General Principles of Postoperative Intensive Care Unit Care

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35

General Principles of Postoperative Intensive Care Unit Care

Regionalization within a health care structure allows for more efficient control and use of limited resources. The intensive care unit (ICU) contains specially trained staff and a variety of support devices, such as mechanical ventilators, intra-aortic balloon pumps, ventricular assist devices, and dialysis machines, which in most cases cannot be used elsewhere. Optimally, the location of a patient is determined by matching the patient’s needs with a location’s resources and expertise.

Generally, the surgical ICU is where experience, staffing, skills, and technology converge to provide services that cannot be provided anywhere else within the hospital. Highly skilled nurses, often greater in number than the patients themselves, work intimately with intensivists and ancillary staff in an environment designed to stabilize, diagnose, and simultaneously treat the most acutely ill patients. ICU management by intensivists allows for improved staff and family satisfaction, reduced complication rates, lower costs, shorter length of stay, improved processes of care, and a morbidity and mortality risk advantage.1–4 ICU systems focused on an environment of safety and compliance with evidence-based standards promote improvement in many outcome metrics.5 Safe and efficient patient throughput allows for greater institutional procedural volume, which, when paired with surgeon procedural volume, has been shown to be associated with reduced mortality risk.6

Classic postoperative indications for ICU admission include advanced age or prolonged duration of the operation, both criteria without specifically defined thresholds. Other factors, such as the need for mechanical ventilation, volume resuscitation, or administration of vasoactive medications, make ICU care unavoidable. Monitoring of level of consciousness, airway, bleeding, pulses, rhythm, acidosis, urine output, and global perfusion also is facilitated by ICU admission. Identifying patients who may need postoperative ICU care can be difficult. Although there are scoring systems to assess risk and fatality (APACHE, SAPS, MPM, SOFA), it is difficult to apply these predictions to specific disease states or individual patients. Some prediction models utilize physiologic data for patients after admission to the ICU and have not been validated as preadmission screening tools.7,8 Physicians may predict mortality risk even better than scoring systems.9 In practice, most physicians do not use these tools to determine postoperative ICU admission. Admission criteria based on priority, diagnosis, and objective parameter models have been published by the Task Force of the American College of Critical Care Medicine and the Society of Critical Care Medicine.10

Postoperative Evaluation

Obtaining a comprehensive medical and surgical history is a fundamental step in understanding a patient in the surgical ICU. The medical record, traditionally written but now more commonly electronic, should contain all of the elements necessary to assemble the story up until the time of ICU admission, although deciphering a chart, particularly when it is long, requires time, patience, and detective skills. Data gathering usually begins by word of mouth from the providers delivering the patient. Effective “hand-off” is essential to maintain the continuity of care and to ascertain important operative events that may have escaped documentation. It is in fact a standard expected by The Joint Commission.11 Certain questions are common to virtually all admissions:

Age, comorbid conditions, and emergency operations all affect mortality risk. The details of the operation are key, often aided by diagrams in the chart. Resections, diversions, anastomoses, transplantations, use of prosthetic materials, and other surgical findings are some of the details that should be obtained. In addition, the type and location of each drain must be accounted for. Only by knowing where a drain is placed can a care provider know how to interpret the quantity and quality of the effluent. Each drain or wire must be labeled correctly. Also, the completion of wound closure must be ascertained (skin and fascia closed?). Finally, if the operation was incomplete or intentionally staged, the health care provider needs to inquire about intentions and timing of return to the operating room.

