SCUC_SI_AAVS_12_s1

INTRODUCTION

In veterinary practice, sevoflurane and propofol are widely used for anesthetic management (Tsai et al., 2007; Steffey et al., 2015; Cattai et al., 2018; Raffe, 2020). People like sevoflurane because it goes into and out of anesthesia quickly and doesn’t slow down breathing as much as some other inhalant anesthetics (Haitjema and Cullen, 2001; Steffey et al., 2015). However, sevoflurane is a dose-dependent cardiorespiratory depressant; increasing its concentration can cause rapid hemodynamic changes (hypotension), hypoventilation, and decreased cardiac contractility (Mutoh et al., 1997; Steffey et al., 2015).Previous studies have reported that a mean minimum alveolar concentration (MAC) of sevoflurane required to inhibit movement in 50% of patients to a noxious stimulus, with values ranging from 2.1% to 2.4% (Wilson et al., 2008; Thengchaisri and Mahidol, 2019; Yamashita et al., 2008; Marzok et al., 2023).

Propofol is a sedative-hypnotic agent that stimulates gamma aminobutyric acid (GABAa) within the central nervous system (CNS). Propofol is good for total intravenous anesthesia (TIVA) because it has good pharmacokinetic properties, such as quickly putting you to sleep, quickly breaking down, and a smooth recovery (Nolan and Reid, 1993; Duke, 2013; Sahinovic et al., 2018). However, higher propofol infusions are required to increase the anesthetic depth for surgery, which is accompanied by profound respiratory depression when it is involved alone in TIVA (Aguiar et al., 2001; Suarez et al., 2012; Bustamante et al., 2022). The mean propofol rate used for maintaining general anesthesia in premedicated dogs (0.18±0.06 mg/ kg/ min) was associated with fewer hemodynamic changes (Cuniberti et al., 2023).

Thus, balanced anesthesia involves using a combination of anesthetic drugs rather than single anesthetic agent to provide sedation and analgesia throughout the preoperative phase, surgery, and recovery (Quandt, 2013). This multimodal approach can provide synergism between analgesics, sedatives, and inhalant anesthetics to reduce the requirement of each component in the anesthetic protocol and decrease adverse effects (Muir et al., 2003; Wilson et al., 2008; Duke, 2013; Cubeddu et al., 2023). The nalbuphine-xylazine combination (0.5mg/kg each) is effective for premedication, providing greater sedation than xylazine alone and improving both handling, comfort and analgesia for the animal (Lester et al., 2003). Furthermore, preemptive multimodal analgesia involves using various analgesics acting on different sites of the pain pathway to enhance the analgesic effect before the surgery (Beverly et al., 2017; Cubeddu et al., 2023).

When used in small amounts, ketamine is a strong painkiller that works by blocking N-methyl D-aspartate (NMDA) in both humans and animals (Schmid et al., 1999; Gorlin et al., 2016; Kalmoe et al., 2020). In humans, administration of ketamine preemptively and intraoperatively can ameliorate the intraoperative cardiovascular response, maintain outlasted analgesia, and reduce the need for rescue analgesia (Saxena et al., 2017). Ketamine was used as an adjunct to isoflurane at a low dose (0.6 mg/kg/h) to inhibit recovery side effects, including ataxia, vocalization, delirium and salivation correlated with increased dosages (Muir et al., 2003). Ketamine (2 mg/kg IV followed by 0.6 mg/kg/h) combined with alfaxalone for total intravenous anesthesia, maintained stable cardiovascular conditions in dogs undergoing dental procedures (Bustamante et al., 2020).

Preoperative ketamine administration can alleviate the hemodynamic response to the surgical stimulus and decrease the requirement for additional analgesia intraoperatively in dogs (Slingsby et al., 2000; Sarturi et al., 2021).

Although multimodal anesthesia is widely used in veterinary practice, there is limited data on the cardiorespiratory effects of low-dose ketamine combined alone with propofol or sevoflurane anesthesia in dogs, particularly concerning its influence on hemodynamic stability in response to surgery and recovery outcomes. We hypothesized that low-dose ketamine when combined with propofol or sevoflurane would help mitigate hemodynamic fluctuations during the anesthetic procedure and surgery in healthy premedicated dogs. Therefore, the present study aimed to evaluate the efficacy and safety of a low-dose ketamine constant-rate infusion combined with propofol or sevoflurane anesthesia on cardiorespiratory function in dogs undergoing laparotomy.

MATERIALS AND METHODS

The study was approved by the Zagazig University Committee of Animal Welfare and Research Ethics (ZU-IACUC/2/F/332/2023) and performed at the Department of Surgery, Anesthesiology, and Radiology, Faculty of Veterinary Medicine, Zagazig University, Egypt. The study was carried out on 16 male mongrel dogs (9 months–1 year old) with an average weight of 20–25 kg. A post-hoc power analysis using G*Power indicated that our sample size was sufficient to achieve a power of approximately 75% which is acceptable.

The American Society of Anesthesiologists, class 1 (ASA I), classified dogs as healthy without underlying diseases. All animals arrived 1 week before the procedure to acclimatize the environment, were housed in separate kennels with free access to food and water. Animals were fasted for 12 hours before the procedure and had free access to water until premedication.

Anesthetic protocol

All dogs were premedicated intramuscularly with xylazine (0.7 mg/kg, Adwia Co., Egypt) and nalbuphine (0.5 mg/kg, Nalufin®, Amoun Pharmaceuticals Co., Egypt) mixed in the same syringe and meloxicam (0.2 mg/kg, Mobitil® Medical Union Pharma, Egypt). After 20 minutes, a 20-gauge intravenous catheter was inserted into each cephalic vein for the administration of the anesthetic drugs and Ringer’s lactate. After 30 minutes (baseline time, T0), physiological parameters include heart rate (HR), respiratory rate (RR), non-invasive arterial blood pressure and rectal temperature (RT). Prior to induction, all dogs were preoxygenated by face mask at 3 L/min for 5 min.

