assessing the health of wild bandicoot populations (Murdoch University AEC permit numbers RW3185/19 & RW3493/23, & University of Tasmania AEC permit 23732). Research was carried out in the Central Coast council area of North West Tasmania, at a mix of privately owned and council‐managed locations. Bandicoots were trapped according to standard trapping procedures ¹⁶ using a 55 × 25 × 25 cm wire‐mesh cage trap with a bait hook mechanism and a water‐impervious fabric covering. Traps were set within an hour of dusk using a peanut butter and bread bait, and a large handful of sugar cane mulch was placed inside to provide further protection from the elements. Traps were checked at dawn the following morning, and on detection the trap containing the bandicoot was immediately placed into a hessian sack and moved on foot to a quiet, secure location (usually within a stationary vehicle) to minimise stress. Trapping did not occur on nights with forecast severe or hazardous weather events (Australian Government Bureau of Meteorology official weather warnings such as damaging winds, heavy rain or severe thunderstorms; www.bom.gov.au). Bandicoots were generally left in the traps until processing. Immediately before processing, bandicoots were transferred to a cotton pillowcase by using the pillowcase to cover the opening to the trap and then gently encouraging them to run into it. In particularly cold or wet weather conditions (ambient temperatures <7°C, chosen as EBB have been shown to successfully cold acclimatise to 5°C ³⁵ ), bandicoots were encouraged into the pillowcases immediately after they were found in the trap. The bandicoot within the pillowcase was then placed into a hessian bag and a hot water bottle at 40°C was placed within the hessian sack before anaesthesia, with the pillowcase arranged in such a manner that the bandicoot could choose to move towards or away from the heat source. Regurgitation is not a common occurrence in bandicoots, so there was no minimum fasting or holding time required before anaesthesia. ¹ When individual animals were recaptured at a subsequent trapping session, the data were treated as independent and included in the analysis.

Anaesthesia

Bandicoots were anaesthetised on site by veterinarians experienced in anaesthesia of domestic small animals and marsupials. Procedures took place in an enclosed trailer custom fitted for field anaesthesia (Figure 1). During anaesthesia several minor procedures were carried out, including physical size measurements, tissue sampling from the ear, subcutaneous microchip implantation and blood collection via jugular venepuncture. Bandicoots were classified as subadult if they had not reached sexual maturity, as evidenced by small testicular size or absence of teat elongation or pouch young. Pouch young, classed as juveniles, were not anaesthetised.

Figure 1.

Trailer fitted out for field anaesthesia with examination table and isoflurane vaporiser. Solar panels have been installed on the roof and connect to a battery, allowing a heat pad and lights to be powered.

Immediately before processing, the corner of the pillowcase was cut off to provide a small hole through which the bandicoot's nose could protrude. Isoflurane was administered in oxygen via a Vet Tech isoflurane vaporiser and a face mask fitted over the snout. Early in the project, the anaesthetic mask was improvised from a small pill container. This was later replaced by a species‐specific mask that we designed and fabricated by 3D printing (Figure 2). In cold weather (ambient temperature <12°C based on the operational temperature range for the vaporiser ³⁶ ) a hot water bottle (at approximately 80°C) was placed underneath the vaporiser and wrapped in bubble wrap to provide warmth. This was necessary as at ambient temperatures below 20°C vaporisers can become inefficient and volatile anaesthetic delivery unpredictable. ²⁶ Isoflurane was administered initially at 5% concentration in oxygen running at a flow rate of 1.5 L/min using a non‐rebreathing circuit (mini Bains circuit, Vetquip, Sydney, NSW, Australia) fitted with a scavenger. Inhalant concentration was dropped to 3–4% once the animal lost its righting reflex and could be removed from the pillowcase, usually within 30 s. A heart rate (HR) taken at this time is referred to as the initial HR. Although intubation is described, ¹ we found correct placement of the tube and the required positioning of the animal during intubation attempts may lead to a drop in oxygen saturation (SpO₂) as well as increasing total anaesthesia time, and so discontinued this method after only a few animals (these animals were excluded from the dataset). Instead, anaesthesia was maintained via face mask. In line with accepted veterinary anaesthesia practice, physiological values including HR (beats per minute), respiratory rate (RR, breaths per minute), body temperature (T _b, °C), SpO₂ (%) and presence/absence of reflexes were recorded throughout the anaesthesia as often as practical, usually every 3–5 min. ²² , ³⁷ HR values were not recorded at >300 as this was the maximum reading by the SpO₂ monitor, and manual calculation was inaccurate at high rates.

Figure 2.

Eastern barred bandicoot under general anaesthesia administered via a 3D printed anaesthesia mask.

Isoflurane concentration was adjusted as necessary during the anaesthesia according to anaesthetic depth. This was judged from changes in HR and RR, absence of withdrawal reflexes and response to stimuli (such as microchip implantation). HR and SpO₂ were measured continuously throughout the anaesthetic via pulse oximetry (Nellcor N‐65 pulse oximeter; Covidien plc., Dublin, Ireland), with most reliable readings found to be from probe placement on the front foot. HR values from the pulse oximeter were periodically compared to manual HR counts and were found to be very accurate so manual counts were only used in the absence of a reliable pulse oximetry reading. RR was taken via manual counts, and T _b via a veterinary digital thermometer (Henry Schein digital rigid tip thermometer, Vetquip, Sydney, NSW, Australia) inserted into the cloaca. Whilst anaesthetised, bandicoots were placed on a heat pad set at 40°C (ICU patient warming pad, Vetquip, Sydney, NSW, Australia), and whenever possible bubble wrap was placed over them to aid in thermoregulation.