The significance of the anesthesia record should not be minimized. The details about trends in gas exchange, blood pressure, urine output, medications, and summary fluid balance should be reviewed. Always identify if the intubation was easy or difficult. Reviewing the ventilator settings that were used in the operating room sheds some light on any possible gas exchange difficulties and provides a first opportunity to make corrections. Tidal volumes in the operating room are often much larger than those used in the ICU. Identification of current medications and the purpose of each help to formulate short-term therapeutic strategies. Assessing the adequacy of intraoperative resuscitation begins with a review of the quantifiable gains and losses. Resuscitation fluids, blood products, urine output, cavity fluid, and blood losses should all be reviewed. Evaporative and extravascular (third space) losses may be more difficult to accurately quantitate. Major surgical procedures such as bowel resection can require 7 to 8 mL/kg/hour of resuscitation fluid and severe blunt or penetrating injury 10 to 15 mL/kg/hour to match these loses. Underresuscitation may occur in patients with congestive heart failure or anuric renal failure for fear of creating a state of uncorrectable fluid overload. What amounted to adequate resuscitation in the operating room may not be the case by the time the patient arrives in the ICU. A careful reassessment of the adequacy of resuscitation is necessary in virtually all postoperative ICU admissions. Typical postoperative maintenance intravenous fluid rates are 80 to 125 mL/hour, but can be substantially higher in the presence of ongoing intravascular volume loss. Isotonic fluids are the most appropriate maintenance fluids. It is useful to inquire about the last time the patient received narcotics, benzodiazepines, or paralytics and if reversal agents were given. Finally, any intraoperative laboratory values, particularly ones that require immediate attention, should be reviewed.

When time permits, attention should be directed back to the medical record. The clinician should scan the history and physical examination, progress notes, and consultations to develop a cohesive story line of events that led up to the operation. Did the illness have an impact on nutrition or functional state? How are other comorbid conditions or past operations related to the current presentation? The past medical history and the medication list should be scrutinized; the two are complementary. Inclusion of a disease in the past medical history and absence of an expected medication warrants further investigation (and vice versa). The medication list should be scanned in particular for antiseizure medications, bronchodilators, antihypertensives, antiarrhythmics, anticoagulants, diuretics, steroids, thyroid replacement, and insulin. It must be decided which medications must be continued in the immediate postoperative period and which can be temporarily delayed. If antibiotics were administered preoperatively, the clinician should identify what they were and how long had they been given and for what indication. In general, if administered preoperatively, bronchodilators, steroids, and insulin are resumed postoperatively. Long-acting antihypertensives should be avoided in the early postoperative period, and short-acting intravenous agents should be used to control hypertension. Diuretics should be avoided in the immediate postoperative period unless directed by invasive monitoring or required because of some other medical necessity. The use of early postoperative beta blockade in patients with coronary artery disease is encouraged if the overall hemodynamic performance allows. Most other medications can be safely delayed until the postoperative patient has shown satisfactory cardiopulmonary performance and stability.

Postoperative laboratory, imaging, and electrocardiogram studies should be selected on a case-by-case basis. Patients who have been moved from operating room table to bed and then transported for any distance are at risk for displacement of tubes and catheters. The admission chest radiograph allows for the evaluation of intravascular catheter and endotracheal, nasogastric, and thoracostomy tube positions in addition to visualization of the pleural, mediastinal, and parenchymal structures. Measurements of blood counts and chemistries are usually routine, but may be deemed unnecessary if preoperative or intraoperative values were unremarkable and the operation was uneventful. Laboratory abnormalities should be followed closely until a favorable trend is established. Patients at risk for perioperative myocardial injury or with new intraoperative arrhythmias should have an electrocardiogram and possibly cardiac enzyme determination.

The physical examination of the patient completes the initial postoperative evaluation. It starts as a cursory survey and concludes as a detailed examination. The examination should expose all parts of the patient that can be accessed, and the examiner should inspect and palpate the patient. Areas that are not under examination should be kept covered to preserve body temperature. If the bed sheets are being changed, it presents an opportunity to examine the back of the patient. An initial assessment of the vital signs, skin, pulses, and urine output provides preliminary insight into clinical perfusion (Box 35.1).

