These are of the form of "we cannulated the coronary arteries of a dog and recorded the changes in SVR when vasopressin was infused". They describe, and that is essentially all. One ought to be careful relating these studies to clinical practice.
Rationale for animal studies
Advantages
Disadvantages: lack of applicability to humans
Defects of methodology
These are a type of analytical observation study. The investigators choose a group with a shared feature (the cases) and another group without those features (the controls). The groups are compared retrospectively, to see if in the past the groups differed in their exposure to something of interest - a risk factor, a treatment, etc. Essentially, it is a case of selecting the outcome you are interested in, and working backwards from it.
These are another type of analytical observation study. The investigators choose a group who have been exposed to some sort of treatment or risk, and a control group which is identical in every way other than that exposure. the groups are then followed prospectively, to see the difference in their outcomes.
Obviously, all of these sorts of "non-trial" studies suffer from inherent bias. In a perfect world, one would not have to base one's clinical decisionmaking on evidence such as this.
Gold standard for evidence. LITFL has a detailed breakdown.
Advantages
Disadvantages
Standardised reporting of trial results
Meta-analysis is a tool of quantitative systematic review. It is used to weigh the available evidence from RCTs and other studies based on the numbers of patients included, the effect size, and on statistical tests of agreement with other trials.
So much detail has been expected from CICM exam candidates in regards to meta-analysis, that the topic merits a chapter all of its own.
Gurwitz, Jerry H., et al. "Reader's guide to critical appraisal of cohort studies: 1. Role and design." BMJ: British Medical Journal 330.7496 (2005): 895. Mamdani, Muhammad, et al.
"Reader's guide to critical appraisal of cohort studies: 2. Assessing potential for confounding." BMJ: British Medical Journal330.7497 (2005): 960. Normand, Sharon-Lise T., et al.
"Readers guide to critical appraisal of cohort studies: 3. Analytical strategies to reduce confounding." BMJ: British Medical Journal 330.7498 (2005): 1021.
von Elm, Erik, et al. "The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: guidelines for reporting observational studies." International Journal of Surgery 12.12 (2014): 1495-1499.
Sanderson, Simon, Iain D. Tatt, and Julian PT Higgins. "Tools for assessing quality and susceptibility to bias in observational studies in epidemiology: a systematic review and annotated bibliography." International journal of epidemiology 36.3 (2007): 666-676.
Carlson, Melissa DA, and R. Sean Morrison. "Study design, precision, and validity in observational studies." Journal of palliative medicine 12.1 (2009): 77-82.