Handbook of Clinical Anesthesia

Chapter 23

Preoperative Patient Assessment and Management

The goals of preoperative evaluation are to reduce patient risk and the morbidity of surgery, as well as to promote efficiency and reduce costs (Hata TM, Moyers JR: Preoperative patient assessment and management. In Clinical Anesthesia. Edited by Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC. Philadelphia: Lippincott Williams & Wilkins, 2009, pp 567–597).

  1. Introduction
  2. The Joint Commission requires that all patients receive a preoperative anesthetic evaluation.
  3. The American Society of Anesthesiologists (ASA) approved its Basic Standards for Preanesthetic Care, which outlines the minimum requirements for a preoperative evaluation.
  4. Conducting a preoperative evaluation is based on the premise that it will modify patient care and improve outcome.
  5. Based on the history and physical examination, the appropriate laboratory tests and preoperative consultations should be obtained.
  6. Guided by the history and physical examination, the anesthesiologist should choose the appropriate anesthetic and care plan.
  7. Changing Concepts in Preoperative Evaluation
  8. The first time the anesthesiologist performing the anesthetic sees the patient may be just before anesthesia and surgery. (The patient has been seen previously by others in a preoperative evaluation clinic.)

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  1. Information technology using preoperative questionnaires and computer-driven programs has helped anesthesiologists preview upcoming patients that will be anesthetized.

III. Approach to the Healthy Patient

  1. The preoperative evaluation form is the basis for formulating the best anesthetic plan tailored to the patient. It should aid the anesthesiologist in identifying potential complications, as well as serve as a medico-legal document. The information obtained must be complete, concise, and legible.
  2. The approach to the patient should always begin with a thorough history and physical examination (may be sufficient without additional routine laboratory tests).
  3. The indication for the surgical procedure may also have implications on other aspects of perioperative management.
  4. Small bowel obstruction has implications regarding the risk of aspiration and the need for a rapid sequence induction.
  5. The extent of a lung resection dictates the need for further pulmonary testing and perioperative monitoring.
  6. Patients undergoing carotid endarterectomy may require a more extensive neurologic examination as well as testing to rule out coronary artery disease (CAD).
  7. The ability to review previous anesthetic records is helpful in detecting the presence of a difficult airway, a history of malignant hyperthermia, and the individual's response to surgical stress and specific anesthetics.
  8. The patient should be questioned regarding any previous difficulty with anesthesia and other family members having difficulty with anesthesia. (History relating an “allergy” to anesthesia should make one suspicious of malignant hyperthermia.)
  9. The history should include a complete list of medications, including over-the-counter and herbal products, to define a preoperative medication regimen, anticipate potential drug interactions, and provide clues to underlying disease.

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Table 23-1 Components of the Airway Physical Examination

Airway Examination Component

Findings Suggestive of Difficult Intubation

Length of upper incisors

Long compared with rest of dentition

Relation of maxillary and mandibular incisors during normal jaw closure

Prominent overbite

Relation of maxillary and mandibular incisors during voluntary protrusion of mandible

Patient cannot bring mandibular incisors anterior to maxillary incisors

Interincisor distance

<3 cm

Visibility of uvula

Not visible when the tongue is protruded with the patient in the sitting position

Shape of palate

Highly arched or very narrow

Compliance of mandibular space

Stiff, indurated, occupied by a mass, or nonresilient

Thyromental distance

<3 finger breadths

Length of neck

Short neck

Thickness of neck

Thick neck

Range of motion of head and neck

Patient cannot touch the tip of the chin to the chest or is unable to extend the neck

  1. Systems Approach
  2. Airway
  3. Evaluation of the airway involves determination of the thyromental distance; the ability to flex the base of the neck and extend the head; and examination of the oral cavity, including dentition (Table 23-1).
  4. The Mallampati classification has become the standard for assessing the relationship of the tongue size relative to the oral cavity, although by itself the Mallampati classification has a low positive predictive value in identifying patients who are difficult to intubate (Table 23-2).
  5. In appropriate patients, the presence of pain or symptoms of cervical cord compression on movement should be assessed. In other instances, radiographic examination may be required.

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Table 23-2 Airway Classification System

Class

Direct Visualization (Patient Seated)

Laryngoscopic View

I

Soft palate, fauces, uvula, pillars

Entire glottic opening

II

Soft palate, fauces, uvula

Posterior commissure

III

Soft palate, uvular base

Tip of epiglottis

IV

Hard palate only

No glottal structures

  1. Pulmonary(Table 23-3)
  2. Cardiovascular System(Table 23-4)
  3. Neurologic System.The patient's ability to answer health history questions practically ensures a normal mental status (exclude the presence of increased intracranial pressure, cerebrovascular disease, seizure history, pre-existing neuromuscular disease, or nerve injuries).
  4. Endocrine System.The patient should be screened for endocrine diseases (diabetes mellitus, adrenal cortical suppression) that may affect the perioperative course.

