Pulse Oximetry

Pulse Oximetry, a way of assessing oxygen levels, involves attaching a device known as a pulse Oximeter to the patient's finger, toe or ear lobes. It is a noninvasive monitoring or determination of oxygen-hemoglobin saturation of the blood and the pulse.

Indications for pulse Oximetry include the need to monitor the adequacy of arterial oxy hemoglobin saturation and gauge the response of O2 saturation to therapeutic interventions.
SpO2 (a measure of oxygen saturation) is used for continuous and prolonged monitoring as in during sleep, exercise or surgical procedures. Results of SpO2 tests validate the basis for ordering the test by reflecting the patient's clinical condition. Normal Oxygen saturation levels are between 94 - 100 %. If the saturation level falls below 90 %, clinical intervention is required.

Reasons for low Oxygen Saturation (SP02) Levels:

1. Respiratory Conditions such as emphysema, pneumonia or Obstructive sleep apnea (OSA).
2. Poor oxygenation due to suffocation or allergic reaction.
3. Presence of air blockage or lower levels of Oxygen - drowning

A pulse Oximeter is based on the different light absorption characteristics of oxygenated and deoxygenated hemoglobin. Using a Red LED and an Infra-red LED with matching photo sensors, a microprocessor in the device calculates the ratio of oxygenated/deoxygenated blood and based on the surge which occurs at every heart beat (hence pulse), it displays the Oxygen Saturation level along with the pulse rate. The usual precaution with such a device is to use it on a clean finger. Any barrier like nail polish, grease or dirt may hamper the function.

Spirometer: A device that is used to test the air capacity of lungs and the amount of air that enters and leaves the lungs during breathing. Spirometry is the procedure that measures air flow and lung volume. It is used to diagnose respiratory diseases such as emphysema.

Arterial blood gases test: A test to analyze the blood for oxygen, carbon dioxide and bicarbonate content, as well as blood pH (acidity level). These tests are primarily intended to test the effectiveness of respiration.

For the Arterial blood gases (ABGs) Test, Blood is drawn from a peripheral artery (radial, brachial or femoral) via a single percutaneous needle puncture or from an arterial cannula, for a direct measurement of partial pressures of carbon dioxide (PaCO2) and oxygen (PaO2), hydrogen ion activity (pH), total hemoglobin (Hbtotal) and oxy hemoglobin saturation (HbO2).

Dyspnea

Dyspnea is commonly known as breathing difficulty or shortness of breath. It is noticed as difficulty in breathing or labored breathing. Tachypnea refers to rapid breathing. Progressively it can lead to hyperventilation such as experienced during an anxiety attack. Studies indicate that the origin of dyspnea is initiated with inaccurate central nervous system to the lungs with respect to breathing.

The etiology of dyspnea is related to conditions such as Pulmonary Embolism (PE), asthma, COPD, pulmonary ischemia and pneumonia. The management of dyspnea is only effective when the underlying causes are treated. In case of trauma, pneumothorax is an acute trigger for initiating the onset of dyspnea and hence emergency care is given to prevent internal bleeding that is caused in the pneumothorax. This condition can also progress into tachypnea and varied lung and heart sounds which has to be managed with effective ER procedures.

Positional dyspnea: If a person suffers dyspnea when lying down, it might be suggestive of CHF or pericardial effusion.

Exertional dyspnea: This occurs when there is reduction in oxygen supply and is mostly noticed in patients suffering cardiac disease or anemia.

Transient dyspnea: This situation usually resolves without medical intervention and is triggered by reversible causes such as panic attacks.

Recurrent dyspnea: Here the patient suffers these episodes many times.

Conditions such as pulmonary embolism can also lead to dyspnea along with tachycardia and diminished breathing patterns. Dyspnea is an immediate progressive condition usually associated with previous history of trauma or illness such as Tuberculosis, bronchopneumonia, infectious mononucleosis and sepsis in certain scenarios. Since dyspnea is an associated condition and it is predominantly an upper airway obstruction, the treatment measures are often related to avoiding exposure to chemicals, pollen, toxic fumes and gases such as carbon monoxide. Diagnostic tools such as Pulse Oximetry, blood tests for anemia, ECG and metabolic study are used to aid the diagnosis and then initiate appropriate treatment.

