Lecture 6Lecture 6

HypoxiaHypoxia

HypocapniaHypocapnia

HypercapniaHypercapnia

AsphyxiaAsphyxia

Oxygen therapyOxygen therapy

DrowningDrowning

Effects of increased barometric pressureEffects of increased barometric pressure

Nitrogen narcosisNitrogen narcosis

Decompression sicknessDecompression sickness

Air embolismAir embolism

Oxygen toxicityOxygen toxicity

Hyperbaric oxygen therapyHyperbaric oxygen therapy

AcclimatizationAcclimatization

HypoxiaHypoxia

It is the deficiency of OIt is the deficiency of O22 at the tissue levels. It is at the tissue levels. It is also termed anoxia.also termed anoxia.

It is divided into 4 categories;It is divided into 4 categories;(1) Hypoxic Hypoxia:(1) Hypoxic Hypoxia:- It is also termed anoxic anoxia & hypoxemia. - It is also termed anoxic anoxia & hypoxemia. It is defined as an adequate POIt is defined as an adequate PO22 in the arterial in the arterial blood.blood.The primary causes of HH in diseases are The primary causes of HH in diseases are hypoventilation, inadequate POhypoventilation, inadequate PO22 in the inspired in the inspired air (such as altitude) or inadequate alveolar-air (such as altitude) or inadequate alveolar-capillary transfer (such as shunt or V/Q capillary transfer (such as shunt or V/Q mismatch).mismatch).

(2) Anemic hypoxia:(2) Anemic hypoxia:- It occurs in which the PaO- It occurs in which the PaO22 is normal but the total O is normal but the total O22 content of the blood is reduced because of inadequate No. content of the blood is reduced because of inadequate No. of erythrocytes, deficient or abnormal Hb or competition for of erythrocytes, deficient or abnormal Hb or competition for the Hb molecules by CO.the Hb molecules by CO.- It occurs due to lowering the O- It occurs due to lowering the O22-carrying capacity of the -carrying capacity of the blood.blood.

(3) Ischemic hypoxia:(3) Ischemic hypoxia:- It is also termed stagnant hypoxia, circulatory hypoxia & - It is also termed stagnant hypoxia, circulatory hypoxia & hypoperfusion hyperoxia.hypoperfusion hyperoxia.It occurs in which the BF to a tissue is too low that adequate It occurs in which the BF to a tissue is too low that adequate OO22, is not delivered to it despite a normal PO, is not delivered to it despite a normal PO22 and Hb conc. and Hb conc.

(4) Histotoxic hypoxia:(4) Histotoxic hypoxia:It occurs in which the quantity of OIt occurs in which the quantity of O22 reaching the tissues is reaching the tissues is normal but the cell is unable to utilize the Onormal but the cell is unable to utilize the O22 because a because a toxic agent – cyanide, for example, has interfered with the toxic agent – cyanide, for example, has interfered with the cells metabolic. cells metabolic.

HypercapniaHypercapniaIt means excess COIt means excess CO22 in the body fluids. in the body fluids.

It usually occurs in association with hypoxia only when the It usually occurs in association with hypoxia only when the hypoxia is caused by hyperventilation or circulator hypoxia is caused by hyperventilation or circulator deficiency.deficiency.

Retention of CORetention of CO22 in the body (hypercapnia) initially in the body (hypercapnia) initially stimulates respiration.stimulates respiration.

Retention of larger amounts produces symptoms due to Retention of larger amounts produces symptoms due to depression of the CNS; confusion, diminished sensory depression of the CNS; confusion, diminished sensory acuity, and eventually coma with respiratory depression acuity, and eventually coma with respiratory depression and death.and death.

COCO22 is so much more soluble than O is so much more soluble than O22 that hypercapnia is that hypercapnia is rarely a problem in patient with pulmonary fibrosis.rarely a problem in patient with pulmonary fibrosis.

HypocapniaHypocapniaIt is the result of hyperVE.It is the result of hyperVE.

