Thiopental and halothane dose-sparing effects of magnesium sulphate in dogs

The effect of intravenous magnesium sulphate infusion on total intravenous anesthesia with propofol in adult dogs: A randomized, blinded trial

OBJECTIVE

To evaluate cardiopulmonary, arterial blood gas and propofol-sparing effects of magnesium sulfate (MgSO4) constant rate infusion (CRI) in mechanically ventilated dogs maintained under total intravenous anesthesia with propofol.

STUDY DESIGN

Blinded, randomized, clinical trial.

ANIMALS

A total of 24 healthy adult dogs.

METHODS

Dogs were premedicated with intramuscular acepromazine (0.05 mg kg-1) and morphine (0.5 mg kg-1), followed by an intravenous (IV) bolus of saline or MgSO4 (50 mg kg-1 over 15 minutes) and propofol (given to effect to induce anesthesia). Anesthesia was maintained with an IV propofol infusion (beginning at 0.3 mg kg-1 minute-1, adjusted as necessary). Concurrently, one of three IV infusions were administered: GS (0.9% NaCl), GM30 (MgSO4, 30 mg kg-1 hour-1) or GM80 (MgSO4, 80 mg kg-1 hour-1). Propofol induction and maintenance doses were recorded. The following variables were recorded at baseline (T0), after bolus treatment (T1), after beginning mechanical ventilation (T5) and every 15 minutes until the end of the procedure (T15-T120): mean arterial pressure, heart rate, peripheral oxygen saturation, end-tidal partial pressure of CO2, temperature, blood gas variables, indirect calorimetry and extubation time. Values of p < 0.05 were considered significant.

RESULTS

Propofol induction bolus dose was lower in GM30 (31.2%, p = 0.04) and GM80 (38.9%, p = 0.003) than in GS. The maintenance propofol infusion rate in GM80 was 16.9% lower (p = 0.03), resulting in fewer propofol CRI rescues during the perioperative period. GM30 and GM80 exhibited faster extubation times than GS (46.2%, p = 0.002 and 48.9%, p = 0.001, respectively).

CONCLUSIONS AND CLINICAL RELEVANCE

Infusion of a 50 mg kg-1 bolus, followed by CRI of MgSO4 (30 and 80 mg kg-1 hour-1), reduces the propofol induction and maintenance (CRI) requirement, maintaining cardiorespiratory stability and reducing the time required to extubation.

Effects of a synergic interaction between magnesium sulphate and ketamine on the perioperative nociception in dogs undergoing tibial plateau leveling osteotomy: a pilot study

Introduction

Magnesium Sulphate (MgSO4) is commonly used in human medicine for the management of perioperative pain in different types of procedures. However, in veterinary medicine, the use of MgSO4 has not been evaluated for its analgesic efficacy in dogs, which has generated conflicts of opinion in this area of veterinary anesthesiology. The aim of this study was to evaluate the perioperative analgesic efficacy of MgSO4 in combination with Ketamine in dogs undergoing Tibial Plateau Leveling Osteotomy (TPLO). Our hypothesis is that MgSO4 plus ketamine have a synergistic action in the management of intra-and postoperative pain.

Methods

Twenty adult mixed breed dogs with average age 5.9 ± 2.6 years and weight 27.8 ± 9.2 kg were included in this prospective, clinical, randomized study. Dogs were randomly assigned to two groups. The MK group received ketamine (0.5 mg/kg as starting bolus followed by continuous infusion rate at 1 mg/kg/h). At the end of the ketamine bolus, MgSO4 (50 mg/kg over 15 min) was administered by the same route, followed by a constant rate infusion (CRI) at 15 mg/kg/h, IV. K group received a bolus of ketamine followed by a CRI at the same dosage described in MK group. Main cardiorespiratory parameters were recorded 10 min before the start of surgery (BASE), after the ketamine bolus (T1) and the MgSO4 bolus (T2), during the skin incision (SKIN), the osteotomy (OSTEOTOMY) and skin suturing (SUTURE). In the postoperative period, the short form of Glasgow Composite Pain scale (SF-CMPS) was used to assess pain at 30, 60, 120, and 180 min after extubation (Post30, Post60, Post120, and Post180, respectively). The main blood electrolytes (Mg2+, Ca2+, Na+, K+) were analyzed at BASE, T2, OSTEOTOMY, SUTURE and T3 (one hour after stopping MgSO4 infusion). Number of rescue analgesia and administration times were recorded both in the intra-and postoperative period.

Results

In K group 7 out of 10 dogs required intraoperatory rescue analgesia compared to MK group (3/10). Furthermore, mean arterial pressure (MAP) and heart rate (HR) were significantly higher at OSTEOTOMY compared to BASE time in both groups. In the postoperative period, at T120, ICMPS-SF score was higher in K group than MK group.

Conclusion

The administration of MgSO4 could guarantee better analgesia in the perioperative period in dogs undergoing TPLO, performing a synergistic action with ketamine.

