Physiologically Difficult Airway – Metabolic Acidosis

Physiologically Difficult Airway - Metabolic Acidosis

Case Presentation

A 32-year-old male with insulin-dependent diabetes mellitus came to your emergency department for shortness of breath. He was referred to the suspected COVID-19 area. His vitals were as follows: Blood pressure, 100/55 mmHg; pulse rate, 135 bpm; respiratory rate, 40/min; saturation on 10 liters of oxygen per minute, 91%; body temperature, 36.7 C. His finger-prick glucose was 350 mg/dl.

The patient reported that he had started to feel ill and had an episode of diarrhea 1 week ago. He developed a dry cough and fever in time. He started to feel shortness of breath for 2 days. He sought out the ER today because of the difficulty breathing and abdominal pain.

The patient seemed alert but mildly agitated. He was breathing effortfully and sweating excessively. On physical examination of the lungs, you noticed fine crackles on the right. Despite the patient reported abdominal pain, there were no signs of peritonitis on palpation.

An arterial blood gas analysis showed: pH 7.0, PCO2: 24, pO2: 56 HCO3: 8 Lactate: 3.

The point-of-care ultrasound of the lungs showed B lines and small foci of subpleural consolidations on the right.
At this point, what are your diagnostic hypotheses?

Two main diagnostic hypotheses here are:

  • Diabetic ketoacidosis (Hyperglycemia + metabolic acidosis)
  • SARS-CoV2 pneumonia

We avoid intubating patients with pure metabolic decompensation of DKA if possible, as they respond to hydration + insulin therapy + electrolyte replacement well and quickly. 

But in this scenario, the patient is extremely sick and has complicating medical issues, such as an acute lung disease decompensating the diabetic condition, probably COVID19. Considering these extra issues may complicate the recovery time and increase the risk of respiratory failure, you decide to intubate the patient in addition to the treatment of DKA.

You order lab tests and cultures. You start hydration and empirical antibiotics while starting preoxygenation and preparing for intubation.

Will this be a Difficult Airway?

Evaluating the patient for the predictors of a difficult airway is a part of the preparation for intubation. Based on your evaluation, you should create an intubation plan. 

This assessment is usually focused on anatomical changes that would make it difficult to manage the airway (visualization of the vocal cords, tube passage, ventilation, surgical airway), thereby placing the patient at risk.

“Does this patient have any changes that will hinder opening the mouth, mobilizing the cervical region, or cause any obstruction for laryngoscopy? Does this patient have any changes that hinder the use of Balloon-Valve-Mask properly, such as a large beard? What about the use of the supraglottic device? Does this patient have an anatomical alteration that would hinder emergency cricothyroidotomy or make it impossible, like a radiation scar? ”

So the anatomically difficult airway is when the patient is at risk if you are unable to intubate him due to anatomical problems.

The physiologically difficult airway, however, is when the patient has physiological changes that put him at risk of a bad outcome during or shortly after intubation. Despite intubation. Or because of intubation, because of its physiological changes due to positive pressure ventilation.

These changes need to be identified early and must be mitigated. You need to recognize the risks and stabilize the patient before proceeding to intubation or be prepared to deal with the potential complications immediately if they happen.

5 main physiological changes need attention before intubation are: hypoxemia, hypotension, severe metabolic acidosis, right ventricular failure, severe bronchospasm.

Back to our patient: Does he have physiologically difficult airway predictors?

  • SI (Shock Index): 1.35 (Normal <0.8) – signs of shock
  • P / F: 93 (Normal> 300) – Severe hypoxemia
  • pH: 7.0: Severe metabolic acidosis – expected pCO2: 20 (not compensating)
  • qSOFA: 2 + Lactate: 3 (severity predictor)

Physiologically Difficult Airway

"Severely critical patients with severe physiological changes who are at increased risk for cardiopulmonary collapse during or immediately after intubation."

Sakles JC, Pacheco GS, Kovacs G, Mosier JM. The difficult airway refocused.

Severe Metabolic Acidosis

In this post, we will focus only on the compensation of the metabolic part, but do not forget that this is a patient who needs attention on oxygenation and hemodynamics as well. That is, this is intubation with very difficult predictions.

What happens during the rapid sequence of intubation in severe metabolic acidosis?

To perform the procedure, the patient needs to be in apnea. During an apnea, pulmonary ventilation is decreased and the CO2 is not “washed” from the airway. These generate an accumulation of CO2, an acid, decreasing blood pH. In a patient with normal or slightly altered pH, this can be very well-tolerated, but in a patient with a pH of 7.0, an abrupt drop in this value can be ominous.