Once the isoflurane was discontinued, delivery of oxygen via the face mask continued until bandicoots regained a strong withdrawal reflex of the hind foot. This was considered the “awake time” The last vitals recorded immediately before isoflurane was discontinued are referred to as the “final” HR, RR and T _b values. Bandicoots were then placed back into their pillowcase and into the hessian sack, ensuring they were positioned comfortably on their side without excessive ventroflexion of the neck that may impact airways. If animals were hypothermic on recovery, a hot water bottle was provided in the hessian sack as previously described for preanaesthetic holding. Animals were left within their holding sacks in a quiet, secure location, protected from weather conditions, with minimal interference to minimise stress until their release back to their site of capture at least an hour after anaesthesia recovery.

Data collection & analysis

Anaesthetic records were manually added to an Excel spreadsheet. The following parameters were determined from each bandicoot's anaesthetic records for use in statistical analysis: preanaesthesia (pre‐GA) hold time, isoflurane time, initial & final HR, initial & final RR, initial and final T _b, average isoflurane percentage for maintenance of anaesthesia, maximum (max) & minimum (min) HR, max & min RR, max & min T _b and T _b change per minute of anaesthesia. Time from animal detection in a trap to the start of processing was recorded in minutes and is referred to as pre‐GA hold time. The duration of isoflurane delivery (referred to as isoflurane time) was measured from the time inhalant anaesthesia was turned on to when it was turned off again. Recovery time was the time from isoflurane being turned off to awake time. Percentage HR change is calculated from the difference in HR from initial to final values, divided by the initial value. A negative value represents a drop in HR over the anaesthetic. T _b loss over the anaesthetic was divided by total anaesthesia time to give a T _b loss per minute value. SpO₂ was not included in analysis, as a drop below 97% would have been considered an adverse anaesthetic event and did not occur in any individuals.

Statistical analysis was run on GraphPad Prism 10 and assumed a Gaussian distribution of data.

Anaesthetic parameters were compiled into a dataset including all animals and then into datasets divided categorically by species, sex and for females by the presence of pouch young. Although some animals were anaesthetised on multiple occasions, the variation in field conditions before anaesthesia (eg season, pre‐GA hold time) and the time interval between anaesthetic events (resulting in physiological and reproductive status change) were judged to negate any intrasubject correlation. Bandicoot physiology is known to vary throughout the year, ³³ likely due to seasonal variation in diet and also activity level/foraging behaviours. ³¹ Bandicoot body temperature also shows marked fluctuation daily in addition to variation between days. ³¹ Consequently, all events were analysed as independent observations for statistical analysis. Outliers were identified using the ROUT method with Q = 1% ³⁸ and excluded from the dataset for t‐test and correlation matrix analysis. The ROUT method was chosen as it is more accurate at detecting more than one outlier. ³⁸ Exclusion of one parameter did not necessitate the exclusion of other data points for that animal. A summary of data before outlier analysis is included in Table A2.

Datasets were compared by parameter using multiple unpaired t‐tests (two‐tailed). False discovery rate was controlled using the two‐stage step‐up method of Benjamini, Krieger and Yekutieli, ³⁹ with Q = 1%. Parameters were further evaluated for correlation using correlation matrix analysis to obtain Pearson correlation coefficients. R ² values were graphed on a heat map for easy evaluation. Simple linear regression models were fitted to parameters showing moderate or strong correlation.

For hypothermia risk analysis animals were categorised as hypothermic if their final temperature was less than 33.0°C ²⁸ (outliers were included for these analyses). Multiple t‐test with the above‐described method was used to compare the group of hypothermic animals to the all‐animal dataset. Relative risk was calculated with a Chi‐square test (P value two‐tailed, confidence interval [CI] calculated with Koopman asymptotic score).

A 95% percentile range for HR and RR during the maintenance phase of anaesthesia was created by creating a dataset including 2 values from each animal: readings from 5 to 10 min and from 15 to 20 min. Animals with anaesthetics less than 15 min duration were not included in this analysis.

Statistical significance was assumed at $\alpha \le 0.05$.

Results

During the project there were a total of 206 anaesthetics, comprising 120 EBB anaesthetics (82 EBB individuals; 33 female, 49 male) and 86 SBB anaesthetics (66 SBB individuals; 33 female, 33 male) of unknown age. 10 EBB and 16 SBB were classed as subadults. Animals were repeat captured a minimum of 2 months apart and up to seven times each (Figure 3). Approximately double the anaesthetics were conducted in winter, due to an increased trapping success rate during these months (Table 1). Approximately 13% of anaesthetics were conducted on female animals with pouch young, predominantly EBB. Animals were anaesthetised for an average duration of 17 min (range 1–50 min).

Figure 3.

Bar graph showing frequency of bandicoot individuals undergoing multiple anaesthetics, with a minimum of one and a maximum of seven repeat anaesthetics per individual. Repeat anaesthetics were separated by a minimum of 2 months.

Table 1.

