Surgery – Diagnostic testing – Measuring fluid pressure in body
Reexamination Certificate
2001-01-05
2003-07-08
Jaworski, Francis J. (Department: 3737)
Surgery
Diagnostic testing
Measuring fluid pressure in body
C600S559000
Reexamination Certificate
active
06589189
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to intracranial pressure (ICP) monitoring. Specifically, the invention relates to a method and apparatus of non-invasively, without requiring a breach of the skin, skull, or dura, monitoring ICP. More specifically, the invention provides a method and apparatus for stimulating and interpreting predictable external effects of elevated ICP such as changes in cochlear impedance coupling to monitor ICP. In one embodiment, the system non-invasively and continuously monitors ICP by stimulating and interpreting predictable changes measured in the otoacoustic emission (OAE) signal of the patient.
BACKGROUND OF THE INVENTION
Intracranial pressure is closely related to cerebral perfusion (blood flow in the brain). Elevated ICP reduces cerebral perfusion pressure (CPP), and if uncontrolled, results in vomiting, headaches, blurred vision, or loss of consciousness, escalating to permanent brain damage, and eventually a fatal hemorrhage at the base of the skull. Increased ICP is a medical/surgical emergency. Particular instances where it is desirable to monitor ICP are in traumatic brain injury (TBI) victims, stroke victims, hydrocephalus patients, and patients undergoing intracranial procedures, “shaken baby” syndrome, kidney dialysis, or artificial liver support. Current methods of monitoring ICP are typically invasive, expensive, and/or difficult to perform outside of a hospital setting.
Traumatic Brain Injury
An estimated 1.75 million TBI's occur annually (extrapolated from 1,540,000 TBI's in 1991) in the United States. The U.S. Department of Education, National Institute on Disability and Rehabilitation Research in conjunction with 17 TBI research hospitals around the U.S. have established a set of indicators for classification of TBI:
1) Documented loss of consciousness for an unspecified time;
2) Amnesia for the event. No recall of the actual trauma;
3) A Glasgow Coma Scale (GCS) score of less than 15 during the first 24 hours.
Of these indicators, amnesia assessment is a preferred indicator of TBI severity. Amnesia of one day is considered moderate, while one month of amnesia indicates severe TBI. Although amnesia is a good indicator of TBI severity and a reasonable predictor of long term outcomes, this slow evaluation method provides no help in emergency response to patient diagnosis or treatment.
The GCS is a TBI severity assessment system using subjective observations in three basic categories: eye opening (E), best motor response (M), and verbal response (V). A patient's GCS score is the sum of the patients E, B, and V scores. This sum ranges from 3 to 15 with 3 indicating severe TBS and 15 indicating no or very mild TBS. The non-invasive nature of CT scans make them a very common procedure for TBI patients whose GCS score is mild or moderate, but the data is slow and expensive. The patient must be brought to the equipment and, in many cases, the patient cannot be immediately moved. The cost is compounded because CTs do not provide direct assessment of ICP (two or more scans are required to assess trends) and in 9-13% of patients, the CT will be normal even with elevated ICP. Due to the invasiveness of current ICP monitoring procedures, the general practice is to not start invasive ICP monitoring unless the patient's GCS score is less than or equal to 8, at which time the drawbacks of the procedure are outweighed by the severity of patient condition. This means 90% of hospitalized TBI patients are assessed only with GCS and possibly a CT scan. Significant rehabilitation problems have resulted in patients with mild or moderate GCS scores, highlighting the need for non-invasive ICP monitoring techniques. GCS assessment and CT scans are helpful, but clearly point out the time-sensitive need for more direct data.
Stroke
First time strokes can unpredictably lead to brain swelling. Strokes are divided into two main categories, (1) hemorrhagic (the bursting of a cerebral blood vessel), and (2) the more common ischemic (the blockage of a cerebral blood vessel). Correct diagnosis of the stroke type is critical because the clot-dissolving drug t-PA (and analogs), used to treat ischemic strokes, is contraindicated for hemorrhagic strokes. Furthermore, the diagnosis of stroke type is time critical because starting t-PA treatment more than 3 hours after stroke could result in a higher rate of bleeding into the brain. Approximately 80% of all strokes each year are ischemic. ICP in this type of stroke initially remains low, but elevates as the loss of blood traumatizes the brain. ICP will also elevate when the clot is removed and blood flow is restored. Hemorrhagic strokes involve the direct complication of elevated ICP.
Hydrocephalus
Ventroperneal shunts are implanted to treat hydrocephalus. A CT scan cannot be used for patients with hydrocephalus because the ventricles of the brain commonly remain swollen even with normal ICP, and the risk of invasive systems cannot be justified. Diagnosis of shunt system problems are currently based on symptoms reported by the patient or caregiver and are thus subjective. OAE is stable over a period of months and an ICP baseline could be stored for these patients and compared with measurements during future visits. Current ICP measurement technology does not provide adequate means for treating patients with hydrocephalus because of the possible inaccurate readings and the risk inherent in invasive measurement procedures.
Intracranial Procedures
There is a current medical need for ICP monitoring for patient recovering from elective intracranial surgery. A retrospective study found elevated ICP postoperatively in 17% of patients who underwent supratentorial or infratentorial surgery. Of these, over one fourth experienced clinical symptoms latent or concurrent to ICP elevation. Medical personnel need to be able to identify these patients and administer therapy before any clinical symptoms are detected. It is interesting to note that during the study, which used invasive methods to measure ICP, the infection rate was 1.2%, highlighting the risk of invasive ICP monitoring.
Laparoscopic and Abdominal Insulflation
Laparoscopic procedures are often performed requiring abdominal insulflation concomitant with Trendelenburg (head down tilt) position. The combination of anesthetic, body position, and insulflation can substantially elevate ICP. Due to the prohibitive additional cost and risk, routine ICP monitoring during these procedures is not done. However, there is growing concern about elevated ICP during these procedures.
Liver and Kidney Support
There is a current medical need to assess ICP variation in patients who are in the latter stages of liver failure and require external liver support (i.e. artificial liver). As the liver fails, toxins build up in the body and this build up generally causes elevation of ICP. One measure of liver function (or therapy function) is to monitor ICP. As toxins build, ICP increases, thus allowing the physician (and possibly the patient) to anticipate when the next therapy session should commence. While on the artificial liver machine, toxins are removed, and ICP should fall, providing an indication of therapy function. A similar situation exists for patients being treated for kidney failure, either by hemodialysis or peritoneal dialysis.
Others
Additional causes for an increase in ICP include the following: meningitis, encephalitis, intracranial abscess, hemorrhage, shunt blockage, tumors, Reye's Syndrome, “shaken baby” syndrome, and benign intracranial hypertension.
Normal intracranial pressure (ICP) for adults is between 5 mm/Hg and 15 mm/Hg. When ICP level is considered abnormal is controversial, however, it becomes a concern as it rises higher than 20 mm/Hg.
ICP is closely related to cerebral perfusion (blood flow in the brain). To a first approximation, the cerebral perfusion pressure (CPP) is the difference between an individual's arterial blood pressure (ABP) and intracranial pressure (ICP). Thus, approximately, CPP=ABP&minu
Avan Paul Alexandre
Buki Bela
Meyerson Scott C.
Fredrikson & Byron , P.A.
Jaworski Francis J.
Rice Creek Medical, LLC
LandOfFree
Non-invasive method and apparatus for monitoring... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Non-invasive method and apparatus for monitoring..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Non-invasive method and apparatus for monitoring... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3086609