Wednesday, April 29, 2015

A Balancing Act

It’s another busy day in the ED when an elderly female comes in from triage with fever, cough, and new oxygen requirement. Even before the patient comes back you are concerned for pneumonia with sepsis. The patient is tachycardic and hypotensive with a shock index greater than one. You institute early antibiotics and fluids and systematically begin to aggressively resuscitate her. The patient requires nearly four liters of normal saline before her blood pressure stabilizes. Your attending suggests that your liberal use of normal saline will induce a hyperchloremic metabolic acidosis, and perhaps you should have used lower chloride containing fluid, like lactated ringers. You perform a brief literature review on the topic of balanced resuscitation using lower chloride containing fluids.

Literature Review:
Strong Ion Difference (Kishen et al)
The main difference between normal saline and balanced fluids, such as lactated ringers, is the strong ions difference (SID), that is, the difference between cations (e.g. Na+) and anions (e.g. Cl-).  Normal saline has a SID of zero (equal parts Na+ and Cl-) where as Lactated ringers has a SID of 28, which is due to the additional cations such as Ca+, K+, and lower anion (Cl-) content.  Importantly, normal plasma SID content ranges from 38-44mmol/L, therefore balanced fluids more closely approximates physiologic SID.  As the SID becomes narrower, as is the case with significant normal saline administration, a non-gap metabolic acidosis develops. [1]

The use of normal saline in large volumes has been shown to produce a reliable drop in serum pH as demonstrated by Scheinraber et al, in a study among patients undergoing elective surgery. [2] However, the development of a hyperchloremic acidosis is of unclear clinical significance. Early animal models in dog kidneys demonstrated that compared to non-chloride fluids, chloride containing solution led to renal vasoconstriction and decline in glomerular filtration rate. Similarly a randomized, double blind crossover study in healthy humans demonstrated a significant reduction in renal blood flow and renal tissue perfusion, after the administration of two liters of normal saline compared to low chloride (98 mEq/L) Plasma-Lyte solution. [3] However, the effect of isotonic saline in acutely ill patients is still not as clear. A prospective cohort study among 175 ICU patients demonstrated that higher chloride levels (109.4 vs 115.1mEq) was an independent factor for increased mortality, although a limitation of this study was they could not distinguish the cause of hyperchloremia (iatrogenic, renal dysfunction, or endogenous hyperchloremia) [4]
Traditional and 'balanced' fluid content (
A large retrospective cohort study of critically ill adults with vasopressor dependent sepsis showed lower in-hospital mortality in patients who received balanced (lower chloride) fluids versus isotonic saline, 19.6% versus 22.8% (RR 0.86; 95% CI,0.78-0.94). A limitation of this study was that patients receiving balanced solutions were younger, less likely to have chronic heart and renal failure, and more likely to receive steroids, colloids and invasive monitoring. [5] A 2014 retrospective study in 109,836 patients that met SIRS criteria and received crystalloid fluid resuscitation, showed that low-chloride loads were associated with lower in-hospital mortality. This mortality difference remained even after adjustment for severity of illness and total fluid volume administered. [6]

Similarly, a before and after study by Yunos et al involving 1644 ICU patients, reported the use of chloride-restricted fluids was associated with lower serum creatinine and decreased rates of renal replacement therapy (6 vs 10%) compared to controls. Like the study by Shaw et al, the difference was independent of severity of illness or total fluid volume administered. However, as mentioned by the authors, determining which component of lower-chloride fluid may have led to the observed effect is difficult, as there was simultaneous administration of lower sodium content, as well as increase in the administration of acetate, lactate, and gluconate. Importantly, this study showed no difference in mortality. [7][8]

Take home points: Administration of large volume of isotonic saline is associated with a metabolic acidosis. Animal models have demonstrated decreased renal perfusion with chloride containing fluids. Several retrospective studies indicate that chloride is an independent risk factor for mortality in acutely ill patients. More and more literature in humans seems to indicate that a ‘balanced resuscitation’ may decrease morbidity, and possibly mortality, in patients receiving large volumes of crystalloids as part of their resuscitation.  A single nonrandomized study demonstrated a correlation between low chloride fluids and decreased use of renal replacement therapy. Blinded, randomized, prospective studies are needed to further elucidate this observed effect.