Table 23-3 Screening Evaluation for the Pulmonary System

History Tobacco use
Shortness of breath
Cough
Wheezing
Stridor
Snoring or sleep apnea
Recent history of an upper respiratory tract infection
Physical Examination
Respiratory rate
Chest excursion
Use of accessory muscles
Nail color
Ability to walk and carry on a conversation without dyspnea
Auscultation to detect decreased breath sounds, wheezing, stridor, and rales

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Table 23-4 Screening Evaluation for the Cardiovascular System

Uncontrolled hypertension
Unstable cardiac disease
Myocardial ischemia (unstable angina)
Congestive heart failure
Valvular heart disease (aortic stenosis, mitral valve prolapse)
Cardiac dysrhythmias
Auscultation of the heart (murmur radiating to the carotid arteries)
Bruits over the carotid arteries
Peripheral pulses

  1. Evaluation of the Patient With Known Systemic Disease
  2. Cardiovascular Disease
  3. The goals are to define risk; determine which patients will benefit from further testing; devise an appropriate anesthetic plan; and identify patients who will benefit from perioperative beta-blockade, intervention therapy, or even surgery (Table 23-5).

Table 23-5 American Society of Anesthesiologists PhysicalStatus Classification

ASA Class

Disease State

1

No organic, physiologic, biochemical, or psychiatric disturbance

2

Mild to moderate systemic disturbance that may not be related to the reason for surgery

3

Severe systemic disturbance that may or may not be related to the reason for surgery

4

Severe systemic disturbance that is life threatening with or without surgery

5

Moribund patient who has little chance of survival but is submitted to surgery as a last resort (resuscitative effort)

ASA = American Society of Anesthesiologists.
E = emergency operation.

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  2. Independent predictors of complications in the Goldman risk index include high-risk type of surgery, history of ischemic heart disease, history of congestive heart failure, history of cerebrovascular disease, preoperative treatment with insulin, and preoperative serum creatinine above 2.0 mg/dL.
  3. The presence of unstable angina has been associated with a high perioperative risk of myocardial infarction (MI).
  4. The presence of active congestive heart failure before surgery is associated with an increased incidence of perioperative cardiac morbidity.
  5. The importance of the intervening time interval between an acute MI and elective surgery (traditionally 6 months or longer) may no longer be valid in the current era of interventional therapy (Table 23-6).

Table 23-6 Clinical Predictors of Increased Perioperative Cardiovascular Risk (Myocardial Infarction, Congestive Heart Failure)

Major
Unstable coronary syndromes
Recent myocardial infarction
Unstable or severe angina
Decompensated congestive heart failure
Significant arrhythmias
High-grade atrioventricular block
Symptomatic ventricular arrhythmias
Supraventricular arrhythmias with uncontrolled ventricular rate
Severe valvular disease
Intermediate
Mild angina pectoris
Prior myocardial infarction by history or pathologic Q waves
Compensated or prior congestive heart failure
Diabetes mellitus
Minor
Advanced age
Abnormal electrocardiogram (left ventricular hypertrophy, leftbundle branch block, ST-T abnormalities)
Rhythm other than sinus (atrial fibrillation)
Low functional capacity (inability to climb one flight of stairswith a bag of groceries)
History of stroke
Uncontrolled systemic hypertension

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  1. Patients with Coronary Artery Disease
  2. For patients without overt symptoms or history, the probability of CAD varies with the type and number of atherosclerotic risk factors present (peripheral arterial disease, diabetes mellitus [autonomic neuropathy the best predictor of silent CAD], hypertension [left ventricular hypertrophy], atherosclerosis associated with tobacco use, hypercholesterolemia).
  3. Although there has been a suggestion in the literature that surgery should be delayed if the diastolic pressure is 110 mm Hg or above, the study often quoted as the basis for this determination demonstrated no major morbidity in that small group of patients.
  4. Other authors state that there is little association between blood pressures of less than 180 mm Hg systolic or 110 mm Hg diastolic and postoperative outcomes (such patients are prone to perioperative myocardial ischemia, ventricular dysrhythmias, and lability in blood pressure).
  5. Importance of Surgical Procedure(Table 23-7)

Table 23-7 Cardiac Risk Stratification for Noncardiac Surgical Procedures

High (reported cardiac risk often >5%)
Emergent major operations, particularly in elderly patients
Aortic and other major vascular
Peripheral vascular
Anticipated prolonged surgical procedures associated with largefluid shifts or blood loss
Intermediate (reported cardiac risk generally <5%)
Carotid endarterectomy
Head and neck
Intraperitoneal and intrathoracic
Orthopedic
Prostate
Low (reported cardiac risk generally <1%)
Endoscopic procedures
Superficial procedure
Cataract
Breast

