Permissive hypercapnia
Encyclopedia
Permissive hypercapnia is hypercapnia
, (i.e. high concentration of carbon dioxide
in blood), in respiratory insufficient patients in which oxygenation
has become so difficult that the optimal mode of mechanical ventilation
(with oxygenation in mind) is not capable of exchanging enough carbon dioxide. Carbon dioxide is a gas
eous product of the body's
metabolism
and is normally expelled through the lung
s.
In acute respiratory distress syndrome
(ARDS), decreasing the tidal volume on the ventilator (usually 8-12 mL/kg) to 4-6 mL/kg may decrease barotrauma by decreasing ventilatory peak airway pressures and leads to improved respiratory recovery. Hypercapnia (increased pCO2) sometimes needs to be tolerated in order to achieve these lower tidal volumes. The permissive hypercapnia leads to respiratory acidosis which might have negative side effects, but given that the patient is in ARDS, improving ventilatory function is more important.
Since hypoxemia
is a major life-threatening condition and hypercapnia is not, one might choose to accept the latter. Hence the term, "permissive hypercapnia."
Altogether, the negative side effects of permissive hypercapnia may outweigh the benefits. For that reason, the implementation of extracorporeal CO2 removal (iLA Membrane Ventilator, Novalung) at an early stage of ARDS, has become a well established standard to allow for protective ventilation and avoid respiratory acidosis.
, extrasystoles, muscle twitches, hand flaps, and possibly a raised blood pressure
. In severe hypercapnia (generally PaCO2 greater than 10 kPa
or 75 mmHg), symptomatology progresses to disorientation, panic
, hyperventilation
, convulsions, unconsciousness
, and eventually death
.
Other description about permissive hypercapnia in ARDS patient
Mechanical ventilation using high tidal volume (VT) and transpulmonary pressure can damage the lung, causing ventilator-induced lung injury. Permissive hypercapnia, a ventilatory strategy for acute respiratory failure in which the lungs are ventilated with a low inspiratory volume and pressure, has been accepted progressively in critical care for adult, pediatric, and neonatal patients requiring mechanical ventilation and is one of the central components of current protective ventilatory strategies.
Hypercapnia
Hypercapnia or hypercapnea , also known as hypercarbia, is a condition where there is too much carbon dioxide in the blood...
, (i.e. high concentration of carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
in blood), in respiratory insufficient patients in which oxygenation
Oxygenation (medical)
Oxygenation occurs when oxygen molecules enter the tissues of the body. For example, blood is oxygenated in the lungs, where oxygen molecules travel from the air and into the blood...
has become so difficult that the optimal mode of mechanical ventilation
Mechanical ventilation
In medicine, mechanical ventilation is a method to mechanically assist or replace spontaneous breathing. This may involve a machine called a ventilator or the breathing may be assisted by a physician, respiratory therapist or other suitable person compressing a bag or set of bellows...
(with oxygenation in mind) is not capable of exchanging enough carbon dioxide. Carbon dioxide is a gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
eous product of the body's
Human body
The human body is the entire structure of a human organism, and consists of a head, neck, torso, two arms and two legs.By the time the human reaches adulthood, the body consists of close to 100 trillion cells, the basic unit of life...
metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
and is normally expelled through the lung
Lung
The lung is the essential respiration organ in many air-breathing animals, including most tetrapods, a few fish and a few snails. In mammals and the more complex life forms, the two lungs are located near the backbone on either side of the heart...
s.
In acute respiratory distress syndrome
Acute respiratory distress syndrome
Acute respiratory distress syndrome , also known as respiratory distress syndrome or adult respiratory distress syndrome is a serious reaction to various forms of injuries to the lung....
(ARDS), decreasing the tidal volume on the ventilator (usually 8-12 mL/kg) to 4-6 mL/kg may decrease barotrauma by decreasing ventilatory peak airway pressures and leads to improved respiratory recovery. Hypercapnia (increased pCO2) sometimes needs to be tolerated in order to achieve these lower tidal volumes. The permissive hypercapnia leads to respiratory acidosis which might have negative side effects, but given that the patient is in ARDS, improving ventilatory function is more important.
Since hypoxemia
Hypoxemia
Hypoxemia is generally defined as decreased partial pressure of oxygen in blood, sometimes specifically as less than or causing hemoglobin oxygen saturation of less than 90%.-Distinction from anemia and hypoxia:...
is a major life-threatening condition and hypercapnia is not, one might choose to accept the latter. Hence the term, "permissive hypercapnia."
Altogether, the negative side effects of permissive hypercapnia may outweigh the benefits. For that reason, the implementation of extracorporeal CO2 removal (iLA Membrane Ventilator, Novalung) at an early stage of ARDS, has become a well established standard to allow for protective ventilation and avoid respiratory acidosis.
Symptoms
Symptoms of early hypercapnia (i.e. where PaCO2 is elevated but not extremely so) include flushed skin, full pulsePulse
In medicine, one's pulse represents the tactile arterial palpation of the heartbeat by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed against a bone, such as at the neck , at the wrist , behind the knee , on the inside of the elbow , and near the...
, extrasystoles, muscle twitches, hand flaps, and possibly a raised blood pressure
Blood pressure
Blood pressure is the pressure exerted by circulating blood upon the walls of blood vessels, and is one of the principal vital signs. When used without further specification, "blood pressure" usually refers to the arterial pressure of the systemic circulation. During each heartbeat, BP varies...
. In severe hypercapnia (generally PaCO2 greater than 10 kPa
Pascal (unit)
The pascal is the SI derived unit of pressure, internal pressure, stress, Young's modulus and tensile strength, named after the French mathematician, physicist, inventor, writer, and philosopher Blaise Pascal. It is a measure of force per unit area, defined as one newton per square metre...
or 75 mmHg), symptomatology progresses to disorientation, panic
Panic
Panic is a sudden sensation of fear which is so strong as to dominate or prevent reason and logical thinking, replacing it with overwhelming feelings of anxiety and frantic agitation consistent with an animalistic fight-or-flight reaction...
, hyperventilation
Hyperventilation
Hyperventilation or overbreathing is the state of breathing faster or deeper than normal, causing excessive expulsion of circulating carbon dioxide. It can result from a psychological state such as a panic attack, from a physiological condition such as metabolic acidosis, can be brought about by...
, convulsions, unconsciousness
Unconsciousness
Unconsciousness is the condition of being not conscious—in a mental state that involves complete or near-complete lack of responsiveness to people and other environmental stimuli. Being in a comatose state or coma is a type of unconsciousness. Fainting due to a drop in blood pressure and a...
, and eventually death
Death
Death is the permanent termination of the biological functions that sustain a living organism. Phenomena which commonly bring about death include old age, predation, malnutrition, disease, and accidents or trauma resulting in terminal injury....
.
Other description about permissive hypercapnia in ARDS patient
Mechanical ventilation using high tidal volume (VT) and transpulmonary pressure can damage the lung, causing ventilator-induced lung injury. Permissive hypercapnia, a ventilatory strategy for acute respiratory failure in which the lungs are ventilated with a low inspiratory volume and pressure, has been accepted progressively in critical care for adult, pediatric, and neonatal patients requiring mechanical ventilation and is one of the central components of current protective ventilatory strategies.