Expert Commentary:

Dr. Schwarz, an Assistant Professor here at Wash U, and both an Emergency Physician and Toxicologist has provided some of his own thoughts on the topic. 

First, I’d like to thank Louis for picking a great topic and generating discussion about a very important subject.  I initially became interested in this topic a few years ago.  Originally, I was much more interested in the mechanism by which normal saline (NS) caused a non-anion gap metabolic acidosis, and that’s when I learned about the strong ion difference and a ‘balanced resuscitation.’  As a full disclosure while I found the pathophysiology really interesting, I initially didn’t think it had much clinical relevance.  However as more investigators have studied this, I’ve come to believe that my initial impressions were incorrect and changed my practice.

 The last time I reviewed the literature, I didn’t see a randomized, controlled trial comparing resuscitation with NS and lactated ringers in the ED.  However I do believe that there are studies out there that are applicable to the ED.  A retrospective study compared patients undergoing elective or emergent general surgery that received either NS or a ‘balanced fluid.’1  Unadjusted mortality and the number of patients developing major complications were higher in the group that received NS; after adjusting with propensity scoring, the mortality was no longer significantly different between the 2 groups.  However, patients that received NS were 4.8 times more likely to require dialysis. In a meta-analysis of patients with sepsis, patients that received a ‘balanced resuscitation’ had a lower mortality than patients receiving NS.2  The trend, however, was not significant.

In a promise to keep this short, I won’t review all the other literature that has been published on this topic and kept the discussion on the 2 articles that I did include short.  I’ll also concede that the literature is not perfect, and as I mentioned earlier, I’m also still waiting for that perfect ED-based study to be completed.  However the cost of NS or a ‘balanced solution’ such as lactated ringers is nearly equivalent.  I’m also not aware of significant complications from administering lactated ringers in most patients. So when the risks, costs, and benefits of implementing a ‘balanced resuscitation’ verses a standard resuscitation with NS are viewed together, I think there is enough evidence to consider changing your resuscitation strategy.

Now like many EDs, lactated ringers is not kept in our department.  It is on shortage but so is NS.  Neither of those are reasons not to use it.  So what do I do? Since I haven’t been able to convince pharmacy to keep lactated ringers in the ED yet, I do my best to guess early on which patients are going to need large-volume resuscitations.  If I think they are going to likely need more than 2-3 liters of fluid, I order additional lactated ringers from the pharmacy when I place their initial orders. In an hour after the patient has received the first few liters of NS, the lactated ringers should be there from the pharmacy.  If they need further resuscitation I can use it or return if they no longer need it.  For those that are interested to read more about this topic, I’d direct you to the upcoming May 2015 edition of Emergency Physicians Monthly. From my understanding, it’s brilliantly written! (Sorry for my shameless plug)

Jamtgaard References:
 [1] Kishen R, Honoré PM, Jacobs R, et al. Facing acid–base disorders in the third millennium – the Stewart approach revisited. International Journal of Nephrology and Renovascular Disease. 2014;7:209-217. doi:10.2147/IJNRD.S62126.
[2] Scheingraber et al. Rapid Saline infusions produces hyperchloremic acidosis in patients undergoing gynecologic surgery. Anesthesiology 1999;90;1265
[3] Chowdhury A et al. .  A randomized, controlled, double-blind crossover study on the effects of 2-L infusions of 0.9% saline and plasma-lyte® 148 on renal blood flow velocity and renal cortical tissue perfusion in healthy volunteers.  Ann Surg. 2012;256(1):18-24
 [4] Boniatti MM et al.  Is hyperchloremia associated with mortality in critically ill patients? A prospective cohort study. J Crit Care. 2011;26:175–179. doi: 10.1016/j.jcrc.2010.04.013
[5] Raghunathan K, Shaw A, Nathanson B et al. Association between the choice of IV crystalloid and in-hospital mortality among critically ill adults with sepsis*. Crit Care Med 2014; 42: 1585–91
[6] Shaw A et al.  Association between intravenous chloride load during resuscitation and in-hospital mortality among patients with SIRS. Intensive Care Medicine. 2014;40(12):1897-1905. doi:10.1007/s00134-014-3505-3.
[7] Waikar SS, Saving the Kidneys by Sparing Intravenous Chloride?.JAMA. 2012;308(15):1583-1585. doi:10.1001/jama.2012.14076.
[8] Yunos N et al. Association between a chloride-liberal vs chloride restrictive intravenous fluid administration strategy and kidney injury in critically ill adults. JAMA 2012; 308: 1566– 72.