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  2. The surgical procedure influences the scope of preoperative evaluation required by determining the potential range of physiologic flux during the perioperative period.
  3. Peripheral procedures performed as ambulatory surgery are associated with an extremely low incidence of morbidity and mortality.
  4. High-risk procedures include major vascular, abdominal, thoracic, and orthopedic surgery.
  5. Importance of Exercise Tolerance
  6. Exercise tolerance is one of the most important determinants of perioperative risk and the need for further testing and invasive monitoring.
  7. An excellent exercise tolerance, even in patients with stable angina, suggests that the myocardium can be stressed without failing.
  8. If a patient can walk a mile without becoming short of breath, the probability of extensive CAD is small.
  9. If patients experience dyspnea associated with chest pain during minimal exertion, the probabil-ity of extensive CAD is high, which has been associated with greater perioperative risk.
  10. There is good evidence to suggest that minimal additional testing is necessary if the patient has good exercise tolerance.
  11. Indications For Further Cardiac Testing (Fig. 23-1)

No preoperative cardiovascular testing should be performed if the results will not change the perioperative management.

  1. Cardiovascular Tests
  2. Electrocardiography
  3. Abnormal Q waves in high-risk patients are highly suggestive of a past MI. (It is estimated that approximately 30% of MIs occur without symptoms and can only be detected on routine electrocardiograms [ECGs].)
  4. The presence of Q waves on a preoperative ECG in a high-risk patient, regardless of symptoms, should alert the anesthesiologist to an increased perioperative risk and the possibility of active ischemia.

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Figure 23-1. Algorithm proposed by the American Heart Association/American College of Cardiology Task Force on Perioperative Evaluation of Cardiac Patients Undergoing Noncardiac Surgery for decisions regarding the need for further evaluation. CHF = congestive heart failure; ECG = electrocardiography; MET = metabolic equivalent. (Adapted with permission from Eagle K, Brundage B, Chaitman B, et al: Guidelines for perioperative cardiovascular evaluation of noncardiac surgery. A report of the American Heart Association/American College of Cardiology Task Force on Assessment of Diagnostic and Therapeutic Cardiovascular Procedures.Circulation 93:1278, 1996.)

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  2. It has not been established that information obtained from the preoperative ECG affects clinical care.
  3. Although controversy exists, current recommendations for a resting 12-lead preoperative ECG include patients with at least one clinical risk factor who are undergoing a vascular surgical procedure and for patients with known CAD, peripheral vascular disease, or cerebrovascular disease who are undergoing intermediate-risk surgical procedures.
  4. Noninvasive Cardiovascular Testing
  5. The exercise ECG represents the most cost effective and least invasive method of detecting ischemia.
  6. Pharmacologic stress thallium imaging is useful in patients who are unable to exercise.
  7. In patients who cannot exercise, dopamine can be used to increase myocardial oxygen demand by increasing heart rate and blood pressure.
  8. The ambulatory ECG (Holter monitoring) provides a means of continuously monitoring the ECG for significant ST-segment changes before surgery.
  9. Stress echocardiography may be of value in evaluating patients with suspected CAD.
  10. Dobutamine echocardiography has been found to have among the best predictive values.
  11. Current recommendations are that patients with active cardiac conditions (unstable angina, congestive heart failure, arrhythmias, valve disease) should undergo noninvasive testing before noncardiac surgery.
  12. Assessment of Ventricular and Valvular Function
  13. Both echocardiography and radionuclide angiography may assess cardiac ejection fraction at rest and under stress, but echocardiography is less invasive and is also able to assess regional wall motion abnormalities, wall thickness, valvular function, and valve area.
  14. Conflicting results exist regarding the predictive value of ejection fraction determinations.
  15. It is reasonable for those with dyspnea of unknown origin and for those with current or prior heart failure with worsening dyspnea to

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have preoperative evaluation of left ventricular function.

  1. Aortic stenosis has been associated with a poor prognosis in noncardiac surgical patients, and knowledge of valvular lesions may modify perioperative hemodynamic therapy.
  2. Coronary angiographyis the best method of defining coronary artery anatomy. (Narrowing of the left main coronary artery may be associated with a greater perioperative risk.)
  3. Perioperative Coronary Interventions
  4. The long-term survival of some patients scheduled for high-risk surgery may be enhanced by revascularization (transluminal coronary angioplasty, coronary stent placement).
  5. Early surgery after coronary stent placement has been associated with adverse cardiac events. Antiplatelet therapy (aspirin, clopidogrel) requires perioperative management to balance the risk of bleeding versus stent thrombosis. The risk of regional versus general anesthesia is a consideration in the presence of antiplatelet therapy.
  6. Pulmonary Disease
  7. Introduction
  8. The site and type of surgery (thoracic and upper abdominal surgery) are the strongest predictors of pulmonary complications.
  9. Diaphragmatic dysfunction occurs despite adequate analgesia and is theorized to be caused by phrenic nerve inhibition.
  10. Duration of anesthesia is a well-established risk factor for postoperative pulmonary complications, with morbidity rates increasing after 2 to 3 hours.
  11. Patient-Related Factors
  12. Preoperative evaluation of patients with pre-existing pulmonary disease should include assessment of the type and severity of disease, as well as its reversibility.
  13. Inquiries should be made regarding exercise intolerance, chronic cough, and unexplained dyspnea.
  14. On physical examination, findings of wheezing, rhonchi, decreased breath sounds, dullness to percussion, and a prolonged expiratory phase are important.

