NCCR – Ventilation

This is the first of a series of posts on the National Continued Competency Requirements (NCCR), each covering a core competency for prehospital providers.

Minute Ventilation

Ventilation with a BVM is arguably one of the most important skills of any prehospital provider. In cases where the patient is not apneic, it is critical that the provider is able to identify when ventilation is appropriate. In EMT class, students are often given the guideline that a respiratory rate less than 8 or greater than 24 requires assisted ventilations with a BVM. While this is perhaps a reasonable guideline, it is only a half-truth. Patients in even mild respiratory distress can have respiratory rates exceeding 24 breaths/min, but obviously do not require assisted ventilations, while a patient with a respiratory rate of 10 breaths/min may require assistance with a BVM. The decision to ventilate a patient should be based on the adequacy of breathing, not the respiratory rate alone.

The key to determining if breathing is adequate or not is the patient’s minute ventilation (MV), or minute volume of respiration, which is their tidal volume (Vt) multiplied by their respiratory rate (or frequency), f.

MV = Vt * f

The average tidal volume, or volume per breath, in a healthy adult is around 500mL, which is the size of a 16.9 oz bottle of water[i]. (This may also be estimated as 4-8 mL per kilogram of body mass). Using the formula above, we can determine the average minute volume to be somewhere between 6,000mL (12 breaths/min) and 9,000mL (18 breaths/min). In other words, a healthy, average-sized adult breathes at a rate of 6-9 liters per minute.

If you’ve ever wondered what constitutes “high flow” vs. “low flow” oxygen, this is it. High flow oxygen refers to administering oxygen at a flow rate greater than the patient’s own rate, while low flow is the opposite. For a 70 kg adult with a respiratory rate of 12 breaths/min, 8 liters per minute might just count as “high flow” oxygen. So why do EMT instructors make their students repeat “high flow oxygen at 15 L/min via NRB” ad nauseam?

Consider the average 70 kg adult with a textbook tidal volume of 500mL and a respiratory rate of 18 breaths/min. Their minute volume is (500 * 18 = 9,000 mL/min = 9 L/min). If their respiratory rate increases to 24 breaths/min, their minute volume is now 12,000 mL/min, or 12 L/min. At 30 breaths/min, which is not uncommon, this becomes 15,000 mL/min, or 15 L/min. Administering oxygen at a rate of 15 L/min ensures that they are getting 100% oxygen with each breath. On the other hand, if her breathing becomes shallower as the rate increases, this can cause a plateauing of minute volume (250 mL/breath x 30 breaths/min = 7.5 L/min).

Therefore, a determination of whether or not a patient’s breathing is adequate must be made based on an assessment of both tidal volume and respiratory rate. Assisting ventilations is required any time the patient’s own ventilations are insufficient, which can be due to an inadequate tidal volume, an inadequate rate, or both. If the patient is determined to be breathing adequately, positive pressure ventilation is not required, but you should continue to determine if other interventions are appropriate.

Alveolar Ventilation

A naive interpretation of the relationship between tidal volume and respiratory rate might suggest that there are an infinite number of combinations that result in the same minute volume. While mathematically correct, this interpretation ignores the presence of anatomic dead space that is present in the airways. Anatomic dead space refers to the parts of the airway that cannot exchange gasses.  Since gas exchange occurs in the alveoli, the anatomic dead space is the volume of the conducting airways (nose and mouth down to the terminal bronchioles). This dead space is around 150 mL on average (West, 1962) but can be larger due to devices like advanced airway adjuncts and SCUBA gear, which physically extend the airway.

Everything except the alveoli is considered dead space.

When dead space is accounted for in the minute ventilation, we can determine the amount of air that moves through the alveoli each minute. This is called the alveolar ventilation (Va) and is calculated by subtracting the dead space from the tidal volume, then multiplying by respiratory rate (Levitzky, 2013).

Va = (Vt – Vd) * f

This metric is more relevant to our assessment than minute volume, as it reflects the actual amount of air available for gas exchange. As tidal volume decreases, an increase in rate alone will not be sufficient; these patients require supplemental volume. Consider our prototype adult (70 kg, Vt = 500mL, f=16) whose tidal volume starts to fall. Initially, her alveolar ventilation is 5.6 L/min. When the tidal volume is cut in half (250mL), the alveolar ventilation falls to below a third of what it was originally.

