An organized approach is imperative in correcting robust misconceptions related to body fluid deficit disorders. First, it is crucial that all faculty members develop a critical understanding of the body-fluids, as misconceptions acquired from faculty members and textbooks are very difficult to eliminate from the minds of young doctors later in their professional lives.
In the following section we present our approach to overcoming misconceptions in a manner that will create a lasting effect on students and prevent them from reverting to their preconceptions.
Tackle the misconceptions
Once identified, we try to make students discontent with their misconceptions. This provides a strong stimulus for refinement or replacement of the flawed concepts with intelligible and plausible ones. Utmost care is given to maintain a favourable learning environment where the students are not ridiculed for holding incorrect preconceptions.
We split teaching into short modules, each with a clear framework and objectives. Most of the modules remain “learner-centred” where students are engaged in meaningful activities which promote thought. Multiple teaching techniques are employed to cater to the diverse learning styles of the students and rekindle students’ interest and participation.
Introductory presentation: We start with a 10-min introductory presentation using visual aids such as a white-board or PowerPoint presentation to orient the students to body fluid compartments. Classifying the body fluid deficit disorder based on the nature of the fluid deficit (water alone vs water with salt) and the main body fluid compartment affected (intracellular vs extracellular) in each disorder generates uneasiness in the minds of those students who misconceive dehydration and volume depletion as one entity. This serves as an important turning point in the students’ learning as they start feeling dissatisfied with their pre-conceptions.
We make a conscious effort to avoid ambiguous linguistic expressions. We use the term “dehydration” to specifically refer to a body-fluid disorder resulting from pure water depletion with consequent hypernatremia, rather than using it as a blanket term for any type of fluid deficit. Furthermore, since the term “volume depletion” gives rise to referential ambiguity (because it does not specify the referent body fluid compartment), we disambiguate this term by adding an adjective, for example, “ECF” or “Intravascular” to indicate the depleted body-fluid compartment. This also encourages students to abandon the habit of using misleading abbreviations.
Clinical encounter: The newly implanted concepts must be supplemented with real life applications within a patient care context ensuring the students do not merely learn the new rote information. Utilizing the “think-pair-share” technique, we invite students to form either pairs or small groups. One group evaluates a pre-selected patient with dehydration while the other group assesses a patient with ECF volume depletion.
Debriefing session 1: After seeing their respective patients, the two groups return to the “classroom”. They are given a 2 min “reflection time” for formulation of ideas after which each group interacts with the other to compare the clinical, laboratory and therapeutic details of their patients. The instructor facilitates the learning process and highlights the contrasting features of the two patients. This session also provides an opportunity for the instructor to point out any common conceptual errors and offer constructive suggestions.
Instead of beginning with the presenting illness, which is the generally considered “norm”, a unique way to provoke curiosity in the minds of the students is to start the discussion with the management of the two patients. This disrupts the students’ expectations, captures their attention and makes them think and reflect retrospectively. An example of this could be asking: “Both the patients are receiving IV fluids because they have body fluid deficits; why is one patient being treated with slow infusion of D5W and the other with rapid administration of 0.9% NS or blood?” or “What factors have influenced the choice of fluid and the rate of infusion?” These queries will encourage the students to talk about the body fluid compartment from which the fluid has been lost in each condition and the concept of replacing “like with like” by choosing appropriate fluids for each condition. These questions also help cement the fact that dehydration and volume depletion are different disorders and hence necessitate different treatments. At this juncture, schematic illustrations of fluid compartments to demonstrate the effect of the addition of different types of fluids (blood, albumin, 0.9% NS, NaHCO3, D5W, etc.) on each body fluid compartment are utilized. Students are interested to note how each type of fluid initially expands the intravascular space but then distributes distinctively through different fluid compartments. This also helps them with the application of theoretical knowledge into direct patient care. The ECF volume maintains blood pressure and perfusion of organs, hence a fluid that is more likely to stay in the ECF compartment (0.9% NS) is administered as a rapid infusion in a volume depleted patient to ensure haemodynamic stability. Conversely, a fluid that predominantly restores the ICF compartment (D5W) is administered to a dehydrated patient in a controlled fashion to prevent the development of cerebral oedema. Again, throughout the session, the terms “ECF volume depletion” and “intravascular volume depletion” are used to dispel referential ambiguity.
