Diseases of the Circulatory and Central Nervous Systems

CST: Clinical Significance

• Surgical technologists should focus on preventing sharps injuries and using PPE to minimize risks from unrecognized microbial pathogens.
• Standard Precautions presume every individual is potentially infectious.
• Hands-free, neutral-zone, and no-touch techniques are essential for handling sharp instruments.
• Blunt suture needles should be used for closing large or deep wounds.
• Eye protection should be worn in every case to prevent blood transfer to conjunctival membranes.

Hematology and Serology

• Hematology: Study of blood and blood-forming tissues, focusing on circulatory system cells:
  • White blood cells (leukocytes): Defend against foreign invaders.
  • Red blood cells (erythrocytes): Transport oxygen and carbon dioxide.
  • Platelets (thrombocytes): Prevent blood loss during injury.
• Plasma: Solution in which blood cells are suspended.
• Centrifugation: Separates blood cells from plasma.
• Total blood volume: Amount of blood in the circulatory system.
  • Average adult: 4 to 8 liters ( $1$ liter = $1.06$ quarts).
• Blood composition:
  • Blood cells: 45% of blood volume.
  • Plasma: 55% of blood volume, comprising 90% water and 10% solids (proteins, carbohydrates, enzymes, vitamins, lipids, and salts).
• Whole blood: Cellular components and plasma.
• Sera: Clear liquid after separating solid elements and removing fibrinogen from plasma.
• Serology: Determines antibodies or antigens in blood samples by calculating serum titers.
  • Laboratory tests: Slide agglutination and ELISA tests.
  • Western blot: Identifies bacteria in serum, including $Borrelia burgdorferi$ (Lyme disease) and HIV.
    • Proteins are separated, transferred to a filter, and dye-tagged antibodies are applied.
    • Positive test: Colored band indicates antibody-antigen bonding.
• Key term: Electrophoresis: Separation of proteins from serum.

Transmission of Infections from Donated Blood Products

• Blood transfusions can transmit blood-borne pathogens despite strict screening.
• Infective agents may cause serious systemic sepsis.
• Pathogenic contaminants:
  • Bacterial: Gram-positive $Staphylococcus aureus$ and $S. epidermidis$ (entry via percutaneous skin puncture).
  • Parasitic: Tick-borne anaplasmosis ($Anaplasma phagocytophilium$) and babesiosis ($Babesia microti$); Chagas disease ($Trypanosoma cruzi$) spread by triatomine bugs; Leishmaniasis ($Leishmania$ protozoa) from sand flies; Mosquito-borne Malaria ($Plasmodium falciparum$).
  • Viral: Hepatitis B virus (HBV), hepatitis C virus (HCV), HIV, human T-lymphotropic virus (HTLV), West Nile virus (WNV), and Zika virus.
  • Prions: Creutzfeldt-Jakob disease (CJD) or variant CJD (vCJD).
• Key term: Transfusions

Circulatory System Infections

Bacteremia

• Bacterial infection of the bloodstream.
• Entry mechanisms: Minor skin injuries, major trauma/surgery, dissemination from other infections, blood transfusions.
• HAIs: Surgical procedures, indwelling catheters, infected wounds, prosthetic devices.

Septicemia

• Expansion of bacteremia, leading to septic shock (systemic inflammatory response syndrome - SIRS).
• Signs: Hyperthermia/hypothermia, confusion, rash, tachycardia, and hypotension.
• Approximately 40% of patients with septicemia progress to septic shock; half of those die from the infection.
• Highest risk: Immunosuppressed/immunocompromised patients.
• Gram-positive and Gram-negative bacteria are equally responsible.
• Common pathogens from other body system infections:
  • Respiratory: $Streptococcus pneumoniae$, $Chlamydia pneumoniae$, $Haemophilus influenzae$, $Legionella spp$.
  • GI tract: $Escherichia coli$, $Bacteroides fragilis$, Group B $Streptococcus$ (neonates), $Yersinia enterocolitica$ (rare).
  • Skin/soft tissues: $S. aureus$, $S. pyogenes$, $Clostridium spp$, $P. aeruginosa$.
  • Genitourinary: $E. coli$, $Klebsiella spp$, $Enterobacter spp$, $Proteus spp$, $Enterococcus spp$.
  • CNS: $S. pneumoniae$, $N. meningitidis$, $L. monocytogenes$, $E. coli$, $H. influenzae$, $P. aeruginosa$, $Staphylococcus spp$.

