The best place to start your review of the treatment of severe asthma is to read Reference (1) Dr. Weingart’s new article Managing Initial Mechanical Ventilation in the Emergency Department [Full Text PDF]. Ann Emerg Med. 2016 Nov;68(5):614-617. doi: 10.1016/j.annemergmed.2016.04.059. Epub 2016 Jun 9.
The above article is an awesome summary of his podcasts on Dominating the Ventilator. Start at that PDF.
And then be sure to review Dr. Weingart’s PDF handout, Spinning Dials: How to Dominate the Ventilator.
And finally be sure to see References (3), (4), (5), (6), and (7) which are all outstanding podcasts from Dr. Scott Weingart of emcrit.org. [I plan to transcribe some or all of the posts just so they’ll be available to me for rapid reference.]
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Reference (2) covers the standard office treatment of asthma. What follows is from that reference:
Asthma presents with recurrent episodes of wheezing, dyspnea, prolonged expiratory phase, and diminished air exchange secondary to narrowing of midsized and small airways. This leads to increased work of breathing with chest retractions, hypoxia (low oxygen saturation less than 93%) and poor feeding. Status asthmaticus exists when there is a failure to respond to initial bronchodilator therapy.
Severe asthma: marked chest tightness, marked wheezing and retractions, cyanosis and inability to speak in sentences, hunched posture, and altered mental status.
Assessment:
ABC’s-vital signs and pulse oximetry – – circulatory respiratory status characterize the degree of respiratory distress (Clinical Respiratory Score*)
Respond appropriately per BLS/PALS protocols
Onset of symptoms, current medications, risk factors for severe disease (below)
Management:
Oxygen:
Administer oxygen to maintain SpO2 to greater than or equal to 92%.
Nasal cannula, blow by oxygen, facemask at 5 L per minute or
Non-rebreather oxygen mask at greater than 10 L per minute
Nebulized bronchodilators:
Albuterol 0.15 mg per kilogram (minimum 2.5 mg; maximum: 5 mg) In combination with Ipratropium (0.25 mg: less than 12 years; 0.5 mg: greater than 12 years)
May repeat every 20 min. for three doses
or
Short acting Beta agonist (albuterol MDI) with valved spacer
If mild: less than two years: 4 puffs; greater than or equal to two years: 6 puffs 1 dose and reassess
If worse: less than two years: 6 puffs; greater than two years: 6 – 8 puffs Q 20 min. up to three doses
If poor air entry and patient unable to cooperate, may administer 1:1000 epinephrine 0.01 mL per kilogram SC (max: 0.3 mL)
Steroids
Administer PO prednisolone 2 mg per kilogram ASAP (max: 60 mg) or PO or IM dexamethasone 0.2 mg per kilogram (Max: 10 mg)
Caution in cases with potential life-threatening asthma: [Emphasis to all that follows is added]
- Previous intubation or ICU admission.
- Greater than or equal to two hospitalizations or greater than or equal to 3 ED visits in the past year.
- Use of greater than 1 canister of short acting Beta agonist per month.
- Poor compliance and access to care.
- Lack of perception of disease severity (parent or child).
- Rapid disease progression.
- Major psychosocial problems.
Transfer to ED/call EMS when
- No improvement in initial three bronchodilator treatments.
- Persisting low oxygen saturation (less than 94%)
- Marked increase work of breathing and exhaustion.
- Poor mental status – – somnolence, agitation, lethargy
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References (3), (4), (5), (6), and (7) are all outstanding podcasts from Dr. Scott Weingart of emcrit.org. [I plan to transcribe some or all of the posts just so they’ll be available to me for rapid reference.]
