Airway & Respiratory, Columns

Ketamine May Aid in Prehospital Management of Severe Asthma

Issue 8 and Volume 42.

An ALS unit that has a 60-year-old female on board in severe respiratory distress. On arrival, you find your patient altered in the back of the ambulance. She’s hypoxic, with oxygen saturation (SpO2) in the upper 60s, and has audible wheezing. She will not keep the non-rebreather mask on.

Initially she was found unresponsive by the ALS crew, who first attempted intubation, but had difficulty doing so as they don’t carry paralytics. An 18-gauge IV had been established in the left antecubital area, and she received 125 mg of solumedrol IV. The first arriving ALS crew has treated her before and indicates she has a history of severe asthma and has been intubated before in the past.

You have a 25-minute air transport over a mountain range that’s 9,000 feet above sea level to the nearest hospital with the appropriate level of care available. You and your partner decide that despite the difficulty in managing asthma patients on a ventilator, the patient will need intubation for airway control and to help further treat her asthma.

Setup for intubation with paralytics is begun to increase the success of intubation. The patient continues to be non-cooperative and combative from her hypoxia.

You plan to give her a sedation dose of ketamine, both to get control of the patient, and to better pre-oxygenate her prior to the intubation attempt. The setup is for a delayed sequence intubation (DSI) using ketamine and rocuronium.

Plans are going well until the patient, in her altered state, pulls out her only working IV before medications can be drawn up and given. Bleeding from the site occurs and is quickly controlled. At first this seems like a major problem for your plan of DSI, however, you have a plan B. Almost immediately, a larger intramuscular (IM) dose of ketamine is given and the patient begins to relax.

The transport ventilator is set up and attached to the bag-valve mask (BVM), and you have intermediate focus on holding a good mask seal and providing controlled ventilation. The patient is supine on the cot and the head of the bed is raised to 30 degrees. She’s ramped to the ear-to-sternal notch position to achieve better oxygenation and intubation conditions. Underneath the mask, a nasal cannula is placed at 20 Lpm in preparation for apneic oxygenation once the paralytic is administered and takes effect.

During this time, another IV is established, and the patient’s SpO2 climbs into the upper 90s. Equipment is checked and prepared, including a video laryngoscope, suction and waveform capnography. Once the patient has been saturating in the upper 90s for a few minutes, you decide to push the rocuronium and attempt the intubation.

To give the rocuronium a chance to fully take effect, a full minute goes by before an intubation attempt is made. The patient continues to be bagged with good mask seal using the ventilator with a nasal cannula underneath.

The mask is removed and your partner inserts the video laryngoscope with ease, finds the epiglottis and exposes the glottic opening. The endotracheal tube is delivered without any desaturation on first attempt. Intubation is confirmed with positive waveform capnography, and the patient is placed on the ventilator.

Keeping in mind that she has an obstructive lung process, her end-tidal carbon dioxide (EtCO2) readings will help guide ventilator management. Her ventilator strategy includes monitoring of peak pressures, waveform capnography and a prolonged expiratory time (a 1:5 inspiratory-to-expiratory ratio).

An in-line DuoNeb (albuterol and ipratropium) and magnesium are administered for her asthma. She’s given another bolus dose of ketamine, this time via IV and started on a ketamine drip with fentanyl for sedation and comfort. The patient is transported without incident comfortably on the ventilator for the 25-minute transport.

Hospital Course

The patient was delivered to the ED and diagnosed with a severe asthma exacerbation. She has no evidence of pneumonia or other infection. After being admitted to the ICU she continues similar treatment to that she received from EMS. She’s extubated within two days and discharged to home in five days.

Discussion

Asthma is a very common disease seen in the field. Roughly 1 in 15 Americans suffer from this disease. Since 1980, the fatality rate from asthma has increased significantly.1 There are many types of intimidating patients that you may encounter in the field, with severe asthmatics being one of those. Underlying inflammation causes swollen airways and excess mucus, which dramatically reduces the size of the airway. The smooth muscles of the airway also constrict, thus narrowing the passage for air exchange with an emphasis on altered exhalation.

Standard treatments in the field and the hospital include drugs such as albuterol, which bronchodilates and ipratropium, which blocks muscarinic receptors in the lungs and allows the muscles around the airways to relax.

Other treatments include magnesium, which is thought to stabilize T cells, thereby limiting the production of inflammatory mediators and reducing swelling. It also acts to stimulate nitric oxide and prostacyclin production, possibly reducing the severity of asthma.2,3 Epinephrine as well as terbutaline can also be used and are potent bronchodilators working through a beta-2 agonist mechanism.

Ketamine is well known for its rapid onset of behavioral control with preservation of airway reflexes, and can be given IV, IM, and intranasal (IN). It’s a drug that’s not commonly thought of as an adjunct in the case of severe asthma exacerbations, which served two very important functions in the management of this patient’s severe asthma exacerbation.

First, it served to gain behavioral control to facilitate further treatment without the loss of airway reflexes in a hypoxic patient. Secondly, ketamine bronchodilates, making it another viable treatment option in patients who are refractory to initial therapies. This is especially true in the case of a severe asthma exacerbation requiring endotracheal intubation.

