infarction and renal failure.45,46 Optimizing the fluid and metabolic status of a patient in end-stage renal

disease is of vital importance. Elective surgery should be delayed until such optimization is performed.

In emergent situations, the urgent need for hemodialysis should be considered intraoperatively or

postoperatively to avoid life-threatening electrolyte and fluid derangements. Although postoperative

renal failure has historically been the focus of cardiac surgery researchers, national data suggest that

nearly 15% of patients undergoing general surgery procedures will also experience postoperative acute

kidney injury, as defined by a 0.3 mg/dL increase in serum creatinine within seven postoperative

days.47 Risk factors for postoperative acute kidney injury in patients undergoing general surgery are

listed in Table 13-11. These data should be considered during the patient consent process.

Table 13-11 Predictors of Postoperative Acute Kidney Injury After General

Surgery Procedures

Obstructive Sleep Apnea

With the rise in obesity prevalence, obstructive sleep apnea (OSA) is emerging as a major comorbidity

that has an impact on postoperative outcomes and costs.48 The physiologic changes on the upper airway,

lungs, pulmonary circulation, heart, and brain are extensive and challenge not only the immediate

perioperative period, but also postoperative management.49 These patients are prone to airway collapse

at induction and emergence, hypoxemia, delayed emergence, respiratory depression, and cardiovascular

collapse.50 Preliminary data demonstrate increased sensitivity to the effects of opiates as well.51

Observational data demonstrate a relationship between OSA treatment and a reduction in postoperative

complications, but prospective interventional trials have yet to be conducted.52,53 Nevertheless, the

standard protocol for all preoperative evaluations should be the use of a locally accepted OSA screening

tool (STOP-BANG questionnaire, Perioperative Sleep Apnea Prediction score, etc.) and ensuring

postoperative access to continuous positive airway pressure therapy for patients currently prescribed

such therapy as outpatients. Some undiagnosed or noncompliant patients may require initiation of

therapy in the immediate postoperative period and the perioperative resources to fulfill clinical urgency

are essential.

RISKS ASSOCIATED WITH REGIONAL TECHNIQUES IN PATIENTS

BEING TREATED WITH ANTICOAGULANTS

As the indications for anticoagulant therapy have increased, ranging from drug-eluting stents to atrial

fibrillation and venous thromboembolism prophylaxis, the number of patients and types of

anticoagulant therapy has continued to increase. In particular, low–molecular-weight heparin (LMWH)

and oral direct factor Xa inhibitors are often part of a patient’s pre- or postoperative therapy plan. The

use of neuraxial or PNB anesthesia in patients with preoperative anticoagulation requires careful

planning and assessment of the risks and benefits of specific anesthetic techniques and withdrawal of

anticoagulant therapy. LMWH raises specific concerns of crippling epidural hematoma formation when

neuraxial techniques are used. For that reason, the American Society of Regional Anesthesia has

published specific guidelines for central conduction block (spinal and epidural anesthesia) to try to

minimize the incidence of this devastating complication54: In general, LMWH therapy requires

coordination of neuraxial administration at least 12 hours after the last dose. Coumadin, clopidogrel,

and ticlopidine should be held for at least 5, 7, and 14 days prior to neuraxial techniques, respectively.

The absence of any reversal agents or reliable diagnostic testing for oral direct Xa inhibitors requires a

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conservative approach of withdrawal of therapy and no data currently exist to establish a specific

threshold. Data regarding risks for PNB are even more scarce and local protocols should be established

and followed. Unlike neuraxial techniques, the PNB techniques involve more compliant fascial planes

that may allow for increased bleeding without compressive injury to nerve structures.

PREOPERATIVE EVALUATION

12 The three goals of the preoperative evaluation are (a) to develop an anesthetic plan that considers

the patient’s medical condition, the requirements of the surgical procedure, and the patient’s

preferences; (b) to ensure that the patient’s chronic disease is under appropriate medical therapy before

an elective procedure; and (c) to gain rapport with and the confidence of the patient, answer any

questions, and allay fears.

