Файл: NMS Surgery_booksmedicos.org.pdf

treatment. Failure to improve after therapy may be an indication of high risk.

Ventilation -perfusion scans, quantitation of carbon dioxide diffusion capacity, exercise testing , and determinations of pulmonary artery pressures may be performed in borderline cases.

Split-lung pulmonary function tests may be required in pulmonary resections because the segment to be resected may be diseased and may not contribute significantly to pulmonary function.

Lung volume reduction surgery may be considered to improve postoperative pulmonary function in patients undergoing resection sufficient to raise concerns of inadequate reserve.

B Pre-existing pulmonary disease

Patients with chronic lung disease are thought to be at increased risk for complications after surgery and may benefit from a preoperative pulmonary evaluation and an education in incentive spirometry.

Cigarette smoking

A history of 20 pack -years or consumption of more than 20 cigarettes per day increases the risk of postoperative pulmonary complications.

Cigarette smoking should be stopped at least 6–8 weeks preceding elective surgery to demonstrate any statistically significant decrease in complication rate.

COPD

Antibiotics should be administered before surgery in patients with acute bronchitis, productive cough, or purulent sputum production. If an elective procedure is planned, it should be delayed until after treatment.

Aerosol β2 -agonists and mucolytic drugs (e.g., acetylcysteine) relieve bronchospasm and may help

to liquefy and mobilize retained secretions. Postural drainage and chest physiotherapy can be used to expedite this in selected cases.

TABLE 3-9 Pulmonary Function Ranges Suggesting Increased Operative Risk

*Criteria for a wedge excision or a segamentectomy.Criteria for a lobectomy.

‡Criteria for a pneumonectomy.

From Pett SB, Wernly JA. Respiratory function in surgical patients: perioperative evaluation and management. Surg Annual. 1988;20:36.

P.77

Bronchodilators (e.g., aminophylline) may also have an inotropic effect on respiratory muscles.

Steroids should be used preoperatively, when necessary, to improve pulmonary function; however, they have adverse effects on wound healing and resistance to infection.

Asthma

Poorly controlled asthmatics are at increased risk for pulmonary complications. The risk of pulmonary complications is reduced by medical management (e.g., use of antibiotics, bronchodilators, β 2 - agonists, steroids) to eliminate wheezing preoperatively.

Peak expiratory flow may be measured before and after bronchodilator therapy to assess the presence, severity, and reversibility of bronchospasm.

Muscle relaxants with muscarinic activity (e.g., d-tubocurare) may stimulate bronchospasm and should be avoided.

Propofol may reduce airway irritation during instrumentation.

Obesity increases the work of ventilation and impairs the function of the chest wall, leading to a restrictive respiratory pattern. Postoperative atelectasis is common in obese patients.

Morbidly obese patients may suffer from sleep apnea or oropharyngeal obstruction.

Consideration should be given to using a transverse rather than vertical surgical incision.

Ambulation and mobilization must be encouraged early in the postoperative period.

Age. A slight decrease in pulmonary function is associated with increasing age. Age >70 years has been identified as an independent risk factor for postoperative complications but should not contraindicate surgery in otherwise healthy patients.

Restrictive lung disease, neuromuscular disorders, or pulmonary vascular disease. These patients have an impaired ventilatory reserve as a result of weak muscles or abnormal mechanics of ventilation.

C Operative variables

The type of surgery influences the pulmonary risk.

Thoracotomy and upper abdominal surgery are associated with the most marked changes in postoperative functional residual capacity (FRC).

Chest wall and diaphragmatic excursion mechanics are altered, leading to decreased total lung capacity (TLC), decreased FRC, and decreased tidal volume (TV), which may persist for 1–2 weeks postoperatively.

Postoperative pain causes hypoventilation and a poor cough reflex, leading to retention of secretions and ventilation -perfusion mismatch.