During voluntary hyperVE, the PaCODuring voluntary hyperVE, the PaCO22 falls from 40 falls from 40 mmHg as low as 15 mmHg while the PmmHg as low as 15 mmHg while the PAAOO22 rises to rises to 120-140 mmHg.120-140 mmHg.

The consequences of hypocapnia are due to the The consequences of hypocapnia are due to the associated respiratory alkalosis, the blood pH associated respiratory alkalosis, the blood pH being being ↑ to 7.5 or 7.6.↑ to 7.5 or 7.6.

Hypocapnia can cause cerebral vasoconstriction, Hypocapnia can cause cerebral vasoconstriction, cerebral hypoxia, dizziness, visual disturbances and cerebral hypoxia, dizziness, visual disturbances and anxiety.anxiety.

AsphyxiaAsphyxiaIt is an inability to breath and suffocation.It is an inability to breath and suffocation.

The symptoms of Asphyxia includes; breathing difficulty, The symptoms of Asphyxia includes; breathing difficulty, rapid pulse, high BP, convulsion, paralysis, coma and death.rapid pulse, high BP, convulsion, paralysis, coma and death.

The above symptoms of Asphyxia may vary on an individual The above symptoms of Asphyxia may vary on an individual basis for each patient. Only your doctor can provide basis for each patient. Only your doctor can provide adequate diagnosis of any signs or symptoms and whether adequate diagnosis of any signs or symptoms and whether they are indeed Asphyxia symptoms.they are indeed Asphyxia symptoms.

The possible causes of Asphyxia includes: choking, foreign The possible causes of Asphyxia includes: choking, foreign body, suffocation, toxin fumes, CO poisoning, whooping body, suffocation, toxin fumes, CO poisoning, whooping cough, drowning, diphtheria, asthma, wound infection, cough, drowning, diphtheria, asthma, wound infection, heart failure and collapsed lung.heart failure and collapsed lung. Treatment of Asphyxia includes; First aid to remove foreign Treatment of Asphyxia includes; First aid to remove foreign body, Emergency resuscitation, Expired Air Resuscitation body, Emergency resuscitation, Expired Air Resuscitation (EAR), and Cardio-Pulmonary Resuscitation (CPR) (EAR), and Cardio-Pulmonary Resuscitation (CPR)

Oxygen therapyOxygen therapyIt is used in the treatment of patient with sever lung It is used in the treatment of patient with sever lung disease who increases the conc of inspired Odisease who increases the conc of inspired O22 or control or control VVEE by means of mechanical ventilator. by means of mechanical ventilator.

It is usually very effective in relieving hypoxemia, It is usually very effective in relieving hypoxemia, except when this is caused by a shunt (BF through except when this is caused by a shunt (BF through unventilated alveoli). In this case the added Ounventilated alveoli). In this case the added O22 does not does not have access to the shunted blood.have access to the shunted blood.

OO22 is now normally administered by small cannulas is now normally administered by small cannulas inserted into the nostrils or by means of a plastic inserted into the nostrils or by means of a plastic oronasal mask.oronasal mask.

Giving too much OGiving too much O22 may lead to Pulmonary edema may lead to Pulmonary edema

DrowningDrowningIt is suffocation by submersion, usually in water.It is suffocation by submersion, usually in water.

Studies of drowned or nearly drowned people show that the Studies of drowned or nearly drowned people show that the most important blood gas changes are severe hypoxemia most important blood gas changes are severe hypoxemia combined with hypercapnia and respiratory acidosis.combined with hypercapnia and respiratory acidosis.

In 10 % of drowning, the first gasp of water after losing In 10 % of drowning, the first gasp of water after losing struggle not to breathe triggers laryngospasm, and death struggle not to breathe triggers laryngospasm, and death results from asphyxia without any water in the lungs. In the results from asphyxia without any water in the lungs. In the remaining cases, the glottic muscles eventually relax and remaining cases, the glottic muscles eventually relax and the lung are flooded.the lung are flooded.

The immediate goal in the treatment of drowning is The immediate goal in the treatment of drowning is resuscitation, but long-term treatment must take into resuscitation, but long-term treatment must take into account the circulatory effects of the water in the lungs. account the circulatory effects of the water in the lungs.

