Scalp Blocks

A. Mean arterial pressure about 14 mmHg lower and heart rate about 12 beats/min lower, with no difference in intraoperative opioid dose

The block also reduced the incidence of intraoperative hypertension, and a similar but smaller effect was seen at skin incision (about 9 mmHg and 9 beats/min). In the subgroup analysis, the scalp block beat scalp infiltration at pin insertion but not at incision — which is what you would expect if the pins are the stimulus a field block is best placed to cover, though the review reports the subgroup result without testing that explanation.

The block covered the supraorbital, supratrochlear, auriculotemporal, occipital and postauricular branches of the greater auricular nerves, using 20 ml of 0.5% bupivacaine. Beyond haemodynamics the trial measured the endocrine stress response — plasma cortisol and adrenocorticotropic hormone, sampled 5 minutes before induction and 5 and 60 minutes after the pin holder went on. Heart rate and mean arterial pressure rose during pinning in the infiltration and control groups but not in the scalp block group, and cortisol and ACTH at both post-pinning time points were significantly lower after the scalp block than after either infiltration or routine anaesthesia.

Infiltration at the pin sites was not equivalent to the block: on both haemodynamics and stress hormones the block did better, and that is what the authors conclude. Why it did better is not something this trial tested. The familiar account — that a field block of the named nerves is less dependent on each pin landing exactly where you infiltrated — is an explanation offered for the result rather than a finding of it.

Scalp block reduced postoperative visual analogue pain scores from 2 through 72 hours, by mean differences of 0.79 to 1.40 points, and reduced opioid requirement by 16.52 morphine milligram equivalents at 24 hours and 15.63 at 48 hours. Overall risk of bias across the trials was low. The honest presentation is that these are modest absolute reductions — around one point of pain and about 16 morphine milligram equivalents — and that is how the authors themselves ask them to be read: the clinical utility of the differences should be interpreted in the context of the modest absolute size, of overall care optimisation, and of the patient population. Note the limits of what you can quote from this paper: it measured pain and opioid consumption, so it will support an argument that the block is a real if small addition to an opioid-sparing pathway, but it did not measure the block's cost, its procedure time or its complication rate, and an argument resting on those has to be sourced elsewhere.

This is the largest randomised evidence base for the block, and the authors themselves ask that the differences be read against the modest absolute size and against the population being treated. Whether a one-point pain reduction and about 16 morphine milligram equivalents matter more in a neurosurgical patient than elsewhere is a judgement this review invites and does not make.