Emergency medicine: Manual non-invasive ventilation with PEEP valve

When a pet arrives that is obviously having labored and difficult breathing, an immediate course of treatment is to provide supplemental oxygen at high concentrations. This is best done with a tight-fitting face mask attached to a valve system and reservoir.

In human medicine this is available commercially and is called a "non-rebreather." Its use is called non-invasive ventilation (NIV). In veterinary medicine, the valve system needed is best met in emergencies with a bag-valve assembly ("Ambu(c)bag") attached to a cone-shaped veterinary face mask (Photo 1).

Photo 1: A bag-valve assembly attached to a cone-shaped veterinary face mask. (Photos: courtesy of Dr. Dennis (Tim) Crowe)

The Ambu(c)bag system has an exhalation valve that directs the exhaled air into the atmosphere and an inhalation valve that allows the inhalation of oxygen from a reservoir. To the end of the exhalation port a positive end-expiratory pressure (PEEP) valve can be attached (Photo 2). Using this added valve increases the amount of air left in the lungs at the end of exhalation, increasing functional residual capacity.

As the top of the valve is rotated, a spring tightens, increasing pressure on a valve that controls the resistance to airflow out of the lungs. The reservoir is a clear-plastic, flexible bag that is filled with oxygen during the patient's exhalation and empties during bag compression, as seen in the photo of a firefighter-paramedic providing bag-valve-mask ventilations in emergency training (Photo 3).

Photo 2: A positive end-expiratory pressure (PEEP) valve attached to the end of the exhalation port increases the amount of air left in the lungs at the end of exhalation, increasing functional residual capacity.

The amount of oxygen in the reser-voir needed to satisfy the patient's inhalation lung volume, which is frequently increased in the patient's stressed state, must be easily supplied in the one-quarter to two seconds inspiratory time.

Photo 3: A clear-plastic, flexible bag is filled with oxygen during a patient's exhalation and empties during bag compression, as seen when a firefighter-paramedic provides bag-valve-mask ventilations in emergency training.

This requires a flow rate of oxygen at the patient's airway during inhalation calculated to be between 12 and 100 liters per minute (avg. 66 L/min). This calculation is based on the tidal volume, minute volume and inhalation time of each breath.

As can be seen, it is impossible to provide this amount of flow rate of inhaled oxygen without the use of a reservoir that can be easily emptied and which contains 100 percent oxygen. Any other systems involving a face mask, where there are no reservoir or valves to control the direction of inhaled and exhaled air, are not recommended in emergency settings in which the work of breathing must not be increased and high concentrations of oxygen are required.

During the inhalation phase of breathing, if there is no reservoir attached to this same type of bag-valve-mask system, the highest percent of oxygen that can be achieved during inhalation is 40 percent to 50 percent; the reservoir oxygen concentrations can reach 100 percent.

Non-mask systems

Of course, most animals having difficulty breathing resist the use of a tight-fitting mask. In these cases, other simple ways of providing supplemental oxygen, such as oxygen cages and simple blow-by techniques, should be tried first.

Research that we performed and published in 2004 revealed that, although oxygen cages can be used for the treatment of these critical patients, they isolate the pet from caregivers and require at least 20 to 25 minutes to see oxygen concentrations approach 40 percent delivered to the patient. This time lag can be of concern.

Other alternatives that provide higher concentrations of oxygen in a much shorter period include blow-by and jet blow-by techniques (reaching 40 percent oxygen within two minutes); placing the patient in a smaller container (compared to the standard oxygen cage, and reaching 60 percent oxygen within five minutes); using a Crowe collar (Photo 4), an Elizabethan collar that is one size larger than would otherwise be used with its most rostral ventral half covered with clear plastic wrap to provide a "boat effect" for the holding of the delivered oxygen around the patient's head (providing 70 percent to 80 percent oxygen within two to three minutes at flow rate of 5 L/min.); placing a nasal cannula (providing 40 percent oxygen within one minute with a flow rate of 4–5 L/min.); placing a nasal catheter (flexible feeding tubes placed unilaterally or bilaterally following slight sedation and providing 40 percent to 70 percent oxygen in two to three minutes of the beginning of oxygen delivery at 50-100 ml per minute per kg); and simply placing the patient in a firm or flexible plastic bubble that is connected to an oxygen supply line (providing 50 percent to 70 percent oxygen within one to three minutes with delivery at 5-10 L/min).

Photo 4: A Crowe collar, an Elizabethan collar that is one size larger than would otherwise be used, with its most rostral ventral half covered with clear-plastic wrap to provide a "boat effect" to hold delivered oxygen around the patient's head. A hand-held analyzer monitors oxygen concentration.

Oxygen concentration in some of these various systems can and should be monitored by using a hand-held oxygen analyzer (Photo 4).