Schwarz References
1. Shaw et al.  Major Complications, Mortality, and Resource Utilization after Open Abdominal Surgery: 0.9% saline compared to Plasma-Lyte. Ann Surg 2012;255:821-829.
2. Rochwerg et al. Fluid Resuscitation in Sepsis. A Systematic Review and Network Meta Analysis. Ann Intern Med 2014;161:347-355.

Submitted by Louis Jamtgaard +Louis Jamtgaard , PGY-3
Faculty Reviewed by Evan Schwarz @TheSchwarziee 

Wednesday, April 15, 2015

Does cardiac standstill on bedside echo equal 100% mortality?

You’re in the midst of catching up on notes during a hectic overnight shift when out of the corner of your eye you see a stretcher zoom into the trauma bay – with an EMT leaning over the side performing chest compressions. As the team gathers, the paramedics give report. The patient is a middle-aged male, no known past medical history, who was acting normally about half an hour ago when he suddenly collapsed in front of his family. They started CPR within a couple minutes of the patient collapsing, and called EMS. The paramedics continued CPR, placed a supraglottic airway, and placed the patient on the monitor. He has had a slow, organized rhythm without pulse throughout the arrest. He has received several doses of epinephrine without response. The patient has been pulseless for a little over half an hour by the time he arrives. The ED crew takes over CPR, IV access is obtained, and the patient switched over to the ER monitors, which show a slow, wide-complex, relatively disorganized rhythm. The patient shows no signs of life. Your attending physician calls for the ultrasound, and calls out to the team that if the bedside echo shows cardiac standstill, you will consider terminating further resuscitative efforts.

Clinical Question:

Does cardiac standstill on bedside echo universally predict mortality in OHCA?

Tuesday, April 7, 2015

Needle that belly!

An infant female with no significant history presents to your trauma bay after reported accidental blunt trauma to the abdomen, the patient arrives from a referral hospital where plain films demonstrated free air. On arrival the patient show signs of hemodynamic instability and an elevated lactate. The patient was decompressed with "needle peritoneumostomy" prior to going to the OR for exploration. 

Clinical Question:

Can “tension pneumoperitoneum” cause hemodynamic instability?

Literature Review:

The presence of "free air" in the peritoneum is often diagnostically significant; however, the gas itself is rarely of clinical importance. An exception to this rule is in the case of a tension pneumoperitoneum. Tension pneumoperitoneum (TPP), also known as hyperacute abdominal
Example of pneumoperitoneum & football sign
compartment syndrome [1], or abdominal tamponade [2], is a rare, but potentially deadly event. Similar to tension pneumothorax, the underlying mechanism is a tissue flap that acts as a one-way valve for air release, resulting in a progressive increase in intra-abdominal pressure. The increasing peritoneal pressures may rapidly lead to respiratory compromise due to diaphragmatic elevation and a drop in cardiac output resulting from decreased venous return or aortic outflow due to occlusion. [3] This can progress to cardiovascular collapse and respiratory failure and eventually death. [2]

In one of the earliest reported cases in 1913, tension pneumoperitoneum was theorized to be a consequence of gas forming bacteria in the abdominal cavity. [4] Now it is known that tension pneumoperitoneum is usually a consequence of hollow viscus perforation, post-operative complications, positive pressure ventilation or other insulflation-dependent procedures (eg, colonoscopy, endoscopy, cystoscopy or air enema). There has even been reported cases from CPR. [9,10] However, there are few published case reports of TPP as a result of blunt force trauma. [3,6]

Friday, April 3, 2015

EKG Challenge No. 12 Case Conclusion: Because We're Only Human

You are working as the "triage physician" in a busy city emergency department when a 34 yo female presents with chest pain.   The pain is retrosternal and burning in nature and has been persistent for 3 hrs.  It is associated with some nausea, but no shortness of breath or diaphoresis.  You order a GI cocktail and get an EKG:

