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Cerebral Embolization Presenting as Delayed, Severe Obtundation in the Postanesthesia Care Unit After Total Hip Arthroplasty

      Catastrophic neurologic events occur rarely postoperatively and must be diagnosed quickly. A 63-year-old woman who had undergone uneventful total hip arthroplasty experienced obtundation after admission to the postanesthesia care unit. Cranial magnetic resonance imaging revealed multiple lesions consistent with ischemia or infarction, and fat cerebral embolism was diagnosed. We describe the numerous complications that may occur in patients in the postanesthesia care unit and review the differential diagnosis of altered mental status in such pa tients. Paradoxical cerebral fat embolization must be considered in the differential diagnosis of altered mental status after pelvic or long bone fracture or lower extremity major joint replacement, and this condition may occur despite normal pulmonary function and no patent foramen ovale or right-to-left intracardiac shunt. Magnetic resonance imaging with T2-weighted sequences is the cranial imaging study of choice for early evaluation of patients with sudden multifocal neurologic deficits and suspected fat embolism syndrome.
      CT (computed tomography), MRI (magnetic resonance imaging), PACU (postanesthesia care unit)
      Adverse events occur commonly in the postanesthesia care unit (PACU), with a complication rate that may exceed 23% to 30%.
      • Hines R
      • Barash PG
      • Watrous G
      • O'Connor T
      Complications occurring in the postanesthesia care unit: a survey.
      • Zelcer J
      • Wells DG
      Anaesthetic-related recovery room complications.
      • de Mello WF
      • Tully A
      • Restall J
      Morbidity in the postanesthesia care unit [letter].
      Pain (16%percnt;) and nausea-vomiting (8%) are the most common complications. Altered mental status is seen in 3% to 9% of cases (Table 1).
      • Zelcer J
      • Wells DG
      Anaesthetic-related recovery room complications.
      • de Mello WF
      • Tully A
      • Restall J
      Morbidity in the postanesthesia care unit [letter].
      • Van der Walt JH
      • Webb RK
      • Osborne GA
      • Morgan C
      • Mackay P
      The Australian Incident Monitoring Study: recovery room incidents in the first 2000 incident reports.
      Delayed emergence and emergence delirium secondary to anesthetic and analgesic medication administered preoperatively and intraoperatively are the principal causes of postoperative mental status changes, but the differential diagnosis is broad (Table 2). We describe a patient who underwent total hip arthroplasty and experienced obtundation after admission to the PACU. Cerebral fat embolization was detected subsequently.
      Table 1Complications in the Post anesthesia Care Unit
      Data from Hines et al,1 Zelcer and Wells,2 and de Mello et al.3
      ComplicationRate (%)
      Unweighted averages.
      Pain16
      Nausea and vomiting8
      Altered mental status7
      Hypoxemia or hypercapnia7
      Hypotension6
      Cardiac dysrhythmias4
      Upper airway obstruction4
      Hypertension2
      Oliguria1
      Major cardiac event<l
      Hypothermia<l
      Hypergtycemia<1
      * Data from Hines et al,
      • Hines R
      • Barash PG
      • Watrous G
      • O'Connor T
      Complications occurring in the postanesthesia care unit: a survey.
      Zelcer and Wells,
      • Zelcer J
      • Wells DG
      Anaesthetic-related recovery room complications.
      and de Mello et al.
      • de Mello WF
      • Tully A
      • Restall J
      Morbidity in the postanesthesia care unit [letter].
      Unweighted averages.
      Table 2Differential Diagnosis of Altered Mental Status in the Postanesthesia Care Unit
      • Residual or prolonged anesthetic effect or overdose (including vapor agents, sedative-hypnotic agents, barbiturates, opioids. muscle rclaxants)
      • Hypoxemia and/or hypercarbia
      • Hypotension
      • Fluid and electrolyte imbalance (including hyperosmolar syndrome, water intoxication)
      • Metabolic encephalopathy (hepatic, renal, endocrine)
      • Hypothermia or hyperthermia
      • Intraoperative complication (air or paniculate embolism. cerebral ischemia, intracranial hemorrhage, hypoxic encephalopathy, hypotension)
      • Preexisting altered mental status
      • Emergence delirium
      • Interaction with prcoperative medications or illicit drugs
      • Alcohol and drug withdrawal
      • Atypical or allergic medication reaction
      • Seizure (status epilepticus or postictal state)