Effects of increased barometric pressureEffects of increased barometric pressureThe ambient pressure increases by 1 atmos for every 10 m The ambient pressure increases by 1 atmos for every 10 m of depth in sea water and every 10.4 m of depth in fresh of depth in sea water and every 10.4 m of depth in fresh water.water.

Therefore, at a depth of 31 m (100ft) in the ocean, a diver Therefore, at a depth of 31 m (100ft) in the ocean, a diver is exposed to a pres of 4 atmos.is exposed to a pres of 4 atmos.

Those who dig underwater tunnels are also exposed to the Those who dig underwater tunnels are also exposed to the same hazards because the press in the chambers in which same hazards because the press in the chambers in which they work is increased to keep out the water.they work is increased to keep out the water.

The hazards of exposure to The hazards of exposure to ↑ barometric press used to be the ↑ barometric press used to be the concern largely of the specialists who cared for deep-sea divers and concern largely of the specialists who cared for deep-sea divers and tunnel workers.tunnel workers.

Examples of the ↑ barometric press includes; OExamples of the ↑ barometric press includes; O22 toxicity, N toxicity, N22 narcosis, decompression sickness and air embolism (see the table). narcosis, decompression sickness and air embolism (see the table).

Nitrogen narcosisNitrogen narcosisNN22 narcosis is a condition that occurs in divers breathing compressed air. narcosis is a condition that occurs in divers breathing compressed air. When divers go below depths of approx 100 ft, increase in the pp of NWhen divers go below depths of approx 100 ft, increase in the pp of N22 produces an altered mental state similar to alcohol intoxication.produces an altered mental state similar to alcohol intoxication.

NN22 narcosis, commonly referred to as "rapture of the deep," typically narcosis, commonly referred to as "rapture of the deep," typically becomes noticeable at 100 ft underwater and is incapacitating at 300 ft, becomes noticeable at 100 ft underwater and is incapacitating at 300 ft, causing stupor, blindness, unconsciousness, and even death. causing stupor, blindness, unconsciousness, and even death.

NN22 narcosis is caused by gases in the body acting in a manner described by narcosis is caused by gases in the body acting in a manner described by Dalton's Law of pp. As the total gas press ↑ with ↑ dive depth, the pp of NDalton's Law of pp. As the total gas press ↑ with ↑ dive depth, the pp of N22 increases and more Nincreases and more N22 becomes dissolved in the blood. This high N becomes dissolved in the blood. This high N22 conc conc impairs the conduction of nerve impulses and mimics the effects of alcohol impairs the conduction of nerve impulses and mimics the effects of alcohol or narcotics.or narcotics.

Symptoms of NSymptoms of N22 narcosis include: giddiness; euphoria; disorientation; loss narcosis include: giddiness; euphoria; disorientation; loss of balance; loss of manual dexterity; slowing of reaction time; fixation of of balance; loss of manual dexterity; slowing of reaction time; fixation of ideas; and impairment of complex reasoning. ideas; and impairment of complex reasoning.

The problem of NThe problem of N22 narcosis can be avoided by breathing mixture of O narcosis can be avoided by breathing mixture of O22 and and helium.helium.

Decompression sicknessDecompression sicknessAs a diver breathing 80% NAs a diver breathing 80% N22 ascends from a dive, the elevated P ascends from a dive, the elevated PAANN22 falls. Nfalls. N22 diffuses from the tissues into the lungs along the pp gradient. If diffuses from the tissues into the lungs along the pp gradient. If the return to atmos press (decompression) is gradual, no harmful the return to atmos press (decompression) is gradual, no harmful effects are observed; but if the ascent is rapid, Neffects are observed; but if the ascent is rapid, N22 escapes from escapes from solution. Bubbles form in the tissues and blood, causing the ?solution. Bubbles form in the tissues and blood, causing the ?“symptoms of decompression sickness.“symptoms of decompression sickness.

Bubbles in the tissues cause sever pains, particularly around joints, and Bubbles in the tissues cause sever pains, particularly around joints, and neurologic symptoms that include paresthesias and itching.neurologic symptoms that include paresthesias and itching.

