History & Evolution of Intensive (Critical) Care Units


              The English nurse Florence Nightingale pioneered efforts to use a separate hospital area for critically injured patients. During the Crimean War in the 1850s, she introduced the practice of moving the sickest patients to the beds directly opposite the nursing station on each ward so that they could be monitored more closely.  In 1923, the American neurosurgeon Walter Dandy created a three-bed unit at the Johns Hopkins Hospital. In these units, specially trained nurses cared for critically ill postoperative neurosurgical patients.

           The Danish anaesthesiologist Bjørn Aage Ibsen became involved in the 1952 poliomyelitis epidemic in Copenhagen, where 2722 patients developed the illness in a six-month period, with 316 of those developing some form of respiratory or airway paralysis. Some of these patients had been treated using the few available negative pressure ventilators, but these devices (while helpful) were limited in number and did not protect the patient’s lungs from aspiration of secretions. Ibsen changed the management directly by instituting long-term positive pressure ventilation using tracheal intubation, and he enlisted 200 medical students to manually pump oxygen and air into the patients’ lungs round the clock. At this time, Carl-Gunnar Engström had developed one of the first artificial positive-pressure volume-controlled ventilators, which eventually replaced the medical students. With the change in care, mortality during the epidemic declined from 90% to around 25%. Patients were managed in three special 35-bed areas, which aided charting medications and other management.

        In 1953, Ibsen set up what became the world’s first intensive care unit in a converted student nurse classroom in Copenhagen Municipal Hospital. He provided one of the first accounts of the management of tetanus using neuromuscular-blocking drugs and controlled ventilation.

         The following year, Ibsen was elected head of the department of anaesthesiology at that institution. He jointly authored the first known account of intensive care management principles in the journal Nordisk Medicin, with Tone Dahl Kvittingen from Norway.

      For a time in the early 1960s, it was not clear that specialized intensive care units were needed, so intensive care resources were brought to the room of the patient that needed the additional monitoring, care, and resources. It became rapidly evident, however, that a fixed location where intensive care resources and dedicated personnel were available provided better care than ad hoc provision of intensive care services spread throughout a hospital. In 1962, in the University of Pittsburgh, the first critical care residency was established in the United States. In 1970, the Society of Critical Care Medicine was formed.

How an epidemic led to development of Intensive Care Unit

How an epidemic led to development of Intensive Care Unit

The number of hospital admissions was more than the staff had ever seen. And people kept coming. Dozens each day. They were dying of respiratory failure. Doctors and nurses stood by, unable to help without sufficient equipment.

It was the polio epidemic of August 1952, at Blegdam Hospital in Copenhagen. This little-known event marked the start of intensive-care medicine and the use of mechanical ventilation outside the operating theatre — the very care that is at the heart of abating the COVID-19 crisis.

In 1952, the iron lung was the main way to treat the paralysis that stopped some people with poliovirus from breathing. Copenhagen was an epicentre of one of the worst polio epidemics that the world had ever seen. The hospital admitted 50 infected people daily, and each day, 6–12 of them developed respiratory failure. The whole city had just one iron lung. In the first few weeks of the epidemic, 87% of those with bulbar or bulbospinal polio, in which the virus attacks the brainstem or nerves that control breathing, died. Around half were children.

Desperate for a solution, the chief physician of Blegdam called a meeting. Asked to attend: Bjørn Ibsen, an anaesthesiologist recently returned from training at the Massachusetts General Hospital in Boston. Ibsen had a radical idea. It changed the course of modern medicine.

Student saviours                                    

The iron lung used negative pressure. It created a vacuum around the body, forcing the ribs, and therefore the lungs, to expand; air would then rush into the trachea and lungs to fill the void. The concept of negative-pressure ventilation had been around for hundreds of years, but the device that became widely used — the ‘Drinker respirator’ — was invented in 1928 by Philip Drinker and Louis Agassiz Shaw, professors at the School of Public Health in Boston, Massachusetts. Others went on to refine it, but the basic mechanism remained the same until 1952.

Iron lungs only partially solved the paralysis problem. Many people with polio placed in one still died. Among the most frequent complications was aspiration — saliva or stomach contents would be sucked from the back of the throat into the lungs when a person was too weak to swallow. There was no protection of the airway.

Ibsen suggested the opposite approach. His idea was to blow air directly into the lungs to make them expand, and then allow the body to passively relax and exhale. He proposed the use of a trachaeostomy: an incision in the neck, through which a tube goes into the windpipe and delivers oxygen to the lungs, and the application of positive-pressure ventilation. At the time, this was often done briefly during surgery, but had rarely been used in a hospital ward.

Ibsen was given permission to try the technique the next day. We even know the name of his first patient: Vivi Ebert, a 12-year-old girl on the brink of death from paralytic polio. Ibsen demonstrated that it worked. The trachaeostomy protected her lungs from aspiration, and by squeezing a bag attached to the tube, Ibsen kept her alive. Ebert went on to survive until 1971, when she ultimately died of infection in the same hospital, almost 20 years later.

