Anesthesia for the "Healthy" Patient Case File

Anesthesia for the "Healthy" Patient Case File

Lydia Conlay, MD, PhD, MBA, Julia Pollock, MD, Mary Ann Vann, MD, Sheela Pai, MD, Eugene C. Toy, MD

Case 10

A 52-year-old man has had progressive knee pain with swelling, and a Baker cyst just behind his right knee. Recently, the pain has increased in intensity, and has kept him from sleeping at night. His orthopedic

surgeon has tentatively diagnosed a torn meniscus, and recommended an arthroscopy as an outpatient. The patient has had no major illnesses other than the typical childhood diseases. He has had no previous operations or anesthetics, nor a family history of problems with anesthesia. He has no allergies to medications, does not smoke, and consumes alcohol occasionally at social events. His laboratory results and physical examination by an internist were all normal. He has had nothing to eat or drink since he went to bed last night. On examination, the patient weighs 160 lb and is 5 ft, 8 in tall. His neck appears to be supple and mobile. He opens his mouth without difficulty, and with his head extended and tongue protruding, his uvula is completely visible.

➤ How are a patient’s general medical condition, and his risk for difficult airway management classified?

➤ In which stage of anesthesia is the patient most vulnerable, and why?

➤ Which components of a pre-anesthetic evaluation are often not included in a patient’s typical history and physical examination?

ANSWERS TO CASE 10:

Anesthesia for the “Healthy” Patient

Summary: A 52-year-old healthy patient with persistent and increasing knee

pain is scheduled for an outpatient arthroscopy. His uvula is completely visible.

➤ A patient’s ASA Physical Status Classification, noted as ASA I-IV, categorizes patients according to their comorbidities. The Mallampati airway classification describes the amount of a patient’s uvula visible when a patient extends his neck and protrudes his tongue, and is one predictor of the risk of difficult airway management.

➤ Patients are most vulnerable in Stage II of anesthesia, since they are hyperexcitable to external stimuli, and have lost both their airway reflexes and autonomic stability.

➤ An anesthetic evaluation prior to surgery should include the patient’s history regarding their response to previous anesthetics, NPO status, presence or absence of gastric reflux, difficulty or ease of airway management, history or family history of malignant hyperthermia or pseudocholinesterase deficiency, an examination of the oral cavity, airway and neck mobility, and the ease of i.v. access.

ANALYSIS

Objectives

1. Introduce the learner to fundamental terminology and processes used by anesthesiologists.

2. Emphasize the anesthesiology-specific components of the pre-anesthetic evaluation which are in addition to typical routine physical examination.

3. Introduce the learner to common categorizations of patients according to their comorbidities using the American Society of Anesthesiologists (ASA) Physical Status Classification, and to their risk for difficult airway management using the Mallampati classification of airways.

4. Familiarize the learner with the stages of anesthesia and their physiologic sequela.

Considerations

A commonly-used method of describing the complexity of a patient’s medical condition is the American Society of Anesthesiologists’ (ASA) Physical Status Classification (Please see Table 10–1). This classification is a useful indicator of surgical mortality. (Please see Figure 10–1.) Since this patient

Table 10–1 ITEMS IN PRE-ANESTHESIA EVALUATION IN ADDITION TO A ROUTINE PHYSICAL EXAMINATION

• Response to previous anesthetics including difficulty or ease of airway management, postoperative intubation, tracheotomy, malignant hyperthermia, or pseudocholinesterase deficiency • NPO status • Presence or absence of gastric reflux • Medications on the day of surgery (particularly bronchodilators) • Examination of the airway and neck mobility • Ease of i.v. access

(Please also see the fundamental information regarding the preoperative evaluation)

Figure 10–1. ASA Physical Status Classification correlates with surgical mortality in two studies. (Reproduced from ASA Newsletter 2002;66(9) [Mark J. Lema, editor]. http://www.asahq.org/Newsletters/2002/9_02/vent_0902.htm. Reprinted with permission of the American Society of Anesthesiologists, 520 N.Northwest Highway,Park Ridge, Illinois 60068-2573.)