Bubbles in the bloodstream, which occure in more sever cases, obstruct Bubbles in the bloodstream, which occure in more sever cases, obstruct the arteries to the brain, causing major paralysis and respiratory failure.the arteries to the brain, causing major paralysis and respiratory failure.

Bubbles in the pulmonary capillaries are apparently responsible for the Bubbles in the pulmonary capillaries are apparently responsible for the dyspnea that divers call “the chokes”. This is characterized by serious dyspnea that divers call “the chokes”. This is characterized by serious shortness of breath, often followed by sever pulmonary edema and, shortness of breath, often followed by sever pulmonary edema and, occasionally, death.occasionally, death.

Bubbles in the coronary artery may cause myocardial damage.Bubbles in the coronary artery may cause myocardial damage.

Treatment of this disease is prompt recompression in a press chamber, Treatment of this disease is prompt recompression in a press chamber, followed by slow decompression. Recompression is frequently life followed by slow decompression. Recompression is frequently life saving. Recovery is often complete, but there may be residual saving. Recovery is often complete, but there may be residual neurologic sequelae due to irreversible damage to the nervous sytstem.neurologic sequelae due to irreversible damage to the nervous sytstem.

Air embolismAir embolism

An AE, or more generally gas embolism, is a medical An AE, or more generally gas embolism, is a medical condition caused by gas bubbles in the bloodstream. condition caused by gas bubbles in the bloodstream. Small amounts of air often get into the blood circulation Small amounts of air often get into the blood circulation accidentally during surgery and other medical accidentally during surgery and other medical procedures, but AE which shows symptoms is relatively procedures, but AE which shows symptoms is relatively rare. Large emboli can be rapidly fatal.rare. Large emboli can be rapidly fatal.AE can occur whenever a BV is open and a press AE can occur whenever a BV is open and a press gradient exists favoring entry of gas. Because the press gradient exists favoring entry of gas. Because the press in most arteries and veins is greater than atmospheric, in most arteries and veins is greater than atmospheric, an air embolus does not always happen when a BV is an air embolus does not always happen when a BV is injured. In the veins above the heart, such as in the injured. In the veins above the heart, such as in the head and neck, the press is less than atmos and an head and neck, the press is less than atmos and an injury may let air in. injury may let air in. Trauma to the lung can also cause an AE. This is often Trauma to the lung can also cause an AE. This is often noticed after the patient is placed on a ventilator and noticed after the patient is placed on a ventilator and air is forced into an injured vein causing sudden death.air is forced into an injured vein causing sudden death.

Symptoms of an AE depend on where the bubbles Symptoms of an AE depend on where the bubbles lodge. They range from skin rashes, joint pain, visual lodge. They range from skin rashes, joint pain, visual disturbances, balance disturbances, breathing disturbances, balance disturbances, breathing difficulties, extreme fatigue/lack of strength, numbness, difficulties, extreme fatigue/lack of strength, numbness, paralysis, unconsciousness and death. If the embolism paralysis, unconsciousness and death. If the embolism occurs in the coronary arteries of the heart, a heart occurs in the coronary arteries of the heart, a heart attack will occur. If it lodges in the lungs, a pulmonary attack will occur. If it lodges in the lungs, a pulmonary embolism will occur, resulting in shortness of breath embolism will occur, resulting in shortness of breath and chest pain.and chest pain.Gas embolism and decompression sickness are very Gas embolism and decompression sickness are very difficult to distinguish, as they have very similar difficult to distinguish, as they have very similar symptoms. The treatment for both is the same, symptoms. The treatment for both is the same, because they are both the result of gas bubbles in the because they are both the result of gas bubbles in the body. In a diving context, the two are often called body. In a diving context, the two are often called decompression illness. decompression illness. Recompression is the only lasting treatment of an AE. Recompression is the only lasting treatment of an AE. Normally this is carried out in a recmpression chamber.Normally this is carried out in a recmpression chamber.

