Ventilators- Modern day Gods.
"Doctor, please switch off the ventilatory support for our patient. We cannot afford the expenses anymore."
As Neurosurgeons, we are faced with this highly sensitive and touchy issue of not just the clinical aspect but the logistics of ventilatory care and management.
The current COVID infection scenario in USA and Europe has brought the spotlight on this extremely crucial role played by ventilators in treating serious patients admitted to Intensive Care Units. The present day Corona Virus infection has highlighted the role of ventilators largely because, the virus selectively targets the lungs and incapacitates their highly critical function of oxygenating the blood.
Modern day ventilators are highly sophisticated and are truly life saving. To understand the complexity of this
'Modern Day Miracle' it will help to have a brief understanding of respiratory physiology.
Our respiration is comprised of inspiration, then a small pause, followed by expiration and a slightly longer pause. This cycle continues. One of the most intriguing facet of this vital activity is that it continues even when we are not aware of it- almost subconsciously and yet is totally under our voluntary control. One can hold the breath if one chooses to and yet again, if we don't pay attention, the breathing continues automatically. The regulatory mechanisms that govern respiration are really very intricate and involve a neurological, chemical, and other pathways. On a lighter note, in our medical school days, we were asked to write in detail the mechanism of respiration in the Physiology theory examination. A bright lad believed in keeping it simple.
"Respiration is made of two parts- Inspiration and Expiration. You first inspire, then you expire. If your don't inspire, you expire." Simple indeed. And yet so complex.
One of the most potent stimulii to activate the respiratory mechanism, is elevated levels of carbon dioxide in the blood. This aspect is utilised by neurologists and neurosurgeons to assess the function of the brainstem. The brain stem- Medulla to be precise that's at the junction of the brain and the spinal cord is where the respiratory centre lies. An apnoea test, wherein the Carbon dioxide is allowed to build up by disconnecting the ventilator briefly is performed. If there are absolutely no efforts seen after this, despite the raised level of carbon dioxide, it almost certainly indicates brainstem death.
Respiration has always fascinated me right from medical school days. Our traditional Yogic philosophy considers breathing to be the 'Prana' or the vital life force. Respiratory rates are possibly linked to the activity of the mind. Certain spiritual practices advocate concentration on the act of respiration as a means of meditation.
Inspiration or breathing in is a process by which, the diaphragm ( a flattened muscular structure, that separates the abdomen and chest cavities) is pulled downward. At the same time, the intercostal muscles ( sheet of muscle attached to adjacent ribs) contract lifting up the ribs like a bucket handle moves. Both these muscular entities increase the capacity of the thoracic cavity, which reduces the pressure with respect to the atmospheric pressure. This causes the air to rush in and travel through the tracheo- bronchial tree to fill up the alveoli. These are miniscule balloons that are elastic. It is these alveoli, that effect the exchange of oxygen for the carbon dioxide from the blood flowing in the pulmonary capillaries.
The alveoli thereafter contract because of their inherent elasticity, and this pushes the carbon dioxide back to the tracheo bronchial tree to be expired out of the respiratory passages. Expiration therefore is a passive process, that depends on the elastic recoil of the alveoli. The loss of this elasticity, and dilatation of the alveoli is called as emphysema- seen in chronic smokers.
Now we come to this highly efficient equipment- The ventilator.
Ventilators can be either Volume Cycled or Pressure Cycled. The earlier ventilators were volume cycled. They could deliver prefixed volumes of oxygen rich air.
Modern day ventilators have evolved and are Pressure Cycled. This pressure cycled system can be triggered by a drop in the ventilator patient interface. When the patient attempts to breathe, the pressure drops and this serves as a trigger. Then depending on the deficient capacity of the patient, the ventilator supplements the patient's drive. These ventilators have multiple modes. To quote a few,
CMV- Continuous mandatory ventilation. This mode is used when the patient has absolutely no respiratory drive. The machine executes the entire task of respiration. The amount of air per breath, the concentration of oxygen, no of breaths, all are fed into the CPU and the machine goes on and on.
The problem arises when the patient has his own respiratory drive, as happens in these viral pneumonias. This is where the modern ventilator proves it's efficacy.
There are sensors, that can sense the attempt made by the patient as mentioned above. . It can determine the extent and depth of the attempt made by the patient, calculate the amount that he is falling short, and deliver the exact amount that the patient is falling short. This is delivered in perfect synchrony with the patients respiratory efforts. One can imagine the chaos, that will arise if this assistance is not synchronized.
There is also a facility that maintains a continuous positive airway pressure. This prevents total collapse of the alveoli at the end of expiration, and decreases the respiratory effort to inflate these partially collapsed alveoli in the next inspiration.
Technology has truly evolved medical devices. There are other modes such as weaning modes, assist control modes, supervised intermittent mandatory ventilation modes, that are required for specific medical conditions. These machines are truly very reliable and life saving. Typically, the modern ventilators with all the modes cost anywhere between 4000 to 9000 US Dollars. The use of pressure cycled ventilators has another big advantage of minimising the possibility of baro trauma.( rupture of alveoli due to positive pressure ventilation).
Technology will continue to develop better, lighter, ventilators in the future and they will certainly serve as life savers in the coming years to deal with a myriad of medical disorders.
Dr. Deepak Ranade
Consultant Neurosurgeon
Professor of Neurosurgery
Pune.