Analysis of the laboratory values: After the debriefing session, we focus on the laboratory investigation results of the two patients. This is done either at the computer station on the ward or in the classroom where lab values from electronic medical records are projected on to the screen. It is important to emphasize the dissimilarity between the urinary and serum biochemical values of the two patients. In the ECF volume depleted patient, the urine becomes concentrated and contains very little Na+ consequent to renal conservation of salt and water. In the dehydrated patient, although urine is concentrated (due to water absorption in the distal tubule), urinary Na+ is not decreased. In fact, hypernatremia in a dehydrated patient can augment renal natriuresis by mechanisms that appear to be independent of changes in atrial natriuretic peptide. In ECF volume depletion, BUN/creatinine ratio rises due to renal hypo-perfusion with variable effects on serum sodium (depending upon the type of fluid loss). In contrast, there is no significant increase in serum urea or creatinine in dehydration; the gold standard is hypernatremia and consequent hypertonicity[1,34].
Back to the patients: After going through the laboratory results, students go back to the patients to demonstrate physical signs. If the physical signs have resolved consequent to the treatment, then students review the medical file to note the physical findings at time of presentation. Important findings include orthostatic hypotension, tachycardia, prolonged capillary refill time and decreased skin turgor. These are defined to students as signs of ECF volume depletion, as dehydration cannot be reliably determined by use of clinical examination. Finally, to complete the chain of events in reverse chronological order, we focus on the modes of presentation of the two patients by reviewing their medical records. ECF volume depleted patients usually present with a history of blood-loss or gastrointestinal fluid loss, conditions that cause third-spacing (e.g., ileus or pancreatitis) or sepsis (vasodilatation induced relative hypovolemia). On the other hand, since intracellular hydration influences cellular function, severely dehydrated patients may present with altered cognitive and neuromuscular function. It is noteworthy that altered mentation can be both a cause (by affecting the patient’s ability to access water) and a consequence (due to the resultant deranged neuro-cellular function) of dehydration. Critically ill patients in the ICU are prone to develop dehydration because they are unconscious, sedated or ventilated and are hence unable to voluntarily control their free water intake.
After going through all the aspects of care for their respective patients, the two groups switch and examine the other patient using the same system. This session is usually shorter as it simply affirms the pre-discussed differences between the two clinical conditions, cementing the newly acquired knowledge in the students’ minds. We find that by the end of this session, most students can appreciate the key differences between dehydration and volume depletion and the clinical implications of each.
Home assignment: The above stated clinical and biochemical differences invariably prompt analysis of different homeostatic mechanisms that operate in ECF volume depletion and dehydration. We direct students to carry out further reading to explore pathophysiological differences between the two disorders (Figure 2). We also provide them with additional learning resources that allow them to adequately explore the whole subject at their own comfortable pace to build up their new conceptual frameworks.
Debriefing session 2: On the following day, the pathophysiology of dehydration and volume depletion are addressed in the final session. Representatives from both student groups are invited to draw simple diagrams on a white board illustrating the homeostatic mechanisms. As they do this, it highlights to the audience that the sensors and effectors of both conditions are different (Figure 2); in dehydration, the osmoregulatory mechanisms are activated whereas in volume depletion the ECF volume regulatory pathways are stimulated to restore a normal physiologic environment. Students should then be able to link up the pathophysiological changes to the symptoms, signs and treatment of dehydration and volume depletion. They appreciate that the therapeutic manoeuvres mimic the response of normal kidneys to these conditions – kidneys retain water in dehydration, so we treat dehydration with water administration; kidneys retain salt and water in volume depletion, hence we infuse 0.9% NS to combat volume depletion.
In the second half of this session, students may share their perspectives on the whole topic. They also reflect on how the new concepts will resolve the problems that previously led to dissatisfaction in the management of such patients, and how their new understanding will benefit them in their future clinical experiences.