Oxygen toxicityOxygen toxicityOT or OT syndrome is severe hyperoxia caused by breathing OOT or OT syndrome is severe hyperoxia caused by breathing O22 at elevated pp. The high conc of O2 damages cells.at elevated pp. The high conc of O2 damages cells.

Hyperoxia is excess OHyperoxia is excess O22 in body tissues or higher than normal pp in body tissues or higher than normal pp of Oof O22. Hyperoxia is caused by breathing air at pressures greater . Hyperoxia is caused by breathing air at pressures greater than normal atmos press or by breathing nitrox or Othan normal atmos press or by breathing nitrox or O22 at normal at normal atmos press for a prolonged period of time.atmos press for a prolonged period of time.

The OT syndrome may occur;The OT syndrome may occur; - as a diving disorder, when divers breathe any breathing gas at - as a diving disorder, when divers breathe any breathing gas at

the high press of depth, the high press of depth, - as a potential complication of mechanical V- as a potential complication of mechanical VEE with pure O2, with pure O2,

where it is called the respiratory lung syndrome.where it is called the respiratory lung syndrome.

- - OT is not a major factor in hyperVE, as some people believe. OT is not a major factor in hyperVE, as some people believe. The problems caused by hyperVE are due to The problems caused by hyperVE are due to CO2 within the CO2 within the blood. With or without hyperVE, it is impossible to develop OT blood. With or without hyperVE, it is impossible to develop OT breathing air at typical surface atmos press.breathing air at typical surface atmos press.

In humans, there are several types of OIn humans, there are several types of O22 toxicity: toxicity:- CNS - CNS OTOT is manifested as convulsions, which is manifested as convulsions, which although not lethal themselves, can cause although not lethal themselves, can cause drowning of divers or lethal pressure damage drowning of divers or lethal pressure damage during a rapid ascent. during a rapid ascent. - The likelihood of this type of accident is directly - The likelihood of this type of accident is directly proportional to the pp of Oproportional to the pp of O22 in the breathing gas in the breathing gas and to the duration of exposure.and to the duration of exposure.- Pulmonary - Pulmonary OTOT is caused by exposure over 16 hrs is caused by exposure over 16 hrs to pp of 0.5 bar or more. The damage to the lungs to pp of 0.5 bar or more. The damage to the lungs may be irreversible. This is rare complication in may be irreversible. This is rare complication in divers, but may be of concern in intensive care divers, but may be of concern in intensive care patients needing high-inspired oxygen patients needing high-inspired oxygen concentrations. concentrations. - Rethinopathic- Rethinopathic OTOT causes damage to the retina. causes damage to the retina. Oxygen may be a contributing factor for the Oxygen may be a contributing factor for the disorder called retenopathy of prematurity. disorder called retenopathy of prematurity.

Hyperbaric OHyperbaric O22 therapy therapyThe intense oxidizing properties of high-press OThe intense oxidizing properties of high-press O22 (hyperbaric O(hyperbaric O22) can have valuable therapeutic ) can have valuable therapeutic effects in several important clinical conditions. effects in several important clinical conditions. Therefore, large press tanks are now available in Therefore, large press tanks are now available in many medical centers into which patients can be many medical centers into which patients can be placed and treated with hyperbaric Oplaced and treated with hyperbaric O22..

The most useful use of hyperbaric OThe most useful use of hyperbaric O22 has been for has been for treatment of gas gangrene, because the treatment of gas gangrene, because the organism cannot live in a high POorganism cannot live in a high PO22 environment. environment. The organism is called clostridial, which best grow The organism is called clostridial, which best grow under anaerobic conditions.under anaerobic conditions.

A hyperbaric chamber is also useful for treating A hyperbaric chamber is also useful for treating decompression sickness, arterial gas embolism, decompression sickness, arterial gas embolism, CO poisoning, osteomyelitis and myocardial CO poisoning, osteomyelitis and myocardial infarction.infarction.

