ALiEM Bookclub: Humble Inquiry

3148In this month’s ALiEM Book Club selection, Humble Inquiry: The Gentle Art of Asking Instead of Telling, author Edgar Schein describes a model of communication termed “humble inquiry” which he defines as “the fine art of drawing someone out, of asking questions to which you do not already know the answer, of building a relationship based on curiosity and interest in the other person”. Although a very quick read (100 short pages!), it is packed with profound insights about the way we communicate and a vision for what might be! Communication is so pertinent to our work in the medical field from encounters with our colleagues, our learners, and our patients. Striving to improve communication is a goal that every provider should have and this powerful book can help!

A free excerpt of the book can be accessed here.

Schein first clarifies the concept of “here-and-now” humility, which is necessary precursor for true humble inquiry. Here and now humility is the recognition of one’s own dependence on another, especially with regards to information. Recognition of dependency is not just for subordinates but it is even more essential for those working in teams or in positions of power.

Consider for example anytime either you have taken a clinical case presentation from a junior learner or had to provide a presentation. Traditionally, this experience was fraught with anxiety or fear, especially if working with a supervising doctor who readily employed communication styles that were considered in the realm of “pimping” – a method whereby evaluative and trivial questions are asked in ascending hierarchical order, using power status to embarrass and humiliate learners in a group environment. For example, when a medical student is presenting a patient with sepsis the supervising physician might interrupt and ask “who coined the term sepsis?” When the student inevitably doesn’t know he shakes his head and turns to the resident. The student feels inadequate when they finally return to discussing the case. Instead consider how differently such an encounter would go if your supervising doctor employed strategies of humble inquiry, which would acknowledge that the learner has just spent a significant amount of time with the patient and holds a wealth of information.

With use of humble inquiry, the information can be gleaned from the learner and together the learner and the attending can come up with a treatment plan with educational pearls taught in a comfortable learning environment. But how to go about doing this and employing the strategy of Humble Inquiry?

“Humble inquiry is the fine art of drawing someone out, of asking questions to which you do not already know the answer, of building a relationship based on curiosity and interest in the other person.”

How to practice humble inquiry? Schein suggests:

Do less talking.
Do more asking.
Get better at listening to and acknowledging others.

Consider your own prior positive educational experiences. Likely the educator minimized interruptions. Questions may have been raised that were not answerable, but helped to foster thoughtful discussion. Most of all, you probably felt listened to and satisfied that the management plan was mutually generated.

Sounds easy, right? Wrong.

Schein explores many impediments to humble inquiry.  In our organizations, norms about the expectations of superiors (attendings) and the preferred deference of subordinates (residents and medical students) make it unnatural for those in a position of power to ask for help. For example, in the current traditional model, the attending physician should not rely on the medical student. Furthermore, the task oriented, rather than personal nature, of many of our jobs makes fostering relationships difficult. Working through lunch and breaks instead of holding short teaching sessions or simply bonding over a meal happens far too frequently because there are so many clinical tasks to accomplish. Unfortunately, there are also forces within ourselves that prevent humble inquiry from being the norm. Occasionally the primitive instinct to be right, to one up another person, takes over. And sadly, sometimes the attending (or the resident, or the medical student) likes to be right, just because.

Applications for patient care

There are obvious advantages to humble inquiry that Schein outlines. Most examples were related to patient-safety issues but it seems that the advantages for patient-care might extend beyond allowing subordinates to speak up when they feel something is going wrong. There must be implications for patient care when junior learners, allied health care professionals, families and patients don’t just feel listened to, but are listened to.

Applications for medical education

Learners are asked many questions but often these questions are not coming from a place of humble inquiry. What muscle is this? What dermatome does it supply? What is the appropriate treatment plan? Schein discusses other forms of questioning, described here, including diagnostic inquiry, confrontational inquiry and process-oriented inquiry that are much more common in medical education but don’t necessarily promote relationships or cooperation towards a common goal. There seems to be a role for humble inquiry in the teaching role.
We look forward to hearing your thoughts about the book and about humble inquiry in our discussions in the comments section and on twitter.
* Thanks to Dr. Goldstein at Queen’s University for directing me to this book. He recommends it to all medical students rotating through the anesthesia department!

Questions for Discussion

  1. How might you apply the concept of humble inquiry to patient care? To medical education?
  2. Think about a situation in which you were the subordinate or had a lower status than another other person yet felt respected and acknowledged. Can you identify what the other person did to make you feel that way?
  3. What are impediments in our culture and within ourselves to practicing humble inquiry? And is humble inquiry appropriate in all circumstances?

ALiEM Bookclub Google Hangout

Want to join in the bookclub discussion?

Tweet us directly at @ALiEMBook

Use hashtag #ALiEMbook.


Watch this for more background on Humble Inquiry:


Disclaimer: We have no affiliations financial or otherwise with the authors, the books, or Amazon.

Edited by:
Nikita Joshi MD

Author information

Eve Purdy, BHSc

Eve Purdy, BHSc

Medical student

Queen's University in Kingston, Ontario, Canada

Student editor at

Founder of

The post ALiEM Bookclub: Humble Inquiry appeared first on ALiEM.

Ultrasound For The Win! Case – 93F with Chest Pain

Welcome to another ultrasound-based clinical case, part of the “Ultrasound For The Win!” (#US4TW) Case Series! In this peer-reviewed case series, we focus on real clinical cases where bedside ultrasound changed the management or aided in diagnoses. In this month’s case, a 93-year-old female presents to the Emergency Department with crushing chest pain.


A 93-year-old female with no available medical history is brought to the Emergency Department by ambulance after she was noted to clutch her chest and collapse while at home. She is unable to provide any history due to altered mental status.

