Time Worn Adjuncts to Mechanical Ventilation - The Good, The Bad, The Ugly

 

Proning is the latest modality for augmenting ventilator 
therapy.  Some vintage measures were not so effective

Recognition of acute respiratory distress syndrome (ARDS) in the early 1970s and treatment with Engstrom ventilators was a game changer, with  mortality plunging from 100% to about 40%. As more experience was gained mortality plunged even further. Deducing what worked and what didn't with ventilators was a rocky road.

It's human nature that clinicians faced with an unstable, critically ill patient want to do everything possible to rescue the person. We referred to situations like this as kitchen sink medicine when just about anything and everything was added to the armamentarium. Sometimes, desperation in medicine results in untoward  outcomes. I'm thinking about radical mastectomies for all breast cancers and surgeries like hemipelvectomies. Some pioneering accompaniments to mechanical ventilation bore little fruit, and did little to avert a vegetative outcome, but just about anything seemed worth a try when the clinical situation seemed so bleak.

Early practitioners in the art of mechanical ventilation were not like the experienced critical care medicine experts of today, but surgeons and anesthetists who saw the benefit ventilators made with ARDS treatment. They were drafted into the new role of managing ventilators and much of what ensued was on the job training..  Science was sometimes, in short supply when empirically based notions were applied as we shall soon see.

Everyone takes in a deep breath from time to time, so why not try this with ventilated patients? It was fairly easy to adapt those ancient, chugging, Engstroms to deliver an occasional deep ventilation, all it took was some monkeying around with that gizmo on top of the Engstrom that looked like an expresso machine, and PRESTO, the "sigh" was invented. A sigh was an occasional cycle with increased tidal volume and the frequency was highly variable.

 Intermittent sighs were a source of dread for sedation deprived ventilator patients, imagine having a hurricane force of air, unpredictably, blasted into your chest via a skinny little tube.  A United airlines pilot recovering from pneumonia said, "Now I know what it's like to suck on an engine of a 747." Unpleasant does not begin to describe the patient experience when the sigh cycle kicked in.

Ventilator driven sighs never really caught on in the hospital where I worked.  Surgeons blamed the sigh cycle for putting undue stress on suture lines and in the event of a rare evisceration, the sigh was always blamed. The elevated intra thoracic pressure was also blamed for barotrauma to vulnerable alveoli. 

Positive end expiratory pressure or PEEP evolved to be the replacement for sighs. PEEP entailed maintaining a low steady pressure (5cm/H20) in the lungs just slightly above ambient atmospheric pressure. Some overzealous physicians figured that if a little bit of PEEP was good, then more is even better. Super PEEP was born with pressure of 25 cm and above which was like blowing an automotive tire up to 100psi. Talk about a rough ride!

Super PEEP worked for a time until complications surfaced. High intra thoracic pressure compromised blood flow in the great vessels which caused big problems. A hemodynamically unstable critically ill patient is not a good thing. Renal problems often developed as a result of compromised circulation. Super PEEP was not such a good idea, but did persist when technology for cardiac output monitoring was developed which enabled fine tuning to allay complications. The father of super PEEP at Montefiore Hospital in Pittsburgh was Arnold Sladen MD. He was either a hero or a scoundrel depending on who you talked to.

Endotracheal tubes exert a seal by an inflatable cuff which contacts and forms a seal with the trachea. Sustained pressure exerted by the cuff can limit the amount of time a patient can be maintained on the ventilator before an invasive tracheotomy must  be done. Long term unremitting pressure from the cuff can cause problems.   Intermittent endotracheal tube cuff inflation was thought to be a way a kinder gentler way of sealing an airway. The cuff was inflated only on inspiration.

Intermittent endotracheal cuff inflation required some complex additional equipment and lengthening the inflation tubing  increased dead space and exacerbated the  potential for  leaks. There was also the ever present risk of aspiration when the cuff was deflated. This overly complicated  modality was usually abandoned with much haste as it just didn't work very well.

There is that old joke about anesthetists passing gas, but in reality, they are passing gases. Fiddling around with the inspired mix of gases was second nature when novice anesthesia folks began overseeing ventilator therapy. Traces of helium mixed with the FiO2 were thought to aid in alveolar dispersion, but in the long run seemed to make little difference. 