Reference (4) EMCrit Podcast 16 – Coding Asthmatic, DOPES and Finger Thoracostomy
December 23, 2009 by Dr. Scott Weingart is outstanding and covers the DOPE mnemonic which we all learn about in ACLS in a very practical manner. And Dr. Weingart adds (S) to the mnemonic so it becomes DOPES. The S refers to breath stacking which is critical to know about for asthmatics on the ventilator. And Dr. Weingart recommends an approach to tension pneumothorax (the P in DOPES) that uses the finger thoracostomy instead of a needle decompression [The finger thoracostomy is well described in the podcast.] His reasoning makes a lot of sense, as usual. [This podcast will be the first I transcribe.]
References (5) and (6) EMCrit Lecture – Dominating the Vent: Part I
and EMCrit Lecture – Dominating the Vent: Part II from Dr. Weingart are videos and are worth watching rather than just listening to the audios. They are Vimeo videos and can be downloaded.
Reference (7), EMCrit #19 Noninvasive Ventilation [PEEP, CPAP, BiPAP] Explained By Dr. Weingart of EMCrit Posted on December 29, 2015 by Tom Wade MD. These are notes that I made on Dr. Weingart’s podcast.
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Reference (8) is from The Manual of Emergency Airway Management 4th edition, 2012, RM Walls and MF Murphy and covers the same material as Dr. Weinberg’s posts above. I’ve excerpted some of the material in the book in a post Acute Severe Asthma: Rapid Sequence Intubation and Mechanical Ventilation on May 10, 2012. The following is from Reference (8) and my post:
These patients (both asthmatics and COPDers) have been working hard to breath for hours and are physically exhausted. Often, the doctor will be “forced to act” meaning that a rapid sequence intubation is indicated even if evaluation suggests that the airway may be difficult (there may not be time for an awake intubation with the fiberoptic bronchoscope). [Non-invasive BiPAP is almost always indicated before intubation unless perhaps the patient is too obtunded to defend his airway.]
Diaphoresis is a particularly ominous sign, and the diaphoretic asthmatic patient who cannot speak full sentences, appears anxious, or is sitting upright and leaning forward to augment respiratory effort should not be left unattended until stabilized.(1)
If time permits, patients with asthma or COPD requiring intubation should receive 1.5 mg per kg of IV lidocaine three minutes before receiving the induction dose of the sedative (ketamine in asthma patients and etomidate in COPD patients who often have other medical problems that argue against ketamine because of its catecholamine release).
Summary for Initial Ventilator Settings (2)
1. Determine the patient’s ideal body weight.
2. Set a tidal volume of 6 to 8 ml per kg with FiO2 of 1.0 (100% oxygen)
3. Set a respiratory rate of 8 to 10 breaths per minute.
4. Set an I/E ratio of 1:4 to 1:5.* Pressure control is preferred. If using pressure control, the I/E ratio is adjusted directly by the I/E ratio parameter or by adjusting the inspiratory time parameter. If using volume control, the I/E ratio can be adjusted by increasing the peak flow rate, and the ramp inspiratory waveform should be selected. Peak IF can be as high as 80 to 100 L per minute.
5. Measure and maintain the plateau pressure (Pplat) at less than 30 cm H2O; try to keep the PIP at less than 50 cm H2O.***
6. Focus on the oxygenation and pulmonary pressures initially. If necessary, allow maintenance or gradual development of hypercapnea to avoid high plateau pressures and [resulting in] increasing auto-PEEP.
7. Ensure continuous sedation and analgesia with a benzodiazepine and a nonhistamine-releasing opiod, such as fentanyl, and consider paralysis with a nondepolarizing muscle relaxant if it is difficult to achieve ventilation goals.
8. Continue in-line beta 2-agonist therapy and additional pharmacologic adjunctive treatment based on the severity of the patient’s illness and objective response to treatment.
*The I/E ratio is the ratio of the inspiratory time to the expiratory time. Because patients with severe asthma [as well as those with COPD] have outflow obstruction, the expiratory time needs to be as long as possible to avoid auto-PEEP. Auto-PEEP is the development of unintended PEEP from incomplete exhalation of the delivered tidal volume. Auto-PEEP increases the risk of lung damage from mechanical ventilation (barotrauma).