Normal: (500 mL/breath – 150 mL/breath) * 16 breaths/min = 5.6 L/min

Hypoventilation: (250 mL/breath – 150 mL/breath) * 16 breaths/min = 1.6 L/min

Increasing her respirations to around 22 breaths/min would maintain her minute volume, but her alveolar ventilation would only rise to 2.2 L/min. To return to her initial Va of 5.6 L/min, this patient would have to breathe at around 100 breaths/min. This is obviously problematic. Instead, increasing the depth of ventilation, either with a BVM or through increased work of breathing, is a better way to increase overall ventilation. If your patient has an excessively high respiratory rate (> 30), intervention is necessary to prevent deterioration in their condition.

As you can see, management of a patient’s ventilations requires careful attention to both rate and depth of ventilation. Assisting ventilations should generally be done at a rate of 10-12 breaths/min (one breath every 5-6 seconds), while delivering enough air to see the chest rise and fall (Weiss, 2008).

Ventilation-Perfusion Ratio

Effective gas exchange requires ventilation and perfusion.
Effective gas exchange requires ventilation and perfusion.

When discussing alveolar gas exchange, alveolar ventilation (Va) is only one half of the picture. The other half comes from alveolar perfusion, which provides the red blood cells that transport oxygen and carbon dioxide throughout the rest of the body. When alveoli are not perfused, perhaps due to a blockage in the pulmonary vasculature (i.e., pulmonary embolism), this creates alveolar dead space. You may also hear the term physiologic dead space, which refers to the sum of anatomic and alveolar dead spaces. Since this post focuses on ventilation, I’ll assume alveolar perfusion is within normal limits here, and cover V/Q ratios in a separate post.

Effects of Ventilation on Cardiac Output

Exceeding these parameters can result in a decreased cardiac output, which is obviously undesirable. As a refresher, cardiac output is comparable to minute ventilation, as it is a function of heart rate and stroke volume. Stroke volume, of course, is the amount of blood ejected from the left ventricle with each contraction. As you inhale, your diaphragm contracts and accessory muscles lift the chest wall up and out, causing a larger cavity. In turn, this creates negative pressure that draws air into the lungs and allows venous blood to return to the right side of the heart.

Positive pressure ventilation (PPV), as the name implies, relies on positive pressure to force air into the chest cavity. In this instance, there is little or no cooperation from the diaphragm and accessory muscles, resulting in air being forced into a fixed-size cavity. (While the chest wall certainly expands to accommodate this increased volume of air, it is doing so reluctantly.) This positive pressure also obstructs the venous return to the heart, and decreases cardiac output.

Respiratory Failure

Respiratory conditions, like many other conditions, can be described in a spectrum ranging from mild distress to respiratory failure. Likewise, episodes can be acute, chronic, or chronic with acute exacerbation. While many of our respiratory patients require only comfort care, it is important to closely monitor your patient for signs of impending respiratory failure. Respiratory failure is characterized by inadequate oxygenation or inadequate alveolar ventilation. The hallmark sign of respiratory failure is deterioration in mental status. This is often accompanied by, or preceded by, a decrease in SpO2, cyanosis, accessory muscle use, grunting, and nasal flaring. Respiratory failure can be further classified by whether or not hypercapnia (elevated levels of carbon dioxide) is present. These patients are severely ill and will likely die without intervention. Once a patient is in respiratory failure, assisting ventilations with a BVM is the best treatment option. Again, this should be done at a rate of 10-12 per minute.

Bag-Mask Ventilation

Using a BVM is simple enough in theory, but numerous studies have shown that we’re just not that good at it. In fact, the AHA recommends against using a BVM in cardiac arrest when there is only one rescuer (mouth-to-mask is better). BVM ventilation is most effective when two trained rescuers are available: one to maintain the airway and mask seal and a second provider to ventilate the patient.

Since cardiac output is reduced during CPR (around 25-33% of normal), gas exchange is also reduced. Therefore, the AHA recommends tidal volumes of 500-600 mL (6-7 mL/kg), which is enough to produce visible chest rise. Be sure to avoid overzealous ventilation, as it can lead to gastric inflation as well as a reduction in cardiac output (Link MS, 2015).