Dogs were randomly allocated into four groups, with four dogs per group (n=4): Group 1 (G1) (control group) was administered slow propofol at a rate of 1 mg/kg/min using Propofol® 1% Fresenius; Fresenius Kabi Co LTD., Germany for anesthesia induction. They also received sevoflurane with an initial end-tidal concentration of 2% for maintenance, adjusted according to the anesthetic depth (Sevoflurane®, Cairo Pharmaceuticals and Chemical Industries Co (CPCI), Egypt, and AbbVie Icn., England). Group 2 (G2) got an IV bolus of ketamine (2 mg/kg, Ketam®; Egyptian International Pharmaceutical Industries Co., EPICO., Egypt), which was given by hand over 15 seconds. This was followed by slow propofol administration at a rate of 1 mg/kg/min for induction and sevoflurane with an initial end-tidal concentration of 2%, in addition to ketamine CRI (0.6 mg/kg/min) for maintenance. Group 3 (G3) (control group) received IV propofol (1 mg/kg/min) for anesthesia induction and was maintained with a propofol constant rate infusion at an initial rate of 0.125 mg/kg/min, adjusted according to the anesthetic depth. Group 4 (G4) received an IV ketamine bolus at a dose of 2 mg/kg, followed by propofol (1mg/kg/min) for induction, propofol CRI (0.125 mg/kg/min) and ketamine CRI (0.6 mg/kg/h) for maintenance. We prepared a ketamine constant rate infusion by calculating the volume of ketamine, adding it to 500 ml of Ringer’s lactate after removing the same amount of solution, and delivering it at a rate of 10 ml/kg/h throughout the procedure. The rate of propofol in all groups was programmed into a syringe pump (injectomate Agilia®; Fresenius Kabi Co., Germany) and set in ml/h for the induction of anesthesia. The propofol infusion continued until the right conditions for endotracheal intubation were met, which included the eyeball being ventromedial, there being no palpebral reflex, jaw tone, swallow reflex, or tongue resistance to laryngoscope blade placement. All animals were intubated with a KRUUSE PVC Endotracheal Tubus (China) that was the right size and had a cuff that was chosen by feeling the outer diameter of the animal’s trachea in the mid-neck area. The endotracheal tube’s (ETT) cuff was inflated with air until no leak was heard, and the adjustable pressure-limiting valve was closed at a pressure of 20 mm H2O. EETs were connected to a rebreathing circle system (COSY., Fabius plus XL., Drägerwerk AG and Co. Lübeck, Germany), and dogs were dependent on spontaneous breathing, receiving 100% oxygen at 1L/min. For assessment of cardiorespiratory function, heart rate (HR) and rhythm were continuously monitored by a Lead II electrocardiogram. A cuff (NIBP Cuff Neonate, Dräger®, Drägerwerk AG and Co. Lübeck, Germany) was placed above the hock joint and its width was approximately about 40% of the limb’s circumference. This was done to measure systolic arterial pressure (SAP), diastolic arterial pressure (DAP), and mean arterial pressure (MAP). The peripheral capillary oxygen saturation (SpO2) was measured by placing a pulse oximeter probe on the tongue. For assessment of respiratory function, a sampling line was connected to the luer lock on the Y-piece of the breathing circuit and an infrared gas analyzer (Scio 4, Dräger®, Drägerwerk AG and Co. Lübeck, Germany) to measure end-tidal concentration of sevoflurane (ETSEVO), end-tidal carbon dioxide (ETCO2), and respiratory rate (RR), all the time. All these variables were measured using a multiparametric monitor (Vista 120, Dräger®, Drägerwerk AG and Co., Lübeck, Germany). Tidal volume (VT) was measured by flow sensor settled at expiratory port of breathing circuit and displayed on the monitor of anesthesia machine. Rectal temperature (RT) was measured by a digital thermometer. Using a heating blanket, the temperature was maintained.

Surgical procedures

All dogs were placed in a dorsal recumbency and underwent a ventral midline exploratory laparotomy under aseptic conditions. All animals were subjected to two consecutive abdominal surgical manipulations by hand, each lasting 1 minute with a 10-minute interval. The expected time of surgery (from the skin incision until the last suture performed on the skin) was 45–50 minutes. All surgeries were performed by the same surgeon. All dogs received ceftriaxone, a broad-spectrum antibiotic (Wintriaxone® 1000 mg, SANOFI, Zeitoun, Egypt) (25 mg/kg IV) 30 min before surgery and continued for 3 successive days after the operation. Data was collected during the maintenance of anesthesia at specific time-points: prior to skin incision (T1), immediately post-skin incision (T2), at the opening of the peritoneum (T3), during abdominal surgical manipulation (55 to 65 min post-induction at 10-minute intervals), during muscle suturing (70 to 75 min post-induction), during subcutaneous suturing (80 min post-induction), and during skin suturing (85 to 90 min post-induction). After the completion of the surgery, we stopped all infusions and inhaled anesthesia, marking the conclusion of the anesthesia phase. When dogs regained their swallowing reflex, they were extubated and allowed to recover undisturbed in a calm room. We recorded the time of extubation (elapsed from the termination of propofol or sevoflurane to extubation), the time to the first head lift, and the time to sternal recumbency for each dog. Animals received meloxicam IM (0.2 mg/kg) for two successive days after the procedure.

Intraoperative interventions

If bradycardia (defined as HR below 60 beats per minute) occurred in a normotensive patient, it was left untreated. Hypotension was defined as a MAP below 60 mmHg, and it was treated if it continued for more than 5 minutes by decreasing the sevoflurane concentration by 20%. When hypotension was accompanied by bradycardia, an intravenous dopamine infusion was initiated at 10µg kg-1 min-1 to effect (Dopasunny, Sunny Pharmaceutical Co., Egypt). We used mechanical ventilation with VT (10 ml/kg), RR (10 breaths/min), and an inspiration to expiration ratio (I: E) of 1:2. If MAP or HR increased 20% above pre-incision values, it was identified as a painful response to surgical stimulation. In such cases, sevoflurane concentrations increased by 20%.

Statistical analysis

The data were tested for normal distribution using the Shapiro-Wilk test and Levene’s test for assessing homogeneity of variance. The coefficient of variation (CV) is reported to monitor the changes between groups over the period of operation. A repeated measure ANOVA with Duncan’s multiple comparison post hoc test was used to investigate differences over time points broken down by four treatment groups. As the data collected over consecutive time points so, El-Bayomi et al. (2019) recommended using repeated measures ANOVA over traditional ANOVA. The analyses were performed using the R language (R Core Team, 2023) and SPSS version 25. The significance level is defined as p < 0.05.

RESULTS and DISCUSSION

Assessing cardiovascular function

Heart rate (HR)

The analysis revealed a significant interaction between time and groups for heart rate (F(71,213)=5.02, P < 0.0001, ƞ²=0.26). This indicates that the observed changes in heart rate over time are influenced by group membership, and this is clear by the ƞ²=0.26 which indicates that the interaction between time and groups explains a substantial portion of the variance in heart rate. HR increased at induction in G1, G2, and G4 compared to baseline. G1 and G3 showed an overall consecutive change (mostly an increase) in HR level until 90 minutes post-induction. Generally, G2 exhibited the most stable HR performance with the lowest percentage of variation (18.7%), followed by G4 as shown in Table 1 and Supplementary Figure S1.

Systolic arterial pressure (SAP)

G2 maintained stable SAP level throughout the anesthetic procedure, with no significant change over-time (F (71:213) = 4.48, p > 0.05, partial eta square(ƞ2) = 0.8), despite the lack of statistical significance, the ƞ² = 0.8 suggests that time explains a substantial amount of variance in SAP levels. This indicates that while there might have been some variability in SAP levels over time, the overall trend was not consistent enough to be statistically significant. In contrast, the SAP levels in G1, G3, and G4 showed significant changes over time compared to the baseline time. G3 and G4 had the highest SAP levels during skin suture (182.5a and 168.8a mmHg, respectively) (Figure 1A, Supplementary Table 1S).

s: Showing heart rate (beats/min) of the 4 groups from baseline values to 90 min post-induction and coefficient of variation.

Time	1	2	3	4
30 m	43.2d	53.4 d	56.3 d	46 d
At induction	60bc	96.2 bc	49.8 d	90.3 bc
Post.15m	68.8 bc	77 bc	59.5 c	60.5 c
Post.20m	79.2 bc	94.8 bc	62.5 c	74.5 bc
Post.25m	80.5 bc	85.2 bc	69.5 bc	74.5 bc
Post.30m	87.8 bc	80.8 bc	80 bc	75.2 bc
Post.35m	96 bc	91 bc	78.5 bc	81.5 bc
Post.40m	100.8 bc	96.5 bc	83.8 bc	84.2 bc
Post.45m	95.2 bc	82 bc	90.2 bc	81.5 bc
Post.50m	89.2 bc	99 bc	85 bc	73.2 bc
Post.55m	99.8 bc	94.8 bc	94 bc	75 bc
Post.60m	95.8 bc	101 bc	94.8 bc	78.8 bc
Post.65m	93.2 bc	101 bc	100 bc	83.5 bc
Post.70m	108 bc	103.5 bc	110.8b	88.2 bc
Post.75m	105 bc	101 bc	120 a	92.5 bc
Post.80m	109 bc	98.5 bc	125.5a	101.5 bc
Post.85m	109 bc	101.3 bc	126.8 a	110.8 b
Post.90m	109.2 bc	106.7 bc	124.2 a	113.5 b
C.V%	23%	18.7%	20.3%	20.5%

ab Means with different superscript within same column are statistically different p < 0.05. AB Means with different superscript within same row are statistically different p < 0.05.

