Coma1

Coma is a common cause for critical illness in children.¹ Coma in the pediatric patient is a medical emergency and must be dealt with in a rapid, organized way. Basic life-support needs, evaluation of history, and physical examination are all of paramount importance and evaluation of these three critical areas must proceed simultaneously. Specific diagnoses must be treated appropriately, but there are key general principals to coma management that must be dealt with sequentially. The outcome in childhood coma is substantially better than adult coma, and in many cases is determined by speed and appropriateness of intervention.² Considerable skill is required to distinguish the group at high risk of further deterioration, potentially leading either to death or severe handicap.³ This review deals with the general aspects of non-traumatic coma in children.

The term, consciousness, is multifaceted. In testing, it is important to distinguish between the content of consciousness and basic arousal. Content refers to higher cognitive and emotional functioning, whereas arousal refers to the activation of the cortex from the ascending activating system (brain stem reticular formation and diffuse thalamic projections).

Though Glasgow coma scale^{5, 6} has been adopted in the treatment of pediatric and adult coma, it should not be used in small children, as the verbal component is not appropriate.⁷ James' adaptation of the Glasgow coma scale⁸ was designed for young children. A grimace score was later developed for the assessment of intubated children to replace the verbal score⁹ (Table 1.1). Response to pain should be examined both with a supraocular pressure and with nail bed pressure (with a pencil). At initial presentation, it is preferable to err on the side of recording too low a score, as it is easier to withdraw treatment from a child who is improving than to resuscitate one, who deteriorates.³

In all children with non-traumatic coma, raised intracranial pressure (ICP) is presumed initially.^3,10 Early and adequate management of raised ICP prevents deterioration leading to death or permanent disability.3

Ischemic cerebral damage and herniation syndromes are the two important complication of raised ICP.^3,11 Mean arterial pressure remaining the same, the cerebral perfusion pressure drops with a rise in ICP. Pressure difference between the brain compartments and the spinal canal results in various herniation syndromes, which results in mechanical damage and the vascular distortion. Careful serial brainstem examination⁴ (Table 1.2) is performed to recognize the progressive herniation syndromes¹² (Table 1.3), so that early appropriate management could be undertaken to prevent the irreversible stage. In acute rise in ICP papilledema is often absent.¹³ Raised ICP should be assumed even if there is no evidence of brain swelling on CT scan.^{12, 14}4

After initial stabilization a search for the etiology and the management of the specific problem has to be instituted (Table 1.5). Discussion on the management of specific etiology is beyond the scope of this review.

EEG could be used to detect nonconvulsive status epilepticus and could aid in the diagnosis of herpes simplex encephalitis. In the appropriate clinical setting, periodic lateralised epileptiform discharges (PLEDs) pattern is diagnostic of herpes simplex encephalitis.²⁸ A child who has an altered level of consciousness without a clear explanation should have a metabolic and toxicological screen.^{3, 29} Certain points help to differentiate toxic metabolic coma from structural coma. Focal neurological deficits are more common in structural lesions. Symmetry is the feature of metabolic causes. However subtle asymmetries are not uncommon. Fluctuating level of consciousness occurs in metabolic causes. Though rapid and deep respiration could occur in pontine lesions or neurogenic pulmonary edema, this pattern is more frequent in toxic metabolic coma. With few exceptions like hypoparathyroidism and lead encephalopathy, papilledema is rare in metabolic causes. Small pupils, with retained light reactivity are classical of nonstructural coma. Structural lesions like subarachnoid hemorrhage, vasculitis, demyelination and meningitis could mimic metabolic diseases. Focal features are more commonly observed in hypoglycemia, hepatic encephalopathy and lead poisoning.³⁰

But this effect is less certain for pneumococcal and tuberculous infection.³³ Children in coma, who had seizures during the illness, should be put on acyclovir to cover the possibility of herpes simplex encephalitis. If this diagnosis is likely, the drug should be continued for two weeks to prevent recurrence.³⁴ Some physicians use erythromycin in idiopathic coma considering the etiological possibility of Mycoplasma pneumoniae, until the results of antibody testing are known.³⁵

