Sunday, June 7, 2015

Preoperative preparation is classified into 3 categories according to urgent degree.

Emergent operation necessary preparations should be done with the shortest time operate immediately.


Caloric sources

Three major sources: protein, carbohydrate, and fat

Amount of glycogen is limited, only can supply 3765.6 KJ900 kcal),comprise ½ of daily requirement

Protein cannot be considered as an energy source.

Body fat is the main energy storage about l5Kg. In starvation fat provides the bulk of calories with little effect on organ function, but certain amount of protein also be oxidized

Anthropometry

Malnutrition: body weight loss > 15%t

Viscera protein: albumin, etc.

Incapable of oral ingestion > 5-7 days

Preoperative preparation of malnutrition patient, digestive tract fistula, acute severe pancreatitis, short bowel syndrome, severe infection, large area burning, and hepatic, renal failure, etc.

PN after major operation is beneficial to patient's recovery, especially abdominal surgery

Intestinal inflammatory diseases: ulcerative colitis, Crohn disease

Nutrition support may promote tumor proliferation and development, so it should be used in combination with chemotherapy.

Glucose

Main energy source of PN, only 100 g/24 h can save protein

Advantages: sufficient origin, low price, convenient to know its utilization status through monitoring blood & urine glucose 

Disadvantages:

  • High concentration: 25% & 50%irritable to vein 
  • Limit of body utilization: 5 mg/(kg·min)
  • Surgical patients combined with DM are more susceptible to   
  • Glucose metabolism disturbance
  • Under stress, body utilization rate decrease, extra glucose turn into fat, dispose in organs

Electrolytes

Potassium, sodium, chloride, calcium, magnesium and phosphorus 

Vitamins

Water soluble: thiamine, riboflavin, niacin, pantothenic acid, pyridoxine, folic acid, B12

Fat soluble: A, D, E, K

Trace metals

Zinc, Copper, Chronium, Selenium, Manganese, Iron

Technical complications: 

  • Related to central venous catheter: pneumothorax, injury of blood vessel, nerve or thoracic duct due to puncture.
  • Air embolism
  • Insufficient replenishment
  • Serum electrolyte disturbance
  • Trace metal deficit
  • Essential fat acid deficit

Hypo/hyperglycemia

  •        Hypoglycemia: over-dosage of extraneous insulin
  •        Glucose infusion rate too rapid
  •        Decreased utilization of glucose

Liver function damage

  •        Liver steatosis due to overfeed of glucose
  •        Use fat emulsion as part of energy source

Stone formation in the gall bladder: long-term PN without food stimulation to the gut

Mild abnormalities of serum transaminase, alkaline phosphatase and bilirubin levels may occur in many parenterally nourished patients. Intestine barrier function impaired due to lack of food stimulus to the intestine and glutamine insufficiency

Infectious complications

Sepsis secondary to contamination of the central venous catheter

Causes:
Systemic sepsis
  • Hematogenous seeding of the catheter with bacteria
  • Failure to observe strict aseptic precautions during preparation & administration of the solutions
  • Clinical manifestations:
  • Sudden development of glucose intolerance
  • Fever
  • Infectious complications
  • Sepsis secondary to contamination of the central venous catheter

Management
  • Other causes of fever also should be investigated
  • If fever persists, the infusion catheter should be removed and cultured
  • Should evidence of infection persists over 24-48 h without a definable source, the catheter should be replaced in the opposite subclavian vein, and antibiotics also should be administrated


Saturday, June 6, 2015

Shock is defined as peripheral circulatory failure causing tissue perfusion to be inadequate to meet the nutritional requirements of the cells and remove the waste products of metabolism.

Definition

A controllable and reversible loss of consciousness induced by intoxication of the central nervous system. Lowered sensitivity to external stimuli (hyporeflexia), analgesia, unconsciousness, muscle relaxation, and amnesia are significant features of general anesthesia.

Tree stages of general anesthesia

  • Induction of anesthesia
  • Maintenace of anesthesia
  • Recovery of anesthesia

Inhalational anesthesia

Inhalation anesthetics are substances that are brought into the body via the lungs and are distributed with the blood into the different tissues. The main target of inhalation anesthetics (or so-called volatile anesthetics) is the brain.

MAC

 Definition: MAC is the “minimum alveolar concentration” of an inhaled anesthetic at atmospheric pressure with 100%O2required to prevent movement in response to a noxious stimulus in 50% of subjects.

§  MAC is analogous to the plasma EC50 (concentration for 50% effect) for intravenous anesthetics.

the alveolar concentration of an anesthetic (Fa)

§   ventilation the first of five factors that govern the pulmonary inhaled anesthetic concentration

§   blood passing through the lung opposes the effect of ventilation by drawing anesthetic from the lung.