You systematically review the EKG.  The heart rate is normal. There is a p wave before every QRS complex, but the p-wave axis is abnormal (negative in lead II).   There is now an extreme rightward axis as the QRS is negative in leads I, II and avF.  As you analyze the ST segments for evidence of ischemia, there appears to be T wave inversions in the inferior distribution of II, III, and avF.  You start considering the differential of ectopic atrial rhythm, right axis deviation, and T wave inversions including PE or ischemia but stop yourself.  You think  "did someone switch the leads?"  You take a brief look at aVR and see that the P, QRS and T waves are positive, making you even more suspicious.

You ask for a repeat EKG to be performed:

The repeat is a completely normal EKG,  confirming your "EKG diagnosis":  Limb lead reversal, specifically Right Arm-Left Leg Lead Reversal.

To think through how this limb lead reversal causes the changes seen in the original EKG, you have to go back to Eintoven's triangle made up of three bipolar leads ( I, II and III) and three augmented unipolar leads (avR, avL and aVF) (Figure below).  The right leg lead serves as the ground.   A lead reads as "positive" when the direction of the electrical impulse the same as the direction of the vector.  In a normal EKG with a normal axis,  the QRS is positive lead I, II and avF because they are directed towards the left side of the heart. aVR is almost always negative because it is directed opposite the cardiac apex.

Lead I                    Difference between LA and RA electrodes
Lead II                   Difference between RA and LL electrodes
Lead III                  Difference between LA and LL electrodes   

Lead aVR            RA - (LA + LL)/2
Lead aVL            LA - (LL + RA)/2                 
Lead aVF            LL - (RA + LA)/2

Right Arm/Left Leg (RA/LL) limb lead reversal is essentially a 180˚ flip of Eintoven's triangle which results in the following changes:
          1. aVR and aVL switch places
          2. lead I becomes an inverted lead III
              lead III becomes an inverted lead I
              lead II is an inversion of itself

Take a moment to compare the two EKGs above, and see that this is what has happened. 

It can mimic left anterior fascicular block and inferior infarction pattern, but can be suspected based on a positive P, QRS and T wave in lead aVR and extreme right axis deviation.
Limb lead reversals are important to recognize in that they can mimic pathology including myocardial infarction, ectopic atrial rhythms,  and conditions characterized by diffuse low voltage (pericardial effusion or pulmonary disease)[1]. You want to be able to catch them because you do not want to make critical clinical decisions based on misinformation. There are case reports of changes in patient management that occurred based on incorrectly acquired EKGs  that mimicked a pseudoinfarction or junctional rhythm pattern, including thrombolytic therapy in a patient with a baseline abnormal EKG and limb lead reversal [2,3].

Fortunately, other than the sense that "that EKG just don't look right!",  there are typical patterns that can clue you in that a limb lead reversal may be present.  

General clues that there may be a lead reversal (limb or precordial) include [4]: 

Limb leads:
1. Abnormal P axis with positive P wave in avR and/or negative P waves in lead I and/or lead II
2. Very low amplitude in the lead I, II, or III
3. Concordant negative QRS and T waves in the leads I, II, III and/or aVF

Precordial leads:
Abnormal R wave progression in leads V1 to V6, especially when the R wave amplitude increases after an initial decrease in the precedent leads.

The above features can be highlighted by reviewing the typical lead reversal patterns [3,5].  Note images below are all from the same "patient" whose EKGs are featured above.

1. Arm electrode (LA/RA) limb lead reversal: This reversal is the most common limb lead reversal.  The tell-tale sign is an inverted p wave, QRS complex, and T wave in lead I.  In the absence of dextrocardia, this is pathognomonic of arm electrode reversal.  Remember, as general rule I and V6 point the same direction and should look the same on the EKG.  aVR and aVF have switched places, so they both look grossly abnormal as well.  An example:
Left Arm - Right Arm Limb lead reversal
In a Right Arm-Left Arm lead reversal:
                  1. Lead I will be a complete inversion of itself
                  2. Lead II and Lead III will switch places
                  3. Lead aVL and aVR will switch places

If you notice, both lead reversals involving the right arm lead to an abnormal appearance of lead aVR.  One more instance where lead aVR, which is often ignored by emergency physicans and cardiologists alike, can be very useful [6]  

2. Left Arm/Left Leg (LA/LL) limb lead reversal:  This is a more subtle limb lead reversal.  You can pick up on it by the fact that the p wave is larger in lead I than lead II.

