NEET MDS Synopsis
Types of Brain Injury
General SurgeryTypes of Brain Injury
Brain injuries can be classified into two main categories: primary and
secondary injuries. Understanding these types is crucial for effective diagnosis
and management.
1. Primary Brain Injury
Definition: Primary brain injury occurs at the moment
of impact. It results from the initial mechanical forces applied to the
brain and can lead to immediate damage.
Examples:
Contusions: Bruising of brain tissue.
Lacerations: Tears in brain tissue.
Concussions: A temporary loss of function due to trauma.
Diffuse axonal injury: Widespread damage to the brain's white
matter.
2. Secondary Brain Injury
Definition: Secondary brain injury occurs after the
initial impact and is often preventable. It results from a cascade of
physiological processes that can exacerbate the initial injury.
Principal Causes:
Hypoxia: Reduced oxygen supply to the brain, which
can worsen brain injury.
Hypotension: Low blood pressure can lead to
inadequate cerebral perfusion.
Raised Intracranial Pressure (ICP): Increased
pressure within the skull can compress brain tissue and reduce blood
flow.
Reduced Cerebral Perfusion Pressure (CPP):
Insufficient blood flow to the brain can lead to ischemia.
Pyrexia: Elevated body temperature can increase
metabolic demands and worsen brain injury.
Glasgow Coma Scale (GCS)
The Glasgow Coma Scale is a clinical tool used to assess a patient's level of
consciousness and neurological function. It consists of three components: eye
opening, verbal response, and motor response.
Eye Opening (E)
Spontaneous: 4
To verbal command: 3
To pain stimuli: 2
No eye opening: 1
Verbal Response (V)
Normal, oriented: 5
Confused: 4
Inappropriate words: 3
Sounds only: 2
No sounds: 1
Motor Response (M)
Obeys commands: 6
Localizes to pain: 5
Withdrawal flexion: 4
Abnormal flexion (decorticate): 3
Extension (decerebrate): 2
No motor response: 1
Scoring
Best Possible Score: 15/15 (fully alert and oriented)
Worst Possible Score: 3/15 (deep coma or death)
Intubated Cases: For patients who are intubated, the
verbal score is recorded as "T."
Intubation Indication: Intubation should be performed
if the GCS score is less than or equal to 8.
Additional Assessments
Pupil Examination
Pupil Reflex: Assess size and light response.
Uncal Herniation: In cases of mass effect on the
ipsilateral side, partial third nerve dysfunction may be noted,
characterized by a larger pupil with sluggish reflex.
Hutchinson Pupil: As third nerve compromise increases,
the ipsilateral pupil may become fixed and dilated.
Signs of Base of Skull Fracture
Raccoon Eyes: Bilateral periorbital hematoma,
indicating possible skull base fracture.
Battle’s Sign: Bruising over the mastoid process,
suggesting a fracture of the temporal bone.
CSF Rhinorrhea or Otorrhea: Leakage of cerebrospinal
fluid from the nose or ear, indicating a breach in the skull base.
Hemotympanum: Blood in the tympanic cavity, often seen
with ear bleeding.
Periodontal Bone Grafts
PeriodontologyPeriodontal Bone Grafts
Bone grafting is a critical procedure in periodontal surgery, aimed at
restoring lost bone and supporting the regeneration of periodontal tissues.
1. Bone Blend
Bone blend is a mixture of cortical or cancellous bone that is procured using a trephine or rongeurs, placed in an
amalgam capsule, and triturated to achieve a slushy osseous mass. This technique
allows for the creation of smaller particle sizes, which enhances resorption and
replacement with host bone.
Particle Size: The ideal particle size for bone blend is
approximately 210 x 105 micrometers.
Rationale: Smaller particle sizes improve the chances of
resorption and integration with the host bone, making the graft more effective.
2. Types of Periodontal Bone Grafts
A. Autogenous Grafts
Autogenous grafts are harvested from the patient’s own body, providing the
best compatibility and healing potential.
Cortical Bone Chips
History: First used by Nabers and O'Leary in 1965.
Characteristics: Composed of shavings of cortical
bone removed during osteoplasty and ostectomy from intraoral sites.
Challenges: Larger particle sizes can complicate
placement and handling, and there is a potential for sequestration. This
method has largely been replaced by autogenous osseous coagulum and bone
blend.
Osseous Coagulum and Bone Blend
Technique: Intraoral bone is obtained using high-
or low-speed round burs and mixed with blood to form an osseous coagulum
(Robinson, 1969).