Continuous Positive Airway Pressure (CPAP)

Patients in impending respiratory failure – exhibiting signs of inadequate oxygenation, but not a change in mental status – can sometimes be managed successfully with Continuous Positive Airway Pressure (CPAP). As the name implies, CPAP works to keep the airways open with positive pressure. (It also increases the A-a gradient, which I’ll cover in the post about ventilation-perfusion ratios.) This is primarily a problem during exhalation in which the small, flexible bronchioles are squeezed shut by the positive intrathoracic pressure surrounding them. By supporting these narrow airways and increasing the A-a gradient, oxygenation is improved and carbon dioxide can exit the body more easily.

The primary advantage of CPAP is mitigating respiratory failure and avoiding unnecessary intubation. Since CPAP does not ventilate the patient, the patient must be alert, able to obey commands, and have a respiratory rate greater than 8 breaths/min. As discussed above, positive airway pressure can impede cardiac function, so CPAP is contraindicated in hypotensive (SBP < 90 mmHg) patients or those with a suspected or known pneumothorax.

Summary

Recognition of respiratory failure is critical for any level of prehospital provider. As the patient begins to experience signs of inadequate oxygenation – cyanosis, decreased SpO2, and accessory muscle use, etc. – the provider should consider interventions to increase alveolar ventilation. CPAP and assisting ventilations with a BVM are basic interventions available to most prehospital providers. CPAP is indicated when the patient is inadequately oxygenated (SpO2 < 90% despite high-flow oxygen), but not yet in respiratory failure. Once the patient’s mental status or respiratory effort begins to deteriorate, immediate ventilation with a BVM is indicated. Ventilation should be performed at a rate of 10-12 breaths/min in most cases. Whenever possible, ventilation should be performed with a basic airway adjunct in place (OPA or NPA).

 

 

 

Bibliography

Levitzky, M. (2013, Jul 15). Alveolar Ventilation. Retrieved Oct 20, 2016, from LSUHSC School of Medicine – Dept. of Physiology: https://www.medschool.lsuhsc.edu/physiology/courses_respiratory_mgl2.aspx

Office of Academic Computing. (1995). Dead Space. Retrieved 10 18, 2016, from Johns Hopkins University School of Medicine: http://oac.med.jhmi.edu/res_phys/Encyclopedia/DeadSpace/DeadSpace.HTML

Weiss, A. L. (2008). Focus On – Bag-Valve Mask Ventilation. ACEP News.

West, J. (1962, Nov). Regional differences in gas exchange in the lung of erect man. Journal of Applied Physiology, 17(6), pp. 893-898.

Link MS, Berkow LC, Kudenchuk PJ, Halperin HR, Hess EP, Moitra VK, Neumar RW, O’Neil BJ, Paxton JH, Silvers SM, White RD, Yannopoulos D, Donnino MW. Part 7: adult advanced cardiovascular life support: 2015 American Heart Association guidelines update for cardiopulmonary resuscitation and emergency cardiovascular care. Circulation. 2015;132:S444–S464.

 

NCCR – Ventilation

Pennsylvania Adopts Critical Care Transport Scope

Today, Pennsylvania announced the scope of practice and medication list for Critical Care Emergency Medical Service Providers. Unfortunately, all of the skills and medications listed apply to interfacility transports and/or must be performed in the physical presence of a PHRN/PHPE/PHP.