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  1. Tobaccois an important risk factor but usually cannot be influenced. Cessation of smoking for 2 days may decrease carboxyhemoglobin levels, abolish nicotine's effects, and improve mucous clearance, but smoking cessation for at least 8 weeks is necessary to reduce the rate of postoperative pulmonary complications.
  2. Asthma
  3. Frequent use of bronchodilators, hospitalizations for asthma, and the requirement for systemic steroids are all indicators of the severity of the disease.
  4. After an episode of asthma, airway hyperreactivity may persist for several weeks.
  5. The possibility of adrenal insufficiency is another concern in patients who have received more than a “burst and taper” of steroids in the previous 6 months.
  6. Obstructive sleep apnea (OSA)(periodic obstruction of the upper airway during sleep leading to episodic oxygen saturation and hypercarbia, chronic sleep deprivation, and daytime somnolence) is estimated to be present (often undiagnosed) in 9% of females and 24% of males (Table 23-8). Preoperative identification of these patients may lead to a formal sleep study to identify the severity of symptoms and the need for preoperative initiation of continuous positive airway pressure (CPAP). A general consensus exists that preoperative institution of CPAP reduces perioperative risk.
  7. Patients with OSA are exquisitely sensitive to the respiratory depressant effects of inhaled anesthetics, sedatives, and opioids.
  8. The ASA has published practice guidelines for the perioperative management of patients with OSA.

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During the preoperative evaluation, specific questions may be asked to determine the patient's likelihood of having OSA (Table 23-9).

Table 23-8 Factors Commonly Associated with an IncreasedRisk of Obstructive Sleep Apnea

Body mass index >35 kg/m2
Increased neck circumference
Severe tonsillar hypertrophy
Anatomic abnormalities of the upper airway

Table 23-9 Questions to Ask During the Preoperative EvaluationRegarding the Presence of Symptoms and Signs of Obstructive Sleep Apnea

Does the patient snore loudly?
Are there observed pauses in breathing during sleep?
Are there frequent arousals during sleep or awakening with a choking sensation?
Is daytime somnolence present?
Do the child's parents notice restless sleep or difficulty breathing?
Is the child aggressive or have trouble concentrating?

  1. Preoperative communication between the surgeon and anesthesia professional is important for planning the management of a patient with OSA (Table 23-10).
  2. Postoperative hospitalization is recommended for OSA patients with other coexisting diseases. When procedures are performed on an outpatient basis, postoperative monitoring (pulse oximetry) should be continued to ensure that the patient is able to maintain room air saturation without obstruction when left undisturbed.

Table 23-10 Management Decisions in Coordination with the Surgeon for Patients with Obstructive Sleep Apnea

Determine if noninvasive approaches for performing the surgerywould reduce the need for postoperative opioids.
Discuss if it is feasible to perform the surgery under neuraxial, regional, or local anesthesia to decrease the amount ofanesthesia or opioids needed.
Determine if NSAIDs are acceptable for postoperative analgesia.
Discuss whether outpatient surgery is a safe option.
Determine if the patient will be able to use CPAP postoperatively.
Determine if postoperative admission to an ICU is needed for a patient who is a first-time user of CPAP.

CPAP = continuous positive airway pressure; ICU = intensive care unit;
NSAID = nonsteroidal antiinflammatory drug.

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VII. Endocrine Disease

  1. Diabetes mellitusis the most common endocrinopathy (0.4% of the US population has type 1, and 8% to 10% of the US population has type 2). This incidence increases increasing with the greater incidence of obesity. Critical illness–induced hyperglycemia (blood glucose >200 mg/dL) in the absence of known diabetes occurs frequently, especially in elderly individuals.
  2. Individuals with diabetes have an increased risk of developing CAD (silent angina caused by diabetic neuropathy), perioperative MI, hypertension, and congestive heart failure.
  3. Peripheral neuropathies (documented preoperatively) and vascular disease make patients with diabetes at risk for positioning injuries.
  4. Autonomic neuropathy is common and may contribute to hemodynamic instability and pulmonary aspiration from gastroparesis.
  5. Stiff joint syndrome caused by glycosylation of proteins may contribute to limited motion of the temporomandibular joint and cervical vertebra, leading to difficult airway management (this should be evaluated preoperatively).
  6. Patients with type 1 diabetes must receive exogenous insulin to avoid development of ketoacidosis.
  7. Elective surgery should be delayed if there is evidence of suboptimal blood glucose control (hemoglobin A1c >6% to 8%, abnormal electrolytes, ketonuria).
  8. Administration of perioperative beta-blockers (no evidence of drug-induced glucose intolerance or masking of hypoglycemic symptoms) should be considered in diabetic patients with CAD to help limit perioperative myocardial ischemia.
  9. Preoperative Glucose Management.Evidence is lacking to be able to set standards for the perioperative management of diabetic patients, but at a minimum, an attempt should be made to control the glucose level within a range of 100 to 200 mg/dL (some argue for a top limit of 150 mg/dL) (Table 23-11).
  10. Adrenal Disorders.There is consensus that for patients taking corticosteroids for long periods that perioperative steroid supplementation is indicated to cover the stresses of anesthesia and surgery.