Box 35.1   Support for Adequate Clinical Perfusion

The endotracheal tube, if present, needs to be secured adequately. The health care provider should listen for obvious air leaks around the cuff. The presence of nasal or oral gastric tubes should be noted. All drainage tubes should be identified, and the quality and quantity of output should be scrutinized: Is it serous? Sanguineous? Bilious? Drainage from raw, inflamed surfaces is often serosanguineous. Frankly bloody drainage in quantities of more than 100 mL/hour suggests either surgical bleeding or coagulopathy. All intravascular catheters should be identified with the goal of determining which should be retained for use and which should be removed. Diagnostic catheters often remain unnoticed, and unused, particularly when in femoral vessels. Intravenous catheters not placed under sterile conditions should be removed immediately.

The neurologic examination may be suboptimal if the patient is still under the effects of anesthesia. Reducing or temporarily withholding narcotics and sedation can provide a window to complete a neurologic assessment. If further analgesia or sedation is still required, it may be resumed after the neurologic assessment. However, withholding sedation should not be done in the early postoperative course if it results in a state of competition with care (severe agitation, inability to oxygenate/ventilate, hemodynamic instability).

Intubation, general anesthesia, and mechanical ventilation can result in a variety of airway or parenchymal injuries. Breath sounds should be equal bilaterally. Asymmetry can be caused by atelectasis (possibly endotracheal tube malposition), pleural effusions, or pneumothorax and can be excluded by careful review of the chest radiograph. Examination of the respiratory system should include evaluation of thoracostomy tubes and the mechanical ventilator if present. Except in the case of pneumonectomy, thoracostomy tubes should be placed to suction pending demonstration of sustained lung inflation or resolution of significant drainage. The mechanical ventilator settings and airway pressures should be noted. Adjustments to mechanical ventilation may need to be made to accommodate shivering, metabolic abnormalities, and hypoxia in the early postoperative period. The clinician should ensure satisfactory initial oxygen saturation and avoid excessive tidal volumes. End-tidal carbon dioxide monitoring facilitates adjustment in ventilation and progress in weaning. Routine blood gas analysis is unnecessary but will be required to manage the more challenging derangements in gas exchange and acid/base disorders.

The cardiovascular examination is primarily directed at assessment of adequate clinical perfusion. Impressions from the initial survey of clinical perfusion plus any available data from invasive monitoring can be used to assess appropriate hourly maintenance fluid rate and the need for further volume resuscitation. Cardiac surgery patients may have mediastinal drains and pacing wires. The former should be connected to suction, and the quantity and quality of drainage should be scrutinized. Pacing wires should be tested for function on admission and can be capped if pacing is not needed. If a postoperative patient comes to the ICU with a permanent pacemaker or an implantable cardiac defibrillator, the device should be interrogated for mode and function at the earliest convenience.

In contrast to the lungs and heart, which can be imaged easily and whose function can be monitored objectively, the abdomen and its contents cannot be evaluated handily. The persistence of anesthesia or administration of narcotics can remove many of the signs and symptoms typically relied on to signal problems. Examination should focus on baseline location and quantity of pain, presence of abdominal distention, firmness to palpation, and quality and quantity of effluent from drains. Bleeding and progressive visceral edema can cause a rapid distention and loss of compliance of the abdomen, often before other findings occur, such as reduction in hemoglobin concentration, urine output, and blood pressure. Frequent follow-up examinations compared with baseline data may be the earliest way of recognizing an intra-abdominal catastrophe. The practitioner should be alert to abdominal distention with associated changes in clinical perfusion (such as low urine output) as a marker of abdominal compartment syndrome. Measurement and trending of bladder pressures can supplement other clinical findings in guiding decision making.

Knowing where the tip of each abdominal drain lies is necessary to evaluate the effluent. A drain lying outside the bowel or biliary system should not drain succus or bile. A drain that suddenly shows these fluids may herald loss of integrity of a surgical repair or de novo perforation. Unexplained or unexpected changes in the quantity of effluent from a drain also are notable.