We know that the respiratory system is one of the most important compensation mechanisms for metabolic acidosis and it starts its action in seconds, increasing the pH by 50 to 75% in 2 to 3 minutes, guaranteeing the organism time to recover. So, even seconds without your proper actions can be risky for critical patients.

In addition, it must be remembered that increased RF is the very defense for the compensation of metabolic acidosis, and most of the time the organism does this very well. So if after the intubation the NORMAL FR and NORMAL minute volume are placed in the mechanical ventilator parameters, again there is an increase in CO2 and a further decrease in pH.

And what’s wrong? After all, a little bit of acidosis even facilitates the release of oxygen in the tissues because it deflects the oxyhemoglobin curve to the right, right?

Severe metabolic acidosis (pH <7.1) can have serious deleterious effects:

  • Arterial vasodilation (worsening shock)
  • Decreased myocardial contractility
  • Risks of arrhythmias
  • Resistance to the action of DVAs
  • Cellular dysfunction

What to do?

Always the primary initial treatment is: treating the underlying cause! In patients with severe metabolic acidosis, it is best to avoid intubation! Especially in metabolic ketoacidosis, which as hydration and insulin intake improves, there is a progressive improvement in blood pH.

Sodium bicarbonate

The use of sodium bicarbonate to treat metabolic acidosis is controversial, especially in non-critical acidosis values ​​(pH> 7.2). If you have acute renal failure associated, its use may be beneficial by postponing the need for renal replacement therapy (pH <7.2).

As for DKA, where sodium bicarbonate is used to the ketoacidosis formed by erratic metabolism due to the lack of insulin and no real deficiency is present, its use becomes limited to situations with pH <6.9.

The dose is empirical, and dilution requires a lot of attention (avoid performing HCO3 without diluting!)

NaHCO3 100mEq + AD 400ml

Run EV in 2h

If K <5.3: Associate KCl 10% 2amp

I would make this solution and leave it running while proceeding with the intubation preparations.

Attention: Remember, according to the formula below, that HCO3 is converted to CO2, and if done in excess, is associated with progressive improvement of the ketoacidosis and recovery of HCO3 from the buffering molecules. In a patient already with limited ventilation, its increase can cause deviation of the curve for the CO2 increase, which is also easily diffused to the cells and paradoxically decrease the intracellular pH, in addition to carrying K into the cell.

H + + HCO3 – = H2CO3 = CO2 + H2O

Mechanical ventilation

I think the most important part of the management of these patients is the respiratory part.

If you choose the Rapid Sequence Intubation: Prepare for the intubation to be performed as quickly as possible: Use your best material, choose the most experienced intubator, put the patient in ideal positioning, decide and apply medications skillfully, to ensure the shortest time possible apnea.

You will need personnel experienced in Mechanical Ventilation and you must remember to leave the ventilatory parameters adjusted to what the patient needs and not to what would be normal!

I found this practice very interesting: First, you calculate what the expected pCO2 should be for the patient, according to HCO3:

Winter’s Equation (Goal C02) = 1.5 X HCO3 + 8 (+/- 2)

And then, according to this table, you try to reach the VM Volume Minute value.
Goal CO2 Minute Ventilation
40 mmHg
6-8 L
30 mmHg
12-14 L
20 mmHg
18-20 L

These are just initial parameters. With each new blood gas analysis repeated in 30 minutes to an hour, you re-make fine adjustments using the formula below:

Minute volume = [PaCO2 x Minute volume (from VM)] / CO2 Desired

With the treatment of ketoacidosis, new parameters should be adjusted, hopefully for the better.

Another safer option for these patients would be to use the Awake Patient Intubation technique so that you would avoid the apnea period. However, Awake Patient Intubation Technique is contraindicated in suspected or confirmed COVID-19 cases due to the risk of contamination.

That’s it, folks, send your feedback, your experiences, and if you have other sources!