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Table 23-11 Recommendations for Perioperative GlucoseManagement in Diabetic Patients

Schedule as the first case of the day to avoid prolonged fasting.
Hold oral hypoglycemic drugs on the day of surgery to avoidreactive hypoglycemia (the exception is metformin, whichshould be held for 24 hours).
Continue usual insulin regimen through the evening before surgery.
Advise the patients to take a glucose tablet or clear juice ifhypoglycemia occurs before arrival at the hospital.
Schedule the patient to arrive NPO in early morning and checkblood glucose, electrolytes, and ketones.
For type 1 diabetics, administer half the usual morning does ofintermediate- or long-acting insulin after arrival for surgery(hold the usual dose of rapid or short-acting insulin).
Continue use of insulin pumps for brief surgeries or convert thepump to an IV insulin infusion for moderate or major surgeries.
Use the patient's own sliding scale to administer short-actinginsulin subcutaneously to maintain the blood glucoseconcentration 100 to 200 mg/dL before surgery.
Measure blood glucose concentrations every 1 to 2 hours duringsurgery.
Prevent postoperative nausea and vomiting and encourage earlyresumption of diet and return to the previous insulin regimen.

IV = intravenous; NPO = nil per os.

VIII. Other Organ Systems

  1. Renal disease has important implications for fluid and electrolyte management, as well as metabolism of drugs.
  2. Liver disease is associated with altered protein binding and volume of distribution of drugs, as well as coagulation abnormalities (this may influence the choice of regional anesthesia).
  3. Musculoskeletal disorders have been associated with an increased risk of malignant hyperthermia.
  4. Osteoarthritis may result in difficulty exposing the glottic opening for tracheal intubation or difficulty in positioning the patient for regional anesthesia.
  5. Perioperative Laboratory Testing
  6. The Value of Preoperative Testing: Normal Values
  7. The vast majority of tests only increase or decrease the probability of disease.

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  1. To determine the clinical relevance, a test must be interpreted within the context of the clinical situation. (There is a high incidence of false-positive test results when tests are performed in normal patients.)
  2. Risks and Costs versus Benefits
  3. The use of medical testing is associated with significant cost, both in real dollars and in potential harm to the patient.
  4. Even if testing better defines a disease state, the risks of any intervention based on the results may outweigh the benefit.
  5. Recommended Laboratory Testing(Table 23-12)
  6. Complete Blood Count and Hemoglobin Concentration.
  7. The current recommendations of the National Blood Resource Education Committee is that a hemoglobin of 7 g/dL is acceptable in patients without systemic disease.
  8. In patients with systemic disease, signs of inadequate systemic oxygen delivery (tachycardia, tachypnea) are an indication for transfusion.
  9. Electrolytes
  10. The only consensus is the lack of routine testing in asymptomatic adults, although creatinine and glucose testing have been recommended in older patients.
  11. In patients with systemic diseases and those taking medications that affect the kidneys, blood urea nitrogen and creatinine testing are indicated.
  12. Coagulation Studies
  13. Patients with abnormal laboratory study results but without clinical abnormalities rarely have perioperative problems.
  14. A prothrombin and partial thromboplastin time analysis are indicated in the presence of previous bleeding disorders (after injuries; after tooth extraction or surgical procedures; and in patients with known or suspected liver disease, malabsorption or malnutrition, and taking certain medications such as antibiotics or chemotherapeutic agents).
  15. Pregnancy Testing.Regarding the need to routinely test women without a pregnancy history, current practice varies dramatically among centers and anesthesiologists and may be a function of the population served.

