16: Preoperative Medication

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CHAPTER 16 Preoperative Medication

Sunil Kumar, MD, FFARCS

1 List the major goals of premedication

Premedication needs to be tailored to the needs of individual patient. Important goals include:

image Sedation and anxiolysis
image Analgesia and amnesia
image Antisialagogue effect
image To maintain hemodynamic stability, including decrease in autonomic response
image To prevent and/or minimize the impact of aspiration
image To decrease postoperative nausea and vomiting
image Prophylaxis against allergic reaction

2 List the most commonly used preoperative medications with the appropriate dose

See Table 16-1.

TABLE 16-1 Common Preoperative Medications, Dosage, and Route*

image

3 What factors should be considered in selecting premedication for a patient?

image Patient age and weight
image Physical status
image Levels of anxiety and pain
image Previous history of drug use or abuse
image History of postoperative nausea, vomiting or motion sickness
image Drug allergies
image Elective or emergency surgery
image Inpatient or outpatient status

4 What factors limit the ability to give depressant medications preoperatively?

image Extremes of age
image Head injuries or altered mental status
image Limited cardiac or pulmonary reserve
image Hypovolemia
image Full stomach

5 What is meant by psychologic premedication?

Most patients are very anxious before surgery. An informative and comforting visit by an anesthesiologist may replace many milligrams of depressant medication and acts as psychologic premedication. During this visit a full description of the planned anesthetic events to anticipate in the perioperative period should be provided to the patient and family members, and all questions the patient or family may have should be answered. However, psychologic preparation cannot accomplish everything and will not relieve all anxiety.

6 Discuss the role of benzodiazepines in premedication

Benzodiazepines are the most popular drugs used for premedication. They act on receptors for the inhibitory neurotransmitter, γ-aminobutyric acid, producing anxiolysis, amnesia, and sedation at doses that do not produce significant cardiovascular or ventilatory depression. These drugs are not analgesic and are not associated with nausea and vomiting. Side effects of benzodiazepines include excessive and prolonged sedation in occasional patients, especially with lorazepam. Sometimes paradoxic agitation rather than anxiolysis may follow these drugs. The most commonly used benzodiazepine in current practice is midazolam, administered intravenously in small incremental doses in the immediate preoperative period. Diazepam is associated with pain on intramuscular or intravenous injection and increased risk of phlebitis.

7 List the most common side effects when opioids are used as a premedication

Pruritus Histamine release
Nausea and vomiting Delayed gastric emptying
Respiratory depression Stiff chest syndrome
Orthostatic hypotension Sphincter of Oddi spasm

8 Describe the reasons to include an anticholinergic agent in premedication

The main indications for these drugs include the following:

image Drying of airway secretions. They are particularly useful for intraoral or airway surgery, before applying topical anesthesia to the airway, and general anesthesia with endotracheal intubation.
image Prevention of reflex bradycardia when vagal overactivity is anticipated, particularly during pediatric anesthetic induction and airway manipulation. Atropine or glycopyrrolate can best be given intravenously just before anticipated vagal stimulation.
image Sedative and amnestic effect: Being tertiary amines, scopolamine and atropine can cross the blood-brain barrier and produce sedation and amnesia. In this regard scopolamine is about 8 to 10 times as potent as atropine. Glycopyrrolate is a quaternary amine, does not cross the blood-brain barrier, and therefore is devoid of appreciable sedative effect.

9 Summarize the effects of commonly used anticholinergic agents

See Table 16-2.

TABLE 16-2 Effects of Commonly used Anticholinergic Agents

image

10 List the common side effects of anticholinergic medications

image Drying and thickening of airway secretions
image Decrease in lower esophageal sphincter tone
image Mydriasis and cycloplegia
image Central nervous system toxicity
image Prevention of sweating
image Hyperthermia

11 A patient in the preoperative holding area is delirious after receiving only 0.4 mg of scopolamine as a premedication. What is the cause of the delirium? How is it managed?

The most likely cause of the delirium is central anticholinergic syndrome produced by scopolamine. Central toxicity can follow the administration of tertiary amine scopolamine (and less frequently following atropine), which crosses the blood-brain barrier. The toxic symptoms are infrequent following the usual premedication dose. However, elderly patients are more prone to this side effect. Physostigmine is the only acetylcholinesterase inhibitor that crosses the blood-brain barrier and can be used to treat the central anticholinergic syndrome in a dose of 15 to 60 mcg/kg intravenously, administered slowly to prevent seizures.