Critical Care Scope of Practice

Category Skill Critical Care Transport Provider (Paramedic, PHRN, PHPE or PHP)
8 Airway/ventilation/oxygenation Chest tube thoracostomy, monitoring of existing tube in a closed system (for example water seal or suction) Yes1
9 Airway/ventilation/oxygenation Chest tube thoracostomy, acute insertion Yes2
12 Airway/ventilation/oxygenation Biphasic positive airway pressure (BiPAP) for patients acutely on BiPAP for <48 hours Yes1
24 Airway/ventilation/oxygenation Endotracheal Intubation—paralytic assisted, rapid sequence induction (RSI) Yes2
25 Airway/ventilation/oxygenation Ventilation—Maintenance of previously initiated neuromuscular blockade Yes1
28 Airway/ventilation/oxygenation Laryngeal mask airway (LMA) Yes1
49 Airway/ventilation/oxygenation Ventilators, transport—single or multi-modal, with or without blender, using volume control mode only, on patients >1 year of age with no anticipated need to actively titrate ventilator settings during transport. Yes1
64 Cardiovascular/circulation Transvenous or Epicardial pacing, Management of Yes2
66 Cardiovascular/circulation Hemodynamic monitoring/assist (pulmonary artery catheter, central venous pressure) Yes2
67 Cardiovascular/circulation Intra-aortic balloon pump or invasive cardiac assist device or extracorporeal membrane oxygenation—monitoring/assist Yes2
69 Cardiovascular/circulation Thrombolytic therapy—initiation Yes2
70 Cardiovascular/circulation Thrombolytic therapy—monitoring Yes2
77 IV Initiation/maintenance/fluids Sub-cutaneous indwelling catheters—access of existing catheters Yes1
79 IV Initiation/maintenance/fluids Venous central line (blood sampling)—obtaining Yes1
81 IV Initiation/maintenance/fluids Arterial line—monitoring Yes1
82 IV Initiation/maintenance/fluids Blood products—initiation and continued administration Yes2
94 Medication administration routes Enteral Feeding Devices, Management of Yes1
103 Medications Medications for Critical Care Transport Providers as published in Pennsylvania Bulletin by the Department Yes1
105 Medications Over-the-counter (OTC) medications (Note: aspirin and glucose covered elsewhere) Yes1
112 Patient Assessment/management Portable blood analysis devices, use of (glucometer covered elsewhere) Yes1
121 Patient Assessment/management Intracranial pressure monitoring/assist Yes2
126 Patient Assessment/management Urinary catheterization Yes1

Yes—The skill is in the scope of practice for paramedics, PHRNs, PHPEs and PHPs who are authorized to function for an EMS agency that has been licensed as a CCT ambulance service. (Emphasis added)

1. Paramedics, PHRNs, PHPEs and PHPs who are authorized to function for an EMS agency that has been licensed as a CCT ambulance service may only perform or assist with these skills during interfacility transport with a CCT ambulance. (Emphasis added)

2. Paramedics who are authorized to function for an EMS agency that has been licensed as a CCT ambulance service may assist a PHRN, PHPE or PHP with this skill only during interfacility transport with a CCT ambulance and when in the direct physical presence of, and supervised by, the higher level provider. (Emphasis added)

 

Critical Care Medication List

  1. Abciximab2
  2. Albumin1,2
  3. Anti-Coagulants/Anti-Platelets: All Types (Not otherwise specified)1,2
  4. Anti-Emetics: All Types (Not otherwise specified)1.2
  5. Anti-Hypertensives: All Types (Not otherwise specified)2
  6. Antivenom1,2
  7. Atenolol1,2
  8. Barbiturates2
  9. Bivalirudin2
  10. Blood Products2
  11. Clopidogrel2
  12. Dextran1,2
  13. Digoxin2
  14. Dilaudid2
  15. Eptifibatide2
  16. Esmolol2
  17. Fibrinolytics/Thrombolytics: All Types2
  18. Glucocorticoids/Mineralcorticoids1,2
  19. Heparin2
  20. Hespan1,2
  21. Hydralazine1,2
  22. Hydroxocobalamin1,2
  23. Insulin2
  24. Ketamine1,2
  25. Ketorolac1,2
  26. Labetolol1,2
  27. Mannitol2
  28. Metaproterenol1,2
  29. Metoprolol1,2
  30. Milrinone1,2
  31. Non-Depolarizing Agents1,2
  32. Norepinephrine2
  33. Other Non-Benzodiazepine Anti-Convulsants2
  34. Phenylephrine2
  35. Phenytoin/Phosphenytoin1,2
  36. Plasmanate1,2
  37. Potassium Chloride2
  38. Propofol1,2
  39. Propranolol1,2
  40. Prostaglandins: All Types2
  41. Quinidine Sulfate/Gluconate2
  42. Romazicon2
  43. Succinylcholine2
  44. Theophylline1,2
  45. Tirofiban2
  46. Tocolytics: All Types (Not otherwise specified)2
  47. Total Parenteral Nutrition2

Footnotes:
1. Paramedics who are authorized to function for an EMS agency that has been licensed as a CCT ambulance service are restricted to the maintenance and monitoring of medication administration that is initiated at the sending medical facility. (Emphasis added)

2. Paramedics who are authorized to function for an EMS agency that has been licensed as a CCT ambulance service may only administer the medication in the direct physical presence of, and supervised by, a PHRN, PHPE or PHP. (Emphasis added)

 

Pennsylvania Adopts Critical Care Transport Scope

2014 Changes to the PA EMS Scope of Practice

The new Scope of Practice for Emergency Medical Service Providers was posted today and is scheduled for release this coming Saturday, November 29th. For reference, the soon-to-be old Prehospital Practitioner Scope of Practice is available here.