Infective Endocarditis (IE)

• Serious infection of the heart's innermost lining (endocardium) and valves.
• Valvular incompetence/insufficiency leads to congestive heart failure (CHF) and myocardial abscesses.
• Occurs in patients with damaged/abnormal heart architecture and exposure to opportunistic bacteria.
• Entry via trauma, dissemination from other infections, IV drug use, and unprotected sex.
• High morbidity; generally fatal if untreated.
• Two types:
  • Subacute IE: Slow to develop, usually caused by α-hemolytic $Streptococcus$ (oral cavity). Enterococcus and $Staphylococcus$ are also common causes.
    • Periodontal, pharyngeal, and remote infections may cause subacute IE.
    • Dentists prescribe prophylactic antibiotics before tooth extractions to prevent bacteria from colonizing pre-existing lesions on heart valves (e.g., rheumatic fever, mitral valve stenosis, congenital heart anomalies).
    • Bacterial colony is protected from phagocytosis by blood clots which can break loose and travel to the lungs or brain, resulting in pulmonary thrombosis or cerebral infarct.
  • Acute IE: Sudden onset, typically caused by $Staphylococcus aureus$ or Group B $Streptococcus$.
    • Bacteria from an existing infection somewhere else in the body become dislodged, allowing entry into the bloodstream. Damages heart valves rapidly.

Prosthetic Valve Endocarditis (PVE)

• Occurs in patients with implanted prosthetic mechanical or bioprosthetic valves; $5–10$ of all endocarditis infections.
• Mechanical valves: Infected within the first 3 months (early onset).
• Bioprosthetic valves: Infected after 1 year (late onset).
• Mitral valves are more likely to be involved than aortic valves.
• $S. aureus$ is the most common cause of both early- and late-onset infections.
• Implanted pacemakers and cardioverter-defibrillators have similar risk to those with PVE.

Intravenous Drug Abuse Infective Endocarditis (IVDA IE)

• Up to 75% of infections involve normal native heart valves; 50% involve the tricuspid valve.

Fungal IE

• Found in intravenous drug users and ICU patients receiving broad-spectrum antibiotics.
• Blood cultures are often negative; diagnosis after microscopic examination of large emboli.
• Fungal infections may result from colonization of $Candida albicans$ or other fungi species.

Clinical Signs of Infective Endocarditis

• 85% of individuals with IE have a detectable heart murmur on auscultation.
• Classic signs in half of patients:
  • Subungual hemorrhages
  • Petechiae of the skin
  • Janeway lesions: Non-tender maculae on palms/soles
  • Osler nodes: Tender subcutaneous nodules usually of the distal pads of the digits
  • Roth spots: Retinal hemorrhages with clear centers, relatively rare (5%)
• Other possible observed signs of disease:
  • Neurological signs of embolic stroke, paralysis, hemiparesis, stiff neck, or delirium
  • Distended neck veins and chest x-ray signs of congestive heart failure
  • Hepatosplenomegaly
  • Pericardial or pleural friction rub
  • Gallops or rales
  • Cardiac arrhythmia
• Antibiotics are primary treatment; surgery for lysis of adhesions, repair/replacement of valves may be needed.
• Treatment for congestive heart failure and supplemental oxygen.
• Renal damage may require hemodialysis.

Myocarditis

• Inflammation of the middle, muscular layer of the heart caused by pathogenic microbes.
  • Bacterial causes: $Chlamydia$, $Mycoplasma$, $Streptococcus$, $Staphylococcus$, $Borrelia$, and $Treponema$.
  • Viral causes: $Coxsackie B$ virus, Cytomegalovirus, Epstein-Barr virus, Hepatitis C virus, Herpes simplex, HIV, and Parvovirus.
  • Fungal causes: $Aspergillus$, $Candida$, $Coccidioides$, $Cryptococcus$, and $Histoplasma$.
• Symptoms are mild or absent, so the infection goes undetected and may lead to cardiomyopathy, a type of heart failure.
• Myocarditis and cardiomyopathy are the leading causes for heart transplantation in the United States.

Pericarditis

• Inflammation of the pericardium (outer layer of the heart).
• Often secondary to other bacterial infections (e.g., lung abscesses or pneumonia) caused by $Streptococcus$.
• Less commonly viral (acute non-specific pericarditis).
• Chronic pericarditis causes pericardium to bind to the heart via adhesions, requiring surgical lysis of adhesions.
• Extrapulmonary tuberculosis pericarditis caused by $Mycobacterium tuberculosis$ results in deposits of calcium and fibrin that thicken and constrict the pericardial sac, entrapping serous pericardial fluid, preventing free movement of the heart, a life-threatening condition called cardiac tamponade.
  • Pericardiocentesis may be required to drain the fluid and relieve the pressure.