She is immediately brought to the ED resuscitation room, where she appears lethargic and unable to follow commands, diaphoretic, with a subtle left-sided facial droop. Bradycardia and a cardiac murmur are appreciated and asymmetric pulses are noted in her lower extremities.


  • BP 110/40
 mm Hg
  • P 50
  • RR 18
  • O2 100% saturation on 2L nasal cannula
  • T 36.9 C


  • Acute Coronary Syndrome
  • Aortic Dissection
  • Arrhythmia
  • Cerebrovascular accident
  • Penetrating ulcer
  • Pericardial tamponade
  • Pneumothorax
  • Pulmonary Embolism

POINT-OF-CARE ULTRASOUND was performed which showed the following:


The bedside echocardiogram reveals a dilated aortic root (blue line) and visible dissection flaps (blue arrows).

The echo findings, taken into consideration with the clinical scenario, is concerning for acute thoracic aortic dissection stemming from aneurysmal aortic disease.


An important aspect of ultrasound is appropriate and optimal image acquisition. The clip obtained is an adequate parasternal long axis (PLAX) view of the heart. This is obtained with the phased array probe placed at the 3rd-5th intercostal space just to the left of the sternum at the sterno-costal angle. The probe marker is oriented to the patient’s right shoulder, at around 10 o’clock, which is typical of an ED echocardiogram. It is important to note that cardiology echocardiograms are done in an opposite probe indicator-to-screen orientation. For further discussion on this, please refer to a previous US4TW case, and Dr. Chris Moore’s paper [1], which is a must-read for anyone who performs echocardiograms.


PLAX Probe Orientation

ED echocardiogram probe orientation. For the parasternal long axis (PLAX) view, the probe marker is oriented to the patient’s right shoulder (blue arrow).



Several aspects of a “good” PLAX view are evident: the left atrium (LA), mitral valves (MV), left ventricle (LV), aortic valves (AV), aortic root (Ao), right ventricle (RV), and descending thoracic aorta (TA) should be identified.

In order to optimize the image, the depth should be increased slightly in order to completely visualize the cross-section of the descending thoracic aorta, allowing for measurement of the aortic diameter.

Lastly, thoracic aortic dissection is noted by the presence of the intimal flap, seen on the images here at both the aortic root and descending thoracic aorta. Thoracic aortic dissection, while a distinct entity in itself, is often preceded by the presence of a thoracic aortic aneurysm. Thoracic aortic aneurysm is defined as a diameter > 4.0-4.5 cm, and is best identified in the parasternal long axis view. Measurements should be made at the largest visualized portion, from “leading edge to leading edge” [2]. To accomplish this, the calipers should be placed perpendicular to the axis of the vessel on the outside border of the aorta in the anterior field to the intimal surface of the posterior wall of the aorta in end-diastole.

For those who have an interest, a suprasternal notch view can also visualize the aortic arch, however this is out of the scope of this case series. More advanced techniques, such as color doppler and spectral doppler, can give further information about the flow (direction and velocity) in the true and false lumen.


The concerning findings on the bedside echocardiogram prompted the team to obtain a CTA which confirmed the diagnosis of an acute thoracic aortic dissection, with extensive aneurysmal dilatation of the ascending and descending thoracic aorta through to the abdominal aorta to below the level of the aortic bifurcation!

Given the high mortality associated with acute aortic dissection, she unfortunately did not survive her condition, but the expeditious workup allowed for the appropriate patient-centered management and goals of care discussions of this grave condition to happen in a timely manner.

Thoracic aortic aneurysms are less prevalent than abdominal aortic aneurysms, however the Emergency Physician must be able to be able to identify symptomatic thoracic aortic aneurysms [2]. Thoracic aneurysms are associated with aortic dissection, and have a high (>50%) mortality within the first 48 hours, making it a diagnosis that must be recognized quickly [3]. Bedside trans-thoracic echocardiogram is often the initial study of choice in many emergency departments for the evaluation of a patient with concern for aortic aneurysm or dissection given its ready availability, low cost, and lack of ionizing radiation. It is within the scope of the Emergency Physician to identify thoracic aortic pathology, and recent consensus statements by ACEP and the American Society of Echocardiography (ASE) support this [4].

However, it is important to recognize that the entire extent of the thoracic aorta cannot be entirely visualized with ultrasound, so if there is suspicion for a symptomatic aneurysm or dissection, a CTA should be obtained. That being said, point-of-care echo can be a beneficial initial screening study; A recent retrospective study by Taylor et al showed that bedside trans-thoracic echocardiogram demonstrated good agreement with CTA measurements of maximal thoracic aortic diameter [5]. Thus, it is important to be aware of the echocardiographic findings that are suggestive of a thoracic aortic aneurysm (visualizing and measuring the aortic root, and descending thoracic aorta), and findings of a dissection (visible dissection flap).


  1. It is important to visualize regions of the thoracic aorta when performing a bedside trans-thoracic echocardiogram (TTE) to look for thoracic aneurysms or dissection.
  2. Although important to obtain multiple views when performing a bedside echocardiogram, the parasternal long axis view is most ideal for visualization and measurement of portions of the thoracic aorta. Make sure you have enough depth to visualize the descending thoracic aorta.
  3. Remember: Normal aortic root < 4.0 cm. Larger than this suggests a thoracic aortic aneurysm and possible type A aortic dissection.


