**7.2. pCO2**

Significant LD differences in pCO<sup>2</sup> were found under K/X anesthesia but not under P and Z anesthesias (**Table 4**). In both light parts of the rat regimen day, significant hypercapnia


(ABL 800 Flex, Radiometer Medical, Copenhagen, Denmark) in the Department of Laboratory Medicine, Faculty Hospital Louis Pasteur in Kosice. The depth of anesthesia was estimated according to whether painful stimuli evoked noticeable motor or cardiovascular responses.

(15 mg/kg, Rometar, SPOFA, Prague, Czech

**Anesthesia Route of administration**

Intraperitoneal

Intramuscular

The data were analyzed using GraphPad InStat (GraphPad Software, USA) and presented as mean ± SD. ANOVA was used to detect significant differences within a single end point. The Tukey-Kramer test was used to identify significant differences between groups; p < 0.05 was considered to be statistically significant. The experiments were performed over the course of an entire year, and the results were averaged independent of season and estrous cycle.

Under P anesthesia, significant LD differences in arterial pH were not found, and values remained at the same levels. Under K/X (p < 0.001) and Z (p < 0.001) anesthesias, the pH was significantly higher in the dark (active) versus the light part of the rat regimen day (**Table 4**, **Figure 2**). In the light part of the day, the pH values reflect acidosis, compared with the range calculated from other authors (**Table 1**) in all types of anesthesia, and there was no significant difference between individual types of anesthesia. In the dark part of the day, mean pH values were significantly higher in K/X (p < 0.05) and Z (p < 0.05) anesthesias compared with P anesthesia. The pH was acidic under P anesthesia, from normal to alkaline under K/X anes-

Z anesthesias (**Table 4**). In both light parts of the rat regimen day, significant hypercapnia

were found under K/X anesthesia but not under P and

thesia and from acidic to normal under Z anesthesia.

Significant LD differences in pCO<sup>2</sup>

**6.1. Statistical analysis**

**Table 3.** Experimental groups.

**Experimental period**

Dark 27

116 Circadian Rhythm - Cellular and Molecular Mechanisms

Dark 13

Dark 12

**Number of animals**

Group 1 Light 16 *Pentobarbital* (40 mg/kg, SPOFA, Prague, Czech Republic)

Republic)

Group 3 Light 10 *Zoletil* (30 mg/kg, VIRBAC, France) Intraperitoneal

Group 2 Light 11 *Ketamine* (100 mg/kg, Narkamon) + *xylazine*

**7. Results**

**7.1. pH**

**7.2. pCO2**

\*\*p < 0.01; and

\*\*\*p < 0.001 statistically significant differences between the light and dark parts of the rat regimen day. pCO2 (kPa) – partial pressure of carbon dioxide, pO2 (kPa) – partial pressure of oxygen; HCO3 − (mmol/l) – bicarbonate; stHCO3 − (mmol/l) – standard bicarbonate; ctCO2 – the sum of carbon dioxide bound to hemoglobin and carbon dioxide dissolved in plasma; BE (mmol/l) – base excess; BB (mmol/l) – total buffer bases; ctO2 – the sum of oxygen bound to hemoglobin and oxygen dissolved in plasma, satO2(%) – saturation of hemoglobin by oxygen.

**Table 4.** Values of acid-base balance parameters for selected type of anesthesia in the light and dark parts of the rat regimen day.

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

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

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

Significant LD differences in total buffer bases (BB) and base excess (BE) were found in K/X and Z anesthesias (**Table 4**). BB moves from 40 to 60 mmol/l in all types of anesthesia and the BE from −8 to +12 mmol/l in both light parts of the rat regimen day under all types of anesthesia. Saturation of hemoglobin by oxygen was practically the same in all types of general anesthesia, and significant LD differences were not found except for K/X anesthesia, with higher saturation in the dark part of the rat regimen day. Significant differences of acid-base parameters between the single type of anesthesias are summarized in (**Table 5**).

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 < 0.05, \*\*p < 0.01, and \*\*\*p < 0.001 were considered to be a statistically significant difference between individual types of anesthesia. Red

−

were detected under K/X and Z anesthesias (**Table 4**). Taking

Chronobiology of Acid-Base Balance under General Anesthesia in Rat Model

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were dependent on the cycle of alternating light

were not found (**Figure 4**).

Significant LD differences in HCO<sup>3</sup>

parts. In K/X anesthesia, the levels of HCO3

the dark part of the rat regimen day (**Figure 5**).

**7.5. BE, BB, and saturation of hemoglobin by O2**

−

**−**

**7.4. HCO3**

**Figure 4.** pO2

dashed lines represent ranges reported in **Table 1**.

**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**.

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 vs. Z [p < 0.01]; and K/X vs. Z [p < 0.001]) were observed (**Figure 3**). Because the pCO2 ranges listed in **Table 1** are considered to be physiological compared with these ranges, the mean pCO2 reported in this study is in the range of hypercapnia for each type of anesthesia in both light parts, except K/X anesthesia in the dark part of the rat day.