Major means of acclimatizationMajor means of acclimatizationMountain climbers have found that when they ascend a mountain Mountain climbers have found that when they ascend a mountain slowly, over a period of days rather than the period of hours, they slowly, over a period of days rather than the period of hours, they breathe much more deeply and therefore can withstand for lower breathe much more deeply and therefore can withstand for lower atmos O2 conc than when they ascend rapidly. This is called atmos O2 conc than when they ascend rapidly. This is called acclimatization.acclimatization.

HyperVHyperVEE is an is an ↑ in V↑ in VEE..Figure show the changes in PFigure show the changes in PAAOO22 and P and PAACOCO22 that occur in that occur in acclimatized subjects and also in subjects acutely exposed to a acclimatized subjects and also in subjects acutely exposed to a low barometric press.low barometric press.The cause of hyperVThe cause of hyperVEE is hypoxic stimulation of the peripheral is hypoxic stimulation of the peripheral chemoreceptors. The resulting low PaCOchemoreceptors. The resulting low PaCO22 and alkalosis of the CSF and alkalosis of the CSF and blood tend to inhibit this and blood tend to inhibit this ↑ in VE activity. This is a suggestion, ↑ in VE activity. This is a suggestion, however, the cause of the sustained hyperVhowever, the cause of the sustained hyperVEE is still not fully understood. is still not fully understood.Polycythemia is another feature of acclimatization of high altitude Polycythemia is another feature of acclimatization of high altitude is an is an ↑ in the RBC conc of the blood. The resulting rise in Hb conc and ↑ in the RBC conc of the blood. The resulting rise in Hb conc and therefore Otherefore O22-carrying capacity, means that, although the PaO-carrying capacity, means that, although the PaO22 and O2 and O2 saturation are diminished, the Osaturation are diminished, the O22 content of the arterial blood may be content of the arterial blood may be normal or even above normal.normal or even above normal.Polycythemia tends to maintain the POPolycythemia tends to maintain the PO22 of mixed venous blood as of mixed venous blood as shown in the figure.shown in the figure.The stimulus for the The stimulus for the ↑ production of RBCs is tissue hypoxia, which ↑ production of RBCs is tissue hypoxia, which release erythropoiten from the kidney, which in turn stimulates the bone release erythropoiten from the kidney, which in turn stimulates the bone marrow. Polycythemia is also seen in many patients with chronic hypoxemia marrow. Polycythemia is also seen in many patients with chronic hypoxemia caused by lung or heart disease.caused by lung or heart disease.

Other features of acclimatization includes;Other features of acclimatization includes;- A shift to the right of the O- A shift to the right of the O22 dissociation curve, which dissociation curve, which result in a better unloading of Oresult in a better unloading of O22 in the venous blood at a in the venous blood at a given POgiven PO22..- - ↑ the conc of capillaries in the peripheral muscles because the ↑ the conc of capillaries in the peripheral muscles because the muscle fiber become smaller. There are also ↑ in some oxidative muscle fiber become smaller. There are also ↑ in some oxidative enzyme inside the cells. The maximum breathing capacity ↑ enzyme inside the cells. The maximum breathing capacity ↑ because the air is less dense and this makes possible the very high because the air is less dense and this makes possible the very high VVEE (upto 200 l/min) which occur on exercise. The maximum O (upto 200 l/min) which occur on exercise. The maximum O22 uptake, however, declines rapidly above 4500m.uptake, however, declines rapidly above 4500m.- Pulmonary vasoconstriction which occurs at high altitude as a - Pulmonary vasoconstriction which occurs at high altitude as a result of alveolar hypoxia.result of alveolar hypoxia.- Pulmonary hypertension which occasionally associated with high - Pulmonary hypertension which occasionally associated with high altitude pulmonary edema. Typically a climber or skier who has altitude pulmonary edema. Typically a climber or skier who has ascended to high altitude, perhaps without an adequate period of ascended to high altitude, perhaps without an adequate period of acclimatization, develops shortness of breath and may cough up acclimatization, develops shortness of breath and may cough up pink, frothy sputum. The treatment is to move the patient to a lower pink, frothy sputum. The treatment is to move the patient to a lower altitude and to give Oaltitude and to give O22 if this is available. if this is available.