The behaviour of polyethylene with different contents in vinyl and t-vinylene groups have been studied by photooxidation with λ>300 nm light or by thermooxidation at a temperature of 100 °C. The oxidation was studied by infrared spectroscopy and it was shown that the same oxidation products were obtained, but with different relative concentrations depending on the conditions of ageing, i.e. photochemical or thermal conditions. The mechanisms by which the oxidation products are formed were recalled. The differences between photo-and thermooxidation were evidenced on the basis of the stability of ketones that do not accumulate in photochemical conditions, as a result of Norrish reactions. The influence of the initial amount of unsaturated groups on the rates of oxidation was characterized. It was shown that the concentration of unsaturations had no effect on the rate of photooxidation but dramatically influenced the stability in thermooxidative conditions.
Objectives:
A single perioperative dose of glucocorticoid or gabapentinoid, or a combination of the 2, may improve postoperative analgesia, but data are still insufficient to be conclusive. In this single-center, randomized, double-blind, and double-dummy trial, we aimed to test whether the analgesic effect of adding preoperative pregabalin, at a dose unlikely to induce side effects, to preoperative dexamethasone improves early mobilization after spinal surgery.
Materials and Methods:
A total of 160 patients undergoing scheduled lumbar disk surgery (145 analyzed) comprised the study cohort. The patients received either 0.2 mg/kg intravenous dexamethasone before incision, or 150 mg oral pregabalin 1 hour before surgery, or a combination of the 2, or none of the above (control). Analgesia was supplemented by acetaminophen and ketoprofen, plus oxycodone ad libitum. The primary outcome was pain intensity during the first attempt to sit up, assessed the morning of the first postoperative day on an 11-point Numerical Rating Scale. Pain at rest and when standing up, opioid consumption, and tolerance were also assessed.
Results:
None of the treatments tested differed from the control group in terms of efficacy or tolerance, even 6 months after surgery. The overall quality of analgesia was good, with only 10% and 30% of pain scores exceeding 3/10 for pain at rest and during movement, respectively.
Discussion:
In this surgical model with the given anesthetic and analgesic environment, there was no advantage gained by adding low-dose pregabalin or dexamethasone. The multimodal analgesic protocol applied to all patients may have reduced the size of the effect.
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