Preoperative Medications
Administration of preoperative medications (premedicants) to patients can be thought of as the start of their operative course. Many different medications are used preoperatively and can be grouped into the following classes: benzodiazepines, opioids, anticholinergics, dissociative anesthetics, gastric motility stimulants, H2-receptor antagonists, antacids, and α-2 agonists.
A key point concerning preoperative medication is that not all patients will require premedicants. A preoperative evaluation by the anesthesia provider ensures that the patient is medically prepared for surgery (e.g., pre-existing medical conditions such as diabetes, hypertension, or asthma are controlled or stabilized), allows the provider to discuss the most appropriate anesthetic and postoperative pain management options with the patient, and helps reassure and educate the patient. Preoperative assessment by an anesthesia provider is an important component of the patient's preparation for surgery. Patients should be assessed individually regarding their need for pharmacologic premedication. If required, premedicants should be selected based on patient-specific needs. Administration of a standard preoperative regimen to all patients should be avoided. Furthermore, the anesthesia provider and the surgeon must determine whether the patient should take his or her regularly scheduled medications the morning of surgery. These medications are often necessary to maintain the patient's physiological condition. The decision to continue or withhold chronic medications before surgery depends on the surgical procedure (e.g., major vs. minor), the patient's current medical condition, the pharmacological effect of the medication, and the potential for drug interactions with anesthetics. Medications that cause bleeding, excessive hemodynamic effects, or withdrawal symptoms are the most problematic. Antihypertensives, bronchodilators, tricyclic antidepressants, selective serotonin reuptake inhibitors, corticosteroids, thyroid preparations, anxiolytics, and anticonvulsants are generally continued up to, and including, the morning of surgery. Alternatively, medications that increase the risk for bleeding (e.g., aspirin, nonsteroidal anti-inflammatory drugs [NSAIDs], warfarin, clopidogrel) may need to be discontinued up to 7 days or more before surgery. Finally, patients with suppression of the pituitary-adrenal axis (e.g., patients currently or recently taking corticosteroids) may not be able to respond to surgical stress. Hydrocortisone can be administered intravenously before surgery, with subsequent doses dependent on the estimated amount of surgical stress and the need for supraphysiological steroid replacement in the postoperative period.
Goals of Premedication
A major goal of premedication is to decrease the patient's fear and anxiety about his or her upcoming surgery. In addition to reducing anxiety, premedication is used for a variety of other reasons. Medications can be used before surgery to produce sedation, provide analgesia, produce amnesia, facilitate a smooth anesthetic induction, reduce anesthetic requirements, prevent autonomic responses resulting in intraoperative hemodynamic stability, decrease salivation and secretions, reduce gastric fluid volume, and/or increase gastric pH. Table 9-1 lists medications commonly used preoperatively and their major indications, routes of administration, and dosages.1,2,3,4,5 Midazolam is by far the most commonly used premedicant.
