OXYGEN THERAPY

OXYGEN THERAPY : OXYGEN THERAPY Anupam Maity DEPT. OF GENERAL MEDICINE, R.G.KAR MEDICAL COLLEGE & HOSPITAL, KOLKATA

BASIC PHYSIOLOGY : BASIC PHYSIOLOGY

OXYGEN TRANSPORT : OXYGEN TRANSPORT

Slide 4 : The O2 delivery system in the body consists of the lungs and the cardiovascular system. O2 delivery to a particular tissue depends on the amount of O2 entering the lungs, the adequacy of pulmonary gas exchange, the blood flow to the tissue, and the capacity of the blood to carry O2. The amount of O2 in the blood is determined by (1). the amount of dissolved O2, (2). the amount of hemoglobin in the blood, and (3). the affinity of the hemoglobin for O2. As oxygen has low solubility in water it needs Hb to be transported in tissue. 99 % of transported oxygen is through Hb.

O2- Hb DISSOCIATION CURVE : O2- Hb DISSOCIATION CURVE

Slide 6 : BOHR AS BLOOD CIRCULATES FROM ARTERIAL TO EFFECT: VENOUS END THE DISSOCIATION CURVE SHIFTS TO THE RIGHT (BECAUSE INCREASED CO2) WHICH FACILITATES DUMPING OF O2 AT THE TISSUE LEVEL. THIS DECREASES HEMOGLOBIN AFFINITY FOR O2 AT LOW PH. HALDANE WHEN HEMOGLOBIN CARRYING O2 (HbO2) EFFECT: LOSES ITS O2, IT WILL FACILITATE THE UPTAKE OF H+ ( ANY CHANGE IN pH. THUS HEMOGLOBIN ACTS AS A BUFFER. consequently, venous blood carrying more CO2 than arterial blood CO2 uptake is fascilitated in the tissue, and CO2 release is fascilitated in the lung. HHb) WITH OUT

OXYGEN DISASSOCIATION CURVE : OXYGEN DISASSOCIATION CURVE SHIFT TO THE LEFT IN O2 CURVE O2 AFFINITY } { 1. CAUSES: pH, CO2, 2-3 DPG, TEMP. O2 SAT. FOR A PaO2 BUT RESULTING IN IN LESS GRADIENT TO MOVE O2 TO TISSUE. (CARRIES MORE O2 BUT MORE DIFFICULT TO RELEASE IT AT TISSUE LEVEL) 3. EXAMPLES: STORED BLOOD LOSES 2-3 DPG A SHIFT TO THE LEFT RESULTS FROM THIS. HYPERVENTILATION, HYPOTHERMIA. 2. RESULTS:

OXYGEN DISASSOCIATION CURVE CONTINUED : OXYGEN DISASSOCIATION CURVE CONTINUED SHIFT TO THE RIGHT IN O2 CURVE O2 AFFINITY } { 1. CAUSES: pH, CO2, 2-3 DPG, TEMP. 2. RESULTS: O2 SAT FOR ANY PaO2 BUT RESULTING IN MORE GRADIENT TO MOVE O2 INTO THE TISSUES. 3. EXAMPLES: HYPOVENTILATION, FEVER, METABOLIC ACIDOSIS.

THE NEED FOR SUPPLEMENTAL OXYGEN : THE NEED FOR SUPPLEMENTAL OXYGEN Oxygen therapy should be used to prevent / correct tissue hypoxia. But recent survey showing that >50% of hospitalized patient were receiving supplemental O2 without any written order (Small D, Duha A, Weiskopf B et al.) So, we should know when to suppliment oxygen.

TOLERANCE to ARTERIAL HYPOXIA : TOLERANCE to ARTERIAL HYPOXIA Though standard indication for O2 supplementations are : PaO2 <60 mm of Hg & SaO2 < 90 % However, clinical observations show that severe degree of hypoxaemia are tollereted with out evidence of inadequate tissue oxygenation. Eldridge FE (NEJM), Abdelsalam M showed this facts in their study.

