Stats

Question 1

Which of the following is NOT an advantage of anesthesia information management systems (AIMS)?

Answer 1

Anesthesia information management systems (AIMS) are being used more frequently and have many positive attributes, however there are still limitations that need to be worked out, especially with cost and integration.

Question 2

Which of the following statistical tests should be used to compare whether the incidence of postoperative vomiting differs between women ages 21-64 in the intensive care unit versus the floor unit?

Answer 2

Chi-square testing is used for comparison of two or more populations with respect to a single variable with categorical data (nominal scale).

Question 3

A recently published study has a β error of 0.2 and a target α of 0.05. Which of the following is the power of this study?

Answer 3

Power = 1-β. Practically speaking, the power tells us the chance that the null hypothesis (e.g. no treatment effect from a particular drug) will be rejected when an alternative hypothesis is actually true (e.g. a drug does have a treatment effect). The larger the sample population (usually denoted as “n = some number”), the greater the power.

Question 4

An investigator wishes to evaluate the mortality benefit of a new intubation technique. His results are as follows: 100 patients died using direct laryngoscopy, while 10 died using the new technique; 900 patients survived using direct laryngoscopy, while 200 survived using the new technique.

Which of the following is the odds ratio for dying using direct laryngoscopy as compared to the new intubation technique?

Answer 4

The odds ratio measures the ratio of the odds that an event will occur to the odds of the event not happening.
Using the table format, OR = (a/b)/(c/d), or, OR = (ad)/(bc)

Question 5

Which of the following is the primary barrier when converting from a paper anesthesia record to automated anesthesia record-keeping?

Answer 5

When compared with paper records, automated records have several advantages including greater speed of filing, faster retrieval, easier transmission of information, and data analysis. Disadvantages include cost, need for anesthesia machine integration, user knowledge, data safety issues, and capture of erroneous data.

Question 6

An investigator wishes to test the efficacy of a novel antiemetic medication on postoperative nausea and vomiting against that of ondansetron. Patients enrolled in the study are randomized to either group. The institution’s pharmacy creates coded labels for the two medications (known only to them) and the investigator injects one vial to patients enrolled in the study 30 minutes prior to extubation. Which of the following MOST accurately describes the blinding of the study?

Answer 6

Double-blinded studies are those in which both patients and investigators do not know which therapeutic measures patients receive.

Question 7

Which of the following is true of the chi-squared test?

Answer 7

The chi-square test is a nonparametric test to compare nominal or ordinal data comprising of one to multiple sample tests.

Question 8

Which of the following equations describes specificity?

Answer 8

Specificity = TN / (TN+FP). Specificity is the percentage of time a test is truly negative. By definition, it takes into account the cases which yield a false positive (FP) test.

Question 9

Which of the following does NOT determine fluid flow rate according to the Hagen-Poiseuille law?

Answer 9

To maximize flow rates the most important aspect is the radius. Other contributing factors to fast flow rates are high pressure, low viscosity, and short tubing. If flow is turbulent, reducing the density helps convert flow to laminar according to Reynolds number.

Question 10

In a study comparing prone versus supine positioning in ICU patients diagnosed with acute respiratory distress syndrome (ARDS), improvement in the PaO2 had a standard deviation of 10 in the prone group. If the study consisted of 100 patients, which of the following would be the standard error of the mean?

Answer 10

Standard error of the mean (SEM) can be calculated by dividing the standard deviation (SD) by the square root of the sample size (n).

Question 11

Assuming a normal distribution, which of the following approximates the percentage of data represented by μ ± σ, where μ = mean, σ = standard deviation?

Answer 11

Normal distribution indicates that data points are evenly distributed around the mean such that one standard deviation + or - from the mean contains 34.1% of points in each direction. Therefore, μ ± σ contains 68% of the data points under a curve that is normally distributed.

Question 12

How is Bayes theorem used in anesthesia practice?

Answer 12

Bayes theorem is used to help develop preoperative testing algorithms by helping clinicians interpret testing results in light of the patient presentation and surgical procedure. Bayes theorem states that the post-test probability of a person having a disease is related to both the sensitivity and specificity of the test and the prevalence of the disease in the population. In other words, it describes the probability of an event, based on conditions that might be related to the event (conditional probability).