  1. Moore C. Current issues with emergency cardiac ultrasound probe and image conventions. Acad Emerg Med. 2008 Mar;15(3):278-84. PMID: 18304059
  2. Daignault MC, et al. Focused cardiac ultrasound diagnosis of thoracic aortic aneurysm: two cases. J Emerg Med. 2014 Mar;46(3)373-7. PMID: 23937808.
  3. Meszaros I, Morocz J, Szlavi J, et al. Epidemiology and clinicopathology of aortic dissection – a population-based longitudinal study over 27 years. Chest. 2000; 117:1271–8. PMID: 10807810.
  4. Labovitz, et al. Focused Cardiac Ultrasound in the Emergent Setting. A consensus statement of the American Society of Echocardiography and the American College of Emergency Physicians.
  5. Taylor, et al. Point-of-care focused cardiac ultrasound for the assessment of thoracic aortic dimensions, dilation, and aneurysmal disease. Acad Emerg Med. 2012; 19(2):244-7. PMID: 22288871.


ALiEM Copyedit


Really nice write-up. I have no major editing concerns. From an educator standpoint, I really like the labelled screen-capture showing where the thoracic aneurysm is. On a similar note, would it be possible to label in this same or different screen-capture the chambers you mention in the discussion: “Several aspects of a “good” PLAX view are evident in the clip; the LA, mitral valves, LV, aortic valves,aortic root, RV, and descending thoracic aorta should be identified.” I naturally wanted to look back up at the image(s) and see where these were. Could you add a labelled image?

[AUTHOR RESPONSE: Great thought! I've added a labelled image of the parasternal long axis view, which should help clarify what I was mentioning.]

Michelle Lin, MD, ALiEM Editor in Chief; Associate Professor of Emergency Medicine, UC San Francisco


Pre-Publication Critique


Super case. These are so important because so many of us would have called a stroke alert on a lady like this and she very well could have gotten tPA, so it really once again demonstrates the importance of having a differential diagnosis list and actually taking a look for some of them before getting tunnel vision on just one.


  1. Can you show a quick diagram/illustration of the probe placement for the PSLA? You describe it well in your text, but it may help people to just see a visual of how we are orienting the probe, especially since there are others who orient it oppositely.
  2. I believe Andrew Taylor’s paper demonstrated that US measurements correlate well with CTA measurements at 3 different locations and that none was necessarily superior to the others. Therefore one should measure the aorta at any of the following (whichever is largest):
    • across the sinuses of valsalve (this is usually the largest diameter of the root)
    • across the sino-tubular junction
    • across the ascending aorta

This is an important distinction because you endorse measuring “just distal to the aortic annulus” but this may not actually be the widest part of the visible anatomy.

You guys are killing it up there. Keep up the good work!


Thanks Drake.

1) Good thought. I'll work on this, and add it to the case.

2) Good point; I've made edits to the wording, to state "at the largest visualized portion".]

Drake Coffey, MD, Assistant Professor, Ultrasound Faculty, Department of Emergency Medicine, UT Health Science Center at San Antonio


Expert Peer Review


Nice case! Agree with suggestions from Michelle and Drake. A few additional comments:

  1. Screen indicator orientation (screen right vs. screen left) and transducer orientation (right shoulder vs. left hip) can be a source of considerable confusion for new learners, given that conventions vary significantly across the EUS community. Chris Moore did a nice review on this topic at Many providers will look at the example clip and image you provide of a parasternal long axis and feel that the image is “backwards”. It’s hard to argue that any of the options are “better”, but I think providers need to be aware of the issues with orientation in order to properly identify normal/abnormal findings, and to communicate these findings effectively to consultants.
  2. There’s a nice dissection flap visible in the descending thoracic aorta in the clip and image you provide. Another great place to look if you’re evaluating for dissection and can’t get a great view of the aortic root. Would be useful to highlight this finding.
  3. I would consider adjusting the angle of the blue line you use to highlight the dilated aortic root to mirror the leading edge, perpendicular technique you discussion the text.


1) I've added some more commentary on the probe indicator differences, and a link to Dr. Moore's paper.

2) Great thought.Good point. I've added mention of the dissection flap in the descending thoracic aorta.

3) I've adjusted the angle of the line. Thank you for the great feedback!]

Mike Stone, MD, Division Chief, Emergency Ultrasound; Emergency Ultrasound Fellowship Director; Department of Emergency Medicine, Brigham and Women's Hospital; Assistant Professor of Emergency Medicine, Harvard Medical School


Author information

Jeffrey Shih, MD

Jeffrey Shih, MD

Emergency Ultrasound Fellow
Instructor in Emergency Medicine
Yale University School of Medicine

The post Ultrasound For The Win! Case – 93F with Chest Pain appeared first on ALiEM.

Why Henderson and Hasselbalch Belong in the ED

the_big_question_9192If you’re like me, you learned and then promptly forgot the Henderson Hasselbalch equation (HH eq) in medical school [1]. After all, in clinical rotations it was never invoked, and our patients seemed to have fared well without it. So why bring up the topic now?

Medicine is changing. The ubiquitous nature of computing allows a level of sophistication exponentially greater than before. To a large extent we’re freed from much of the onerous work of rote memorization. In the ideal, that should free us to be more thoughtful about the way we approach our work and to have a deeper understanding of health and disease. Going forward, medicine will become increasingly computational. With that in mind, I’ll make three points about the HH eq.

3 Important Points About the Henderson Hasselbalch Equation

  1. The HH eq is a classic example of science at its best. There aren’t that many situations in medicine where understanding is achieved in a mathematically elegant and robust form. It should be astonishing to us that pH, pCO₂, and bicarbonate concentration are so intricately related and that we can perfectly quantitate that relationship.
  2. We are capable of both understanding and manipulating the HH Eq. The logarithms are easy if you know just a few simple declarations. Log(A × B) is equal to logA + logB, and similarly log(A ÷ B) is the same as logA – logB. Finally, if logA = 4, then A  = 10⁴ .  That’s it. That’s all you need to know to derive the equation!
  3. We can and should use it in the emergency department. One example of its use is for rapid estimation of pH and pCO₂ in patients with metabolic acidosis when the only data point available is a serum bicarbonate from a Chem 7. This requires the assumption of appropriate respiratory compensation.