§   An increased inspired concentration of anesthetic decreases the effect of uptake (the concentration effect), and at 100% inspired concentration, uptake no longer opposes the effect of ventilation.

the alveolar concentration of an anesthetic (Fa)

§  Metabolism of anesthetics can increase uptake.

§  Anesthetic uptake may be enhanced by movement of anesthetic between tissues (intertissue diffusion)

§  Three factors determine uptake by blood: solubility (the blood-gas partition coefficient),

§  pulmonary blood flow (cardiac output),

§   the difference in anesthetic partial pressure between the lungs and venous blood returning to the lungs

The toxicity of inhaled anesthetics

§   Halothane, enflurane, isoflurane, and desflurane have been reported to induce liver injury in susceptible patients. halothane (20%) enflurane (2.5%) isoflurane (0.2%) > desflurane (0.02%). Sevoflurane does not produce acylated protein adducts.

§   inorganic fluoride levels50umol/L, fluoride-associated renal injury has not been reported.

Common inhaled anesthetics

§   Nitrous oxide: weak inhaled anesthetic potency ,have no significant effect on cardiac output ,heart rate and blood pressure. Clinical  concentration 50%-70%, oxygen concentration must be higher than 0.3,so as to prevent hypoxemia. To prevent diffused hypoxemia,100% oxygen should be inhaled for 5-10 min after stopping nitrous oxide. increase  the pressure of the sealed cavity.

§  Enflurane: higher inhaled anesthetic potency ,have effect on EEG, depress the cardiovascular system, depress the respiratory system, but have no irritation to airway. To maintain  anesthesia with concentration 0.5%-2%,be careful to use on the patient with epilepsy.

§  Isoflurane: high inhaled anesthetic potency , mildly depress the cardiovascular system and the respiratory system,  have no irritation to airway. To maintain  anesthesia with concentration 0.5%-2%,can be used for controlled hypotension.

§  sevoflurane: higher inhaled anesthetic potency , mildly depress the cardiovascular system,  severely depress the respiratory system,  have no irritation to airway. To maintain  anesthesia with concentration 1.5%-2.5%.

Intravenous Anesthesia

Intravenous anesthetics is administered via the intravenous route - that is, directly into the patient's bloodstream. This allows them to reach a therapeutic level quickly and affect the brain quickly.

Common intravenous anesthetics

§   Thiopental:  rapid onset of action and short duration , water-soluble barbiturate salts in alkaline solutions PH10-11,usual concentration 2.5%. action on GABA receptor ,decrease cerebral metabolism, depress the cardiovascular system,  the respiratory system and the sympathetic system .

§   Side effect: larygospasm bronchospasm

§   Induction:4-6mg/kg

§   Treat convulsions:1-2mg/kg

§   Ketamine: significant analgesic effect ; It usually does not depress the cardiovascular and respiratory systems, but it does possess some of the adverse psychological effects ;

§   dissociative anesthesia ; increase ICP; increase in intraocular pressure; increase salivation; a bronchial smooth muscle relaxant

§   Induction:1-2mg/kg iv,duration 15-20min

§   Basel anesthesia:5-10mg/kg im for children ,duration 30min

§   Etomidate:Etomidate is used primarily for induction of anesthesia, especially in elderly patients and patients who have cardiovascular compromise. It has a rapid onset of effect and a rapid offset even after a continuous infusion. Prolonged infusion results in inhibition of adrenocortical synthesis. The major advantage of etomidate is its minimal effect on the cardiovascular and respiratory systems. It is associated with a high incidence of burning on injection, thrombophlebitis, and postoperative nausea and vomiting (PONV). The induction dose is 0.2 to 0.3 mg/kg.

§   propofol :propofol provides rapid onset and offset with context-sensitive decrement times of approximately 10 minutes when infused for less than 3 hours and less than 40 minutes when infused for up to 8 hours. Its mechanism of action of γ-aminobutyric acid (GABA). At therapeutic doses, propofol produces a moderate depressant effect on ventilation. It causes a dose-dependent decrease in blood pressure primarily through a decrease in cardiac output and systemic vascular resistance. A unique action of propofol is its antiemetic effect.

§    induction : 1 to 2 mg/kg

§    maintenance: infusion of 100 to 200 µg/kg/min.

Muscle relaxants

§   This class of drugs has its effect at the neuromuscular junction by preventing the effects of acetylcholine. Normally, when a nerve stimulus acts to contract a muscle, it releases acetylcholine. The binding of this acetylcholine to receptors causes the muscle to contract

Different Mechanism between nondepolarizing and depolarizing relaxants

§   Nondepolarizing muscle relaxants produce neuromuscular blockade by competing with acetylcholine for postsynaptic receptors.  Depolarizing ones produces prolonged depolarization that results in decreased sensitivity of the postsynaptic nicotinic acetylcholine receptor and inactivation of sodium channels so that propagation of the action potential across the muscle membrane is inhibited.