Demographics of the bandicoot study population (categorised by species, sex & presence of pouch young) displayed by season in which anaesthesia took place

	Autumn	Winter	Spring	Summer	Total
SBB female no pouch young	15	10	4	5	34
SBB female with pouch young	3	3	0	4	10
SBB male	5	20	8	9	42
EBB female no pouch young	9	3	4	7	23
EBB female with pouch young	2	14	4	3	23
EBB male	11	35	17	11	74
Total	45	85	37	39	206

There were no deaths during the study, and hypothermia was the only anaesthetic‐associated adverse event that occurred. Anaesthetics were discontinued in three animals: one SBB due to unexplained bleeding from the cloaca (suspected rodenticide toxicity), one EBB due to concerns over the health of the pouch young (cold and poorly reactive despite female being normothermic) and one due to the high activity of the pouch young (advanced in age).

Outlier analysis removed 39 data points. A summary of the all‐animal dataset, inclusive of these outlier points, is included in Table A1.

Mean, standard deviation (SD) and standard error of mean (SEM) data for each dataset are shown in Table 2 (with further breakdown by sex included in Tables A2 and A3). There was a highly significant difference in both initial and final RRs between the two species (P < 0.001). SBB had a mean initial RR of 26 and final RR of 19, compared to EBB with initial RR of 16 and final RR of 12. When analysed by sex, there were no significant differences in parameters for either species, and similarly there were no significant differences in the vitals of females of either species when compared by the presence of pouch young. Full results of multiple t‐tests, including df, may be found in Table A4.

Table 2.

Descriptive statistics for the measured anaesthesia parameters. The all bandicoot dataset can be compared to values for each species (eastern barred bandicoot; EBB and southern brown bandicoot; SBB). A mean, SEM and SD are included for each parameter. Full descriptive statistics (including further breakdown by sex and presence of pouch young) may be found in the appendices

	All bandicoot				EBB				SBB
	Mean	SEM	SD	N	Mean	SEM	SD	n	Mean	SEM	SD	n
Weight (kg)	0.86	0.02	0.22	203	0.84	0.02	0.18	120	0.89	0.03	0.26	83
Pre‐GA holding time (mins)	87.44	4.05	58.05	205	91.57	5.24	57.34	120	81.62	6.39	58.88	85
Iso time (mins)	16.46	0.34	4.97	201	15.98	0.42	4.57	118	17.13	0.57	5.45	83
Recovery time (mins)	2.65	0.10	1.48	197	2.78	0.13	1.44	116	2.5	0.16	1.51	81
Average iso %	2.86	0.03	0.46	199	2.8	0.04	0.44	115	2.929	0.05	0.49	84
Initial HR	249	3.20	45.20	199	256	3.84	41.00	114	239	5.31	48.98	85
Final HR	193	2.79	38.98	195	195	3.42	36.38	113	191	4.68	42.40	82
Max HR	255	2.90	40.75	197	261	3.50	37.25	113	247	4.80	43.96	84
Min HR	189	2.80	39.04	195	192	3.35	35.56	113	186	4.79	43.41	82
% HR change	−21.09%	1	16.07	192	−22.32%	1	15.19	111	−19.41%	2	17.16	81
Initial RR	20	0.72	10.27	201	16	0.72	7.87	118	26	1.14	10.42	83
Final RR	15	0.44	6.16	195	12	0.43	4.65	117	19	0.69	6.05	78
Max RR	21	0.71	9.98	199	17	0.72	7.82	118	27	1.09	9.83	81
Min RR	13	0.37	5.03	187	11	0.35	3.84	117	16	0.60	5.04	70
Initial T b (°C)	35.04	0.08	1.17	204	35.09	0.10	1.12	120	34.97	0.14	1.25	84
Final T b (°C)	34.21	0.09	1.18	193	34.39	0.11	1.14	116	33.93	0.14	1.21	77
Max T b (°C)	35.06	0.08	1.17	203	35.12	0.10	1.12	119	34.98	0.14	1.25	84
Min T b (°C)	34.18	0.08	1.17	193	34.36	0.10	1.12	116	33.91	0.14	1.20	77
T b loss (°C)	0.83	0.05	0.64	195	0.69	0.06	0.59	116	1.04	0.07	0.64	79
T b change per min	0.05	0.00	0.04	200	0.04	0.00	0.04	117	0.06	0.00	0.04	83

Bandicoots recovered very quickly from anaesthesia, with an average recovery of 2.65 min (range 0–15 min). On average, animals were maintained at 3% isoflurane (range 2–4%). The mean initial HR was 249 (SD 45, range 112 to >300). HR dropped a mean of 20% throughout anaesthesia, to a mean of 193 (SD 39, range 100 to >300). Figure 4 presents min and max values for HR, RR and T _b in violin graphs. When HR data from maintenance phase of anaesthesia were compiled, based on 5% and 95% percentile ranges we calculated a HR reference interval of 140–285 (mean 208, SEM 2.6, SD 42.72) and a RR reference interval of 10–34 for SBB (mean 21, SEM 0.86, SD 8.89) and 8–20 for EBB (mean 12, SEM 0.37, SD 4.72).

Figure 4.

Violin graphs showing distribution of vital signs for eastern barred (EBB) and southern brown (SBB) bandicoots during an isoflurane general anaesthesia of an average duration of 17 min. Included in plots is a bolded dashed line representing the median, and dotted lines representing the quartiles. (A) Distribution of heart rate, with a maximum possible value of 300 beats per minute recorded due to difficulty in accurately recording values exceeding this. Data for all bandicoot are displayed together as there existed no significant difference between species. (B) Distribution of body temperature (T _b) measured via a cloacal thermometer. Data for all bandicoot are displayed together as there existed no significant difference between species. (C) Distribution of respiratory rate, displayed divided by species, with EBB shown in darker color. SBB had significantly higher respiratory rates than EBB (P < 0.001).