Further Reading

  1. Frank Lodeserto MD, “Simplifying Mechanical Ventilation – Part 3: Severe Metabolic Acidosis”, REBEL EM blog, June 18, 2018. Available at: https://rebelem.com/simplifying-mechanical-ventilation-part-3-severe-metabolic-acidosis/.
  2. Justin Morgenstern, “Emergency Airway Management Part 2: Is the patient ready for intubation?”, First10EM blog, November 6, 2017. Available at: https://first10em.com/airway-is-the-patient-ready/.
  3. Salim Rezaie, “How to Intubate the Critically Ill Like a Boss”, REBEL EM blog, May 3, 2019. Available at: https://rebelem.com/how-to-intubate-the-critically-ill-like-a-boss/.
  4. Salim Rezaie, “RSI, Predictors of Cardiac Arrest Post-Intubation, and Critically Ill Adults”, REBEL EM blog, May 10, 2018. Available at: https://rebelem.com/rsi-predictors-of-cardiac-arrest-post-intubation-and-critically-ill-adults/.
  5. Salim Rezaie, “Critical Care Updates: Resuscitation Sequence Intubation – pH Kills (Part 3 of 3)”, REBEL EM blog, October 3, 2016. Available at: https://rebelem.com/critical-care-updates-resuscitation-sequence-intubation-ph-kills-part-3-of-3/.
  6. Lauren Lacroix, “APPROACH TO THE PHYSIOLOGICALLY DIFFICULT AIRWAY”, https://emottawablog.com/2017/09/approach-to-the-physiologically-difficult-airway/
  7. Scott Weingart. The HOP Mnemonic and AirwayWorld.com Next Week. EMCrit Blog. Published on June 21, 2012. Accessed on July 15th 2020. Available at [https://emcrit.org/emcrit/hop-mnemonic/ ].
  8. IG: @pocusjedi: “Pocus e Coronavirus: o que sabemos até agora?”https://www.instagram.com/p/B-NxhrqFPI1/?igshid=14gs224a4pbff

References

  1. Sakles JC, Pacheco GS, Kovacs G, Mosier JM. The difficult airway refocused. Br J Anaesth. 2020;125(1):e18-e21. doi:10.1016/j.bja.2020.04.008
  2. Mosier JM, Joshi R, Hypes C, Pacheco G, Valenzuela T, Sakles JC. The Physiologically Difficult Airway. West J Emerg Med. 2015;16(7):1109-1117. doi:10.5811/westjem.2015.8.27467
  3. Irl B Hirsch, MDMichael Emmett, MD. Diabetic ketoacidosis and hyperosmolar hyperglycemic state in adults: Treatment. Post TW, ed. UpToDate. Waltham, MA: UpToDate Inc. https://www.uptodate.com (Accessed on July 15, 2020.)
  4. Cabrera JL, Auerbach JS, Merelman AH, Levitan RM. The High-Risk Airway. Emerg Med Clin North Am. 2020;38(2):401-417. doi:10.1016/j.emc.2020.01.008
  5. Guyton AC, HALL JE. Tratado de fisiologia medica. 13a ed. Rio de Janeiro(RJ): Elsevier, 2017. 1176 p.
  6. Kraut JA, Madias NE. Metabolic acidosis: pathophysiology, diagnosis and management. Nat Rev Nephrol. 2010;6(5):274-285. doi:10.1038/nrneph.2010.33
  7. Calvin A. Brown III, John C. Sakles, Nathan W. Mick. Manual de Walls para o Manejo da Via Aérea na Emergência. 5. ed. – Porto Alegre: Artmed, 2019.
  8. Smith MJ, Hayward SA, Innes SM, Miller ASC. Point-of-care lung ultrasound in patients with COVID-19 – a narrative review [published online ahead of print, 2020 Apr 10]. Anaesthesia. 2020;10.1111/anae.15082. doi:10.1111/anae.15082
Cite this article as: Jule Santos, Brasil, "Physiologically Difficult Airway – Metabolic Acidosis," in International Emergency Medicine Education Project, November 25, 2020, https://iem-student.org/2020/11/25/physiologically-difficult-airway-metabolic-acidosis/, date accessed: December 5, 2022

More Posts by Dr. Santos

3D Video Laryngoscopes

Laryngoscopy can be described as endoscopy of the larynx, which used to facilitate tracheal intubation during general anesthesia or cardiopulmonary resuscitation. For decades, direct laryngoscopy has been the standard technique for tracheal intubation. But today, there are two main types of laryngoscopy: direct and indirect. Indirect laryngoscopy means the provider visualizes the patient’s vocal cords without having a direct line of sight. Indirect Laryngoscopy includes video laryngoscopes, fiberoptic bronchoscopes, and optically-enhanced laryngoscopes. Video laryngoscopy introduced in recent years and it aims to overcome the limitations of direct laryngoscopy by using a camera attached to the laryngoscope. While it has clear advantages over direct laryngoscopy, video laryngoscopy still has a high cost of investment. It remains a rare commodity for Emergency Medicine clinics, especially in resource-limited settings.