      REPORT OF A CASE

      A 63-year-old woman who weighed 65 kg and had a history of hypertension controlled with amlodipine-benazepril, idiopathic hypothyroidism treated with Ievothyroxine, and seasonal asthma underwent total hip arthroplasty for degenerative osteoarthritis; a combination of spinal and general anesthesia was used. A preoperative medical evaluation disclosed no evidence of coronary artery or neurologic disease. Her preoperative blood pressure was 110/70 mm Hg. The preoperative laboratory investigation revealed normal findings on electrocardiography and chest radiography, as well as normal serum electrolytes. The preoperative hemoglobin concentration was 11.0 g/dL after she was given 2 U of autologous blood.
      Spinal anesthesia was established with hyperbaric bupivacaine, 12mg, epinephrine, 0.2 mg, and preservative-free morphine, 0.25 mg. General endotracheal anesthesia was induced with propofol, 140 mg, and maintained with isoflurane (0.6%-1.2%) and nitrous oxide-oxygen (0%- 66%). Continuous intraoperative monitoring included electrocardiography, pulse oximetry, capnography, oscillometric blood pressure determinations, and esophageal temperature. The cardiac rhythm remained in normal sinus, and the oxygen saturation was 100% throughout the intraoperative anesthetic course. The systolic blood pressure ranged from 90 to 120 mm Hg, the mean blood pressure ranged from 60 to 80 mm Hg, and the heart rate ranged from 52 to 72 beats/min. Crystalloid, 1300 mL, was administered, and the estimated blood loss was 300 mL during the operative procedure, which lasted 1 hour and 27 minutes.
      While awake, the patient was taken to the PACU and extubated; she responded appropriately to verbal stimuli. Throughout the PACU stay, her blood pressure, monitored at 5-minute intervals, and findings on continuous electrocardiography remained normal; the oxygen saturation by pulse oximetry ranged from 96% to 100%. She complained of nausea and was given intravenous ondansetron, 4.0 mg on 2 occasions. The patient was noted to be lethargic 21½ hours after PACU admission, and over the following 50 minutes, obtundation progressed to the point that reintubation was required for airway protection. Before reintubation, arterial blood gas determinations obtained while the patient was receiving supplemental oxygen via an updraft face tent at 10 L/min revealed a pH of 7.35, Pco2, of 39 mm Hg, Po2 of 91 mm Hg, and oxygen saturation of 96%. The patient exhibited spontaneous eye opening but did not follow commands. Pupillary light and corneal reflexes were preserved, but a left lower facial droop, leftward gaze preference, and minimal withdrawal from painful stimulus were noted. The patient exhibited diffuse hyporeflexia and bilateral extensor plantar reflexes. No skin, conjunctival, or funduscopic abnormalities were found. Intravenous administration of 100 μg of naloxone resulted in no clinical improvement. Electrocardiographic findings, serum electrolytes, and glucose level were normal. Chest radiography showed prominent bilateral interstitial markings. Electroencephalography showed diffuse slowing but no ictal discharges. Findings on cranial computed tomography (CT) without contrast were normal, as were those on cerebral digital subtraction arteriography performed 5 hours after onset of symptoms. Cranial magnetic resonance imaging (MRI) with T 2-weighted sequences performed the following morning revealed multiple cortical and subcortical lesions in both cerebral and cerebellar hemispheres, highly suggestive of an embolic event (Figure 1), and probable cerebral fat embolism was diagnosed. Transesophageal echocardiography with a contrast agent disclosed no patent foramen ovale, intrapulmonary shunting, or cardiac abnormality. Subsequent electroencephalography revealed diffuse slowing, and MRI performed 12 days postoperatively revealed resolution of many of the brain lesions (Figure 2). The patient gradually regained consciousness and her ability to communicate, and she was transferred to a rehabilitation facility 19 days after her initial hospital admission.
      Figure thumbnail gr1
      Figure 1Cranial magnetic resonance images reveal multiple regions of abnormally increased signal intensity. Left, Multiple focal abnormalities in the cerebellum, especially on the left. Right, Multiple cortical and subcortical abnormalities in watershed distributions (regions between large vascular territories) bilaterally and in the left periventricular region.
      Figure thumbnail gr2
      Figure 2Cranial magnetic resonance images obtained 12 days later, demonstrating resolution of a substantial majority of the abnormal signals, suggesting that most of the abnormalities seen initially were areas of transient ischemia.