There was a moderate correlation between initial and final HR (r = 0.479) and initial and final RR (r = 0.603). Percentage HR change was moderately correlated with final HR (r = 0.504) and negatively correlated with initial HR (r = −0.452). A Pearson correlation matrix is presented in Figure 5. When fitted to simple linear regression models, the data displayed a high level of variability, with all R ² values <0.40. Models evaluated were initial HR versus final HR (Y = 0.4321X + 86.49, R ² = 0.2369), initial RR versus final RR (Y = 0.3915X + 7.287; R ² = 0.3906), percentage HR change versus initial HR (Y = −122.8X + 224.6, R ² 0.2318) and percentage HR change versus final HR (Y = 113.3X + 217.6, R ² 0.2456).

Figure 5.

Pearson r Correlation Matrix with r values shown. A negative value reflects an inverse correlation and is shown in blue, whilst positive values are in red. +1 and −1 represent a perfect correlation.

Mean initial body T _b was 35.0°C (SD 1.2). T _b dropped during anaesthesia in 94.6% of anaesthetics (n = 195). In 14.5% of anaesthetics (n = 30) bandicoots had a T _b that dropped below 33.0°C, with the lowest recorded T _b 30.6°C. All but one animal that dropped below 33.0°C started anaesthesia at less than 34.5°C, with animals with an initial T _b of 33–34.5°C having an odds ratio of 20.52 (95% CI 5.58–77.19) for ending anaesthesia at <33.0°C as compared to those with initial temperature >34.5°C. The highest recorded T _b was 38.5°C. Animals averaged a T _b loss of 0.05°C per minute of anaesthesia, with initial and final T _b strongly correlated (r = 0.854, Pearson r correlation, Figure 5), meaning animals starting at a higher initial T _b also had a higher final T _b (Figure 6). T _b loss was slightly lower in summer than in other seasons, but this difference was not statistically significant (Figure 7). When the population of animals with hypothermia were compared to the general population with a multiple t‐test, the only significant difference was initial T _b (P < 0.001, df 227) with hypothermic animals having a lower mean initial T _b of 33.5°C (SEM 0.1609, SD 0.8047) compared to 35.0°C for the general population. Recovery times for hypothermic animals (mean 2.68 min, SEM 0.364) were not significantly different from the all‐animal mean (2.65 min, SEM 0.10).

Figure 6.

Simple linear regression of initial versus final body temperature (Y = 0.8713X + 3.669; R ² = 0.7289).

Figure 7.

Mean + 95% confidence interval for T _b loss per minute of anaesthesia (°C) grouped by season of capture. Bandicoots had a lower mean T _b loss in summer, though there is overlap of mean CI between all seasons making the difference nonsignificant.

Discussion

Our results present the first detailed account of physiological parameters in EBB and SBB under general anaesthesia and demonstrate the safety of isoflurane as an anaesthetic agent in these species. Despite field conditions, animals were successfully maintained at a safe plane of anaesthesia, as evidenced by the lack of bradycardia or hypoxaemia developing, the absence of critical anaesthesia‐related incidents and the safe release of all the study animals. No elevations in body temperature or other abnormalities occurred that were suggestive of animals developing capture myopathy. ²⁰ We found that the anaesthetic parameters HR and T _b did not vary between bandicoots of the two different species or by sex. Females with pouch young had the same vital sign ranges as females without pouch young, including body temperature. The only clinically significant parameter difference was an increased respiratory rate in SBB as compared to EBB. Weight did not affect any physiological values or response to anaesthesia for bandicoots in our study. These findings support current field‐anaesthesia protocols that are standard between bandicoots of different weight, sex, species and reproductive status.

Observed RR ranges during anaesthesia (12–47 for SBB and 8–24 for EBB) were lower than the generally accepted range of 30–40 ²⁸ despite all animals maintaining SpO₂ levels of 99–100%. SBB had higher respiratory rates than EBB, but the minimum values were similar. With no clinically evident hypoxia developing in any cases, this suggests that when receiving 100% oxygen delivered by face mask, bandicoots can adequately ventilate at much lower respiratory rates than previously reported. There is currently limited primary literature on the normal HR of bandicoots, being restricted to a 2003 conference proceeding by Larry Vogelnest ²⁸ and a 1965 paper reporting the minimum HR of selected marsupial species. ⁴⁰ No animals became bradycardic during our documented anaesthetics, according to these reported normal HR ranges of 90–200 and >84 respectively. Our lowest recorded HR was 100 with no decline in SpO₂ or other concerning effects evident. However, blood pressure was not monitored, so we must be cautious in concluding the haemodynamic stability of this individual. Conversely, our HR results were markedly higher than reported HR ranges, with a 95% percentile interval of 140–285. These elevations may represent stress responses associated with capture and handling in these wild animals, especially if previously described ranges are based on captive animals. Dependent on the depth of anaesthesia, bandicoots may have also had increases in HR in response to stimulation or pain, with minimally invasive procedures such as microchipping and venepuncture being conducted during this study. Bandicoots had an average drop in HR of 21%, which is consistent with reported findings of a 25% HR drop in laboratory mice undergoing isoflurane general anaesthesia. ⁴¹

There was a moderate correlation between initial and final HR (r = 0.479) and initial and final RR (r = 0.603). Percentage HR change was moderately correlated with final HR (r = 0.504) and negatively correlated with initial HR (r = −0.452). Despite significant correlations, precision is very low in the models. This reflects the high number of variables that can affect a biological parameter and limit ability to make clinical predictions for individual animals. Individual variation in responses to the stimulation of examination and sampling during our anaesthetics, as well as variation in the timing of stimuli and observations, may have introduced variability into our observations of both HR and respiratory rates. However, from these observations we recommend that, in addition to comparing absolute values with the reference intervals we have developed, decision making during anaesthesia should also consider changes from the values at the start of anaesthesia.

