Malignant hyperthermia (MH) is a type of severe reaction that occurs in response to particular medications used during general anesthesia, among those who are susceptible. Symptoms include muscle rigidity, high fever, and a fast heart rate. Complications can include muscle breakdown and high blood potassium. Most people who are susceptible are generally otherwise unaffected when not exposed.The cause of MH is the use of certain volatile anesthetic agents or succinylcholine in those who are susceptible. Susceptibility can occur due to at least six genetic mutations, with the most common one being of the RYR1 gene. These genetic variations are often inherited from a persons parents in an autosomal dominant manner. The condition may also occur as a new mutation or be associated with a number of inherited muscle diseases, such as central core disease.In susceptible individuals, the medications induce the release of stored calcium ions within muscle cells. The resulting increase in calcium concentrations within the cells cause the muscle fibers to contract. This generates excessive heat and results in metabolic acidosis. Diagnosis is based on symptoms in the appropriate situation. Family members may be tested to see if they are susceptible by muscle biopsy or genetic testing.Treatment is with dantrolene and rapid cooling along with other supportive measures. The avoidance of potential triggers is recommended in susceptible people. The condition affects one in 5,000 to 50,000 cases where people are given anesthetic gases. Males are more often affected than females.
The mechanism of mydriasis depends on the agent being used. It usually involves either a disruption of the parasympathetic nerve supply to the eye (which normally constricts the pupil) or overactivity of the sympathetic nervous system (SNS). Pupil diameter also increases in reaction to cognitive tasks requiring memory and attention, and this phenomenon is used as an indicator of mental activation (‘arousal’) in psychophysiological experiments. Drugs
A mydriatic is an agent that induces dilation of the pupil. Drugs such as tropicamide are used in medicine to permit examination of the retina and other deep structures of the eye, and also to reduce painful ciliary muscle spasm (see cycloplegia). One effect of administration of a mydriatic is intolerance to bright light (photophobia). Purposefully-induced mydriasis via mydriatics is also used as a diagnostic test for Horners syndrome. Mydriasis can be induced via modulation of adrenergic or cholinergic signalling. Drugs that can cause mydriasis include:

Stimulants (typically monoaminergics) such as amphetamines, cocaine, MDMA, and mephedrone. Anticholinergics such as diphenhydramine, atropine, hyoscyamine, and scopolamine antagonize the muscarinic acetylcholine receptors in the eye. Blocking acetylcholine receptors reduces the pupillary muscles ability to constrict and causes dilation (which is critical in eye surgery procedures such as cataract surgery which require uninterrupted access to the inner eye via the pupillary aperture, thus requiring that the eye be both paralyzed and anesthetized before the procedure can go ahead). The antimuscarinic, tropicamide, may be used as a mydriastic agent during surgery. Serotonergics such as LSD, psilocybin mushrooms, mescaline and 2C-B. These drugs are typically hallucinogens.