Perioperative Management

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Chapter 182 Perioperative Management

Basheal M. Agrawal, Seth M. Zeidman, Laurence Rhines, Nathan H. Lebwohl, Gregory R. Trost

The spectrum of spine surgery ranges from straightforward cervical procedures in healthy, young adults to emergent fixation of unstable thoracolumbar spine fractures in clinically unstable patients with multiple traumatic injuries. Preoperative evaluation and postoperative care share equal importance with the surgical procedure. The continuum of care begins at the initial meeting of the surgeon and patient and continues long after surgery. The clinician should be cognizant of coexisting medical problems and their implications, commonly used anesthetic and surgical techniques, potential postoperative complications, and prophylactic measures that can minimize postoperative morbidity. This chapter provides an overview of these issues.

The purpose of preoperative evaluation is to identify problems affecting surgical risk and, in so doing, reduce perioperative morbidity and mortality. Preoperative evaluation often uncovers other health problems that need attention, regardless of whether they directly affect the proposed operation. A complete health history should be obtained, including the present illness, past illnesses, and associated diseases. One should inquire about bleeding tendencies, current medications, and allergies. Coexisting medical problems are common in spine surgery patients and can be associated with an increased incidence of postoperative complications and a lengthy hospital stay.

General Conditions Affecting Surgical Risk

Age

Patients at either extreme of the life span are at risk for complications or death from operation because of their narrower margin of safety. Small errors that are well tolerated by young, healthy adults are quickly compounded in children or geriatric patients, sometimes with catastrophic results.

Infants and young children have a relatively low tolerance for infection, trauma, blood loss, and nutritional and fluid disturbances.1 The management of these disorders in infants and children differs from their treatment in adults. Particular aspects of surgical care deserving special attention include fluid and electrolyte management, nutrition, and temperature maintenance.1,2

Advanced age is an independent risk factor for postoperative morbidity, and the prevalence of coexisting medical problems increases with age.3 As a result, elderly patients who undergo spine procedures have higher rates of postoperative complications, including excessive bleeding, postoperative confusion, and urinary tract infections.4 They tend to recuperate more slowly than do their younger counterparts. A recent study has shown that age is a positive risk factor for postoperative complications in multilevel thoracolumbar spine fusion surgery. Furthermore, it is correlative with higher rates of reoperation.5

It is safe to consider every patient older than 65 years of age to be at high risk for generalized atherosclerosis and for potential limitation of myocardial and renal reserve. Elderly patients often develop cardiac failure if they are fluid overloaded. Close monitoring of vital signs, intake, output, body weight, and serum electrolytes is mandatory. Elderly patients generally require smaller doses of narcotics, sedatives, and anesthetics than do younger patients. Barbiturates, sedatives, and steroids may cause confusion, and narcotics can produce respiratory depression.6

Osteoporosis and falls are common in the geriatric population and result in an increased incidence of spine fractures with advancing age. Elderly patients with spine fractures after a fall pose special problems. In addition to assessing the overall medical condition, the clinician should evaluate the cause of the fall because it may uncover an important coexisting medical condition and, in turn, help to prevent future injury. Nonoperative measures may be more appropriate in the elderly patient with a spine fracture if he or she is unable to tolerate the rigors of a prescribed treatment. Furthermore, bracing of the elderly patient is different from that of younger patients. For example, use of a halo vest in the geriatric population is fraught with morbidity.

Although most falls are results of accidents or environmental factors, they can also be caused by important cardiovascular or neurologic disorders, including arrhythmia, orthostatic hypotension, and cerebral ischemia. Special consideration should also be given to alcohol and drug use as possible causes. The incidence of falls in the elderly has been correlated with use of benzodiazepines, antidepressants, and diuretics.

Finally, advanced age is an important independent risk factor for postoperative deep venous thrombosis and pulmonary embolism, which are major causes of morbidity and mortality after surgical procedures.

