![]() RT: For Decision Makers in Respiratory Care Mechanical Ventilation and the COPD Patient The challenge of mechanically ventilating a patient with COPD can be met by preventing autoPEEP and dynamic hyperinflation. ![]() Mechanical Ventilation And The Copd Patient PaCO2 is proportional to VCO2/VA VCO2 = CO2 production by the body VA = alveolar ventilation an increase in arterial pCO2 can occur by one of three possible mechanisms: presence of excess CO2 in the inspired gas decreased alveolar ventilation increased production of CO2 by the body CAUSES Inadequate Alveolar Ventilation central respiratory depression drug depression of respiratory centre (eg by opiates, sedatives, anaesthetics) neuromuscular disorders lung or chest wall defects airway obstruction inadequate mechanical ventilation Over-production of CO2 -> hypercatabolic disorders Malignant hyperthermia Thyroid storm Phaeochromocytoma Early sepsis Liver failure Increased Intake of Carbon Dioxide Rebreathing of CO2-containing expired gas Addition of CO2 to inspired gas Insufflation of CO2 into body cavity (eg for laparoscopic surgery) EFFECTS CO2 is lipid soluble -> depressing effects on intracellular metabolism RESP increased minute ventilation via both central and peripheral chemoreceptors CVS increased sympathetic tone peripheral vasodilation by direct effect on vessels acutely the acidosis will cause a right shift of the oxygen dissociation curve if the acidosis persists, a decrease in red cell 2,3 DPG occurs which shifts the curve back to the left CNS cerebral vasodilation increasing cerebral blood flow and intracranial pressure central depression at very high levels of pCO2 potent stimulation of ventilation this can result in dyspnoea, disorientation, acute confusion, headache, PATHOPHYSIOLOGY arterial pCO2 is normally maintained at a level of about 40 mmHg by a balance between production of CO2 by the body and its removal by alveolar ventilation. DEFINITION Respiratory acidosis = a primary acid-base disorder in which arterial pCO2 rises to an abnormally high level. ![]()
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