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Table 23-12 Recommended Laboratory Testing

Blood Count
Neonates
Physiologic age ≥75 yr
Class C procedure
Malignancy
Renal disease
Tobacco use
Anticoagulant use or bleeding disorder
Electrolytes
Renal disease
Diabetes
Diuretic, digoxin, or steroid use
CNS disease
Endocrine disorders
Blood Glucose
Physiologic age ≥75 yr
Diabetes
Steroid use
CNS disease
Electrocardiography
Physiologic age ≥75 yr
Class C procedure
Cardiovascular disease
Pulmonary disease
Radiation Therapy
Diabetes
Digoxin use
CNS disease
Coagulation Studies
Chemotherapy
Hepatic disease
Bleeding disorder
Anticoagulants
BUN and Creatinine
Physiologic age ≥75 yr
Class C procedure
Cardiovascular disease
Renal disease
Diabetes
Direct or digoxin use
CNS disease
Liver Function Tests
Hepatic disease
Hepatitis exposure
Malnutrition
Chest Radiography
Recent upper respiratory infection
Physiologic age ≥75 yr
Cardiovascular disease
Pulmonary disease
Malignancy
Radiation therapy
Tobacco ≥20 pack years
Pregnancy Test
Possible pregnancy
Albumin
Physiologic age ≥75 yr
Class C procedure
Malnutrition

CNS = central nervous system; BUN = blood urea nitrogen.

  1. Chest Radiography
  2. Preoperative chest radiography may identify abnormalities that may lead to delay or cancellation of the planned surgical procedure or modification of perioperative care.

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  1. Routine testing in a population without risk factors can lead to more harm than benefit.
  2. Preoperative chest radiography is indicated in patients with a history or clinical evidence of active pulmonary disease and may be indicated routinely only in patients with advanced age.
  3. Pulmonary function testscan be divided into spirometry and an arterial blood gas (ABG) analysis.
  4. With the advent of pulse oximetry, the use of preoperative ABG sampling has become less important.
  5. A normal serum bicarbonate level virtually excludes the diagnosis of CO2retention.
  6. Preoperative Medication

Preoperative Medication consists of psychological and pharmacologic preparation of patients before surgery. Ideally, all patients should enter the preoperative period free from apprehension, sedated but easily arousable, and fully cooperative.

  1. Psychological preparationis provided by the preoperative visit and interview with the patient and family members serving as a nonpharmacologic antidote to apprehension (Table 23-13).
  2. Pharmacologic Preparation
  3. Drugs selected for preoperative medication are administered orally with up to 150 mL of water 1 to 2 hours before the anticipated induction of anesthesia. Drugs may be administered intramuscularly (IM)

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if the oral route of administration is not judged to be effective or possible. Alternatively, drugs may be administered intravenously (IV) in the immediate preoperative period.

Table 23-13 Areas to be Discussed During a Preoperative Interview

Review the medical history with patient, including coexistingdiseases, chronic drug therapy, and prior anesthetic experience.
Describe the anesthetic techniques available and their associatedrisks.
Review the planned preoperative medication and the time of thescheduled surgery.
Describe what to expect on arrival in the operating room.
Describe the anticipated duration of surgery and expected timeto return to the room.
Describe methods available to manage postoperative pain, including patient-controlled analgesia and neuraxial opioids.

Table 23-14 Goals for Preoperative Medication

Relief of anxiety
Sedation
Amnesia
Analgesia
Drying of airway secretions
Prevention of autonomic reflex responses
Reduction of gastric fluid volume and increased pH
Antiemetic effects
Reduction of anesthetic requirements
Facilitation of smooth induction of anesthesia
Prophylaxis against allergic reactions

  1. Various Goals for Pharmacologic Premedication(Table 23-14)
  2. Determinant of Drug Choice and Dose(Table 23-15)
  3. Several classes of drugs are available to facilitate achievement of the desired individual goals for pharmacologic premedication (Table 23-16).
  4. There is no best drug or drug combination for preoperative medication.
  5. The choice may be influenced by tradition and the anesthesiologist's previous experience.
  6. Timing of drug delivery is as important as drug selection.

Table 23-15 Determinant of Drug Choice and Dose

Patient age and weight
ASA physical status classification
Level of anxiety
Tolerance for depressant drugs
Prior adverse experiences with premedication
Drug allergies
Elective versus emergency surgery
Inpatient versus outpatient

ASA = American Society of Anesthesiologists.

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Table 23-16 Drugs Used for Pharmacologic Premedication

Drug

Route of Administration

Adult Dose (mg)

Lorazepam

PO, IV

0.5–4.0

Midazolam

PO (children)

0.5 mg/kg

 

IV

1.0–2.5

Fentanyl

IV

25–100 µg

Morphine

IV

1.0–2.5

Meperidine

IV

10–25

Cimetidine

PO, IV

150–300

Ranitidine

PO

50–200

Metoclopramide

IV

5–10

Atropine

IV

0.3–0.4

Glycopyrrolate

IV

0.1–0.2

Scopolamine

IV

0.1–0.4

IV = intravenous; PO = per os.

