Ictal Hypoxemia in Localization-Related Epilepsy: Analysis of Incidence, Severity and Risk Factors

Lisa M. Bateman; Chin-Shang Li; Masud Seyal

Disclosures

Brain. 2008;131(12):3239-3245. 

In This Article

Summary and Introduction

Summary

Ictal hypoxemia has been reported in small series of cases and may contribute to sudden unexpected death in epilepsy (SUDEP). We sought to determine the incidence and severity of ictal hypoxemia in patients with localization-related epilepsy undergoing in-patient video-EEG telemetry. We examined whether seizure-associated oxygen desaturation was a consequence of hypoventilation and whether factors such as seizure localization and lateralization, seizure duration, contralateral spread of seizures, patient position at seizure onset and body mass index influenced ictal-related hypoxemia. A total of 304 seizures with accompanying oxygen saturation data were recorded in 56 consecutive patients with intractable localization-related epilepsy; 51 of 304 seizures progressed to generalized convulsions. Pulse oximetry showed oxygen desaturations below 90% in 101 (33.2%) of all seizures with or without secondary generalization, with 31 (10.2%) seizures accompanied by desaturations below 80% and 11 (3.6%) seizures below 70%. The mean duration of desaturation below 90% was 69.2 ± 65.2 s (47; 6-327). The mean oxygen saturation nadir following secondary generalization was 75.4% ± 11.4% (77%; 42-100%). Desaturations below 90% were significantly correlated with seizure localization [P = 0.005; odds ratio (OR) of temporal versus extratemporal = 5.202; 95% CI = (1.665, 16.257)], seizure lateralization [P = 0.001; OR of right versus left = 2.098; 95% CI = (1.078, 4.085)], contralateral spread of seizures [P = 0.028; OR of contralateral spread versus no spread = 2.591; 95% CI = (1.112, 6.039)] and gender [P = 0.048; OR of female versus male = 0.422; 95% CI = (0.179, 0.994)]. In the subset of 253 partial seizures without secondary generalized convulsions, 34.8% of seizures had desaturations below 90%, 31.8% had desaturations below 80% and 12.5% had desaturations below 70%. The degree of desaturation was significantly correlated with seizure duration (P = 0.001) and with electrographic evidence of seizure spread to the contralateral hemisphere (P = 0.003). Central apnoeas or hypopnoeas occurred with 50% of 100 seizures. Mixed or obstructive apnoeas occurred with 9% of these seizures. End-tidal carbon dioxide (ETCO2) was recorded in seven patients (19 seizures). The mean increase in ETCO2 from preictal baseline was 18.6 ± 17.7 mm Hg (13.2; 2.8-77.8). In these 19 seizures, all oxygen desaturations below 85% were accompanied by an increase in ETCO2. Ictal hypoxemia occurs often in patients with localization-related epilepsy and may be pronounced and prolonged; even with seizures that do not progress to generalized convulsions. Oxygen desaturations are accompanied by increases in ETCO2, supporting the assumption that ictal oxygen desaturation is a consequence of hypoventilation. Ictal hypoxemia and hypercapnia may contribute to SUDEP.

Introduction

Mortality in patients with epilepsy is increased with a standardized mortality ratio of 1.6-9.3 in the general epilepsy population. Causes of increased mortality include accidental death, suicide, status epilepticus and sudden unexpected death in epilepsy (SUDEP). SUDEP is the most common cause of death in patients with epilepsy, with the highest incidence of SUDEP in patients being evaluated in epilepsy referral centres and in patients being assessed for epilepsy surgery (Tellez-Zentano et al., 2005). In the latter population, the annual incidence is 2.2-10 per 1000 population per year (Tellez-Zentano et al., 2005). Both cardiac and respiratory dysfunction have been implicated as possible precipitating causes in SUDEP.

Asphyxia with partial seizures without convulsive activity was first described by Hughlings Jackson (1899). Electrical stimulation of the hippocampal gyrus, the ventral and medial aspects of the temporal pole, the anterior portion of the insula and the anterior limbic gyrus results in inhibition of respiratory movements (Kaada and Jasper, 1952). In small series of patients with partial onset seizures, hypoxemia has been observed using pulse oximetry in adults and children (Hewertson et al., 1996; Nashef et al., 1996; Blum et al., 2000). It has not been determined whether the observed oxygen desaturation reflects hypoventilation or is a consequence of seizure-associated peripheral vasoconstriction (Blum et al., 2000).

The study was designed to determine the incidence and severity of hypoxemia in a population of patients with localization-related epilepsy undergoing inpatient video-EEG telemetry. We sought to confirm that seizure-associated oxygen desaturation is a consequence of hypoventilation. We also examined whether factors such as seizure localization and lateralization, seizure duration, contralateral spread of seizures, patient position at seizure onset and body mass index (BMI) might contribute to or exacerbate ictal-related hypoxemia.

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