Abstract
ABSTRACT It is important to identify the best inspired fraction of oxygen in a variety of situations, including sevoflurane or isoflurane anesthesia, in spontaneously breathing rabbits. For this, 64 rabbits were assigned to eight groups: GI100 (FiO2= 1,0 + isoflurane), GS100 (FiO2= 1,0 + sevoflurane), GI80 (FiO2= 0,8 + isoflurane), GS80 (FiO2= 0,8 + sevoflurane), GI60 (FiO2= 0,6 + isoflurane), GS60 (FiO2= 0,6 + sevoflurane), GI21 (FiO2= 0,21 + isoflurane), GS21 (FiO2= 0,21 + sevoflurane). The induction was performed with (2.5MAC) of the anesthetic. The vaporizer was setted at 1.5 MAC and FiO2 as attributed for each group. After the induction, the concentration was changed to 1 MAC. Measurements of parameters were performed 30 minutes after induction (T0), and then at 15 minute intervals (from T15 to T60). The arterial partial pressures of oxygen (PaO2), alveolar oxygen partial pressure (PAO2) and alveolar-arterial oxygen gradient [P(A-a)O2] were higher with the use of high FiO2. The GI80 showed higher levels of PaO2 FiO2 ratio and respiratory index (RI). In conclusion, the FiO2 of 0.21 is not indicated, because it causes hypoxemia. The isoflurane determines better ventilation when compared to sevoflurane, but isoflurane associated with 80% of oxygen promotes intrapulmonary shunt increase.
Highlights
The primary function of the cardiovascular and respiratory systems is to meet the metabolic needs of tissues in the body through adequate supply of oxygen (O2) (Romaldini, 1995)
Induction of the anesthesia was performed by means of a sealed naso-oral mask with isoflurane (Isoforine - Cristália, Campinas, SP, Brazil) or sevofluorane (Sevocris - Cristália, Campinas, SP, Brazil) at 2.5 CAM diluted in total flow of 1l/min of oxygen to 100%, provided by anesthetic circuit without gas rebreathing (Mapleson D - Baraka balloon 1/2L - ProtecCotia / SP), by means of calibrated vaporizer (OHMEDA - ISOTEC mod 5 - Datex OhmedaMiami, USA) for the anesthetic agent
Evaluating the arterial oxygen partial pressure, it was observed that the mean of this parameter increased as larger FiO2 were used, (Table 1)
Summary
The primary function of the cardiovascular and respiratory systems is to meet the metabolic needs of tissues in the body through adequate supply of oxygen (O2) (Romaldini, 1995). The maintenance of oxygenation at adequate levels during anesthetic procedures is extremely important. It has been proven that O2 administered at high concentrations or for an extended period of time can induce pulmonary lesions with formation of atelectatic areas (Hartsfield, 1996). In Veterinary Medicine, 100% oxygen is still routinely used during anesthetic procedures. Hartsfield (1996) stated that, in humans, 100% oxygen should not be administered for more than 12 hours, but in dogs, it should not be offered for more than 24 hours. Nelson and Couto (1998) stated that dogs should not be submitted for more than 12 hours to O2 above 50%
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