While the COVID-19 pandemic was affecting the world, the people who were under the most significant risk were healthcare workers. We know that the risk of transmission of the disease is quite high, especially when performing high-risk medical procedures such as endotracheal intubation. It is a known fact that personal protective equipment such as masks or face shields are very important in protection. But it is even more important to stay physically away from the patient whenever possible. When intubating a patient, video laryngoscopy has a clear advantage in terms of eliminating the need to approach the patient’s head and trying to have a direct line of sight.

Video laryngoscopy devices are expensive. But, if you think about the essential components of it, you can easily realize that it doesn’t have to be this way. You need a blade, a camera system, a display, and a way to attach the blade and the camera system. While laryngoscopy blades are essential for Emergency clinics anyway, I can safely assume every Emergency clinic has them. A camera system and a display are also both fairly cheap and easy to obtain for most of the places on earth. Find those three and voila! You have a cheap video laryngoscope (In this post, I will not elaborate on the technique of combining a normal blade with a video camera).

For those who want to go to the next level, there are some ways of making your very own prettier video laryngoscopy devices. You just need a 3D printer, but luckily it is possible to find 3D printers in many cities these days.

So here we go.

Umay

The pandemic paved the way for innovation in many ways. Numerous doctors from all over the world rolled up their sleeves to develop new medical devices. Yasemin Özdamar, an Emergency Medicine specialist from Turkey, designed 3D-printable video laryngoscope blades named “Umay” (possibly an allusion to Orkhon inscriptions) in pediatric and adult forms based on normal laryngoscope blades.

The printing files of these blades can be downloaded for free in formats suitable for printing with PLA material, which is frequently used in 3D printers, and PA12, which is preferred for more professional printing. You can download the files here: Pediatric – Adult.

AirAngel

AirAngel is a not-for-profit tutorial center dedicated to making video laryngoscopes accessible in under-resourced nations. You can purchase the blade or video laryngoscopy devices from their website with a fairly low price of US$100-180. You can also get the file of the blade for free and 3D print it yourself. Its design is really similar to a D blade. You can head to AirAngel’s website and grab the printing file now.

Here is an example tutorial for AirAngel:

In our tests (in Turkey), the cost of printing one blade approximately 50 Turkish Liras (roughly equal to US$7 with today’s exchange rates). We also bought a “Borescope USB Camera” with a camera head outer diameter of 5.5mm from our local internet store for approximately US$13 (A similar product from Amazon). So, the cost was US$20 in total, which is cheaper than AirAngel’s offer, and a lot cheaper than a conventional video laryngoscope. We have attached the camera to the blade using special parts on them and connected the camera to a phone. And under a minute, a video laryngoscope was born.

Please note: The intended purpose of these designs is to be used as a training tool. They do not replace any medical-grade video laryngoscope systems. They are not in any way approved medical device designs, nor have they been reviewed by the FDA or any other organization. Be aware that many plastics vary in strength, heat resistance, and chemical resistance. The strength and durability of the blade will vary depending on what you print it with. Harmful and life-threatening complications may occur if pieces break in the airway.

Cite this article as: Ibrahim Sarbay, Turkey, "3D Video Laryngoscopes," in International Emergency Medicine Education Project, May 4, 2020, https://iem-student.org/2020/05/04/3d-video-laryngoscopes/, date accessed: December 5, 2022

Some Hints About Airway!

Some Hints About Airway!

Introduction

The airway is one of the most critical topics in the ER. Read everything about the airway; it is not a waste of time. Even if you have to spend one year just for airway, it is worth it. You will always be confident in dealing with whatever situation that might come to you. Although reading is essential, practicing and getting experience on airway issues is essential too. So, reading along with exposing many patients is a great combination to achieve good skills.

Build your own skills by reading then summarizing your own words. As long as it is correct and safe, the way accomplishing or securing the airway may not be important in many patients.

Here are some tips in airway management at the Emergency Department (ED)

I will mention some points that might help in the management of typical scenarios at the ED. They might look random, but trust me, it is the real deal.

  • Preparations

  • Attach the patient to monitor
  • Check the vitals,
  • Check saturation continuously,
  • Open IV lines (2x) and attach a bag of normal saline,
  • If the blood pressure is low use pressure cuff on the fluid’s bag,
  • If the patient maintains oxygenation don’t bag, just leave the mask on. Moreover, do not forget; bagging is not a safe procedure.
  • Your equipment’s; choose your tube size depending on the patient’s size, size of the laryngoscope
  • Make capnography ready
  • Call the respiratory therapist, if you don’t have one, you check the ventilation machine by yourself
  • Keep bougie on the side, and SUCTION! Doesn’t matter Yankuer or not anymore, as long as it takes away whatever is on your way. Don’t go too deep to avoid vomiting.
  • Raise the bed highest, keep the level of the patient up to your chest or even higher, the higher the better.
  • Have someone on your side in case you needed tracheal manipulation or pressure to facilitate the view.
  • Pay attention to hemodynamic parameters