      DISCUSSION

      Differential Diagnosis of Altered Mental Status

      Delayed emergence from general anesthesia due to the residual effects of oral, intravenous, and inhalational sedative, analgesic, and anesthetic medications is a frequent cause of mental status alteration found in patients in the PACU. This situation may be complicated by preexisting mental dysfunction, postoperative hypothermia, or unrecognized preoperative ingestion of alcohol, opioids, benzodiazepines, and other prescription and illicit drugs that potentiate the effects of anesthesia-related medications (Table 2).
      Emergence delirium, a behavioral manifestation of recovery from general anesthesia ranging from mild confusion and lethargy to extreme excitement and combativeness, is the second most common mental status abnormality found in patients in the PACU. Return of cognitive function after general anesthesia may be slower in the elderly population in the immediate postoperative period, whereas agitation and combativeness are more frequently observed in children and young adults.
      • Mecca RS
      Postoperative recovery.
      Emergence delirium may also be produced by perioperative operative administration of ketamine or an anticholinergic medication such as scopalomine or atropine and by postoperative withdrawal from alcohol or illicit drugs. Moreover, it may be seen preoperatively in patients receiving long-term meperidine. Emergence delirium may be amplified by anxiety and by discomfort such as surgical pain, nausea, pruritis, and gastric or urinary bladder distention.
      Abnormal mental status after surgery may be an indication of hypoxemia and/or hypercarbia due to residual effects of anesthetic agents, incomplete reversal of neuromuscular blockade, airway obstruction, pneumothorax, or pulmonary aspiration.
      • Mathew JP
      • Roscnbaum SH
      • O'Connor T
      • Barash PG
      Emergency tracheal intubation in the postanesthesia care unit: physician error or patient disease?.
      • Daley MD
      • Norman PH
      • Colmenares ME
      • Sandier AN
      Hypoxaemia in adults in the post-anaesthesia care unit.
      • Rose DK
      • Cohen MM
      • Wigglesworth DF
      • DeBoer DP
      Critical respiratory events in the postanesthesia care unit: patient, surgical, and anesthetic factors.
      Rarely, metabolic derangements such as hypoglycemia or hyperglycemia, hyponatremia, hypercalcemia, or hypermagnesemia may contribute to abnormal mental status in patients in the PACU. Finally, once reversible causes of acutely altered sensorium are excluded, neurologic events such as seizure activity and embolic or hemorrhagic stroke must be considered.

