8 V/Q mismatchVentilated but not perfused: increased dead space ventilation, VT=VD+VAVD= VD equipment + VD anatomic + VD physiologicPerfused but not ventilated: shunt>20% Shunt fraction, minimal improvement with increased FiO2
9 Hypoxia Hypoxemic Hypoxia Anaemic Hypoxia Stagnant Hypoxia ( distributive or low CO)Histotoxic HypoxiaVDO2= CO x Hb x SAT/100 x 1.34ml/gHb+ (PaO2 x 0.003mlO2/100ml/mmHg)
16 Bad medicineTo withhold Oxygen out of fear of hypercarbic ventilatory failure is poor practiceIdentify patients at risk (COPD)Use Venturi masks FiO2.ABG’s/ O2-sat to direct therapySupport ventilation (BiPAP, intubation)
17 Oxygen Hazards Fire ( airway fires) Tissue toxicity, pulmonary and retinaDecreased hypoxemic drive and increased VD in COPD.Seizures (hyperbaric)Mucosal damage due to lack of humidity
18 Oxygen administration Low flow systemsHigh Flow systems (HFOE)
27 Take home messageAcute 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 hypercarbiaAvoid overzealous treatment- Adequate saturation for the patient. COPD 88-90%
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