Ketamine will produce the necessary sedation for endotracheal intubation as well as associated bronchodilation. It’s thought to work both directly on the bronchial smooth muscles and indirectly by causing the release of endogenous catecholamines, stimulation of the sympathetic nervous system, or inhibition of reuptake of catecholamines.4,5

In one study, the beta blockade effects of propranolol didn’t inhibit ketamine’s ability to bronchodilate.4 Another known anesthetic agent to bronchodilate is propofol, however this agent is very short acting, and can cause apnea and hypotension.5,6 Ketamine can be given to asthma patients not requiring intubation, and can also be used as a continuous drip on both intubated and non-intubated asthma patients.7,8

Teaching Points

The severe asthmatic patient is one of the most difficult patients for prehospital providers to manage. First, the EMS provider’s assessment needs to be accurate. Wheezing alone can’t direct course of action. Is it an allergic/anaphylactic reaction? Is there hemodynamic instability? Is another obstructive lung process to blame? Are the breath sounds equal bilaterally, or has your asthmatic developed a tension pneumothorax? In the case of toddlers and young children, have they aspirated a foreign body? Absence of breath sounds can be a sign of impending respiratory failure.

A detailed patient history must be taken, if possible, including previous attacks, treatment already rendered and current medications, history of previous intubations and hospitalizations. Knowing what inhaler your patient has been using is important as tachyphylaxis, develops over time from repeated use of a medication. Also known as tolerance, it leads to the need for higher doses to achieve the same effect. Tachyphylaxis is common with the beta-2 agonists drugs used in asthma.

How much time do you have before respiratory arrest? The first line drugs of albuterol and ipratropium have somewhat delayed onsets of action in the 10-25 minute range, and steroids even longer.9-12 When your patient’s condition is refractory to this route of management, something else must be considered.

Ketamine has an onset of action around 3-4 minutes when given IM, and around 60 seconds when given IV.13

Waveform capnography will be beneficial in monitoring this type of patient, both intubated and non-intubated. You can monitor their expiratory phase and assess for breath stacking and further CO2 retention. Whatever you define as your level of care, be sure to continue treatment of the underlying problem during your transport.

Conclusion

Ketamine is a consideration in conjunction with other standard asthma medications as part of a thorough treatment strategy in the severe asthma patient. Endotracheal intubation of the severe asthmatic shouldn’t be undertaken lightly. A strategy focusing on the underlying ventilatory problem and excellent pre-oxygenation should be the highlights of a well-thought-out plan.

This case highlights the advantages ketamine gave the crew in this including: behavioral control, bronchodilation, optimize pre-oxygenation and continued sedation for comfort. In conjunction with appropriate ventilator settings, an in-line DuoNeb and magnesium, ketamine provided an effective and comfortable patient transport on the ventilator that might otherwise have been difficult to obtain. jems

References

  1. Bledsoe B, Buchannan K, Hodnick R. Late-night wheezer: Providers respond to pediatric asthma patient. JEMS. 2012;37(1):26,28.
  2. Bichara M, Goldman R. Magnesium for treatment of asthma in children. Can Fam Physician. 2009;55(9):887-889.
  3. Guerrera MP, Volpe SL, Mao JJ. Therapeutic uses of magnesium. Am Fam Physician. 2009;80(2):157-162.
  4. Gateau O, Bourgain J, Gaudy J, et al. Effects of ketamine on isolated human bronchial preparations. Br J Anaesth. 1989;63(6):692-695.
  5. Brown R, Wagner E. Mechanisms of bronchoprotection by anesthetic induction agents: Propofol versus ketamine. Anesthesiology. 1999;90(3):822-828.
  6. Sarma V. Use of ketamine in acute severe asthma. Acta Anaesthesiologica Scandinavica, 1992;36(1):106-107.
  7. Benken S, Goncharenko A. The future of intensive care unit sedation: A report of continuous infusion ketamine as an alternative sedative agent. J Pharm Pract. May 2, 2016. [Epub ahead of print.]
  8. Umunna BP, Tekwani K, Barounis D, et al. Ketamine for continuous sedation of mechanically ventilated patients. J Emerg Trauma Shock. 2015;8(1):11-15.
  9. Albuterol. (n.d.) Medscape. Retrieved April 1, 2017, from http://reference.medscape.com/drug/proventil- hfa-ventolin-hfa-albuterol-343426#10.
  10. Ipratroprium. (n.d.) Medscape. Retrieved April 1, 2017, from http://reference.medscape.com/drug/atrovent- atrovent-hfa-ipratropium-343416#10.
  11. Decadron. (n.d.) Medscape. Retrieved April 1, 2017, from http://reference.medscape.com/drug/decadron- dexamethasone-intensol-dexamethasone-342741#10.
  12. Solu-Medrol. (n.d.) Medscape. Retrieved April 1, 2017, from http://reference.medscape.com/drug/medrol- medrol-dosepak-methylprednisolone-342746#10.
  13. Ketamine. (n.d.) Medscape. Retrieved April 1, 2017, from http://reference.medscape.com/drug/ketalar- ketamine-343099#10.