Brain Stem Auditory EvokedPotentials in Medical Coma

Nazir Ahmad p .Tahmina Ruhi

BAEPS are coming up as an important investigatory tool in thehands of present clinicians and have a diagnostic and prognostic

significance. The present study was carried on 25 patients. BAEPSwere recorded at the time of admission and analysed. AbsentBAEPS were associated with high mortality. Abnormal BAEPS

were seen in infective and CVA group. Followup BAEPS showedno change in those patients who died.

rain stem auditory evoked potentials(BAEPS) are rated as an importantinvestigatory tool and have a diagnostic

and prognostic significance in diverseconditions affecting the central . nervoussystem and its nerves.

BAEPS were first recorded by Sahper andFeinmesser in 1967. It was Jewett (1971), whofirst of all described the BAEPS as far fieldauditory responses (FAR), as he stimulatedthe ear and recorded the responses at adistant place (Vertex). Then Chiappa et aldescribed the origin of BAEPS.

Table -

Cause No. of Percen-pts tage

Cerebro vascular 9 36accidents (CVA)Bacterial meningitis 4 16Uraemia 3 12Hepatic 2 8Hypoxic 2 8Poisoning 2 8Electrolyte imbalance. 2 8ICSOL 1 4

The major usefulness of BAEPS comesfrom the fact that they are resistant to manysedative and CNS depressant drugs. They areof prime importance in the management ofpatients in intensive care units and for theevaluation of brain death for organ donation.

The time interval of each peak from thetime of stimulation is called its absolute peaklatency (APL) and the time interval betweenvarious peaks is calied interpeak latency (IPL).

The criteria used to classify IPLS intonormal and delayed was done according to a

study done by Nataloni et al (1988). Theystudied BAEPS in 30 patients and consideredmorphology of tracings, the interwave latencyof I-III, III-V,I-V and VI amplititude ratio andBAEPS were graduated into 5 levels.

I. Normal I-III = 2.1 t 0.16 msec,

III -V = 1.90 t 0.20 msec,

I-V = 4.05 ± 0.20 msec.

II. Moderate increase of I-V latency > 4.25< 4.32 with normal morphology.

III. Important increase of I-V latency > 4.32< 4.40, V/I ratio I with moderate changein morphology.

IV. Remarkable change of I-V latency > 4.40and morphology or waves with V/I ratio < 1.

V. Absence of all waves except waves I.

Meterial and Method

The present study was carried out on 25patients in medical coma (Glasgow comascore of less than 8) in the departments ofE.N.T. and Medicine, S.M.H.S. Hospital (overa period of one year). All patients with middleear pathology were excluded from the study.A detailed history and physical/systemic/CNSexamination were done and . recored.Graduation into class of coma was donemainly according to glassgow coma scale(G.C.S.). The BAEPS were recorded at thetime of admission to the casualty and BASPSwere recorded and repeated within first weekin those who survived.

Apparatus and Procedure

BAEPS were studied by Medelec SensorEr 94 system and the data rocorded on apaccard havelet recorder.

For this procedure, the patient was placedin supine position and attached to the sensorthrough ER 94 amplifiar which was sited up

Nazir Ahmad,Registrar Dept. of E.N.T.,Govt. Medical College,Srinagar

Tahmina RuhiResidentJ.V.M.C. Hospital,Srinagar.

Address for Reprints

Dr. Nazir Ahmed.C/o, Hall Mohmad YousufDeputy Post Master, GPO,Srinagar - 190 001

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Brain Stem Auditory Evoked Potentials in Medical Coma = Ahmed & Ruhi

Table Ila

Controls

Peak Ear Latency in mSec. Mean P Value Latency in mSec. Mean

R 1.15-3.63 1.77± .51 <.05 1.58-1.86 1.72± .046

L 1.31 - 3.79 1.94 ± 0.52 < .05

II R 2.16-5.60 2.69± .79 <.05 2.60-2.84 2.72± 0.03

L 2.21 - 5.59 2.98 ± .79 < .05

III R 3.00 - 6.89 3.98 ± 0.90 < .02 3.59 - 3.69 3.65 ± .010

L 2.59-6.81 4.01 ± 0.93 <.02

IV R 4.13-6.78 4.93± 0.68 > 0.1 4.89-5.05 5.00± 0.024

L 4.10-6.76 4.92± 0,66 > 0.1

V R 4.14-8.39 6.13± 0.83 <.01 5.38-5.47 5.43± 0.012

L 4.09-8.39 6.09± 0.84 <.01

(Statistical procedure employed was students T-test)