Our finding of an initial T _b of 35.0°C (SEM 0.08) is consistent with other studies in conscious bandicoots. Previous research in Tasmania found that at low ambient temperatures (consistent with the early morning temperatures during our study) EBB had a mean T _b of 34.0°C, ²⁹ whereas at a higher ambient temperature of 30°C they were found to have a mean T _b of 35.1°C. ²⁹ Another study reported the temperature range for free‐ranging SBB as 33.4–39.8°C (mean 36.5°C) with a nychthemeral pattern. ³¹ Australian marsupial texT _books quote the normal body temperature range of bandicoots as 33–35°C, ²⁸ by which definition hypothermia occurred in 12.6% (n = 26) of anaesthetics. Hypothermia is one of the most common anaesthetic complications in small animal species, estimated to affect over 80% of dogs that undergo general anaesthesia. ⁴² It has been shown that approximately 80% of heat loss during the first hour of general anaesthesia is due to redistribution from the core to the extremities. ⁴³ , ⁴⁴ A commonly cited veterinary study recommends that active warming should be implemented for animals that will be under anaesthesia for more than 20 min. ⁴⁵ Smaller animals are more prone to developing hypothermia due to increased body surface area‐to‐body weight ratio, ⁴⁶ with one study showing dogs and cats weighing less than 10 kg will drop 3–4 degrees in temperature during an hour of general anaesthesia when not provided external heat sources. ⁴⁷ We observed a mean T _b loss of 0.83°C over an average anaesthetic duration of 17 min. The low incidence of hypothermia, coupled with the apparent lack of an effect of season on temperature loss, suggests that measures taken to keep bandicoots warm (heat pad, bubble wrap) were successful in preventing an excessive drop in T _b. There was a strong correlation between initial and final T _b (r = 0.854), but no correlation between weight and T _b loss. The only significant difference between bandicoots who developed hypothermia and those who remained normothermic was a lower mean initial T _b in the hypothermic group, with analysis showing animals that started anaesthesia at T _b less than 34.5°C had 20 times the risk of developing hypothermia than those that had initial T _b greater than 34.5°C. Indeed, no animals with initial T _b above 35°C developed hypothermia. We consequently recommend increased vigilance in relation to thermoregulation under anaesthesia in bandicoots with an initial T _b of less than 34.5°C. Hypothermic animals did not have longer recovery times than the general population despite low T _b being shown to prolong recovery from anaesthesia in dogs. ⁴⁸

Bandicoots anaesthetised as part of this study were of unknown age and included low numbers of subadult animals, so these results cannot necessarily be extrapolated to juvenile bandicoots. As with any species, it is possible that younger animals with less developed physiology would be more prone to hypothermia or the cardiovascular effects of anaesthesia. It is also possible that hypothermia or hyperthermia would be more common if trapping in extreme or unseasonal weather, or if bandicoots were not acclimatised to the local weather conditions. Bandicoots have a wide thermoregulatory zone ²⁹ , ³¹ with a thermoneutral zone of approximately 25°C, ³² , ³⁴ but are likely acclimatised to the colder weather of Tasmania. ³⁵ For anaesthetics performed in more extreme climatic conditions than we encountered in Tasmania, different protocols aimed at avoiding hypothermia or hyperthermia may need to be developed. Our greater trapping success in winter may have slightly biased results towards the development of hypothermia rather than hyperthermia. As T _b was not taken before induction of anaesthesia, it is difficult to quantify the effect that prewarming may have had on animals, and whether it would become more important at lower ambient temperatures. T _b was also not taken before release, so we cannot comment on the efficacy of post‐GA warming in returning bandicoots to normothermia. Whilst our results are likely useful in informing anaesthesia protocols of many comparably sized marsupial species, more research is needed to continue the development of accurate and evidence‐based physiological ranges for Australian native species. We would encourage any researchers utilising anaesthesia or sedation in their work to use the format above to publish anaesthesia monitoring data, so that a more comprehensive dataset is available for reference to aid clinicians utilising chemical restraint.

Our results show that inhalant anaesthesia is a safe option to reduce stress when performing minor procedures on wild bandicoots in the field, and so its use should be considered whenever examining wild bandicoots. We know that being trapped and handled is stressful for wildlife, ⁴⁹ , ⁵⁰ with wide acceptance that regardless of the species, blood glucocorticoid levels significantly increase within 5 min of being trapped. ⁵¹ Use of general anaesthetic to reduce stress is a common procedure within exotic and wildlife veterinary medicine, ²³ but studies examining its usage in reducing stress responses in free‐ranging wildlife are limited. One study in Northern elephant seals found that use of manual restraint significantly increased cortisol and metabolic stress responses as compared to chemical immobilisation. ⁵² Berris et al. mention that “some species of bandicoots, such as the western barred bandicoot, are susceptible to stress during handling, which can be fatal if stress myopathy occurs” ¹⁶ but we are not aware of any specific research that elaborates on this. Although some guidelines describe species such as the northern brown bandicoot (Isoodon macrourus) as “amenable to handling”, ¹⁸ wildlife professionals should be cautious not to use ease of handling/sampling as the only criterion for use of chemical restraint. We suggest that the freeze response found in some marsupials should not preclude the use of chemical immobilisation or sedation techniques, as animal welfare can be negatively impacted by stress in these animals. Studies have shown differences in predator avoidance behaviours between marsupials, but also differences between bandicoot species. ⁵³ In our trapping, we have noted differences between individuals in their behavioural responses: to either freeze or attempt escape within the traps, in the pillowcases, and on their release. We would encourage anyone handling bandicoots to consider that docility may be a severe stress response, and given our findings regarding the high level of safety of field anaesthesia the use of isoflurane should be considered to mitigate possible stress during handling.