"Doctor, please switch off the ventilatory support for our patient. We cannot afford the expenses anymore."
As Neurosurgeons, we are faced with this highly sensitive and touchy issue of not just the clinical aspect but the logistics of ventilatory care and management.
The current COVID infection scenario in USA and Europe has brought the spotlight on this extremely crucial role played by ventilators in treating serious patients admitted to Intensive Care Units. The present day Corona Virus infection has highlighted the role of ventilators largely because, the virus selectively targets the lungs and incapacitates their highly critical function of oxygenating the blood.
Modern day ventilators are highly sophisticated and are truly life saving. To understand the complexity of this
'Modern Day Miracle' it will help to have a brief understanding of respiratory physiology.
Our respiration is comprised of inspiration, then a small pause, followed by expiration and a slightly longer pause. This cycle continues. One of the most intriguing facet of this vital activity is that it continues even when we are not aware of it- almost subconsciously and yet is totally under our voluntary control. One can hold the breath if one chooses to and yet again, if we don't pay attention, the breathing continues automatically. The regulatory mechanisms that govern respiration are really very intricate and involve a neurological, chemical, and other pathways. On a lighter note, in our medical school days, we were asked to write in detail the mechanism of respiration in the Physiology theory examination. A bright lad believed in keeping it simple.
"Respiration is made of two parts- Inspiration and Expiration. You first inspire, then you expire. If your don't inspire, you expire." Simple indeed. And yet so complex.
One of the most potent stimulii to activate the respiratory mechanism, is elevated levels of carbon dioxide in the blood. This aspect is utilised by neurologists and neurosurgeons to assess the function of the brainstem. The brain stem- Medulla to be precise that's at the junction of the brain and the spinal cord is where the respiratory centre lies. An apnoea test, wherein the Carbon dioxide is allowed to build up by disconnecting the ventilator briefly is performed. If there are absolutely no efforts seen after this, despite the raised level of carbon dioxide, it almost certainly indicates brainstem death.
Respiration has always fascinated me right from medical school days. Our traditional Yogic philosophy considers breathing to be the 'Prana' or the vital life force. Respiratory rates are possibly linked to the activity of the mind. Certain spiritual practices advocate concentration on the act of respiration as a means of meditation.
Inspiration or breathing in is a process by which, the diaphragm ( a flattened muscular structure, that separates the abdomen and chest cavities) is pulled downward. At the same time, the intercostal muscles ( sheet of muscle attached to adjacent ribs) contract lifting up the ribs like a bucket handle moves. Both these muscular entities increase the capacity of the thoracic cavity, which reduces the pressure with respect to the atmospheric pressure. This causes the air to rush in and travel through the tracheo- bronchial tree to fill up the alveoli. These are miniscule balloons that are elastic. It is these alveoli, that effect the exchange of oxygen for the carbon dioxide from the blood flowing in the pulmonary capillaries.
The alveoli thereafter contract because of their inherent elasticity, and this pushes the carbon dioxide back to the tracheo bronchial tree to be expired out of the respiratory passages. Expiration therefore is a passive process, that depends on the elastic recoil of the alveoli. The loss of this elasticity, and dilatation of the alveoli is called as emphysema- seen in chronic smokers.
Now we come to this highly efficient equipment- The ventilator.
Ventilators can be either Volume Cycled or Pressure Cycled. The earlier ventilators were volume cycled. They could deliver prefixed volumes of oxygen rich air.
Modern day ventilators have evolved and are Pressure Cycled. This pressure cycled system can be triggered by a drop in the ventilator patient interface. When the patient attempts to breathe, the pressure drops and this serves as a trigger. Then depending on the deficient capacity of the patient, the ventilator supplements the patient's drive. These ventilators have multiple modes. To quote a few,
CMV- Continuous mandatory ventilation. This mode is used when the patient has absolutely no respiratory drive. The machine executes the entire task of respiration. The amount of air per breath, the concentration of oxygen, no of breaths, all are fed into the CPU and the machine goes on and on.
The problem arises when the patient has his own respiratory drive, as happens in these viral pneumonias. This is where the modern ventilator proves it's efficacy.
There are sensors, that can sense the attempt made by the patient as mentioned above. . It can determine the extent and depth of the attempt made by the patient, calculate the amount that he is falling short, and deliver the exact amount that the patient is falling short. This is delivered in perfect synchrony with the patients respiratory efforts. One can imagine the chaos, that will arise if this assistance is not synchronized.
There is also a facility that maintains a continuous positive airway pressure. This prevents total collapse of the alveoli at the end of expiration, and decreases the respiratory effort to inflate these partially collapsed alveoli in the next inspiration.
Technology has truly evolved medical devices. There are other modes such as weaning modes, assist control modes, supervised intermittent mandatory ventilation modes, that are required for specific medical conditions. These machines are truly very reliable and life saving. Typically, the modern ventilators with all the modes cost anywhere between 4000 to 9000 US Dollars. The use of pressure cycled ventilators has another big advantage of minimising the possibility of baro trauma.( rupture of alveoli due to positive pressure ventilation).
Technology will continue to develop better, lighter, ventilators in the future and they will certainly serve as life savers in the coming years to deal with a myriad of medical disorders.
Dr. Deepak Ranade
Consultant Neurosurgeon
Professor of Neurosurgery
Pune.
No comments:
Post a Comment