Advantages: Overcomes disadvantages of cortical
bone chips, such as inability to aspirate during collection and
variability in quality and quantity of collected bone.
Applications: Used in various periodontal
procedures to enhance healing and regeneration.
Intraoral Cancellous Bone and Marrow
Sources: Healing bony wounds, extraction sockets,
edentulous ridges, mandibular retromolar areas, and maxillary
tuberosity.
Applications: Provides a rich source of osteogenic
cells and growth factors for bone regeneration.
Extraoral Cancellous Bone and Marrow
Sources: Obtained from the anterior or posterior
iliac crest.
Advantages: Generally offers the greatest potential
for new bone growth due to the abundance of cancellous bone and marrow.
B. Bone Allografts
Bone allografts are harvested from donors and can be classified into three
main types:
Undermineralized Freeze-Dried Bone Allograft (FDBA)
Introduction: Introduced in 1976 by Mellonig et al.
Process: Freeze drying removes approximately 95% of
the water from bone, preserving morphology, solubility, and chemical
integrity while reducing antigenicity.
Efficacy: FDBA combined with autogenous bone is
more effective than FDBA alone, particularly in treating furcation
involvements.
Demineralized (Decalcified) FDBA
Mechanism: Demineralization enhances osteogenic
potential by exposing bone morphogenetic proteins (BMPs) in the bone
matrix.
Osteoinduction vs. Osteoconduction: Demineralized
grafts induce new bone formation (osteoinduction), while
undermineralized allografts facilitate bone growth by providing a
scaffold (osteoconduction).
Frozen Iliac Cancellous Bone and Marrow
Usage: Used sparingly due to variability in
outcomes and potential complications.
Comparison of Allografts and Alloplasts
Clinical Outcomes: Both FDBA and DFDBA have been
compared to porous particulate hydroxyapatite, showing little difference in
post-treatment clinical parameters.
Histological Healing: Grafts of DFDBA typically heal
with regeneration of the periodontium, while synthetic bone grafts (alloplasts)
heal by repair, which may not restore the original periodontal architecture.
Window of Infectivity
Conservative DentistryWindow of Infectivity
The concept of the "window of infectivity" was introduced by Caufield in 1993
to describe critical periods in early childhood when the oral cavity is
particularly susceptible to colonization by Streptococcus mutans, a key
bacterium associated with dental caries. Understanding these windows is
essential for implementing preventive measures against caries in children.
Window of Infectivity: This term refers to specific
time periods during which the acquisition of Streptococcus mutans occurs,
leading to an increased risk of dental caries. These windows are
characterized by the eruption of teeth, which creates opportunities for
bacterial colonization.
First Window of Infectivity
A. Timing
Age Range: The first window of infectivity is observed
between 19 to 23 months of age, coinciding with the
eruption of primary teeth.
B. Mechanism
Eruption of Primary Teeth: As primary teeth erupt, they
provide a "virgin habitat" for S. mutans to colonize the oral
cavity. This is significant because:
Reduced Competition: The newly erupted teeth have
not yet been colonized by other indigenous bacteria, allowing S.
mutans to establish itself without competition.
Increased Risk of Caries: The presence of S.
mutans in the oral cavity during this period can lead to an
increased risk of developing dental caries, especially if dietary habits
include frequent sugar consumption.
Second Window of Infectivity
A. Timing
Age Range: The second window of infectivity occurs
between 6 to 12 years of age, coinciding with the eruption
of permanent teeth.
B. Mechanism
Eruption of Permanent Dentition: As permanent teeth
emerge, they again provide opportunities for S. mutans to colonize
the oral cavity. This window is characterized by:
Increased Susceptibility: The transition from
primary to permanent dentition can lead to changes in oral flora and an
increased risk of caries if preventive measures are not taken.
Behavioral Factors: During this age range, children
may have increased exposure to sugary foods and beverages, further
enhancing the risk of S. mutans colonization and subsequent
caries development.
4. Clinical Implications
A. Preventive Strategies
Oral Hygiene Education: Parents and caregivers should
be educated about the importance of maintaining good oral hygiene practices
from an early age, especially during the windows of infectivity.
Dietary Counseling: Limiting sugary snacks and
beverages during these critical periods can help reduce the risk of S.
mutans colonization and caries development.
Regular Dental Visits: Early and regular dental
check-ups can help monitor the oral health of children and provide timely
interventions if necessary.
