Respiratory depression during VP shunting in Arnold Chiari malformation Type-II, a rare complication (Case reports and review of literature).

The VP Shunt is a common pediatric surgical procedure in our country. Hydrocephalus is commonly associated with meningomyelocele in Arnold Chiari malformation-II and the ventriculoperitoneal shunt insertion is the common surgical procedure for the management of hydrocephalus. The standard protocol is to rule out any hydrocephalus by preoperative MRI. If associated with hydrocephalus, insertion of the VP shunt is indicated before the repair of MMC whereas the absence of hydrocephalus indicates that the surgical repair of MMC is to be undertaken immediately. Anesthetic management of the patient during the insertion of ventriculoperitoneal shunt may pose problems. We report here two cases of ACM-II (lumbar MMC with associated hydrocephalus) who had respiratory depression / delayed emergence after an otherwise uneventful procedure. Although the VP shunt (first procedure) required postoperative ventilation which improved later, the phenomena of respiratory depression / delayed emergence did not occur after the MMC repair (second surgery). The possible mechanisms involved in these events and their various clinical aspects are discussed below.

Introduction

The VP Shunt is a routine procedure in pediatric neurosurgery for hydrocephalus. ACM Type-II patients have anatomical intracranial anomalies and meningomyelocele with hydrocephalus before primary MMC repair shunting is done to decrease ICT. Respiratory depression has been rarely documented as complication.

ACM is a clinical and anatomical processes that involves the hindbrain. Caudal herniation of the cerebellar vermis, brainstem, and IVth ventricle as well as other intracranial anomalies have been reported in ACM Type II cases, and almost all have myelomeningocele and hydrocephalus, which may be present at birth or a few days after surgery. The patient may present with the clinical symptoms of apnea, inspiratory wheeze or stridor, breath holding, retrocollis or opisthotonous, irritability, aspiration pneumonia, dysphagia, dysarthria, nystagamus, strabismus, and quadriparesis with hypotonia. ACM type II may also present postoperatively in the form of tense and bulging fontanels with features of lethargy, irritability, vomiting, or even respiratory depression. MMC associated with hydrocephalus requires the insertion of a VP shunt at the time of surgical repair.[6]

Case Report

Two male children, one a 45 day-old / 5 kg and the second a two month-old / 6 kg, presenting with lumbar meningomyelocele and hydrocephalus with no other congenital anomalies and normal neurological status, were posted for VP shunt insertion. The results of a systemic examination of the respiratory and cardiovascular systems were within normal limits. Results of hematological and biochemical investigations and of echocardiography were also within normal limits.

The children were premedicated with syrup diazepam 0.1 mg/kg. After beginning the monitoring by ECG, NIBP, SPO2, temperature, and ETCO2, induction was done with Sevoflurane (mask induction)and IV access was secured. This was followed by the administration of injection fentanyl 10 mcg. Nasotracheal intubation with uncuffed endotracheal tube of size 3.5 was facilated with a depth of sevoflurane. Anesthesia was maintained with 66% nitrous oxide in oxygen and isoflurane 1–1.5%. After positioning, the ventilation was controlled with one dose of atracurium 4 mcg using a modified Jackson-Rees circuit with ETCO2 monitoring. Intraoperative 0.45 % Normal saline + 5%Dextrose fluid was administered (to prevent hypernatremia and hypoglycemia).

The procedures lasted 45 and 55 minutes each and were uneventful. After the procedure, there were no respiratory efforts or response to oral suction and both pupils were constricted and reacting. Naloxone 25 mcg was administered in divided dosage for suspected fentanyl sensitivity, but the pupil as well as respiratory efforts showed no changes. Also, there was no change in the level of consciousness or motor activity. After 2 h of ventilation, no limb movements appeared in response to painful stimuli. ABG was within normal limits and needed no correction. Reversal of the neuromuscular blockage was attempted with atropine 20 mcg/kg and neostigimine 50 mcg/kg but did not succeed. Hypothermia, hypoglycemia, and hypocalcemia were ruled out. An acute rise in intracranial pressure (ICP) was suspected and 20%mannitol 0.5 g/kg was administered intravenously; no pupillary changes were seen. After 2–3 h, the patients’ condition did not improve, so the patients were shifted to the Neuro ICU for elective ventilation with monitoring of the vitals and care. After six and eight hours, some respiratory efforts and limb movements were seen, so the children were weaned off gradually over the next two hours and extubated successfully. The children were fully conscious, crying normally, with stable vitals and temperature, and the ABG was normal; the rest of the postoperative monitoring was uneventful.