Bringing our results together, we recommend the following as guidelines to assist the safe anaesthesia of adult and subadult EBB and SBB with isoflurane:

• Standard inhalational anaesthetic protocols are suitable for bandicoots of different weight, sex and reproductive status

• HR reference interval of 140–285 beats/minute

• Respiratory rate reference interval of 10–34 breaths/minute for SBBs

• Respiratory rate reference interval of 8–20 breaths/minute for EBBs

• In addition to comparing absolute values with the reference intervals, the magnitude of any changes in HR and respiratory rate should be noted and marked changes acted upon, with a 20% drop in HR to be expected.

• External heating should be provided during anaesthesia of any duration to mitigate heat loss.

• Increased vigilance in relation to thermoregulation should be taken for bandicoots with an initial body temperature of less than 34.5°C.

Conflicts of interest and sources of funding

The authors declare no conflicts of interest or external funding for this work.

Appendix A.

Table A1.

Descriptive statistics from the total dataset before outlier removal.

	N	Min	25% percentile	Median	75% percentile	Max	Mean	SD	SEM	Lower 95% CI of mean	Upper 95% CI of mean
Pre‐GA hold time (mins)	206	2	49	74	124	550	90	66	5	81	99
Iso time (mins)	205	1	13	16	20	50	17	6	0	16	18
Recovery time (mins)	205	0	2	2	4	15	3	2	0	3	3
Average maintenance iso %	199	2	3	3	3	4	3	0	0	3	3
Initial HR	199	112	220	258	284	>300	249	45	3	242	255
Final HR	195	100	166	190	216	>300	193	39	3	188	199
Max HR	197	137	230	265	290	>300	255	41	3	249	261
Min HR	195	100	160	184	214	>300	189	39	3	184	195
% HR change	196	0%	−32%	−23%	−13%	+47%	−21%	19%	1%	−24%	−19%
Initial RR	203	4	12	16	24	60	20	11	1	19	22
Final RR	198	4	12	12	20	64	15	8	1	14	17
Max RR	203	6	16	20	28	64	22	11	1	20	23
Min RR	198	4	8	12	17	40	14	6	0	13	15
Initial T b (Celsius)	204	31.3	34.1	35.0	35.9	38.5	35.0	1.2	0.1	34.9	35.2
Final T b (Celsius)	193	30.6	33.3	34.2	35.1	36.9	34.2	1.2	0.1	34.0	34.4
Max T b (Celsius)	203	31.3	34.2	35.1	35.9	38.5	35.1	1.2	0.1	34.9	35.2
Min T b (Celsius)	193	30.6	33.3	34.1	35.0	36.9	34.2	1.2	0.1	34.0	34.3
Total T b loss (Celsius)	196	−0.8	0.4	0.8	1.3	36.6	1.0	2.6	0.2	0.6	1.4
T b loss per min (Celsius)	201	−0.06	0.02	0.04	0.08	0.48	0.05	0.05	0.00	0.04	0.06

Table A2.

Southern brown bandicoot descriptive statistics for the measured anaesthesia parameters.