Obesity

Obesity increases the technical difficulty of surgery and anesthesia. Obese surgical patients have a greater incidence of serious concomitant disease and higher rates of postoperative wound breakdown, thromboembolic complications, and pulmonary disease. Early patient mobilization, aggressive pulmonary toilet, and appropriate prophylaxis against deep venous thrombosis are all necessary adjuncts to good perioperative care. Occasionally, it may be advisable to delay elective surgery until the patient loses weight by appropriate dietary measures. There are increasing data to suggest that minimally invasive techniques, including tubular surgery, diminish the risks incurred by obesity.7

Coagulation Abnormalities

Spine procedures may result in substantial blood loss. Excessive bleeding at the surgical site increases the chances of wound infection and impaired wound healing. Although the prevalence of underlying coagulopathies is no higher in patients undergoing spine surgery, many regularly take nonsteroidal anti-inflammatory drugs (NSAIDs). Because NSAIDs are reversible inhibitors of platelet aggregation, their use can increase postoperative bleeding. NSAIDs should be discontinued at least 1 week before a major spine procedure. NSAIDs have also been shown to inhibit the healing of spine fusions. In patients undergoing spine fusion, NSAIDs should be avoided in the postoperative period as well.8,9

Malnutrition

Increasing evidence suggests that many surgical patients are moderately to severely malnourished.10 The increased metabolic demands of patients undergoing or recovering from spine surgery are often unmet because of insufficient caloric intake. With inadequate caloric intake, the hypercatabolic state induced by trauma or surgery results in significant visceral and skeletal protein depletion. Malnourished patients have increased rates of mortality and morbidity from sepsis, wound complications, impaired healing, and protracted rehabilitation. Although no single test demonstrates malnutrition conclusively, a variety of laboratory studies and physical measurements can help reveal nutritional inadequacies.11 These include preoperative weight loss of more than 10 pounds, a serum albumin level of less than 3.5 g/dL, and a total lymphocyte count less than 1500 to 2000 cells/μL.12

If malnutrition is identified, a vigorous regimen of nutritional supplementation should begin, preferably before surgery, and the patient should be monitored throughout the perioperative period.11 Total or peripheral parenteral nutrition should be considered in patients who either cannot tolerate or cannot meet their caloric needs with enteral nutrition alone.13–16

Smoking

The harmful effects of smoking tobacco on the rate of postoperative pulmonary, cardiac, and thromboembolic complications are well known. In a recent study of 875 patients undergoing orthopaedic reconstructive surgery, the incidence of cardiopulmonary complications in smokers was double that of nonsmokers. In that study, smoking was identified as the single most important risk factor for the development of complications after elective hip or knee arthroplasty. Similarly increased rates of pulmonary complications were identified in a multicenter review of 400 patients undergoing abdominal surgery.17–20

A review of wound infections after dorsal spine operations involving instrumentation implicated smoking as a significant risk factor for development of an infection.21

Wound complications in soft tissue procedures have also been reported to occur much more frequently in smokers. In a study of 425 patients undergoing reconstruction after breast cancer surgery, the risk of skin flap necrosis was nine times as high in heavy smokers as in nonsmokers. Similarly, in a review of patients undergoing face lift, the risk of skin slough was 12.5 times as high in smokers compared with nonsmokers.22,23 In spine surgery, current smoking increases the rate of postoperative wound infection and subsequently increases hospital stay and 30-day mortality rates.24

Stopping smoking before surgery has been shown to decrease the rate of postoperative complications, but only if a significant amount of time elapses between smoking cessation and surgery. A 2-week smoke-free period in a study of 60 patients before colorectal surgery did not decrease the rate of postoperative complications. In contrast, 4 weeks of smoking cessation significantly reduced the rate of wound infections in a randomized, controlled trial of minor dermatologic procedures. In another randomized trial of 120 patients scheduled to undergo hip or knee replacement, enrollment in a smoking cessation program at least 6 weeks before surgery resulted in a substantial decrease in complication rates. The rate of wound complications decreased from 31% to 5%, and of cardiovascular complications from 10% to 0%.25–27