Indications for oxygen therapy : Indications for oxygen therapy Respiratory compromise Cyanosis Tachypnoea Hypoxaemia Partially obstructed airway Respiratory failure. V/Q mismatch. ete

Indications for oxygen therapy : Indications for oxygen therapy Cardiac compromise Chest pain, AMI Shock Tachycardia Arrhythmias Neurological deficits CVA Spinal injuries Coma

Aims of oxygen therapy : Aims of oxygen therapy to increase PaO2 to acceptable level with concentration of oxygen. to decrease respiratory rate and work of breathing. Hypoxaemia with high PaCO2 24% initially careful monitoring with regular ABG’s To decrease cardiac workload. To improve cell function

TYPES OF HYPOXIA AND COMMON CAUSES : TYPES OF HYPOXIA AND COMMON CAUSES I. HYPOXEMIC (DECREASED TISSUE OXYGEN TENSION) A. HYPOXEMIC HYPOXIA (INADEQUATE ARTERIAL OXYGEN TENSION) CAUSES: B. ANEMIC HYPOXIA (DEFICIENT OXYGEN-CARRYING CAPACITY OF THE BLOOD) CAUSES: A. ANEMIA (DECREASED HEMOGLOBIN) B. CARBON MONOXIDE POISONING C. SULFHEMOGLOBIN AND METHEMOGLOBIN A. V/Q MISMATCH (EX: COPD, PATIENT LAYING ON THEIR SIDE, PE) B. SHUNT (EX: ATELECTASIS, PULM. EDEMA) C. HYPOVENTILATION (Eg: DRUG INDUCED)

TYPES OF HYPOXIA AND COMMON CAUSES CONTINUED : TYPES OF HYPOXIA AND COMMON CAUSES CONTINUED C. CIRCULATORY HYPOXIA (DECREASE PERIPHERAL CAPILLARY BLOOD FLOW) CAUSES: D. HISTOTOXIC HYPOXIA (DECREASED UTILIZATION OF OXYGEN AT THE CELL LEVEL) CAUSES: A. DECREASED CARDIAC OUTPUT B. VASCULAR INSUFFICIENCY (SEPSIS) A. CYANIDE POISONING B. ALCOHOL POISONING (RARE)

IMPORTANT THINGS TO REMEMBER : : IMPORTANT THINGS TO REMEMBER : Among them histotoxic hypoxia is not well corrected by oxygen therapy, as cellular enzyme system ( cytochrome oxidase) is inactivated by toxins. Its also to remember that oxygen only corrects hypoxia, but not the root cause of hypoxia eg. V/Q mismatch, right to left shunt etc. Again oxygen content of blood not only depends on Pao2, but mainly on Hb. Conc. Of blood.

ANOTHER IMPORTANT THING : : ANOTHER IMPORTANT THING : Before starting oxygen therapy two things should be kept in mind : (A) Does the patient have normal sensitivity to respiratory centre?/ normal control over respiration? If such, he will tolerate high conc. of oxygen (6-8L/min) and correction of hypoxaemia will not cause CO2 retention. Such patients has normal sensitivity of respiratory centre to rise of PaCO2 , except when the centre is severely depressed by drugs. Eg. Most of the pulmonary causes of hypoxia like I.L.D., pneumonia, pulmonary oedema, atelectasis.

Slide 18 : (B). Does the patient has abnormal control over respiration ??? In these patient respiratory centre is comparatively insensitive to increase in PCO2 & respiratory drive is significantly dependent on the hypoxic stimulus. So, inhaling high conc. Of O2 will cause sharp reduction in respiratory drive. This will result in hypoventilation & dangerous rise In PaCO2. Eg. Severe COPD. In these patient controlled conc. Of O2 (24-30%) should be started, & should be assessed carefully.

Types of oxygen delivery : Types of oxygen delivery Nasal cannulae Fixed concentration mask Non-rebreathe bag Humidified circuits High flow systems

METHODS OF OXYGEN ADMINISTRATION : METHODS OF OXYGEN ADMINISTRATION (1). ROUTINE O2 THERAPY WITH LOW FLOW DEVICES: They can only rise moderate amount of O2. approx. 40% of O2 may be achieved by them, if flow rate is 6-8 /min. (A). NASAL CATHETER & PRONGS : Tip should not cross soft palate, as it can produce gaseous distension of stomach. Nostril should be changed every 4 houtly. At flow rate of 1L/min O2 conc. is approx.24%. At flow rate of 6-8 L/min O2 conc. Of 40% is achieved. Precise control over inspired O2 conc.is not possible as the inspired O2 depends not only on O2 conc. but also on tidal volm., minute ventilation also. So, not suitable for I.C.U.