**The plateau pressure (Pplat) is the pressure measured during a 0.2 to 0.4 second pause at end-inspiration. The goal is to keep Pplat at a level of less than 30 cm H2O because at that level of pressure is not usually associated with lung damage (barotrauma). Auto-PEEP is unlikely with a Pplat below 30.
***The peak inspiratory pressure (PIP) is the highest airway pressure measured during inspiration. It is not as predictive of barotrauma as the plateau pressure. However, it is a very important parameter to follow because: “A sudden rise in PIP should be interpreted as indicating tube blockage, mucous plugging, or pneumothorax until proven otherwise. A sudden dramatic fall in PIP may indicate extubation.” (3)
Monitoring the Mechanical Ventilation
“If initial ventilator settings disclose a Pplat of more than 30 cm H2O, consider lowering minute ventilation and increasing IF (inspiratory flow), both of which will prolong expiratory time and attenuate hyperinflation. If Pplat is unavailable, PIP may be used as a surrogate.” (4)
Controlled Hypoventilation
“The concept of controlled hypoventilation (permissive hypercapnia) promotes gradual development (over 3 to 4 hours) and maintenance of hypercapnia (PCO2 up to 90 mm H2O and acidemia (pH as low as 7.2).” (5) The purpose is to reduce the incidence of lung injury and hypotension from auto-PEEP. The way to do it is by reducing the minute ventilation and increasing the IF to 80 to 120 L per minute. This requires sedation and analgesia and, sometimes , neuromuscular blockade.
Hypotension in Mechanical Ventilation
Hypotension in mechanical ventilation can be due to tension pneumothorax or to relative or absolute volume depletion from decreased venous return due to increased intrathoracic pressure.
Tension pneumothorax is the least common cause. And now it can rapidly and reliably be diagnosed by bedside ultrasound exam as well as by chest x-ray.
If tension pneumothorax is ruled out, then empiric infusion of 1 to 2 liters of normal saline is indicated.
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Resources:
1. Managing Initial Mechanical Ventilation in the Emergency
Department [PubMed Abstract] [Full Text PDF]. Ann Emerg Med. 2016 Nov;68(5):614-617. doi: 10.1016/j.annemergmed.2016.04.059. Epub 2016 Jun 9.
2. The Complete Resource on Pediatric Office Emergency Preparedness. 2013. Springer. This excellent book is brief and to the point. The authors are from Texas Children’s Hospitaland Texas Children’s Pediatrics. Asthma, pp 17 + 18.
3. EMCrit Podcast 15 – the Severe Asthmatic
December 8, 2009 by Dr. Scott Weingart of EmCrit.com
- Addendum brief mp3 response to the above.
4. EMCrit Podcast 16 – Coding Asthmatic, DOPES and Finger Thoracostomy
December 23, 2009 by Dr. Scott Weingart
5. EMCrit Lecture – Dominating the Vent: Part I
May 24, 2010 by Dr. Scott Weingart
6. EMCrit Lecture – Dominating the Vent: Part II
June 1, 2010 by Dr. Scott Weingart
7. EMCrit #19 Noninvasive Ventilation [PEEP, CPAP, BiPAP] Explained By Dr. Weingart of EMCrit Posted on December 29, 2015 by Tom Wade MD.
8. Manual of Emergency Airway Management 4th edition, 2012, RM Walls and MF Murphy. pp. 368 – 376. [ The pages are summarized in my post Acute Severe Asthma: Rapid Sequence Intubation and Mechanical Ventilation. Posted on May 10, 2012 by Tom Wade MD]
9. Asthma Imaging from emedicine.medscape.com Updated: Mar 04, 2016
10. Computerized Tomography Scans in Severe Asthma: Utility and Clinical Implications [PubMed Abstract] [Full Text HTML] [Full Text PDF]. Curr Opin Pulm Med. 2012 Jan;18(1):42-7. doi: 10.1097/MCP.0b013e32834db255.