The most noticeable update is the much-anticipated inclusion of the Advanced EMT (AEMT) skills. As usual, one step forward comes with one step back: the EMR (formerly, First Responder) skill set was scaled back a bit. The EMT has gained some new abilities, and both EMTs and Paramedics have lost a couple of skills. The following is a quick breakdown to save you the time of comparing the documents.

I’ve also uploaded a comparison chart. Major additions/deletions are highlighted in blue. Lines that are blacked out indicate that nobody is allowed to perform that particular skill.

Items in italics indicate that skills may be performed only in the presence and under direct supervision of a Paramedic or higher.

Items in bold indicate that additional training and authorization by the service’s medical director is required. The service must also comply with DOH requirements for performing a skill.

Emergency Medical Responder (EMR)

According to the document, EMRs can no longer:

  • Use a BVM with an inline nebulizer
  • Use EtCO2
  • Use Pulse oximetry
  • Use CO-oximetry
  • Operate a transport ventilator
  • Apply ECG electrodes
  • Apply cervical collars

Despite being too stupid (in the state’s eyes) to apply a cervical collar or use a pulse oximeter, EMR’s are now allowed to administer naloxone via an auto-injector or the intranasal route.

Emergency Medical Technician (EMT)

EMT’s have gained the following skills:

  • Perform tracheobronchial suctioning via an advanced airway (that’s already been placed)
  • Administer oxygen via a Venturi mask
  • Use a mechanical CPR device
  • Automatic transport ventilators no longer require additional training (footnote removed).

EMTs are no longer allowed to perform EtCO2 monitoring.

Advanced Emergency Medical Technician (AEMT)

Since all of the AEMT skills are new, here’s a quick rundown of what the AEMT can and can’t do. This isn’t an exhaustive list, but rather a quick dispelling of the rumors and hearsay that have been running around. Consider checking out the AEMT Information page as well.

Allowed:

  • Most medication routes, as discussed in class.
  • IV:
    • Start a saline lock (no fluid)
    • Administer a fluid bolus (crystalloid solutions, as published by DOH)
  • Application of electrodes, including transmission of 12-lead ECGs
  • Irrigation with a corneal contact device (Morgan lens)
  • Blood glucose assessment
  • Intraosseous insertion in the physical presence and under direct supervision of Paramedic+.
  • Peak expiratory flow assessment

Not allowed:

  • Chest decompression
  • Medication administration via IV/IO, ET, or NG
  • Interpretation of ECGs
    • Any manual electrical or pharmacological intervention that is based on interpreting ECGs (AED is OK)
  • Accessing central lines, or external jugular (EJ) cannulation
  • Monitoring an IV infusion with added medication, even with an IV pump

Paramedic

  • Footnote for “additional training required” was removed for ITD
  • BiPAP is no longer allowed
  • Blended/multi-mode ventilators are no longer allowed
  • Urinary catheterization is no longer allowed

In addition to the above highlights, some wording has changed and various lines have been removed, added and/or otherwise reorganized (please review the original document). Fortunately, all of us are allowed to perform “Patient management per Statewide EMS Protocols and Department approved protocols” (isn’t that the point of them?); however, they no longer spell out that we’re allowed to use PPE, do tripsheets, use the radio, or talk to the hospital staff, and there’s no mention of whether or not we’re allowed to perform clean technique. (According to the previous scope, only Paramedics were allowed to wash their hands, use clean gloves and make an effort to prevent direct contamination of equipment and supplies.)

Things nobody likes doing anyway.

 

Again, please read the original document. There’s a chance I’ve missed something. If you do notice any inaccuracies, let me know.

2014 Changes to the PA EMS Scope of Practice