Question 13

A study is being designed to determine which of two techniques for bowel re-anastomosis will result in the fastest return of bowel function following surgery. Patients are to be randomized to one of the two groups following the induction of anesthesia and details are not discussed after emergence. The surgeons who perform the procedure will record how many hours following surgery each patient had his/her first bowel movement. At the conclusion of the study, all data will be analyzed by the hospital’s statistical team. Which of the following BEST describes the type of blinding used in this study?

Answer 13

Single blinded studies are those in which only the participants are masked to which group they belong. Double blinded studies are those in which the participants and investigators are masked to participant assignment. Triple blinded studies are those in which the participants, investigators, and an additional third-party are masked. An unblinded study does not involve any masking.

Question 14

In a study of 100 patients with acute coronary syndrome, the average troponin was 7 with a standard deviation (σ) of 1. Which of the following is the standard error of the mean of their average troponins?

Answer 14

Standard error of the mean is equal to the standard deviation divided by the square root of the sample size. If standard deviation is 1 and population size is 100, then SEM = 0.1.

Question 15

What is the standard error when the standard deviation is 4 , the sample size 100, upper limit 2, and lower limit 8?

Answer 15

SE = SD / square root (N)

TrueLearn Insight : The standard error is a type of standard deviation and is a measure of the precision of the sample mean.

Question 16

A 45-year-old female has tracheal stenosis with plans to have a tracheal stent placed. Prior to having the operation, she develops an upper respiratory infection and begins to decompensate. The anesthesiologist involved would like to maintain laminar flow during pre-oxygenation to decrease the work of breathing. Which one of the following should be avoided because it promotes turbulent flow?

Answer 16

Reynolds number (R) = v * p * d / n = velocity * density * diameter / viscosity.
The Reynolds number (R) is used to predict turbulent flow.  When R < 2000, laminar flow is present.  When R > 4000, turbulent flow is more likely.
Ways in which laminar flow will become turbulent include high gas flow rates, sharp angles within a tube, branch points within a tube, and an increase in the diameter of the tube.  Increasing the density of gases flowing or decreasing viscosity also promotes turbulent flow.

Question 17

During a sitting craniotomy, a patient’s blood pressure is measured to be 120/60 mmHg, mean 80 mmHg, using a radial arterial catheter with the transducer at the level of the right atrium. Assuming the height difference between the radial artery catheter and the right atrium is 10 cm and the height difference between the right atrium and the circle of Willis is 10 cm, which of the following best estimates the patient’s mean arterial pressure at the level of the circle of Willis?

Answer 17

Raising or lowering a pressure transducer or estimating a pressure at a different level from the transducer results in a pressure change of approximately 7.5 mm Hg per 10 cm height difference. Raising the transducer or estimating a pressure at a level higher than the transducer lowers the pressure reading. Lowering the transducer or estimating a pressure at a level lower than the transducer raises the pressure reading.

Question 18

A researcher assigns patients to one of four groups based on age (infant, pediatric, adult, and geriatric) and then measures each patient 24-hour opioid usage after inguinal hernia repair, during which 1 mcg/kg dexmedetomidine was administered. Which of the following statistical tests would be MOST appropriate to determine whether any one group had a significantly different postoperative opioid requirement?

Answer 18

Use a form of ANOVA whenever more than two groups are compared. Use a t-test if only two groups are studied.

Question 19

An investigator wishes to assess the age of patients in a postanesthesia care unit. The outpatient surgical center employs 4 cosmetic breast surgeons and a pediatric dentist. Which of the following would be the MOST accurate measure of the central tendency of the data?

Answer 19

The central tendency of interval data sets, especially those that are not normally distributed, is most accurately represented by the median.

Question 20

Which of the following is the definition of a type I error?

Answer 20

Errors:
Type I or α error = incorrectly accepting Ha (false positive)
Type II or β error = incorrectly accepting Ho (false negative)

Question 21

Which of the following statistical tests should be used to compare the effect of sevoflurane versus the effect of remifentanil on mean arterial blood pressure in patients undergoing craniotomy?

