Ictal hypoxemia in localization-related epilepsy: analysis of incidence, severity and risk factors

Abstract

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.

Fig. 1

(A) Oxygen saturation nadir (percent saturation) for each seizure. Recorded saturation values below 50% were truncated at 50%. The vertical lines above the hatched bar separate data from the 56 individual patients. (B) Pronounced oxygen desaturation with a complex partial left temporal onset seizure without secondary generalization. Patient was a 19-year-old male with a BMI of 19.9. Seizure onset occurred with the patient awake and sitting in bed. He became unresponsive with lip smacking, a slight head turn to the left followed by forceful head turning to the right. He remained sitting for the duration of the seizure. The heart rate (b.p.m.) at various times is shown. Two other complex partial seizures in this patient (one left and one right temporal onset) were accompanied by oxygen desaturations below 50%. Oxygen saturation percent is shown on the ordinate.

Fig. 2

Plot of seizure duration versus level of desaturation. Oxygen saturation = 94.704 – 0.083 × seizure duration.

Fig. 3

Complex partial seizure with secondary generalization recorded in a 31-year-old woman; 60 s per frame. Frame 1 shows right temporal onset seizure with central apnoea. Secondary generalization occurs in Frame 2 and oxygen desaturation is seen. Seizure ends in Frame 3 with resumption of breathing and continued but improving oxygen desaturation.

Fig. 4

(A) Partial onset seizure with secondary generalization. There is an increase in ETCO2 above 65 mm Hg accompanying a drop in oxygen saturation. Respiratory rate increases during the period of hypercarbia. The longer arrow indicates seizure onset; the shorter arrow indicates seizure end. (B) Left temporal onset complex partial seizure. There is an abrupt increase in ETCO2 with concomitant drop in oxygen saturation. ETCO2 elevation persists above preictal levels for >30 min after the end of the seizure.