Optimally, to complete this task, an anesthesiologist would meet every patient before the planned

surgical procedure to review the medical history, complete a physical examination, discuss the options

and associated anesthetic risks, and develop an anesthetic plan. In the past, this was accomplished when

the anesthesiologist visited the patient in the hospital the night before surgery. Currently, it is rare to

have patients admitted the night before surgery even before the most comprehensive and complex

surgical procedures. The evaluation must still be accomplished, but it must be done on an ambulatory

basis, which creates associated logistical problems.

A patient’s medical conditions should be optimized before an elective surgical procedure. This

optimization is best performed by the primary care physician, with medical specialty consultation, if

necessary. The following questions must be answered when evaluating a patient undergoing an elective

surgical procedure (Table 13-12). What must be included in the preoperative evaluation? Second, who is

involved in this process? When and where are all the steps in this process to be conducted? How should

all the information be coordinated so that it is available to the appropriate personnel at the appropriate

time? If the procedure is deemed a surgical emergency, the anesthesiologist is responsible for assessing

the patient quickly, developing the appropriate anesthetic plan, and proceeding to the operating room

as soon as possible. In an emergency situation, the anesthesiologist is not obligated to seek medical

consultation to evaluate chronic medical problems because time is essential.

The following steps must be completed before moving the patient into the operating room:

1. A comorbidity-focused history and physical examination

2. Appropriate laboratory studies and medical consultations

3. An anesthesiologist’s preoperative evaluation with assignment of an American Society of

Anesthesiologists (ASA) physical status

4. Discussion with the patient the options and risks

5. Development and communication of the anesthetic plan to the patient and surgeon

6. Acute optimization of any pertinent medical conditions

Table 13-12 Results Hospital Mortality Rates in Relation to Age, Preoperative

Disease, and Surgery

The history and physical examination have repeatedly been shown to be the most valuable parts of

the preoperative assessment. To enable ideal operative planning and postoperative care, it is the

surgeon’s responsibility to obtain a basic history that includes current medical conditions, current

medication, and previous surgical history. In addition, the anesthesiologist must review previous

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anesthetic problems experienced by the patient or blood relatives, the patient’s exercise tolerance, and

additional details regarding general medical conditions. This evaluation not only determines the

laboratory tests that may be required but also allows for the assignment of ASA physical status (PS)

(Table 13-13). The classification serves as a general measure of the patient’s state of well-being, taking

into account all problems the patient brings to the operating room, including systemic disturbances

caused by the surgical illness. Although studies of anesthetic mortality show a correlation with the PS

classification, this categorization does not describe the risk directly. The risk of any operation is

determined not only by patient-related factors but also by procedure-specific ones. For patients with

complex medical problems, it is frequently helpful to supplement the surgical history and physical

examination with a recent assessment by the patient’s primary physician in order to assess the patient’s

long-term health trajectory. There are no data demonstrating the value of routine preoperative medical

consultation.55

The value of preoperative laboratory studies has undergone substantial reevaluation since the mid1980s. In the past, a surgical procedure was an opportunity to obtain a battery of baseline laboratory

tests, even for ASA PS-1 patients. The current thinking is that a laboratory test should not be ordered

unless a change in the surgical or anesthetic plan is anticipated. The only preoperative screening test

required at the University of Michigan, for instance, is an ECG within a year of the planned surgical

procedure for men older than 50 years and women older than 60 years of age. For procedures with

significant anticipated blood loss, a type and cross match is ordered, and a preoperative hematocrit is

also required. All other tests should have an indication based on history and physical examination. A

current strategy for selecting tests indicated by patient history is presented in Table 13-14. Electronic

patient questionnaires have also been developed, allowing the appropriate laboratories to be selected

based on the patient’s response to questions.56

Table 13-13 Physical Status Classification of the American Society of

Anesthesiologists

Table 13-14 Simplified Strategy for Preoperative Testing

Discussions of the options of anesthetic techniques and anesthetic risks are best performed by the

anesthesiologist who will provide the anesthetic. If the surgeon prefers a specific anesthetic technique,

this is best communicated directly to the anesthesiologist rather than recommended to the patient. The

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development of the anesthetic plan must be determined by the anesthesiologist.

