Dr Surinder Singh IGMC Shimla Oxygen Therapy Dr Surinder Singh IGMC Shimla

Basic Concepts: Oxygen Cascade: Inspired = 150 mmHg at Sea Level SML120 ↓ Alveolar PO2= 103 ↓ Arterial=100 ↓ Capillary= 51 ↓ Mitochondrial= 1-10 (FiO2 expressed as 0.21-1.0 or 21- 100%)

Oxygen Availability: Normal Oxygen Flux or O2 availability/min: = (Hb content+ Plasma content) x Q = (1.39x Hb x SaO2 + 0.003 x PaO2 ) x Q ml 100 100 = (1.39 X 14.5 X 97.5+.003 X 100) X 5000 100 100 = 985+ 15 = 1000ml Coefficient of Oxygen utilisation: O2 consumed/ O2 available = 250 =25% Safety margin= 75% 1000

Oxygen Availability: Disease state Low CO eg. 50%+ Normal Hb = 500 ml Safety=50% Low CO eg 50%+ Low Hb 7gm= 250 ml Safety=?? Hemorrhagic Shock= ↓CO+↓Hb=↓↓↓↓ O2 MS+Anemia= ↓CO+↓Hb=↓↓↓↓ O2 Critical Flux= 500ml Last 250ml can’t be extracted The narrow safety margin is further reduced if oxygen demand increases in such patients

Perioperative State: ↑ Oxygen demand due to shivering, fever, sepsis, hypercatabolic state. Patients may be unable to increase cardiac output or VE or both A vicious cycle of hypoxemia may start .

Factors ↓ O2 Availability: Low arterial O2 content: ↓ FiO2, ↓PaO2 ↓ Diffusion eg ARDS, CPE ↓ pH or acidosis Low Hemoglobin: ↓ Hb ↑ COHb MetHb Low cardiac output states

Factors ↑ O2 Requirement: Pregnancy: ↑ 7-8 ml/kg/min Normal=4-5 ml/kg/min Sepsis , Hypercatabolic state Shivering= ↑ 500% of the Normal requirements Fever: 7% increase /oC rise of body temperature ↑ Work of breathing ↑ Myocardial work: Tachycardia

How to ↓O2 Consumption: Minimize exertion Digitalize, treat cardiac failure Prevent & Treat fever Under extreme circumstances: Paralysis and IPPV Induce hypothermia ECMO CPB

How to ↑ O2 availability: Raise Arterial PaO2 & SaO2 Oxygen Therapy Treat Bronchospasm/ respiratory lesions Ventilation, PEEP, CPAP Raise Hemoglobin: Hb: BT, Pack cell transfusion Raise Cardiac Output: Correct Acidosis Correct Hypovolemia Inotropic Support Treat Cardiac Lesions/ Shunts

Efficacy of oxygen therapy ∆ O2 /100 ml Art. Blood/percent ↑ FiO2 Diffusion Hypoxia & High Altitude 3 ml Respiratory depression 3 ml ARDS/CPE Anemia 0.03 ml Shock, Valve defects 0.03 ml MetHb 0.03 ml Cytotoxic Hypoxia 0.03 ml

BTS Indications: High concentration Additional Comments Target Sp O2 94 - 98% Grade of Recommendation Cardiac arrest or resuscitation Bag- valve- mask D Shock, sepsis, major trauma, near drowning, Target maximal SpO2 Add other treatments Major Head Injury Early intubation and ventilation if needed Carbon monoxide poisoning Bag valve with high flow to avoid rebreathing SpO2 will be high PaO2 will be normal Patient will be hypoxic C

BTS Indications: Medium concentration Additional comments Evidence grade Asthma Supplement oxygen C Pneumonia Lung cancer Postop breathlessness Treat underlying cause, CPAP, BiPAP Acute Heart failure Consider CPAP, NIV Intubation and ventilation+PEEP D Pulmonary embolism Most do not require Severe ones not benifitted Pleural effusions Drainage of effusion Pneumothaorax Drainage/ aspiration of pneumothorax ILD (Ac deterioration) Bag valve mask if SpO2 < 85% Severe anemia Transfuse and correct anemia B& D Sickle cell crisis Useful in hypoxemia; treat aggravating factors B Nasal cannulae 2- 6 LPM or simple mask 5-10 LPM Target 94-98% SpO2 Reservoir mask if no improvement. If high risk hypercapnea; target 88-92% SpO2