Slide 21 : (B). FACE MASK : O2 can be given @ 6-10 L/min. O2 should first be humidified. The mask acts as a small reservoir increasing the O2 conc. & O2 conc. may be increased by increasing the mask size. O2 conc. can be achieved approx. 33-35% Less easy & less comfortable than nasal catheter / prong. A major disadvantage is that it has to be removed when the patient speaks, eats or expectorates.

OTHER LOW FLOW DEVICES : : OTHER LOW FLOW DEVICES : (C). FACE MASK WITH RESERVOIR BAG : The reservoir bag increases the conc. of O2 O2 flow rate of 8-12 l/min can be achieved. O2 conc. Of 80% can be achieved. Flow rate of O2 must be adjusted so that the bag is not be emptied to half during inspiration.

Slide 23 : (D).FACE MASK WITH RESERVOIR BAG & DIRECTIONAL VALVES: Side ports are fitted with unidirectional valves. During expiration valve opens and air passed out. Flow rate of approximately 10 – 15 l/min . High oxygen conc. Of 95% can be achieved. Disadvantage: If reservoir bag is inadvertently emptied, asphyxia occurs.

CORRELATION BETWEEN o2 FLOW & CONC. OF LOW FLOW DEVICES: : CORRELATION BETWEEN o2 FLOW & CONC. OF LOW FLOW DEVICES:

(2). CONTROLLED / HIGH FLOW O2 THERAPY: : (2). CONTROLLED / HIGH FLOW O2 THERAPY: Provides complete control of the inhaled gas mixture & deliver a constant % of oxygen regardless the ventilatory pattern. PRINCIPLES: Bernouilli principle O2 is delivered to mask at low flow rates, but at the inlet of the mask, the O2 is passed through a narrowed orifice & this creates a high velocity stream of gas (analogous to the effect created by nozzle on garden hose). The high velocity jet generates viscous drag which pulls room air into the mask.

Slide 26 : WHEN NECESSARY? : Its needed in patients who show hypercapnic response to a unlimited / uncontrolled O2 administration. Eg. COPD The purpose of controlled O2 therapy is to relieve dangerous hypoxia by providing an adequate increase in PAO2, PaO2 yet limit the associated rise in PaCO2.

Slide 27 : 14 l/min air entrained 14 l/min air entrained 2 l/min oxygen jet 2 l/min oxygen jet 30 l/min The Bernoulli Effect

VENTIMASK : : VENTIMASK :

VENTURI MASK : : VENTURI MASK : A fixed proportion of room air (1:10/ 1:20 etc) is enters through side pores. The ratio depends on the nozzle size of different mask. O2 concentration of the inspired gas is thus independent of flow rate. ADVANTAGES: O2 Conc. Is independent of flow rate. O2 conc. Is also independent of tidal volume / min.vol Easy to use by everybody. requires no spl. Adjustment. O2 conc. is not at the mercy of faulty flowmeter/ valves.

O2 DELIVERY DEVICES FOR E.T. / TRACHEOSTOMY TUBES : : O2 DELIVERY DEVICES FOR E.T. / TRACHEOSTOMY TUBES : (A). TRACHEOSTOMY MASK :

Slide 31 : (B). T-PIECE :

Recommended target saturations : Recommended target saturations Target saturations : Most patients 94 - 98% Risk of hypercapnic respiratory failure 88 – 92%.

HYPERBARIC OXYGEN : : HYPERBARIC OXYGEN : Oxygen is administered at a pressure higher than atmospheric pressure in a chamber. USES : Carbon monoxide poisoning. Sepsis secondary to wounds contaminated by gas forming organism. Treatment of wounds with poor blood supply.

