Untersuchungen zur künstlichen Beatmung bei der Maus (Mus musculus) mit dem UNO Micro-Ventilator

In the present experimental essay the effect of controlled
ventilation with the UNO Micro-Ventilator? (UMV) on the mouse is
examined. The UMV is a pressure controlled and volume limited
ventilation device with a sinus ventilation pattern and lowflow
rebreathing of the respiration gas. Not only the impact of a
preoxygenation is assessed but also the effect of different
respiratory rates on mice of different weight. The assessment is
made with blood gas analysis, circulatory parameters and
histological examinations of the lungs. The animals can be assigned
to nine groups: The non-preoxygenized animals are split up in six
groups and the preoxygenized ones in two groups. Additionally,
group H serves as histological control group. The non-preoxygenized
animals of N100 are ventilated with a respiratory rate of 100 /min
(n = 6), i.e. the animals of the N130 with 130 /min (n = 6). The
animals in N100L (n = 8 settings) are non-preoxygenized, weigh
between 25 and 38 grams and the respiratory rate is adjusted to 100
/min. The animals of the group N100S (n = 7) which weigh between 39
and 50 grams are not preoxygenized either. In P80L (n = 7,
settings) the animals are ventilated with 80 /min, are
preoxygenized, and their weight varies between 25 and 38 grams.
Grouped in P80S (n = 7) are animals which weigh between 39 and 50
grams. Group H (n = 7, animals) was not ventilated and serves for
the histological examination. To expose the animals to as little
stress as possible they are premedicated to the intubation with the
completely antagonizable injectable anesthesia medetomidine,
midazolam, and fentanyl (MMF). With the beginning of the anesthesia
with isoflurane (the concentration of the isoflurane is 2.7 vol.-%)
the injectable anesthesia is antagonized with atipamezol,
flumazenil, naloxone (AFN). The anesthesia lasts 100 minutes. The
A. carotis of all ventilated animals is canulated in order to
measure the blood pressure and take blood samples. Besides the
blood gas results (pHa, pa CO2, paO2, BE, HCO3¯) the measured
parameters are the blood pressure (in mmHg) and the heart rate (in
beats /min). To ascertain the normal distribution the
Kolmogorov-Smirnov test is carried out. The comparison between the
groups is made with the distribution-free Mann-Whitney test. The
level of significance is fixed at p < 0.05 (5 %). The mice of
group N130 stay in the physiological sector with their blood gas
results. Animals of group N100L show a respiratory acidosis. The
preoxygenized P80L and P80S require a lower respiratory rate than
non-preoxygenized animals independent of their weight. The medium
arterial blood pressure of all groups sinks steadily while the
heart rate increases at the same time. In the histological
preparations of all groups including the control groups
atelectasis, perivascular edemas, congestions and emphysemas can be
seen. However, on what these pathological findings are based cannot
be thoroughly explained. Therefore, mice should be preoxygenized 5
minutes prior to a ventilation. Thus, a respiratory rate of 80 per
minute is sufficient for all weights. If not preoxygenized, a
respiratory rate of 130 /min is suggested for animals up to 39
grams and approximately 110 /min for mice over 39 grams. With these
settings the UNO Micro-Ventilator is to be recommended for the
ventilation of mice.