through ER 94 amplifiar which was sited upto 10 metersfrom the main unit and close to recording point in order tominimise induced interference in the electrode connections.The active electrode was placed over the left mastoid, thereference electrode over the vertex (VS) and groundelectrode over the forearm. The resistance of electrodeswas less than 5000*ohms and stimulus intensity was 70

dB and the masking voice 20 dB. Monoaural stimulationwas done and the number of average signals were 1024.Analysis time was 10 'm seconds, and amplifier gain was5-10 m volts. Common mode rejection technique (1 : 1 lack)was used. The whole procedure was repeated twice underthe same conditions. The wave pattern was recorded onplottar paper 9280 - 0589 (8.5" x 10 ).

Table - Ilb

( Mean absolute peak latencies in various groups.

Peaks I m Sec II m Sec III m Sec IV m Sec V m Sec

Control 1.72 2.76 3.64 5.04 5.44

0.04 ± 0.04 ± 0.013 ± 0.026 ± 0.013

CVA 1.93 3.143 4.24 5.14 6.332

0.471 0.882 ± 1.01 ± 0.847 ± 0.926

P > 0.05 P > 0.05 P > 0.05 P>0.01 P < 0.01

Infective 1.79 3.17 4.127 4.70 6.125.

meningitis ± 0.59 ± 1.0 ± 1.056 ± 0.681 ± 1.087

Encepphalitis P > 0.5 P > 0.1 P > 0.1 P < 0.01 P < 0.01

Uraemia 1.86 2.978 3.827 5.54 5.59

0.518 ± 0.586 t 0.669 ± 0.52 ± 0.698

P > 0.85 P>0.5 P > 0.5 P > 0.5 P>0.2

Heaptic 2.04 3.229 4.068 5.654 5.876

0.938 ± 1.354 ± 1.62 ± 0.90 ± 1.059

P>.05 P > 0.2 P>0.5 P > 0.2 P > 0.2

Hypoxia 1.78 2.713 3.686 5.106 5.476

0.056 ± 0.023 ± 0.0213 ± 0.50 ± 0.061

P>0.05 P>0.2 P>0.5 P>0.2 P>02

Poisoning 1.78 2.762 3.730 5.06 5.49

0.056 ± 0.028 ± 0.141 ± 0.028 ± 0.070

P05 P>0.2 P>0.5 P>0.2 P>0.2

Electrolyte 1.74 2.78 3.69 5.12 5.41

imbalance ± 0.141 ± 0.56 ± 0.014 -_ 0.042 ± 0.042

P>.05 P>0.5 P>0.2 P>0.2 P>0.2

( Statistical procedure employed was students t-test

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Brain Stem Auditory Evoked Potentials in Medical Coma - Ahmad & Ruhi

Table - IIIComparison of interpeak latencies in various groups of medical coma patients.

IPL Right Ear Left Ear

I-Ill III-IV I-V I-III III-IV I-V

Controls 1.97 ± 1.75 ± 3.70 ± 1.92 ± 1.77 ± 3.69.052 .052 0.052 .051 .026 .051

Patients

Cerebro- 2.29 ± 2.14 ± 4.47 ± 2.29 ± 2.15 w 4.45 svascular .66 .61 .66 .66 .62 .73accidents (P<.05) (P<.05) (P<.01) (P<.05) (P<.05) (P<.01

Bacterial 2.33 ± 1.92 ± 4.59 ± 2.33 ± 1.94 ± 4.49meningitis .77 .65 1.02 .78 .66 1.01

(P>.1) (P>.2) (P<0.02) (P<.1) (P>.2) (P<0.02)

Uremia 1.95 ± 1.68 ± 3.66 ± 2.01 ± 1.68 ± 3.61.19 1.48 .26 0.22 .14 0.26

(P>.5) (P>.1) (P>.1) (P>.5) (P<.1) (P>.1)

Hepatic 2.03 ± 2.07 t 3.65 ± 2.04 ± 2.07 ± 3.640.70 1.10 .82 .71 1.09 .81

(P>.5) (P>.5) (P>.5) (P>.5) (P>.5) (P>.5)

