The bulbocavernosus reflex indicates the absence or presence
of spinal shock. Spinal shock usually occurs between 24-72 hours after a spinal
injury. Spinal shock is manifested by the absence of the bulbocavernosus
reflex, hypotension, bradycardia, and complete loss of motor sensation and
reflexes. When the reflex is absent, this means that the patient is in spinal
shock because the anal sphincter will not contract when the reflex is absent.
When the reflex is present, this signals the end of spinal
shock; the anal sphincter will contract when the reflex is present. The reflex
is check by monitoring anal sphincter contraction in response to squeezing of
the penis of clitoris, or by pulling on an indwelling Foley catheter. It is a
polysynaptic response mediated by S2-S4.
What is Spinal Shock?
Spinal shock is the loss of sensation and motor power
following a spinal cord injury. Spinal shock is the loss of sensation and motor
power following a spinal cord injury. After an injury to the spine, if the
patient has no motor or sensory below the level of the lesion, the physician
must determine if the patient is in spinal shock by checking the
bulbocavernosus reflex.
If there is no anal contraction (absent bulbocavernosus
reflex), this indicates that the patient is still in shock and the prognosis
cannot be determined. If anal contraction is present (positive bulbocavernosis
reflex), this indicates the end of spinal shock. The patient’s condition and
prognosis at this point can be determined by examining sacral sparing (positive
sacral sparing indicates an incomplete lesion).
Loss of sensation and motor power below the level of injury
indicates complete spinal cord injury. Once the diagnosis of neurogenic shock
is established, the blood pressure should be managed with vasopressors to prevent
fluid overload. With the end of spinal shock, the prognosis can be determined. Examine
the patient thoroughly, including sacral sparing. The patient may have normal,
partial, or complete indications.
