Disorders of Sodium Homeostasis Following Neurosurgery

Due to the location of many pituitary and suprasellar tumors, neurosurgery in these areas may lead to postoperative disorders under hormonal control from the pituitary stalk. These common disorders can occur in isolation or in combination. ^,

Posterior Reversible Encephalopathy Syndrome

PRES is a clinical syndrome consisting of headache, impaired consciousness, seizures, visual disturbances, nausea and vomiting, and occasionally focal seizures. These clinical features in the setting of specific cofactors often lead to its diagnosis. Cofactors, such as acute hypertension, ^, preeclampsia or eclampsia, chemotherapeutic agents, ^, posttransplant immunosuppression, and other diseases of inflammation, ^{, , ,} have been associated with the development of PRES.

The best understanding of the etiology of PRES is that it is a disturbance in cerebral autoregulation, often in the face of severe hypertension, generating vasogenic edema. Clinical diagnosis is often confirmed by magnetic resonance imaging (MRI). Classically, PRES affects the parieto-occipital region of the brain, ^, although it can also be located in the temporal and frontal lobes and posterior fossa. ^, On T2 and fluid-attenuated inversion recovery MRI, white matter intensities are demonstrated in the affected areas, confirming the diagnosis ( Fig. 52.1 ). ^,

MRI abnormalities in posterior reversible encephalopathy syndrome are mainly posterior. (A) T2-weighted image of a child who became hypersensitive on treatment with steroids for juvenile rheumatoid arthritis; high signal is seen posteriorly. (B) Diffusion-weighted abnormalities are more widespread, involving both frontal and posterior regions.

From Sharma, Madhu, Kupferman, Juan C, MD, et. al., The effects of hypertension on the paediatric brain: a justifiable concern, The Lancet Neurology , Volume 9, Issues 9. Pages 933–940. © 2010.

Treatment of encephalopathy, headache, and other neurologic findings surrounds the treatment of the underlying cause, and removing the offending medicines that are related to the PRES. ^{, , , ,} Hypertension requires timely intervention, including admission to a PICU, initiation of antihypertensive therapy, and close invasive blood pressure monitoring. Calcium-channel blockers or beta blocker infusions have been used in the acute treatment of hypertensive emergencies in children. Treatment of PRES-associated seizures with valproic acid has been advocated for its favorable mechanism of action. ^,

Last, the removal of medications that are thought to contribute to the development of PRES should be strongly considered. Patients in whom the chemotherapy used to treat their underlying cancer diagnosis is thought to be the offending agent present difficult challenges to oncologists. The same is true for transplant physicians in managing immunosuppression following an episode of PRES, as cyclosporine and tacrolimus have both been implicated in the development of PRES and are staples of posttransplant immunosuppression. ^{, ,}

Convection-Enhanced Delivery

The delivery of chemotherapy to malignant gliomas has proven challenging. Systemic chemotherapy and more direct methods such as chemotherapy-infused wafers and intrathecal administration of chemotherapy have been ineffective at delivering tumor-directed therapy to deep gliomas. Developed in the 1990s, CED utilizes a syringe pump to generate a pressure gradient at the interstitium to enhance delivery of the therapy to the desired target.

Diffuse intrinsic pontine glioma (DIPG) is a rare but lethal brain tumor seen in children. DIPG accounts for 15%–20% of all CNS tumors in children, and more than 90% will die within 2 years of diagnosis, with conventional fractionated radiation as the primary means of treatment. In recent years, pediatric neurosurgeons have explored the use of CED in the delivery of tumor-directed therapy to children with DIPG ( Fig. 52.2 ).

(A) Stereotactic placement of the infusion catheter via supratentorial (transfrontal) route with fully MR-compatible navigational interface (ClearPoint, MRI Interventions, Irvine, CA, USA). (B) Radiolabeled ¹²⁴ I-8H9 on infusion to the desired tumor site. (C) Radiolabeled ¹²⁴ I-8H9 at completion of the infusion.

In phase I, dose-escalation trial using the radiolabeled antibody monoclonal ¹²⁴ I-8H9, the first 16 subjects received the entire infusion under general anesthesia in the operating room, while the remaining 12 subjects were observed while receiving the infusion in the PICU after cessation of anesthesia for more complete neurologic monitoring. In this cohort, the most common adverse event was the development of a transient facial palsy, which occurred in 9 of the 28 subjects. There was one grade 4 adverse reaction (respiratory failure requiring reintubation after the completion of the infusion) in the cohort. In a second phase I trial exploring the use of CED in the treatment of DIPG, investigators used the recombinant chimera of human interleukin 13 (IL-13) and the enzymatically active portion of Pseudomonas exotoxin A, which effectively targeted glioma cells in preclinical studies. In this cohort, all subjects received the infusion (up to 13 h) in the operating room under general anesthesia. Similarly, the adverse reaction profile was acceptable, suggesting that further studies are warranted to study clinical effectiveness, including the use of liposomal doxorubicin via CED in DIPG.

