**7.3. pO2**

Similar to pH, LD differences in pO<sup>2</sup> were only significant in K/X (p < 0.001) and Z (p < 0.05) anesthesias (**Table 4**). However, it is interesting to note that for all types of general anesthesia used in this study, hypoxia was detected in spontaneously breathing rats in both light parts of

**Figure 3.** pCO2 in the light (yellow columns) and dark (blue columns) parts of rat regimen day in pentobarbital (P)-, ketamine/xylazine (K/X)-, and zoletil (Z)-anesthetized rats. Data presented as mean ± SD. \*\*p < 0.01, \*\*\*p < 0.001 were considered to be a statistically significant difference between individual types of anesthesia. Red dotted lines represent the ranges reported in **Table 1**.

the rat regimen day. Statistically significant differences were found in a light part between P and K/X (p < 0.001), P and Z (p < 0.05), and between K/X and Z anesthesia (p < 0.001), with the lowest values under K/X anesthesia. In the dark part, more pronounced hypoxia was under Z anesthesia (p < 0.05) compared with K/X anesthesia. Differences between P and Z anesthesias were not found (**Figure 4**).

#### **7.4. HCO3 −**

ranges

occurred under P and Z anesthesias. More pronounced hypokapnia was found under K/X anesthesia in the dark part. In the light part, there was a significant difference between P and Z anesthesia (p < 0.001), with higher values in P anesthesia. In the dark part of the rat regime day, significant differences between all selected types of anesthesia (P vs. K/X [p < 0.001]; P

**Figure 2.** pH in the light (yellow columns) and dark (blue columns) periods in pentobarbital (P)-, ketamine/xylazine (K/X)- and zoletil (Z)-anesthetized rats. Data presented as mean ± SD. \* p < 0.05 was considered to be a statistically significant difference between individual types of anesthesia. Red dotted lines represent the ranges reported in **Table 1**.

listed in **Table 1** are considered to be physiological compared with these ranges, the mean

anesthesias (**Table 4**). However, it is interesting to note that for all types of general anesthesia used in this study, hypoxia was detected in spontaneously breathing rats in both light parts of

in the light (yellow columns) and dark (blue columns) parts of rat regimen day in pentobarbital (P)-,

ketamine/xylazine (K/X)-, and zoletil (Z)-anesthetized rats. Data presented as mean ± SD. \*\*p < 0.01, \*\*\*p < 0.001 were considered to be a statistically significant difference between individual types of anesthesia. Red dotted lines represent

reported in this study is in the range of hypercapnia for each type of anesthesia in both

were only significant in K/X (p < 0.001) and Z (p < 0.05)

vs. Z [p < 0.01]; and K/X vs. Z [p < 0.001]) were observed (**Figure 3**). Because the pCO2

light parts, except K/X anesthesia in the dark part of the rat day.

pCO2

**7.3. pO2**

**Figure 3.** pCO2

the ranges reported in **Table 1**.

Similar to pH, LD differences in pO<sup>2</sup>

118 Circadian Rhythm - Cellular and Molecular Mechanisms

Significant LD differences in HCO<sup>3</sup> − were detected under K/X and Z anesthesias (**Table 4**). Taking into account that the normal range of bicarbonate (from **Table 1**) is from 23.8 to 26.78 mmol/l, increased levels were measured in P anesthesia, which would correspond to metabolic alkalosis in both light parts of the regimen. Normal levels were detected in Z anesthesia in both light parts. In K/X anesthesia, the levels of HCO3 − were dependent on the cycle of alternating light and darkness. Under this type of anesthesia, in the light part, values moved around the normal range; however, in the dark part of the day, levels were reduced to what corresponds to metabolic acidosis. Between individual anesthetics, significant differences were found, especially in the dark part of the rat regimen day (**Figure 5**).