After two weeks, the children were planneded for the repair of the meningomyelocele. General anesthesia was induced in the same fashion, with premedication, induction, and maintenance with the same doses of anesthetics as before in the VP shunt. Time taken for the repair was the same as before for the VP shunt; the repair was uneventful intraoperatively and the vitals were stable. Adequate respiratory efforts and limb movement occurred within five minutes of withdrawal of all anesthetics. This time, extubation was done successfully after the reversal of neuromuscular blockage. Recovery was good, the children opened eyes, and the vitalswere stable at the end of the surgery.

Discussion

Delayed awakening from anesthesia may be due to various causes, includeing overdose of intravenous and volatile anesthetics, opioids or neuromuscular blocking agents, hypoxia, hypothermia, metabolic and endocrine abnormalities, paradoxical air embolism into the cerebral circulation, or if any preexisting occult or overt ICH leads to herniation of the cerebral cortex across the tentorium cerebelli or the brainstem through the foramen magnum.[12]

Overdose of the anesthetic agent was ruled out as the cause in our case as the accidental administration or drug overdose was cross-checked. Hypoxia during the procedure was unlikely as the ETT position and bilateral air entry was checked before and after turning the patient. Also, continuous oxygen saturation was monitored to exclude out any desaturation.[3]

Hypothermia and hypoglycemia were also excluded as possible causes.[5] Venous air embolism could have been a possibility, but it is usually associated with a decrease in ETCO2 and bradyarrythmias, which were not observed in our cases.

Acute transtentorial herniation or ‘coning’ can be a possible explanation as it occurs following a sudden change in the pressure gradient across the tentorium. Increase in pressure in the supratentorial compartment or a decrease in the infratentorial compartment could lead to this condition, as in ill-advised lumbar punctures / VP shunts.[4]

The uncal herniation initially causing oculomotor nerve irritation resulting in pupillary constriction followed by compression of the oculomotor nerve resulting in pupillary dilatation then subsequently,devlops coma ,it is not seen in our cases.

Central herniation, heralded by miotic pupils, causes progressive brainstem compression with sequential loss of pupillary responses and abnormal or absent eye movements.[4] (Ropper ,). Herniation of the intracranial contents through the foramen magnum can clinically manifest as tachycardia and hypertension (due to pressure over the trigeminal or any sensory nerve nucleus) or reflex bradycardia, it can leads to sudden cessation of spontaneous respiratory efforts (due to pressure over the respiratory center). It can also causes pupillary constriction (due to oculomotor nerve irritation)and pupillary dilatation (due to oculomotor nerve paralysis), and papilloedema (due to defective drainage of CSF). (Ropper , 1998)

Patients in deep metabolic coma may, however, show a total loss of eye movements but retain pupilary reflexes.

The main cause of death in children with chiari II malformation and MMC, usually due to respiratory dysfunction and episodic symptoms of brain stem dysfunction are frequent. Neither surgical decompression nor intensive care prevented the fatal outcome, which was both unpredictable and inevitable.(Lopez-Pison ., Nishino , Setz and Shiraishi ,) Brain stem compression by the tonsillor herniation and caudal displacement of the brain stem may be the causes of delayed recovery and respiratory depression following the shunt in our two cases. Compression to the brain stem was relieved, hence, no such delayed recovery was found in subsequent procedures. Measures to prevent the increase in the transtentorial pressure gradient should be considered, such as the selection of appropriate anesthetic agents[7] and techniques[8] , avoidance of the sudden release of pressure from the sac, and adhering to a head-low position. Postoperative ventilatory support should be considered for every ACM patient.