290

Air-line

explosions and low-flying drills

SiR,—The steady hum of a drill during a routine extraction of wisdom teeth was interrupted one morning by a sudden and loud explosion. The scrub nurse stumbled from her platform, twisting her ankle just as the hand piece of a dental drill whizzed dangerously past the surgeon’s head. Simultaneously, a compressed air cylinder discharged its contents with a deafening hiss from the severed end of a violently flaying air-line, scattering theatre staff in all directions. The surgeon with commendable alacrity pounced on the air-line and subdued it while the air cylinder was turned off. Needless to say, only the patient was unmoved. Four other incidents in the same district general hospital over the past three years prompt this report. In two cases, old air-driven drills were being used as substitutes for more modern drills being repaired or overhauled. In two others, examination of the air-line revealed fraying and obvious signs of wear and tear, probably accounting for the incident. On one occasion the air hose connecting the drill to the compressed air cylinder was noted to balloon by about 5 cm shortly before it burst. In another, as the surgeon was testing the drill a nurse, having noted that the cylinder mains was off, turned it on abruptly and without warning. The sudden surge of pressure probably accounted for the perforation from a worn out air-line. In all cases air pressure from the feeding cylinders was set at the correct operating level. These incidents are especially regrettable since the UK is the only country with specific practical performance test criteria for compressed air-lines.! Similar incidents have occurred with medical gas hose assemblies fitted to medical equipment, prompting guidelines from the then Department of Health and Social Security,2 some of which are equally applicable here. The guidelines include visual inspection for evidence of fraying, ballooning, or damage, ideally done before every operation where a drill may be used. The lifespan of three to five years suggested for medical gas hose assemblies is probably inappropriate for air-line hoses. Meanwhile, such potentially lethal incidents are best prevented by abandoning the use of old or obsolete dental drills, instruction in the proper use of compressed gas cylinders, and checking and maintenance of equipment by skilled engineers. The anaesthetist should play an active part in the institution of these measures. Department of Anaesthesia, London Hospital, London E1 1BB, UK

D. SURESH

1. White N,

Ryan CM, Breyesse PN, Corn M. Critical review of international standards respiratory protective equipment III. practical performance tests. Am Ind Hyg Assoc J 1983, 44: 768-73. 2. Medical gas hose assemblies. London: Department of Health and Social Security, safety information bulletin 9, 1983: R/A 1010/143. for

Raised plasma endothelin in aneurysmal subarachnoid haemorrhage SiR,—Dr Masoaka and colleagues (Dec 9, p 1402) report increased plasma endothelin-1 (ET-1) in patients with subarachnoid haemorrhage, especially those with symptomatic vasospasm. They suggest that endogenous ET-1 could be a causal factor in cerebral vasospasm, in accordance with its in-vivo vasoconstrictor effect on feline and canine basilar arteries. This effect was observed in cerebral vessels when ET-1was applied from the adventitial but not

from the luminal side, possibly because of the blood-brain barrier or tight capillary junctions.1 Yaganisawa et all speculated that ET-1 is an endogenous agonist of the dihydropyrine-sensitive Calchannels because of structural homologies with a specific group of peptide toxins that act on membrane calcium channels. This hypothesis was not confirmed by Chabrier et allwho showed that contraction induced by ET-1 was not affected by direct classes of calcium entry blockers, which suggests that action of ET-1 is not associated with an activation of voltage-dependent Ca2’ channels. Calcium channel blockers are very effective in the prevention of subarachnoid haemorrhage-related vasospasm. Nimodipine, a

1,4-dihydropyridine derivative

which

crosses

the blood-brain

barrier, significantly reduces the occurrence of severe neurological deficits from spasm in patients with subarachnoid haemorrhage.1 We found that nimodipine effectively prevented vasospasm in such patients, especially when given prophylactically during and after operation and when combined with early surgical management (within 48-96 h). The high frequency of spontaneous vasospasm5 led us to study calcium channel blockers in a randomised prospective investigation of the effects of nimodipine versus placebo in 160 patients with subarachnoid haemorrhage from intracranial aneurysms.

Nimodipine

treatment

(initially

2

mg/h intravenously

followed by 360 mg/day orally, on the basis of angiographic results) was associated with a significantly lower occurrence of severe postoperative vasospasm (42% vs 20%, p

Raised plasma endothelin in aneurysmal subarachnoid haemorrhage.

290 Air-line explosions and low-flying drills SiR,—The steady hum of a drill during a routine extraction of wisdom teeth was interrupted one...
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