					Southern brown bandicoot
	All bandicoot				All SBB				Males				Females				Females without pouch young				Females with pouch young
	Mean	SEM	SD	N	Mean	SEM	SD	n	Mean	SEM	SD	n	Mean	SEM	SD	n	Mean	SEM	SD	n	Mean	SEM	SD	n
Weight (kg)	0.86	0.02	0.22	203	0.89	0.03	0.26	83	0.91	0.05	0.32	39	0.87	0.03	0.2006	44	0.88	0.04	0.22	34	0.846	0.04	0.14	10
Pre‐GA holding time	87.44	4.05	58.05	205	81.62	6.39	58.88	85	73.20	7.96	51.06	41	89.48	9.79	64.94	44	95.59	12.01	70.04	34	68.7	12.41	39.26	10
Iso time (mins)	16.46	0.34	4.97	201	17.13	0.57	5.45	83	18.26	0.85	5.98	39	16.14	0.72	4.782	44	16.85	0.80	4.69	34	13.7	1.42	4.47	10
Recovery time (mins)	2.65	0.10	1.48	197	2.5	0.16	1.51	81	2.5	0.24	1.58	40	2.5	0.22	1.451	41	2.5	0.29	1.63	31	2.3	0.21	0.67	10
Average ISO %	2.86	0.03	0.46	199	2.929	0.05	0.49	84	2.95	0.07	0.44	40	2.91	0.08	0.5313	44	2.84	0.09	0.50	34	3.15	0.18	0.58	10
Initial HR	249	3.20	45.20	199	239	5.31	48.98	85	233	6.68	42.75	41	246	8.12	53.88	44	244	9.28	54.14	34	249	17.62	55.70	10
Final HR	193	2.79	38.98	195	191	4.68	42.40	82	186	6.54	41.38	40	196	6.69	43.35	42	194	7.62	44.44	34	200	14.41	40.77	8
Max HR	255	2.90	40.75	197	247	4.80	43.96	84	239	6.84	43.79	41	254	6.62	43.39	43	251	7.95	46.35	34	263	9.96	29.88	9
Min HR	189	2.80	39.04	195	186	4.79	43.41	82	180	6.54	41.34	40	192	6.95	45.04	42	190	8.07	47.06	34	198	13.21	37.36	8
% HR change	−21.09%	1	16.07	192	−19.41%	2	17.16	81	−19.33%	3	16.61	39	−19.48%	3	17.86	42	−18.32%	3	18.68	34	−24.40%	5	13.76	8
Initial RR	20	0.72	10.27	201	26	1.14	10.42	83	28	1.83	11.41	39	23.7	1.36	8.996	44	24	1.62	9.46	34	22	2.32	7.33	10
Final RR	15	0.44	6.16	195	19	0.69	6.05	78	20	1.01	6.06	36	17.7	0.91	5.89	42	18	1.11	6.36	33	17	1.33	4.00	9
Max RR	21	0.71	9.98	199	27	1.09	9.83	81	29	1.78	11.14	39	25.1	1.25	8.073	42	26	1.50	8.60	33	23	1.94	5.83	9
Min RR	13	0.37	5.03	187	16	0.60	5.04	70	18	0.85	4.82	32	15.3	0.82	5.024	38	15	0.90	4.87	29	16	1.94	5.81	9
Initial T b (°C)	35.04	0.08	1.17	204	34.97	0.14	1.25	84	35.13	0.20	1.31	41	34.82	0.18	1.184	43	34.86	0.23	1.30	33	34.69	0.23	0.73	10
Final T b (°C)	34.21	0.09	1.18	193	33.93	0.14	1.21	77	34.08	0.21	1.28	37	33.80	0.18	1.134	40	33.8	0.22	1.23	31	33.81	0.25	0.76	9
Max T b (°C)	35.06	0.08	1.17	203	34.98	0.14	1.25	84	35.18	0.20	1.31	41	34.80	0.18	1.166	43	34.83	0.22	1.28	33	34.69	0.23	0.73	10
Min T b (°C)	34.18	0.08	1.17	193	33.91	0.14	1.20	77	34.03	0.21	1.28	37	33.79	0.18	1.132	40	33.79	0.22	1.23	31	33.81	0.25	0.76	9
T b loss (°C)	0.83	0.05	0.64	195	1.04	0.07	0.64	79	1.08	0.10	0.64	38	1.01	0.1	0.6527	41	1.02	0.12	0.69	32	0.96	0.18	0.54	9
T b change per min	0.05	0.00	0.04	200	0.06	0.00	0.04	83	0.05	0.01	0.04	41	0.06	0.01	0.04112	42	0.06	0.01	0.04	32	0.06	0.01	0.04	10

The dataset is further categorised by sex and presence of pouch young. A mean, SEM and SD are included for each parameter. Values for the all‐animal dataset are included for comparison on the left‐hand side of the table.

Table A3.

Eastern barred bandicoot descriptive statistics for the measured anaesthesia parameters.