Table 10–2 MALLAMPATI CLASSIFICATIONS
Mallampati class 1	The uvula is entirely visible	Easy intubation
Mallampati class 2	The uvula is partially visible	Intubation may be challenging
Mallampati class 3	The uvula is not visible	Intubation likely to be difficult

has no medical comorbidities, he is classified as an “ASA Class 1.” He has not had anything to eat or drink since midnight, so he can be considered as “NPO.” The potential ease or difficulty of intubation is often addressed using the Mallampati airway classification. In this particular patient, the uvula is completely visible when the patient’s head is extended and his tongue protruded (Please see Table 10–2). Thus, this patient is anticipated to pose little or no difficulty with airway management and his airway is classed as Mallampati Class 1. Since he is undergoing a quick procedure such as an arthroscopy, a general anesthetic would provide the fastest recovery with few complications.

APPROACH TO

The “Healthy” Patient: ASA I, Mallampati Class I

DEFINITIONS

AIRWAY PROTECTION: The ability to prevent the aspiration of gastric contents into the lungs which could cause pneumonia.

ASA PHYSICAL STATUS CLASSIFICATION: Addresses the extent of a patient’s medical comorbidities prior to surgery as ASA I to IV. Comorbidities are often associated with an increase in postoperative complications. Both comorbidities and complications influence the likelihood that this ambulatory patient could be discharged on the day of surgery, versus needing to remain in the hospital. For an emergency case, an “E” is added. The ASA classifications are also commonly used by other specialties. (Please see Table 10–3.)

DEPTH OF ANESTHESIA: The level of a patient’s progression from consciousness to unconsciousness following the administration of anesthesia. Depth is indicated by the stages of anesthesia. (Please see Table 10–4.)

MALLAMPATI CLASSIFICATION: One of the factors predicting the difficulty of airway management and the placement of an endotracheal tube. It refers to the amount of the uvula visible when a patient’s head is extended and his or her tongue protruded. (Please see Table 10–2.)

Table 10–3 ASA CLASSIFICATIONS
ASA I	No systemic disease
ASA II	Mild systemic disease	Smoking, controlled hypertension, etc.
ASA III	Major systemic disease	Stable coronary artery disease, reactive airway disease, mild renal or hepatic impairment, etc.
ASA IV	Severe systemic disease	Unstable coronary artery disease, chronic renal failure, severe COPD, etc.,or a combination
ASA V	Imminent death	Ruptured aortic, aneurysm, etc.

E is added to the above to signify an emergency case.

CLINICAL APPROACH

The preparation for any surgical procedure includes an history, a physical examination, and laboratory tests which are appropriate when considering the patient’s age, medical problems, and the type of procedure. In addition to the typical presurgical “work up,” an anesthetic evaluation is also important prior to the administration of anesthesia—whether general, regional anesthesia, or monitored anesthesia care (local infiltration with monitoring and sedation by an anesthesia provider). The pre-anesthesia evaluation addresses factors such as the patient’s NPO status, the presence or absence of gastric reflux, his or her response to previous anesthetics, a reconciliation of medications taken on the day of surgery, and any pertinent family history including direct queries regarding malignant hyperther

Table 10–4 PHASES AND STAGES OF ANESTHESIA
PHASES OF ANESTHESIA	STAGES OF ANESTHESIA
Induction	I. Analgesia. Patient is awake and responsive. II. Hyper-excitable, delirium,movement, autonomic instability, loss of airway protection, significant risk of complications. Protective airway reflexes lost.
Maintenance	III. Return of autonomic stability, preservation of vital functions. Stage III is separated into 4 planes. Planes 2 and 3 are surgical anesthesia. IV. Depression of vital functions, autonomic instability V. Cardiac arrest
Emergence from anesthesia	Stage III, Stage II, then Stage I. Stage II also happens at emergence.

or pseudocholinesterase deficiency. In addition to the routine history and physical, this information is necessary to allow the formulation of a safe and effective anesthetic plan. (Please also see the chapter on preoperative evaluation).

