Incidence and characteristics of cerebral hypoxia after craniectomy in brain-injured patients: a cohort study

OBJECTIVE

After craniectomy, although intracranial pressure (ICP) is controlled, episodes of brain hypoxia might still occur. Cerebral hypoxia is an indicator of poor outcome independently of ICP and cerebral perfusion pressure. No study has systematically evaluated the incidence and characteristics of brain hypoxia after craniectomy. The authors' objective was to describe the incidence and characteristics of brain hypoxia after craniectomy.

METHODS

The authors included 25 consecutive patients who underwent a craniectomy after traumatic brain injury or intracerebral hemorrhage and who were monitored afterward with a brain tissue oxygen pressure monitor.

RESULTS

The frequency of hypoxic values after surgery was 14.6% despite ICP being controlled. Patients had a mean of 18 ± 23 hypoxic episodes. Endotracheal (ET) secretions (17.4%), low cerebral perfusion pressure (10.3%), and mobilizing the patient (8.6%) were the most common causes identified. Elevated ICP was rarely identified as the cause of hypoxia (4%). No cause of cerebral hypoxia could be determined 31.2% of the time. Effective treatments that were mainly used included sedation/analgesia (20.8%), ET secretion suctioning (15.4%), and increase in fraction of inspired oxygen or positive end-expiratory pressure (14.1%).

CONCLUSIONS

Cerebral hypoxia is common after craniectomy, despite ICP being controlled. ET secretion and patient mobilization are common causes that are easily treatable and often not identified by standard monitoring. These results suggest that monitoring should be pursued even if ICP is controlled. The authors' findings might provide a hypothesis to explain the poor functional outcome in the recent randomized controlled trials on craniectomy after traumatic brain injury where in which brain tissue oxygen pressure was not measured.

In-depth characterization of a long-term, resuscitated model of acute subdural hematoma-induced brain injury

OBJECTIVE

Acute subdural hematoma (ASDH) is a leading entity in brain injury. Rodent models mostly lack standard intensive care, while large animal models frequently are only short term. Therefore, the authors developed a long-term, resuscitated porcine model of ASDH-induced brain injury and report their findings.

METHODS

Anesthetized, mechanically ventilated, and instrumented pigs with human-like coagulation underwent subdural injection of 20 mL of autologous blood and subsequent observation for 54 hours. Continuous bilateral multimodal brain monitoring (intracranial pressure [ICP], cerebral perfusion pressure [CPP], partial pressure of oxygen in brain tissue [PbtO2], and brain temperature) was combined with intermittent neurological assessment (veterinary modified Glasgow Coma Scale [MGCS]), microdialysis, and measurement of plasma protein S100β, GFAP, neuron-specific enolase [NSE], nitrite+nitrate, and isoprostanes. Fluid resuscitation and continuous intravenous norepinephrine were targeted to maintain CPP at pre-ASDH levels. Immediately postmortem, the brains were taken for macroscopic and histological evaluation, immunohistochemical analysis for nitrotyrosine formation, albumin extravasation, NADPH oxidase 2 (NOX2) and GFAP expression, and quantification of tissue mitochondrial respiration.

RESULTS

Nine of 11 pigs survived the complete observation period. While ICP significantly increased after ASDH induction, CPP, PbtO2, and the MGCS score remained unaffected. Blood S100β levels significantly fell over time, whereas GFAP, NSE, nitrite+nitrate, and isoprostane concentrations were unaltered. Immunohistochemistry showed nitrotyrosine formation, albumin extravasation, NOX2 expression, fibrillary astrogliosis, and microglial activation.

CONCLUSIONS

The authors describe a clinically relevant, long-term, resuscitated porcine model of ASDH-induced brain injury. Despite the morphological injury, maintaining CPP and PbtO2 prevented serious neurological dysfunction. This model is suitable for studying therapeutic interventions during hemorrhage-induced acute brain injury with standard brain-targeted intensive care.

