Tuesday, August 14, 2012

1980-2012: Evolution of Artificial Respiration

1980sDown's Flow Generator:  Continuous Positive Airway Pressure, something that was researche in the 1930s but basically ignored as the iron lung was the popular mode of ventilating patients, made a comeback in the 1980s as studies showed it was effective in treating patients with COPD and sleep apnea.  The most common method of delivering CPAP in the hospital setting was with a Down's Flow Generator. The device was plugged into a wall oxygen outlet and hooked up to wide bore tubing.  The tubing was connected to a face mask that was securely strapped to the patient's face.  A pressure manometer is attached to the mask and an oxygen analyzer is added to the circuit via a T-piece to monitor percent of oxygen delivered to the patient.  A venturi system allowed you to adjust the FiO2 delivered to the patient.  Studies show a CPAP of 7.5 increases the partial pressure of alveolar air by 1 percent which is enough to force enough oxygen into the blood to make a clinical difference.  This was used until the mid to late 1990s when larger machines such as the Vision were determined to be more efficient deliverers of CPAP.  From my experience, CPAP is rarely ever used by itself in the hospital setting as BiPAP is usually preferred (see below).  However, when oxygen alone is the issue, CPAP may work just fine.  CPAP is, however, used as an effective means of weaning patients from ventilators, and thus is incorporated as a mode in most modern ventilators.  A downside to these generators is they didn't have any alarms.  A variety of CPAP generators are presently still available, such as the WhisperFlow generator which allows for contorl of flow and accurate FiO2s and various Caradyne Isobaric CPAP Valves to allow the clinician to adjust CPAP based on the patient's clinical condition. 

1983:  Puritan Bennett 7200

This was the first microprocessor ventilator to hit the market.  The machine was very durable and simple to use.  The settings were set by scrolling through an led screen, and alarms were set in the same way. It was easily used, portable, and worked well for the patient.  It quickly became the "most widely used ventilator around the world, capturing a 60 percent share of the international market by the end of the decade.  (c)

1987:   The Bird 6400ST

This ventilator was the first of the new generation of volume ventilators to hit the market.  It was a rectangular shaped ventilator with all your basic knobs on the front, including volume control, assist control, SIMV, PS and CPAP modes.  It also had a PEEP valve that was easily adjusted by a dial, and a full set of alarms.  The only knock on this simple device was the expiratory valves needed to be cleaned between each use and were a pain in the butt to put back together and keep in functioning order.  It was a very compact ventilator for its time.  We actually used this ventilator as either our main vent or back-up until about 2008.  

1991:  Servo 300 Ventilator

This was a replacement ventilator for the Servo 900 and was generally created to complete with the the Puritan Bennett 7200.  It was much simpler to use than the old 900 version, and therefore was less intimidating.

It had a new mode called Pressure Regulated Volume Control (PRVC) which made it so the patient could get a guaranteed volume, yet a sensor in the machine sensed changes in patient lung compliance to make sure the lowest pressure possible was given.  This is a ventilator that is still used where I work, although as a back up to the Servo i.

The ventilator also had an option called automode that allowed the patient to switch from a controlled rate (such as PRVC, or pressure control) to a patient driven mode (such as volume support or pressure support).  Many newer ventilators have their own version of PRVC and automode.

Another neat feature was it was one of the first ventilators that it provided the option of allowing either pressure or flowby to be used.  Before this all positive pressure ventilators sensed a patient breath as pressure was decreased when the patient inhaled.  Flowby is actually more sensitive in that all the patient has to do is inhale a small amount of flow and this is sensed by the machine.

 It also had a nice set up of graphics screen so you could see what the patient was doing and make adjustments accordingly.  This feature was nice because it allowed the patient to control the ventilator instead of the other way around.  It had a few flaws, yet it was a great ventilator.

It was also the first ventilator that could be adjusted so it could supply breaths to a patient of any age or size.  It was a good ventilator for newborns, pediatrics and adults. As you look at the entilator the what the patient was doing was lit up as red, and the ventilator settings were green.  So we'd often tell nurses:  "Green machine, red bed."  (d)

1992:  V.I.P. Bird Infant Pediatric System

It was referred to as the T-Bird ventilator. At the time it was also the first and only ventilator that was mobile.

1995BiPAP:  Noninvasive Positve Airway Pressure, sometimes referred to as simply Bilevel Positive Airway Pressure (which is a patented name but we often generic it), became common in the 1990s as another method of ventilating patients in a more non-invasive manner.  This is a means of providing support breaths with CPAP or PEEP, which is generally called end positive airway pressure (EPAP) on these machines.  Some of the initial models were crude and called for supplemental oxygen to be connected into the system, but new systems, such as the Vision, are touch screen, have flow and pressure waveforms, and allow the machines to be used pretty much like a ventilator.  The advantage is you can ventilate a patient and improve oxygenation without having to intubate the patient.  Masks can be removed for eating and drinking and taking medicine, and also oral care.  Studies show these machines work great for COPD, CHF and even some asthma patients.  They also work well for home use for patients with obstructive sleep apnea. Modern BiPAP machines are also more effective than the aforementioned down's flow generator in delivering CPAP, and the machines also allow for alarms and patient monitoring. 

2000:  Servo i, 840, Avea Ventilators

It has all the same features as the Sero 300 except that the flaws of the 300 have been corrected.  Instead of having all the dials on the front the settings are set by an easy to use touch screen.  The basic settings of rate, tital volume, and FiO2 could be set either this way or by quick access dials on the bottom of the screen.  The ventilator was also connected to a graphics screen for easy to see ventilator graphics.  (d)  Other similar ventilators include the Puritan-Bennett 840 and the Avea Ventilator.  These newer vents are microprocessor vents that include a variety of modes to improve patient comfort.  They also include waveforms to monitor the patient, and a variety of alarms.  Modern vents are also upgradeable. 

The future:  What will the future bring?  

  1. (d)"About us:  History of Ventilation," maquet.com,  http://www.maquet.com/sectionPage.aspx?m1=112599762812&m2=112599885558&m3=112600545105&m4=112806653448&wsectionID=112806653448&languageID=4, accessed February 27, 2012

1 comment:

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