Diastolic and mean arterial pressure (DAP and MAP)

Significant interactions between time and groups were observed for both DAP (F (71,213) =5.04, P < 0.0001, ƞ2=0.96) and MAP (F (71,213) =5.02, P = 0.007, ƞ2=0.70), respectively. G2 and G4 showed stable DAP and MAP levels, while G1 and G3 exhibited significant fluctuations throughout anesthesia. In G3, MAP sharply increased during muscle, subcutaneous and skin suture at 75, 80 and 90 min post-induction, respectively. No hypotension (MAP< 60mm Hg) was observed in any group during anesthesia maintenance. Overall, G2 showed a semi-steady pace of DAP and MAP, as indicated by the lowest percentage of variation (CV) of 22.4% and 15.8%, respectively (Figure 1B, C; Supplementary Table 1S).

Peripheral oxygen saturation (SpO2)

The results of SpO2 showed a non-significant interaction between time and treatments (groups 1, 2, 3, and 4) (F (16, 238) =1.89, P > 0.05, ƞ2=0.12). There was no difference among groups and the effect size is small, as shown in (Table 2).

Assessing respiratory function

End-tidal sevoflurane (ET SEVO)

In G1 and G2, there was a statistically significant interaction between the time of anesthesia and the type of treatment (F (16, 109) =4.68, p< 0.05), and the value of ƞ2=0.50 indicates that 50% of the variance in the ET SEVO measure can be attributed to the interaction between time and treatment type. G1 showed higher levels of ET SEVO that started 60 minutes post-induction during surgical procedure. This increase revealed a significant difference compared to G2 (Figure 2A, Supplementary Table S2).

Respiratory rate (RR)

Analysis of respiratory rate (RR) revealed fluctuations across all groups throughout the anesthetic period. G1 exhibited the greatest average change in RR, followed by G3.G3 exhibited significant decrease during suture (75 to 90 min post-induction) compared to the baseline. In contrast, G2 and G4 demonstrated the most stable RR patterns, as shown in (Figure 2B, Supplementary Table 3S).

Tidal volume (VT)

The results showed that the interaction between the time of anesthetic procedure and the type of treatment is statistically significant (F (16, 236) =1.34, p <0.05, ƞ2=0.10). G3 showed unstable and highly variable values of tidal volume (VT), as CV value was 23% compared to other groups. At 35 minutes post-induction, G3 recorded the lowest VT (166) among the groups. On the other hand, the level of VT in G2 was more steady, with less variability (CV = 15.91%) compared to other groups (Figure 3A, Supplementary Table 3S).

End-tidal carbon dioxide (ETCO2)

The results for ETCO2 did not show a significant interaction between time and treatments (groups 1, 2, 3, and 4). However, the simple effect analysis for testing changes in ETCO2 over the duration of the experiment revealed a significant change in G3, with the lowest mean (29.2) at 35 minutes post-induction (Figure 3B, Supplementary Table 4S).

Assessment of rectal temperature (RT)

RT gradually decreased throughout the procedure, with no significant differences between groups. However, G2 had a lower RT (36.9°) than G3 (38.2) at 30 minutes after the induction, and G1 had a lower RT (36.8°) than G3 (38°) at 60 minutes after the induction.

During a surgical procedure

The results for heart rate showed a statistically significant interaction between the time of the experiment and the type of anesthetic protocol (G1 to G4), with p < 0.05. Compared to baseline (T0), all groups showed a significant increase from the prior skin incision (T1) until the opening of the peritoneum (T3) (Table 3).

Table 2: Estimated marginal means for simple effects of the SPO2% level change between groups at each time point and over times for each of the 4 groups.

Time	1	2	3	4	Significance among groups
Post.15m	98%	98.5%	97.8%	98%	P > 0.05ns
Post.20m	98%	98.5%	97.8%	97.5%	P > 0.05ns
Post.25m	98.3%	98.3%	97.5%	97.5%	P > 0.05ns
Post.30m	98.3%	98.5%	97.3%	98.3%	P > 0.05ns
Post.35m	98%	98.5%	97.5%	98.8%	P > 0.05ns
Post.40m	98%	97.8%	97%	98%	P > 0.05ns
Post.45m	97.5%	97.3%	97%	97.5%	P > 0.05ns
Post.50m	96%	97.5%	97%	97.3%	P > 0.05ns
Post.55m	96%	97%	96.5%	96.8%	P > 0.05ns
Post.60m	96.3%	97%	96%	96%	P > 0.05ns
Post.65m	96.3%	97.3%	97%	96.3%	P > 0.05ns
Post.70m	96.5%	97.3%	96.5%	96.3%	P > 0.05ns
Post.75m	96.5%	97.5%	96.8%	96.3%	P > 0.05ns
Post.80m	96.8%	97%	96.8%	96%	P > 0.05ns
Post.85m	96.5%	96.5%	97%	96%	P > 0.05ns
Post.90m	96.3%	97.3%	97%	96.3%	P > 0.05ns
Significance of simple effect over time	P > 0.05ns	P > 0.05ns	P > 0.05ns	P > 0.05ns

ns: non-significant difference P > 0.05; * significantly different P < 0.05.

The respiratory rate over time was significantly influenced by the type of treatment (p < 0.05). G2 showed the most stable RR value after skin incision (T2) and at the opening of peritoneum (T3) with the lowest variability 9% for both (Table 3).

SAP level remained relatively stable, G3 and G4 recorded higher SAP levels T2 and T3, G3 had higher DAP and MAP levels at T2 and T3, while G2 and G4 showed more stable response to surgical stimulus (Table 3).

The average change rate of propofol in G4 was not significantly different from G3 (0.18 ± 0.01) and (0.2 ± 0.02) mg/kg/min throughout anesthetic procedure, respectively (p > 0.05).

Recovery

Extubation time was not significantly different among groups (P > 0.05). However, there was a significant difference in the first head lift time between groups. G1 and G2 showed the shortest times to the first head lift (6.5±0.65c, 7.25±0.48c minutes, respectively) (P< 0.05), while G3 and G4 recorded the longest times (15.0±1.6a, 11.25±1.3b minutes, respectively). There was a highly significant difference in the time to sternal recumbency and standing and walking among groups (P< 0.001). G1 had the shortest sternal recumbency time (8.75±0.85 minutes). Additionally, G1 and G2 recorded the shortest times (10.5±0.65 c and 12.5±0.65 c minutes, respectively) for standing and walking compared to G3, G4, and G5. Overall, the longest times were found in G3.

Table 3: Mean ± SEM of heart rate HR (beats/min), systolic arterial pressure SAP (mmHg), diastolic arterial pressure DAP (mmHg), mean arterial pressure MAP (mmHg), respiratory rate RR (breaths/min). T0, baseline time (30 minutes after premedication); T1, prior skin incision; T2, after skin incision; T3, at the opening of peritoneum, and CV coefficient of variation.

