This is an experiment in rescue breathing designed to study the influence of curare and other relaxant drugs on the selection of method of expired air resuscitation.
We shall illustrate.
Volunteers were anesthetized with barbiturates, belladonna, and opiates by vein and nitrous oxide by mask.
The intravenous drugs were given to stop breathing by purposely elevating the volunteers carbon dioxide threshold.
Resuscitations were tried with and then without the flaxid paralysis of curare or succinyl choline.
To safeguard the condition of the anesthetized volunteer, mechanical ventilation with 40 % oxygen was used before resuscitation trials.
Hypoxia was avoided by limiting trials to two minutes.
This is a new pickup devised for continuous measurements of tracheal airflow and gas concentrations.
A standard tracheal tube was cut away so as to leave only its cuffed tip in which was built a flow meter.
Fine polyethylene tubes lead to a mass spectrometer for oxygen measurements, a Liston -Becker analyzer for carbon dioxide, a Harvard transducer for flow, and a strain gauge for pressure.
These determinations were recorded continuously on a Sanborn polyviso.
Watch the right side of the tracing for the arrows.
This tracing shows in order from above downward the respired oxygen and carbon dioxide concentrations, the airflow, and the pressure in the trachea.
Now look at the upper left hand corner.
With each respiratory cycle, the oxygen concentration falls from 43 % in the inspired air to 40 % in the alveolar air.
The alveolar carbon dioxide concentration is shown with each breath, and during this brief period of hyperventilation falls from 6 .5 to 5 .5%.
Peak air flow as produced by the mechanical ventilator is over 60 liters per minute during each inspiration.
Endotracheal peak pressure here is 15 centimeters of water.
The carbon dioxide and oxygen traces lag 6 tenths and 10 seconds respectively behind flow and pressure because of travel time in the catheters.
The middle part of the tracing is recorded at slower chart speed than the two ends, one millimeter instead of 10 millimeters per second.
Here is a model showing the tracheal pickup placed between the larynx and the carina after topical anesthesia with lidocaine.
An ordinary tracheal tube, the white one, rests with its tip just through the vocal cords prior to the resuscitation trials.
The tracheal pickup imposes minimal distortion in the upper airway.
It avoids the pitfall of a guaranteed open airway provided by a tracheal tube.
Unlike a mask or a mouthpiece, it can be secured in place without encumbering the jaw.
Removal of the conventional tube leaves the tracheal pickup in place and the upper airway unsupported and undistorted.
Three flexible plastic catheters about two millimeters in diameter traverse the upper airway.
These catheters are tied to a narrow strip of the tracheal tube.
150 cc of gas per minute are aspirated from the trachea for carbon dioxide analysis and an aliquot for oxygen analysis.
The other two catheters are used for flow and pressure measurements.
While the volunteer is still paralyzed by succinylcholine, the white tracheal tube is removed, leaving only the catheters from the tracheal pickup within the upper airway.
Extubation must be cautious to avoid disturbing the tracheal pickup.
As soon as ventilation with 40 % oxygen is stopped, the interval timer is set for two minutes.
Now for a trial of mouth -to -mouth breathing.
Note how relaxed and mobile the volunteer's jaw remains during succinylcholine infusion.
It is easy to open the mouth and pull the jaw forward.
The thorax is very compliant, permitting high peak flows with low pressures.
Note the good chest expansion, typical of the relaxed volunteer.
In fact, ventilation is so efficient that the reserve oxygen supply in the patient's lung is washed out within eight breaths.
This oxygen washout down to 20 % is illustrated in the top tracing.
Note in the second tracing that the rescuer's alveolar carbon dioxide value appears as the shoulder just preceding the victim's alveolar plateau value.
During this sequence, the rescuer's carbon dioxide concentration was 4 .5%, while that of the paralyzed volunteer was 6 .3%.
The peak flows here are about 90 liters per minute during inspiration, requiring 15 to 20 centimeters of water pressure.
Similarly, in the subject receiving relaxant drugs, it is easy to insert an S -tube like this one.
Either end may be used, depending upon the size of the victim.
Again, the rescuer encounters little difficulty inflating large volumes at low pressure.
Even when leakage occurs around the tube, adequate ventilation is achieved.
The record confirms the delivery of satisfactory tidal volumes.
The small excursions in the initial oxygen and carbon dioxide traces during apnea are not related to artificial respiration, but rather to the heartbeat.