Risk factors for postoperative complications after laparotomy [Hall JC, Tarala RA, Hall JL, et al. A multivariate analysis of the risk of pulmonary complications after laparotomy. Chest . 1991;99(4):923–927]:

ASA class >II

Upper abdominal procedures

Residual intraperitoneal sepsis

Age greater than 59 years

A body mass index (BMI) higher than 25 kg/m 2

Preoperative stay for longer than 4 days

Colorectal or gastroduodenal surgery

Lower abdominal surgery is associated with fewer pulmonary complications than thoracic and upper abdominal surgery.

Extremity surgery rarely affects postoperative pulmonary function.

Minimally invasive surgery

May reduce postoperative pulmonary complications by improving the forced expiratory volume in 1 second (FEV 1 ), FRC, oxygenation, and ventilation. Definitive improvements in outcome

have not been demonstrated, and the site of surgery (i.e., upper abdominal) may be more important than the specific operative technique.

Requires intraperitoneal insufflation and may be associated with intraoperative CO2 retention.

Vertical incisions are more susceptible to respiratory complications when compared with transverse, muscle -splitting incisions.

P.78

Length of surgery. Surgical procedures lasting longer than 3.5 hours are associated with increased pulmonary complications.

Anesthesia

General anesthesia may decrease the FRC for up to 1–2 weeks postoperatively.

Endotracheal intubation and inhalational anesthetics may exacerbate bronchospasm.

Mechanical ventilation impairs many protective mechanisms, such as ciliary function and mucus transport. It also increases the risk of pneumothorax secondary to barotrauma.

Spinal anesthesia shows no difference from general anesthesia in terms of pulmonary morbidity.

Regional block is associated with lower pulmonary risk than either general or spinal anesthesia.

D Perioperative management

Preoperative education. Controlled studies in elective surgical patients demonstrate that the maximal reduction in pulmonary complications is obtained when interventions are begun preoperatively.

Incentive spirometry and deep -breathing exercises are inspiratory maneuvers to recruit alveoli and to counteract the postoperative reduction in FRC. The most effective and simplest intervention is the instruction to cough, deep breathe (5 deep breaths, holding each at full inspiration for 5–6 seconds), and change position hourly while awake.

Other modalities

Continuous positive airway pressure (CPAP) has been demonstrated to improve pulmonary function values, but it is not clear that use of this modality leads to a reduction of pulmonary complications.

Postural drainage and chest physiotherapy are useful in mobilizing secretions but should be reserved for patients with lobar collapse or high sputum production because they may exacerbate bronchospasm. In addition, these maneuvers are often difficult to do during the postoperative period because of patient discomfort.

Extubation. Discontinuation of mechanical ventilatory support after general anesthesia should be performed only after the patient is awake, is hemodynamically stable, and has full respiratory muscle strength.

Parameters for extubation follow (Table 3-10).

Assess for adequate oxygenation.

Assess for adequate ventilation.

Other considerations (Table 3-10).

Protocol-based weaning of mechanical ventilation has been shown to decrease the time on mechanical ventilator support and to reduce the incidence of ventilator-associated pneumonia.

Once criteria for weaning have been met, tolerance of a 30 -minute spontaneous breathing trial has been associated with decreased time to extubation when compared with intermittent mandatory ventilation (IMV) or pressure support modes.

In patients who require mechanical ventilation >24 hours, causes of ventilator dependency should be identified and all possible contributing factors reversed.

After extubation, respiratory sufficiency should be carefully observed and evaluated. If in doubt about the patient's respiratory sufficiency, the physician should perform a physical examination , followed by arterial blood gases and chest roentgenography, if indicated.

Noninvasive ventilation (CPAP, bilevel positive airway pressure [BiPAP]) may provide respiratory support and lower reintubation rates in patients managing only borderline function following extubation.

Early mobilization. Patients should be out of bed and upright as much as possible because this simple maneuver improves the FRC between 10% and 20%. This action allows gravity to assist more in respiration and also helps to minimize the retention of secretions.