      Diagnostic and Therapeutic Approach to Sudden-Onset Altered Mental Status

      Our patient received naloxone in the PACU because of concerns that her respiratory depression might be in part related to her having received intrathecal morphine. Prior studies suggest that naloxone can prevent
      • Johnson A
      • Bengtsson M
      • Soderlind K
      • Lofslrom JB
      Influence of intrathecal morphine and naloxone intervention on postoperative ventilatory regulation in elderly patients.
      and reverse
      • Jones RD
      • Jones JG
      Intrathecal morphine: naloxone reverses respiratory depression but not analgesia.
      respiratory depression due to intrathecal morphine. We did not think that intrathecal morphine caused obtundation in our patient. However, administration of naloxone enabled us to exclude an adverse drug effect as a contributing factor in our patient's altered mental status.
      Spinal anesthesia with intrathecal morphine, in combination with light general anesthesia, was used because of reported benefits of spinal anesthesia, including less blood loss and lower risk of thrombophlebitis. We have also found that patients return more rapidly to a normal mental status with light general anesthesia than with deeper sedation, particularly elderly patients. However, general anesthesia alone and spinal anesthesia alone are widely accepted techniques for total hip arthroplasty. We do not believe that the choice of anesthesia had a bearing on our patient's postoperative condition.
      The diagnosis of basilar artery thrombosis should be considered in a patient who becomes unresponsive suddenly and spontaneously and has signs of bilateral corticospinal tract dysfunction, including quadriparesis with or without spasticity, ankle clonus, and extensor plantar responses. In the early period after a brainstem stroke, patients may have spinal shock consisting of hypotonic quadriparesis, absent muscle stretch reflexes, and absent plantar responses. Our patient had sudden unresponsiveness and bilateral extensor plantar responses, suggesting basilar artery thrombosis; however, other findings on the neurologic examination, such as lower facial paresis, suggested multifocal bihemispheric dysfunction. Ischemic stroke is a complication of general surgery in 0.08% to 2.9% of cases and typically occurs within the first 2 weeks after the procedure.
      • Limburg M
      • Wijdicks EF
      • Li H
      Ischemie stroke after surgical procedures: clinical features, neuroimaging, and risk factors.
      Findings on CT without contrast and on digital subtraction angiography were normal in our patient, but results of MRI were strikingly abnormal and supportive of the diagnosis of cerebral fat embolism. Other investigators have found that T2-weighted MRI is sensitive for detecting cerebral fat embolism, even in the acute stage.
      • Takahashi M
      • Suzuki R
      • Osakabe Y
      • et al.
      Magnetic resonance imaging findings in cerebral fat embolism: correlation with clinical manifestations.
      • Stoeger A
      • Daniaux M
      • Felber S
      • Stockhammer G
      • Aichner F
      • zur Nedden D
      MRI findings in cerebral fat embolism.
      • Bardana D
      • Rudan J
      • Cervenko F
      • Smith R
      Fat embolism syndrome in a patient demonstrating only neurologic symptoms.
      • Yoshida A
      • Okada Y
      • Nagata Y
      • Hanaguri K
      • Morio M
      Assessment of cerebral fat embolism by magnetic resonance imaging in the acute stage.
      Magnetic resonance imaging is more sensitive than CT in detecting cerebral fat embolism.
      • Stoeger A
      • Daniaux M
      • Felber S
      • Stockhammer G
      • Aichner F
      • zur Nedden D
      MRI findings in cerebral fat embolism.
      • Satoh H
      • Kurisu K
      • Ohtani M
      • et al.
      Cerebral fat embolism studied by magnetic resonance imaging, transcranial Doppler sonography, and single photon emission computed tomography: case report.
      and the extent of T2-weighted abnormalities correlates with the severity of neurologic impairment.
      • Takahashi M
      • Suzuki R
      • Osakabe Y
      • et al.
      Magnetic resonance imaging findings in cerebral fat embolism: correlation with clinical manifestations.
      We suggest that, when feasible, an emergent brain MRI with T2-weighted sequences be the first cranial imaging study performed in patients with sudden multifocal neurologic deficits after total hip arthroplasty. Magnetic resonance imaging may be particularly useful in patients with fat embolism who demonstrate only neurologic signs.
      • Bardana D
      • Rudan J
      • Cervenko F
      • Smith R
      Fat embolism syndrome in a patient demonstrating only neurologic symptoms.
      Transcranial Doppler ultrasonography is also helpful in diagnosing fat emboli. In the case of long bone fractures, transcranial Doppler ultrasonography can detect transient microemboli resolving within 4 days after injury.
      • Forteza AM
      • Koch S
      • Romano JG
      • et al.
      Transcranial Doppler detection of fat emboli.