Vasculitis

• Or angiitis; inflammation of the blood vessels.
• Vascular inflammation can lead to narrowing of the internal lumen that reduces blood flow; complete constriction, causing ischemia and possible necrosis; or dilatation, leading to aneurysm formation.
• Severity of disease process depends on size of the vessels and numbers involved.
• $Pseudomonas aeruginosa$ is a common pathogen that produces a characteristic blue pus due to the pigment pyocyanin which can mediate tissue damage.
  • The bacterial cells show an affinity for invading blood vessels, a syndrome called ecthyma gangrenosum that begins as superficial skin lesions (buttocks, perineum, axillary region, extremities) that grow, and center of each lesion turns black, a result of necrosis caused by destruction of capillaries, arterioles, and venules.
    • Mortality rate is high among patients with neutropenia.
    • Deep wounds, open bone fractures, and severe burns are also subject to developing osteomyelitis caused by $P. aeruginosa$.

Pseudomonas aeruginosa Infections

• Patients with prosthetic heart valves and IV drug users are prone to endocarditis caused by $P. aeruginosa$.
• Injection drug users tend to be younger males who usually have no outstanding health problems other than their substance use disorder and acquire the infection from using drug paraphernalia contaminated with water-borne bacterial cells.
• The tricuspid valve between the right atrium and ventricle is more often involved than the other heart valves.
• A severe form of the infection also may affect the left heart (left-sided endocarditis) and presents the patient with a poor prognosis.

Blood-Brain Barrier

• A physiological barrier between systemic blood and brain parenchyma, designed to prevent entrance of antibodies and certain large molecules but remains permeable to water, oxygen, carbon dioxide, and non-ionic solutes such as alcohol, glucose, and anesthetic drugs.
• Tight junctions between choroid plexus and arachnoid epithelial cells, and capillary endothelial cells create the barrier.
  • Clearance of potentially harmful invasive substances once the barrier is penetrated is difficult.
• No barrier exists between the brain and cerebrospinal fluid (CSF) and extracellular fluid in the brain and CSF is in direct contact with brain matter.
• Free movement between inflammatory cells or pathogenic organisms within the extracellular fluid of the brain is restricted because the cellular space between neurons is smaller than the diameter of the smallest viruses.

Infections of the Central Nervous System

• Although the tissues of the CNS are remarkably resistant to infection by various pathogens, they are not fully impervious to them and if infection does occur, the resulting damage can be severe.
• Infection of the brain and spinal cord from bacteria, viruses, or fungi are relatively uncommon, considering the system does not have an intrinsic immune system, and can result in a wide range of neurological deficits.
• Quick diagnosis and treatment are critical to preventing death or permanent neurologic deficits (damage).