Derivation of the Henderson Hasselbalch Equation

All acids in solution dissociate in a mathematically quantifiable way. Kₐ is the acid dissociation constant for that relationship.

Figure 11

In medicine it is the convention to refer to acidity using pH instead of [H⁺], so the logarithm of both sides of the equation is taken.

Figure 2


Remember that log(A × B) is equal to logA + logB, so we can rewrite the equation as follows:

Figure 3


Since we want the equation to solve for pH, we’ll move the log[H⁺] to the left hand side of the equation and the log Kₐ to the right.

Figure 4


By definition, pH means the negative log (base 10) of the hydrogen ion concentration. Similarly, pKₐ means the negative log of Kₐ, so we can rewrite the equation as follows:

Figure 5


We will be using the equation to scrutinize the bicarbonate buffer system, so carbonic acid and bicarbonate are substituted for HA and A⁻ respectively.

Figure 6


Now we get to the really interesting part of the derivation. Carbon dioxide in solution forms carbonic acid, and there is a solubility constant described by Henry’s law that quantifies the relationship.

Figure 7


The solubility constant is 0.03, so we can substitute that into the equation to reach our final state. We’ll also substitute in the constant for pKₐ which is 6.1:

Figure 8. The Henderson Hasselbalch Equation as used in medicine
the final version of HH eq

Now we’re ready to take this show on the road!

The Equation In Clinical Practice

Consider a patient with a bicarbonate value of 12 mEq/L on a chemistry panel. A bicarbonate value of 24 is considered normal, with a range of 22 – 26. In most laboratories an autoanalyzer is used that measures total CO₂ content as an approximation of bicarbonate. This estimation will exceed the actual bicarbonate value by 1-2 mEq/L [2], so we may need to adjust for that. In this example we will use the actual value.

The low bicarbonate value indicates that an acidosis is present.

From our history and physical examination we will have a good sense whether our patient has some degree of respiratory compromise resulting in a respiratory acidosis. If it appears the patient has no respiratory compromise — and this could be confirmed by end tidal CO₂ monitoring — then we conclude there is a metabolic acidosis.

Winter’s Equation

To estimate pH, we need one more value, the pCO₂. Assuming normal respiratory compensation, the pCO₂ is estimated using Winter’s equation [3], as follows:

Figure 9. Winter’s equation


So our patient’s pCO₂ is 12 × 1.5 + 8 ± 2, which is 26 ± 2.

Entering those values into the HH eq gives a pH estimate of 7.27 (7.26 – 7.31). So what we’ve just accomplished is rapid estimation of pH starting with a bicarb value from a Chem 7. Or from a mathematical perspective, we used 2 equations to solve a three variable problem.

These estimations can be prepared in advance to create a quick reference (Table 1).

Table 1. Blood gas values derived from Winter’s equation and the Henderson Hasselbalch Equation.
Quick lookup table derived from HH eq and Winters eq

The Decimal Digits Rule (aka “last 2 digits” rule)

As an alternative to the Winter’s equation, there’s another great way to estimate pCO₂ in metabolic acidosis using the “decimal digits” rule, sometimes referred to as the “last 2 digits” rule [4]. The rule states that in patients with metabolic acidosis and appropriate respiratory compensation, the pCO₂ equals the decimal digits of the pH. The best way to understand this is with an example.

Imagine you are caring for a patient with DKA and you obtain a blood gas to estimate the severity of the illness. The results come back pH 7.27, pCO₂ 27, and bicarb 12.0. (The pO₂ is not relevant for the acid base analysis.) It’s helpful to know that the pH is 7.27, but equally important is whether there is adequate respiratory compensation for the acidosis. The “decimal digits” rule says that if the pH is 7.27, then the predicted pCO₂ in a patient with adequate respiratory compensation is 27. If your measured pCO₂ is close to predicted, then compensation is adequate. A pCO₂ much higher indicates inadequate respiratory compensation. This could be the case if your patient is extremely ill with respiratory muscle fatigue. A pCO₂ much lower indicates a primary respiratory alkalosis. Your patient is hyperventilating, and you should ask yourself why.

For the purposes of our work as emergency physicians, I’m arguing that we should work backwards using the “decimal digits” rule. Let’s start from scratch to create a lookup table that gives pH, pCO₂, and bicarb values that are compatible with the rule. How is that done? You guessed it. Using the Henderson Hasselbalch equation.

Start with pH 7.37 and a pCO₂ of 37 and calculate the predicted bicarb using HH eq. Then do the same thing for pH 7.36 and a pCO₂ of 36. Continue until you’ve reached a pCO₂ of 12, which is about the lower limit of respiratory compensation.

This technique works best if you actually use a pH with 3 decimal digits (i.e, 7.350 instead of 7.35) and a pCO₂ with 1 decimal digit (35.0 instead of 35). That way you can get bicarb results with three significant figures. OK, too much information. Take a look at the resulting table:

Table 2. Blood gas values derived from the “decimal digits” rule and the Henderson Hasselbalch Equation.
Quick lookup table 2 derived from last 2 digits rule

How do we use this table? The idea here is that when a Chem 7 result comes back with a significantly low bicarb, we know there is a metabolic acidosis. We use the table to predict pH and pCO₂ under the assumption that our patient has adequate respiratory compensation for the acidosis. So if my patient’s bicarb is 10, I expect to see a pCO₂ of 24 and a pH of 7.24.