Oxygen should be administered if necessary but with caution in patients with COPD. The oxygen should be heated and humidified.

P.79

TABLE 3-10 Criteria for Weaning Mechanical Ventilation

Absence of excessive secretions

Absence of active myocardial ischemia

Absence of neurologic impairment

Absence of airway compromise

FIo2, fraction of inspired oxygen; PaCO2, partial pressure of carbon dioxide in arterial blood; PaO2, partial pressure of oxygen in arterial blood.

Summarized from MacIntyre NR, Cook DJ, Ely EW Jr, et. al. Evidence-based guidelines for weaning and discontinuing ventilatory support: a collective task force facilitated by the American College of Chest Physicians; the American Association for Respiratory Care; and the American College of Critical Care Medicine. Chest. 2001;120(6)(suppl): 375S–395S; Coates NE, Weigelt JA. Weaning from mechanical ventilation. Surg Clin North Am. 1991;74(4):860.

Narcotics should be used judiciously to avoid oversedation and respiratory depression.

The use of regional or epidural anesthesia can provide excellent perioperative analgesia, reduce respiratory depression secondary to parenteral narcotics, and allow improved pulmonary toilet.

Inducing respiratory depression must be avoided when using parenteral or epidural narcotics.

E

Pulmonary complications occur in the perioperative period in up to 50% of patients with chronic lung disease and in up to 70% of patients with abnormal pulmonary function tests.

Atelectasis is the most common complication, followed by pulmonary infection, both of which may lead to pulmonary failure. Pulmonary secretions tend to accumulate after hypoventilation secondary to decreased FRC and splinting from pain.

Aspiration of gastric contents occurs in up to 25% of emergency cases but may occur in as many as 8%– 10% of elective cases. The main causes of aspiration are the diminished loss of consciousness and abnormal motility of the gastrointestinal tract during anesthesia.

Acid aspiration alone causes an inflammatory pulmonary reaction, even in the absence of bacterial contamination. Histamine (H2 ) blockers or proton pump inhibitors (PPI) are often administered preoperatively in patients who have a high risk of aspiration or gastroesophageal reflux.

Bronchoscopy is indicated only for removal of large aspirated particulate matter.

Steroid therapy is not indicated after aspiration.

A nasogastric tube should be placed for gastric decompression if an ileus is present. Once gastric emptying is satisfactory, the nasogastric tube should be removed promptly to allow the patient to cough more effectively.

Other significant postoperative complications include the following:

Bronchospasm

Pulmonary edema

Pneumothorax

Pulmonary embolism

Adult respiratory distress syndrome

P.80

IV The Surgical Patient with Chronic Renal Failure

The preoperative condition of patients with chronic renal failure is strongly dependent on the residual glomerular filtration rate (GFR) and the presence of underlying disease. Volume and electrolyte homeostasis is altered.

The metabolism or excretion of medications (especially many antibiotics and radiopaque, iodinated angiographic dye) is impaired.

A Assessment of renal function

History

Congenital abnormalities; obstructive uropathy; polycystic kidney disease; and chronic, recurrent urologic infection may be associated with significant renal dysfunction.

The presence of underlying systemic disease (e.g., diffuse arteriosclerosis, diabetes mellitus, hypertension, autoimmune diseases, collagen vascular disease) should alert the physician to the possibility of associated renal disease.

Known renal insufficiency should be carefully investigated, including fluid and dietary restrictions, as well as the requirement for dialysis.

Physical examination. Careful attention should be paid to the following:

Volume status

Intravascular volume overload is common; manifestations include pulmonary rales, jugular venous distention, and peripheral edema.

Certain renal diseases (e.g., chronic pyelonephritis, medullary cystic disease, other interstitial disease) may result in salt wasting and subsequent dehydration.

Evidence of coagulopathy includes petechiae and ecchymoses.