Abdominal wounds are not always closed at the end of an operation. The clinician needs to determine if the skin or fascia has been left open and, if so, what kind of temporary closure is employed. If a temporary abdominal closure device is used, the quality and quantity of effluent from that device should be examined and documented. It is important to remember that temporary abdominal closure devices are not proof against abdominal compartment syndromes. The provider should be prepared to loosen the outer layers of an abdominal closure or dressing to provide temporary relief. Surgical or traumatic wounds, regardless of location on the body, should be examined for closure integrity, erythema, and induration.

Examination of pulses is important after vascular surgical procedures. Scheduled reassessments should document the presence and strength of pulses. Sudden reduction or loss of pulse signal can represent proximal vascular occlusion, a distal outflow obstruction, or increase in compartment pressures. Baseline cyanosis and mottling of extremities should be noted for subsequent comparison. In addition, a clinical examination (palpation) of the compartments should be performed to provide the practitioner a baseline for further comparison. Should the mechanism of injury increase the risk of muscle swelling and compartment syndromes, the practitioner can utilize invasive monitoring to measure compartment pressures, and should be prepared to pursue extremity fasciotomies.

Evaluation of a postoperative trauma patient in the ICU can be restricted by the presence of dressings and immobilizing casts and neck collars. Sometimes only toes or fingers are visible for examination. Postoperative admission to the ICU is a good opportunity to look for injuries missed during the initial evaluation and management period. In addition, the practitioner should be alert to potential iatrogenic injuries from intraoperative events; this would include electrical burns from ungrounded cautery circuits, infiltrated intravenous lines, and compression injuries from positioning in the operating room.

Recovery From Anesthesia

Postoperative Resuscitation

Assessment

“Adequate resuscitation” is a state, often temporary, that allows for good clinical perfusion and physiologic stability. Patients with good clinical perfusion (expected heart rates, blood pressures, and urine outputs; absence of acidosis) may require no further resuscitation other than maintenance intravenous fluids. The correct maintenance fluid rate will be just enough to match intravascular losses out of proportion to that which is mobilizable from the interstitium but not so much as to needlessly expand the third space or interstium with edema. Subtle abnormalities in any of these parameters of perfusion may suggest a more serious physiologic derangement warranting further investigation and intervention. Resuscitation is the process of optimizing macroscopic and microscopic metabolic substrate delivery with the goal of avoiding an imbalance between supply and demand. The most fundamental concept is to ensure adequate oxygen delivery (DO2) and meet the oxygen consumption (image) needs of tissues and organelles. Because the moment when image exceeds DO2 is difficult to determine, resuscitation “targets” serve as proxy markers of adequate DO2. Resuscitation targets are reproducible, quantifiable values, such as pressures, outputs, metabolites, inflammatory mediators, or oxygen saturations, which represent therapeutic goals. Resuscitation targets provide an important opportunity for study and outcome validation. Despite the seemingly simple logic of employing resuscitation targets, few of these therapeutic goals have been shown to improve clinical outcome. Even routine data derived from a pulmonary artery catheter have not been shown to improve outcome in patients undergoing surgery with decompensated cardiogenic shock or acute lung injury.12,13

Management Theory

Evaluation and optimization of blood pressure, filling pressures, DO2, heart rate, and rhythm often occur simultaneously, particularly in unstable patients (Fig. 35.1). This may require ongoing volume resuscitation and support with vasopressors and inotropes. Restoration of “normal” blood pressure, heart rate, and urine output, however, do not ensure adequate DO2 at the level of the microvasculature.14 Overzealous resuscitation and supranormal DO2 not only do not improve outcome but also may be detrimental.15 Not all patients require the same type of resuscitation. Although the fundamental principles are the same, the particular resuscitation technique end points may differ among the different types of shock.16,17 Crystalloid resuscitation may be appropriate in septic shock but detrimental in the early resuscitation of penetrating traumatic injury.18,19 Even low-volume resucitation plays a role in the management of patients with penetrating traumatic injury or severe intraoperative hemorrhage.20 Early goal-directed therapy with parameter-specific targets has not completely survived prospective validation. However, the principle of timely intervention remains a cornerstone for virtually all types of resuscitation. End points specific to particular mechanisms of injury can vary significantly.21–23