If the child remains unconscious for more than six hours despite adequate mean arterial pressure ICP monitoring may be considered. If there are clinical evidence for irreversible brainstem damage or the electroencephalogram (EEG) is predictive of poor outcome, ICP monitoring is not beneficial³ There are no data from randomized controlled trials that can clarify the role of ICP monitoring in acute coma.³⁶ However, there is a large body of published clinical experience that indicates that ICP monitoring

As the outcome is more related to cerebral perfusion pressure (CPP) than maximum ICP, adequate CPP should be maintained.³⁹ Current trend is to maintain CPP above 50 mm Hg³. Controlling fever to reduce the brain's metabolic demands helps to keep the CPP at the desired level.²⁷ Intermittent hikes in ICP can be prevented by maintaining the mean arterial pressure if necessary, with fluids, plasma or inotropic support.

In comatose patients, continuous EEG (cEEG) may provide otherwise unobtainable information and influence therapeutic management, and also help determine the prognosis of patients with acute brain injury. This technique is best used for the detection of sub clinical seizures, which may frequently occur during or after treatment of convulsive status epilepticus and after many types of acute brain injury, particularly trauma.⁴⁹ The other main application of cEEG is as a primary monitor of brain function. cEEG can detect focal cerebral ischemia, such as that caused by vasospasm after subarachnoid hemorrhage, as well as global ischemia related to intracranial pressure elevation and insufficient cerebral perfusion pressure. Other potential applications include prognostication in coma and titration of continuous infusion sedative therapy. New technologic developments include continuous digital video EEG, automated seizure-detection software, and user-friendly online quantitative EEG analysis.¹⁶

Once the life threatening problems have been controlled, the demand for information concerning prognosis from the parents' side is usually pressing and needs to be addressed by the pediatrician. Literature regarding the outcome of pediatric non-traumatic coma mainly deals with hypoxic ischemic damage. As serious co-morbid conditions or pre-existing neurological diseases adversely affect the outcome, such cases are generally excluded in the analysis of outcome. A clear knowledge regarding the underlying cause and the course of the illness is necessary to predict the prognosis⁵⁰. Four important clinical features that help to determine the prognosis are: etiology, depth of coma, duration of coma, and clinical signs.⁵¹ The outcome of coma is related to the cause independent of the physical signs, depth of coma or length of coma. This is most important and shown most dramatically in coma caused by drug overdose. All such patients should be regarded as potentially salvageable and with a good prognosis, provided that they can be supported and complications are avoided during the period of coma. In general, metabolic causes of coma have a better prognosis than anoxic-ischemic causes. The level of coma as measured on the Glasgow coma scale is predictive of outcome. The longer a patient remains in a coma the poorer his or her chance of recovery and the 11greater the chance that he or she will enter a vegetative state. By the third day the chance of making a moderate or good recovery is reduced to only 7%, and by the 14th day is as low as 2%. By the end of the first week almost half of those patients who have not recovered consciousness are in a vegetative state.⁵² Absence of a papillary light reflex at the time of admission, the absence of spontaneous eye movements after 1 day, alack of withdrawal of an extremity after painful stimulus after 3 days, no spontaneous eye opening after 1 week, and inability to follow motor commands after 2 weeks, all predicted a very low likelihood of good recovery.⁵⁰ Widespread use of sedative drugs limits the role of EEG as an outcome predictor. However, serial EEG recording could provide valuable information on the prognosis.⁵³ An isoelectric baseline or a burst suppression pattern during the first week has 100% specificity in predicting poor prognosis.⁵⁴ EEG combined with somatosensory evoked potential and brainstem auditory evoked potential testing provides additional information on prognosis. However, there is no consensus in the literature on the criteria for these procedures in the prediction of recovery.⁵⁵ Wide spread low density suggesting global ischemia in brain imaging indicates poor prognosis.⁵⁶

Whether to continue treatment of patients, who do not immediately recover from coma, is a difficult issue that often confronts physicians. Although the prognosis for recovery is undoubtedly an important factor in decision-making, regarding withdrawal of support, pediatrician must also consider other factors such as a patient's acute illness, premorbid function and family's wishes. In caring for patients with stupor and coma, all physicians should be familiar with the key steps of neurological examination. Proper observation helps with the initial localization and diagnosis and with the subsequent determination of prognosis. This, together with the supportive data such as medical history, laboratory tests results, and brain imaging, will further guide timely and appropriate treatment.