BTS Indications: Low Concentrations COPD and other conditions requiring low dose oxygen therapy (2 – 6 LPM) COPD 24- 28% oxygen, 88-92% SpO2 ABG to assess PaCO2 D If normocapnea target SpO2 of 94-98% If below 88% despite 28% FiO2 switch over from ventimask to nasal cannula 2-6 LPM Repeat ABG after 30-60 min or on deterioration for PaCO2 LTOT > 17 hour/day improved quality of life and survival A Oxygen Alert card for Hypercapnic respiratory failure patients should guide oxygen therapy Chronic NM disorders eg MND, LAS Chronic and subacute conditions require nocturnal CPAP, NIV and eventually end of life care C Acute neuromuscular disorders Rapidly progressing LGBS and Myasthenia gravis often require tracheal intubation and ventilatory support Neurotoxins also fall in this category A& B*

Specific conditions Specific conditions MI, ACS Not hypoxic, benefits/harms of oxygen therapy unknown D Stroke Harmful in nonhypoxemic mild to moderate stroke patients B Pregnancy& Obstetric patients Major trauma, sepsis, shock states give oxygen to target 94-98% SpO2 Harmful to fetus in nonhypoxemic mothers causes, Fetal acidosis Use left lateral tilt in POG > 20wks A – D Hyperventilation& dysfunctional breathing Oxygen not justified Rebreathing may cause hypoxia thus not recommended C Drug poisoning, overdose Hypoventilation if present, treat with antidotes e.g. naloxone Avoid hyper-oxygenation as hypercapnea may be present Perform ABG Paraquet/ bleomycin Avoid oxygen

General considerations PIFR: Low: Respiratory depression V High: Tachypnea, ARDS Expiratory pause Longer: Resp depression Shorter: Tachypnea ARDS

General considerations Use mask in distress :Mouth breathing Humidification not useful < 10LPM Use upright posture to the extent permissible Appropriate FiO2 to achieve Target SPO2 Confirm oxygen delivery to the patient Prescribe& document oxygen therapy Monitor SpO2 ABG, Vitals, Narcosis Diagnose and treat the underlying cause MOST INDICATIONS FALL IN EVIDENCE LEVEL-D OR C

Devices for oxygen :History BLB Mask 1938 Boothby Lovelace Bulbulian Nasal mask with reservoir

Devices Nasal Catheters: : No/ low capacity Variable performance 2-4 LPM (BTS 2-6) Upto 35% FiO2 Advantages: Economical, Gas economy No VD/ rebreathing Eating, drinking, speaking possible Useful for low FiO2 Can be used in Tracheal/ Tracheostomy tube Disadvantages: Irritation, No humidification Encrestations, Ulceration

Nasal Prongs/ oxyarm: No/ Low capacity Variable performance Better tolerance Performance same as nasal catheters Reservoir 20-30ml ETCO2 sampling Oxyarm: Cloud of 28-35% FiO2 in front of nose& mouth

Simple Mask: Low capacity Variable performance Simple Face Mask: No limit of O2 flow Usually 4-6 LPM FiO2 ≈ oxygen flow Usually 2- 4%/ LPM-1 Advantages: Simple, No Flow limit/ FiO2 limit Disadvantages: ? FiO2, Cross Infection No Humidification

Ventury masks: Fixed performance High flow Medium Conc. Mask: Comes with one adapter set at 35% Required 5 LPM Set of adapters Multi Vent: One or two adjustable adapters Anaesthesia Breathing Circuits: Low flow Fixed performance

Devices: High capacity Reservoir mask 60 – 95% FiO2 FiO2 dependant on FGF Inversely related to VË Rebreathing directly related to VË and inversely related to FGF Valve between the reservoir & mask prevents rebreathing Requires continued flow and observation

Hood, tent and Incubator Large capacity for oxygen and CO2 Unpspecified FiO2

Ambulatory devices . .

Oxygen Toxicity: Described by Sir joseph Priestley Generation of Superoxide radicals O - Absorption atelectasis ↓ Surfactant production Drying of mucosal epithelium and secretions ROPM, Fibrocystic dysplasia, ARDS ↑ PCO 2 in COPD patients: Narcosis FiO 2 100%= 4 hrs FiO 2 80%= 8 hrs FiO 2 70%= 12 hrs FiO 2 60%= 24 hrs FiO 2 ≤ 50%= Indefinite

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