Barbituates

Chapter 10

Basic Pharmacology

1. During a modified rapid sequence induction using thiopental and pancuronium, you are dismayed to find the 22 gauge IV (which you placed on the 4th attempt) has abruptly stopped working. What happened?

2. A new induction agent is being touted by local drug reps. When you arrive at the in-service, you find the detail person has vanished leaving only a dozen pepperoni pizzas and a description of the chemical structure of the drug. It is a barbituric acid compound with a branched 3 carbon side chain at the 5 position, a sulfur substitution at position 2, and it is methylated in position 1. After your second pizza, you feel compelled to theorize about the potency, speed of onset and duration of action of this agent.

3. What is the currently accepted theory of barbiturates' mechanism of action?

4. Describe the classic pharmacokinetic model of thiopental disposition.

5. How is the hypnotic action of thiopental terminated? How about methohexital?

6. Given your answers to #5, how do you explain the shorter duration of action of methohexital?

7. Contrary to explicit instructions from the Committee On Waste, you drew up 16 syringes of pentothal this morning. The last 15 cases in your room are canceled. Rather than risk public ridicule in the department newsletter as a wastrel, you decide to use the remaining pentothal in multiple doses over the course of the gastric bypass added to your room. As preparation for your presentation at Complications Conference, describe the pharmacokinetics and clinical results of your decision.

Clinical Pharmacology

1. List the usual induction doses, time to maximum effect, and duration of action of thiopental for:

• Healthy adults
• Healthy children
• Healthy infants

2. Should older patients receive a smaller dose of thiopental? Why/why not?

3. Using thiopental, you induce a patient who takes phenobarbital for seizures. The patient is otherwise healthy and has no known allergies. Immediately after injection of the pentothal, the patient becomes hard to ventilate and appears to be suffering from bronchospasm. Could pentothal be the cause? What should you do next? (no credit for "Call staff")

4. During induction for ECT, you notice that the IV has infiltrated just after injection of methohexital. What are the potential consequences? What treatment is indicated? What would be the likely consequences if the agent were thiopental?

5. At 04:00 on your first call night, a horrible auto accident occurs in front of UMHC. Several patients are severely injured, are aggressively resuscitated in the ER, and moved quickly to the OR. Your patient arrives in OR 10 accompanied by the CA-2, who has assisted in the ER by placing an A-line and a large bore central venous line. The transducer ports on these lines are carefully labeled. The patient arrives somewhat obtunded and thrashing. Your surgical colleagues are calmly, but insistently, urging you to "put the patient to sleep". Feeling a bit rushed, you begin your rapid sequence induction by giving pentothal via the transducer port labeled "CVP". At the moment of injection, the patient moans in pain and the arterial tracing goes flat. What happened? What are the potential sequelae? What, if any, further treatment should be given?

Systemic Effects

1. Would a barbiturate induction agent be a good choice for induction of the hypovolemic accident victim described above. What CV effects would influence your answer? If the only agent available was pentothal, what precautions would you take to optimize the patient's induction?

2. Describe the respiratory effects of barbiturate induction agents.

3. True or False: Barbiturate induction agents blunt laryngeal and tracheal reflexes.

4. True or False: Barbiturate induction agents can cause bronchospasm or laryngospasm.

5. Would a barbiturate induction agent be a good choice for induction of the accident victim with closed-head trauma? What CNS effects would influence your answer? If the only agent available was pentothal, what precautions would you take to optimize the patient's induction?

6. Patients with renal and/or hepatic disease often have hypoproteinemia. Can thiopental be used safely as an induction agent in patients with such problems? What adjustments (if any) in dosing are indicated?

7. What hematologic disorder is a contraindication to induction with barbiturates?