Depolarizing muscle relaxants

§   Succinylcholine is the only available neuromuscular blocker with a rapid onset of effect and an ultrashort duration of action.

§   Induction:1-2mg/kg peak time:60sec

§   Side effect:sinus bradycardia; increase plasma potassium;increase intragastric pressure, increase ICP; increase in intraocular pressure

Nondepolarizing muscle relaxants

§   Pancuronium: onset time:3-6min;duration :100-120min; Induction:0.1-0.15mg/kg

§   Vecuronium: onset time:2-3min;duration :25-30min; Induction:0.07-0.15mg/kg

§   Rocuronium: onset time:1-1.5min;duration :25-30min; Induction:0.6-1.2mg/kg

§   Cisatracurium: onset time:2-3min;duration :50-60min; Induction:0.15-0.2mg/kg,hofmann elimination


Wednesday, December 3, 2014


Tuesday, October 7, 2014

cohort studyA cohort study is a type of observational investigation in which subjects are classified on the basis of level of exposure to a risk factor and followed to determine subsequent disease outcome.

Cohort study characteristics

  1. Observational study: No manipulation of the study factors
rs
  2. Have control group.
  3. From ‘cause’ to ‘outcome’.
l  “Prospective” = forward looking in time
l  Can be historical perspective
l  Also called follow-up, incidence, panel, or longitudinal study
  4. Could examine the causal association between the exposure and the outcome.

Cohort study types

1. Prospective cohort study: The basic type of cohort study
2. Historical cohort study Or retrospective cohort study
3. Ambispective cohort study

Prospective cohort studies

Prospective cohort studies are conducted by making all observations on exposure and disease status after the onset of the investigation

Retrospective cohort studies

Retrospective cohort studies involve observations on exposure and disease status prior to the onset of the study

Cohort Study design and practice

·         Selection of Subjects
       The Exposed Group
       The Unexposed Group
       The Outcome Event
l    Follow up
l    Data Collection

Selection of exposed group

Exposure determining is based on descriptive study and case-control study.The degree of exposure may differ depending on the goals of the study.

The investigator should identify an accessible population that is motivated to participate in the study and unlikely to discontinue participation

When the purpose of a cohort study is to investigate a community, such as in the Framingham Heart Study that community is the source of the unexposed persons.

Data Collection

Possible sources of data an exposure status include records, Interviews or Questionnaires, or Direct Measurements Made on Cohort Members.
Records

The available records include that Occupational records, medical and pharmacy records, census records and so on

Direct Measurements

Many exposures of interest cannot be determined with any accuracy, or perhaps at all, for individual study subjects from either records or interviews, but can be determined by direct measurement.

Cumulative incidence rate

Number of new cases of disease occurring over a specified period of time in a population at risk at the beginning of the interval.

Cumulative Incidence

the probability (risk) of an individual developing the disease (outcome) during a specific period of time.

Incidence density

Number of new cases of disease occurring over a specified period of time in a population at risk throughout the interval. The probability (risk) of an individual developing the disease (outcome) during a specific period of time, using total person-time as the denominator.  One subject followed one year contributes one person-year (PY). 

Incidence density requires us to add up the period of time each individual was present in the population, and was at risk of becoming a new case of disease.
                                                                               
Incidence density characteristically uses as the denominator person-years at risk.  (Time period can be person-months, days, or even hours, depending on the disease process being studied.)




descriptive studyDescriptive study includes activities relates to characterizing the distribution of disease within a population. Descriptive studies can yield valuable information about a population's health
status, and they can be used to measure risks and generate hypotheses. It is also useful in health service evaluation and can be used periodically to determine whether a particular service is improving

The type of descriptive study

  • Case reports
  • Case series
  • Cross sectional studies
  • Ecologic studies

Case reports and series

Case report: describes an observation in a single patient.
ª  “I had a patient with a cold who drank lots of orange juice and got better.  Therefore, orange juice may cure colds.”
Case series: same thing as a case report, only with more people in it.
ª  “I had 10 patients with a cold who drank orange juice….”

Cross sectional studies

A cross-sectional study is a descriptive study in which disease and exposure status are measured simultaneously in a given population. Also called a “survey” or “prevalence” study Cross-sectional studies can be thought of as providing a "snapshot" of the frequency and characteristics of a disease in a population at a particular point in time. This type of data can be used to assess the prevalence of acute or chronic conditions in a population.