Case Studies

Case 1

25 year old man, brought in for evaluation of a suspected suicide attempt by medication overdose. Chem 7 shows a bicarb of 13 and an anion gap of 20. If he has a pure metabolic acidosis with an appropriate degree of respiratory compensation, what would you expect his pCO₂ and pH to be?

Starting with the bicarb of 13, we can estimate the pCO₂ using Winter’s equation, so the expected pCO₂ is 13 × 1.5 + 8 ± 2 = 27.5 ± 2. Plugging those numbers into the Henderson Hasselbalch equation gives an expected pH of 7.28 (7.27 – 7.33). We would get the same results with the table generated by the “Decimal Digits” rule.

Here’s his actual blood gas: pH 7.50, pCO₂ 17. The pCO₂ is much lower than predicted indicating a respiratory alkalosis superimposed on the high anion gap metabolic acidosis. This is a classic finding in early aspirin overdose.

Case 2

19 year old man found down unconscious, bicarb of 5, anion gap of 35. What are his expected pH and pCO₂?

Using the lookup table derived from the “Decimal Digits” rule, we expect a pH of 7.15 and a pCO₂ of 15. The actual values were pH of 7.00 and pCO₂ of 20. As you can see, the higher pCO₂ significantly lowers the pH. Any further compromise in his respiratory drive will push the pH into the dangerous sub 7 realm.

To App or Not to App?

Should I use a look up table in a Paucis Verbis card, a mobile app, a web app, or something built into my EHR? How much time do you have? There probably are many situations in our practice where we just want an answer. That may seem shallow, but we don’t want to see or know the derivation if there’s not enough time or if we’re lacking the mental stamina at that particular moment. No problem. I’m like that. A lot. Use the tool that’s available and fast. But we can and should have the opportunity to take a deep dive from time to time, and that’s where a well designed app can make a difference if it has the ability to educate as well as spit out a result. Showing formulas and providing references is a minimum requirement. Particularly valuable is the use of animation. For now, be aware that you can accomplish the same end goal through a variety of means.

Take Home Points

If you have a patient with a significantly low bicarb on a Chem 7, use these quick look-up tables to rapidly estimate pH and pCO₂ based on that single bicarbonate value. Alternatively, run the calculations from scratch, which is pretty awesome when you’re teaching residents and medical students at the bedside. Or use an app. Regardless of what method you choose, if you go on to get a blood gas, compare actual to predicted pCO₂.

If the pCO₂ agrees with predicted values, your patient has an appropriate respiratory compensation attenuating the acidosis. If the pCO₂ is too high, your patient also has a primary respiratory acidosis. The latter is a potentially dangerous scenario that may have an impact on how you manage the airway. On the other hand, if the pCO₂ is lower than expected, your patient has a primary respiratory alkalosis in addition to a metabolic acidosis. Think about aspirin overdose or other reasons why your patient might be hyperventilating.

And always remember to pay tribute to Henderson and Hasselbalch every time you interpret a blood gas.


  1. Story DA. Bench-to-bedside review: a brief history of clinical acid-base. Crit Care. 2004;8(4):253-8. PMID: 15312207
  2. Centor RM. Serum Total Carbon Dioxide. In: Walker HK, Hall WD. Clinical methods, the history, physical, and laboratory examinations. Butterworth-Heinemann; 1990. Accessed September 21, 2014.
  3. Albert MS, Dell RB, Winters RW. Quantitative displacement of acid-base equilibrium in metabolic acidosis. Ann Intern Med. 1967;66(2):312-22. PMID: 6016545
  4. Fulop M. A guide for predicting arterial CO2 tension in metabolic acidosis. Am J Nephrol. 1997;17(5):421-4. PMID: 9382159

Disclosures: Dr. Ruiz is the creator of the “Acid Base” app for the iPhone and “Likelihood” app for the iPad.

ALiEM Copyedit 1

October 15, 2014

Editor reviewing for educational merit:

Hi Frank:

I really liked this piece – it breaks down a complicated concept, but most notably, brings it back to the clinical setting.

I think for me one of the biggest jumps was in the last bit – from the “last 2 digits” rule to the Take Home Points. I think you have to highlight the concept a bit more… and highlight the predicted vs. actual measured bicarb. Linking this to the idea of the delta-gap ( or double gap… These might be important because the learners are often learning all these concepts in tandem.

Alternatively, you could write up these other two concepts too… but I think they need to addressed in relation to this piece in order for learners to get the most out of it…

Love the equation diagrams – so clear! :D

[AUTHOR RESPONSE: I revised the last 2 digits rule to try to make sense out of it. As for the delta gap… if this piece is well received I would like to actually have a three part series, the second of which would be “acid base without the blood gas” which would include the delta gap, double gap, and some other cool stuff. Part three would be a gentle introduction to the physicochemical (Stewart) approach to acid base.

I wanted to add a comment about the intent of the post. It’s really a bit schizophrenic in that it’s a combination of a review of the HH eq, but it is presenting my own concept of quick look up tables derived using the HH eq to achieve rapid prediction of pH and pCO2. So it’s a mashup of a review and a trick of the trade piece. As far as I know, I’m the only one who applies HH eq in this manner.]