  1. Ideally, the specific drugs selected are based on the goals of premedication balanced against the potential undesirable effects these drugs may produce. It is important to recognize that some patients (e.g., elderly patients and those with decreased level of consciousness, intracranial hypertension, severe pulmonary disease, or profound hypovolemia) may not need or should not receive depressant drugs for preoperative medication.
  2. Benzodiazepinesact on specific brain receptors (γ-aminobutyric acid) to produce selective antianxiety effects at doses that do not produce excessive sedation, depression of ventilation, or adverse cardiac effects.
  3. Lorazepamproduces intense amnesia, but sedation and prolonged duration of action detract from its use for short surgical procedures and in outpatients. Peak effects after oral administration may not occur for 2 to 4 hours.
  4. Midazolamhas replaced diazepam in its use for preoperative medication and conscious sedation. An oral form of midazolam is particularly useful for preoperative medication in children. The incidence of side effects after administration of midazolam is low, although depression of ventilation and sedation may be greater than expected,

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especially in elderly patients and when the drug is combined with other central nervous system depressants. The onset after IV administration of midazolam is in 1 to 2 minutes, and recovery occurs rapidly, reflecting this drug's poor lipid solubility and rapid distribution to peripheral receptors compared with diazepam. Furthermore, the metabolites of midazolam are not likely to be pharmacologically active. For all these reasons, midazolam should usually be administered within 1 hour of induction of anesthesia.

  1. Opioidsare used for preoperative medication when there is a need to provide analgesia, such as before institution of a regional anesthetic or when patients have pain owing to their surgical disease. Anesthesiologists often use a combination of an opioid, benzodiazepine, and scopolamine for preoperative medication in patients who are likely to be unusually apprehensive, as before cardiac surgery or cancer surgery. Administration of opioids has the potential to produce multiple side effects, which may be exaggerated when other depressant drugs are also included in the preoperative medication (Table 23-17).
  2. Morphineproduces peak effects within 45 to 90 minutes after IM injection. Inclusion of morphine in the preoperative medication decreases the likelihood that undesirable increases in heart rate will accompany surgical stimulation.
  3. Meperidineis often administered in combination with promethazine. Peak effects after IM injection of meperidine may be unpredictable.

Table 23-17 Side Effects of Opioids as Used for Pharmacologic Premedication

Depression of ventilation
Nausea and vomiting
Synergistic effects, especially when administered with benzodiazepines
Orthostatic hypotension
Delayed gastric emptying
Pruritus
Choledochoduodenal sphincter spasm

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Table 23-18 Summary of Fasting Recommendations to Reduce the Risk of Pulmonary Aspiration*

Ingested Material

Minimum Fasting Period (Applied to All Ages) (hours)

Clear liquids (water, fruit juice without pulp, carbonated beverages, clear tea, black coffee)

2

Breast milk

4

Infant formula

6

Non-human milk

6

Light meal (toast and clear liquids)

6

*These recommendations apply only to healthy patients who are undergoing elective procedures and are not intended for women in labor. Following these guidelines does not guarantee complete gastric emptying.

  1. Fentanyl(which is 75 to 125 times more potent than morphine as an analgesic) may be administered IV to provide a rapid onset of preoperative analgesia.
  2. Gastric Fluid pH and Volume
  3. Despite the predictable presence of acidic fluid in the stomach at the time of induction of anesthesia, clinically significant pulmonary aspiration of gastric fluid is rare in healthy patients undergoing elective surgery. The ASA has adopted guidelines for preoperative fasting (Table 23-18).
  4. Maintenance of a patent airway is more important than routine pharmacologic prophylaxis in otherwise healthy patients undergoing elective surgery.
  5. Ingestion of clear fluids in the 2 hours preceding the induction of anesthesia does not increase gastric fluid volume. Patients who are permitted to ingest clear fluids before surgery are more comfortable than those who have fasted. Under no circumstances are solid foods permitted in the period preceding induction of anesthesia for elective surgery.
  6. Drugs Used to Decrease Gastric Fluid Volume and Increase Gastric Fluid pH(Table 23-19)
  7. Antiemeticsmay be administered in the preoperative or intraoperative period as prophylaxis against

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postoperative nausea and vomiting, especially in patients considered to be at increased risk for this complication (history of vomiting, obesity, ophthalmologic or gynecologic surgery) (Table 23-20).

Table 23-19 Drugs Used to Decrease Gastric Fluid Volume and Increase Gastric Fluid pH

Anticholinergics (do not reliably increase gastric fluid pH at clinical doses and may relax the lower esophageal sphincter, making gastroesophageal reflux more likely)
H2-receptor antagonists (not 100% effective in increasing gastric fluid pH)
   Cimetidine (inhibits mixed-function oxidase enzyme systems and decreases hepatic blood flow, which may prolong the elimination half-time of some drugs)
   Ranitidine (more potent and longer lasting than cimetidine)
   Famotidine (has the longest duration of action of all H2-receptor antagonists)
Antacids (nonparticulate antacids are recommended to decrease the risk of pulmonary reaction if the antacid is inhaled; in contrast to H2-receptor antagonists, there is no lag time before gastric fluid pH is increased)
Omeprazole (increases gastric fluid pH by blocking secretion of hydrogen ions by parietal cells)
Gastrokinetic agents
   Metoclopramide (onset in 30–60 minutes after oral administration and 3–5 minutes after IV administration; gastric emptying effects may be offset by opioids, anticholinergics, or antacids)

IV = intravenous.

