Miscellaneous Flashcards
transfusion related lung injury
Transfusion related lung injury is most common following the transfusion of plasma components such as platelets and FFP. The condition is due to leucocyte antibodies in the transfused plasma. This causes leucocyte sequestration and degranulation in the lung. This produces marked microvascular and tissue damage with the development of a non cardiogenic pulmonary oedema. Because the primary problem is one of tissue injury, diuretic therapy is largely unhelpful.
anaesthetic agentsis most likely to induce adrenal suppression
Etomidate is a recognised cause of adrenal suppression, this has been associated with increased mortality when used as a sedation agent in the critically ill.
power calculation
The components that are nearly always needed for power calculations are :
Size of effect
Significance level
Sample size used to detect the effect
Desired power value
Type 1 Error
A test rejects a true null hypothesis. Analogous to false positive. It usually equates to the significance level assigned to a test.
Related to the p value
Type 2 Error
A test fails to reject a false null hypothesis. It is related to the power of a test.
Statistical power
The power of a test is the probability that the test will reject the null hypothesis when it is false (thereby avoiding a type 2 error). Increasing the power of a test will reduce the probability of a type 2 error. Usually a value of 0.8 is selected.
ASA grading
1 No organic physiological, biochemical or psychiatric disturbance. The surgical pathology is localised and has not invoked systemic disturbance.
2 Mild or moderate systemic disruption caused either by the surgical disease process or though underlying pre-existing disease
3 Severe systemic disruption caused either by the surgical pathology or pre-existing disease
4 Patient has severe systemic disease that is a constant threat to life
5 A patient who is moribund and will not survive without surge
Anal SCC virus
Infection with human papilloma virus 16 is a risk factor for the development of intra epithelial dysplasia of the anal skin with subsequent increased risk of invasive malignancy.
Nominal
Numbers are assigned to data that has no underling numerical value (e.g. marital status)
Ordinal
Has numbers that can be assigned to a natural underlying order (e.g. tumour grades)
Discrete
Data has a discrete numerical value, that has to be a whole number (e.g. number of deaths)
Continuous
Data has a numerical value that may not be a whole number and often reflects a direct measurement (e.g. weight)
Normal distribution
if the mean, median and mode overlap numerically then the data will be normally distributed
Parametric vs Non parametric
Parametric methods of data analysis assume that the underlying data set has a normal distribution. Non parametric methods do not make assumptions about the nature of the underlying data.
Parametric tests
T test
Paired T test
Non parametric tests
Mann Whitney U
Chi squared
Spearman’s Rank Correlation
Wilcoxon Signed Rank test
T test
Direct comparison of data sets which are normally distributed
Mann Whitney U
Ranked method for non parametric data
Wilcoxon matched pairs/ signed rank
Analog of the paired T Test, data must be interval, data based on magnitude of differences
Spearmans Rank Correlation
Statistical dependence between 2 variables. May be used for continuous or discrete variables
Chi Squared test
Test of association between two qualitative variables,valid if 80% expected frequencies exceed 5 or all exceed 1. Fishers exact test may be used for small samples
Note that where numbers are less than 40, Yates correction may be required, this can reduce the value of Chi Square. The numbers used in Chi Squared tests are proportions rather than actual values.
GI melanoma metastasis
The small intestine is the most common site of GI tract metastasis from cutaneous melanoma. These tumours are often polypoidal and may cause small bowel obstruction either by mass effect or as a result of intussusception. Surgical resection is the usual management. Ultimately most patients will go on to die from distant disease, survival figures of up to 4 years are quoted in some case series.
Cryoprecipitate
Blood product made from plasma
Usually transfused as 6 unit pool
Indications include massive haemorrhage and uncontrolled bleeding due to haemophilia
Composed of Factor 8, fibrinogen, vWF, F 13 ( main part is F8)
Hereditary spherocytosis
Most common disorder of the red cell membrane, it has an incidence of 1 in 5000. The abnormally shaped erythrocytes are prone to splenic sequestration and destruction. This can result in hyperbilirubinaemia, jaundice and splenomegaly. In older patients an intercurrent illness may increase the rate of red cell destruction resulting in more acute symptoms.
Severe cases may benefit from splenectomy.