The plan was hatched to use this technique on all the patients in Blegdam who needed help to breathe. The only problem? There were no ventilators.

Very early versions of positive-pressure ventilators had been around from about 1900, used for surgery and by rescuers during mining accidents. Further technical developments during the Second World War helped pilots to breathe in the decreased pressures at high altitudes. But modern ventilators, to support a person for hours or days, had yet to be invented.

What followed was one of the most remarkable episodes in health-care history: in six-hour shifts, medical and dental students from the University of Copenhagen sat at the bedside of every person with paralysis and ventilated them by hand. The students squeezed a bag connected to the trachaeostomy tube, forcing air into the lungs. They were instructed in how many breaths to administer each minute, and sat there hour after hour. This went on for weeks, and then months, with hundreds of students rotating on and off. By mid-September, the mortality for patients with polio who had respiratory failure had dropped to 31%. It is estimated that the heroic scheme saved 120 people.

Major insights emerged from the Copenhagen polio epidemic. One was a better understanding of why people died of polio. Until then, it was thought that kidney failure was the cause. Ibsen recognized that inadequate ventilation caused carbon dioxide to build up in the blood, making it very acidic — which caused organs to shut down.

Three further lessons are central today. First, Blegdam demonstrated what can be achieved by a medical community coming together, with remarkable focus and stamina. Second, it proved that keeping people alive for weeks, and months, with positive-pressure ventilation was feasible. And third, it showed that by bringing together all the patients struggling to breathe, it was easier to care for them in one place where the doctors and nurses had expertise in respiratory failure and mechanical ventilation.

So, the concept of an intensive-care unit (ICU) was born. After the first one was set up in Copenhagen the following year, ICUs proliferated. And the use of positive pressure, with ventilators instead of students, became the norm.

In the early years, many of the safety features of modern ventilators did not exist. Doctors who worked in the 1950s and 1960s describe caring for patients without any alarms; if the ventilator accidentally disconnected and the nurse’s back was turned, the person would die. Early ventilators forced people to breathe at a set rate, but modern ones sense when a patient wants to breathe, and then help provide a push of air into the lungs in time with the body. The original apparatus also gathered limited information on how stiff or compliant the lungs were, and gave everyone a set amount of air with each breath; modern machines take many measurements of the lungs, and allow for choices regarding how much air to give with each breath. All of these are refinements of the original ventilators, which were essentially automatic bellows and tubing.

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what is Mechanical ventilator? A machine critical to save life


A medical ventilator (or simply ventilator in context) is a machine designed to provide mechanical ventilation by moving breathable air into and out of the lungs, to deliver breaths to a patient who is physically unable to breathe, or breathing insufficiently.

While modern ventilators are computerized machines, patients can be ventilated with a simple, hand-operated bag valve mask.

Ventilators are chiefly used in intensive care medicine, home care, and emergency medicine (as standalone units) and in anesthesiology  (as a component of an  anesthesia machine .

Medical ventilators are sometimes colloquially called “respirators”, a term stemming from commonly used devices in the 1950s (particularly the “Bird Respirator”). However, in modern hospital and medical terminology, these machines are never referred to as respirators, and use of “respirator” in this context is now a deprecated anachronism signaling technical unfamiliarity.

Function                                  

In its simplest form, a modern positive pressure ventilator consists of a compressible air  reservoir or turbine, air and oxygen supplies, a set of valves and tubes, and a disposable or reusable “patient circuit”. The air reservoir is pneumatically compressed several times a minute to deliver room-air, or in most cases, an air/oxygen mixture to the patient. If a turbine is used, the turbine pushes air through the ventilator, with a flow valve adjusting pressure to meet patient-specific parameters. When over pressure is released, the patient will exhale passively due to the lungs’ elasticity, the exhaled air being released usually through a one-way valve within the patient circuit called the patient manifold.

Ventilators may also be equipped with monitoring and alarm systems for patient-related parameters (e.g. pressure, volume, and flow) and ventilator function (e.g. air leakage, power failure, mechanical failure), backup batteries, oxygen tanks, and remote control. The pneumatic system is nowadays often replaced by a computer-controlled  turbo-pump.

Modern ventilators are electronically controlled by a small embedded system to allow exact adaptation of pressure and flow characteristics to an individual patient’s needs. Fine-tuned ventilator settings also serve to make ventilation more tolerable and comfortable for the patient. In Canada and the United States and in many parts of world, respiratory therapists are responsible for tuning these settings, while biomedical technologists are responsible for the maintenance.

The patient circuit usually consists of a set of three durable, yet lightweight plastic tubes, separated by function (e.g. inhaled air, patient pressure, exhaled air). Determined by the type of ventilation needed, the patient-end of the circuit may be either noninvasive or invasive.

