Oxygenation and Acid and Base Balance

Oxygenation and Acid and Base Balance Learning Objectives 1. 2. 3. 4. Define the physiological limits of normal blood gases. List the factors that affect oxygen delivery and consumption. Describe the criteria for intubating and extubating a patient. Describe the anticipated arterial blood gas changes that might be obtained in patients with acute metabolic acidosis, acute and chronic respiratory acidosis, acute respiratory alkalosis and compensated metabolic acidosis. Normal Blood Gas Limits Factors that affect oxygen delivery and consumption Factors that affect oxygen delivery     Changes in cardiac output Haemoglobin saturation Haemoglobin concentration Carbon dioxide, pH levels and body temperature. - Carbon dioxide:  When there is Co2 in the blood, it will react with water to form HCO3- and water.  This will cause more H+ being produced which will decrease the blood pH. - -  This will shift the oxygen-haemoglobin curve to the right -> decreases affinity for oxygen -> increased oxygen unloading to peripheral tissues and less oxygen uptake. Blood pH levels:  Same as above.  In alkalosis there is shifting to the left -> increased Hb affinity for oxygen. Body temperature:  Increases will shift the graph to the right -> decreased Hb affinity for oxygen and increased oxygen unloading.  Decreases will shift to the left -> increases Hb affinity for oxygen and decreased oxygen unloading. Factors that affect oxygen consumption        Metabolic demand Active tissues: - Such as muscles during exercise. Physical activity. - Higher intensity needs higher consumption. - Higher activity leads to increased oxygen ventilation. Body size and consumption: - Larger people have a higher oxygen demand and higher oxygen consumption as they have greater mass tissue and higher lead body mass (muscles). Age - Decreases with age by 2% per year after 30s. Gender - Males have greater consumption than females. Health conditions - Fever: increases metabolic demand as the body fights of the infection ot inflammation -> needs higher oxygen demands. - Hypothyroidism: this is because there is reduced metabolic rate and liver oxygen consumption. Criteria for intubating and extubating a patient. criteria for intubation          Respiratory failure -> hypoxic or hypercapnic Apnoea Reduced levels of consciousness -> less than or equal to 8. Rapid change of metal status Airway injury Impending airway compromise Upper airway obstruction. Higher risk of aspiration Trauma to the larynx  Neuromuscular weakness. Contraindications for intubation           When not possible consider a surgical airway. Conditions that make it hard or impossible to pass an endotracheal tube. Severe airway trauma or obstruction. Laryngeal edema Laryngeal fracture Epiglottitis Laryngotracheobrnochitis Base of skull fracture and CSF rhinorrhoea. - Should be avoided as there is a risk of tube reaching the cranium or chasing CSF to leak through the nose. Bleeding disorders: - Coagulopathies - Bleeding disorders. - All of these increase the risk of bleeding during intubation. Nasal polyps, abscess or foreign body: - These conditions obstruct the tube and may make intubating challenging. - Previous nasal surgery can be a relative contraindications. Criteria for Extubating       Disease resolution Adequate oxygenation and gas exchange (PaO₂ > 60 mmHg on FiO₂ < 40%, stable chest X-ray). Stable hemodynamic: - Minimal vasopressor use is needed. - Stable cardiac rhythm. Stable mentation: - Rousable no continuous sedation. Spontaneous breathing trial: - Criteria for successful for spontaneous breathing trial:  Awake and easily arousable.  Able to follow commands.  Minimal respiratory secretions.  Intact gag and cough reflex. Cuff leak test: - Cuff leak test to check for laryngeal edema.  Laryngeal edema can cause upper airway obstruction following extubating.