Teresa Chan, MD, ALiEM Associate Editor; Assistant Professor, Division of Emergency Medicine, McMaster University


ALiEM Copyedit 2

October 19, 2014

Hi Frank – nice post! Made the esoteric very clear. Some notes:

  1. Can you make descriptive labels for Tables 1 and 2.
  2. At the risk of sounding redundant, perhaps you can end with a short clinical scenario/ case to illustrate your take home point? I think readers who are pretty new to this concept would appreciate it.
  3. Agree with Teresa about the slight leap in concepts moving from Winters to the “last 2 digits” concept. Another alternative is to bridge this gap through your take-home example.
Michelle Lin, MD, ALiEM Editor in Chief; Associate Professor of Emergency Medicine, UC San Francisco


ALiEM Copyedit 3

October 21, 2014

Good morning Dr. Ruiz–really great post. As a learner, this was easy to follow and provided relevant depth to a topic that is often ineffectively covered.

Just a few additional copyedits I made, pending your review:

  1. Table 2 was re-aligned for better centering.
  2. Case studies have been placed under droppable menus.
  3. Take home points were bolded and separated for easy recognition and emphasis.

Overall great post, with a very clear derivation and impact.

Scott Kobner, Medical Student @ NYU, ALiEM-EMRA Social Media and Digital Scholarship Fellow, Founder,


Pre-Publication Critique

October 20, 2014

Good morning Frank–

Thank you for this post. The easy to understand derivation of the HH eq was a great thing for me to review and is well done.

Under “The Equation in Clinical Practice”, I might add a reference range for normal bicarb values after 12 mEq/L as this blog attracts learners of all levels.

I really like the last 2 digits rule but wish it had a different name, like FTDAD– (first two digits after decimal, obvi) because the technique works best if you use pH with three decimal digits and the last two digits in that setting do not equal the predicted pCO2. Is there a way to explain this eloquently?

I agree with bringing it all home with a take home example that makes the leaps from concept to concept. An example where being able to calculate pH and pCO2 from a bicarb level and comparing it to VBG really gives you a clue as to how to manage a critically ill patient quickly and appropriately.

I love that you explain how all of this works so that we aren’t just mindlessly typing numbers into an app and not really understanding why/how things work. However, going back to the charts might not be as ‘quick reference’ as we’d like. Do you have any calculators or alternatives that you recommend once we get the underlying concepts down?

As an aside, I have recently joined a community practice and can see how it could take a lot of effort it can take to keep up with the latest and greatest when you don’t have residents bring in new info to shifts and students challenging your assumptions. I think the way you have really embraced technology, kept up with the changes in medicine, and are are now imparting your wisdom to help others understand some of the more difficult topics in medicine is pretty awesome and inspiring.

[AUTHOR RESPONSE: Thank you so much for your kind words! I’m like Mark Twain. I could live for a month on a single complement. Your suggestions were great. I added the bicarb normal range. The “last 2 digits” rule is not a legitimate name – everyone calls it something different. So I changed it to the decimal digits rule. Your point about looking things up in a table or punching data into a black box and getting an answer that lacks insight is well taken. I added a section about that: To app or not to app. The drawback is that I am getting self conscious about writing about apps. See what you think.]

Meghan Schott, MD, Clinical Fellow, Emergency Medicine, UCSF School of Medicine


Expert Peer Review

October 30, 2014

To go along with it, here is the reference list:

  1. Albert MS, Dell RB, Winters RW. Quantitative Displacement of Acid-Base Equilibrium in Metabolic Acidosis. Ann Intern Med 1967;66(2):312.
  2. Story DA. Bench-to-bedside review: A brief history of clinical acid-base. Crit Care 2004;8(4):253.
  3. Kishen R et al. Facing acid-base disorders in the third milleniu – the Stewart approach revisited. Int J Nephro Renovac Dis 2014;7:209.

and the formula:

[AUTHOR RESPONSE: Listening to Dr Weingart’s comments, I was reminded of a patient I took care of who told me that she was allergic to “chloride”. I resisted the temptation to tell her that chloride ions were present in every cell of her body. I cannot, however, resist telling Dr Weingart that the Henderson Hasselbalch equation is an essential component of the Stewart physicochemical approach of acid base analysis, which Dr Weingart espouses.

Let’s take a look:

Peter Stewart took the Henderson Hasselbalch equation and combined it with 5 other equations to derive his theory of acid base. If you accept Stewart’s approach, you must accept the scientific validity and clinical importance of the Henderson Hasselbalch equation. The bottom line is that the Henderson Hasselbalch equation is a fundamental component of both classical and modern (physicochemical) acid base analysis.

The pragmatic ED physician:

In the emergency department, as opposed to Dr Weingart’s ICU, we are on the front lines. We are the first to see the patient, and we initially have a limited data set. Most of our patients with acid base disorders are not sick enough to require hospitalization, and most will not require blood gas analysis. To do a precise physicochemical analysis requires, at a minimum, basic electrolytes, a serum albumin, and a blood gas. But a preliminary acid base assessment is possible without a blood gas analysis, and if you choose to do so, you can incorporate the Henderson Hasselbalch equation into that preliminary assessment. It’s fast, it’s easy, and it’s practical.

The best of both worlds:

It looks like there’s a real need for physicians who care about acid base to have a debate on what we should be teaching our students, residents, and colleagues. We need to resolve the conflict between classical and physicochemical approaches in a way that benefits our specialty. My perspective is that the classical approach is a subset of the physicochemical approach. This can be shown mathematically. For most purposes in the ED, the classical approach yields a fast, actionable assessment. The physicochemical approach refines one's initial assessment and is essential in many situations, for example, where there are derangements of albumin or with infusions of low SID fluids. I think the intellectual ED doc will want the best of both worlds.]