Mucoepidermoid carcinoma
30% of all parotid malignancies
Usually low potential for local invasiveness and metastasis (depends mainly on grade)
Adenoid cystic carcinoma
Unpredictable growth pattern
Tendency for perineural spread
Nerve growth may display skip lesions resulting in incomplete excision
Distant metastasis more common (visceral rather than nodal spread)
5 year survival 35%
Mixed tumours
Often a malignancy occurring in a previously benign parotid lesion
Acinic cell carcinoma
Intermediate grade malignancy
May show perineural invasion
Low potential for distant metastasis
5 year survival 80%
Adenocarcinoma
Develops from secretory portion of gland
Risk of regional nodal and distant metastasis
5 year survival depends upon stage at presentation, may be up to 75% with small lesions with no nodal involvement
Lymphoma
Large rubbery lesion, may occur in association with Warthins tumours
Diagnosis should be based on regional nodal biopsy rather than parotid resection Treatment is with chemotherapy (and radiotherapy)
Most comman cause for sepsis in asplenic patients
In spite of immunization, S. Pneumoniae accounts for more than 50% of OPSI cases.
Antibiotics : mechanism of action
Inhibit cell wall formation
penicillins
cephalosporins
Inhibit protein synthesis
aminoglycosides (cause misreading of mRNA)
chloramphenicol
macrolides (e.g. erythromycin)
tetracyclines
fusidic acid
Inhibit DNA synthesis
quinolones (e.g. ciprofloxacin)
metronidazole
sulphonamides
trimethoprim
Inhibit RNA synthesis
rifampicin
Acute dystonic reaction
Procyclidine will help to reverse the event. This is most likely to have occurred because the patient is on long term anti psychotics and has then received metoclopramide.
Ordinal data
Ordinal data expresses relative differences between subjects when the actual numerical differences are either unknown or cannot be derived. Quantitative comparisons cannot be made for ordinal data. As a result the descriptive statistic of choice for ordinal data is the median and inter quartile range. The inter quartile range describes data between the 25th and 75th centile, with the median illustrating the 50th percentile rank.
False positives
Test has a high sensitivity
A false positive may occur when a screening test falsely identifies individuals as having a condition when none is present. This is a price that is paid for having a sensitive screening test. In surgical practice both faecal occult blood testing and mammography probably generate the greatest burden and worry as a result of false positive results.
Dupuytrens contracture
In Dupuytrens disease the palmar fascia becomes hyperplastic and subsequently contracts. It is associated with the condition Peyronies disease in which the penis may become distorted. It is associated with liver disease, drugs such as phenytoin which can induce epithelial hyperplasia and chronic infections. A number of surgical excisional therapies are described and should be reserved for those with progressive or debilitating symptoms.
Drug trial types
Phase 0- Safety and efficacy data
Usually sub therapeutic dose given
Small number of patients
Phase I -Small number of patients
Safe dose range
Side effect profile
Dose escalation studies often used
Phase II - Larger number of participants
May be compared to existing therapies
Adverse effect data captured
Phase III Large number of participants
Comparison to placebo or existing therapy
Often randomised
Phase IV Done following licensing
Determine long term safety and efficacy
Pre-test probability
The proportion of people with the target disorder in the population at risk at a specific time (point prevalence) or time interval (period prevalence)
For example, the prevalence of rheumatoid arthritis in the UK is 1%
Post-test probability
The proportion of patients with that particular test result who have the target disorder
Post-test probability = post test odds / (1 + post-test odds)
Pre-test odds
The odds that the patient has the target disorder before the test is carried out
Pre-test odds = pre-test probability / (1 - pre-test probability)
Post-test odds
The odds that the patient has the target disorder after the test is carried out
Post-test odds = pre-test odds x likelihood ratio
where the likelihood ratio for a positive test result = sensitivity / (1 - specificity)
Mri weightings
T1 images water is dark and fat bright
T2 images fat is dark and water bright
Brain death -life support
Half of all patients who are declared brain dead and who continue to receive full and active treatment will succumb in 24 hours. Almost all patients will die in spite of treatment within 72 hours.
Anaethetics and porphyria
Sodium thiopentone and etomidate are contraindicated in porphyria.
Recall Bias
Recall bias represents a major threat to the internal validity of studies using self-reported data. It arises with the tendency of subjects to report past events in a manner that is different between the two study groups. This pattern of recall errors can lead to differential misclassification of the related variable among study subjects with a subsequent distortion of measure of association in any direction from the null, depending on the magnitude and direction of the bias. Although recall bias has largely been viewed as a common concern in case-control studies, it also has been documented as an issue in some prospective cohort and randomized controlled trial designs
Central tendency
Median and inter quartile range is the best method for establishing central tendency and is least susceptible to outliers. Remember that the data set will be derived from symptomatic individuals (who may have been taking mediation and been malnourishe for some time).