As Eintoven's triangle is flipped 180˚ around the axis formed by aVR, the following happens to the EKG:
        1. Lead I and II switch places (hence the p wave larger in I than II)
        2. Lead III becomes an inversion of itself
        3. Leads aVL and aVF switch places

3. Right Arm/Right Leg (RA/RL) limb lead reversal: The key to picking up this reversal is an isoelectric recording in lead II.
Right Arm/Right Leg Limb Lead Reversal
This "flat-lining" of lead II happens because the right leg (ground) lead - which the electrocardiographic processor recognizes as having no potential difference from the left leg - into the right arm position.  Since lead II is the difference between the Right arm and Left leg, this comes out as a flatline.  aVR and aVF are also switched, resulting in uncharacteristically positive QRS in aVR.

 4. Left Arm/Right Leg (LA/RL) limb lead reversal: The key to picking up this reversal is an isoelectric recording in lead III.  The "flat-lining" occurs for the same reason above, except that this time there is no perceived difference between the right arm and the right leg.
Left Arm/Right Leg Limb lead reversal

5. Right Leg/Left Leg limb lead reversal usually leads to an EKG that is indistinguishable from normal.

6. Precordial Leads: Alterations  in placement of the precordial leads results in abnormal R wave progression pattern and can mimic posterior or anterolateral myocardial infarction.
Precordial leads altered to the following pattern: V6V5V4V3V1V2

Peberdy et. al. [1]  published an excellent summary of expected EKG changes:

 For more review, Life in the Fast Lane has a great explanation of Eintoven's triangle in limb lead reversals.

Take Home Points:  When evaluating EKGs, be on the lookout for the EKG findings suggesting limb lead reversals as these can mimic pathology include acute MI, abnormal atrial rhythms, and conditions causing low voltage.  Clues to finding these are abnormal P wave axis, extreme axis deviation, concordant negative QRS and T waves in the leads I, II, III and/or aVF.  When in doubt, repeat the EKG.

Submitted by Maia Dorsett (@maiadorsett), PGY-3
Faculty Reviewed by Joan Noelker and Doug Char

1. Peberdy, M. A., & Ornato, J. P. (1993). Recognition of electrocardiographic lead misplacements. The American journal of emergency medicine, 11(4), 403-405.
2. Chanarin, N., Caplin, J., & Peacock, A. (1990). “Pseudo reinfarction”: a consequence of electrocardiogram lead transposition following myocardial infarction. Clinical cardiology, 13(9), 668-669.
3. Guijarro-Morales, A., Gil-Extremera, B., & Maldonado-Martín, A. (1991). ECG diagnostic errors due to improper connection of the right arm and leg cables. International journal of cardiology, 30(2), 233-235.
4. Rudiger, A., Hellermann, J. P., Mukherjee, R., Follath, F., & Turina, J. (2007). Electrocardiographic artifacts due to electrode misplacement and their frequency in different clinical settings. The American journal of emergency medicine, 25(2), 174-178.
5. Harrigan, R. A., Chan, T. C., & Brady, W. J. (2012). Electrocardiographic electrode misplacement, misconnection, and artifact. The Journal of emergency medicine, 43(6), 1038-1044.
6. Pahlm, U. S., Pahlm, O., & Wagner, G. S. (1996). The standard 11-lead ECG: neglect of lead aVR in the classical limb lead display. Journal of electrocardiology, 29, 270-274.

Thursday, April 2, 2015

Consultant Teachings No. 1: Acute Neuromuscular Respiratory Failure

Clinical Scenario: You are working in EM 2. It’s 3 AM and a 32 year old woman is roomed with the chief complaint of shortness of breath. She has been getting progressively more short of breath for the past 2 days. She’s also noticed that she just can’t keep her eyes open, though her right eyelid droops more than her left. You notice her head is falling forward. When you question her about that, she says she has had trouble holding it up for 4 days. Your general exam is normal, with no wheezing and normal heart sounds. Her neuro exam shows weakness on eye closure, neck flexion, and neck extension. She has no weakness anywhere else.

