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Keywords:
Eyes, CNS, Gastrointestinal tract, Ultrasound, MR, Ultrasound-Colour Doppler, Screening, Staging, Education and training, Economics, Cirrhosis
Authors:
G. S. P. Gupta1, R. Singh2, A. Chandra2; 1Abu Dhabi, Ab/AE, 2Lucknow/IN
DOI:
10.1594/ecr2014/C-1627
Conclusion
CONCLUSIONS:
Based on the observations made in the present study we draw following conclusions:–
- The optic nerve diameter can be reliably measured by ultrasound.
Ultrasound is not only reliable but also carries high degree of reproducibility with insignificant inter observer variability (p-value,
0.95).
Using a 10 MHz transducer and four readings per optic nerve the margin of error in optic nerve diameter measurement is only+0.17 mm.
- The male-female difference and right-left difference in OND is insignificant (p-value,
0.75 and 0.66 respectively).
- Accurate measurement of OND is achieved at 3mm position in axial view.
This plane of scan can be achieved in all patients (irrespective of patient cooperation and state of consciousness).
The ultrasound examination is rapid (takes only few minutes) and carries no side effects.
None of our patients complained of any discomfort following the examination.
- Mean ONSD of normal subject less than 5 years of age is 3.21 mm.
- Mean ONSD of normal subject greater than 5 years age is 3.81 mm.
- An ONSD>5.00mm (> 4.99mm) in age greater than 5 years and>4.00 mm in age less than 5 years should be regarded as pathological and under appropriate clinical circumstances,it indicate raised ICT.
Thus,
an ONSD >4.0 mm and >4.98 mm in age less than 5 years and greater than 5 years respectively,
entails poor prognosis in patients with hepatic encephalopathy. All such patients should be given intensive ICT lowering therapy.
However whether such a therapy will decrease mortality,
remains to be seen.
- On measuring of OND at 3 mm position and keeping upper normal limit of ONSD as 4.99 mm (for age group >5 years) resulted in 100% sensitivity and 90% specificity in detection of patients of hepatic encephalopathy with poor prognosis.
The positive predictive value of this technique was 92.3%
- Based on ONSD,
hepatic encephalopathy patient may be classified into three grades – Grade A,
B and C.
Patients in Grade A (ONSD <4.75 mm) tend to have good prognosis.
Patients in Grade B (ONSD = 4.75-5.15 mm) may either deteriorate or improve.
In the present study,
25% of such patients improved and 75% deteriorated.
The outcome of these patients may further be predicted by observing trend of ONSD on serial sonographic study.
Thus,
patients with declining trend of ONSD are likely to improve and those with non-declining trend are unlikely to improve.
Patients in Grade C (ONSD>5.15 mm) are likely to deteriorate and should be managed aggressively.Although repeated measurements of ONSD provide important information about the prognosis of hepatic encephalopathy patients,however in the present study it was observed that even a single ONSD reading is clinically relevant and may be used to classify and triage these patients.
This proposed classification of hepatic encephalopathy (based on ONSD),
correlates well with old classification based on clinical criteria.
- None of our patient with increased ONSD showed papilledema.
This can be explained by the fact that papilledema is known to occur only in patients with chronic intracranial hypertension.
In all our patients intracranial hypertension occurred acutely.
Thus,
the increase in ONSD to pathological range occurs well before papilledema develops.
- The decrease in ONSD seen in one of the group 3 patient,
with consequent improvement of general condition,
indicates that the dilation of the optic nerve sheath diameter is likely to be a reversible phenomenon.
Limitation of study and future scope
The Limitations
1.No definitive technique was used to verify presence of ICHT in patients of hepatic encephalopathy with increased Optic nerve sheath diamter.
Based on enormous evidence (that has been briefly provided and presented here),
dilatation of optic nerve sheath was presumed to be due to intracranial hypertension.
2.Although the present study proves that Optic nerve sheath diamter can act as a prognostic marker in HE patients,
the study design did not include effect of intracranial pressure lowering therapy on Optic nerve sheath diamter & on the prognosis of these patients.
Future study should be designed to concentrate on this aspect.
3.We realize that provision of a portable ultrasound machine would have allowed bedside examination of Optic nerve sheath diamter and would have been very useful in the study.
Many of the patients with grade 4 HE could not be included in the study because of inability to transfer such a terminally ill patients to radiology department.
Future Scope
1.The future scope of the technique used in the present study is great.
The measurement of Optic nerve sheath diamter by a portable ultrasound machine will allow rapid and effective triaging of patient with conditions that may lead to raised ICT.
At the scene of mass disaster where CT scan cannot be performed,
this is highly desirable.
Similarly,
a rapid ultrasound examination at emergency department will allow effective triaging of patients with conditions like stroke and head trauma.
2.The classification of hepatic encephalopathy patients (based on Optic nerve sheath diamter) proposed in the present study is a convenient and useful way to classify these patients.
Future studies should evaluate this classification system prospectively. It is also important to investigate that whether some kind of therapeutic intervention (like ICT lowering therapy) can shift a patient in Group C (ONSD>5.15 mm) to Group A (ONSD<4.75 mm).
3.The use of Optic nerve sheath diamter as a prognostic marker of hepatic encephalopathy patients will revolutionize the ICU management of Hepatic failure patient. Moreover,
Optic nerve sheath diamter may be used to select the patients for orthotropic liver transplant (as shown by Hensen & Helmke)3.
This will obviate the need for invasive intracranial pressure monitoring,
which is the ultimate goal of the search for a noninvasive techniques of ICP monitoring.