Parameter		1	2	3	4
HR	T0	43.2d	53.4 d	56.3 d	46 d
	T1	94.2 a	93.2 a	85.5 bc	78.5 bc
	T2	91.5 ab	97.2 a	89.2 ab	81.5 bc
	T3	97.8 a	97 a	88.8 abc	77 c
	C.V	28 %	22.8%	17.7 %	21.6 %
	C.V#	5 %	2 %	7 %	6 %
RR	T0	15.8 ab	13.8 bc	14.5 bc	17.7 a
	T1	11 bc	12.8 c	10.2 c	13.5 b
	T2	16 ab	11.5 c	11.2 bc	16.8 a
	T3	14.2 bc	13.5 bc	9.5 c	13 bc
	C.V	19 %	9 %	20 %	17 %
	C.V#	19 %	9 %	12.6 %	15 %
SAP	T0	132 ab	138 ab	145 ab	142 ab
	T1	115 c	119 b	137 ab	146 a
	T2	123 b	120 bc	151 a	149 a
	T3	124 b	122 b	151 a	149 a
	C.V	8 %	6 %	6 %	5 %
	C.V#	8 %	2 %	7 %	5 %
DAP	T0	79.8 ab	93.2 ab	91.8 ab	88 ab
	T1	76.5 ab	57.5 c	92.2 ab	92.5 ab
	T2	79.5 ab	60.5 c	108.5 a	105.5 ab
	T3	81 ab	59.5 c	108.2 a	100.5 ab
	C.V	13.35%	23 %	13 %	11 %
	C.V#	12.8 %	6 %	13 %	11 %
MAP	T0	102 ab	108.5 ab	108.5 ab	107.8 ab
	T1	88.5 ab	91.5 c	111.8 ab	111.8 ab
	T2	96 bc	94 bc	126.2 a	119 ab
	T3	97 bc	86.8 c	126.2 a	119 ab
	CV	12 %	9 %	8 %	6 %
	CV#	11%	5 %	7 %	6 %

abc Means with different superscript are statistically different p < 0.05 for each parameter independently. CV: Coefficient of variation. # Coefficient of variation from prior to skin incision till the opening of the peritoneum.

Hemodynamic changes, such as tachycardia and increased blood pressure, along with alterations in breathing patterns, can be evaluated to assess intraoperative pain (Katoh et al., 1999; Hernández-Avalos et al., 2020; Interlandi et al., 2022; Cardozo et al., 2024). In humans and animals, the addition of ketamine to the anesthetic plan can improve hemodynamic stability throughout the entire anesthetic and surgical procedure (Smischney et al., 2012; Jalili et al., 2016; Lee et al., 2017). Our findings are consistent with this, showing stable vital parameters (HR, SAP, DAP, and MAP) in both G2 and G4.

In this study, a reduced hemodynamic response to the surgical stimulus was observed in G2, and G4 compared to G1, and G3, likely due to the low dose of ketamine CRI combined with the anesthetic protocols. The stable HR and MAP levels in G2 due to the reduced sevoflurane concentration combined with ketamine’s sympathetic stimulatory effect throughout surgery. These finding fit with what Love et al. (2011) found: Giving dogs low doses of ketamine (0.75 mg/kg/min) along with sevoflurane reduced blood pressure fluctuations from a noxious electrical stimulus (50 V, 50 Hz, 10 ms) and lowered their need for sevoflurane (2.62±0.02) to keep their blood pressure stable. This effect has also been emphasized in humans undergoing laparoscopic cholecystectomy received low -dose ketamine (loading dose 0.5 mg/kg, followed by 0.6 mg/kg/h), exhibited stable hemodynamics in response to pneumoperitoneum (Chen et al., 2021).

In addition, Seliskar et al. (2007) reported that using ketamine (loading dose 1 mg/kg; CRI 2mg/kg/h) with propofol CRI (0.075mg/kg/min) in premedicated dogs, Kennedy and Smith (2015) observed that (0.3mg/kg/min) a propofol-ketamine CRI in unpremedicated dogs, Reed et al. (2015) found that ketamine (loading dose 2mg/kg; CRI 1.2mg/kg/h) with a propofol CRI(0.60±0.1 mg/kg/min) in unpremedicated dogs , were more effective in maintaining MAP than propofol alone in the absence of an actual surgical stimulus. These studies used higher doses of ketamine compared to our study. Among groups, G3 exhibited the highest values of HR and MAP during suturing and necessitating an increase in the infusion rate. This finding is consistent with Jia et al. (2015), where a propofol rate was (0.4-0.6 mg/kg/min) to maintain adequate anesthesia depth in dogs undergoing splenectomy. However, the mean propofol infusion rate in the current was lower (0.2 ± 0.02), to maintain surgical anesthesia compared to the previous study.

According to Murrell et al. (2005) and Suarez et al. (2012), the effective average propofol rate in G3 was different and lowers than the mean propofol rates (0.33 ± 0.03 mg/kg/min) and (0.37 ± 0.09 mg/kg/min) in dogs that were given premedicaion before abdominal surgeries.

The effective average propofol rate in G4 was lower than the rate reported by Bustamante et al. (2022), which was 0.23 ± 0.08 mg/kg/min using a ketamine CRI of 1.5 mg/kg/h, twice the ketamine CRI (0.18 ± 0.01 mg/kg/min) used in the present study.

Propofol reduces the heart rate in a dose-dependent manner by depressing sinoatrial node activity and myocardial contraction (Nagashima et al., 1999). However, the animals in G3 did not show a significant drop in HR after starting low-propofol CRI. The increased HR in G1 and G3 prior to the surgical procedure counteracted the vasodilatory effects of sevoflurane and propofol. This finding aligns with Wang et al. (2004), Kato et al. (2024) and Fabus et al. (2024). Furthermore, Su et al. (2022) said that the body’s baroreceptor-induced rise in HR can be stronger than propofol’s calming effects on them. Another cause, as declared by Wang et al. (2004) and Fabus et al. (2024), is that propofol shifts sympathetic/parasympathetic autonomic balance, leading to reduced parasympathetic effects with slow propofol infusion. In our study, sevoflurane was linked to less respiratory depression than propofol alone. This was shown by the fact that G3 patients needed more help breathing. This finding may be due to the respiratory motor system being less sensitive to volatile anesthetics compared to injectable ones (Yang et al., 2020). This result aligned with Quickfall et al. (2024), which examined the effects of these drugs on humans without assisted ventilation. Moreover, sevoflurane tends to reduce tidal volume in animals (Steffey et al., 2015). According to Saraswat (2015), this reduction may be accompanied by an increased respiratory rate while maintaining the minute volume. Increased VT in G2 compensated for the significant decrease in RR, providing adequate ventilation, as evidenced by the values of ETCO2 and SpO2. The current study found that SpO2 and end-tidal CO2 levels were all within clinically acceptable ranges across all groups. This meant that the four different anesthetic protocols used were able to keep peripheral tissue perfusion high.

In the current study, hypopneic hypoventilation was observed, defined as low ETCO2 of 30 mmHg or less, as reported by Langhan et al. (2015). This resulted from decreased tidal volume and increased air in anatomical dead space instead of alveoli, leading to less CO2 being exhaled. In G3, a low ETCO2 level was observed with a mean value of 29.5, corresponding to a decrease in VT. This finding is similar to that of Aşkın et al. (2023), who reported hypopnea in patients receiving propofol with a mean value of 29.6 mmHg. Redondo et al. (2012) defined hypothermia as a temperature decrease below 36.5°, a temperature that was not observed in the present study.

There was a greater fluctuation in the respiratory rate among groups. Respiratory depression is a common complication in anesthesia maintenance with propofol in dogs, as reported by Ambros et al. (2008) and Reed et al. (2015). In G3, which received propofol CRI alone, three dogs showed respiratory depression in the first half-hour of maintenance and required manual and mechanical ventilation. This is because propofol is a dose-dependent respiratory depressant. Propofol stops the breathing response to low oxygen and high carbon dioxide levels by lowering breathing centers in the brain stem. This lowers the drive to breathe. This can be influenced by the depth of sedation, resulting in decreased tidal volume, minute volume, and respiratory rate (Glowaski and Wetmore, 1999; Liu et al., 2017; Jansen et al., 2024).