B. Targeted Interventions
Fluoride Treatments: Application of fluoride varnishes
or gels during these windows can help strengthen enamel and reduce the risk
of caries.
Sealants: Dental sealants can be applied to newly
erupted permanent molars to provide a protective barrier against caries.
Pharmacodynamics
Pharmacology
Pharmacodynamics
Pharmacodynamics is the study of what drugs do to the body and how they do it.
Dose-Response Relationships
- Basic Features of the Dose-Response Relationship: The dose-response relationship is graded instead of all-or-nothing (as dose increases, response becomes progressively larger).
- Maximal Efficacy and Relative Potency
- Maximal Efficacy: the largest effects that a drug can produce
- Relative Potency: Potency refers to the amount of drug that must be given to elicit an effect.
- Potency is rarely an important characteristic of a drug.
- Potency of a drug implies nothing about its maximal efficacy.
Clavulanic acid
Pharmacology
Clavulanic acid is often combined with amoxicillin to treat certain infections caused by bacteria, including infections of the ears, lungs, sinus, skin, and urinary tract. It works by preventing bacterium that release beta-lactamases from destroying amoxicillin.
Enflurane
Pharmacology
Enflurane (Ethrane) MAC 1.68, Blood/gas solubility ratio 1.9
- Extremely stable chemically.
- Less potent and less soluble in blood than is halothane.
- Respiratory depression is similar to that seen with halothane.
- Cardiac output is not depressed as much as with halothane, and the heart is not sensitized to catecholamines to the same degree.
- Enflurane produces better muscle relaxation than does halothane.
- Metabolism of this agent is very low. Inorganic fluoride is a product of metabolism, but is not sufficient to cause renal problems.
- Enflurane differs from halothane and the other inhalational anesthetic agents by causing seizures at doses slightly higher than those that induce anesthesia.
- Nausea appears to occur somewhat more often following Enflurane than it does following halothane.
Alcohols as Antiseptics
Oral and Maxillofacial SurgeryAlcohols as Antiseptics
Ethanol and isopropyl alcohol are commonly
used as antiseptics in various healthcare settings. They possess antibacterial
properties and are effective against a range of microorganisms, although they
have limitations in their effectiveness against certain pathogens.
Mechanism of Action
Antibacterial Activity: Alcohols exhibit antibacterial
activity against both gram-positive and gram-negative bacteria,
including Mycobacterium tuberculosis.
Protein Denaturation: The primary mechanism by which
alcohols exert their antimicrobial effects is through the denaturation
of proteins. This disrupts cellular structures and functions,
leading to cell death.
Effectiveness and Recommendations
Contact Time:
According to Spaulding (1939), for alcohol to achieve maximum
effectiveness, it must remain in contact with the microorganisms for at
least 10 minutes. This extended contact time is crucial
for ensuring adequate antimicrobial action.
Concentration:
Solutions of 70% alcohol are more effective than
higher concentrations (e.g., 90% or 100%). The presence of water in the
70% solution enhances the denaturation process of proteins, as reported
by Lawrence and Block (1968). Water acts as a co-solvent, allowing for
better penetration and interaction with microbial cells.
VIRAL DISEASES -RABIES
General Pathology
VIRAL DISEASES
RABIES (Hydrophobia)
An acute infectious disease of mammals, especially carnivores, characterized by CNS pathology leading to paralysis and death.
Etiology and Epidemiology
Rabies is caused by a neurotropic virus often present in the saliva of rabid animals
Pathology
The virus travels from the site of entry via peripheral nerves to the spinal cord and the brain, where it multiplies; it continues through efferent nerves to the salivary glands and into the saliva.
microscopic examination shows perivascular collections of lymphocytes but little destruction of nerve cells. Intracytoplasmic inclusion bodies (Negri bodies), usually in the cornu Ammonis, are pathognomonic of rabies, but these bodies are not always found.
Sign/Symptoms
In humans, the incubation period varies from 10 days to > 1 yr and averages 30 to 50 days.
Rabies commonly begins with a short period of depression, restlessness, malaise, and fever. Restlessness increases to uncontrollable excitement, with excessive salivation and excruciatingly painful spasms of the laryngeal and pharyngeal muscles. The spasms, which result from reflex irritability of the deglutition and respiration centers, are easily precipitated Hysteria due to fright
Prognosis and Treatment
Death from asphyxia, exhaustion, or general paralysis usually occurs within 3 to 10 days after onset of symptoms