Hypoxic 1.66 ± 1.97 ± 3.53 ± 1.60 ± 1.97 ± 3.45.18 .29 .07 0.17 .23 .07

(P>.5) (P>.2) (P>.02) (P>.2) (P<.1) (P>.02)

Electrolyte 1.44 ± 2.01 ± 3.48 ± 1.45 ± 2.02 3.48imbalance .18 .03 .97 .15 t .04 t .99

(P>.2) (P>.04) (P>.02) (P>.1) (P>.2) (P>.5)

Poisoning 1.70 t 1.87 ± 3.60 ± 1.70 ± 1.88 ± 3.61.08 .20 .12 .084 .21 .12

(P>.01) (P<.1) (P>.5) (P>.03) (P>.5) (P>.02)

( Statistical procedure employed was students t-Test )

Results Etiological factors are shown in Table-I.

X-ray skull was normal in all the patients. CT was done15 patients (60 per cent) were male and 10 (40 per on 10 cases, which revealed intracerebral leak in 9 cases

cent) were female. The age group ranged from 10-15 years. and ICSOL in one case. Blood analysis in 2 patents with

Table - IVRelationship of IPL to outcome

IPL Inference C.V.A. Infective Uraemic Hepatic Hymoxic Poinsoning Electrolyte P.group groups (3) (2) (2) (2) imbalance Value

(9) (4) (3)

D R D R D R D R D R D R D R R R

- III Normal 1 3 1 2 1 2 1 1 - 2 - 2 - 3 P > .05Delayed 2 3 1 - - - - - - - - - - -

III - V Normal 1 2 1 2 1 2 1 1 - 2 - 2 - 3 P > .05

Delayed 2 3 1 - - - - - - - - - -

I-VV Normal 1 3 - 1 1 2 1 1 - 2 - 2 - 3 P>.05

Delayed 2 2 2 1- - - - - - - - - -

( Statistical procedure employed was Chi square test

D = Death

R = recovered

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Brain Stem Auditory Evoked Potentials in Medical Coma - Ahmad & Ruhi

Table - Va

Comparison of 1st. and Follow us BAEPS in 11 patients (2 Died, 9 Recovered)

Peak I Peak II Peak III Peak IV Peak V

1st 2nd 1st 2nd 1st 2nd 1st 2nd 1st 2nd

Died - - - - - - - - - _

Recovered 1.98 1.76 2.92 2.20 3.80 3.76 5.00 4.48 5.96 5.64- 1.96 3.52 3.26 4.52 3.96 5.04 4.64 5.84 5.44- - - - 3.48 4.84 - - 6.20 6.04

1.96 1.96 - 2.76 3.96 4.00 5.08 4.96 6.60 5.76- 1.56 - 2.62 - 3.74 - 4.42 6.16 5.70

1.58 1.52 2.88 2.96 3.40 3.42 4.92 4.76 5.88 5.96- 1.86 3.40 2.92 4.28 3.76 5.28 4.46 6.48 5.84

1.68 1.68 2.54 2.70 3.64 2.72 4.96 4.98 5.98 5.881.76 1.82 2.76 2.76 3.78 3.80 4.96 4.96 5.92 5.56

Mean 1.79 1.76 3.02 2.77 3.92 3.88 5.03 4.70 6.11 5.76.17 .16 ± .35 .30 .49 .39 .11 .24 .27 ± .19

P>.5 P>.1 P>.5 P<.01 P<.01

( Statistical procedure = Chi aquare test )

poisoning revealed raised levels of Diazepam in both thepatients.

As is evident from Table-Ila, the absolute peak latencies(APL) of peak 1,11,111, V were significantly delayed (P<.02)but peak IV latency was not so (P<.1).

Interpeak latencies (IPL) of each group were comparedto the IPL of controls. It was observed that all the 3 IPL(i.e., I-III, III-V, and I-V) were significantly delayed in CVAgroup and IN IPL of infective groups were also significantlyprolonged, I-III and III-IV IPL of infective groups were longerthan control but not statistically significantly delayed. In restof the groups the IPL were not significantly delayed.

In CVA group, one patient had absent BAEPS andexpired. The repeat BAEPS study within the first week ofadmission was done in 11 patients. In those patients whohad abnormal BAEPS at the first recording and recoveredlater, repeat BAEPS in most of them were normal. As isevident from the table - relationship of IPL to outcome wasnot statistically significant (P<.05`.