Selection Criteria
Factors to consider when selecting a preoperative drug for a patient include his or her American Society of Anesthesiologists (ASA) physical status class, medical conditions, degree of anxiety, age, surgical procedure to be performed, length of procedure, postoperative admission status (e.g., inpatient vs. outpatient), drug allergies, previous experience with medications, and concurrent drug therapy. The ASA physical status classification system classifies patients as I through V. ASA-I patients are healthy with little medical risk, whereas ASA-V patients have little chance of survival. Severe systemic disorders (e.g., uncontrolled diabetes mellitus, coronary artery disease) are present in ASA-III through ASA-V patients. Selection of preoperative medications in this group of patients will be more difficult. These patients generally have limited physiological reserve; thus, administration of a cardiovascular depressant agent, for example, can be harmful. Furthermore, these patients will be taking a significant number of medications; hence, chances for drug interactions are increased. The patient's other medical conditions are important to consider to prevent the administration of contraindicated medications. For example, the benzodiazepines are contraindicated in pregnancy.3 A patient's age will play a role in the response seen with premedicant administration. The elderly are often more sensitive to preoperative opioids and benzodiazepines, as well as to the central nervous system (CNS) effects of anticholinergic agents.6
Familiarity with the surgery to be performed will aid in selecting appropriate premedicants. In surgical cases in which painful procedures (e.g., vascular cannulation, peripheral nerve block) will be performed on the patient, an analgesic premedicant may be warranted. The length and type of the procedure is important to consider when selecting premedicants. For example, a patient undergoing emergency surgery who has not fasted is often administered a nonparticulate antacid because he or she is at risk for aspiration of gastric contents.1 Likewise, in short duration, outpatient surgery, agents with a long duration of action should be avoided because residual effects can prolong discharge time. Some drugs should not be administered to patients because of drug allergies; however, genuine allergies must be differentiated from adverse effects. For example, patients often state allergies to opioids after having experienced nausea and vomiting, which are common adverse effects of these drugs. A patient's previous experience with premedicants can assist in agent selection. If a medication has caused trouble in the past, it should be avoided. Finally, it is important to review the patient's current drug therapy before selecting an agent to prevent potentially harmful drug interactions.
Timing and Routes of Administration
The timing and route of administration is almost as important as the choice of the agent. For optimal results, the agent's peak effects should occur before the patient arrives in the OR suite. This will require the agent to be administered at varying times before surgery, depending on the route of administration. Preoperative agents are administered by several routes: IV, intramuscular (IM), oral (PO), and intranasal (IN). As a general rule, agents administered by the IV route produce the fastest onset of action and are often given after the patient arrives in the OR, whereas medications administered via the IM route are usually administered 30 to 60 minutes before the patient arrives in the OR. If possible, the IM route should be avoided because it is painful and undesirable for the patient. Onset of peak effect is the slowest with PO administration of agents, which should be administered 60 to 90 minutes before the patient's scheduled arrival in the OR.1
Drug Interactions
Preoperative medications can interact with one another, as well as with drugs the patient is receiving currently or will receive in the OR. These drug interactions can be advantageous and intentionally produced, or they can be problematic. For example, patients must be closely monitored when they concurrently receive a benzodiazepine and an opioid for premedication due to synergistic respiratory and cardiovascular adverse effects.1 The α-2 agonists, however, can reduce the requirements for inhalational anesthetics and opioids.4
Administration of a Premedicant
1. K.J., a 21-year-old man, is scheduled to undergo a laparoscopic hernia repair on an outpatient basis under general anesthesia. This is the first time K.J. has undergone surgery, and he is highly anxious in the preoperative area. Should K.J. receive premedication, and, if so, what medication(s) should be administered?
The administration of a preoperative sedative to a patient undergoing outpatient surgery was formerly controversial; however, with midazolam, the delayed recovery and discharge that had been associated with agents used in the past (e.g., lorazepam, triazolam, temazepam) is less of a concern. Midazolam should be titrated to the desired effect (in increments of 0.5-1 mg IV), with the average adult generally requiring 2 mg IV. Elderly patients who receive as little as 0.5 mg midazolam intravenously can experience decreased oxygen saturation in the preoperative period and longer recovery time in the postanesthesia care unit (PACU) following short duration surgery.7 Midazolam premedication produces sedation and provides anterograde amnesia and anxiolysis,7,8 which can be problematic if these effects continue into the postoperative period when outpatients are provided with discharge instructions. In children, premedication with oral midazolam can reduce both the child's and the parents' anxiety during the preoperative period,8 the likelihood of a child's distress at induction of anesthesia,9 and the manifestation of negative behavioral changes in the child during the first 7 postoperative days.10 The use of oral midazolam premedication in children who are undergoing outpatient surgery, however, can delay discharge.9 Therefore, nonpharmacologic approaches to reduce anxiety must be optimized. If explanation of upcoming events and reassurance by the anesthesia provider has not sufficiently allayed K.J.'s anxiety, small titrated doses of IV midazolam can be administered.
0 comments:
Post a Comment