Oxygen therapy is an essential tool in the prehospital environment as it can help the patient maintain tissue oxygenation and essential life functions while minimizing cardiopulmonary work. The primary indication for oxygen therapy is hypoxemia (decreased level of oxygen in the blood) which can be measured with a pulse oximeter (see pulse oximetry in the Vitals section). Oxygen therapy, which raises the percentage oxygen from 21% (room air) to as much as 100% (non-rebreather mask on high flow) greatly increases the efficiency of the patient's breathing.
The decision to start Oxygen therapy is often made during your primary assessment (ABCs) based on clinical signs such as:
- Tachypnea or low respiratory rate which can both be clinical signs of hypoxia
- Cyanosis and/or delayed capillary refill
- Respiratory distress, labored breathing and anxiety.
- Oxygen saturation under 94% by pulse oximetry in the otherwise healthy patient.
For the patient to maintain adequate oxygen levels in the blood and delivery of that oxygen to the tissues, the entire respiratory chain must be intact. An interruption or interference in any of these steps can result in hypoxia (inadequate perfusion of the tissues). It is helpful to understand where in the respiratory chain the patient's difficulty is coming from, as it can guide additional therapies or trigger rapid transport.
Indications for Oxygen Therapy[edit | edit source]
|"Broken link" in the respiratory chain||Pathology||Clinical signs||Additional therapies for the EMT to consider|
|Airway obstruction (upper or lower)||Foreign body obstruction, Severe allergic reactions, Airway swelling or damage from trauma, Asthma, Bronchitis, and COPD can all significantly impede airflow into the lungs||Airway narrowing often produces a variety of adventitious (abnormal) sounds. Listen for wheezing and stridor||Suction, bronchodilators, epinephrine, and airway adjuncts to address cause of the obstruction|
|Overwhelming Work of Respiration.
The contractions of the diaphragm and intercostal muscles must be strong enough to expand the lungs
|Pulmonary fibrosis or other pathologies that stiffen the lungs, and patient exhaustion from work of breathing can both result in inadequate expansion.||Look for signs the patient is using accessory muscles to breathe, has low chest rise, or appears exhausted. In children, respiratory arrest can quickly lead to cardiac arrest.||Assisted ventilations|
|Inadequate tidal volume (air per breath)||Pneumothorax or hemothorax decouples the lung from the chest wall so that the lungs do not fully expand with the intake of breath||Look for signs of injury to the chest wall, tracheal deviation and listen for faint or absent breath sounds||Assisted ventilations|
|Inadequate minute ventilation (average volume of breath per minute)||Stroke, drug overdose and other central nervous system issues can depress respiratory drive.||Respiratory rates (Breaths per Minute) that are too low indicators of inadequate breathing:
|Impaired gas exchange. The alveoli must be open enough and have adequate surface area allow air in for gas exchange||Pneumonia, congestive heart failure can both fill the alveoli with fluid, preventing gas exchange and emphysema or other COPDs can lead to "dead air trapping" in lungs||Auscultate for "crackles" and diminished breath sounds at the base of the lungs indicating fluid build up||CPAP|
|Diminished Pulmonary Blood Flow. The lungs must have adequate blood flow through the capillaries to allow gas exchange with the blood||Pulmonary Emboli can block large portions of the lung vasculature preventing blood flow to that portion of the heart, and right sided heart failure can result in insufficient pulmonary blood pressure to get adequate perfusion||Patients can report pain with breathing, and show profound hypoxia with otherwise clear airways and adequate tidal volume||Rapid Transport|
|Inadequate oxygen carrying capacity. The blood must have enough active hemoglobin to transfer oxygen from the lungs to the tissues||Carbon monoxide or cyanide poisoning can occupy hemoglobin sites and prevent oxygen binding, and in anemia there are simply too few binding sites because the blood is dilute||Headaches, extreme fatigue, cherry red lips (cyanide) and skin pallor despite brisk capillary refill. Often will have "normal" SpO2 readings. Anemia may be caused in the field by volume resuscitation after significant blood loss||Removal from environment where poisoning may have occurred|
|Hypotension. There must be enough blood pressure to get oxygenated blood to all the tissues.||Acute heart failure, excessive blood loss or any source of hypovolemic shock can prevent otherwise oxygenated blood from reaching the body's tissues||Lightheadedness, dizziness, pale, diaphoretic, slow capillary refill||IV Volume replacement|
Cautions/Contraindications[edit | edit source]
Care should be taken with patients with chronic hypercapnic conditions. Their values for oxygen saturation can be as low as 80%, and supplemental oxygen can interfere with respiratory drive or worsen hypercapnia- you should be prepared to transition to assisted ventilation in these patients if necessary.
Equipment[edit | edit source]
Supplemental oxygen can be delivered via:
- Low Flow - Nasal cannula
- High Flow - Non rebreather Mask
- In conjunction with assisted ventilations - Bag valve mask
- As part of a CPAP (continuous positive airway pressure) system.