In addition to the aforementioned general postoperative problems, tobacco smoking has been associated with unique complications after spine surgery. Smoking was identified as a significant risk factor in the development of postoperative airway obstruction after cervical corpectomy. In a review of 133 patients undergoing cervical corpectomy, 6 of 7 patients who developed airway obstruction were smokers. Two of these patients died as a result of this complication. Other risk factors were myelopathy and multilevel surgery. In patients with these risk factors, the authors recommend delayed extubation and careful assessment of the airway for swelling before extubation.28

Smoking has been shown to inhibit the healing of spine fusions in many clinical reviews. This effect has been well documented in patients undergoing spine fusion surgery and in animal models. In a randomly selected retrospective study of 50 smokers and 50 nonsmokers undergoing uninstrumented lumbar dorsolateral fusion, the pseudarthrosis rate was 40% for smokers and 8% for nonsmokers. A corresponding diminution in resting oxygen saturation was identified. The authors theorized that this relative hypoxia was responsible for the failure of the arthrodesis to heal.29

Animal studies, however, have shown that the inhibition of fusion can be attributed directly to the pharmacologic effects of systemically administered nicotine, without hypoxia.30 Inhibition of bone graft vascularization has been shown in animal models. Cytokine expression is decreased, suggesting that the inhibitory effects of nicotine involve more than just local vasoconstriction.31,32

Although the effect of hypoxia has not been studied independently, these observations suggest that the negative effects of smoking on arthrodesis cannot be avoided by switching from inhaled tobacco to oral or transdermal nicotine.

Smoking has been demonstrated to be a risk factor for nonunion after thoracic and cervical fusion surgery as well. In a review of 90 patients undergoing ventral instrumented spine fusion for adolescent scoliosis, 4 of 5 patients who developed a nonunion were smokers.33

A retrospective review of 131 patients who had multilevel cervical discectomies and fusions with autogenous interbody graft without instrumentation found a pseudarthrosis rate of 50% in smokers compared with 24% in nonsmokers.34

In animal models, bone morphogenetic protein was effective in reversing the inhibitory effects of nicotine on spine fusion.35

In some clinical series, the use of instrumentation and electrical stimulation has been reported to help overcome the inhibitory effects of smoking on spine fusion.36,37

Two studies have assessed whether the negative effects on fusion can be reversed by smoking cessation, with conflicting results. Glassman et al.9 reported that whereas smokers had a nonunion rate of 26.5% after lumbar fusion surgery, those who stopped smoking for more than 6 months after surgery had a successful arthrodesis rate of 82.9%. This was not significantly different than the union rate of 85.8% in nonsmokers. However, Deguchi et al.8 found no improvement in arthrodesis rate in their patients who stopped smoking.

Infection

Urinary tract infections are frequent in patients undergoing spine surgery. When associated with bacteremia, these infections are of particular concern because of the possibility of bacterial seeding of hardware. Thus, it is important to identify and treat established urinary tract infections before spinal instrumentation is applied.38

Compromised Host

The capacity of a compromised host to respond to infection or trauma is significantly impaired by disease or medication. Increased susceptibility to infection and delayed wound healing are the major postoperative problems in these patients and may arise from drugs such as corticosteroids, immunosuppressive agents, or cytotoxic agents and from prolonged antibiotic therapy. Infections in these patients can be caused by either common or opportunistic organisms. Malnutrition, renal failure, diabetes mellitus, and other immunocompromising diseases, including acquired immunodeficiency syndrome, significantly increase susceptibility to infection.