Ketamine has a sympathomimetic effect on the central nervous system (CNS) and can increase the respiratory rate. However, high doses of ketamine or its combination with other CNS depressant drugs can cause respiratory depression by blunting the sympathomimetic effect (Lerche et al., 2000). A small amount of ketamine (2 mg/kg loading dose, 0.6 mg/kg/min CRI) was given to dogs that had already been given xylazine, nalbuphine, sevoflurane, or propofol. This combination may have a synergistic effect on respiratory depression in the first half-hour of maintenance. Additionally, the adjunctive use of ketamine in G4 provided beneficial effects for reducing respiratory depression and decreased the need for supportive mechanical ventilation compared to propofol alone in G3. This finding is in line with Aşkın et al. (2023), who reported that ketamine-propofol causes less respiratory depression compared to propofol alone in humans.

In the current study, multimodal analgesia involving NSAIDs, opioids, and NMDA receptor antagonists was used to improve analgesia efficacy and reduce anesthetic doses. It is reported that synergy can be obtained by combining NSAIDS and NMDA receptor antagonists. They effectively inhibit peripheral and central sensitization by inhibiting prostaglandin production after surgical trauma (Mathews et al., 2001; Kelly et al., 2001; Pozzi et al., 2006; Yamashita et al., 2008).

Prolonged recovery times were observed in G3 and G4. This is associated with a prolonged infusion of propofol for approximately 90 minutes, which agrees with the findings of Jia et al. (2015). However, our recovery times were shorter than those in the previous study, likely due to the use of a lower infusion rate, despite the longer infusion duration in the present study.

Instead of giving more painkillers, increasing the end-tidal concentration of sevoflurane or the propofol rate controlled the rise in blood pressure in response to surgery. This is to alleviate the bias in the study, aligning with Cardozo et al. (2024), who emphasized that additional analgesia could interfere with other anesthetics.

The current study has several limitations. First, blood pressure was measured using non-invasive technique instead of invasive blood pressure (IBP) monitoring, which is the gold standard for accuracy. The study conducted on only male dogs, which may limit the extrapolation of findings to female dogs. Finally, sample size was limited as ethical considerations are strictly applied. It would be better if sample size increased for better generalizability of results.

Conclusions and Recommendations

Mixing a low-ketamine CRI with either sevoflurane or propofol made the blood pressure stable enough with only a little breathing depression and a lower need for sevoflurane. However, it had a less profound effect on the percentage change of propofol CRI in dogs undergoing laparotomy. We recommend incorporating low-dose ketamine infusion with sevoflurane or propofol for a procedure lasting longer than one hour to stabilize hemodynamic parameters and decrease the need for additional anesthetic interventions. Further research should evaluate the effectiveness of low-dose ketamine combined to sevoflurane or propofol in orthopedic surgeries, as these procedures may present different challenges related to intensity and the duration of the procedure.

Acknowledgement

This research was not supported by any fund.

Novelty Statement

A low dose of ketamine (2mg/kg IV, followed by a continuous rate infusion at 0.6 mg/kg/h) effectively attenuates the cardiorespiratory depression of propofol or sevoflurane in spontaneously breathing dogs undergoing laparotomy.

Author’s Contribution

All authors contributed equally to the manuscript.

Conflict of interest

The authors have declared no conflict of interest.

REFERENCES

Aguiar AJ, Luna SP, Oliva VN, Eugênio FR, Castro GB (2001). Continuous infusion of propofol in dogs premedicated with methotrimeprazine. Vet. Anaesth. Analg., 28(4): 220–224. https://doi.org/10.1046/j.1467-2987.2001.00048.x

Ambros B, Duke-Novakovski T, Pasloske KS (2008). Comparison of the anesthetic efficacy and cardiopulmonary effects of continuous rate infusions of alfaxalone-2-hydroxypropyl-beta-cyclodextrin and propofol in dogs. Am. J. Vet. Res., 69(11): 1391–1398. https://doi.org/10.2460/ajvr.69.11.1391

Aşkın A, Çelik HK, Doğanay Z (2023). The effects of propofol and ketofol on hemodynamics, end-tidal carbon dioxide, integrated pulmonary index and recovery in patients undergoing endoscopy and colonoscopy. Cyprus J. Med. Sci., 8(4): 264-270. https://doi.org/10.4274/cjms.2023.2022-45

Beverly A, Kaye AD, Ljungqvist O, Urman RD (2017). Essential elements of multimodal analgesia in enhanced recovery after surgery (ERAS) guidelines. Anesthesiol. Clin., 35(2): e115–e143. https://doi.org/10.1016/j.anclin.2017.01.018

Bustamante R, Canfrán S, de Segura I, Aguado D (2022). Intraoperative effect of low doses of ketamine or dexmedetomidine continuous rate infusions in healthy dogs receiving propofol total intravenous anaesthesia and epidural anaesthesia: A prospective, randomised clinical study. Res. Vet. Sci., 143: 4-12. https://doi.org/10.1016/j.rvsc.2021.12.017

Bustamante R, Gómez de Segura IA, Canfrán S, Aguado D (2020). Effects of ketamine or midazolam continuous rate infusions on alfaxalone total intravenous anaesthesia requirements and recovery quality in healthy dogs: A randomized clinical trial. Vet. Anaesth. Analg., 47(4): 437–446. https://doi.org/10.1016/j.vaa.2019.10.010

Cardozo HG, Monteiro ER, Correia BS, Victor B, Ferronatto J, Almeida-Filho FT, Alievi MM, Valle SF (2024). Influence of intravenous fentanyl or dexmedetomidine infusions, combined with lidocaine and ketamine, on cardiovascular response, sevoflurane requirement and postoperative pain in dogs anesthetized for unilateral mastectomy. Vet. Anaesth. Analg., 51(4): 381–390. https://doi.org/10.1016/j.vaa.2024.04.006

Cattai A, Rabozzi R, Ferasin H, Isola M, Franci P (2018). Haemodynamic changes during propofol induction in dogs: New findings and approach of monitoring. BMC Vet. Res., 14(1): 282. https://doi.org/10.1186/s12917-018-1608-8

Chen C, Pang Q, Tu A, Wang J, Tu F (2021). Effect of low-dose ketamine on MACBAR of sevoflurane in laparoscopic cholecystectomy: A randomized controlled trial. J. Clin. Pharma. Therapeut., 46(1): 121–127. https://doi.org/10.1111/jcpt.13263

Cubeddu F, Masala G, Sotgiu G, Mollica A, Versace S, Careddu GM (2023). Cardiorespiratory effects and desflurane requirement in dogs undergoing ovariectomy after administration maropitant or methadone. Animals, 13(14): 2388. https://doi.org/10.3390/ani13142388

Cuniberti B, Huuskonen V, Hughes JL (2023). Comparison between continuous rate infusion and target-controlled infusion of propofol in dogs: A randomized clinical trial. Vet. Anaesth. Analg., 50(1): 21–30. https://doi.org/10.1016/j.vaa.2021.08.048

Duke T (2013). Partial intravenous anesthesia in cats and dogs. Can. Vet. J., 54(3): 276–282.