Scott Weingart, MD, ED Intensivist at Stony Brook University, Host of the EMCrit Podcast, Twitter: @emcrit


Author information

Frank Ruiz, MD

Frank Ruiz, MD

Attending Physician, Emergency Department

Kaiser Permanente Medical Center

Redwood City, CA

Creator of the "Acid Base" app for the iPhone and "Likelihood" for iPad


The post Why Henderson and Hasselbalch Belong in the ED appeared first on ALiEM.

Trick of the Trade: Naloxone Dilution for Opioid Overdose

NaloxoneTraditional teaching recommends naloxone doses of at least 0.4 mg IV to reverse opioid toxicity. Drs. Lewis Nelson (@LNelsonMD) and Mary Ann Howland (@Howland_Ann) co-authored the opioid antagonist chapter in Goldfrank’s Toxicologic Emergencies [1]. They write:

“However, this dose [0.4 mg] in an opioid-dependent patient usually produces withdrawal, which should be avoided if possible. The goal is to produce a spontaneously and adequately ventilating patient without precipitating significant or abrupt opioid withdrawal. Therefore, 0.04 mg is a practical starting dose in most patients, increasing to 0.4 mg, 2 mg, and finally 10 mg.”

Trick of the Trade: Naloxone Dilution for IV Use

Given that many ED overdose patients are not opioid-naive, lower naloxone doses are generally sufficient. Here is a quick way to prepare and administer naloxone in doses that will reverse opioid toxicity while limiting the chances of severe withdrawal.

  1. Obtain a 1 mL vial or syringe of naloxone 0.4 mg/mL.
  2. Grab a 10-mL syringe. Draw up 9 mL of normal saline.
  3. Draw up the 1 mL of naloxone. You now have 10 mL of a 0.04 mg/mL naloxone solution.
  4. Clearly label the syringe with drug name and concentration. 
  5. Administer 1-2 mL IV every 60 seconds until the patient is responsive (and breathing) to the desired level.


This trick also provides a more precise ‘wake up dose.’ If a naloxone infusion is needed, you’ll likely have a more accurate starting rate.

A Few Caveats

  1. If a patient is apneic, in respiratory arrest, or close to respiratory arrest from a suspected opioid overdose, this is NOT the technique to use. Administer at least 0.4 mg IV to reverse toxicity immediately.
  2. While it would be simple to use a saline flush for this technique, be advised that the Institute for Safe Medication Practices (ISMP) recommends against drawing up meds into a flush due to the concern for using an unlabeled syringe.  [ISMP safety alert link]


  1. Nelson LS, Howland M. Antidotes in Depth (A6): Opioid Antagonists. In: Nelson LS, Lewin NA, Howland M, Hoffman RS, Goldfrank LR, Flomenbaum NE. eds. Goldfrank’s Toxicologic Emergencies, 9e . New York, NY: McGraw-Hill; 2011. Accessed October 25, 2014.

Author information

Bryan D. Hayes, PharmD, FAACT

Bryan D. Hayes, PharmD, FAACT

ALiEM Associate Editor

Clinical Assistant Professor, University of Maryland (UM)

Clinical Pharmacy Specialist, EM and Toxicology

The post Trick of the Trade: Naloxone Dilution for Opioid Overdose appeared first on ALiEM.

EM Match Advice: Post Interview Communications

EM Match iconWith interview season now in full swing this winter season, we gathered a few more of our favorite program directors to discuss the hot topic of making the post-interview communication etiquette. We feature Dr. Jim Colletti (Mayo Clinic), Dr. Jessica Smith (Brown University), and Dr. Jeff Schneider (Boston Medical Center). Thanks again to Dr. Mike Gisondi (Northwestern) for spearheading this innovative and helpful EM Match Advice video series for medical students.

EM Match Advice #6: Post Interview Communications


  • 00:00 Dr. Gisondi introduces the expert panel, the topic of post-interview communication etiquette, and relevant publications.
  • 04:31 Dr. Colletti discusses general NRMP Code of Conduct rules regarding post-interview communication.
  • 09:48 Dr. Colletti starts the discussion on whether students should contact programs after the interview day. Does this make a difference? Does it help or hurt you?
  • 18:28 Dr. Colletti starts the discussion which addresses the question of whether applicants should tell a program that they are #1 on their rank list.
  • 26:52 Dr. Smith launches the conversation about thank-you notes — yes or no? Does it affect how you sit on the program’s rank list?
  • 34:00 Dr. Smith talks about what is “the second look”, whether/when do to it, how to schedule, what to wear.
  • 43:09 Dr. Schneider discusses whether students should expect programs to contact them. If contacted, what does it all mean?!
  • 47:55 Dr. Lin summarizes what she learned from the discussion.
  • 49:44 The panelists discuss pearls and pitfalls, as well their institutional practices on how they handle post-interview communications.
  • 55:53 The panelists talk about something that applicants might not know about their program.


  1. Jena AB, Arora VM, Hauer KE, et al. The prevalence and nature of postinterview communications between residency programs and applicants during the match. Acad Med. 2012 Oct;87(10):1434-42. PMID: 22914523
  2. Swan EC, Baudendistel TE. Relationship between postinterview correspondence from residency program applicants and subsequent applicant match outcomes. J Grad Med Educ. 2014 Sep;6(3): 478-83.
  3. Thurman RJ, Katz E, Carter W, Han J, Kayala E, McCoin N, Storrow AB. Emergency medicine residency applicant perceptions of unethical recruiting practices and illegal questioning in the match. Acad Emerg Med. 2009 Jun;16(6):550-7. PMID: 19388912
  4. Yarris LM, Deiorio NM, Gaines SS. Emergency medicine residency applicants’ perceptions about being contacted after interview day. West J Emerg Med. 2010 Dec;11(5):474-8. PMID: 21293769

Watch the other EM Match Advice series videos!