Discussion

BAEPS are now largely employed inOtological/Neurological practice and their validity has beenconfirmed by recent studies on patients in medical coma.In this study the role of BAEPS was studied in 25 patientsin medical coma over a period of one year.

Absent BAEPS

In this study only one patient had absent BAEPS andexpired and this is in agreement with most of the BAEPstudies published. Nataloni et al (1988) reported 100 percent mortality in 5 patients with absent peaks. Seales et al(1979) found absent BAEPS in 3 patients, all of whom died.Jain and Maheswari (1985) found that absent peaks wereassociated with fatal outcome in comatosed patients of CVAgroup.

Absolute Peak Latency Abnormalities

Varied observations have been made by differentobservers about the abnormalities of peak latencies andamplitudes. In the present study, except for the absolutepeak latency of wave IV, all other absolute peak latencieswere found to be significantly delayed. Best recovery wasseen in patients with normal latencies and worst in thosewith absent peaks.

Takashi et al (1980) have discovered markedprolongation of latency of peaks in 36 out of 64 comatosedpatients.

A decrease in the amplitude and prolongation ofabsolute, peak latencies were changing frequently observedin 10 records (out of 20) by Uzeil et al (1978).

Interpeak Latency (ipl)

The present study reveals that all the three inter peaklatencies in the CVA group and IN IPL in the infective groupwere significantly delayed (P < .05). In the uraemic group,out of 3' patients one died, although none of the inter peaklatencies were significantly delayed.

Similarly, both hepatic coma patients had IPL withinnormal limits but expired. All the 7 patients in the hypoxic,poisoning and electrolytic imbalance groups recovered andtheir inter peak latencies had not significantly altered. Scherget al (1984) found no differences between the patients andcontrol groups with regards to IPL. Nataloni et al (1986)graded their patients into 5 BAEPS levels on the basis ofincreasing IN latency. Progressively increasing mortality andmorbidity were observed in the five groups.

Follow Up BAEPS

Follow up study was done in 11 patients which revealedthat those patients who had abnormal BAEPS initially andhad rocovered later, significant reduction in peak latencies

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Table - Vb

Comparison of 1st. and Follow us BAEPS in 11 patients (2 Died, 9 Recovered)

Peak I Peak II Peak III Peak IV Peak V

1st 2nd 1st 2nd 1st 2nd 1st 2nd 1st 2nd

Died 1.64 1.76 2.64 2.56 3.76 3.96 - - 5.92 5.96

1.92 - - - - - - - - -

Recovered 1.76 1.90 2.56 2.42 3.76 3.82 5.04 4.48 6.26 5.842.00 2.00 - 2.96 4.20 4.10 5.36 4.96 5.96 5.74

- 1.68 - - - 4.16 5.12 - 6.32 5.691.64 1.76 2.60 2.42 3.72 3.42 5.00 4.20 6.00 5.96

1.52 1.52 2.64 2.46 3.76 3.82 4.48 4.40 5.96 5.421.68 1.76 2.76 2.96 3.64 3.42 4.84 4.75 5.96 5.96

1.60 1.88 2.64 2.86 4.12 3.80 5.20 5.02 6.16 5.761.84 1.70 2.86 2.70 3.72 3.96 4.96 4.74 5.58 5.50

1.82 1.82 2.80 2.82 3.76 3.76 4.98 4.92 5.52 5.46

Mean 1.73 1.78 2.69 2.70 3.83 3.80 4.99 4.68 5.97 5.70

.15 t .14 ± .11 ± .23 ± .20 t .25 ± .26 ± .29 ± .27 .20P>.2 P>.5 P>.5 P<.02 P<.05

( Statistical procedure = Chi aquare test )

electrolytic imbalance.

Absent BAEPS were associated with the worstprognosis.

Increased absolute peak latencies and inter peaklatencies were associated with poor prognosis and lowrecorvery rates as compared to those with normallatencies.

Follow up BAEPS within the first week of admissionshowed no change in patients who died, while it showedimprovement in latencies in those who recovered.

were observed for peaks IV and V in the subsequent BAEPS.However the mean values of I, II and III peak latencies did 3not show a significant difference in the subsequent BAEP.

Conclusion 4

1. Absolute peak latencies (I, II, III and V) were found tobe significantly delayed in patients of coma as comparedto the controls.

52. Abnormal BAEPS were seen in coma of infective and

OVA origin while BAEPS were normal in patints withcoma due to hepatic, uremic, hypoxic, poisoning and

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