Meningitis

• Bacteria and other pathogens can reach the meninges and other areas of the brain through the bloodstream, or they can enter through a penetrating wound or as a result of a surgical procedure.
• Abscesses can spread from adjoining structures such as the nasal sinuses or periodontium.
• Non-infectious diseases such as sarcoidosis and some cancers, as well as drugs used to treat cancer and prevent organ rejection, can inflame the meninges and cause symptoms similar to those of infectious meningitis.
• Acute bacterial meningitis is an infection of the meningeal pia mater and arachnoid layers, a life-threatening disease that requires immediate medical treatment.
  • Pathogens in bacterial infection are $Haemophilus influenzae$ type B, $Streptococcus pneumoniae$, $Neisseria meningitidis$, and $Escherichia coli$.
  • These bacteria are normal residents of the nose, upper respiratory system, or GI tract and often infect the CNS if immune system is depressed.
  • Meningitis may be a complication of other diseases like endocarditis, pneumonia, or otitis media (middle ear infection).
  • Any penetrating injury (including surgery) of the skull can also allow the entrance of bacteria into the CNS.
• Meningitis is common in small children because of their immature immune systems and susceptibility to infections.
  • In neonatal period, infections from group B $Streptococcus$, $E. coli$, or $Listeria monocytogenes$ are most common.
  • In infants over 1 month, infections are usually from $Streptococcus pneumoniae$, $Haemophilus influenzae$ type B (Hib), and $Neisseria meningitidis$.
  • Except for a surgical infection or head injury, bacterial meningitis in adults is usually caused by $N. meningitidis$, $S. pneumoniae$, and $L. monocytogenes$.
  • Symptoms of meningitis include headache, stiff neck, sore throat (usually after respiratory illness), and vomiting.
  • Physician examining a patient will try to lower patient’s chin to the chest, but it may be too painful.
  • Older children and adults may become irritable and confused, with progression from drowsiness to stupor, coma and death.
  • Haemophilis influenzae meningitis – $Haemophilus influenzae$ type b (Hib) can spread from the upper respiratory tract to the sinuses and middle ear of children and adults, causing otitis media with children at elevated risk.
    • If bacterial cells invade the bloodstream, they can travel to the lymph nodes, and invade the meninges of the brain and spinal cord, causing meningitis although it is not understood how H. influenzae type b cells cross the blood–brain barrier to reach the CNS.
    • Infants aged 3 months and younger are protected by maternal antibodies; infection is rare in this age group, but between 6 months and 1 year of age, maternal antibodies have declined, and this corresponds with a peak incidence in the disease and up to 90% mortality in untreated patients.
    • Enduring deficits after recovery: hearing loss, blindness, chronic seizures, hydrocephalus, and developmental problems.
    • Diagnostic methods include cerebrospinal fluid (CSF) from spinal tap, blood samples, sputum, nasopharyngeal swabs, and exudates from infected conjunctivae from patients suspected to have a Haemophilus species infection.
    • Blood cultures are highly effective in isolating the bacteria involved.
    • Identification of the specific bacterial species is critical to prescribing the optimal antibiotics because other bacteria can cause ear infections and meningitis.
    • The Hib vaccine is a routine childhood immunization in the United States.
    • Three monovalent conjugate Hib vaccines and three combination vaccines that contain Hib.
    • Depending on the vaccine used, infants are given a series of injections at ages 2, 4, and 6 months or at ages 2 and 4 months. Booster doses are recommended at 12 to 15 months. Since the vaccine protocols have been in place, the incidence of Hib infections in children younger than age 5 years has decreased 99 percent in the United States.
• Fungal meningitis – Certain fungal infections, especially $Cryptococcus$, develop slowly in comparison with acute bacterial infections and can result in chronic meningitis.
  • Other fungi known to cause meningitis are $Histoplasma$, $Blastomyces$, and $Coccidioides$, which are found in the soil, and $Candida$, which is nearly always an HAI.
• Parasitic meningitis – A rare form of meningitis caused by the microscopic amoeba, $Naegleria fowleri$, is called primary amoebic meningoencephalitis (PAM).
  • The parasite gains access into the body through the nose when diving or swimming in bodies of warm freshwater such as lakes, ponds, rivers, underchlorinated pools, or warm springs.
    • Water from contaminated water heaters used to irrigate sinuses with devices such as Neti pots has been reported; parasite travels to the brain through the sinuses.
    • Drinking contaminated water is not a route of transmission.
    • $Naegleria fowleri$ is not found in saltwater bodies such as coastal waters.
• Viral meningitis – The most common form of meningitis infections.
  • The non-polio enteroviruses, coxsackievirus, enterovirus, echovirus, and parechovirus, are often the cause.
    • Other frequent causes include mumps (paramyxovirus of genus Rubulavirus), herpes viruses (including herpes simplex virus and varicella-zoster virus), measles virus, influenza virus, West Nile virus, and lymphocytic choriomeningitis virus.
    • Cytomegalovirus and HIV/AIDS may also result in a chronic infection.

Encephalitis

• An inflammation of the brain parenchyma; more dangerous than viral meningitis and caused by the same viruses as meningitis as well as arboviruses and rabies.
• Herpes simplex encephalitis is the most common type in the U.S. and if left untreated, has up to 70% mortality.
• Paralytic poliomyelitis is a virus that targets select motor neurons of the CNS.
• Rabies is a type of encephalitis created from the lyssavirus that causes rabies. In the U.S., lyssavirus is endemic in wild animals, especially skunks, foxes, raccoons, and bats, and has a characteristic bullet shape when viewed under a scanning electron microscope.
  • Transmission is by a bite from an infected animal.

Brucellosis

• Bacterial infection affects both the cardiovascular system and the CNS. The disease has been given various names based on the areas where outbreaks occurred, such as Malta fever, fever of Crete, Mediterranean fever, or based on the clinical presentation (undulant fever or gastric remittent fever).
• Acute brucellosis infections present with flu-like symptoms in addition to weight loss, and abdominal, joint, and back pain. Most cases of acute brucellosis resolve with appropriate antibiotic treatment.
• Chronic cases, similar to tuberculosis, can cause recurrent symptoms for years.
• The most serious complications of brucellosis are infective endocarditis, meningitis, and encephalitis.

Brain Abscess

• A collection of pus, usually found within frontal or temporal lobes of the cerebrum, which may be free or encapsulated and may occur in multiple areas of the brain.
• It is typically secondary to another infection somewhere in the body. Cases of otitis media, sinusitis, or mastoiditis are typical primary infections.
• Bacteria can travel to the brain from a tooth abscess or infections in the heart or lungs.
• Symptoms are those that are typically associated with abnormally increased intracranial pressure (ICP).
• Subdural empyema is a collection of pus just under the dural meninges of the brain; frequently a complication of sinusitis or otitis media, but it can also result from bacteria entering through a penetrating head injury. Surgery may be required to drain the pus and relieve intracranial pressure.