Clinical Question: How should acute neuromuscular respiratory failure be evaluated and managed?

Literature Review
Neuromuscular respiratory failure is relatively rare but constitutes a medical emergency with significant morbidity and mortality, particularly with delays in recognition. The most common causes are acute inflammatory demyelinating polyneuropathy (e.g. Guillain-Barre syndrome, GBS) myasthenia gravis (MG), motor neuron disease (e.g. amyotrophic lateral sclerosis, ALS) and some forms of myopathy. A study in Northern Ireland found the causes of acute respiratory failure due to neuromuscular conditions were GBS (62%), MG (18%), ALS (9%), then a variety of other conditions (2, 3). Early recognition of these conditions by history and physical exam, combined with specific bedside testing, can help appropriately triage and manage these patients. GBS has an incidence of 1-4 per 100,000 and represents the most common cause of acute paralysis. It is also often missed early in the disease, with patient’s requiring an average of 2 ED visits before diagnosis [1]. GBS can progress from symptom onset to respiratory failure in 48 hours, so early identification is important. The mechanism of respiratory failure is loss of activity of the diaphragm and accessory muscles of respiration, and can often be complicated by aspiration due to craniobulbar weakness. The diaphragm is innervated by the phrenic nerve, derived from the C3-5 nerve roots (remember: “C3, 4, and 5 keep you alive”).

The initial evaluation should begin with a careful history, including the time from symptom onset to ED presentation. When taking the history, it is important to ask specifically about:

1) Drooping eyes (ptosis)

2) Double vision (diplopia)

3) Change in speech (breathy or nasal)

4) Difficulty swallowing including nasal regurgitation (food/liquid coming out the nose)

5) Fatigue with chewing

6) Head drop (inability to support their head)

All of these can be findings of bulbar and high cervical spine pathology, and can be warning signs for impending respiratory failure. The history should also include characterization of weakness in other places (i.e. leg or arm weakness), sensory symptoms (ascending numbness or paresthesias) and autonomic symptoms (new-onset orthostatic symptoms, bowel or bladder retention/incontinence, changes in sexual functioning).

On physical exam, after doing a routine medical exam, specifically test:

1) Eye movements (looking for impairment of extraocular musculature)

2) Eye closure strength

3) Mouth closure strength

4) Tongue strength and palate elevation

5) Assess for a weak cough

6) Neck flexion and extension strength

7) Breath count (ask the patient to count up at a rate of one number per second after taking a full breath. This is a crude estimate of vital capacity, with each number being ~100 ml.)

Numbers 1-5 detect craniobulbar weakness. Neck flexion and extension are well correlated with diaphragmatic strength. Neck flexion weakness correlates with impaired respiratory function, while neck extension weakness should be considered a warning sign of impending respiratory failure.

Laboratory testing: History and exam should guide testing, but a full set of screening labs is generally appropriate (CBC, BMP, HFP). Other bloodwork that can be obtained include CK, TSH, and ESR [4].

Respiratory therapy should measure forced vital capacity (FVC) and negative inspiratory force (NIF). FVC < 20 ml/kg (~ 1- 1.5L) or NIF < -30 cm H20 are warning signs for impending respiratory failure [5].  It is important to discuss the effort provided and the quality of the lip seal with the respiratory therapist that performs the testing.

If there is evidence of severe diaphragmatic weakness (very weak neck extension or low NIF/FVC), it is reasonable to check an ABG or VBG for hypercapnea and a respiratory acidosis, consistent with inadequate ventilation.

If there are signs of impending respiratory failure, it is important to determine if non-invasive ventilation (e.g. BiPAP) or intubation and mechanical ventilation is most appropriate. This is a decision that should be made with the consulting neurologist and with the admitting ICU. However, if the objective findings (NIF/FVC and ABG) or trajectory (rapid deterioration) are poor, it is reasonable to electively intubate in the ED instead of an emergent intubation in the ICU.  Concurrent craniobulbar weakness and/or a weak cough are relative contraindications for use of non-invasive ventilation given the increased risk of aspiration.