El-Bayomi K, Mohamed F, Eltarabany M, Gouda H (2019). Application of different biostatistical methods in biological data analysis. Zagazig Vet. J., 47(2): 203-212. https://doi.org/10.21608/zvjz.2019.11121.1034

Fabus MS, Sleigh JW, Warnaby CE (2024). Effect of propofol on heart rate and its coupling to cortical slow waves in humans. Anesthesiology, 140(1): 62–72. https://doi.org/10.1097/ALN.0000000000004795

Glowaski MM, Wetmore LA (1999). Propofol: Application in veterinary sedation and anesthesia. Clin. Tech. Small Anim. Pract., 14(1): 1–9. https://doi.org/10.1016/S1096-2867(99)80021-8

Gorlin AW, Rosenfeld DM, Ramakrishna H (2016). Intravenous sub-anesthetic ketamine for perioperative analgesia. J. Anaesthesiol. Clin. Pharmacol., 32(2): 160–167. https://doi.org/10.4103/0970-9185.182085

Haitjema H, Cullen L (2001). Clinical experience with SEVO in dogs. Austral. Vet. J., 79: 339–341. https://doi.org/10.1111/j.1751-0813.2001.tb12008.x

Hernández-Avalos I, Valverde A, Ibancovichi-Camarillo JA, Sánchez-Aparicio P, Recillas-Morales S, Osorio-Avalos J, Rodríguez-Velázquez D, Miranda-Cortés AE (2020). Clinical evaluation of postoperative analgesia, cardiorespiratory parameters and changes in liver and renal function tests of paracetamol compared to meloxicam and carprofen in dogs undergoing ovariohysterectomy. PLoS One, 15(2): e0223697. https://doi.org/10.1371/journal.pone.0223697

Interlandi C, Di Pietro S, Costa GL, Spadola F, Iannelli NM, Macrì D, Ferrantelli V, Macrì F (2022). Effects of cisatracurium in sevoflurane and propofol requirements in dog-undergoing-mastectomy surgery. Animals, 12(22): 3134. https://doi.org/10.3390/ani12223134

Jalili M, Bahreini M, Doosti-Irani A, Masoomis R, Arbab M, Mirfazaelian H (2016). Ketamine-propofol combination (ketofol) vs propofol for procedural sedation and analgesia: Systematic review and meta-analysis. Am. J. Emerg. Med., 34(3): 558–569. https://doi.org/10.1016/j.ajem.2015.12.074

Jansen SC, van Lemmen M, Olofsen E, Moss L, Pergolizzi JV, Jr., Miller T, Colucci RD, van Velzen M, Kremer P, Dahan A, van der Schrier R, Niesters M (2024). Reversal of propofol-induced depression of the hypoxic ventilatory response by BK-channel Blocker ENA-001: A randomized controlled trial. Anesthesiology, 140(6): 1076-1087. https://doi.org/10.1097/ALN.0000000000004915

Jia N, Zhao C, Wang L, Li Y, Cui J, Cao S, Wen A (2015). The effects of a propofol/alfentanil admixture on total intravenous anaesthesia in dogs undergoing splenectomy. Vet. Med., 60(4): 194–201. https://doi.org/10.17221/8107-VETMED

Kalmoe MC, Janski AM, Zorumski CF, Nagele P, Palanca BJ, Conway CR (2020). Ketamine and nitrous oxide: The evolution of NMDA receptor antagonists as antidepressant agents. J. Neurol. Sci., 412: 116778. https://doi.org/10.1016/j.jns.2020.116778

Kato K, Itami T, Oyama N, Yamashita K (2024). Cardiorespiratory effects of intramuscular alfaxalone combined with low-dose medetomidine and butorphanol in dogs anesthetized with sevoflurane. Open Vet. J., 14(5): 1251–1258. https://doi.org/10.5455/OVJ.2024.v14.i5.20

Katoh T, Kobayashi S, Suzuki A, Iwamoto T, Bito H, Ikeda K (1999). The effect of fentanyl on sevoflurane requirements for somatic and sympathetic responses to surgical incision. Anesthesiology, 90: 398–405. https://doi.org/10.1097/00000542-199902000-00012

Kelly DJ, Ahmad M, Brull SJ (2001). Preemptive analgesia I: Physiological pathways and pharmacological modalities. Can. J. Anaesth., 48: 1000–1010. https://doi.org/10.1007/BF03016591

Kennedy MJ, Smith LJ (2015). A comparison of cardiopulmonary function, recovery quality, and total dosages required for induction and total intravenous anesthesia with propofol versus a propofol-ketamine combination in healthy Beagle dogs. Vet. Anaesth. Analg., 42: 350–359. https://doi.org/10.1111/vaa.12218

Langhan ML, Shabanova V, Li FY, Bernstein SL, Shapiro ED (2015). A randomized controlled trial of capnography during sedation in a pediatric emergency setting. Am. J. Emerg. Med., 33: 25–30. https://doi.org/10.1016/j.ajem.2014.09.050

Lee M, Kim S, Moon C, Park J, Lee H, Jeong SM (2017). Anesthetic effect of different ratios of ketamine and propofol in dogs. J. Vet. Clin., 34: 234–240. https://doi.org/10.17555/jvc.2017.08.34.4.234

Lerche P, Nolan AM, Reid J (2000). Comparative study of propofol or propofol and ketamine for the induction of anaesthesia in dogs. Vet. Rec., 146: 571–574. https://doi.org/10.1136/vr.146.20.571

Lester PA, Gaynor JS, Hellyer PW, Mama K, Wagner AE (2003). The sedative and behavioral effects of nalbuphine in dogs. Contemp. Top. Lab. Anim. Sci., 42: 27–31.

Liu L, Wu AP, Yang Y, Liu SQ, Huang YZ, Xie JF, Pan C, Yang CS, Qiu HB (2017). Effects of propofol on respiratory drive and patient-ventilator synchrony during pressure support ventilation in postoperative patients: A prospective study. Chin. Med. J., 130: 1155–1160. https://doi.org/10.4103/0366-6999.205864

Love L, Egger C, Rohrbach B, Cox S, Hobbs M, Doherty T (2011). The effect of ketamine on the MACBAR of sevoflurane in dogs. Vet. Anaesth. Analg., 38: 292–300. https://doi.org/10.1111/j.1467-2995.2011.00616.x

Marzok M, Almubarak AI, Kandeel M, El-Deeb W, Babiker H, El-Hawari FS (2023). A randomized crossover study of the effect of butorphanol-lidocaine and tramadol-lidocaine on sevoflurane’s minimum alveolar concentration in dogs. Front. Vet. Sci., 9: 1057580. https://doi.org/10.3389/fvets.2022.1057580

Mathews KA, Pettifer G, Foster R, McDonell W (2001). Safety and efficacy of preoperative administration of meloxicam, compared with that of ketoprofen and butorphanol in dogs undergoing abdominal surgery. Am. J. Vet. Res., 62: 882–888 https://doi.org/10.2460/ajvr.2001.62.882.

Muir WW, Wiese AJ, March PA (2003). Effects of morphine, lidocaine, ketamine, and morphine-lidocaine-ketamine drug combination on minimum alveolar concentration in dogs anesthetized with isoflurane. Am. J. Vet. Res., 64: 1155–1160. https://doi.org/10.2460/ajvr.2003.64.1155

Murrell JC, van Notten RW, Hellebrekers LJ (2005). Clinical investigation of remifentanil and propofol for the total intravenous anaesthesia of dogs. Vet. Rec., 156: 804–808. https://doi.org/10.1136/vr.156.25.804

Mutoh T, Nishimura R, Kim HY, Matsunaga S, Sasaki N (1997). Cardiopulmonary effects of sevoflurane, compared with halothane, enflurane, and isoflurane, in dogs. Am. J. Vet. Res., 58: 885–890. https://doi.org/10.2460/ajvr.1997.58.08.885

Nagashima Y, Furukawa Y, Hirose M, Chiba S (1999). Cardiac effects of propofol and its interaction with autonomic nervous system in isolated, cross-circulated canine atria. J. Anesth., 13: 34–39. https://doi.org/10.1007/s005400050019

Nolan A, Reid J (1993). Pharmacokinetics of propofol administered by infusion in dogs undergoing surgery. Br. J. Anaesth., 70: 546–551. https://doi.org/10.1093/bja/70.5.546

Pozzi A, Muir WW, Traverso F (2006). Prevention of central sensitization and pain by N-methyl-D-aspartate receptor antagonists. J. Am. Vet. Med. Assoc., 228: 53–60. https://doi.org/10.2460/javma.228.1.53

Quandt J (2013). Analgesia, anesthesia, and chemical restraint in the emergent small animal patient. The veterinary clinics of North America. Small Anim. Pract., 43(4): 941–953. https://doi.org/10.1016/j.cvsm.2013.03.008

Quickfall D, Sklar MC, Tomlinson G, Orchanian-Cheff A, Goligher EC (2024). The influence of drugs used for sedation during mechanical ventilation on respiratory pattern during unassisted breathing and assisted mechanical ventilation: A physiological systematic review and meta-analysis. E Clin. Med., 68: 102417. https://doi.org/10.1016/j.eclinm.2023.102417

R Core Team (2023). R A language and environment for statistical computing. R Foundation for Statistical Computing, 2023; Vienna, Austria.