Effect of the degree of head elevation on the incidence and severity of venous air embolism in cranial neurosurgical procedures with patients in the semisitting position

OBJECTIVE The semisitting position of a patient confers numerous advantages in various neurosurgical procedures, but venous air embolism is one of the associated complications of this position. To date, no prospective studies of the relationship between the degree of head elevation and the rate and severity of venous air embolism for patients undergoing a procedure in this position have been performed. In this study, the authors compared changes in the severity of venous air embolism according to the degree of head elevation (30° or 45°) in patients undergoing an elective cranial neurosurgical procedure in the semisitting position. METHODS One hundred patients undergoing an elective infratentorial craniotomy in the semisitting position were included, and each patient was assigned to 1 of 2 groups. In Group 1, each patient's head was elevated 30° during surgery, and in Group 2, each patient's head elevation was 45°. Patients were assigned to their group according to the location of their lesion. During surgery, the standard anesthetic protocol was used with total intravenous anesthesia, and transesophageal echocardiography was used to detect air in the blood circulation. Any air embolism seen on the echocardiography screen was classified as Grade 0 to 4. If multiple events occurred, the worst graded attack was used for statistical analysis. During hemodynamic changes caused by emboli, fluid and vasopressor requirements were recorded. Surgical and anesthetic complications were recorded also. All results were compared statistically, and a p value of < 0.05 was considered statistically significant. RESULTS There was a statistically significant difference between groups for the total rates of venous air emboli detected on transesophageal echocardiography (22.0% [n = 11] in Group 1 and 62.5% [n = 30] in Group 2; p < 0.0001). The rate and severity of air embolism were significantly lower in Group 1 than in Group 2 (p < 0.001). The rates of clinically important venous air embolism (Grade 2, 3, or 4, venous air embolism with decreased end-tidal carbon dioxide levels and/or hemodynamic changes) were 8.0% (n = 4) in Group 1 and 50.0% (n = 24) in Group 2 (p < 0.0001). There was no association between the rate and severity of venous air embolism with patient demographics (p > 0.05). An association was found, however, between the rate of venous air embolism and the type of surgical pathology (p < 0.001); venous embolism occurred more frequently in patients with a meningioma. There were no major surgical or anesthetic complications related to patient position during the postoperative period. CONCLUSIONS For patients in the semisitting position, an increase in the degree of head elevation is related directly to a higher rate of venous air embolism. With a 30° head elevation and our standardized technique of positioning, the semisitting position can be used safely in neurosurgical practice.

Intrathoracic meningocele associated with neurofibromatosis Type 1 and a novel technique for surgical repair: case report

Neurofibromatosis Type 1 (NF1) is a neurocutaneous disorder that can have associated spinal abnormalities related to both bone and dural dysplasia. Thoracic meningoceles are one spine anomaly associated with NF1, although they are a fairly uncommon pathology. Surgical techniques to treat these meningoceles, usually undertaken only when the patient is symptomatic, are targeted at decreasing the size of the protrusion and improving lung capacity. Surgical interventions discussed in the literature include shunting the pseudomeningocele, primary repair with laminectomy, thoracoscopic plication, and reinforcement of the closure with cement, muscle, or fascia. Authors here report the case of a 43-year-old woman with NF1 with worsening pulmonary function tests and in whom shunting of the pseudomeningocele failed. Subsequently, a posterolateral thoracotomy was performed. The dura mater was reconstructed and primarily closed. On this closure a Gore-Tex soft-tissue patch was placed along with polypropylene mesh and Evicel fibrin sealant, followed by titanium mesh. At the end of the procedure, a chest tube was left in place and therapeutic pneumoperitoneum was performed to decrease the dead space as the lung did not fully expand with positive-pressure ventilation. The patient's pulmonary function tests improved after the procedure. Thoracic meningoceles are uncommon and difficult pathologies to treat surgically. Although shunting is arguably the least invasive surgical option, it can fail in some patients. When it does fail, there are other options that require a multidisciplinary approach and careful attention to the dural closure and reinforcing layers.