Life on a ventilator was unpleasant at best. Before propofol came along, anesthetists would sometimes  "trace an agent," or install an in line vaporizer to sneak in a whiff of halothane to settle things like "bucking" down. Progress in IV sedation put a halt to anesthesia  vaporizers on ventilators except, of course, in the OR.

Ventilators are an unforgiving entity and that ominous click...hiss...pause  always overshadowed the cheerful cacophony of melodious alarm tones, quickly becoming  the dominant noxious noise in the ICU. Ventilators really strummed a different sort of tune that frequently foreshadowed impending doom.

In the rapidly gathering storm leading up to intubation and subsequent ventilation, impending consequences were often conveniently overlooked. Rendering someone mute with an endotracheal tube and lashing them to a machine forcefully converting air into breathe has all the grace of getting clobbered by a linebacker on steroids.

Late at night, numbed by fatigue induced hopelessness, strange thoughts percolated through my mind when caring for a poor soul on a ventilator. We all want a nice linear, progressive, and predictable path from illness to health. Sometimes, though, ventilator patients are too far along on their journey to the other side. If  I'm ever in this predicament, I hope my caregivers reconsider my path and don't interfere with my final journey.

When I'm on that peaceful river journey to the other side, I better not come across a ventilator masquerading as a life boat!

The Emerson 3PV Ventilator (Circa 1964)

Gather round the ol' manually cranked  hospital critical care bed all ye Whippersnapperns and take a quick little quiz on the history of air becoming breath. What do you get when you combine a Westinghouse hot plate, an ordinary natural gas meter, a couple of AC delco automotive switches, a trombone slide, copper mesh and a V belt from a 1960 Chevrolet Brookwood? House them all together with an air pump in a Maytag washing machine cabinet and you have a pioneering ventilator known as the Emerson 3PV.

The control panel of the Emerson 3PV ventilator shows it's

Maytag roots. Does that black knob control the rinse cycle or tidal volume?

Although a high school dropout, Jack Emerson was an innovative young man. His 2 brothers were physicians and Jack being an inquisitive young man, asked them what they needed in their medical practice. At age 22, Jack bought a rudimentary machine shop at an estate sale and began manufacturing medical equipment. His first device was an automatic agitator for laboratory use.

The idea for a cost effective ventilator came to light when he heard one of the leading trauma experts of the day, R. Adams Cowley, complaining about the high cost and availability of Engstrom ventilators which were the standard of the day. Dr. Cowley received  a $100,000 dollar grant to research shock following trauma and had to spend most of it on expensive Engstrom ventilators. A cost effective ventilator would free up grant money for other vital research.

After some tinkering in his Cambridge, Massachusetts machine shop, the ever enterprising Emerson cobbled together a ventilator created from a hodge podge of ordinary and readily available household and automotive parts. His unique creation was the first ventilator marketed with a humidifier thanks to the hot plate and a water vessel.

 Modern ventilators have filters to prevent contamination, but Emerson's 3PV went a step further. He incorporated copper mesh in the return tubing. Copper has antimicrobial properties and actually kills bacteria and viruses by degrading the cell membrane or protein coat of the virus.

One thing missing from Emerson's pioneering ventilator was an electronic monitoring screen made by extracting toxic elements from the earth via a process that is probably slowly killing us. Old school practitioners were satisfied with watching the rise and fall of the chest and auscultating breath sounds to verify ventilatory function.

Simple devices like Emerson ventilators have an inherent beauty. One way or another we could all wind up flat on our backs with a ventilator chugging away in the background. While we are thinking, "Is this all there is?" an image of the ventilator blowing air into our wounded meatsacks appears in our peripheral vision. I know my emotional bandwidth will feel like it's been hit by a grenade if I see a computerized microprocessor controlled gizmo keeping me alive. Find one of those old Emerson's in the basement somewhere and I'll be smiling even with that endotracheal tube jammed down my old, foolish craw.