Targeted resuscitation strategies provide an orderly approach to resuscitation, monitoring, and outcome validation. In general, such strategies optimize cardiovascular performance and concurrently measure markers of adequate global DO2 and image. Increased serum lactate concentration, decreased mixed venous oxygen saturation, and decreased central venous oxygen saturation are the proxy markers for inadequate global DO2. However, normal values of mixed venous oxygen saturation and central venous oxygen saturation do not guarantee normal use of oxygen in the tissues, particularly at the regional level. Appropriate targets for microcirculatory resuscitation remain elusive. Noninvasive techniques have reduced the need to obtain physiologic data by the use of a pulmonary artery catheter.24 Pulse and pressure wave analysis along with their derivitives (cardiac output and stroke volume variation) offer a less invasive way of measuring hemodynamic performance and predict volume responsiveness in the appropriate patient population.25 Gastric tonometry, sublingual capnography, near-infrared spectroscopy, and orthogonal polarization spectral imaging are less mainstream technologies available to assess the effectiveness of resuscitation at the regional level.26

Resuscitation products should target the intravascular components that are inadequate, including red blood cell concentrates, platelets, coagulation factors, and acellular resuscitation fluids. Fluid type, bolus volume, and maintenance rate must be individualized. The optimal resuscitation fluid effectively should expand the intravascular space and minimize the inflammatory response (particularly in hemorrhagic shock27,28). All resuscitation fluids leak to some degree out of the intravascular space into the interstitium of the extracellular space. Hypotonic resuscitation fluids are inappropriate for volume resuscitation because of their inability to remain exclusively in the extracellular space. Volume per volume, hypertonic fluids cause more intravascular expansion than isotonic fluids. Hypertonic fluids yield no better outcomes than isotonic crystalloids, however, in the resuscitation of trauma patients.29 Similarly, isotonic crystalloids are at least as efficacious or may be better than colloids to reach the same end points.14 In trauma, burn, and general surgery patients, resuscitation with colloids, as compared to crystalloids, has not been shown to reduce the risk of death.30

Metabolic consequences are associated with virtually all resuscitation fluids. Ringer’s lactate can activate neutrophils and cause a potent inflammatory response.31 Hypertonic saline and dextran combinations cause less of an inflammatory response but any mortality benefit is unproved.32,33 Greater than 1 L of hypertonic saline typically results in the development of hypernatremia. Resuscitation exclusively with isotonic NaCl results in a hyperchloremic acidosis. Recent literature has suggested that hetastarch is associated with greater adverse events when compared to saline resuscitation.34 Hetastarch can cause coagulopathy if greater than 1.5 L is given. All acellular resuscitation fluids, if given in sufficient quantities, cause dilutional anemia. As one can infer from this confusing and sometimes contradictory collection of recommendations, no single resuscitation fluid is satisfactory on its own.

Temperature Control

Postoperative patients can come to the ICU with moderate to severe hypothermia. Heat is lost in the operating room as a result of vasodilation from volatile anesthetics, cool intravenous fluids and air temperature, large open surfaces, and evaporation. Excluding patients with potentially anoxic central nervous system injuries,35 hypothermia complicates initial postoperative care by creating an in vivo coagulopathy, even when in vitro coagulation studies (normalized to 37° C) are normal. In trauma patients, reduction in enzyme activity and platelet function, leading to abnormal fibrin polymerization, occurs at temperatures less than 34° C.36 Care must be taken when administering large volumes of cold blood products or even room temperature crystalloids. Fluid warming devices are available not only to prevent but also to treat hypothermia. All patients with postoperative hypothermia less than 36° C should be actively warmed with forced air blankets, and when normothermia has been achieved, patients should be kept covered to prevent heat loss. Active warming does not cause peripheral vasodilation and subsequent hypotension, and it does not paradoxically cause core cooling owing to heat exchange in cold extremities.

