The effects of magnesium infusions on haemodynamic and nociceptive variables in minipigs undergoing thoracotomy.

Magnesium regulates myocardial depolarisation, vascular tone, neuromuscular function and provides analgesia. This study examined its analgesic and haemodynamic effects, comparing the effects of intravenous saline 0.9% (NaCl; control n = 8) and magnesium (n = 7) infusions in minipigs undergoing thoracotomy. Preoperative single-housed activity was recorded for 1 h. Intraoperatively, arterial blood pressure (BP) and heart rate (HR) were recorded once telemetry was established; data from the final 60 min of anaesthesia were compared between groups. Postoperative activity, HR and BP were recorded continuously using in-pen CCTV and telemetry, respectively. Indicators of pain, including HR and BP were sampled after tracheal extubation (TTE) at +0.5, +2.5, +4.5, +6, +8.5, +15.5, +17.5, +19.5, +20, +23, +25.5, +26 and +29 h. Changes in HR and BP before and after analgesia at TTE +6, +17.5, +23 and +29 h, and pre- and post-pain assessments at TTE +2.5, +6, +17.5, +20, +23, +26 and +29 h were compared using a paired t-test. During anaesthesia, no electrocardiography derangements were noted. There was no difference between groups in the area under the curve for any cardiovascular variable. Magnesium-treated animals had an increased incidence of hypotension during anaesthesia. Postoperatively, activity decreased significantly for both groups for duration (all time points) and frequency (TTE +0.5, +4.5, +8.5, +15.5 h), but no treatment effect was observed. Pain scores were comparable between groups. Following pain assessment and analgesia administration at TTE +17.5, Group NaCl had significant increases in HR and mean arterial pressure The magnesium dose evaluated produced no harm nor obvious benefit.