Diazepam effects produce minimal depressant effects on ventilation with 0.2 mg/kg IV dose in Respiration system. The slight increase in PaCO2 is due primarily to a decrease in tidal volume. Nevertheless, nearly, small doses of diazepam (<10 mg IV) have produced apnoea.
Combination of diazepam with other CNS depressants (opioids, alcohol) or administration of this drug to patients with chronic obstructive airway disease may result in exaggerated or prolonged depression of ventilation.
Diazepam administered in doses of 0.5 to 1 mg/kg IV for induction of anesthesia typically produces minimal decreases in systemic blood pressure, cardiac output, and systemic vascular resistance.
There is a transient depression of baroreceptor-mediated heart rate responses. Diazepam effects appear to have no direct action on the sympathetic nervous system, and it does not cause orthostatic hypotension.
The incidence and magnitude of systemic blood pressure decreases produced by diazepam seem to be less than those associated with barbiturates administered IV for the induction of anesthesia.
Skeletal Muscle Relaxation:
Skeletal muscle relaxation property of diazepam is due to effect on spinal internuncial neurons and not at the neuromuscular junction.
Presumably, diazepam effects diminishes the tonic facilitator influence on spinal gamma neurons and thus skeletal muscle tone is increased. Tolerance occurs to the skeletal muscle relaxant effects of benzodiazepines.