Research aim of prevalence survey

  • To describe distribution of disease
  • To discovery clue of pathogenesis
  • Be used in secondary prevention
  • To evaluate prevention and cure effect
  • Surveillance of disease
  • Health demand, health project and health policy decision

Describe the distribution of disease or health status by person, place and time, then analyze that which factors are relate to the disease or health status.

Secondary prevention seeks to minimize adverse outcomes of disease through early detection, even before symptoms develop and care is sought. Mammography for early detection of breast cancer in asymptomatic women is an example.

An occupational physician planning a coronary prevention program might wish to know the prevalence of different risk factors in the workforce under his care so that he could tailor his intervention accordingly.



Friday, September 12, 2014


The acute phase response is a quickly mobilized non-specific defensive response elicited in response of the host to  infection, tissue injury or inflammation.

Acute phase proteins 

Acute phase proteins have been defined as the proteins whose plasma concentration increases (positive acute phase proteins) or decreases (negative acute phase proteins) during the acute phase responses.

Acute phase proteins: Composition and Resource

APs are synthesized mainly by hepatic cells, the monocytes, and fibroblasts.

Acute phase proteins: Main Functions

1. To help the immune system adapt to various environmental stresses. removal of exogenous substance and necrotic tissue to promote the healing .for example:c-reactive protein c-reactive protein + combine with bacterial wall  activate complement classic pathway promote phagocytosis induce the expression of inflammatory cytokines and tissue factor in monocytes.
2. Inhibit the activity of protease: The protease inhibitors can protect tissues from over injuries by protease 
3. up-regulation of fibrinogen in the acute phase response is beneficial  to increasing the hemostatic power and the wound healing
4. ceruloplasmin,haptoglobin and hemopexin can bind copper and heme, and avoid the injuries of tissues by overmany copper and iron. Ceruloplasmin exhibit an antioxidant function against oxidative stress injuries.
5. serum amyloid protein A associated HDL3 seems to facilitate the uptake and removal of cholesterol from moncytes/macrophages at the inflammatory site



Monday, July 28, 2014

Material metabolism in liver

liver metabolism
  • carbohydrate metabolism
  • lipid metabolism
  • protein metabolism
  • vitamin metabolism
  • hormone metabolism 

Carbohydrate metabolism

Functions

Maintaining the constancy of the concentration of sugar in blood; supplying energy to peripheral tissues, especially to brain and erythrocytes.

Main pathways for carbohydrate metabolism

  • gluconeogenesis
  • glycogenesis and glycogenolysis
  • glycolysis 

Carbohydrate metabolism in varied nutrient conditions in liver

    --  glycogenesis↑
          --  excess carbohydrate is converted to fatty acids and exported in VLDL form
  • postabsorption state
     --  glycogenolysis↑→release glucose to replenish blood sugar
  • starvation state
     --  gluconeogenesis
     --  lipid mobilization↑→acetone body↑→saving glucose

Lipid metabolism


Functions: 

Play important role in digestion, absorption, synthesis, catabolism and transportation of lipids.  

 Main pathways lipid metabolism

  • oxidation of fatty acids
  • synthesis of fatty acids and esterification
  • formation of ketone bodies
  • synthesis of lipoproteins and apolipoproteins (VLDLHDLapoC II)
  • degradation of lipoproteins

Role of liver in varied processes of lipid metabolism

  • digestion and absorption
    --  biliation.  Bile acid is essential for lipid digestion and  absorption
     --  liver dysfunction→fatty diarrhea
  • synthesis
     --  fatty acid, triacylglycerol, ketone body, cholesterol,phospholipid
     --  liver dysfunction→fatty liver, Ch/ChE↑
  • catabolism
     --  β-oxidation of fatty acids, degradation and excretion of cholesterol, degradation of LDL
  • tranportation
     --  synthesis and secretion of VLDL, HDL, apoC II and LCAT

Protein metabolism


Functions: synthesis (γglobulin is excepted), secretion and elimination (albumin is excepted) of plasma proteins.

Liver dysfunction:

  • albumin↓→edema, A/G↓
  • plasma thromboplastin component ↓ →disturbance of blood coagulation
  • blood ammonia
  • amine↑→hepatic encephalopathy 

Vitamin metabolism

Functions

  • absorption of fat-soluble vitamins
  • storadge of vitamins (VA, VK,VE,VB12)
  • transpotation of vitamins synthesis of retinol-binding protein and VitD-binding protein
  • transformation of vitamins
  • β-carotene→VitA Vit D3 → 25-(OH)-Vit D3 water-soluble vitamins →cofactors

Liver dysfunction

  • biliary obstruction→VitK↓→hemorrhagic tendency
  • hepatic rickets

Hormone metabolism

Functions: inactivation of hormones
Manner: biotransformation

Liver dysfunction:

  • Spider angioma of skin
  • liver pulms
  • cutaneous pigmentation
  • hypoglycemia



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