      Fat Embolism Syndrome

      Systemic embolization associated with lower extremity intramedullary operative procedures may not become evident clinically until several hours postoperatively and may present as mental status change without associated pulmonary dysfunction.
      • Heine TA
      • Halambeck BL
      • Mark JB
      Fatal pulmonary fat embolism in the early postoperative period.
      • Findlay JM
      • DcMajo W
      Cerebral fat embolism.
      • Font MO
      • Nadal P
      • Bertran A
      Fat embolism syndrome with no evidence of pulmonary involvement [letter].
      • Jacobs S
      • al Thagafi MY
      • Biary N
      • Hasan HA
      • Sofi MA
      • Zuleika M
      Neurological failure in a patient with fat embolism demonstrating no lung dysfunction [letter].
      Embolic showers of medullary contents occur in almost all cases of pelvic and long bone fractures and lower extremity major joint replacement.
      • ten Duis HJ
      The fat embolism syndrome.
      • Christie J
      • Robinson CM
      • Pell AC
      • McBirnie J
      • Burnett R
      Transcardiac echocardiography during invasive intramedullary procedures.
      • Lafont ND
      • Kalonji MK
      • Barre J
      • Guillaume C
      • Boogaerts JG
      Clinical features and echocardiography of embolism during cemented hip arthroplasty.
      However, the fat embolism syndrome, characterized by progressive respiratory dysfunction, petechiae, thrombocytopenia, and mental status deterioration, is uncomrnon.
      • ten Duis HJ
      The fat embolism syndrome.
      • Ereth MH
      • Weber JG
      • Abel MD
      • et al.
      Cemented versus non-cemented total hip arthroplasty-embolism, hemodynamics, and intrapulmonary shunting.
      • Bulger EM
      • Smith DG
      • Maier RV
      • Jurkovich GJ
      Fat embolism syndrome: a 10-year review.
      • Byrick RJ
      Cement implantation syndrome: a time limited embolic phenomenon [editorial].
      Respiratory insufficiency may occur and is generally manifested as dyspnea and hypoxemia. The most likely pathogenesis of respiratory insufficiency in the fat embolism syndrome is noncardiac pulmonary edema secondary to lung injury from fat deposition in the pulmonary circulation.
      In the general population, a patent foramen ovale has an incidence of approximately 25% in the 4th through 8th decades of life, and paradoxical embolization of fat, air, microthrombi, spicular bones, and other intramedullary debris may occur via this passage.
      • Hagen PT
      • Scholz DG
      • Edwards WD
      Incidence and size of patent foramen ovale during the first 10 decades of life: an autopsy study of 965 normal hearts.
      • Etchells EE
      • Wong DT
      • Davidson G
      • Houston PL
      Fatal cerebral fat embolism associated with a patent foramen ovale.
      • Pell AC
      • Hughes D
      • Keating J
      • Christie J
      • Busuttil A
      • Sutherland GR
      Brief report: fulminating fat embolism syndrome caused by paradoxical embolism through a patent foramen ovale.
      Transpulmonary systemic embolization may also occur. In an animal orthopedic surgery model, fat globules were observed to traverse the pulmonary circulation readily, and transesophageal Doppler echocardiography in 6 patients who had developed the fat embolism syndrome after long bone fractures showed no evidence of an intracardiac right-to-left shunt or patent foramen ovale.
      • Fabian TC
      Unravelling the fat embolism syndrome [editorial].
      • Byrick RJ
      • Mullen JB
      • Mazer CD
      • Guest CB
      Transpulmonary systemic fat embolism: studies in mongrel dogs after cemented arthroplasty.
      • Nijsten MW
      • Hamer JP
      • ten Duis HJ
      • Posma JL
      Fat embolism and patent foramen ovale [letter].
      Contrast echocardiography may not detect transpulmonary migration of fat emboli. We suspect that the different rheological properties of air and fat may explain the lack of detection of a shunt on air-contrast echocardiographv in our patient.
      The diagnosis of the fat embolism syndrome is usually presumptive in the setting of severe trauma and/or orthopedic surgery. It should be considered in any patient who develops confusion, respiratory distress, and/or petechiae within 3 days of such an event.
      Our patient had a delayed onset of neurologic symptoms despite the fact that embolization likely began intraoperatively. The most plausible explanation for this delayed presentation is from a study by Forteza et al
      • Forteza AM
      • Koch S
      • Romano JG
      • et al.
      Transcranial Doppler detection of fat emboli.
      who demonstrated that, in patients with long bone fractures, fat microembolization occurs 3 to 4 days after the fracture. Neurologic symptoms probably appear only after a threshold lesion burden has developed within the central nervous system.
      Treatment of the fat embolism syndrome is generally supportive and directed at management of the arterial hypoxemia. Such support ranges from supplemental oxygen to full mechanical ventilation depending on the severity of lung injury. Prophylactic corticosteroids have been used successfully to reduce the incidence of the fat embolism syndrome in patients with skeletal trauma.
      • Schonfeld SA
      • Ploysongsang Y
      • DiLisio R
      • et al.
      Fat embolism prophylaxis with corticosteroids: a prospective study in high-risk patients.
      • Kallenbach J
      • Lewis M
      • Zallzman M
      • Feldman C
      • Orford A
      • Zwi S
      'Low-dose' corticosteroid prophylaxis against fat embolism.
      The indications for corticosteroids, mechanism of protection, and dose range remain ill defined. In addition, concerns of increased infection rates and poor wound healing limit the widespread use of corticosteroids in this setting.

      CONCLUSIONS

      Although delayed emergence from general anesthesia and/or sedatives and emergence delirium are the most common causes of mental status changes found in the PACU setting, immediate evaluation must also include consideration of potentially catastrophic conditions such as hypoxemia, incomplete reversal of neuromuscular blockade, and pulmonary aspiration. Cerebral fat embolization is unusual, but it must always be considered in the differential diagnosis of mental status changes in the setting of pelvic and long bone fractures as well as lower extremity major joint replacement because embolic showers of medullary debris occur in virtually all these cases. The diagnosis is clinical, and no specific test is conclusive. Cerebral fat embolization may occur without associated pulmonary dysfunction and is not ruled out by lack of a patent foramen ovale. Emergent brain MRI with T2-weighted sequences is the cranial imaging study of choice for early evaluation of patients with sudden multifocal neurologic deficits after pelvic or long bone fracture or lower extremity major joint replacement.

      ACKNOWLEDGMENT

      We thank Dr Frank W. Rubino for providing clinical follow-up information.

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