Author information

Michelle Lin, MD

ALiEM Editor-in-Chief

Editorial Board Member, Annals of Emergency Medicine

UCSF Academy Endowed Chair for EM Education

UCSF Associate Professor of Emergency Medicine

San Francisco General Hospital

The post EM Match Advice: Post Interview Communications appeared first on ALiEM.

ALiEM-Annals of EM Journal Club: Spontaneous pneumothorax, pigtail catheters, and outpatient management

ALiEM-AnnalsEM-SquareWe are very excited this month to bring you another installment of the ALiEM-Annals of EM Global Journal Club. The highlighted article is Voison et al. on the “Ambulatory Management of Large Spontaneous Pneumothorax With Pigtail Catheters.” We hope you will participate in an online discussion based on the clinical vignette and questions below from now until Nov 17, 2014. These Respond by commenting below or tweeting using the hashtag #ALiEMJC. In a few months, a summary of this journal club will be published in Annals of EM.

On Fri, Nov 15, 2014 at 1230 EST, we will be hosting a 30-minute live Google Hangout with Dr. Stéphane Jouneau, the senior author of the Annals of EM publication who resides in France.

Google Hangout with Dr. Jouneau

[Coming on Nov 15, 2014]

Journal Club Paper

Voisin F, Sohier L, Rochas Y, Kerjouan M, Ricordel C, Belleguic C, Desrues B, Jouneau S. Ambulatory management of large spontaneous pneumothorax with pigtail catheters. Ann Emerg Med. 2014 Sep;64(3):222-8. PMID: 24439715.


STUDY OBJECTIVE: There is no consensus about the management of large spontaneous pneumothoraces. Guidelines recommend either needle aspiration or chest tube drainage and most patients are hospitalized. We assess the efficiency of ambulatory management of large spontaneous pneumothoraces with pigtail catheters.

METHODS: From February 2007 to January 2011, all primary and secondary large spontaneous pneumothoraces from Lorient’s hospital (France) were managed with pigtail catheters with a 1-way valve. The patients were discharged immediately and then evaluated every 2 days according to a specific algorithm.

RESULTS: Of the 132 consecutive patients (110 primary, 22 secondary), 103 were exclusively managed as outpatients, with full resolution of the pneumothorax by day 2 or 4, which represents an ambulatory success rate of 78%. Mean time (SD) of drainage was 3.4 days (1.8). Seven patients were initially hospitalized but quickly discharged and had full resolution by day 2 or 4, leading to a total success rate of 83%. The use of analgesics was low. The 1-year recurrence rate was 26%. If successful, this outpatient management is potentially cost saving, with a mean cost of $926, assuming up to 2 outpatient visits and 1 chest radiograph, compared with $4,276 if a chest tube was placed and the patient was admitted to the hospital for 4 days.

CONCLUSION: Ambulatory management with pigtail catheters with 1-way valves could be a reasonable first-line of treatment for large spontaneous pneumothoraces. Compared with that of other studies, our protocol does not require hospitalization and is cost saving.


Open Access Online Content on Topic

Website Title Author Type Country Date
EP Monthly Pigtail Insertion Azan, Lim, Guthrie News network USA Mar 25, 2014
Pediatric EM Morsels Chest Tubes – Pigtail Fox Blog Australia ?
The Trauma Profesional’s Blog Pigtail Catheters Instead of Chest Tubes? McGonigal Blog USA 2010?


Featured Questions

Four questions are featured here to spark discussion and reflection about the highlighted paper. For more of a deep-dive into the methodologies, check out the Journal Club questions published in Annals of EM [free PDF] . If you have additional questions, feel free to pose them!

  • Q1: How do you (and/or your centre) manage patients with new or recurrent large spontaneous pneumothorax (defined as >2-3 cm from lung apex). Catheter aspiration? Inpatient 8-12F chest tube? Pigtail catheter? Other?
  • Q2: If you were designing the randomized controlled trial (RCT) of ambulatory pigtail catheter insertion for spontaneous pneumothorax (PTX), what would your comparator be? What outcome measures would you like to see? What measure of difference in this outcome(s) would convince you to change your practice?
  • Q3: All the pigtail catheters were placed by respirologists in this study (there were 5 physicians who performed all the insertions). Are there complications that might be more likely to occur in the hands of less experienced operators?
  • Q4: Assuming that the ambulatory pigtail catheters are shown to be equivalent or superior to traditional care in a future RCT, do you think this protocol would be feasible in your setting? Are there barriers to implementation at your hospital?

Please participate in the journal club by answering either on the ALiEM blog comments below or by tweeting us using the hashtag #ALiEMJC. Please denote the question you are responding to by starting your reply with Q1, Q2, Q3, or Q4. 

Best Blog and Tweet

NEW! Contest for Best Blog Comment and Tweet

We are implementing a contest for the Best Blog Quote and Best Tweet. The winners will be announced in our Annals of EM publication curating this discussion.

Disclaimer: We reserve the right to use any and all tweets to #ALiEMJC and comments below in a commentary piece for an Annals of EM publication as curated conclusion piece for this global journal club.  Your comments will be attributed, and we thank you in advance for your contributions.

Author information

Michelle Lin, MD

ALiEM Editor-in-Chief

Editorial Board Member, Annals of Emergency Medicine

UCSF Academy Endowed Chair for EM Education

UCSF Associate Professor of Emergency Medicine

San Francisco General Hospital

The post ALiEM-Annals of EM Journal Club: Spontaneous pneumothorax, pigtail catheters, and outpatient management appeared first on ALiEM.