Biomedical Engineering Reference
In-Depth Information
blindness, abdominal pain, and possible death) (Cook et al., 1991). The
latency period, before visual effects are noted, following ingestion of
methanol is not an estimate of the severity of the poisoning. The
concurrent ingestion of ethanol may help delay the onset of acidosis
and other effects of methanol toxicity. Blurred vision strongly supports
the diagnosis of methanol toxicity (Barceloux et al., 2002).
Mortality correlates best with the degree of acidosis and formate
concentration rather than serum methanol concentration (Barceloux
et al., 2002).
Ophthalmoscopic examination following methanol poisoning
showed local increase in blood flow of the optic disc was the first
change seen in the eyes. This was followed by a white striated edema
appearing to surround the retina. The degree of white striated edema
appears to correlate with the seriousness of the effect of methanol on
vision (Kavet and Nauss, 1990). CNS effects appear when blood
methanol levels reach 200mg/l and blindness is seen above 500mg/l
(Anonymous, 1997).
There are numerous case reports on accidental methanol poisoning.
In addition to effects reported above other effects such as long-term
paralysis of vocal cords, visual effects, and difficult in walking (Riegel
and Wolf, 1966). Magnetic resonance imaging (MRI) and cat (CT) scan
effects have also been reported. Focal necroses in the brain white matter
and in the Putamen are commonly seen on MRI and CT scans of
seriously effected individuals. Bilateral hemorrhagic in the putamen is
also seen (Vira-Cartrodeza et al., 2007; Keles et al., 2007; Gaul et al.,
1996; Phang et al., 1988; Bessell-Browne and Bynevelt, 2007).
3.3.3.2 Blood and Urine Methanol
In addition to clinical symptoms,
methanol and its metabolites have been measured in blood urine and
breath. Urinary methanol levels greater than 10mg/l suggests total
exposure to methanol was too high (above the TLV) (Ferry et al., 1980).
The CERHR (2003) established a “safe level” of methanol in the blood
at 10mg/l. Only at air levels above the workplace exposure limit of
200 ppm does blood methanol exceed this level. In humans exposed by
inhalation to methanol at 400 ppm, blood levels of methanol were
reported at 13.4mg/l (Franzblau et al., 1995).