  1. Anticholinergics
  2. Routine inclusion of anticholinergics as part of the pharmacologic premedication is not mandatory but

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should be individualized based on the patient's needs and the pharmacology of the anticholinergic (Table 23-21).

Table 23-20 Antiemetics Used to Prevent or Treat Postoperative Nausea and Vomiting

Droperidol (sedation and dysphoria may be side effects; inexpensive; its use is limited by rare risk of prolongation of the QTc interval)
Possibly metoclopramide
Transdermal scopolamine patch (should be applied several hours before induction of anesthesia)
Ondansetron or granisetron

Table 23-21 Comparative Effects of Anticholinergics*

 

Atropine

Scopolamine

Glycopyrrolate

Antisialagogue effect

+

+++

++

Sedative and amnesic effects

+

+++

0

Central nervous system toxicity

+

++

0

Relaxation of gastroesophageal sphincter

++

++

++

Mydriasis and cycloplegia

+

++

0

Increased heart rate

+++

+

++

*Intravenous administration.
0 = none; + = mild; ++ = moderate; +++ = marked.

  1. Indications for Anticholinergics(Table 23-22)
  2. Side Effects of Anticholinergic Drugs(Table 23-23)
  3. Adrenergic Agonists
  4. Clonidine (5 mg/kg orally as preoperative medication) produces sedation, decreases the anesthetic requirements for inhaled and injected drugs, and attenuates the sympathetic nervous system response (hypertension, tachycardia, catecholamine release) to tracheal intubation.
  5. Dexmedetomidine is a more selective α-adrenergic agonist than clonidine that has also been used for preoperative medication.

Table 23-22 Indications for Anticholinergics

Antisialagogue effect (not necessary when regional anesthesia planned)
Sedation and amnesia (doses should be decreased in elderly patients; scopolamine is the most effective)
Vagolytic action (IM administration is not as effective as IV injection just before the anticipated vagal stimulus)

IM = intramuscular; IV = intravenous.

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Table 23-23 Side Effects of Anticholinergic Drugs

Central nervous system toxicity (restlessness and confusion, especially in elderly patients; this is unlikely with glycopyrrolate because it minimally crosses the blood–brain barrier)
Relaxation of the lower esophageal sphincter (may not be clinically significant)
Mydriasis and cycloplegia (miotic eye drops should be continued in patients with glaucoma)
Increased physiologic dead space
Drying of airway secretions
Interference with sweating (an important consideration in febrile patients, especially children)
Increased heart rate (unlikely after IM administration)

IM = intramuscular.

  1. Side effects (hypotension, bradycardia, dry mouth) limit the usefulness of these drugs for preoperative medication.
  2. Other Drugs Given with Preoperative Medication(Table 23-24)
  3. Differences in Preoperative Medication Between Pediatric and Adult Patients
  4. Children differ from adults regarding preoperative medication in terms of psychological preparation,

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greater use of oral medications, and more frequent use of anticholinergics to reduce vagal activity.

Table 23-24 Other Drugs Given with Preoperative Medication

Beta-blockers (patients with known or suspected CAD may be protected; the goal is to achieve a heart rate of 50–70 bpm and systolic blood pressure <110 mm Hg)
Statins (may protect patients with CAD; they should be continued in the perioperative period if the patient is being treated preoperatively)
Antibiotics (these should be administered 1 hour before incision [2 hours for vancomycin]; if a tourniquet is used, they should be administered before cuff inflation; they may potentiate neuromuscular blocking drugs)
Steroids (history of hypoadrenocorticism or treatment of nonadrenal diseases)
Insulin

CAD = coronary artery disease.

  1. Psychological Factors in Pediatric Patients
  2. Age is probably the most important factor in the success of a preoperative visit and interview.
  3. Children who do not ask questions or appear disinterested during the preoperative interview may be masking a high level of anxiety.
  4. Some children wish to take an active part in the induction of anesthesia. In this regard, it may be helpful to have the parents accompany these children to the operating room.
  5. Differences in Pharmacologic Preparation
  6. Use of pharmacologic premedication in children older than age 6 months is controversial and has not been proven to decrease unwanted psychological outcomes. More important in avoiding long-lasting psychological problems is a pleasant induction of anesthesia.
  7. Oral administration (often midazolam in a flavored liquid) is preferred to IM injections in children.
  8. Some anesthesiologists prefer to administer atropine IM or IV just before the induction of anesthesia to protect against vagal reflexes in response to airway manipulations.

Editors: Barash, Paul G.; Cullen, Bruce F.; Stoelting, Robert K.; Cahalan, Michael K.; Stock, M. Christine

Title: Handbook of Clinical Anesthesia, 6th Edition

Copyright ©2009 Lippincott Williams & Wilkins

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