Central nervous system changes include lethargy and altered mental status.

Pericardial or pleural rubs and effusions may occur.

Laboratory studies

Serum electrolytes, BUN, and creatinine allow assessment of the volume and electrolyte and acid– base status of the patient.

The hematocrit is decreased in renal failure secondary to decreased production of erythropoietin.

Urinalysis should be performed to evaluate the ability of the kidneys to concentrate and acidify the urine and also to assess for proteinuria and glucosuria as well as for microscopic evaluation.

Calculation of the creatinine clearance and fractional excretion of sodium gives objective

evidence of the underlying GFR and the degree of parenchymal function.

A chest radiograph and an ECG should be performed to assess the patient's volume status and degree of cardiac dysfunction.

B Pre-existing renal disease

If the GFR is 25% of normal , the kidney loses its ability to correct many different abnormalities.

Fluid and electrolyte homeostasis is altered, which results in

Hypertension

Peripheral edema

Salt retention

Hyponatremia, as a result of fluid retention

Hyperkalemia

Metabolic acidosis, as a result of failure to excrete organic acids (e.g., phosphates, sulfates)

Hematologic functions are altered.

Anemia occurs as the GFR drops, and it becomes profound as the GFR approaches zero.

Coagulation defects occur as a result of altered platelet adhesion and aggregation as well as abnormalities in the coagulation cascade (see Chapter 1, III A ).

Altered calcium metabolism and altered parathyroid hormone metabolism result in secondary hyperparathyroidism and bone disease with hypocalcemia and hyperphosphatemia.

Cardiac and other vascular abnormalities develop, including

Increased incidence of atherosclerosis

Pericarditis and pericardial effusions

P.81

Nutritional status is impaired, secondary to

Proteinuria, which may be as high as 25 g/day

Decreased body stores of nitrogen, which are catabolized as uremia progresses

Decreased dietary intake, which may result from anorexia, nausea, malabsorption, or dietary restrictions placed by the physician

Immune function disorders can result in

Increased urinary tract infections caused by oliguria

Impaired mucocutaneous barriers, which may be secondary to pruritus or epidermal atrophy

Increased pulmonary infections, which are related in part to decreased pulmonary clearance mechanisms

Increased incidence of malignancies

Impaired phagocytosis

Mildly impaired response to vaccines

Impaired elimination of certain viruses, such as hepatitis B virus. This impairment is a major problem in dialysis patients because as many as 60% of these patients become chronic antigen carriers once they contract the infection.

If the GFR is less than 5% of normal, dialysis is required for maintenance of bodily functions.

Dialysis corrects or improves many of the uremic symptoms and abnormalities (e.g., fluid and electrolyte problems, hypertension, nutritional problems related to dietary intake).

Complications related to dialysis

Peritoneal dialysis is associated with an increased risk of peritonitis.

Hemodialysis requires systemic heparin levels that may worsen the coagulopathy of chronic renal failure. In addition, the vascular access necessary for dialysis is associated with blood - borne infections, especially staphylococcal infections.

C Dialysis

Preoperative dialysis

Routine dialysis should be undertaken 24 hours before elective surgery both to minimize the effects of the intravenous heparin given with dialysis and to allow the patient to stabilize after treatment.

More emergent treatment is required for the following conditions:

Hyperkalemia must be addressed expeditiously.

A reading of the potassium level must be obtained immediately preceding surgery, and treatment must be instituted if the level is greater than 5 mEq/L.

ECG changes (e.g., a tall, peaked T wave, loss of P waves, and widened QRS complexes) require immediate treatment. Intravenous calcium will block the effect of excess potassium at the cellular level.

Sodium bicarbonate or a combination of insulin and glucose may be administered intravenously to temporarily shift potassium to the intracellular compartment.

Exchange resins , such as sodium polystyrene sulfonate (Kayexalate), can control potassium levels and may be given as an enema.