When Air Becomes Breath - A Historical Perspective

"After 8 more arm raise cycles, It's time to check her ABGs"

A 1910's critical care nurse has just found her patient apneic and beginning to turn that dreaded inky, cyanotic color. All is not lost. It's time to initiate artificial respiration. Of course before all the heroic measures start, it's always prudent to check the upper airway for an obstruction. Every old nurse knows the time honored mouth opening trick of placing a thumb on the mandibular arch and the index finger positioned above on the maxilla and then rapidly crisscrossing her fingers. The other hand  finger is free to probe the oropharynx for obstructions. If you encounter a hot dog segment, Brazil nut, or hunk of steak all you have to do is yank it out and  hope for the return of spontaneous breathing.

If the chest has ceased that comforting sight of rising and falling, it's time for artificial respiration. Pull your supine patient to the very  head of the cart, table, or bed and get a gorilla grip on her forearms. To initiate expiration, pull her arms down and adducted into her chest with her fists at the base of her lungs. Now for the fun part. Rapidly pull her arms overhead and below her body for inspiration. One caveat: just as modern CPR can crack ribs, this old school method can wreak havoc with elbows dislocations. Just how do you explain that to the family? This complication is also not favorable to Press Ganey Satisfaction Surveys so be careful lest those pesky patient relationship builder consultants  appear on the scene. (As an Oldfoolrn, I give thanks everyday that I never had to deal with that!) Hats off to you bright, whippersnapperns that are forced to submit to this nonsense.

There was one other old school artificial respiration trick  procedure done with the patient prone. The nurse jumps up into the bed or litter and straddles the patient. The patients arms are flexed at the elbows with forearms at a right angle to the body. For expiration the nurse pushes down and forward at the base of the lungs and inspiration involves grabbing the flexed elbows and pulling them toward and into the head. This was the popular Red Cross method taught to 1960's lifeguards. These techniques probably moved just enough air to clear the dead space in the pharynx, larynx, and trachea.

Unfortunately these techniques ignored one of the most basic anatomic characteristics of the chest which except for some intercostal movement during respiration is a very rigid, unyielding  cage like structure. When the diaphragm moves down the volume of the chest increases, lowering the intrathoracic pressure causing inspiration. A very clear example of what happens with a non rigid chest occurs with traumatic injury breaking ribs causing a flail chest. Not a pretty picture when the chest wall is mobile and it's really time to head to the OR.

An Engstorm in action. Who needs piped in

Oxygen with those handy dandy "J' cylinders?

Moving them around was like wrestling a

Sumo Wrestler.

A lifesaving (oh, how I hate that term) innovation for critically ill patients was the introduction of  volume respirators such as the mid 1960's Engstroms. These precision machines from the Karolinska Institute in Sweeden cost $8,000 USD in 1960 and had the capability of expanding the lungs at the alveolar level. This was the birth of PEEP (positive end expiratory pressure.)

These early ventilators were impressive looking machines. The control panel looked like something from an airplane cockpit and was ingeniously tilted to prevent nurses from stacking anything on top of it. I can tell you from personal experience this was no place to temporarily set down that Albumin bottle.Cleaning up the sticky substance laced with glass shards is a lesson that sticks with you.


As much as Oldfoolrns love old, familiar analog medical machines, they could have some truly vexing and potentially fatal problems. Being a 100% mechanical device the Engstrom had zilch in the way of electronic alarms. A nurse could be lulled into a false sense of security by that reassuring whoosh/whoosh as the macines bellows appeared to inflate the patient's lungs. Without a continuous monitoring of pressure in the breathing circuit, a patient's trach tube could disconnect from the ventilator tubing without an audible warning. Nurses really had to be right at the bedside watching for the rise and fall of the patient's chest.

I cannot resist the segue to a foolish tale from yesteryear. Ventilator supported patients in the times before oximeters and capnography required frequent arterial blood sampling (ABGs)  to monitor respiratory status. If the patient had an arterial line in place this was no problem. Without an arterial line nurses had to tap a radial or femoral artery for a sample inflicting pain and trauma. We hated doing these on a frequent basis and if the critical care fellow ordered ABG's too often we threatened to put a plastic trash can liner over his head and draw his blood gases in 30 minutes. The young physicians were conditioned so that whenever a nurse began removing a  plastic trash can liner from the waste basket, it was time to rethink the blood gas order.