Week 6: Pulmonary Part 1

This patient is suffering from respiratory distress and impending respiratory failure. Rocuronium is a nondepolarizing paralytic agent; succinylcholine is a depolarizing paralytic agent. One side effect of depolarizing agents is an increase in serum potassium. On average, succinylcholine raises the serum potassium by about 0.0–0.5 mEq. But in patients with certain underlying conditions, the rise in serum potassium can be more dramatic (1.0–2.0 mEq), leading to hyperkalemic dysrhythmias. These conditions include burns, denervation injuries, crush injuries, myopathies, and prolonged immobility. The more dramatic rise results from the upregulation of acetylcholine receptors at the neuromuscular junction, which takes 5 days to develop. Thus in patients with an acute burn, acute crush injury, or acute denervation, the risk of succinylcholine-induced hyperkalemia is minor. The dose of succinylcholine is 1.5 mg/kg and rocuronium is 1.0 mg/kg. Rocuronium and other nondepolarizing agents do not cause a rise in serum potassium.

In this patient, succinylcholine (C and D) would be contraindicated because the patient has suffered a denervation injury (CVA) and is bed bound. Rocuronium or another nondepolarizing agent would be a more appropriate drug. Etomidate, a short-acting hypnotic agent, should be dosed at 0.3 mg/kg during rapid-sequence intubation. A dose of 0.1 mg/kg of etomidate (B) can be used for procedural sedation.

This intubated patient began to decompensate shortly after returning from the radiology suite. It is essential to establish a quick and logical approach to the unstable patient on mechanical ventilation when the ventilator alarms are sounding and the patient is hemodynamically compromised. The first critical action is to disconnect the patient from the ventilator. Removing the ventilator from the equation limits the number of variables in solving this life-threatening challenge and immediately eliminates it as a primary culprit.

The patient may be decompensating from a pulmonary embolism, but until more basic causes are ruled out, thrombolytics (A) should not be administered. A chest radiograph (C) can aid in determining why the patient is decompensating, but it should be obtained after the patient is disconnected from the ventilator. In the absence of clear signs of tension pneumothorax (decreased breath sounds, tracheal deviation, JVD), needle thoracostomy (D) should not be performed empirically.

Endotracheal intubation occurs in approximately 2% of all asthma exacerbations and about 10-30% of patients requiring intensive care admissions. Management of patients with severe asthma who are mechanically ventilated is challenging and therapies aimed at avoiding intubation should be employed. Magnesium sulfate administered intravenously at doses of 2 to 3 g promotes bronchodilation and leads to decreased rates of intubation in the severe asthmatic. Noninvasive ventilation with BiPAP is another therapy shown to decrease rates of intubation in these patients.

Heliox (A) therapy has been employed as a means to improve the administration of medication into the distal branches of the airway. Heliox is a mixture of helium and oxygen, which in combination has a decreased density compared with air and allows for more laminar flow into the distal airway. Given the mixture of oxygen with helium, 100% oxygen cannot be delivered and this therapy is cautioned in severely hypoxemic patients. In theory, the use of heliox will improve the effectiveness of medication delivery and effect and potentially avoid intubation although no data has linked its use with decreased rates of hospitalization or intubation. Inhaled corticosteroids (B) have shown benefit when used either alone or in combination with systemic corticosteroids presumably through their anti-inflammatory effects locally within the airway tissue. Steroids typically begin to have effect within hours of their treatment. Inhaled corticosteroids are associated with decreased rates of hospital admission. Leukotriene inhibitors like montelukast (D) are useful in asthmatics due to overproduction of leukotrienes by these patients leading to increased airway inflammation. Patients who receive oral montelukast have more improvement of peak flow the morning after admission, but its use has not decreased rates of hospital admission or intubation.

Myoclonus is a common side effect after administration of etomidate in procedural sedation. Etomidate is a amnestic agent that is commonly used in rapid sequence intubation and for conscious sedation. The onset of action of an intravenous dose of etomidate is roughly 30 seconds and the drug has a short half-life leading to an awake and alert patient within 5-15 minutes of drug discontinuation. The primary adverse effects of the drug are myoclonus, nausea, vomiting and respiratory depression. The myoclonus is benign but can be mistaken for seizure activity and can make certain procedures more difficult (e.g. orthopedic reduction).

