 Hypothermia as the term indicates is a decrease in core body temperature. So when the core body temperature becomes less than 35 degree Celsius then this term hypothermia is used. And here we are talking about accidental hypothermia because for certain surgeries the induction of hypothermia is also done. So here we will talk about accidental hypothermia. If we consider the causes then the cause can be primary cause where the person is actually exposed to cold environment, too cold environment and exposure of a healthy person to cold environment where his body is not able to produce as much heat as is required or there is excessive heat loss. So that is primary cause of accidental hypothermia or there can be secondary causes which are very common actually because what happens in primary cause exposure of individual to cold environment, healthy individual to cold environment he can know about that and he can take precautionary measures to cause decrease in heat loss and the preventive measures will help the person. So in secondary causes when we say then there are certain predisposed individuals in which hypothermia can occur and the presence of basically systemic diseases predisposes individual to this secondary hypothermia then basically if you try to categorize them then maybe that the person is more susceptible to hypothermia. So more susceptible who will be the people first of all there will be elderly people and especially immobile people because when immobility is there then obviously the metabolic activity is less and if you are suffering from systemic illness then it becomes more predisposing then there can be new needs because in new needs what happens that there is increase in surface area to mass ratio and increased surface area means that there are more predisposed to heat loss because more of their surface area will come in contact with the environment plus in new needs there is lack of effective shivering as well you know that new needs have actually brown eddy post issue which is protective but the shivering mechanism is not that developed. Then the causes which lead to hypoglycemia you see shivering requires adequate presence of neutrons that neutrons will be metabolized during shivering so if there are causes which predispose to hypoglycemia then the person becomes more susceptible and what can be these causes first of all obviously malnutrition because in malnutrition there is a decrease in glycogen reserve so they cannot shiver for very long time so that is malnutrition also in malnutrition there is decreased subcutaneous tissue so when this is there then there is high chances of energy being transferred from the core to the surface so subcutaneous tissue actually is preventing heat loss from the body so in malnutrition decreased subcutaneous tissue is a factor then there can be some endocrine abnormalities which can lead to hypoglycemia as example is adrenal insufficiency hypopiturism so these can also predispose the individual to accidental hypothermia then hepatic failure hepatic failure also what happens that there is decrease in glycogen reserve so that is also one predisposing cause so these are certain conditions which lead to hypoglycemia and hence predispose the individual to hypothermia obviously if the person is exposed to cold environment and especially remember just want to add if cold environment and there is presence of water right suppose if the person falls in water then it is very high chances that they can be accidental hypothermia because there is too much heat loss when the environment is water also the water keeps moving so the conviction also is added so say suppose a cold rainy day and plus cold winds are also blowing so that is going to also add to the wind chill effect for all these terms of wind chill effect and how the body is generating heat or losing heat there is another video on physiology of temperature regulation that you can see but here we will restrict our set to accidental hypothermia coming to other causes say psychiatric disorders in certain psychiatric disorders the person is predisposed to hypothermia because the patient doesn't want to actually defend himself from excessive cold then occupational hazard occupational hazard in this basically it is a primary cause that the person for long duration is exposed to cold environment so these were certain causes of accidental hypothermia with this let us go into the pathophysiology of hypothermia and what are the stages of hypothermia first fundamental you should remember that when we are talking about hypothermia that is decrease in cold body temperature what will happen that decrease in temperature is going to decrease the metabolic rate understanding so here we are talking about the effects of hypothermia one thing is that decrease metabolic rate as in case of hypothyroidism can itself lead to hypothermia the person is becoming susceptible but once hypothermia develops because of decrease in temperature there will be decrease in metabolic rate because all the enzymatic reactions in our body depend on the temperature so this decrease in metabolic rate is further going to decrease the heat production so now what happens actually it's kind of positive feedback which is developing because further decrease in heat production it is further making the person more hypothermic because in actual physiological response to decrease in temperature should be increasing the metabolic rate like increase in the shivering so when everything is working normally then what will happen increase thyroid hormones will be released increase sympathetic activity will be there so that will need to increase in heat production but once this state starts of decrease in body temperature then this process can go into a positive feedback and thus there are various stages of hypothermia from mild moderate to severe so what are these various stages of hypothermia and what is their path of physiology and what are the bodily responses in these various changes so when one fundamental you remember when we are talking about different stages in mild stage the symptoms and signs which you will see are basically related to the body's responses to hypothermia that is the body is trying to correct the hypothermia in mild stage that you will see while in moderate and severe you will see what