Multiple Trauma

Many spine surgery patients are the victims of severe accidents and have sustained multiple concomitant traumatic injuries. In such cases, urgent repair of spine injuries almost always takes precedence over assessment and treatment of chronic medical problems because acute spine stabilization dramatically reduces mortality, incidence of acute respiratory distress syndrome, length of hospital stay, and need for mechanical ventilation. Nonetheless, it is important to realize that the severity of neurologic injury, number of comorbidities, and use of high-dose steroids increase the risk of complication after thoracolumbar spine fracutrues.39

Patients with multiple trauma are often in their best state of health on admission. Efforts to delay spine stabilization may not be in their best interest.

After surgery, it is important to search for factors contributing to the accident, including alcohol and drug abuse, and unrecognized or untreated conditions such as liver disease, withdrawal syndromes, myocardial infarction (MI), arrhythmias, seizures, and hypoglycemia. All these conditions have postoperative implications and may require specific diagnostic and therapeutic interventions.

Rheumatologic Conditions

Patients with rheumatoid arthritis undergo a variety of spine procedures, particularly cervical fusion. These patients experience high complication rates for all surgical procedures. Wound breakdown, infection, loosening of instrumentation, and pseudarthrosis occur more frequently in patients with rheumatoid arthritis and can be attributed to poor tissue integrity, compromised vascular status, and the use of immunosuppressive drugs.40,41

Patients with rheumatoid arthritis should be examined for cervical spine involvement. Dynamic flexion and extension radiographs should be obtained to exclude occult instability before the administration of general endotracheal anesthesia. A variety of other problems, including anemia, pulmonary fibrosis, and pleural effusions, may be present. Chronic steroid use often results in adrenal suppression, requiring administration of perioperative stress-dose steroids. Similarly, patients with systemic lupus erythematosus and other rheumatologic conditions require thorough preoperative evaluation and may prove difficult to manage.42

Particular attention should be paid to patients with ankylosing spondylitis. These patients warrant very different management than the typical spine surgery patient with degenerative disease, especially with regard to positioning, traction, and orthoses.

Nonsurgical Diseases Affecting Surgical Risk

Cardiac Disease

Preoperative Evaluation

The most common symptoms of heart disease are dyspnea, fatigue, chest pain, and palpitation. It is important to inquire about exercise tolerance, paroxysmal nocturnal dyspnea, orthopnea, peripheral edema, irregular heartbeat, and chest pain. One should document significant past illnesses such as congenital heart disease, rheumatic fever, MI, atherosclerotic cerebrovascular and peripheral vascular disease, diabetes mellitus, hypertension, and autoimmune disease. Also, use of cardiac pacemakers, previous cardiac surgery, and past or present use of diuretics, digitalis, coronary vasodilators, antihypertensive drugs, and antiarrhythmic drugs should be noted. A history of angina pectoris, MI, Adams-Stokes attacks, stroke, cerebral ischemic attacks, intermittent claudication, or previous treatment for heart disease or hypertension should alert the surgeon to the possibility of a cardiac abnormality requiring further evaluation.

Conditions contraindicating elective surgery because of increased risk are acute MI, recent or crescendo angina pectoris, aortic stenosis, and atrioventricular block.

Physical Examination

The heart rate and rhythm must be recorded and any cyanosis, clubbing, petechiae, neck vein distention, and peripheral edema noted. The lungs should be auscultated for rales or wheezes. Auscultation permits evaluation of the first and second heart sounds, as well as of gallops and murmurs.

Radiologic Examination

Most preoperative patients require an anteroposterior chest radiograph to exclude cardiac enlargement, pulmonary vessel distention, and pulmonary infiltrates. Lateral views permit diagnosis of individual chamber enlargement.

Electrocardiography

An electrocardiogram (ECG) can help detect arrhythmias, conduction defects, chamber enlargement, and myocardial ischemia. Routine preoperative ECGs are obtained on all adult patients undergoing spine surgery. The ECG is useful diagnostically and also as a baseline measurement to evaluate subsequent changes in the myocardium and conduction system. In general, a stable abnormality on the ECG, in the absence of cardiac failure or angina pectoris, is indicative of only slightly increased perioperative risk.