Awakening from Anesthesia

Before completing a successful resuscitation, sedation, analgesia, and anxiolysis should be maintained to facilitate patient comfort and to prevent interference with medical care (e.g., mechanical ventilation or motor activity jeopardizing airway, drains, and intravenous catheters). Selected agents should have minimal hemodynamic sequelae and relatively short duration of action so that frequent neurologic assessment can be performed. Daily interruption of continuous sedation has been shown to reduce ICU length of stay, duration of mechanical ventilation, and incidence of posttraumatic stress disorder.37,38

Narcotics such as fentanyl, morphine, and hydromorphone make ideal first-line analgesics. Delivered by continuous infusion and supplemented as needed, successful analgesia reduces pain-driven tachycardia and hypertension and facilitates cough and deep breathing. The sensation of anxiety is a potent dysphoric stimulus that can result in restlessness and interfere with care. Anxiety can be treated with short-acting intravenous benzodiazepines, such as lorazepam. Very short-acting benzodiazepines, such as midazolam, are less useful because of the dosing frequency necessary to prevent symptoms from returning. It is important not to use scheduled benzodiazepines to treat restlessness due to delirium. This practice can exacerbate delirium and worsen outcomes. Delirium can be identified using simple evaluation tools such as the Confusion Assessment Method for the ICU (CAM-ICU). Competitive restlessness due to delirium is best managed with atypical antipsychotics such as haloperidol, ziprazadone, and quetiepine.39 Persistant restlessness, agitation, or delirium can compete with mechanical ventilation, confound hemodynamic stability, and impede the provision of care. If further reduction of level of consciousness is necessary, propofol or dexmedetomidine can be added and titrated to desired effect. Dexmedetomidine, a weak analgesic, can reduce narcotic requirements.40 Propofol, however, has no intrinsic analgesic properties. In a patient who has serious pain, neither propofol nor dexmedetomidine should be used without the concurrent administration of a narcotic. The use of most agents mentioned can be limited by their tendency to reduce blood pressure and, in the case of dexmedetomidine, decrease heart rate.

When patients are resuscitated adequately, consideration can be given to awakening from residual sedation. On arrival to the surgical ICU or recovery room, unconsciousness, if present, is due to the residual effects of volatile anesthetics, narcotics, benzodiazepines, and paralytics. The effects of volatile anesthetics can persist for 20 to 60 minutes after their discontinuation, particularly if the agent is fat-soluble, the patient is obese, and the surgery was long. Paralytics can have longer than expected duration of action, and this should be suspected when a postoperative patient remains very weak (cannot perform a 10-second head lift) or does not move. A train-of-four twitch monitor can address this issue. Persistent chemical paralysis can be reversed with neostigmine and glycopyrrolate.

Reentry into consciousness may be accompanied by disorientation, anxiety, pain, and varying degrees of restlessness. In the absence of underlying encephalopathy, it is usually possible to get patients to follow commands, answer questions, and participate in the extubation process. The discomfort of an endotracheal tube can lead to unplanned self-extubation. It is important for the bedside care provider to maintain control of the recovery process by ensuring analgesia and anxiolysis. Small doses of narcotic or benzodiazepine or both can usually correct these problems without inducing further sedation and delay of extubation.41 Patients with encephalopathy resulting from sepsis or shock may not recover a level of consciousness that allows participation in the weaning process. It is controversial whether such a patient should be extubated (avoiding the complications of prolonged extubation) or remain intubated until the ability to protect the airway is more certain. Dexmedetomidine can reduce restlessness without respiratory suppression and may be useful to facilitate extubation of a restless patient. Patients who require sedation for an extended time should receive doses of medication no higher than necessary to achieve the therapeutic target. Sedation scales, such as the Ramsay and Richmond Agitation Sedation Scale,42 are useful to avoid oversedation and ultimately promote earlier liberation from mechanical ventilation.