is happening there is progressive decrease in the body temperature and hence there is depression of the various body systems and hence you see deteriorating science in moderate and severe hypothermia so we will talk about each system one by one let's talk about central nervous system what will be the science when we talk about central nervous system what we see is that there is decrease in the cns metabolism obviously because temperature is decreasing so there is a decrease in cns metabolism and hence leading to cns depression and there is a particular order in which we see the various signs and symptoms the order is in terms of you see first there is decrease in the motor function okay then there is progressive decline in higher order function and then there is further there is decrease in the reflexes so that is how the progression of symptoms we see in different stages of hypothermia so in milder stages what will be the symptoms there will be ataxia okay motor symptoms will start there will be ataxia there will be slurred speech we will see in mild hypothermia plus there will be some minor cognitive impairment also so there will be impaired judgment this is actually higher functions but we start seeing the sign so motor signs appear first and then there is this slight decrease in cognitive impairment also see that is impaired judgment and why we are seeing this because you see that decrease in temperature what it causes it causes decrease in the motion of the molecule so everything in body starts working slowly so there is a decrease in the opening of the ion channel as the speed which to open up is decreased and hence there is decrease in the conduction velocity so this decrease in conduction velocity what will happen there will be decrease in action potential generation or conduction of the action potential impulse also will be impaired and once that conduction velocity is less what we will see slower movement because the impulses are coming from top to the muscles so they are traveling very slow so there will be slower movement however shivering will be intact okay shivering is intact slowly slowly fatigue will settle but shivering remember in mild hypothermia is intact coming to moderate stage what we will see in moderate stage now we start seeing progressive loss of consciousness okay so progressive decrease in consciousness is occurring plus other higher order disturbances will occur so we have talked about impaired judgment which is occurring in mild hypothermia here the person will develop apathy apathy is basically he doesn't want to respond to the environment so that is apathy and there is something known as what is seen is paradoxical undressing so instead of clothing himself the person undresses so hence making him more prone to hypothermia so that is known as paradoxical undressing and what I said what will be the third thing there will be decrease in reflexes so that will start coming in moderate stage however it will not be total loss of the reflexes but less response of the reflexes which will we will see so there will be pupil dilation and sluggish responses will occur sluggish responses okay finally what we see here is this loss of shivering because this the motor symptoms have started here though shivering was intact in moderate hypothermia loss of shivering will occur right so the person will not be able to generate heat as well so you see how it is going into a positive feedback and finally in severe hypothermia what we see there is further decrease in metabolism and when there is further decrease in metabolism there will be decrease in carbon dioxide production and carbon dioxide is very important factor which is responsible for cerebral blood flow regression so once carbon dioxide production decreases there is decrease in cerebral blood flow and this decrease in cerebral blood flow further will decrease in the oxygen supply to the neurons so what is going to happen loss of the reflexes so what we see is loss of conial reflexes right so we don't see any responses then loss of any ocular reflexes we will not see pupillary reflexes so that will also disappear and other motor reflexes also will be gone so there will be generalized air reflex here will be present plus what will be the state of consciousness you see here in moderate there was progressive decrease in consciousness so there will be development of coma in case of severe stage so that was signs and symptoms in central nervous system coming to cardiovascular system in cardiovascular system in mildest hypothermia what we see is the responses which are going to preserve the heat so because of increase in sympathetic activity there is vasoconstriction which is actually the normal response which we see for conservation of the heat so there is vasoconstriction now once this vasoconstriction happens there will be movement of the blood for the core right that means on the superficial surfaces there will be less blood and obviously this will cause less heat loss plus due to some increase in sympathetic activity there will be increase in heart rate and vasoconstriction there will be increase in peripheral resistance there will be increase in blood pressure increase heart rate leads to increase in cardiac output again causing increase in the blood pressure so what we see is tachycardia and increase in the blood pressure so these are the normal responses but then there will be movement to depression stage that means all these functions will start decreasing so what we see in moderate hypothermia that because of decrease in the generation of the nerve impulse from SA node and conduction also is affected so these all decrease okay conduction of nerve impulse decrease decrease in generation of SA node impulse why same reason decreased opening of the ion channels will decrease this conduction velocity as well as generation of the impulse so there will be development of bradycardia so the pulse rate is going to fall when we talk about moderate stage of hypothermia and with this the functioning of the heart is also going to decrease so there will be decrease in the cardiac output decrease in the cardiac output what it will lead to decrease in the blood pressure so you see how their progression is occurring here we are seeing how the body responses are trying to conserve the heat so