Laboratory Tests

Serum concentrations of hemoglobin, sodium, potassium, and calcium may be relevant in the assessment of cardiac function. Arterial blood gas and pH studies indicate the adequacy of oxygenation.

Hemodynamic Studies

Pulse rate and cuff blood pressure are useful indicators of cardiac function. Monitoring arterial pressure with an intra-arterial line provides a more accurate value and permits waveform analysis. Central venous pressure (CVP) and pulmonary capillary wedge pressure (PCWP) indicate cardiac preload. PCWP reflects left ventricular filling pressure and left ventricular performance, whereas CVP reflects right ventricular function.

Elevations of CVP above 10 mm Hg suggest right ventricular failure. In most patients, left heart function correlates with right heart function. CVP exceeding PCWP by greater than 5 mm Hg indicates pulmonary artery hypertension; PCWP exceeding CVP by more than 5 mm Hg indicates isolated left ventricular failure. However, presence of a normal CVP does not exclude left ventricular failure. A PCWP below 10 mm Hg may be associated with shock and a PCWP above 25 mm Hg, with pulmonary edema.

For patients with cardiac or pulmonary disease, monitoring of PCWP with a Swan-Ganz catheter provides the best indication of left ventricular preload. Cardiac output can be measured by thermodilution using a Swan-Ganz catheter. Serial measurements can guide fluid therapy, even in the presence of left ventricular failure.

Echocardiography is a noninvasive method of studying cardiac anatomy and function. Cardiac catheterization with coronary angiography remains the most definitive cardiac diagnostic study, showing the vascular supply to different areas of the myocardium. This type of study is not without inherent risks.

Preoperative Preparation

The cardiac status of a spine surgery patient with cardiac dysfunction should be optimized before surgery. Special attention should be paid to correction of electrolyte imbalance, fluid excess, and anemia. It is important to avoid hypotension, hypoxia, fluid overload, and undue pain or excitement.

Cardiac Contraindications

Relative cardiac contraindications to operation are recent MI, uncontrolled congestive heart failure (CHF), unstable angina pectoris, intractable cardiac arrhythmias and conduction defects, and uncontrolled hypertension. Preoperative evaluation is directed toward detecting and treating these conditions.

The mortality rate after a major operation is 25% if the surgery is within 3 weeks of MI, 10% if within 3 months, and 5% if within 6 months. A patient with a healed MI has an added mortality risk of about 3%. Only emergent and urgent operations are indicated within 3 months; only semiurgent procedures are indicated from 3 to 6 months. Elective operations should be postponed until 6 to 12 months after MI.

Treatable causes of CHF include myocardial ischemia and its sequelae, valvular disease, bacterial endocarditis, sepsis, arrhythmias, hyperthyroidism, and hypertension. Careful perioperative management of these conditions will certainly decrease morbidity. Anginal chest pain may reflect severe coronary artery disease. Symptoms and signs denoting severe angina include associated sweating and nausea, poor response to coronary vasodilators (nitroglycerin), no relief with rest, frequent attacks, prolonged pain, and ECG evidence of ischemia.

High-risk coronary artery lesions include left main coronary artery occlusion, high left anterior descending artery lesions, and lesions in multiple vessels. Elective procedures should be postponed in patients with such lesions. Nonelective procedures may necessitate preliminary or coincident coronary artery bypass surgery. Patients who need urgent or emergent procedures require intensive perioperative management.

In hypertensive patients the blood pressure should be normalized before surgery. There is a linear correlation between preoperative blood pressure and postoperative myocardial ischemia.34

Postoperative Management

Patients with significant cardiac disease require close postoperative monitoring. Monitoring typically includes treatment in an intensive care setting for the first 24 hours after surgery.