Postoperative Extubation

Liberation from mechanical ventilation requires clinical readiness to begin weaning and demonstration of adequate physiologic reserve before extubation. Clinical readiness assesses completion of perioperative tasks at hand and questions any need for early return to the operating room. Resuscitation should be complete, hemostasis should be achieved, metabolic acidosis should be resolving, vasoactive support and gas exchange abnormalities should be minimized, anesthetic agents should be cleared, the ability to protect the airway should be present, and the patient should be awake and reasonably cooperative. These criteria have not been validated clinically, but similar consensus guidelines have been published.43 Daily, if not more frequent, reassessment of clinical readiness is necessary to determine if it is reasonable to consider weaning.44

Patients who are ready clinically to progress to extubation should have an assessment of physiologic reserve. Having the patient breathe without mechanical assistance allows observation of respiratory rate, mechanical coordination of chest and abdomen, vital signs, end-tidal carbon dioxide concentration, and subjective comfort. If the patient was not mechanically ventilated preoperatively, the perioperative course has been uneventful, the patient is comfortable with stable vital signs, no tachypnea or respiratory muscle dyssynchrony is present, and there is no short-term plan to return to the operating room, the patient should begin spontaneous breathing trials and be evaluated for extubation.

Patients who do not achieve these basic criteria may require continued mechanical ventilation that maximizes patient comfort and unloads the respiratory muscles. These patients require a structured, evidence-based approach to ventilator weaning and assessment of adequate physiologic reserve. For more detailed information on weaning, refer to Chapter 43.

Best Practices

Achieving optimal outcomes should be pursued by providing optimal care. This is especially true for patients with longer length of stay. Effort should be expended pursuing interventions that have been shown to reduce complications, cost, morbidity, and mortality risk. Because a postoperative ICU patient is different in many ways from other ICU patients, some of these fundamental practices are applied with slight nuance and warrant additional mention.

Prevention of Venous Thromboembolism and Deep Venous Thrombosis

All postoperative ICU patients should be considered for venous thromboembolism (VTE) or deep venous thrombosis (DVT) prophylaxis. The risk of postoperative VTE depends upon both the type of procedure and modifying attributes such as age, prior VTE, history of cancer, obesity, or hypercoagulable state. Risk has been quantified and grouped based on the Modified Caprini Risk Assessment Model.45 Low-risk general and abdominal-pelvic surgery patients should receive intermittent pneumatic compression (IPC) over no prophylaxis or anticoagulant-based prophylaxis. Moderate-risk general and abdominal-pelvic surgery patients should receive anticoagulant-based prophylaxis. Low-dose unfractionated heparin, low-molecular-weight heparin, or fondaparinux should be started in the absence of postoperative bleeding. High-risk general and abdominal-pelvic surgery patients should receive low-dose unfractionated heparin three times a day, low-molecular-weight heparin, or fondaparinux. The highest risk patients should receive mechanical prophylaxis via IPC devices, in addition to low-dose unfractionated heparin, low-molecular-weight heparin, or fondaparinux. In general surgery patients with a high risk of postoperative bleeding, mechanical prophylaxis should be the initial preventive modality until the risk of bleeding has decreased enough to allow for anticoagulant prophylaxis.46

Neurosurgical procedures or the use of neuraxial analgesia also require special consideration. Anticoagulant prophylaxis should not be in effect while epidural catheters are placed or removed and should be used with caution while an epidural catheter is in place. Patients undergoing intracranial surgery should receive mechanical prophylaxis with sequential compression devices. Anticoagulant prophylaxis should be added in neurosurgical patients at high risk for VTE/DVT beginning 24 hours postoperatively.

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