[11:40, 05/06/2022] Erik Verrynne: Douw/Hendrik/ André. Do you think the potential drop in peripheral blood pressure caused by the medetomidine can reduce muscle perfusion and increase the risk of muscle damage in heavy animals such as rhinos? Is it something one need to look out more than for other combinations? [11:43, 05/06/2022] David Pretorius: Erik. They have not seen this in over 100-150 3-4 hour immobilisations. I did some CK values on 30min 1 hr and 1.5hr and they remain normal. [11:47, 05/06/2022] Andre Uys: My gut feel is the muscular activity seen in opioid immobilisations is worse for the legs. I have had animals down sternal in one position with medetomidine and no issues. [12:50, 05/06/2022] Alex Lewis: I agree if you see how they stand up afterwards, the legs are stronger so something is better. [14:28, 05/06/2022] Leith Meyer: Erik, I think this is something important to consider. Not only do the alpha-2 agonists cause intense vasoconstriction (both in the systemic and pulmonary systems) they also reduce cardiac output (systemic and pulmonary blood flow), both potentially causing a severe reduction in tissue and lung perfusion. One benefit though is that they mostly reduce metabolism and oxygen requirements. However, the negative cardiovascular effects in the lungs cause V/Q mismatching and pulmonary hypertension with congestion and potentially also oedema, all resulting in quite severe hypoxaemia. The combination of this hypoxaemia and reduced perfusion pose significant risks that people must be aware of, and consider, especially when immobilization morbidity and mortality occurs. It’s important to also remember that effects of hypoxia are often delayed. CK takes 10-12 hours to start rising and only peaks around 24-36 hours, and cardiac troponin I takes 4-12 hours to start rising and peak around 24-48 hours. So it’s very difficult to assess the full impact of drug effects on the body during the immobilization time. See the difference between human and rhino oxygen dissociation curves, and the implications for hypoxia below: [14:37, 05/06/2022] David Pretorius: Has anyone been able to check CK values 24 hours post immobilization? [14:49, 05/06/2022] Leith Meyer: Another important point is that clinical hypoxaemia, where one should consider responding with treatment, starts at 90% SpO2 from a pulse oximeter. 80% SpO2, and below, is severe hypoxaemia and means significant risks to an animal. Rhino have a left shifted ODC curve which means their haemoglobin picks up oxygen easier in hypoxic conditions, but it also tells you that at 80% SpO2 they have PaO2 values below 35mmHg (it should be 80-100mm Hg), so very little oxygen is getting from their lungs into the blood, which should be of significant concern. [14:56, 05/06/2022] David Pretorius: Is there any drug combo known that doesn’t cause severe hypoxia in rhino currently? [14:58, 05/06/2022] Andre Uys: Seems we need to get some habituated rhino orphans and train them to accept venipuncture so we can take samples 12, 24, 36 and 48 hours post immobilisation to get some clinical data. [14:59, 05/06/2022] David Pretorius: Do you know where we can get? I will sponsor the study for an undergraduate. Maybe Ben maybe interested? This is a quick and easy thing we may be able to do. [15:00, 05/06/2022] Andre Uys: I am sure there are many available. Ours are unfortunately all re-wilded and I am hoping not to get anymore!!!! [15:13, 05/06/2022] Leith Meyer: Definitely worthwhile doing. We’re busy trying to figure out which cardiac troponin assay will be of value in rhino, the ones used in horses don’t seem to work in rhino. Once we have this figured out then this type of study will be very important to do to assess safety of drug combos in rhino.