Most postoperative MIs occur on the second or third postoperative day, and hence serial ECGs for 3 days are indicated in patients with known coronary artery disease. Chest pain is often difficult to evaluate in the postoperative period, and an MI may become apparent only because of hypotension or arrhythmia. Serial cardiac isoenzyme studies are especially useful for identifying postoperative infarcts, and should be obtained as well. Postoperative treatment for MI entails vigorous support and monitoring. Arrhythmias and cardiac failure should be treated as they arise.

Typically, cardiac failure shows symptoms of hypotension or oliguria and is most often a result of hypovolemia in the postoperative patient. If hypotension or oliguria persists after IV fluids are administered, the patient must undergo complete evaluation. When cardiac failure results from hypertensive crisis, blood pressure can be reduced with nitroprusside.

Cardiac failure unresponsive to other measures may respond to afterload reduction. Judicious use of drugs with a positive inotropic effect (e.g., dopamine, dobutamine, isoproterenol, and digitalis) may also prove to be beneficial. Heart performance is most efficient at a rate of 100 to 120 beats/min.

Pericardial restriction resulting from constrictive pericarditis or pericardial effusion is suggested by a decreased cardiac output with a high CVP. Typically, jugular veins are distended, and a paradoxical pulse may be present. Echocardiography may assist in making the diagnosis. Treatment consists of pericardiocentesis or pericardiotomy.

In the presence of bradycardia, one should look for anesthetic excess, hypoxia, atrioventricular block, or vagal stimulation by visceral traction, carotid sinus compression, or traction on extraocular muscles.

In the presence of falling blood pressure, one should look for anesthetic excess, myocardial ischemia, or inadequate preload caused by blood or fluid losses, obstruction of venous return, or vasodilation. Absence of blood pressure, carotid pulse, or respiration is an ominous sign. Treatment should include identification of the underlying cause and immediate correction of the abnormality (e.g., for ventricular fibrillation, electrical defibrillation should be used; for asystole, cardiac massage, vagolytic or sympathomimetic drugs, or cardiac pacing should be used). Cardiopulmonary resuscitation should be initiated immediately and continued until the underlying problem has been corrected. Four minutes without blood flow to the brain results in a fatal ischemic injury. Preexisting inadequacy of cerebral blood flow and oxygenation shortens the time available for correction. Closed chest cardiopulmonary resuscitation is the initial method of resuscitation. Open chest cardiac massage should be undertaken only as a last resort.

Treatment of the major arrhythmias is a complex problem requiring close collaboration of the internist and surgeon. If the surgeon is required to provide emergency treatment until the internist arrives, a general knowledge of cardiac arrhythmias and their treatment is important. Diagnosis of the arrhythmia is made from the ECG.

Atrial fibrillation decreases cardiac efficiency and may cause congestive failure. Treatment involves slowing the rate by adequate digitalization. Calcium channel blockers can be used in patients with no history of heart failure or cardiomyopathy. Conversion to normal sinus rhythm by quinidine or direct current (DC) countershock may be required if shock or pulmonary edema is noted.

Atrial flutter often causes congestive failure. Digitalization will slow the rate, either by increasing the degree of block or converting the flutter to sinus rhythm or atrial fibrillation. DC countershock is the treatment of choice, especially if the rhythm is poorly tolerated.

Paroxysmal supraventricular tachycardia often occurs in patients with otherwise normal hearts. In the absence of heart disease, serious effects are rare. Digitalis toxicity must be excluded as a cause. Vagal stimulation (carotid sinus massage, Valsalva maneuver) should be tried initially. If mechanical measures fail, pharmacotherapy is indicated. There is, however, no unanimity on the most effective medical therapy. Digitalis, vasopressors, procainamide, and propranolol can all be tried. Continuous ECG and blood pressure monitoring are essential. DC cardioversion may be indicated if the patient’s condition deteriorates.

Ventricular tachycardia and ventricular fibrillation are usually associated with myocardial damage, especially MI. Lidocaine is the drug of choice for emergency treatment because of its short duration of action. If the arrhythmia recurs, an IV infusion may be given or the IV injection repeated. If lidocaine has no effect, DC cardioversion is preferable to additional pharmacotherapy.

