The extradural pressure profile in goats following extradural injection.

Objective: To measure the extradural pressures in goats before and after extradural injection, and to investigate the occurrence of extradural pressure waves.

Study Design: Prospective experimental trial.

Animals: Nine healthy adult goats weighing 59.4 +/- 6.4 kg, scheduled for stifle arthroscopy.

Methods: The goats were pre-medicated with midazolam and anaesthesia was induced with propofol and maintained with sevoflurane. The goats were placed in lateral recumbency and extradural puncture was performed via the lumbosacral space. Correct placement of the needle was assessed by lack of resistance to the injection of saline. The needle was connected to an electronic pressure transducer to record extradural pressure. Measurements were taken before and after extradural injection of methadone (0.1 mg kg(-1), diluted to a total volume of 0.2 mL kg(-1)) and 10 minutes later. Contrast medium was injected and correct extradural needle placement confirmed by radiography.

Results: Lack of resistance to injection of saline occurred in all goats, but there were no pressure waves observed before injection in any animal. Radiography indicated incorrect needle placement in four animals and one had pressure waves synchronous with the arterial pulse after methadone injection. Correct needle placement was confirmed in the remaining five animals which exhibited pressure waves after extradural methadone injection. In the five goats with successful needle placement the baseline extradural pressure ranged from 0.4 to 2.5 kPa (3-19 mmHg), increasing to 4.4-39.9 kPa (33-300 mmHg) after injection. Ten minutes after injection, extradural pressure remained elevated and ranged from 2.5 to 17.3 kPa (19-130 mmHg).

Conclusions And Clinical Relevance: Extradural pressure waves were not useful to confirm correct extradural needle placement in laterally recumbent goats. The presence of such waves after injection of 0.2 mL kg(-1) may be indicative of correct placement but even here we saw one of nine animals with extradural pressure waves where we failed to confirm correct needle placement. Extradural pressure increases after extradural injection.