  • Never intubate before knowing the blood pressure readings.
  • Never intubate with low blood pressure below 90 systolic.
  • Resuscitate then intubate.
  • Neutral hemodynamic resuscitation (some studies tried the use of paralytic agent alone, with local anesthetic on the glottis, the same idea as awake intubation, in case of hemodynamic instability to avoid the use of induction agents that might decrease hemodynamics). The risk of using multiple doses of an induction agent can cause hemodynamic instability.
  • However, if there is no contraindication, you can think of using ketamine to help boost the blood pressure.
  • Double the dose of your medication if the patient has low cardiac output. As with low cardiac output, the medication won’t reach fast; it might take longer than 4 min. There is no harm in increasing paralytic agents ONLY IF THE AIRWAY IS NOT DIFFICULT. Induction agents can be used as boluses also, but again be careful if the patient is unstable as it might worsen the condition.

Here is a great video summarizing hemodynamic issues in airway management

  • Intubation and beyond

  • Use direct laryngoscopy first, use the old school equipment to keep your skills fresh, but keep the video laryngoscope ready on the side. Some experts recommends using video laryngoscope blade for direct laryngoscope and if you need, just look to the screen.
  • Still failed multiple trials with the laryngoscope? Consider difficult airway. One of the recommendations is to “leave the tube in the esophagus and insert another tube; the other opening is definitely the trachea.” By the way, there are tools to understand the difficulty of the airway, so know and use it.
iEM-infographic-pearls-airway - Assessing Airway Difficulty
  • Rapid Sequence Intubation (RSI) and Delayed RSI: Delayed RSI used mainly in the ICU, and many authors hate this term. However, there is no harm if the patient is maintaining oxygenation, you can give a sedative and look before proceeding to RSI. Just don’t call this approach “RSI.”
  • Rocuronium or Succinylcholine; both will paralyze the patient; it is not about which one is better; it depends on the type of airway you are dealing with. If it is a difficult airway, you do not want to use rocuronium and end up bagging the patient for one hour. Using a short-acting agent is a smart move.
  • However, if it is easy, use it as it would help in paralyzing the patient for an hour, but doesn’t mean the patient is fine, do not forget analgesia/sedation!
  • The tube is in, yay! Good for you, but your work is not done yet. All of us been through the situation where we jump into the airway, insert the tube and leave. This is not a skill lab; it is a real patient. The patient is not moving does not mean he is fine, you paralyzed him but he can still feel. Insert the tube, attach capnography, bag, auscultate, make sure of the level of the tube’s depth, order x-ray STAT then start analgesia/sedation infusion! No matter how naive you are or had a blackout, use midazolam and fentanyl! However, please learn other options too, because different patients may require different agents.
  • Propofol infusion, the bright side of Propofol is its analgesic and sedative effect, although it has a high risk of causing hypotension.
  • The dilemma of which medication to use, as for induction or paralyzing. No one can tell you that one medication is better than the other. Read everything about each medication, understand it, then you make your own mixture.

As long as you keep reading, and updating your knowledge, with of course practice and exposure to different type of situations, you will always know how to deal with every situation.

Further Reading

Cite this article as: AlHanouv AlQahtani, KSA, "Some Hints About Airway!," in International Emergency Medicine Education Project, July 17, 2019, https://iem-student.org/2019/07/17/some-hints-about-airway/, date accessed: December 5, 2022

Airway Tips by Manrique Umana

Dr. Manrique Umana from Costa Rica presented a fantastic lecture during the 30th Emergency Medicine Conference of Mexican Society in Cancun/Mexico. Every emergency physician should know the airway tips he gave in the talk. Moreover, medical students and interns should also be aware of these clues. Therefore, we asked him to summarize his speech for iEM. You will find English and Spanish version of the summary on the below videos. Enjoy!

Airway Tips

This video includes a summary of “physiologically difficult airway” presentation given by Dr. Manrique Umana from Costa Rica.

Consejos de la vía aérea

Este video incluye un resumen de la presentación de la “vía aérea fisiológicamente difícil” realizada por el Dr. Manrique Umana de Costa Rica.

Cite this article as: iEM Education Project Team, "Airway Tips by Manrique Umana," in International Emergency Medicine Education Project, March 22, 2019, https://iem-student.org/2019/03/22/airway-tips-by-manrique-umana/, date accessed: December 5, 2022

Assessing Airway Difficulty – LEMON