12 How does the concern for aspiration pneumonitis influence the choice of premedication?

Aspiration is discussed more fully in Chapter 39. The actual incidence of clinically significant aspiration pneumonitis is extremely rare in healthy patients having elective surgery. In the past many anesthesiologists routinely administered pharmacologic agents such as H2 antagonists, antacids, and gastrokinetics in an attempt to reduce the volume and increase the pH of the gastric contents of their patients in the preoperative period. In view of the extremely low incidence of clinically significant aspiration pneumonitis in healthy patients having elective surgery, routine and indiscriminate use of antacids, gastric acid secretion blockers, antiemetics, anticholinergics, and gastrokinetic medications is not warranted.

KEY POINTS: Preoperative Medication image

1. A preoperative visit by an informative and reassuring anesthesiologist provides useful psychologic preparation and calms the patient’s fears and anxiety before anesthesia.
2. The choice of premedication depends on the physical and mental status of the patient, whether the patient is an inpatient or outpatient, whether the surgery is elective or emergent, and whether the patient has a history of postoperative nausea and vomiting.
3. The risk of clinically significant aspiration pneumonitis in healthy patients having elective surgery is very low. Routine use of pharmacologic agents to alter the volume or pH of gastric contents is unnecessary.
4. In the patients considered to be at increased risk of pulmonary aspiration, a 15- to 30-ml oral dose of nonparticulate acid given 15 to 30 minutes before induction of anesthesia is the most effective way to raise gastric pH above 2.5.
5. Many patients require little or no premedication.
6. Pediatric patients are especially prone to bradycardia during anesthesia and benefit from anticholinergic premedication.

13 Is it safe to allow patients to drink some water to swallow preoperative medications?

Yes, it is acceptable to allow patients to take preoperative medications, including the patient’s usual medications, with up to 150 ml of water in the hour preceding induction of anesthesia.

14 What are the differences between premedication of pediatric vs. adult patients?

Pediatric patients have the following special needs:

image They are more difficult to prepare psychologically for surgery and anesthesia.
image There is greater emphasis on the oral route of administration because most children fear needles.
image Vagolytics are used more frequently because of a greater incidence of bradycardia on induction.

15 How does the age of pediatric patients influence premedication?

Children up to 6 months of age do not appear to suffer anxiety when separated from parents. However, preschool children older than 6 months are at greatest risk of separation anxiety and may suffer long-term psychologic trauma from a negative hospital experience. It is difficult to reassure and explain the expected events to this group. It is easier to communicate with patients older than 5 years, who can be reassured. Parental behavior is also important in the psychologic preparation of pediatric patients. The needs of each patient must be assessed individually. Most children older than 1 year benefit from some sedative premedication. Oral midazolam (0.5 mg/kg dissolved in flavored syrup, to a maximum dosage of 20 mg) is commonly used. Atropine may be given intravenously once venous access has been obtained, just before airway manipulation, which can provoke vagal reflexes.

16 Describe the preoperative management of a morbidly obese patient with a difficult airway. Assume that the patient is otherwise healthy

A morbidly obese patient is considered at increased risk of pulmonary aspiration during induction of anesthesia because of delayed gastric emptying and the possibility of difficult airway management. Therefore H2 blockers given the evening before (if possible) and the morning of surgery, preoperative metoclopramide, and oral nonparticulate antacids are in order. Glycopyrrolate is useful for planned fiberoptic intubation. It improves visualization by drying secretions, increases the effectiveness of the topical anesthesia, and decreases airway responsiveness. Opioids and benzodiazepines should be judiciously titrated, using supplemental oxygen and close observation to ensure an awake, appropriately responding patient who can protect his or her own airway.

SUGGESTED READINGS

1. Dotson R., Wiener-Kronish J.P., Ajayi T. Preoperative evaluation and medication. In: Stoelting R.K., Miller R.D., editors. Basics of anesthesia. ed 5. New York: Churchill Livingstone; 2007:157-177.

2. Kararmaz A., Kaya S., Turhanoglu S., et al. Oral ketamine premedication can prevent emergence agitation in children after desflurane anaesthesia. Paediatr Anaesth. 2004;14:477-482.

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