Fentanyl (B) is an opioid used for pain control in sedation and can cause respiratory depression. Midazolam (C), a benzodiazipine, and propofol (D) are both potent sedative agents that can cause respiratory depression and hypotension. Propofol very rarely can cause myoclonus, but is much less likely than etomidate to have this effect

The Mallampati score was developed in order to predict difficulty of orotracheal intubation based on the structures visualized upon inspection of the oropharynx. In order to perform the Mallampati evaluation, the patient is seated with the neck extended. The patient is asked to open the mouth and protrude the tongue, with or without phonating. Complete visualization of the oropharynx including the tonsillar pillars is a Class I view. Class I and II predict adequate oral access for laryngoscopy. Class III predicts only moderate access and Class IV predicts a significant difficulty. Research has shown that the Mallampati score is a valid predictor of difficult laryngoscopy. In a Class III view demonstrated above, the soft palate and base of the uvula is visible.

A Class I (A) view allows full visualization of the soft palate, uvula, fauces and tonsillar pillars. A Class II (B) view shows the soft palate, uvula and fauces but no tonsillar pillars. A Class IV (D) view only shows the hard palate and is most predictive of a difficult intubation.

A needle cricothyrotomy is a recommended last resort emergency department procedure for complete upper airway obstruction. Very little literature supports its use or safety due to the exceedingly rare circumstances in which it should be used. To perform a needle cricothyrotomy place a towel under the shoulders extending the neck and forcing the trachea anteriorly and palpate for the cricothyroid membrane. This may be difficult to find in small children and you may need to cannulate the proximal trachea instead. Place a finger and thumb on either side to stabilize the trachea and cannulate it at a 30° angle directed caudally with a 14G over-the-needle catheter. Aspirate air into a 3- or 5-mL syringe to ensure entry into the trachea. Without firm cartilaginous rings the trachea collapses easily making it difficult not to penetrate the back wall of the trachea. Once you aspirate air, gently slide the catheter off the needle and attach the 3.0 mm ETT adapter to which you can attach a bag-valve mask. You will need significant pressure to overcome the resistance of the small diameter catheter, well above the limits of a regular pop-off valve that must be disabled. Watch and wait for chest fall between each breath which may be significantly delayed due to the small diameter catheter. Hold the catheter at all times even after it has been secured. Remember this is a temporizing measure only to provide oxygenation for a brief period while additional resources are summoned. Jet ventilation has also been defended but has been shown to cause barotrauma.

With a 5 mL syringe, 3.0 mm ETT adapter, and 20G over-the-needle catheter (B) you may not be able to provide sufficient oxygen; use the largest bore needle available. A 5 mL syringe, 5.0 mm ETT adapter, and 14G over-the-needle catheter (C) or a 5 mL syringe, 5.0 mm ETT adapter, and 20G over-the-needle catheter (D) do not have the correct adapter size that will fit your catheter.

*Alternatively, a 3 mL luer-lock syringe is compatible with a 7.0 mm ET tube, which you can connect together and attach to your angiocath

Asthma results in over 1.5 million emergency department visits yearly, and while the vast majority of these patients are treated and subsequently discharged home, a small percentage have severe symptoms that require endotracheal intubation and mechanical ventilation. Indications for intubation are based on clinical findings and include depressed mental status, declining respiratory rate, worsening hypercapnia and progressive hypoxia despite adequate treatment. Rapid sequence intubation (RSI) is the preferred method of intubation. Ketamine is the induction agent of choice when intubating severe asthmatics. A dissociative anesthetic, ketamine has potent bronchodilator effects, making it an ideal choice. It acts as a smooth muscle dilator, increases circulating catecholamines and does not cause histamine release. Ketamine (1-2 mg/kg IV) should be given followed by succinylcholine (1.5 mg/kg) or a competitive neuromuscular blocking agent such as rocuronium.