HUMIDIFICATION OF OXYGEN : : HUMIDIFICATION OF OXYGEN : BEFORE DELIVERY O2 SHOULD BE HUMIDIFIED BECAUSE: Ventilation of dry O2 causes heat loss, causing decrease in body temp. which can increase the O2 demand. Dry O2 can cause dehydration of respiratory mucosa. Most dangerous effect of dehydration of mucosa is loss of muco-ciliary escalator with sputam retention causing V/Q mismatch & accentuates hypoxia.

TYPES OF HUMIDIFIER: : TYPES OF HUMIDIFIER: 1. Vapourizers (unheated). 2. heated vaporizer 3. nebulizers

Heat and moisture exchanger ( hme) : : Heat and moisture exchanger ( hme) : When connected to an artificial airway it will extract heat & moisture from expired gas, and returns them to inspired gas. Can retain at least 70% of expired moisture. ADVANTAGES ARE : Humidification is satisfactory with artificial airway. Breathing system remains dry. Inexpensive, disposable, don’t need external power source. Prevents nosocomial infections. DISADVANTAGES: Increases dead space. Expectorated sputum can obstruct the exchanger membrane. Increases the resistance of breathing.

DARK SIDE OF OXYGEN THERAPY : : DARK SIDE OF OXYGEN THERAPY : Overzealous & unregulated supplementation of oxygen can act as a powerful and even lethal toxin. Contrary to the notion that oxygen is protective for a cell, actually it causes cell injury by toxic metabolites GRANULOCYTE ACTIVATION : As a part of inflammatory response of granulocyte RESPIRATORY BURST occurs producing toxic metabolites causing cell injury. Eg. ARDS, SIRS.

COMPLICATIONS OF OXYGEN THERAPY : : COMPLICATIONS OF OXYGEN THERAPY : PROGRESSIVE HYPERCAPNIA: Seen in COPD. CIRCULATORY DEPRESSION : when hypoxia causes catacholamine surge , the only drive of cvs then correction of hypoxia may cause circulatory failure. managed by volume overloacd or sympathomimetics. DRYING AND CRUSTING OF RESPIRATORY SECRETIONS. OXYGEN TOXICITY : LUNG TOXICITY – Atelectasis, damage to surfactant, interalveolar oedema, interstitial fibrosis and thickening. Toxic level of FIO2 is 0.6 for O2 therapy of > 48 hrs.

CONTD….. : CONTD….. B. RETROLENTAL FIBROPLASIA : Related to high PaO2 in (>160mm of Hg for a few hours) in neonates. CEREBRAL OXYGEN TOXICITY : Observed in hyperbaric oxygen therapy. presents with fits called Paul Bert effect, after the name of 1st patient.

TISSUES ARE NORMALLY HYPOXIC ! : TISSUES ARE NORMALLY HYPOXIC ! Normally human body tissues operate in a low oxygen environment. DISTRIBUTION OF O2 IN TISSUE : This demonstrates that human tissues normally operated in a oxygen deficient environment.

A STUDY OF 7 COPD PATIENTS WITH SEVERE HYPOXAEMIA (PaO2 <40 mm of Hg) : A STUDY OF 7 COPD PATIENTS WITH SEVERE HYPOXAEMIA (PaO2 <40 mm of Hg) Blood lactate level is a marker of tissue hypoxia (normal level < 4mmol/L ) SEVERE HYPOXAEMIA WITHOUT ANY EVIDENCE OF ANAEROBIC METABOLISM: Ref Eldridge FEet al.

FINAL WORDS : : FINAL WORDS : ROUTINE USE OF OXYGEN SHOULD BE ABANDONED. MORE ATTENTION SHOULD BE GIVEN TO THE ANTIOXIDANT STATUS OF INDIVIDUAL PATIENTS TO ASSESS THE RISK OF PULMONARY OXYGEN TOXICITY. COPD PATIENTS SHOULD NOT BE TREATED WITH HIGH CONC. OF OXYGEN. Always consider humidification.

AN INTERESTING FACT : : AN INTERESTING FACT : Oxygen was discovered for the first time by a Swedish Chemist, Carl Wilhelm Scheele, in 1772. Joseph Priestly, an English chemist, independently, discovered oxygen in 1774 and published his findings the same year, three years before Scheele published

Slide 44 : THANKING YOU………