This is much more profound in patients who have an already increased sympathetic drive, like patients who have high blood pressure or congestive heart failure. It does not affect the contractility of the heart when regular doses are administered. Muscle rigidity
If high boluses of fentanyl are administered quickly, muscle rigidity of the vocal cords can make bag-mask ventilation very difficult. The exact mechanism of this effect is unknown, but it can be prevented and treated using neuromuscular blockers. Wooden chest syndrome
A prominent idiosyncratic adverse effect of fentanyl also includes a sudden onset of rigidity of the abdominal muscles and the diaphragm, which induces respiratory failure; this is seen with high doses and is known as wooden chest syndrome. The syndrome is believed to be the main cause of death as a result of fentanyl overdoses.Wooden chest syndrome is reversed by naloxone and is believed to be caused by a release of noradrenaline, which activates α-adrenergic receptors and also possibly via an activation of cholinergic receptors.Wooden chest syndrome is unique to the most powerful opioids—which today comprise fentanyl and its analogs—while other less-powerful opioids like heroin produce mild rigidity of the respiratory muscles to a much lesser degree. Overdose
Fentanyl poses an exceptionally high overdose risk in humans, due to having an extremely unpredictable fatal dosage when mixed with other drugs. In its pure form, overdoses are only moderately unpredictable, with most overdose deaths occurring at serum concentrations of between 150 and 250 ng/mL.
Pseudostrabismus is the false appearance of crossed eyes. When the eyes are actually crossed or not completely aligned with one another, it is called strabismus. Pseudostrabismus is more likely to be observed in East Asian or Native American infants, due to the presence of epicanthic folds obscuring the medial aspect of each eye. Pseudostrabismus generally occurs in infants and toddlers, whose facial features are not fully developed. The bridge of their nose is wide and flat, creating telecanthus (increased distance between medial canthus of both eyes). With age, the bridge will narrow, and the epicanthic folds in the corner of the eyes will go away. This will cause the eyes to appear wider and thus not have the appearance of strabismus. To detect the difference between strabismus and pseudostrabismus, clinicians use a flashlight to shine into the childs eyes. When the child is looking at the light, a reflection can be seen on the front surface of the pupil. If the eyes are aligned with one another, the reflection from the light will be in the same spot of each eye. If strabismus is present, the reflection from the light will not be in the same spot of each eye. Rakels Textbook of Family Medicine states, "A common misconception is that children with crossed eyes outgrow the condition, but this is generally not the case. This belief stems from the confusion between true strabismus and pseudostrabismus.