The history, physical examination, and laboratory studies should be performed by the surgeon as soon

as the surgical procedure is scheduled. The results of the laboratory studies must be evaluated well in

advance of the day of surgery so that positive findings can be attended to in a timely manner. For

healthy patients (ASA PS-1 and PS-2), the preoperative anesthetic assessment can be conducted by the

anesthesiologist on the day of the procedure. If the patients have complex medical problems (ASA PS-3

or greater) or have significant concerns they want to discuss with an anesthesiologist, they should be

evaluated before the day of surgery. Because of the logistical problems of scheduling, most institutions

have developed preoperative anesthesia clinics where this process can take place.

13 In addition, the patient’s medication regimen should be reviewed to ensure that appropriate

medications are continued or discontinued in the days and hours leading up to an elective procedure. In

general, diuretics and ACE-I/ARB medications should not be taken the day of surgery. Several important

classes of medications should be continued as per the patient’s normal regimen: chronic pain therapy

(including opioids), beta-blockers, statins, and proton pump inhibitors. The decision regarding

anticoagulant therapy is a complex one that must take into account the indication for therapy, the

likelihood and impact of surgical bleeding, and the risk of perioperative thrombosis. Insulin and oral

hypoglycemic agents should be continued at a reduced dose given the fasting state of the surgical

patient. Patients receiving chronic pain or opioid addiction therapy with buprenorphine (Subutex,

Suboxone) can be particularly challenging to manage in the postoperative period and should be

immediately referred to their primary care physician and an anesthesiologist to create a pain

management plan prior to the day of surgery. Buprenorphine is mixed opioid agonist/antagonist that

tightly binds at the μ receptor and has a long and varied half-life (24 to 60 hours). It can inhibit the

analgesic benefits of traditional opioids in the postoperative period, resulting in uncontrolled pain,

decreased patient satisfaction, and the potential for adverse events due to the need for very high doses

of opioids.57 A management protocol used at the University of Michigan is demonstrated in Algorithm

13-2.

An obvious problem that concerns anesthesiologists is the potential of a difficult intubation. This can

be assessed as discussed earlier (Fig. 13-1 and Table 13-18). Even if a patient has no medical problem,

the possibility of a difficult airway warrants that the patient be seen preoperatively and evaluated.

These patients can always be approached by an awake fiberoptic technique, but this takes planning and

can cause a significant delay if there is no prior warning.

MONITORING THE SURGICAL PATIENT

One of the more obvious changes in anesthesia care has been the routine use of an array of electronic

monitoring devices to provide continuous surveillance of physiologic status. Because the art and science

of anesthesiology involves titrating pharmacologic agents to produce desired physiologic effects, there

must be a measured parameter to which drug dosages are titrated. Depending on the severity of preexisting disease and the extent and duration of the surgical procedure, invasive techniques can be used

to provide comprehensive continuous data to guide the titration of fluid therapy and cardiovascular

agents.

Monitors of Oxygenation

Pulse oximetry has been called the most significant advance in patient monitoring to date. This device

continuously, noninvasively, and inexpensively provides arterial hemoglobin saturation (SaO2

) and

peripheral pulse by measuring light absorption in a manner similar to that of a laboratory co-oximeter.

A laboratory co-oximeter shines light through a cuvette filled with a blood sample. Each hemoglobin

species absorbs light in direct proportion to its concentration (Beer–Lambert law). A cooximeter

requires one wavelength of light for each hemoglobin species to be measured, that is, one wavelength

for oxyhemoglobin and one for reduced hemoglobin. To measure other hemoglobins, such as

carboxyhemoglobin or methemoglobin, the device requires four wavelengths of light.

The traditional pulse oximeter uses two wavelengths of light, one red and one infrared, that shine

through a tissue bed, usually a finger. Opposite the light sources is a photodiode that measures the

transmitted light intensity. A large proportion of the light absorbed as it passes through the tissues is

not associated with arterial blood but with other components of the tissue, such as skin, muscle, bone,

and venous blood. Therefore, the device analyzes only the pulsatile component of absorption and

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