Assisted ventilation

If, after oxygen has been administered for up to 30 minutes with any of these non-mask systems, the patient continues to have serious respiratory effort (and a quick preliminary ultrasound has ruled out significant pleural space disease), the patient may benefit significantly from the application of mild sedation and placement of a tight-fitting mask and using an Ambu(c) resuscitation bag, plus adding assistance by squeezing the Ambu(c)bag with each breath.

As positive pressure breathing is begun, with timing as best as possible along with squeezing of the bag with the onset of each spontaneous breath, within a few minutes the patient's respiratory rate and effort should decrease and become less labored (Photo 5).

Photo 5: As positive-pressure breathing is begun, with timing as best as possible along with squeezing of the bag with the onset of each spontaneous breath, a patient's respiratory rate and effort should gradually decrease.

This simple technique, called assisted ventilation, is effective in decreasing the effort the patient takes to continue to breathe. It has been my experience that many patients, once they acclimate to the assisted ventilation and settle into a rhythm, fall asleep within a few minutes because they were so exhausted from trying to breathe.

Continuing the assisted ventilation for at least 30 minutes is recommended in most cases if they are still conscious and positive clinical effects are observed.

For emergency patients, once any shock is addressed, a PEEP valve can be added to the exhalation side of the Ambu(c)bag to treat pulmonary edema, contusions, etc. This valve has a spring that gets tighter and increases the amount of pressure needed to open the exhalation valve.

With the valve pressure set at 5 cmH20 the airway pressure at the end of exhalation is elevated (i.e., PEEP). When positive pressure ventilation is added to the tightly applied Ambu(c)bag-valve-mask, manual non-invasive ventilation with a PEEP valve is being performed.

Emergency patients that arrive in significant shock and with pulmonary injury should be managed immediately with this technique if they are still conscious (Photo 6).

Photo 6: Emergency patients that arrive in significant shock and with pulmonary injury should be managed immediately via manual non-invasive ventilation (with PEEP valve) if they are still conscious. If breathing is not assisted, but positive-pressure breathing is being used, it is called continuous positive airway pressure (CPAP).

If breathing is not assisted, but positive-pressure breathing is being used, it is called continuous positive airway pressure (CPAP).

Both types of breathing will increase the patient's functional residual cavity and are easily accepted by most patients. In most cases, manual non-invasive ventilation (with the PEEP valve set at 5-10 cmH2O) is initiated with patients that are not responding to supplemental oxygen alone. The procedure is done for 20 to 30 minutes, and then the patient is re-evaluated.

Re-evaluation may include watching the patient's breathing pattern and effort, auscultating breath sounds and performing thoracic radiographs, thoracic ultrasonography and arterial blood gas analysis.

For patients that do not respond well, invasive positive-pressure ventilation, with intubation and CPAP and PEEP, are needed. For patients that improve with the non-invasive ventilation, it has been my experience that approximately 50 percent will need only a few more treatment sessions and then require continued supplemental oxygen therapy with methods that are very effective (even if a small amount of sedation is required to keep the patient comfortable and accept the therapy), such as a bilateral nasal catheter or a Crowe collar.

Record of success

This technique has been used by the author and colleagues in an estimated 400 veterinary and human patients over a decade, beginning in 1997. It has been very successful as a rescue procedure. I continue to use similar techniques in my human patients when I work as an advanced EMT and first responder on the county rescue unit.

I estimate that, without this technique, mortality would have been 100 percent, but through its use more than 80 percent were able to come out of the crisis without intubation or ventilation. I also recommend the use of NIV with a bag-valve-mask system for at least a few breaths before intubation in cases of the pulseless, non-breathing and unconscious patient.

If the patient is not oxygenated well and is acidotic, any movement can induce ventricular asystole or fibrillation caused by vasovagal and sympathetic stimulation. Bag-valve-mask ventilation requires the head to be extended, the tongue pulled forward, the jaw closed and the application of the tight-fitting mask, as opposed to all the manipulation necessary to perform endotracheal intubation.

I have observed that NIV, as described, provides a rapid way to provide oxygen and lower the CO2 level in the bloodstream and tissues, helping prevent catastrophic complete arrest for patients that were near arrest.

It is recommended to perform NIV with the Ambu(c)bag and reservoir connected to an oxygen supply and being delivered at 5-15 L/minute immediately on all unconscious patients who are unresponsive and not already intubated.

The technique has been one of the best life-saving procedures I have ever done.

The use of a manual system (bag-valve-mask) has been the focus of this article; however, this can be converted to a mechanical ventilation system. It involves a mechanical ventilator that provides a positive pressure cycle of ventilation to a tight-fitting face mask, often with the addition of a cloth muzzle and/or tape to make the mask tight against the animal's face to help prevent leaks. I have used various commercial ventilators; the most useful I have found are the pressure-cycled systems. These have allowed the NIV to continue to be used from less than an hour to more than 24 hours.

Readers with questions can reach me by e-mail at traumadoc@dtimcrowe.com or they can call me at (706) 296-7020.

Dr. Crowe is chief of staff at Pet Emergency Clinics and Specialty Hospital, Ventura, Calif.