that kind of cardiovascular responses we are seeing but in moderate stage because of the depression of the working of the organ system we are seeing bradycardia and decrease in the blood pressure plus because of decrease in the conduction through the muscle itself the person gets pre discourse to the development of the arrhythmia okay so how decrease in conduction through the cardiac muscle can lead to arrhythmia that you can see in my video on mechanisms of arrhythmia but whenever there is slow conduction time through the cardiac muscle then it can lead to arrhythmia and here in this case actually the all the muscle fibers it is not that conduction time decreases through all the muscle fibers it is kind of a patchy state somewhere it is less conduction time somewhere it is more conduction time and that is the case where the predisposition to arrhythmia happens that is the reentry arrhythmia further what we will see in severe hypothermia now actually the catecholamine response becomes too much blunted the sympathetic system gets depressed the catecholamine response is the blunted there is decrease in the release of the catecholamine so further there is decrease in the cardiac output further there is decrease in the heart rate and ultimately the vasodilation occurs and when vasodilation occurs you see what is happening now the person can no longer conserve that heat the blood volume which was kept to the core now has come to the surface and then there will be more and more heat loss so you see that positive feedback how it works the depression of the system and then loss of the mechanism to maintain the body temperature moreover in severe hypothermia now there will be development of the arrhythmia so there is risk of ventricular tibrelation and the person can die due to cardiac arrest so that was about serious changes coming to renal system in renal system what is going to happen we will just discuss here itself so in renal initially what we are seeing because of vasoconstriction and central movement of the blood what happens that there is something known as cold diuresis so initially we will see increase in the urination so there is cold diuresis because the central volume is increasing so venous return to the heart is increasing and what we see is release of iterative peptide and hence which causes diuresis then in moderate stage what we see is that due to decrease in the cardiac output there will be decrease in the GFR right but because local auto regulation is intact we see due to local changes in the renal circulation renal auto regulation which is there renal blood flow actually increases so as to maintain this GFR so there is increase in renal blood flow despite decrease in the cardiac output because of intact renal auto regulation but in severe stage what happens that this cardiac output decrease ultimately decreases renal blood flow too much and there is decrease in GFR so there will be oligouria and the symptoms of renal failure will start moving on to the next system that is the respiratory system what will be the features in respiratory system again there will be neuronal depression and neurons are the one which initiate the respiration remember that okay so initially in mild stage because of the body trying to generate heat by shivering and increase in the oxygen requirement because of the shivering there will be increase in the respiratory rate so there will be tachypnea however remember that due to decrease in the body temperature the functioning of the respiratory system is now going to decrease so cilia especially their function decreases the kind of parallels and there is accumulation of the mucus secretions in the bronchus and that is known as bronchoria so accumulation of this viscous secretions within the bronchus occurs because of paralysis of the cilia further what will happen as we saw in other systems that there will be respiratory depression because of the decreased functioning of the neuron so what we get is decrease in respiratory rate and then there is decrease in the ventilation also the depth of ventilation also decreases so if this causes hypoventilation thus there is further decrease in oxygen delivery to the tissues and obviously more and more these are bronchus secretions are going to accumulate then what will happen in the severe stage see there is going to be hypoxia there is the decrease in oxygen delivery to the tissues yeah their requirement is also decreased because of decreased functioning but this depression in the respiratory system is further exaggerating that and because of decrease in oxygen delivery to the tissues what will happen there will be increase in capillary permeability yes this is going to happen throughout the body this increase in capillary permeability but we are seeing what will be the effects in the respiratory system because of this increase in capillary permeability there will be development of pulmonary congestion and edema right so further whatever oxygen is there it will not be able to diffuse as well and further it will lead to hypoxia so you see how positive feedbacks are developing again and again so that was about respiratory system coming to the last part that is the endocrine system what is going to happen initially in mild stage again the body is trying to respond so there is increase in the sympathetic activity increase sympathetic activity means there will be increase in the norepinephrine and epinephrine release in the body then there is increase in thyroid hormone secretion as well this leads to increase in the metabolism then sympathetic activity is responsible for uncoupling at the level of the mitochondria so that is also going to increase right so this is trying to increase the heat production but later on again as I told you before in cardiovascular system there is decrease in the sympathetic response and decrease in norepinephrine and epinephrine release so that is going to further decrease the basal metabolism so ultimately all the systems are getting depressed so that was all about hypothermia I hope you understood how there is progression to the mild to moderate to severe stages of hypothermia and what is the pathophysiology behind it thanks for watching the video if you liked it do press the like button share the 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