Faisal Malmstrom, Critical Care Department SKMC Oxygen Therapy Faisal Malmstrom, Critical Care Department SKMC

Carl Wilhelm Scheele Priestly and Lavoisier

ABC Air goes in and out, blood goes round and round. Any variation on this is a bad thing. Airway obstruction needs to be addressed immediately

Respiratory failure Type 1 (hypoxemic) Saturation < 90%. PaO2 <60 mm Hg Type 2 (hypercapnic) PCO2>50 mmHg, pH<7.35

Definitions Hypoxemia Hypoxia

Hypoxemia Low alveolar oxygen tension (ambient, hypoventilation) Ventilation-perfusion mismatch Right to left shunt (venous admixture) intracardiac extracardiac Impaired oxygen diffusion (uncommon)

Alveolar gases

V/Q mismatch Ventilated but not perfused: increased dead space ventilation, VT=VD+VA VD= VD equipment + VD anatomic + VD physiologic Perfused but not ventilated: shunt >20% Shunt fraction, minimal improvement with increased FiO2

Hypoxia Hypoxemic Hypoxia Anaemic Hypoxia Stagnant Hypoxia ( distributive or low CO) Histotoxic Hypoxia VDO2= CO x Hb x SAT/100 x 1.34ml/gHb+ (PaO2 x 0.003mlO2/100ml/mmHg)

Symptoms of Hypoxemia and Hypoxia Dyspnea, tachypnea. Hyperventilation +/- Cyanosis ( Hb, perfusion) >15g/l Impaired mental performance----coma Seizures, permanent brain injury Tachycardia/Hypertension – Hypotension/Bradycardia( 30 mmHg) Lactic acidosis

Indications for Oxygen therapy Cardiac and respiratory arrest Hypoxemia ( pO2 < 58.5 mmHg, Sat<90%) Hypotension ( Systolic BP < 100 mmHg) Low Cardiac Output and Metabolic Acidosis ( bicarbonate <18 mmol/l) Respiratory distress ( RR>24/minute) American College of Chest Physicians and NHLBI

Treatment I Empiric oxygen treatment Cardiac/ respiratory arrest Hypotension Respiratory Distress Trauma GCS decrease from any cause Postoperative

Treatment II Verify hypoxemia Pulse oximetry ABG’s Start Oxygen treatment. Treatment goal ( sat level) Administration mode, flow, when to stop

The oxyhaemoglobin dissociation curve showing the relation between partial pressure of oxygen and haemoglobin saturation Currie, G. P et al. BMJ 2006;333:34-36 Copyright ©2006 BMJ Publishing Group Ltd.

Charting Oxygen treatment Dodd, M E et al. BMJ 2000;321:864-865 Copyright ©2000 BMJ Publishing Group Ltd.

Bad medicine To withhold Oxygen out of fear of hypercarbic ventilatory failure is poor practice Identify patients at risk (COPD) Use Venturi masks 0.24 -0.28 ---- FiO2. ABG’s/ O2-sat to direct therapy Support ventilation (BiPAP, intubation)

Oxygen Hazards Fire ( airway fires) Tissue toxicity, pulmonary and retina Decreased hypoxemic drive and increased VD in COPD. Seizures (hyperbaric) Mucosal damage due to lack of humidity

Oxygen administration Low flow systems High Flow systems (HFOE)

Nasal Prongs

Bateman, N T et al. BMJ 1998;317:798-801 Copyright ©1998 BMJ Publishing Group Ltd.

Face Mask (“Hudson”)

Non-rebreather

Venturi Mask

Venturi valve

Bateman, N T et al. BMJ 1998;317:798-801 Copyright ©1998 BMJ Publishing Group Ltd.

Long term oxygen therapy prolongs survival in hypoxaemic patients with COPD when used for ≥15 hours/day. (Results from the nocturnal oxygen therapy trial (NOTT) and the MRC trial) Currie, G. P et al. BMJ 2006;333:34-36 Copyright ©2006 BMJ Publishing Group Ltd.

Take home message Acute empiric oxygen treatment is ok but hypoxemia should be verified with pulse oximetry and /or ABG’s when situation more stable. Oxygen is a drug and should be ordered as such: mode of administration, flow rate, FiO2 (venturi), treatment goal, monitoring, when to stop. Never withhold oxygen out of fear of possible hypercarbia Avoid overzealous treatment- Adequate saturation for the patient. COPD 88-90%