Answer 21

Data Types/Type of Experiment:
Discrete Continuous Survival (events) Ordinal (rank)
Single Variable Chi-Square or Fisher’s Exact (n< 10) t-test Kaplan-Meier Analysis Wilcoxon-Mann-Whitney
Multivariable Logistics Regression
(“Chi-Squared on steroids”) ANOVA Cox Proportional Hazard Analysis Kruskal-Wallis

Question 22

A researcher plans to design an experiment testing the efficacy of an antihypertensive drug in diabetic patients. The plan is to take two groups of 500 diabetic patients and measure baseline and post-treatment blood pressures for group A (the treatment group) and group B (the control group), and then compare the change in blood pressure in group A versus the change in blood pressure in group B. Which of the following would be the MOST appropriate statistical test?

Answer 22

A paired t-test compares outcomes in a single group who serve as their own control, whereas an unpaired t-test compares an outcome in two different groups.

TrueLearn Insight : T-tests are only appropriate for normally distributed data (Parametric data). Parametric data is best represented by the mean.

Question 23

Which of the following statements regarding the power of a study is TRUE?

Answer 23

There are four ways to increase power (decrease type II error):
1) Increase alpha: the smaller the alpha, the greater the chance of a false-negative conclusion (risky, as this increases type I error).
2) Decrease population variability (difficult to control).
3) Increase the sample size.
4) Make the difference between the conditions greater (most important factor in decreasing a type II error but difficult to control/manipulate).
Increasing the alpha (type I error/false-positive) will increase the power. The larger the alpha, the lower the chance of a false-negative conclusion (type II error/beta). Conversely, increasing the beta will decrease the power. Power = 1 - beta.

Question 24

Given a normal distribution, which of the following is the approximate percentage of data that is greater than one standard deviation to the right (positive) of the mean?

Answer 24

In a normal distribution, 15.9% of the data is greater than one standard deviation to the right of the mean (similarly, 15.9% of the data is greater than one standard deviation to the left of the mean).

Question 25

Researchers want to determine whether there is an association between patients who experienced bronchospasm during intubation and daily use of NSAIDs. The researchers selected patients who experienced bronchospasm and those who did not. The groups were then analyzed to see which patients had daily exposure to NSAIDs. An odds ratio was then determined from the data. What type of study was performed?

Answer 25

This study is a case-control study because 2 groups of patients were selected and grouped on the basis of the outcome (bronchospasm). The outcome was then analyzed to determine the exposure (NSAIDs) of each group, and an odds ratio was calculated.

Question 26

Researchers want to determine whether fish oil supplementation is effective in reducing succinylcholine-induced myalgias. They conduct a database search and identify 6 relevant randomized controlled studies, each with between 60 and 80 participants. Results of each study provide evidence of a positive effect between fish oil supplementation and a reduced incidence of myalgias. The participants from all studies were pooled and statistically analyzed to determine the effect of the relationship between fish oil supplementation and succinylcholine-induced myalgias. What type of study was performed?

Answer 26

A meta-analysis is a type of study in which relevant data from multiple similar studies are combined to develop a single conclusion that has more statistical power compared with an individual study.

Question 27

Most laboratory values use standard deviation to obtain normal ranges. What percentage of values will be within two standard deviations of the mean?

Answer 27

Standard deviation is the variability of values around the mean. In a normal distribution, 95% of values will be within two standard deviations and 68% will be within one standard deviation on either side of the mean.

Question 28

A 26-year-old female is scheduled for a carpal tunnel release with intravenous regional anesthesia (Bier block) using 30 mL of 0.5% lidocaine. However, only 2% lidocaine is available. What volume of 2% lidocaine should be diluted to create 30 mL of 0.5% lidocaine?

Answer 28

Diluting 7.5 mL of 2% lidocaine into a total volume of 30 mL will produce a 0.5% lidocaine solution.The following equation (proportion calculation) can be used to determine how much of a concentrated solution is required to create a desired volume of a dilute solution: V1 = (V2 x C2)/C1
Where: V1 = volume of initial drug needed, C1 = concentration of initial drug, V2 = desired volume of dilute drug, C2 = desired concentration of dilute drug.