Anesthesia Pharmacology: Anxiolytics and Sedative-Hypnotics
Except in overdosage, cardiovascular effects of benzodiazepines in normal subjects are minor.
If used as preanesthetic medication, benzodiazepines decrease blood pressure and increase heart rate.
At pharmacological hypnotic doses, benzodiazepines do not affect respiration in normal subjects.
Severely benzodiazepine-intoxicated patients may require assistance in breathing if other CNS depressant drugs have been taken
If a patient, however, has a sleep-related breathing syndrome such as obstructive sleep apnea (OSA), benzodiazepines may be contraindicated.
In patients with obstructive sleep apnea, hypnotic doses of benzodiazepines may decrease muscle tone in the upper airway and accentuate or worsen the impact of apneic episodes on alveolar hypoxia, pulmonary hypertension and cardiac demand.
At higher doses, such as those used for endoscopy or when given as preanesthetic medication, benzodiazepines somewhat depress alveolar ventilation causing a respiratory acidosis secondary to a decrease in hypoxic drive (rather than hypercapnic drive).
These effects are more severe in patients with COPD (chronic obstructive pulmonary disease) and maybe sufficiently detrimental to induce alveolar hypoxia and/or CO2 narcosis.
Central Nervous System
With increasing doses, benzodiazpines can progressive cause sedation, then hypnosis and then stupor.
Benzodiazepines do not cause general anesthesia since awareness persists.
These agents have anti-anxiety / sedative-hypnotic properties.
Some benzodiazepines (clonazepam (Klonopin)) are effective muscle relaxants, whereas most others are not.
Hibbs, W.R, Rall, T.W., and Verdoorn, T.A., Hypnotics and Sedatives: Ethanol In, Goodman and Gillman's The Pharmacologial Basis of Therapeutics,(Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) TheMcGraw-Hill Companies, Inc.,1996, pp. 364-367.
Barbiturates: Effects on the cardiovascular and central nervous system
In sedative or doses for pharmacological hypnosis, barbiturates have minimal cardiovascular effects.
When thiopental is used in general anesthesia, following pre-anesthetic medication:
Plasma renal flow decreases
Cerebral blood flow decreases
CSF pressure decreases
Significant depression of myocardial contractility occurs in barbiturate poisoning.
Central Nervous System
Barbiturates depress respiratory drive
At doses somewhat (three times) higher than required for pharmacological hypnosis, neurogenic is abolished and the hypoxic respiratory drive is reduced and the chemoreceptor drive is attenuated.
At still higher doses, the hypoxic drive is abolished.
Hibbs, W.R, Rall, T.W., and Verdoorn, T.A., Hypnotics and Sedatives: Ethanol In, Goodman and Gillman's The Pharmacologial Basis of Therapeutics,(Hardman, J.G, Limbird, L.E, Molinoff, P.B., Ruddon, R.W, and Gilman, A.G.,eds) TheMcGraw-Hill Companies, Inc.,1996, pp. 377.