Raffe MR (2020). Total intravenous anesthesia for the small animal critical patient. Vet. Clin. North Am. Small Anim. Pract., 50: 1433-1444. https://doi.org/10.1016/j.cvsm.2020.07.007

Redondo JI, Suesta P, Serra I, Soler C, Soler G, Gil L, Gómez-Villamandos RJ (2012). Retrospective study of the prevalence of postanaesthetic hypothermia in dogs. Vet. Rec., 171: 374. https://doi.org/10.1136/vr.100476

Reed RA, Seddighi MR, Odoi A, Cox SK, Egger CM, Doherty TJ (2015). Effect of ketamine on the minimum infusion rate of propofol needed to prevent motor movement in dogs. Am. J. Vet. Res., 76: 1022–1030. https://doi.org/10.2460/ajvr.76.12.1022

Sahinovic MM, Struys MMRF, Absalom AR (2018). Clinical pharmacokinetics and pharmacodynamics of propofol. Clin. Pharmacokinet., 57: 1539–1558. https://doi.org/10.1007/s40262-018-0672-3

Saraswat V (2015). Effects of anaesthesia techniques and drugs on pulmonary function. Indian J. Anaesth., 59: 557-564. https://doi.org/10.4103/0019-5049.165850

Sarturi VZ, Teixeira LG, Coradini GP, Milech V, Hartmann HF, Linhares MT, Martins LR, de Oliveira JS, Brun MV (2021). Total intravenous anesthesia with propofol associated or not with remifentanil, ketamine, or s-ketamine for laparoscopic ovariectomy in female dogs. Topics Compan. Anim. Med., 45: 100575. https://doi.org/10.1016/j.tcam.2021.100575

Saxena D, Dixit A, Kumar N, Arya B, Sanwatsarkar S, Bhandari S (2017). Efficacy of low-dose ketamine as sole analgesic agent in maintaining analgesia and intraoperative hemodynamics during laparoscopic gynecological surgeries. Anesth. Essays Res., 11: 385-389. https://doi.org/10.4103/0259-1162.206276

Schmid RL, Sandler AN, Katz J (1999). Use and efficacy of low-dose ketamine in the management of acute postoperative pain: A review of current techniques and outcomes. Pain, 82: 111–125. https://doi.org/10.1016/S0304-3959(99)00044-5

Seliskar A, Nemec A, Roskar T, Butinar J (2007). Total intravenous anaesthesia with propofol or propofol/ketamine in spontaneously breathing dogs premedicated with medetomidine. Vet. Rec., 160: 85–91. https://doi.org/10.1136/vr.160.3.85

Slingsby LS, Waterman-Pearson AE (2000). The post-operative analgesic effects of ketamine after canine ovariohysterectomy a comparison between pre- or post-operative administration. Res. Vet. Sci., 69: 147–152. https://doi.org/10.1053/rvsc.2000.0406

Smischney NJ, Beach ML, Loftus RW, Dodds TM, Koff MD (2012). Ketamine/propofol admixture (ketofol) is associated with improved hemodynamics as an induction agent: A randomized, controlled trial. J. Trauma Acute Care Surg., 73: 94–101. https://doi.org/10.1097/TA.0b013e318250cdb8

Steffey EP, Mama KR, Brosnan RJ (2015). Inhalation anesthetics. In: Veterinary anesthesia and analgesia: The 5th edition of Lumb and Jones, John Wiley and Sons, UK. pp. 297–322. https://doi.org/10.1002/9781119421375.ch16

Su H, Eleveld DJ, Struys MMRF, Colin PJ (2022). Mechanism-based pharmacodynamic model for propofol haemodynamic effects in healthy volunteers. Br. J. Anaesth., 128: 806–816. https://doi.org/10.1016/j.bja.2022.01.022

Suarez MA, Dzikiti BT, Stegmann FG, Hartman M (2012). Comparison of alfaxalone and propofol administered as total intravenous anaesthesia for ovariohysterectomy in dogs. Vet. Anaesth. Analg., 39: 236–244. https://doi.org/10.1111/j.1467-2995.2011.00700.x

Thengchaisri N, Mahidol C (2019). Evaluating the effects of continuous intravenous infusions of tramadol and tramadol-lidocaine on sevoflurane minimum alveolar concentration (MAC) and entropy values in dogs. J. Vet. Med. Sci., 81(5): 682–688. https://doi.org/10.1292/jvms.18-0448

Tsai YC, Wang LY, Yeh LS (2007). Clinical comparison of recovery from total intravenous anesthesia with propofol and inhalation anesthesia with isoflurane in dogs. J. Vet. Med. Sci., 69: 1179-1182. https://doi.org/10.1292/jvms.69.1179

Wang X, Huang ZG, Gold A, Bouairi E, Evans C, Andresen MC, Mendelowitz D (2004). Propofol modulates gamma-aminobutyric acid-mediated inhibitory neurotransmission to cardiac vagal neurons in the nucleus ambiguus. Anesthesiology, 100: 1198–1205. https://doi.org/10.1097/00000542-200405000-00023

Wilson J, Doherty TJ, Egger CM, Fidler A, Cox S, Rohrbach B (2008). Effects of intravenous lidocaine, ketamine, and the combination on the minimum alveolar concentration of sevoflurane in dogs. Vet. Anaesth. Analg., 35: 289–296. https://doi.org/10.1111/j.1467-2995.2007.00389.x

Yamashita K, Okano Y, Yamashita M, Umar MA, Kushiro T, Muir WW (2008). Effects of carprofen and meloxicam with or without butorphanol on the minimum alveolar concentration of sevoflurane in dogs. J. Vet. Med. Sci., 70: 29–35. https://doi.org/10.1292/jvms.70.29

Yang Y, Ou M, Liu J, Zhao W, Zhuoma L, Liang Y, Zhu T, Mulkey DK, Zhou C (2020). Volatile anesthetics activate a leak sodium conductance in retrotrapezoid nucleus neurons to maintain breathing during anesthesia in mice. Anesthesiology, 133: 824–838. https://doi.org/10.1097/ALN.0000000000003493

Supplementary Table 1S: Showing systolic arterial pressure (SAP) level (mmHg), diastolic arterial pressure (DAP) level in mmHg, and mean arterial pressure (MAP) level mmHg in 17th consecutive time points in the 4 groups.

SAP (mmHg)

DAP (mmHg)

MAP (mmHg)

30 m

132.5abcd

137.5a

145 bcd

142.2 abc

79.8 bc

93.2 bc

91.8 bc

88 bc

102 ab

108.5ab

108.5 ab

107.8 ab

at.ind.

