Anaesthesia induction in small mammal´s using an instrumented anaesthetic chamber

Anaesthesia chambers are a method to induce an anaesthetic state to small mammals in laboratory procedures (e.g. mice), when animal handling can alter the outcome of the tests performed due to induced stress [1]. Loss of rightning reflex (LORR) and respiratory rate (RR) are parameters in which the technician relies to evaluate the anaesthesia depth on a visual evaluation. Piezoelectric elements have been successfully presented as a method to monitor vital signs, namely RR, in mice as a non-invasive method [2]. In previous work of this research team, an instrumented chamber with built-in piezoelectric sensors was presented and an accurate measure of the subject´s RR was achieved [3]. The aim for this work is to present a preliminary integrated solution for LORR detection and RR monitoring, in order to be implemented in future anaesthesia studies. The tests were conducted on three white NMRI female mice´s, aging 2 months old and weighing between 38.6 and 40.8g. Each mice was placed inside the chamber and the anaesthetic state was induced at a 5% isoflurane concentration (Isoflo, Esteve Farma Lda., Carnaxide, Portugal) in 100% oxygen at 1 L/min until LORR. Then, the anaesthesia delivery was interrupted, and 100% oxygen at a delivery rate of 2 L/min was provided until recovery of the reflex was observed. One piezoelectric KPSG-100 (30 Vp-p, 1.2±0.2 kHz, Kingstate) sensor was placed underneath the anaesthesia chamber´s footholds. The sensor was connected to a Kistler 5073-A model charge amplifier (Kistler Corporation, NY, USA). The charge amplifier was configured using Kirstler´s ManuWare software. The amplified signal output was then measured using a NI DAQ USB-6251, 16-bit, Multifunction I/O device (National Instruments, Austin, TX, USA) and filtered using a point-to-point 2nd order Butterworth band-pass filter with bandwidth from 0.5 Hz to 5 Hz, in a developed acquisition application in LabVIEW 2013 (National Instruments, USA). LORR detection was achieved- through the implementation of an identification algorithm, regarding piezoelectric signal obtained through the mice movement within the chamber or from its breathing cycle. RR was calculated using a peak-to-peak detection algorithm. In the tests performed, it was possible to correctly identify the LORR moment and to achieve RR monitoring during the anaesthesia protocol (Fig 1.). RR variation due to the anaesthesia depth was also noticeable, from a lowering RR right after LORR, to a dissipation of anaesthetic until the moment of recovery. Comparing with the previous results [3], the implementation of the new setup enables a simple LORR detection method with an enhanced RR related signal amplitude (8 mVp-p to 32 mVp-p). Further tests are recommended to observe the system response to mice weight variations and positioning within the chamber. Nonetheless, with the respective validation, the presented system indicates a novel method for anaesthesia related studies and laboratory animal handling.