Prediction of outcome in coma

Having made an assessment of the cause of coma, established its severity, and introduced appropriate treatment, the physician should be able to prognosticate the likely outcome to colleagues and to friends and relatives of the patient. Sedative drugs or alcohol overdose is not usually lethal and carries a good prognosis provided that circulation and respiration are protected. The physician can reasonably give a good prognosis in patients suffering from self-poisoning with sedative drugs provided that the complications of cardiac dysrhythmia, aspiration pneumonia and respiratory arrest are avoided or corrected. In non-traumatic coma other than that which is drug induced, those factors that determine the outcome have been defined33 and include the cause of coma, the depth of coma, the duration of coma, and certain clinical signs, among the most relevant of which are brain stem reflexes. Overall only 15% of patients with non-traumatic coma for more than 6 hours will make a good or moderate recovery; the other 85% will die, remain vegetative, or reach a state of severe disability in which they remain dependent.

Patients whose coma is due to metabolic factors, including infections, organ failure, and biochemical disturbances, have a better prognosis. Thirty-five per cent of patients will achieve moderate or good recovery; of those whose coma follows hypoxic-ischaemic insult only 11% will make such a recovery; of those in coma due to cerebrovascular disease only 7% can be expected to make such a recovery. Twenty per cent of patients in coma following a hypoxic-ischaemic injury will enter the vegetative state due to the likelihood of hypoxic ischaemia resulting in bihemispheric damage with relative sparing of the brain stem.

Apart from the diagnosis, the depth of coma affects the individual prognosis. Those patients not showing eye opening after 6 hours of coma have only a 10% chance of making a good or moderate recovery whereas those who eye open in response to painful stimuli have a 20% chance of making a good recovery. The longer the coma persists the less likely there is to be recovery; 15% of patients in coma for 6 hours make a good or moderate recovery, compared with only 3% who remain unconscious for one week.34

A study of 500 patients reported by Levy et al.34 using prospective data from patients with clearly defined levels of coma, diagnoses, and outcomes showed that some clinical signs are significantly associated with poor prognosis: in the total cohort of 500 patients, corneal reflexes were absent 24 hours after the onset of coma in 90 patients and this sign was incompatible with survival. In a more uniform group who suffered anoxic injury there were 210 patients: 52 of these had no pupillary reflex for 24 hours, all of whom died by the third day; 70 were left with a motor response poorer than withdrawal and all died by the seventh day; the absence of roving eye movements was seen in 16 patients, all of whom died. The 95% confidence intervals for all of these criteria are given in Table 1.2.

Table 1.2 Clinical signs and prognosis

Patients

False-

95%

with

positive

confidence

Time

Sign

Cohort

the sign

survivors

interval (%)

24 hours

Absent corneal response

500

90

0

0-5

24 hours

Absent pupillary response

210

52

0

0-5

3 days

Motor poorer than withdrawal

210

70

0

0-5

7 days

Absent roving eye movements

210

16

0

0-5

Summarised from Levy et a/.34

Summarised from Levy et a/.34

At the opposite end of the scale more than 25% of patients who show roving conjugate eye movements within 6 hours of the onset of coma or who show withdrawal responses to pain or eye opening to pain, will recover independence and make a moderate or good recovery. The use of combinations of clinical signs helps to improve the accuracy of prognosis: at 24 hours the absence of corneal responses, pupillary light reaction, or caloric or doll's eye response is not compatible with recovery to independence. Patients who are able to speak words within 24 hours or who show nystagmus on caloric testing are likely to make a good recovery (Table 1.3).35

A recent reassessment of this data to present the individual signs with their sensitivity and specificity may be helpful in aiding prognosis in the individual patient (Table 1.4).36

The most accurate prediction of outcome in a patient in medical coma is still that which is obtained from the use of clinical signs. There is little to be added by more sophisticated testing other than identifying the cause of the coma. It is possible to predict those patients who will not make a recovery and who will die in coma or who will enter a vegetative state within the first week of coma. It is rare for patients in medical coma who are in a vegetative state at one month to show any form of recovery.37

Table 1.3 Prediction of outcome of coma at 24 hours by a combination of clinical signs

500 patients 1

Any two reacting:

No

Pupils

Corneals

Oculovestibular

Percentage of patients with different outcomes

patients D/PVS SD MD/GR

120 97 2 1

83 80 8 12

135 69 14 17

106 58 19 23

56 46 13 41

83 80 8 12

Summarised from Levy et a/.34

D/PVS = death or vegetative; SD = severe disability; MD/GR = moderate or good recovery.

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