Ventricular fibrillation produces cardiac arrest and requires defibrillation and cardiopulmonary resuscitation. DC cardioversion is often effective in converting patients back to sinus rhythm. If the initial attempt at cardioversion is unsuccessful, repetition with sequentially higher energy levels is indicated.

Pulmonary Disease

Preoperative Evaluation

The most common symptoms of pulmonary disease are dyspnea at rest or after minor exertion, cough, sputum production, wheezing, chest pain, and hemoptysis. It is important to document any history of tuberculosis, recent upper respiratory infection, chronic pulmonary disease, or asthma. One must determine the degree of tobacco and alcohol use as well as previous occupational exposures to coal dust, asbestos, and silica dusts. Establishment of a medication history, particularly regarding the use of corticosteroids, is especially important.

Physical Examination

The examiner must look for physical signs of pulmonary disease such as cyanosis or nail clubbing. It is important to observe the respiratory rate and respiratory effort as well as to percuss the chest for dullness or hyperresonance and to determine inspiratory diaphragm excursion. Auscultation of the chest allows the examiner to hear rales, rhonchi, wheezes, and decreased breath sounds.

Radiologic Examination

The chest radiograph may demonstrate pulmonary infiltrates, granulomas, atelectasis, hyperlucency, pneumothorax, abnormalities of pulmonary vasculature, or a mass. A negative radiograph does not exclude pulmonary disease. If any question exists, a CT scan of the chest may be obtained.

Laboratory Examination

Yellow, green, or brown sputum suggests active infection. Sputum culture is indicated to identify specific organisms and to determine antibiotic sensitivities. Arterial blood gas measurements help evaluate pulmonary gas exchange. The arterial partial pressure of oxygen (Pao2) is an indicator of oxygen uptake by the blood in its passage through the lungs. Pao2 is affected by the fraction of inspired oxygen, right-to-left shunting, and diffusion capacity across the alveolocapillary membrane. Normally, Pao2 is 70 mm Hg or greater. A Pao2 of 60 mm Hg indicates mild respiratory failure; a Pao2 of 50 mm Hg or less indicates severe pulmonary disease. The oxygen saturation (Sao2) reflects the percentage of hemoglobin actually bound by oxygen. Normally, Sao2 is 93% or more; an Sao2 of 90% indicates mild respiratory failure; an Sao2 of 84% or less indicates severe pulmonary disease. The arterial partial pressure of carbon dioxide (Paco2) reflects the adequacy of ventilation. Normally, Paco2 is 38 to 43 mm Hg. A Paco2 of 44 to 54 mm Hg indicates mild impairment of ventilation; a Paco2 of 55 mm Hg or greater indicates severely impaired ventilation. Arterial blood pH is affected by both metabolic and respiratory factors. Normally, the arterial blood pH is 7.38 to 7.42.

Spirometry

The vital capacity (VC) is the maximum volume expired after a maximum inspiration. VC is decreased in restrictive disease but is usually normal in obstructive disease. A VC that is 50% or less of predicted indicates severe disease. The forced expiratory volume is the maximum volume expired after a maximum inspiration. Forced expiratory volume equals VC in restrictive disease but is less than VC in obstructive disease.

Preoperative Preparation

Patients without pulmonary symptoms can be expected to tolerate surgery from a respiratory standpoint. If a patient can climb two flights of stairs without shortness of breath, further evaluation of respiratory status is generally unnecessary. Factors that can predispose a patient to postoperative pulmonary complications are long-term cigarette smoking, chronic obstructive pulmonary disease, upper abdominal and thoracic procedures, acute respiratory infections, and restrictive disorders such as obesity, pulmonary fibrosis, and neuromuscular and skeletal disease. Patients with one or more of these factors require careful preoperative preparation, and most should undergo complete pulmonary evaluation. Elective procedures should be postponed until maximum pulmonary function has been achieved. All patients should stop smoking at least 2 weeks before any elective operation. Overweight patients should try to achieve ideal body weight. All patients should receive preoperative instruction in coughing, deep breathing, and use of the incentive spirometer.