Etomidate (A) is a sedative-hypnotic frequently used for RSI and is a good choice in hypotensive patients as it the most hemodynamically neutral of the sedative agents used. However, it does not have any bronchodilator effects making ketamine the better choice. Midazolam (C) is a rapidly acting benzodiazepine that can be used for RSI but it can cause moderate hypotension so it would not be a good choice in this case. Propofol (D) is a lipid-soluble alkylphenol derivative that acts at the GABA receptor to cause sedation and amnesia. It also has some bronchodilator effects making it a good choice in asthmatic patients. However, it can also cause hypotension and, therefore, would not be the best choice in this case.

Bilevel positive airway pressure (BiPAP) is a method of noninvasive positive-pressure ventilation that uses two different pressure settings, one during inspiration and one during expiration. The inspiratory pressure is triggered when the patient takes a breath. Both continuous positive airway pressure (CPAP) and BiPAP can be used in patients with acute cardiogenic pulmonary edema and help avoid the need for endotracheal intubation. CPAP and BiPAP reduce the work of breathing, increase inflation of alveoli, and improve compliance. They also decrease preload, thus offsetting ventricular filling pressures.

Albuterol/ipratropium (B) is used in the treatment of asthma. It has not been shown to reduce rates of intubation in pulmonary edema. High-flow nasal cannula oxygen (C) is an emerging method of respiratory support for patients with severe dyspnea. In the pediatric patient with bronchiolitis, it has been shown to improve oxygenation and reduce the need for intensive care unit admission. But it has not been specifically evaluated in the management of adults with acute cardiogenic pulmonary edema. A non-rebreather mask (D) delivers oxygen but does not provide significant positive pressure. Therefore, it does not have the same beneficial effects that BiPAP or CPAP has in patients with pulmonary edema.

The term permissive hypercapnia defines a ventilatory strategy for acute respiratory failure in which the lungs are ventilated with a low inspiratory volume and pressure. The aim of permissive hypercapnia is to minimize lung damage during mechanical ventilation; its limitation is the resulting hypoventilation and carbon dioxide (CO2) retention.

The major concern for mechanically ventilated patients with obstructive airway disease is dynamic hyperinflation (also known as auto-PEEP, intrinsic PEEP, breath stacking, or air trapping). This condition occurs when gas becomes trapped in the lungs during mechanical ventilation. The air trapping is caused by inadequate time for exhalation allowing for delivery of the next breath before the patient has time to completely exhale. This leads to increased alveolar pressures, decreased venous return, and decreased cardiac output ultimately leading to hemodynamic instability. Auto-PEEP can be detected on the ventilator waveform because the flow will not return to zero before the next breath.

Strategies to avoid auto-PEEP would be any factor that decreases the I:E ratio which include decreasing the minute-ventilation (respiratory rate and/or tidal volume), or increasing the inspiratory flow rate (the standard flow rate is 60 L/min, this can be increased up to 80-100 L/min). These factors allow more time for the patient to complete exhalation minimizing the risk of hyperinflation. In severe cases, deep sedation and paralysis may be necessary to improve ventilator synchrony and avoid auto-PEEP.

Rates of asthma mortality have decreased over time. Mortality rates are higher in women and African-Americans. Assessing risk factors related to increased rates of mortality are important to identify in the evaluation of a patient with an acute exacerbation. A history of prior intubations is associated with increased mortality in patients with an acute asthma exacerbation. Other factors include:

History of hospitalization at age 18 (A), Recent use of nebulized albuterol (B), and peak flow 70% predicted (C) are not predictive of increased mortality as isolated risk factors. A history of hospitalization at age 18 does suggest that the patient has had an episode of severe asthma in the past, but hospitalizations are predictive within the last year or month. Recent use of corticosteroids not albuterol is associated with increased risk of mortality. During an acute exacerbation, there is impairment of expiratory flow. A peak flow 70% predicted suggests mild airway obstruction but is not an independent predictor of mortality. Some studies have linked an increasing severity score of asthma with mortality, however a severe asthma exacerbation is marked by a PEF <40%