The analgesic effects of magnesium in veterinary patients: a qualitative evidence synthesis

OBJECTIVE

To perform a qualitative evaluation of the analgesic effects of magnesium in domestic animals, including its anaesthetic sparing effects.

STUDY DESIGN

All database searches were made using PubMed and Google Scholar. Studies published after 1990, evaluating the use of magnesium and reporting information on analgesia, in dogs, cats, horses, cows, goats and sheep were selected (last search in August 2023). A reference check in the selected papers was performed to identify any study which was omitted. The CERQual (Confidence in Evidence from Reviews of Qualitative research) approach was used to assess confidence and analyse the evidence.

RESULTS

A total of 20 studies relevant to the analgesic effects of magnesium in veterinary patients and two reviews were included. All were published after 2006. Of the 20, five studies provided information about analgesia in the postoperative period in dogs with heterogenous results. Magnesium added epidurally increased the duration of the sensory block in several species. Motor block was also observed when added to spinal analgesia. Results regarding volatile agents sparing effect were conflicting. Occasional moderate adverse effects were reported in dogs, such as nausea and vomiting, when administered as a bolus in conscious animals, and hypotension when administered intraperitoneally. Collapse was reported in horses after epidural administration.

CONCLUSIONS AND CLINICAL RELEVANCE

The evidence of an analgesic effect of magnesium in veterinary patients remains scarce considering the paucity and low quality of published data. Further research may be helpful to establish the efficacy and indications of magnesium in multimodal analgesia in animals.

Intravenous magnesium sulphate in standing horses: effects on physiological parameters, plasma concentration of magnesium and nociceptive threshold tests

A bolus of 50 mg kg ^-1 MgSO₄ (treatment Mg) or the same volume of saline (treatment S) was infused over 15 minutes in 5 adult healthy horses. T0 was the end of the infusion. Physiological parameters were recorded throughout the study period. Measurements of electrical, thermal and mechanical nociceptive thresholds were performed at the pelvic limbs at baseline (before T0), and at specific timepoints. Blood samples were taken at fixed timepoints before, during and until 12 hours after the infusion. For statistical analysis, the 95% confidence intervals (CI's) for the differences in nociceptive thresholds between treatments were calculated. Physiological parameters were compared using a linear mixed model (global α = 0.05, with Bonferroni correction α = 0.0125). The concentrations of ions were also compared with baseline values at specific timepoints, using a linear mixed model. The Pearson's correlation coefficient was derived between the ion concentrations. The 95% CI's of thermal, mechanical and electrical thresholds were [-1; +2]°C, [0; +3] N and [-1; +1] mA (positive differences indicate higher thresholds for treatment Mg), respectively. Heart rate was significantly higher (p < 0.0001) and non-invasive systolic arterial pressure (p < 0.0001) and respiratory rate (p = 0.0002) significantly lower after treatment Mg compared to treatment S. Additionally, non-invasive systolic arterial pressure was significantly different at T45 (p < 0.001). Although mild changes in cardiovascular parameters and plasma concentrations were seen with intravenous administration of MgSO₄, no changes in nociceptive thresholds were detected in standing non-sedated horses.

Effects of magnesium sulfate and propofol on the minimum alveolar concentration preventing motor movement in sevoflurane-anesthetized dogs

OBJECTIVE To evaluate the effect of MgSO4, alone and in combination with propofol, on the minimum alveolar concentration preventing motor movement (MACNM) in sevoflurane-anesthetized dogs. ANIMALS 6 healthy purpose-bred adult male Beagles (least squares mean ± SEM body weight, 12.0 ± 1.1 kg). PROCEDURES Dogs were anesthetized 3 times at weekly intervals. The MACNM was measured 45 minutes after induction of anesthesia (baseline; MACNM-B) and was determined each time by use of a noxious electrical stimulus. Treatments were administered as a loading dose and constant rate infusion (CRI) as follows: treatment 1, MgSO4 loading dose of 45 mg/kg and CRI of 15 mg/kg/h; treatment 2, propofol loading dose of 4 mg/kg and CRI of 9 mg/kg/h; and treatment 3, MgSO4 and propofol combination (same doses used previously for each drug). A mixed-model ANOVA and Tukey-Kramer tests were used to determine effects of each treatment on the percentage decrease from MACNM-B. Data were reported as least squares mean ± SEM values. RESULTS Decrease from MACNM-B was 3.4 ± 3.1%, 48.3 ± 3.1%, and 50.3 ± 3.1%, for treatments 1, 2, and 3, respectively. The decrease for treatments 2 and 3 was significantly different from that for treatment 1; however, no significant difference existed between results for treatments 2 and 3. CONCLUSIONS AND CLINICAL RELEVANCE MgSO4 did not affect MACNM, nor did it potentiate the effects of propofol on MACNM. Administration of MgSO4 in this study appeared to provide no clinical advantage as an anesthetic adjuvant.