In the last respiratory cycle, alveolar oxygen is 20 % and alveolar carbon dioxide is 6%.
Now we will shut off the succinylcholine infusion, and all subsequent resuscitation will be attempted without the benefit of relaxant drugs.
Now apnea will be sustained by the prolonged effect of opiate and barbiturate drugs, and oxygenation will be assured by repeated ventilation with 40 % oxygen or higher.
The effects of succinylcholine were allowed to wear off for 30 minutes, while oxygenation was ensured with a mechanical ventilator.
Excessive ventilation was avoided, maintaining the volunteer's carbon dioxide at levels consistent with mild asphyxia.
Now that the volunteer is no longer flexed, the foregoing maneuvers will be repeated.
The first step of opening the volunteer's mouth or insertion of the thumb fails.
His lips are mobile, but he promptly clenches his teeth.
Now airway insertion is no longer possible in a non -paralyzed volunteer.
When the teeth are clenched, the rescuer can't blow through the mouth because the tongue blocks it.
Even when the thumb can be forcibly inserted, injury by sharp teeth is a possible hazard.
During such a period of apnea, the cardiac effects are again noted, and with the first breath by the ventilator, the alveolar oxygen concentration was over 40%, more than twice normal, but the alveolar carbon dioxide had reached an early asphyxia level of 7 .2 % in 25 seconds.
Here we have hypercapnea without hypoxia.
Now another rescuer will try the mouth -to -mouth method, but the teeth are clenched because the jaw muscles are still contracted.
One alternative for mouth -to -mouth breathing is to hold the mandible in this manner, to open the jaw and lips, and then to blow through the mouth.
But the mouth -to -mouth method, or the use of an S -tube, depend on a patent oral air passage.
If jaw muscles are contracted and the teeth cannot be separated, it becomes impossible to insert a tube.
Time for the ventilator again.
The next trial will utilize the nose.
Although the jaw muscles are contracted, the head can still be tilted back, and the mandible can be elevated sufficiently to prevent blockage by the tongue in the posterior pharynx.
Bilateral lifting at the angles of the jaw can be effectively applied even when neither thumb nor an airway can be inserted between the teeth.
In this and in other volunteers, mouth -to -nose breathing has consistently yielded satisfactory results.
In every instance in which excessive muscle tone prevented access to the mouth for ventilation, mouth -to -nose breathing was successful.
Airway obstruction was easily overcome by lifting the jaw when the nasal passages were used in this manner in 20 anesthetized patients.
Here is the record.
Pulmonary ventilation by mouth -to -nose equals or exceeds that by procedures tried so far.
After eight breaths, the oxygen washout reached 20 percent.
The carbon dioxide fell from 7 to 6 .5 percent.
Peak flows reached 50 liters per minute, but required pressures approaching 30 centimeters of water.
These higher pressures are correlated with the reduced compliance of the non -paralyzed volunteers thorax.
But the simple mouth -to -nose procedure must be one alternative in any teaching of expired air resuscitation.
Note the diminished expansion of the chest since succinylcholine has worn off.
Exaggerated lift of the chest is routinely observed when these studies utilize a paralyzed volunteer.
Mouth -to -nose breathing does not actually require direct contact.
The use of a handkerchief has been suggested for practice purposes upon conscious volunteers.
Dr.
Ralph Waters described this version 15 years ago.
For some, the barrier may make the procedure more acceptable.
It is important for the rescuer to blow with his mouth widely opened.
An auronasal mask is equally suited to the challenge of the clenched jaw.
This soft vinyl folding resuscitation mask covers the nose and mouth of a child or adult and thereby makes use of the nasal air passage or the oral air passage or both.
Watch the chest.
No tube is in the mouth.
It is imperative under these circumstances that the jaw be lifted and the head tilted back as in the mouth -to -nose technique.
A snug fit of the mask is usually obtained by thumbs and forefingers held along the sides of the mask.
As in all methods of expired air resuscitation, air may be blown into the stomach.
Be sure to watch for regurgitation of stomach contents during its decompression.
In our series with non -flaxid victims, excessive gastric dilatation has not been a problem.
It should be emphasized that the mask using the nasal passage sometimes works when an S -tube cannot be inserted.
Either a mask or an S -tube enables the rescuer to see the chest rise.
The S -tube is a non -flaxid victim.