Respiratory infections should be treated before elective operations. Viral infections resolve with symptomatic treatment; bacterial infections can be treated with the appropriate antibiotics. Whenever possible, preoperative preparation and treatment should be performed on an outpatient basis to avoid superinfection with hospital-acquired antibiotic-resistant organisms. Adequate hydration, humidified air, and expectorants can help liquefy sputum. Postural drainage and chest percussion can help clear these secretions. Bronchodilators are often helpful for patients with chronic obstructive pulmonary disease. In addition, patients with bronchospasm or asthma may benefit from the administration of bronchodilators either by aerosol or by intermittent positive-pressure ventilation. Corticosteroids may be necessary for patients with severe asthma or pulmonary fibrosis.

If aspiration is observed, endotracheal intubation, airway suctioning, and saline lavage should be performed immediately. Bronchorrhea will neutralize the acidic gastric juices within 10 minutes so lavage after this interval is of no benefit. Moreover, steroid treatment has no objective benefit. Antibiotics should be reserved to treat specific organisms and should not be used prophylactically.

No patient should be denied operation for emergent and urgent conditions because of pulmonary disease. Whenever possible, the risks should be recognized and pulmonary function optimized.

Postoperative Management

The postoperative effects of major procedures under general anesthesia include decreases in total lung capacity, vital capacity, functional residual volume, and compliance. Aggressive postoperative care minimizes these effects. Administering low doses of analgesics at frequent intervals promotes improved respiration by controlling pain without compromising respiratory drive. Frequent change of position and early ambulation are also beneficial. Changing the volume of ventilation prevents atelectasis. Incentive spirometry promotes deep inspiration that can also help prevent atelectasis.

Oxygen administration should be used when necessary but with judiciousness; 100% oxygen promotes atelectasis and may result in oxygen toxicity. Administering oxygen to patients with chronic hypercapnia may depress respiratory drive. The elderly and patients with acutely impaired respiratory function may require ventilatory support over the first postoperative night. Arterial blood gases and fluid therapy should be closely monitored; administration of both insufficient and excessive fluid impairs respiratory function. Patients with bronchospasm may benefit from bronchodilator therapy.

Pulmonary Complications

Ventilatory impairment is typical after ventral thoracic and lumbar approaches to the spine. In most instances, the impairment does not prevent spontaneous breathing. However, if the operative procedures are extensive, if there has been massive trauma, if the patient is elderly, or if the patient has preexisting chronic disease or malnutrition, ventilatory impairment may be so great that a period of assisted ventilation is necessary.

The first postoperative hours are critical because this is when acute ventilatory failure most commonly occurs. The effects of muscle relaxants may not have worn off completely, and muscle weakness can cause reduced vital capacity. If a respiratory complication develops, decreased lung compliance may also contribute to inadequate ventilatory function.

Pneumothorax is an uncommon complication in elective surgical procedures, but it should be considered in any patient who develops acute respiratory distress or intraoperative deterioration. The principal cause of pneumothorax in hospitalized patients is iatrogenic lung puncture during percutaneous central venous catheter placement. It can also occur in a patient who coughs and thereby ruptures a pulmonary bleb or bulla. Diagnosis is made on the basis of decreased or absent breath sounds on the affected side, with hyperresonance to percussion. When a tension pneumothorax develops there may also be a lateral shift of the trachea away from the affected side. Any patient who develops respiratory distress after insertion of a central venous catheter should be presumed to have a pneumothorax, and a chest tube should be inserted immediately and not delayed for the radiograph. If pneumothorax is suspected but the patient is comfortable, one should first obtain the chest radiograph and insert a chest tube if indicated.

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