Oxygen therapy

O2 Used in clinical practice for more than 200 years. Widely prescribed in pre-hospital and hospital environment. Life saving and part of first line management in critical illness. Note  not only for the lungs but delivery to the tissues. So it is vital to have: a) a good cardiac output b) adequate haemoglobin concentration c) efficient circulation

As with any drug, O2 should be used a) when indicated b)In appropriate dosage ( concentration ) c)Correctly administered for a planned duration.

Hypoxemia – O2 tension in the arterial blood is less than 80 mmHg Hypoxia – deficiency of O2 at the tissue level 4 types of hypoxia: 1)Hypoxic hypoxia – low arterial O2 tension in blood 2)Anaemic hypoxia – not enough Hb to carry O2 3)Stagnant hypoxia – blood flow to the tissue is so slow 4)histotoxic hypoxia – toxic agent prevents cell from using O2

Clinical features of hypoxia ( non specific ) :  Altered mental status (agitation, confusion, drowsy, coma )  Nausea, vomitting  Cyanosis  Dyspnoea, tachypnoea, hypoventilation  Arrythmia  Hypo / hypertension  Peripheral vasoconstriction with sweaty extremities  cyanosis

Cyanosis – blue colouration of mucous membrane due to presence of deoxygenated Hb > 5 gm % in blood Peripheral arterial O2 ( SaO2 < 95% ) – pulse oxymeter Arterial O2 tension < 80 mmHg – arterial blood gas analysis

Oxygen therapy ( Indications ) The American college of Chest Physicians, National Heart, Lungs and Blood Institute’s recommendation : 1.Cardiac and respiratory arrest 2.Hypoxemia ( PaO2 < 59mmHg and SaO2 < 90% ) 3.Systemic hypotension 4.Low cardiac output and metabolic acidosis ( bicarb < 18mmol/L ) 5.Respiratory distress ( respiration rate >24/min ) 6.In anaesthesia – added O2 during and after anaesthesia to prevent perioperative hypoxia

Controlled O2 Therapy is indicated in : 1)Chronic obstructive pulmonary disease who rely on hypoxic drive for respiration (normal person  CO2 stimulates respiration) can loss respiratory drive if high concentration of O2 is given. So O2 should start with 24-28%, carefully monitored and aim to achieve PaO2 above 50 mmHg and SaO2 of 85-90%. 2)Premature infant because of the danger of developing retrolental fibroplasia

No controlled O2 therapy in : 1)Asthma 2)Pneumonia 3)Respiratory distress 4)Cardio pulmonary arrest 5)Carbon monoxide poisoning 6)Pulmonary embolus 7)Shock :  Septic shock  Cardiogenic – heart failure, myocardial infarct  Hypovolemic shock – acute GE, massive bleeding

Monitoring of oxygen therapy 1.Clinical – concious level, heart rate and respiratory rate,blood pressure, capillary refill time (normal 1-2 second), cyanosis 2.Pulse oxymetry -- % saturation of oxygenated Hb 3.Arterial blood gass (ABG) – blood sample is taken from artery and analysed PaO2 level

Risks of oxygen therapy 1)Fire – O2 support combustion of other fuels. 2)Absorption atelectasis – prolong administration of high concentration of O2 causes basal atelectasis 3)Retrolental fibroplasia – blood vessels growing into vitreous followed by fibrosis which causes blindness later. Low birth weight premature baby is at risk until 44 weeks post conceptual age. 4)In patients on chemotherapy – bleomycin can cause pulmonary fibrosis if high concentration of O2 is given. O2 concentration that can maintain SaO2 of 90-95% is given.

O2 manufacture and storage a)Vacuum insulated evaporators ( VIE ) b)Cylinder c)Concentrator VIE – liquid O2 Cylinder – O2 gass under pressure Concentrator – extract atmospheric O2 using xeolite ( N2 is filtered out and O2 is produced )

Liquid oxygen store in hospital

Oxygen cylinder

Oxygen concentrator

Oxygen delivery system 2 main types of devices : 1.Variable performance device – delivers variable concentration of O2 through nasal cannula, nasal catheter, plastic O2 mask 2.Fixed performance device – the patients breath a fixed concentration of O2 enriched air through anaesthetic breathing circuit, head boxes for neonate and high air flow oxygen enrichment devices ( HAFOE ).

High airflow O2 enrichment devices With colour code

Flow of O2 in litre/minuteInspired O2 concentration % High Air Flow Oxygen Enrichment devices

Nasal cannula

Nasal catheter

Variable performance devices O2 concentration delivered depend on 1)Patients factor like respiration rate, PEFR 2)O2 flow rate Advantages:  No dead space  No rebreathing  More tolerable than masks  A gass flow of 150ml/kg/min can give inspired concentration of 50% in children less than 2 years.

Hyperbaric oxygen therapy Breathing 100% O2 under increased atmospheric pressure. 1 ATM = 760 mmHg 2 types of chamber 1)Multi place chamber 2)Mono place chamber

Physiologic mechanism of hyperbaric O2 therapy 1)Hyper oxygenation 2)Decreased gass bubble size 3)Vasoconstriction 4)Angoigenesis 5)Fibroblast proliferation / collagen synthesis 6)Leucocyte oxydative killing – Clostridial infection 7)Reduces lipid peroxidation 8)Toxic inhibition 9)Antibiotic synergy

Indications for hyperbaric O2 therapy 1.Decompression sickness 2.Air embolism 3.Carbon monoxide poisoning 4.Enhancement of healing in selected problem wounds 5.Crushed injury 6.Compartment syndrome 7.Delayed radiation injury 8.Refractory osteomylitis

Hyperbaric O2 Increases generation of O2 free radicals  a)Oxidise proteins and membrane lipids b)Damage DNA c)Inhibit bacterial metabolic function d)Facilitates O2-dependent peroxidase system of leukocytes e)Especially effective against anaerobes

Absolute Contraindications to hyperbaric O2 therapy : reason Untreated pneumothoraxGass emboli, tension pneumothorax, pneumomediastinum bleomycinInterstitial pneumonitis cisplatinImpaired wound healing disulfiramInhibits superoxide dismutase doxorubicincardiotoxicity Relative contraindication – asthma, claustrobia,eustacian tube dysfunction, high fever, seizure.

Complications of hyperbaric O2 therapy Barotrauma  Middle ear  Sinus  Dental Pulmonary – cough, burning pain Lens morphology Cataract O2 toxicity in CNS -- seizure

Hyperbaric oxygen therapy – breathinh 100% O2 under increased atmospheric pressure

Oxygen therapy 1.Meaning of hypoxemia, hypoxia 2.Types of hypoxia 3.Indications for controlled O2 therapy and why it is necessary 4.to control the O2 concentration while treating hypoxia 5.Monitoring during O2 therapy 6.Type of devices to deliver O2 7.Physiologic effects of O2 8.Types of hyperbaric O2 chamber 9.Indications for hyperbaric O2 therapy 10.Toxic effect of O2