Choosing the correct delivery system[edit | edit source]
First and foremost, your patient should be treated based on their signs/symptoms and pulse oximetry readings. The general rule is patients with minor SOB or hypoxia generally only need a nasal cannula while patients with moderate to severe SOB or hypoxia will need a NRB. If the patient is apneic or breathing with an insufficient rate or tidal volume, a BVM is often used. The CPAP system is used for patients in severe respiratory distress who would benefit from the continuous pressure it provides which helps increase alveolar pressures and recruitment of alveoli. Differences and comparisons between oxygen delivery systems will be discussed next.
Nasal cannula vs. NRB[edit | edit source]
Nasal cannulas are useful for delivery of low flow rate oxygen to patients through two nasal prongs. Some cannulas have nasal cushions that provide a tight seal and allow for flow rates up to 15 lpm, but most prehospital providers carry nasal cannulas that are utilized from 1-6 lpm. The main drawback of a nasal cannula is that the patient must be breathing through their nose to gain the most effect from the cannula. Patients in respiratory distress will rarely breathe through their noses as mouth breathing allows for a much faster flow of air in and out of the airway. Because of this, patients with respiratory distress greater than mild should generally be placed on a NRB, at minimum.
Additionally, even though 100% oxygen is flowing through the nasal cannula (with no oxygen blender), the patient is in reality receiving a much lower concentration of oxygen as they breathe. This is because as the patient inhales, they are also inhaling normal air around the prongs of the cannula, in effect mixing large volumes of 21% oxygen (room air) with 1-6 lpm of 100% oxygen. Because a NRB contains a reservoir bag of 100% oxygen that the patient inhales from, the patient receives an effectively much higher oxygen content breath from a NRB than a nasal cannula.
Patients who are on the line between needing a nasal cannula and NRB can be started on a nasal cannula and upgraded to a NRB if they do not improve. This is because, although the nasal cannula may be uncomfortable in the nostrils due to its prongs, the NRB can cause some patients to feel claustrophobic as it is tightly held to their face by an elastic band. For patients who require more oxygen than a nasal cannula but who cannot tolerate a NRB, blow-by oxygen delivery may be used.
NRB vs. blow-by oxygen delivery[edit | edit source]
If the patient is unable to tolerate the non-rebreather mask despite coaching from rescuers, blow-by oxygenation may be provided by removing the mask from the patient's face and holding the mask in front of the patient's nose and mouth with the flow rate turned up to 15 lpm. This allows the 100% oxygen from the mask to somewhat displace the 21% oxygen in the surrounding air; effectively increasing delivery of oxygen to the patient without the need for a mask held onto their face. While this does not allow for high levels of oxygen delivery, it may be helpful in reducing the patient's anxiety enough to allow for further treatment. The patient may also be placed on a nasal cannula, but it may not be especially effective at increasing inhaled oxygen concentrations.
NRB vs. BVM[edit | edit source]
If the patient is apneic, a NRB or CPAP would be insufficient interventions to control the patient's airway and oxygenation. In this case, a BVM would be used as it allows for both positive pressure ventilation and exhalation. If the patient is breathing spontaneously, but insufficiently (i.e. grossly tachypneic with poor tidal volume or grossly bradypneic), a BVM may be used to "track" the patient's respirations by providing supported ventilations at a rate determined by the provider. This method of tracking the patient's respirations can be incredibly scary and uncomfortable for a conscious patient, so the rescuer should always anticipate reduced compliance and potential combative behavior. If there is an underlying cause to the insufficient respiration that can be easily and rapidly fixed by the provider without negatively impacting patient care, a NRB or CPAP may be used as supportive oxygenation until the underlying cause is resolved.
BVM tracking vs. CPAP[edit | edit source]
One of the main differences between tracked respirations and CPAP is that CPAP requires that the patient not have any significant impairments to LOC and not be hypotensive. This is to prevent potential aspiration, fighting the mask, or worsening hypotension. Tracking may be used despite these conditions but care must be taken while tracking a patient's respirations as the same issues found with CPAP administration can be found while tracking a patient's respirations.
BVM tracking is often used for patients who are bradypneic and require an increased respiratory rate; CPAP should not be used for these patients as it does not increase the natural respiratory rate of a patient but rather increases the pressure of each inspiration and exhalation. Both BVM tracking and CPAP will work to increase tidal volume by providing positive pressure on inhalation, but unless the BVM is fitted with a PEEP valve only the CPAP will provide expiratory pressure that can help decrease atelectasis.
If the patient is tachypneic with a normal tidal volume, BVM tracking should not be used, as its primary function in the tachypneic patient is to increase inspiratory volume in an attempt to help slow down respiratory rate and increase gas exchange and oxygenation.