Intubation in patients with neuromuscular weakness carries special risks.   In myasthenia gravis, due to a complex interaction between the number of ACh receptors at the neuromuscular junction, antibodies inhibiting those receptors, and the effects of treatment such as plasmapheresis and enzyme inhibitors, neuromuscular blockade can have unpredictable effects.
Image source:
Myasthenia patients have net loss of AChR at the neuromuscular junction (see Figure), making these patients relatively resistant to succinylcholine.  However, in cases where myasthenic crisis is treated with plasmapharesis, which also incidentally rcmoves the enzymes required for breakdown of paralytic agents, patients can have very  prolonged neuromuscular blockade.  While the effect of succinylcholine can go either way, patients with myasthenia gravis can be extremely sensitive to nondepolarizing blockade (one study found that the effective dose of vecuronium in MG was 1/5 that in controls) [6,7].

 In addition to the unpredictable effects of neuromuscular agents, patients with neuromuscular weakness is general are at higher risk of developing critical illness myopathy following exposure to paralytics. Avoidance of any paralytic is the goal when intubating a patient with MG, so consider using topical lidocaine with a sedative such as propofol [8]. Patients with GBS often develop significant autonomic dysfunction, with concomitant extreme swings in blood pressure and heart rate [9]. Autonomic dysfunction can be exacerbated during intubation. It is important to avoid treating these swings in blood pressure and/or heart rate unless there is evidence of end organ damage. Treating these rapid swings places the patient at a high risk of iatrogenic injury when their blood pressure or heart rate spontaneously rebounds and this rebound is exaggerated by the medications provided.

Clinical Take home:1) Have a high index of suspicion for neurologic causes of respiratory failure.
2) Check craniobulbar and neck flexion/extension strength in patients in whom you suspect neuromuscular pathology.
3) Check NIF/FVC and an ABG on any patient with a suspected neuromuscular condition and dyspnea.
4) Intubate with a reduced dose of non-depolarizing agent or preferably no paralytics at all
5) Expect heart rate and blood pressure swings, especially during intubation. Don’t treat them unless there is end-organ damage, as they are likely to spontaneously resolve.

Submitted by Alex Dietz, Neurology PGY-3
Additional Review by Jennifer Griffith
Faculty Reviewed by Robert C. Bucelli (Neurology)

Everyday EBM Editor: Maia Dorsett

[1]Noto A, Marcolini E. Select topics in neurocritical care. Emerg Med Clin North Am 2014;32:927-938.
[2]Carr AS, Hoeritzauer AI, Kee R, et al. Acute neuromuscular respiratory failure: a population-based study of aetiology and outcome in Northern Ireland. Postgrad Med J 2014;90:201-204.
[3]Pfeffer G, Povitz M, Gibson GJ, Chinnery PF. Diagnosis of muscle diseases presenting with early respiratory failure. J Neurol 2014.
[4]Flower O, Bowles C, Wijdicks E, Weingart SD, Smith WS. Emergency neurological life support: acute non-traumatic weakness. Neurocrit Care 2012;17 Suppl 1:S79-95.
[5]Lawn ND, Fletcher DD, Henderson RD, Wolter TD, Wijdicks EF. Anticipating mechanical ventilation in Guillain-Barré syndrome. Arch Neurol 2001;58:893-898.
[6] Roppolo, L. P., & Walters, K. (2004). Airway management in neurological emergencies. Neurocritical care, 1(4), 405-414.
[7]Martyn JA, White DA, Gronert GA, Jaffe RS, Ward JM. Up-and-down regulation of skeletal muscle acetylcholine receptors. Effects on neuromuscular blockers. Anesthesiology 1992;76:822-843.
[8]Della Rocca G, Coccia C, Diana L, et al. Propofol or sevoflurane anesthesia without muscle relaxants allow the early extubation of myasthenic patients. Can J Anaesth 2003;50:547-552.
[9]Rabinstein AA, Wijdicks EF. Warning signs of imminent respiratory failure in neurological patients. Semin Neurol 2003;23:97-104.