This is a real possibility when using such a small amount of local anaesthetic and could easily occur, especially if surgery lasts longer than 30 - 40 minutes, as may be the case with an inexperienced surgeon, or with unexpected surgical difficulties. It must be emphasised however that any spinal anaesthesia, and especially when using larger amounts of local anaesthetic that the usual rules apply. Included in these are that the patient must be fully fluid resuscitated with intravenous fluids and that they should be free of significant cardiac disease. In these situations spinal anaesthesia with a larger amount of local anaesthetic may be dangerous or even fatal. Although he is rightly worried about the risks of a higher spinal block including hypotension, the level of spread of a heavy solution is limited somewhat by the natural thoracic kyphosis, especially if a pillow is placed beneath the upper body to exaggerate this.
Hypotension can be a problem but is easily treated with appropriate fluid.
If necessary a vasopressor such as ephedrine may be used. One ampoule of 30mg can be diluted into a 10 ml syringe with saline and the anaesthetic assistant or nurse can inject boluses of 1 - 2mls as required to elevate the blood pressure. Alternatively one or two ampoules of ephedrine can be added to a bag of intravenous fluid and the rate of infusion adjusted in accordance with the blood pressure. There can be little doubt that using a smaller dose of local anaesthetic lessens the cardiovascular effects of spinal anaesthesia. We are aware that vasopressors can sometimes be unavailable and that fluid resuscitation is sometimes limited.