Additional items on the physical examination include a careful evaluation of the patient’s airway anatomy and neck mobility, and the ease of i.v. access. In particular, the airway examination, including the “fingers breadth” of mouth opening, hyomental distance, and Mallampati classification, provide information regarding the potential difficulty or ease of intubation. The patient’s NPO status, and presence or absence of gastric reflux or of a syndrome that significantly increases gastric volume may signal the need for a rapid sequence induction (Please see Case 11), and similarly influences the anesthetic plan.

The anesthetic plan should allow for a rapid return of mental function, and especially in the case of outpatients, recovery of psychomotor skills prior to discharge, as well as to minimize complications. Patients must be able to walk (if they could walk prior to the procedure), be medically stable, and free of pain, and nausea or vomiting prior to discharge from the hospital.

The temporal progression of an anesthetic can be separated into several phases: the beginning is typically referred to as induction, the middle, as maintenance, and the end, emergence. The depth of anesthesia, or progression to and from unconsciousness, is referred to as the stages of anesthesia. (Please see Table 10–4). Stage I lasts from full consciousness until a patient closes his eyes. Stage II begins when the patient closes his eyes. It is characterized by a hyperexcitability to external stimuli which may include vocalization and movement, the loss of protective airway reflexes, and autonomic instability. Stage II ends when patients regain autonomic stability. It is during this stage that patients are most vulnerable. Stage III is the stage of surgical anesthesia. It is divided into four planes; planes 3 and 4 are optimal for surgery.

Prior to the induction of anesthesia, monitors are placed including a blood pressure cuff, an electrocardiogram, a pulse oximeter, a capnograph (which monitors end-tidal CO2, detecting any deficit in ventilation or metabolism or elimination of CO2), and an oxygen analyzer in the breathing circuit (which confirms the continuous flow of oxygen).

Anesthesia is most frequently induced using an intravenous anesthetic such as propofol, etomidate, or sodium thiopental. Patients perceive intravenous anesthetics as a pleasant way to go to sleep, and these agents rapidly render the patient into Stage III of anesthesia, quickly traversing the troublesome Stage II.

Once anesthesia is induced and patients enter Stages II or III, the oral and pharyngeal muscles lose tone and the patient’s airway often begins to obstruct. The airway can be managed by tilting the head back and moving the jaw forward at the angle of the mandible until the airway is patent. An oral airway

may be helpful in preventing the tongue from obstructing the pharynx, or it may not be necessary. Induction can also be accomplished with inhalational anesthetics, and with the newer agents, can be quite pleasant. However, patients do not traverse Stage II as rapidly, and are thus vulnerable to aspiration and difficult airway management for that short period of time.

Table 10–5 INDICATIONS FOR TRACHEAL INTUBATION

• Airway access • Airway protection • Need for muscle relaxation (paralysis) • Length of procedure (> 2 hours) • Need for mechanical ventilation

Anesthesia is typically maintained with an inhalation agent such as desflurane or sevoflurane, or with an intravenous infusion of propofol. Oxygen and inhalation anesthetics are administered with a mask or through airway device such as a laryngeal mask airway (LMA) or an endotracheal tube. It should be noted that after a period of 2 hours, pressure on nerves from a mask may cause nerve palsies involving small branches of the facial nerves, particularly in the peri-oral region, potentially yielding hyperesthesia or analgesia on the face. The laryngeal mask airway can similarly cause pressure on the recurrent laryngeal nerves, leading to (usually transient) vocal cord paralysis.

Unlike a mask or laryngeal mask airway, the placement of an endotracheal tube usually requires paralyzing a patient with a neuromuscular blocker. Since paralysis removes the patient’s ability to breathe, and since intubation requires the mechanical instrumentation of the pharynx and trachea (which can lead to complications), intubation is only performed when there is an indication. (Please see Table 10–5.)

The maintenance of anesthesia is often supplemented with an opiate to reduce pain during and after surgery. This in turn facilitates a reduction in the amount of anesthetic that is required. This patient, for example, would receive desflurane as the inhalation agent, O2, and a small amount of fentanyl added near the end of the procedure to minimize postoperative pain.