					Eastern barred bandicoot
	All bandicoot				All EBB				Males				Females				Females without pouch young				Females with pouch young
	Mean	SEM	SD	N	Mean	SEM	SD	n	Mean	SEM	SD	n	Mean	SEM	SD	n	Mean	SEM	SD	n	Mean	SEM	SD	n
Weight (kg)	0.86	0.02	0.22	203	0.84	0.02	0.18	120	0.86	0.02	0.17	74	0.82	0.03	0.20	46	0.76	0.05	0.23	24	0.88	0.03	0.15	22
Pre‐GA holding time	87.44	4.05	58.05	205	91.57	5.24	57.34	120	90.51	6.85	58.92	74	93.26	8.16	55.31	46	81.25	10.26	50.24	24	106.40	12.52	58.71	22
ISO time (mins)	16.46	0.34	4.97	201	15.98	0.42	4.57	118	16.56	0.48	4.08	73	15.04	0.77	5.17	45	17.61	0.83	3.97	23	12.36	1.06	4.96	22
Recovery time (mins)	2.65	0.10	1.48	197	2.78	0.13	1.44	116	2.83	0.16	1.37	70	2.72	0.23	1.56	46	2.67	0.31	1.49	24	2.77	0.34	1.66	22
Average ISO %	2.86	0.03	0.46	199	2.8	0.04	0.44	115	2.8	0.05	0.40	72	2.8	0.07	0.49	43	2.7	0.10	0.47	24	2.8	0.12	0.53	19
Initial HR	249	3.20	45.20	199	256	3.84	41.00	114	262	4.43	37.86	73	244	6.93	44.37	41	229	9.72	44.52	21	260	8.75	39.13	20
Final HR	193	2.79	38.98	195	195	3.42	36.38	113	196	4.35	37.20	73	193	5.57	35.21	40	184	7.63	34.95	21	203	7.76	33.84	19
Max HR	255	2.90	40.75	197	261	3.50	37.25	113	265	4.05	34.64	73	254	6.50	41.11	40	240	9.10	41.70	21	269	8.25	35.95	19
Min HR	189	2.80	39.04	195	192	3.35	35.56	113	193	4.28	36.53	73	189	5.37	33.93	40	180	7.80	35.75	21	198	6.81	29.67	19
% HR change	−21.09%	1	16.07	192	−22.32%	1	15.19	111	−23.35%	2	161.7	71	−20.48%	2	13.28	40	−21.07%	2	10.07	20	−19.89%	4	16.13	20
Initial RR	20	0.72	10.27	201	16	0.72	7.87	118	16.39	0.94	8.10	74	14.91	1.13	7.46	44	15	1.72	8.44	24	15	1.41	6.30	20
Final RR	15	0.44	6.16	195	12	0.43	4.65	117	12.16	0.56	4.75	73	12.36	0.68	4.52	44	13	0.93	4.55	24	12	1.03	4.60	20
Max RR	21	0.71	9.98	199	17	0.72	7.82	118	17.66	0.94	8.07	74	15.89	1.11	7.35	44	16	1.69	8.26	24	15	1.40	6.25	20
Min RR	13	0.37	5.03	187	11	0.35	3.84	117	10.92	0.42	3.58	73	11.30	0.64	4.26	44	11	0.87	4.28	24	11	0.97	4.35	20
Initial T b (°C)	35.04	0.08	1.17	204	35.09	0.10	1.12	120	35.26	0.12	1.03	74	34.80	0.18	1.21	46	34.79	0.27	1.33	24	34.82	0.24	1.11	22
Final T b (°C)	34.21	0.09	1.18	193	34.39	0.11	1.14	116	34.61	0.12	1.03	72	34.04	0.18	1.22	44	34.09	0.27	1.33	24	33.98	0.25	1.10	20
Max T b (°C)	35.06	0.08	1.17	203	35.12	0.10	1.12	119	35.29	0.12	1.02	74	34.84	0.18	1.23	45	34.85	0.27	1.34	24	34.82	0.25	1.13	21
Min T b (°C)	34.18	0.08	1.17	193	34.36	0.10	1.12	116	34.57	0.12	1.03	72	34.00	0.18	1.17	44	34.07	0.26	1.28	24	33.93	0.23	1.03	20
T b loss (°C)	0.83	0.05	0.64	195	0.69	0.06	0.59	116	0.66	0.07	0.57	72	0.75	0.10	0.64	44	0.70	0.13	0.63	24	0.81	0.15	0.66	20
T b change per min	0.05	0.00	0.04	200	0.04	0.00	0.04	117	0.04	0.00	0.03	72	0.05	0.01	0.04	45	0.04	0.01	0.04	24	0.06	0.01	0.05	21

The dataset is further categorised by sex and presence of pouch young. A mean, SEM, and SD are included for each parameter. Values for the all‐animal dataset are included for comparison on the left‐hand side of the table.

Table A4.

P values for multiple unpaired t‐tests run comparing the bandicoot demographic groups. Discoveries (FDR Q = 1%) are shaded grey.

	SBB versus EBB		SBB females versus SBB males		EBB females versus EBB males		SBB females with versus without pouch young		EBB females with versus without pouch young
	P value	Df	P value	Df	P value	Df	P value	Df	P value	Df
Weight (kg)	0.1439	201	0.5283	81	0.2284	118	0.6430	42	0.0429	44
Pre‐GA holding time	0.2275	203	0.2046	83	0.7996	118	0.2544	42	0.1248	44
ISO time (mins)	0.1063	199	0.0767	81	0.0789	116	0.0664	42	0.0003	43
Recovery time (mins)	0.1262	195	0.9694	79	0.6845	114	0.6876	39	0.8207	44
Average ISO %	0.0696	197	0.7016	82	0.5793	113	0.1032	42	0.4608	41
Initial HR	0.0110	197	0.2235	83	0.0290	112	0.8038	42	0.0220	39
Final HR	0.4697	193	0.3238	80	0.6568	111	0.7293	40	0.1014	38
Max HR	0.0152	195	0.1236	82	0.1340	111	0.4636	41	0.0289	38
Min HR	0.3241	193	0.2246	80	0.4950	111	0.6894	40	0.0816	38
% HR change	0.2162	190	0.9689	79	0.3416	109	0.3930	40	0.7829	38
Initial RR	<0.0001	199	0.0354	81	0.3254	116	0.4629	42	0.8688	42
Final RR	<0.0001	193	0.0770	76	0.8227	115	0.8280	40	0.7305	42
Max RR	<0.0001	197	0.0614	79	0.2363	116	0.4775	40	0.6050	42
Min RR	<0.0001	185	0.0464	68	0.6060	115	0.8580	36	0.9939	42
Initial T b (°C)	0.4734	202	0.2571	82	0.0282	118	0.6959	41	0.9344	44
Final T b (°C)	0.0078	191	0.3119	75	0.0081	114	0.9818	38	0.7693	42
Max T b (°C)	0.4040	201	0.1639	82	0.0332	117	0.7438	41	0.9362	43
Min T b (°C)	0.0084	191	0.3847	75	0.0070	114	0.9635	38	0.6964	42
T b change per min	0.0288	193	0.6236	77	0.2143	114	0.7198	39	0.1694	42

Bullen, AF. , Macgregor, JW. , Corbin, B. and Warren, K. , Physiological parameter changes during field anaesthesia of bandicoots. Aust Vet J. 2025;103:506–517. 10.1111/avj.13472

Data availability statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.