In all cases, admission to the PICU is necessary if patients are transferred from the operating room. Even small volumes delivered to the pons may cause acute neurologic changes that warrant close monitoring.

Metastatic Lung Disease

Children with metastatic lung disease may require intensive care. One example of lung metastases in children is osteosarcoma, which is the most common bone tumor in children and young adults. Metastatic lung disease can occur within the first year after diagnosis and more than 30% of patients with osteosarcoma relapse. In order to maximize survival, complete metastatic tumor surgical resection is needed, as systemic antitumor therapies are not as reliable a treatment modality for improving survival. Patients undergoing surgical resection of pulmonary metastases often need management and monitoring in the PICU before and following their surgery.

The surgical approach for patients with metastatic lung disease depends on several factors. The majority of patients have bilateral lung involvement but the literature shows that 24%–40% of patients may have unilateral disease. The most common approach to surgical resection is thoracotomy; however, single-staged operations via median sternotomy are sometimes performed.

Pediatric patients who have undergone thoracotomy often recover in the PICU or a surgical step-down unit. Postoperative complications include bleeding, pain control, and respiratory failure. Anticipating these potential complications can mitigate harm and shorten the length of stay in the PICU. Monitoring for bleeding requires close monitoring of hemoglobin and platelet counts as well as coagulation factors, especially in patients who may have recently received chemotherapeutic agents, suppressing marrow production of blood cells. Pain control is the most common postoperative complication. The use of thoracic epidural patient-controlled analgesia (ePCA) has been proven to be safe and effective in controlling pain. ^, The use of ePCA can decrease the need for systemic analgesics, particularly opiates, in an effort to expedite mobility and reduce hospital length of stay. The care of patients with pulmonary metastatic disease requires a multidisciplinary team to achieve the best outcomes.

Neuroblastoma

Neuroblastoma accounts for 8%–10% of all pediatric cancers and as high as 15% of all deaths in children with cancer, prognosis of which depends on the stage of the tumor, determined using several tumor-specific and histologic factors. Patients with high-risk neuroblastoma often undergo complete surgical resection. Thoracoabdominal resections for neuroblastoma are tedious, long surgeries, during which blood loss, fluid shifts, and respiratory failure give rise to the need for intensive care monitoring. This unique patient population differs from other postsurgical patients in that some patients require additional exogenous catecholamines. This has been hypothesized to be caused by underlying neuroblastoma cells secreting catecholamines, which once removed may cause hemodynamic instability.

Postoperative management of large thoracoabdominal resections in patients with neuroblastoma requires close attention from a team of providers, nurses, therapists, and other members of the care team. The development of a postoperative management protocol for patients undergoing any major surgical resection allows for a systematic approach, thereby ensuring that all aspects of care are met. Patients should have adequate blood pressures to ensure perfusion to all end organs, including adequate urine output (typically between 0.5 and 1 mL/kg/h for children), monitoring of central venous pressure, and trending of serum lactate. Administration of crystalloid fluid is recommended if any of these parameters are not met. The use of vasoactive medications, such as norepinephrine, should be considered if hypotension and hypoperfusion exist following fluid resuscitation or if there are signs of hypoperfusion in the setting of an elevated central venous pressure. The use of stress dose glucocorticoids should be considered if adrenal insufficiency is a concern.

Early extubation is the goal for postoperative patients in the PICU with stable hemodynamics, adequate ventilation and pulmonary compliance, and no major postoperative bleeding. Target respiratory goals include normal ventilation and oxygenation, while medical teams should anticipate the third spacing of fluid causing pulmonary edema, if large volumes of crystalloid or blood products are required perioperatively. Postoperative transfusion thresholds are discussed later. As with thoracotomies, ePCA is ideal for analgesia to minimize the systemic need for opiates or sedating medications. Maintenance of monitoring lines is imperative, including arterial lines and central venous catheters, along with assessing the daily need for any surgical drains, nasogastric tubes, and urinary catheters.

Wilms Tumor

Childhood kidney cancers account for approximately 7% of all pediatric cancers. Wilms tumor is the primary type for all pediatric kidney cancers. CT or MRI of the abdomen is imperative to assess disease burden. Approximately 11% of Wilms tumor patients have renal vein involvement and 4% present with inferior vena cava or atrial involvement. Embolization of a caval thrombus to the pulmonary artery is a rare occurrence but can be fatal, necessitating precise surgical planning. Initial nephrectomy is recommended as the first-line treatment for stage I and II Wilms tumors by North American experts, and postoperative management often occurs in the intensive care unit or pediatric floor. Complications include the need for extensive resections, removal of addition organs, and intraoperative tumor contamination in stage III–V Wilms tumors.