As wound closure begins, the anesthetic agent is discontinued. Emergence begins, and the patient is allowed to awaken. He traverses the stages of anesthesia in reverse order, including Stage II. In fact, Stage II is more likely to be observed at emergence than induction, because at induction, patients receive an intravenous induction agent and pass rapidly (and almost imperceptibly) through Stage II.

CLINICAL SUMMARY

This healthy man undergoing an arthroscopy will be monitored with a blood pressure cuff, electrocardiogram, pulse oximeter, end-tidal CO2 monitor (capnograph), and a circuit oxygen analyzer. His anesthetic will be induced with propofol, a laryngeal mask placed, and his anesthetic maintained with desflurane including a small amount of opiate at the end of the case. Once he awakens and can respond to commands (meaning that he has successfully traversed Stage II), the laryngeal mask will be removed.

Comprehension Questions

10.1. A 32-year-old woman is scheduled for a laparoscopic tubal ligation. A surgical admission history and physical, and pre-anesthesia evaluation are performed. The patient’s personal and family history of problems with anesthesia (ie, malignant hyperthermia or pseudocholinesterase deficiency), her NPO status, the presence or absence of gastric reflux, and medications taken on the day of surgery are elicited. Which of the following should also be included in her preoperative management?

    A. An abdominal examination, noting any tenderness and/or rebound.

    B. An electrocardiogram and chest x-ray.

    C. An airway examination including the degree of mouth opening and neck range of motion.

    D. A prescription for postoperative analgesics.

10.2. A 63-year-old man presents for an elective laparoscopic cholecystectomy. He is obese, has angina unpredictably and at rest, and chronic obstructive pulmonary disease (COPD). Which of the following would be his ASA classification?

    A. ASA I

    B. ASA II

    C. ASA III

    D. ASA IV

    E. ASA V

10.3. With his neck extended, mouth open, and tongue protruded, the patient’s uvula is not visible. His airway should be classed as which of the following?

    A. Mallampati 1

    B. Mallampati 2

    C. Mallampati 3

10.4. As this patient awakens from a general anesthetic for an arthroscopy, he coughs, moves his arm, squirms on the table, and phonates when touched by the surgeon. He does not open his eyes or squeeze his hand on command. Which of the following is most accurate?

    A. Movement and phonation indicate that the patient is “awake.”

    B. The patient is emerging from anesthesia. Since he can phonate, he can protect his airway.

    C. Stage II is the stage at which the risk of complications is greatest.

    D. This stage of anesthesia is observed more frequently at induction than emergence.

ANSWERS

10.1. C. An anesthetic evaluation includes an airway examination addressing the patient’s degree of mouth opening typically expressed in “fingers breadths,” and neck range of motion including flexion and extension, and side-to-side motions. An electrocardiogram is not necessary for young, healthy patients, and a chest x-ray is only necessary as medically indicated.

10.2. D. The patient is obese, with angina unpredictably and at rest, and COPD. His angina at rest represents a systemic disease which is unstable, and which could be life threatening. In addition, he also has another comorbidity, COPD. His classification is ASA IV. Because this is a scheduled case, no “E” is added after the “IV.”

10.3. C. Since this patient’s uvula is not visible, his airway is classed as Mallampati 3, suggesting a difficult intubation.

10.4. C. During Stage II of anesthesia, patients are hyperexcitable to external stimuli, and may phonate, move, manifest autonomic instability including arrhythmias, and cannot protect their airways. This is the stage at which the risk of complications is greatest. Because of the rapidity with which patients receiving intravenous induction agents pass through Stage II, this stage of anesthesia is observed more frequently at emergence than induction. The patient’s ability to phonate is not related to his ability to protect his airway.

Clinical Pearls

➤ The pre-anesthetic evaluation determines the anesthetic plan.

➤ Difficult intubations may often be predicted.

➤ The excitement stage of anesthesia (Stage II) happens at induction and emergence.

➤ Intubation requires an indication.

References

Miller RD, ed. Anesthesia, 6th ed. Philadelphia, PA: Elsevier Churchill Livingstone; 2005.

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