133.33 abcd

146.5 a

141.75 bcd

169a

77.7 bc

93 bc

94.5 bc

107.3 b

98.7 ab

111.8ab

110.2 ab

124 ab

post.15m

121.2bcde

122.5 a

136.2 bcd

137.8 a

67 bc

67.2 bc

81.8 bc

83 bc

88.5 ab

90.5ab

101.2 ab

103.5 ab

post.20m

111.2cde

121 a

128.2 cd

127.2 c

65 bc

63.2 bc

84.2 bc

70.8 bc

82.8 ab

84ab

103 ab

90.5 ab

post.25m

108.5bde

122 a

130.2 cd

129.8 bc

59.5 bc

57.5bc

81 bc

73.2 bc

75b

78.5 ab

100 ab

99 ab

post.30m

100.2e

118.2 a

124.5 d

128.5 c

55c

72.2 bc

74 bc

73.5 bc

73b

89.2ab

94.2 ab

94.8 ab

post.35m

96.5e

113.8 a

124.5 d

131 bc#

56.2c

64.8 bc

75.5 bc

82.8 bc

71b

85ab

95.2 ab

101 ab

post.40m

97.2e

114.8 a

128.5 cd

128 c#

53.8c

65.5 bc

84.5 bc

82 bc

73b

86.8ab

100.8 ab

97 ab

post.45m

105.2de

125.2 a

133.5 bcd

133.5 a

65.2 bc

69.8 bc

89.8 bc

84.2 bc

82 ab

94.8ab

108 ab

103.2 ab

post.50m

132.5abcd

119.5 a

146.2 bcd

139.8 abc

88 bc

69.5 bc

101.8 b

86.8 bc

107.5 ab

91.2ab

116 ab

102.8 ab

post.55m

152.2a

132.8 a

160 abc

146.2 abc

107.5 b

84.5 bc

112.2 b

94.5 bc

123.8 ab

96.5ab

128.5 ab

113.8 ab

post.60m

155a

136.8 a

167.8 abc

157.5 abc

108.2 b

86.2 bc

118.2 b

109 b

128.8ab

101.8ab

135.5 ab

125.8 ab

post.65m

145.5ab

141.5 a

176.2ab

156.2 abc

101 b

87.8 bc

122.8 b

108 b

118.8 ab

102.2ab

136.2 ab

124 ab

post.70m

145.2ab

140.5 a

165.8abcd

160.5 abc

103 b

78.5 bc

130.5ab

110.2 b

117.2 ab

104.2ab

144a

127.2 ab

post.75m

143.2a

142.2 a

173.8 ab

162.5 abc

95.5 b

91.8 bc

126.5 ab

113.5 b

111.8 ab

100.5ab

143.8a

133 ab

post.80m

143.5a

142 a

170.8 abc

165.2 ab

99 b

91.5 bc

126 ab

116.5 b

114 ab

106.5ab

147.2a

135.2 ab

post.85m

139.2abc

138.5 a

156 abcd

165.8 ab

93.8 bc

90.2 bc

102 b

116.5 b

109.8 ab

105.5ab

133.6 ab

133.5 ab

post.90m

138.5abc

122.6 a

182.5a

168.8 a

***

90.5 bc

81.7 bc

133.2a

118.5 b

106.8 ab

91.8ab

145.7a

134 ab

C.V

28%

22.4%

26%

25.4%

23%

15.8%

20.3%

20.5%

abcd means with difference superscript within same column are statistically difference p < 0.05

Supplementary Table 2S: The estimated marginal means and coefficient of variation of the ET SEVO level change over the time of anesthetic procedure for G1 and G2.

Time	1	2
Post.15m	2.1b	1.95c
Post.20m	2.1b	2b
Post.25m	2.12b	1.95c
Post.30m	2.1b	2b
Post.35m	2.08b	2.05 b
Post.40m	2.12 b	2.05 b
Post.45m	2.15 b	2.12 b
Post.50m	2.17 b	2.23 b
Post.55m	2.2 b	2.25b
Post.60m	2.27 ab	2.25 b
Post.65m	2.27 ab	2.12 b
Post.70m	2.33 a	2.2 b
Post.75m	2.35 a	2.12 b
Post.80m	2.38 a	2.2b
Post.85m	2.4 a	2.17b
Post.90m	2.4 a	2.17 b
C.V	7%	7%

abc means with different superscript are statistically different p < 0.05

Supplementary Table 3S: Showing the estimated marginal means for respiratory rate (RR) breath/minute, tidal volume (VT) in the 4 groups during the anesthetic procedure at consecutive time points (post 15 min to post 90).

	RR (breaths/min)				VT (ml)
	1	2	3	4	1	2	3	4
30 m	15.75 b	13.67 bc	15.25 b	16.25 ab
Post.15m	6.75 e	10.5 cd	10 cd	11.25bc	230ab	217 ab	217 ab	200 ab
Post.20m	9.25d	12.25 bc	10 cd	11.5 bc	187 ab	229 ab	222 ab	236 ab
Post.25m	9.75 d	13 bc	10.5 cd	13 bc	195 ab	217 ab	216 ab	171 c
Post.30m	10.5 cd	12 bc	7.75 e	12.75 bc	194 ab	209 ab	174 c	219 ab
Post.35m	11 bc	12.25 bc	7.75 e	13.5 bc	286a	227 ab	166 c	183 ab
Post.40m	12 bc	7e	10 bc	16 ab	264 ab	196 ab	229 ab	197 ab
Post.45m	15b	6.75 e	8.5 d	13 bc	177 ab	205 ab	230 ab	183 ab
Post.50m	12.25 b	10.25 cd	10.75 b	11.25 bc	228 ab	238 ab	241 ab	254 ab
Post.55m	14.25 b	7.75 e	11.25 b	11.25 bc	219 ab	214 ab	191 ab	211 ab
Post.60m	12.75 b	6.75 e	10.5 b	12.25 bc	204 ab	196 ab	245 ab	208 ab
Post.65m	12.75 b	8.5d	11.75 bc	16.75 ab	199 ab	239 ab	224 ab	180 ab
Post.70m	19.5a	7.75 e	15 b	12 bc	171c	222 ab	252 ab	202 ab
Post.75m	12.75 b	9 c	8d	16 ab	209 ab	220 ab	254 ab	175 ab
Post.80m	14.25 b	9.5 c	9.25c	13.5 bc	216 ab	215 ab	257 ab	203 ab
Post.85m	16.5 ab	11 b	10 cd	17.25a	221 ab	235 ab	246 ab	179 ab
Post.90m	11.5b	9.33 c	10.25 cd	12.75 bc	216 ab	217 ab	253 ab	243 ab
C.V	35%	27%	32%	26%	19.75%	15 %	23%	19%

abc means with different superscript are statistically different for each measured parameter, p < 0.05.

Supplementary Table 4S: Estimated marginal means of the ETCO2 level change over the time of the anesthetic procedure for the 4 groups.

Time	1	2	3	4	Significance of simple effect between groups at each time point
Post.15m	46.8	42	46.2 ab	44	P > 0.05ns
Post.20m	43	45.8	41.2 ab	44.8	P > 0.05ns
Post.25m	48.2	41.5	46.5 ab	45	P > 0.05ns
Post.30m	49A	42.8B	44 abB	44.5B	< 0.05*
Post.35m	44.8 A	45.2 A	29.2 b B	45.5 A	P < 0.05*
Post.40m	43.5	45	45.5 ab	42.2	P > 0.05ns
Post.45m	43.2	45	46.2 ab	44	P > 0.05ns
Post.50m	42.2	45	45.8 ab	45.8	P > 0.05ns
Post.55m	40.5	43	43.8 ab	47.2	P > 0.05ns
Post.60m	44.5 A	35 B	43.8 ab A	44.2 A	P < 0.05*
Post.65m	43.8	41.2	43 ab	43.5	P > 0.05ns
Post.70m	41.5	44.8	46.8 ab	44.8	P > 0.05ns
Post.75m	43.2	41	47.5a	44.5	P > 0.05ns
Post.80m	44.2	43.2	46.5ab	42.8	P > 0.05ns
Post.85m	44.2	44.3	47.2a	45.2	P > 0.05ns
Post.90m	43	43.7	48a	45.2
Significance of simple effect over time	P > 0.05ns	P >0.05ns	P<0.05*	P >0.05ns

ab means with different superscript within same column are statistically different p < 0.05. AB means with different superscript within same row are statistically different p < 0.05. ns: non-significant difference P > 0.05; * significantly different P < 0.05.