The anesthetist assumes responsibility for the patient when the preoperative medication is administered. An anesthetist or other responsible clinician should accompany an unstable patient during transport to the OR.

A. Preoperative evaluations may be performed minutes to weeks before the administration of the anesthetic and sometimes not by the anesthetist of record. A detailed history and physical exam should be performed, and preoperative optimization should be completed. The administering anesthetist performs an airway examination and checks for interim changes in the patient’s condition, medications, laboratory data, and consultant notes. Time of last oral intake is confirmed (see Table 15.1). Tube feeds in critically ill intubated patients may be continued before and during procedures outside the abdomen and thorax. Allergies and the anesthetic
plan are reviewed with the patient, and proper informed consent for the administration of anesthesia is obtained from either the patient or his or her legal proxy.

B. Intravascular Volume. Patients may arrive in the OR with intravascular or total body hypovolemia due to prolonged NPO status, severe inflammatory illness, hemorrhage, fever, vomiting, or diuretic use. Currently available isotonic bowel preparations may not directly induce water loss but can decrease absorption of fluids ingested before surgery. The patient’s volume status is evaluated either clinically or with appropriate monitors. If a fluid deficit is present, the patient should be adequately hydrated before the induction of anesthesia. The fluid deficit for fasting adults is estimated at 60 mL/h + 1 mL/kg/h for each kilogram greater than 20 kg (maintenance fluids). In general, at least half of this deficit is corrected before induction; the remainder may be corrected intraoperatively. The type and amount of fluids given may be modified in the presence of systemic diseases (see Chapters 2 to 6) or for specific types of surgery (Chapters 22 and 25).

C. IV Access. The size and number of IV catheters placed varies with the procedure, anticipated blood loss, and the need for continuous drug infusions. At least one large bore IV (>16-gauge) catheter should be placed when rapid fluid or blood infusion is anticipated. When continuous drug infusions are to be delivered concurrently with rapid fluid infusion, an additional IV catheter often is dedicated for this purpose. Some medications used for cardiovascular support (e.g., norepinephrine) are best delivered via a central venous catheter placed either before induction, if indicated, or after (see below under Monitoring).

1. Anxiety. The preoperative period is one of high anxiety, especially for patients who have not had a prior interview with an anesthetist. Anxiety may be managed effectively with calm reassurance and expression of interest in the patient’s well-being. When deemed appropriate, a benzodiazepine (e.g., diazepam and midazolam) with or without a small dose of an opioid (e.g., fentanyl and morphine) may be administered. Oral diazepam or lorazepam may be given with a small amount of water 30 to 60 minutes before the procedure. Patients complaining of pain on arrival in the OR may be given analgesics in incremental amounts to alleviate symptoms. Dosages are based on the patient’s age, medical condition, and anticipated time of discharge (see Chapters 1 and 12). Appropriate monitoring should be used and resuscitative equipment available.

2. Drugs to neutralize gastric acid (H₂-antagonists, PPIs, nonparticulate antacids) and decrease gastric volume (metoclopramide, H₂-antagonists, PPIs) should be used only when the patient is at increased risk of
aspiration of gastric contents (i.e., recent meal, trauma, bowel obstruction, pregnancy, history of gastric surgery, increased intra-abdominal pressure, difficult airway, or history of active reflux; see Chapter 1). When bowel obstruction is present, promotility drugs may increase retrograde peristalsis and are contraindicated.

E. Monitoring. Standard ASA monitoring (see Chapter 10) is established before the induction of anesthesia. Invasive hemodynamic monitors (e.g., arterial catheter, central venous line, and pulmonary artery catheter) should be placed before induction of anesthesia when indicated by the patient’s medical condition and potential anesthetic effects (e.g., an arterial line for a patient at risk for cerebral ischemia). Invasive monitors may be placed after induction of anesthesia when indicated primarily by the surgical procedure (e.g., a central line for a patient undergoing elective aortic surgery). Surgical-specific monitoring (e.g., evoked potentials) should be discussed with the surgical team to ensure compatibility with anesthetic plans.

Induction of anesthesia produces an unconscious patient with depressed reflexes who is dependent on the anesthetist for maintenance of homeostatic mechanisms and safety.

A. The environment in the OR should be warm and with minimal noise. All members of the OR team (scrub nurse, circulating nurse, and surgeon) should focus their attention on the patient and be ready to give immediate assistance to the anesthetist if needed.

B. The patient’s position for induction is usually supine, with extremities resting comfortably on padded surfaces. The head should rest on a raised firm padded support, and tilted back in a “sniff” position (see Chapter 14). Routine preinduction administration of oxygen (denitrogenation) minimizes the risk of hypoxia developing during induction of anesthesia. High flow (8 to 10 L/min) oxygen should be delivered via a face mask placed gently on the patient’s face. The patient can be instructed to take deep breaths and exhale fully to speed the exchange of oxygen. Angling upward the OR table back (semisitting position) or the entire table (reverse Trendelenburg position) can improve the ventilatory function and comfort of obese patients or those who experience orthopnea. These positions also reduce the risk of pulmonary aspiration of gastric contents.

C. Induction Techniques. The choice of induction technique is guided by the patient’s medical condition, anticipated airway management (i.e., risk of aspiration, difficult intubation, or compromised airway), and patient preference.

1. IV induction begins with administration of a potent short-acting hypnotic drug (specific agents and doses are given in Chapter 12). After loss of consciousness, inhalation or additional IV agents are administered to maintain anesthesia. Most of the IV induction agents are powerful respiratory depressants, so loss of consciousness is often accompanied by a short period of apnea requiring controlled ventilation. Depending upon the choice and dose of maintenance anesthetics, ventilation may be controlled, or the patient may breathe spontaneously or with assistance (see section III.C).

2. An induction using only inhalational anesthetics may be used to maintain spontaneous ventilation when there is a compromised airway or to defer the placement of an IV catheter (e.g., in pediatric patients). After preoxygenation, inhalational anesthetics are added at low concentration (0.5 times minimum alveolar concentration [MAC]) and
then increased every three to four breaths until the depth of anesthesia is adequate for IV placement or airway manipulation. Alternatively, a “single vital capacity breath” inhalation induction can be achieved using a high concentration of a less pungent agent like halothane or sevoflurane. Physiologic signs should be closely observed to assess anesthetic depth (Table 15.2).

3. Intramuscular injection of ketamine, rectal methohexital, oral transmucosal fentanyl, and oral midazolam are induction techniques more commonly used in uncooperative patients or young children (see Chapters 11 and 31).

D. Airway Management (see Chapter 14). The patency of the patient’s airway is critically important during induction of anesthesia. Patients with difficult or unstable airways may be intubated safely before the induction of anesthesia. The anesthetized patient’s airway may be managed using a face mask, oral or nasopharyngeal airway, cuffed oropharyngeal airway, laryngeal mask airway (LMA), or endotracheal tube (ETT). If tracheal intubation is planned, a muscle relaxant may be given to facilitate laryngoscopy and intubation. The ability to ventilate the patient via face mask should be demonstrated before muscle relaxant administration. An exception to this rule is the “rapid sequence induction” for patients at risk for pulmonary aspiration (see Chapter 14). Remifentanil at 4 µg/kg also has been shown effective in facilitating rapid intubation but frequently causes bradycardia and hypotension.