Hypoxia

The body needs a specific amount of Oxygen to function normally and when this amount is lowered the body experiences hypoxia. Hypoxia literally means lack of oxygen for effective ventilation.

Hypoxemia refers to a state of abnormally low level of Oxygen in the blood.
Anoxia refers to the condition of absence of Oxygen supply to an organ or tissue
Anoxemia refers to the condition where the blood stream contains below normal amount of Oxygen.

Hypoxia is primarily classified into:

Generalized hypoxia: affects the entire body, may occur in normal healthy people when they scale high altitudes.
Local hypoxia: affects one particular region of the body.

When the level of oxygen in the blood reduces, it leads to the condition. People suffering from conditions like ischemia or blockage/constriction of blood vessels may suffer from hypoxia. In general when people travel from low to high altitudes, they may face this problem as the oxygen level depletes with altitude.

Hypoxia causes

Any condition wherein the body is deprived of oxygen can lead to hypoxia. Major causes that lead to the condition include:

• Severe head trauma
  
• Ischemia
  
• Asthma Severe Asthma can result in hypoxia and in Hypercarbia or Hypercapnia (elevated levels of Carbon dioxide CO₂ in blood)
  
• Pulmonary embolism
  
• Carbon monoxide poisoning
  
• Chronic alveolar hypo ventilation
  
• Shock can result in cellular hypoxia in the extremities
  
• Suffocation
  
• Choking
  
• High altitude climbing
  
• Inadequate ventilation

Types of hypoxia

Hypemic hypoxia: Obstruction in the ability of the blood to deliver oxygen, caused by carbon monoxide poisoning.

Anemic Anoxia: Occurs due to a decrease in the hemoglobin or RBC making it too little for the blood to carry oxygen. Anemia may be the result of iron deficiency, hemorrhage or shortened life span of RBC owing to an autoimmune disease.

Histotoxic: When the required amount of oxygen reaches the body part, however it does not utilize it because of its reduced ability, it is called as histotoxic hypoxia. Cyanide poisoning, for example, incapacitates a cellular enzyme essential for oxygen utilization. Other causes include: Alcohol, narcotics, acetone, formaldehyde and some anesthetic agents.

Hypoxic: Also called as Hypoxemic Anoxia: When the body does not receive the required amount of oxygen it leads to low partial pressure of oxygen in the blood thus leading to hypoxic hypoxia. The oxygen pressure of the blood which gets supplied to other body tissues is too low to push and flood the hemoglobin with oxygen. High altitude has lower density of air and lower pressure of oxygen than at sea level. Altitude Sickness occurs because the partial pressure of oxygen decreases with altitude. Hypoxemia is the direct result of lower oxygen in the high altitude which translates to lower level oxygen in the blood.

Stagnant: Obstruction of blood that carries oxygen. It can be due to exposure to cold, diseases which stifle blood circulation to the extremities or ergot poisoning.

Pulse Oximetry, a non invasive test is useful to diagnose Hypoxia. A blood test like serum lactate test can show elevated levels of lactic acid - the result of starvation of oxygen in tissues. The normal level of lactic acid is less than 2 mmol/L. However an increase in lactic acid alone does not indicate hypoxia and some form of Anoxia does not increase the lactic acid concentration. Symptoms may be dangerous on the onset and may include the following:

Generalized hypoxia

• Tachypnea or rapid breathing
  
• Severe headache
  
• Dizziness
  
• Nausea
  
• Tingling sensation
  
• Visual impairment
  
• Shortness of breath
  
• Bluish tint on the lips or on finger tips
  
• Coma
  
• Seizures
  
• Euphoria
  
• Mental fatigue
  
• Muscle fatigue

• Hot and cold flashes
  
• Discoloration of skin
  
• Pain in the area of hypoxia
  
• Severe hypoxia may cause gangrene

Hypoxia Treatment

Some types of Hypoxia cannot be prevented. Treatment depends on the severity of the condition and the appearance of the clinical symptoms. Treatment may include the following:

• Restoration of the tissue oxygen by supplementing the air supply with 100 % oxygen.
  
• Blood pressure and heart rate should be brought back to normal.
  
• In case of high altitudes, the person should be given sufficient rest and should not climb any further.
  
• Hypoxemic hypoxia patients can be put on blood transfusion.
  
• Proper medication and timely treatment can help save the life.