Noninvasive methods, which are adequate for patients who require a ventilator only while sleeping and resting, mainly employ a nasal mask. Invasive methods require     intubation.  For long-term ventilator dependence will normally be a tracheostomy  cannula, as this is much more comfortable and practical for long-term care than is larynx or nasal intubation.

Life-critical system

Because failure may result in death, mechanical ventilation systems are classified as a life critical-system and precautions must be taken to ensure that they are highly reliable, including their  power supply .

Mechanical ventilators are therefore carefully designed so that no single point of failure can endanger the patient. They may have manual backup mechanisms to enable hand-driven respiration in the absence of power (such as the mechanical ventilator integrated into an  anesthetic machine . They may also have safety valves, which open to atmosphere in the absence of power to act as an anti-suffocation valve for spontaneous breathing of the patient. Some systems are also equipped with compressed-gas tanks, air compressors, and/or backup batteries to provide ventilation in case of power failure or defective gas supplies, and methods to operate or call for help if their mechanisms or software fail.

history of ventilator

source 

History of mechanical ventilator 


                

The history of mechanical ventilation begins with various versions of what was eventually called the iron lung, a form of noninvasive negative pressure ventilator widely used during the polio epidemics of the 20th century after the introduction of the “Drinker respirator” in 1928, improvements introduced by John Haven Emerson in 1931,  and the Both respirator in 1937. Other forms of noninvasive ventilators, also used widely for polio patients, include Biphasic Cuirass Ventilation, the rocking bed, and rather primitive positive pressure machines.

In 1949, John Haven Emerson developed a mechanical assister for anesthesia with the cooperation of the anesthesia department at Harvard University. Mechanical ventilators began to be used increasingly in anesthesia and intensive care during the 1950s. Their development was stimulated both by the need to treat polio patients and the increasing use of muscle relaxants during anesthesia. Relaxant drugs paralyze the patient and improve operating conditions for the surgeon but also paralyze the respiratory muscles.

In the United Kingdom, the East Radcliffe and Beaver models were early examples, the latter using an automotive wiper motor to drive the bellows used to inflate the lungs. Electric motors were, however, a problem in the operating theaters of that time, as their use caused an explosion hazard in the presence of flammable anesthetics such as ether and  cyclopropane .

In 1952, Roger Manley of the Westminster Hospital, London, developed a ventilator which was entirely gas driven, and became the most popular model used in Europe. It was an elegant design, and became a great favorite with European anesthetists for four decades, prior to the introduction of models controlled by electronics. It was independent of electrical power, and caused no explosion hazard. The original Mark I unit was developed to become the Manley Mark II in collaboration with the Blease company, who manufactured many thousands of these units. Its principle of operation was very simple, an incoming gas flow was used to lift a weighted bellows unit, which fell intermittently under gravity, forcing breathing gases into the patient’s lungs. The inflation pressure could be varied by sliding the movable weight on top of the bellows. The volume of gas delivered was adjustable using a curved slider, which restricted bellows excursion. Residual pressure after the completion of expiration was also configurable, using a small weighted arm visible to the lower right of the front panel. This was a robust unit and its availability encouraged the introduction of positive pressure ventilation techniques into mainstream European anesthetic practice.

The 1955 release of Forrest Bird’s “Bird Universal Medical Respirator” in the United States changed the way mechanical ventilation was performed, with the small green box becoming a familiar piece of medical equipment.  The unit was sold as the Bird Mark 7 Respirator and informally called the “Bird”. It was a pneumatic device and therefore required no electrical power source to operate.

Intensive care environments around the world revolutionized in 1971 by the introduction of the first  Servo 900 ventilator Elema – Schonander . It was a small, silent and effective electronic ventilator, with the famous SERVO feedback system controlling what had been set and regulating delivery. For the first time, the machine could deliver the set volume in volume control ventilation.

Ventilators used under increased pressure (hyperbaric) require special precautions and few ventilators can operate under these conditions. In 1979, Sechrist Industries introduced their Model 500A ventilator which was specifically designed for use with hyperbaric chambers.

In 1991 the SERVO 300 ventilator series was introduced. The platform of the SERVO 300 series enabled treatment of all patient categories, from adult to neonate, with one single ventilator. The SERVO 300 series provided a completely new and unique gas delivery system, with rapid flow-triggering response.

In 1999 the LTV (Laptop Ventilator) Series was introduced into the market. The new ventilator was significantly smaller than the ventilators of that time weighing ~14 lbs and around the size of a laptop computer. This new design kept the same functionality of the in hospital ventilators, while now opening up a world of opportunity of mobility for the patients.

A modular concept, meaning that the hospital has one ventilator model throughout the ICU department instead of a fleet with different models and brands for the different user needs, was introduced with SERVO-i in 2001. With this modular concept the ICU departments could choose the modes and options, software and hardware needed for a particular patient category.

mechanical ventilator

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