Effects of Positive Pressure Ventilation PDF

Chapter 2 Effects of Positive Pressure Ventilation  Positive Pressure Ventilation Positive pressure ventilation (PPV) is an unnatural way to deliver gases into the lungs. PPV can affect and alter the normal functions of these systems: – Pulmonary, cardiova...

Chapter 2 Effects of Positive Pressure Ventilation  Positive Pressure Ventilation Positive pressure ventilation (PPV) is an unnatural way to deliver gases into the lungs. PPV can affect and alter the normal functions of these systems: – Pulmonary, cardiovascular, hemodynamic, renal, hepatic, abdominal, gastrointestinal, nutritional, and neurologic.  Positive Pressure Ventilation During normal spontaneous breathing, a negative pressure gradient is required (i.e., the pressure within the lungs is less than atmospheric pressure). During PPV, gas flow is delivered to the lungs with a positive pressure gradient (i.e., airway pressure is greater than alveolar pressure)  During PPV, the volume delivered to the patient is mainly determined by one of two ways: Pulmonary – Set pressure Consideratio (during pressure- ns controlled ventilation) or – Set volume (during volume-controlled ventilation)  Air trapping, aka auto- PEEP and intrinsic PEEP, are two issues related to PPV The occurrence and degree of air trapping Pulmonary and auto-PEEP may be reduced by using... Considerati – Lower tidal volume ons or frequency – Higher peak inspiratory flow – Shorter inspiratory time  Positive pressure in the lungs directly increases the intrathoracic pressure. Cardiovascul ar Through a series of Consideratio physiologic events (next ns slide) the cardiac output and oxygen delivery are reduced. Cardiovasc ular Considerat ions  Positive pressure in the lungs can negatively affect the hemodynamic status: Hemodyna – ↓ pulmonary blood mic volume and ↑ systemic blood volume Consideratio – ↓ CVP ns i c – ↓ PAP a c. h r o e… – ↓ ventricular filling r t a a us I n t C pressure and output i g h res H ssu Pre Hemodynamic Considerations  Use of PPV with positive end-expiratory pressure (PEEP) can Hemodynami lead to c – ↑ pulmonary artery Consideratio pressure ns – ↑ CVP – ↓ aortic pressure – ↓ cardiac output Hemodynamic Considerations  Renal Considerations PPV lowers the cardiac output and perfusion to major organs. Since kidneys receive about 25% of circulating blood volume, a reduction in blood volume (e.g., hypovolemia) or cardiac output (e.g., PPV) may lead to renal insufficiency and eventual renal failure.  Signs of renal insufficiency / failure – Reduced urine output (oliguria) (normal urine output >400 mL in 24 hrs or >160 mL in 8 hours) – Elevation of blood urea Renal nitrogen (BUN) (normal 10 to 20 Consideratio mg/dL) ns – Elevation of creatinine (normal 0.7 to 1.5 mg/dL) – Other indicators of renal failure (next slide) Renal Considerations  Effects of renal failure – Reduced filtration of wastes – Ineffective regulation of fluid (e.g., fluid retention), electrolytes (e.g., hyperkalemia), and acid- Renal base balance (e.g., metabolic acidosis) Considerati – Reduced clearance of ons drugs (those depend on glomerular filtration, tubular secretion, and reabsorption) – Increased likelihood of drug toxicity  PPV lowers the cardiac output and perfusion to major organs Hepatic Since the liver Consideratio receives about 15% of ns circulating blood volume, hepatic perfusion also decreases when PEEP is added to PPV  Hepatic Considerations Indicators of liver dysfunction – Increased coagulation time (prothrombin time >4 sec over control) – Increased bilirubin (>50 mg/L) – Decreased albumin level (15 cm H2O) and increased IAP (>20 cm H2O) can adversely affect the cardiovascular, renal, and pulmonary systems  Abdominal Considerations  Decreased perfusion to the GI tract and medications used in mechanical ventilation may cause Gastrointesti – Erosive esophagitis nal – Stress-related Consideratio mucosal damage ns – Diarrhea – Decreased bowel activity (e.g., opioids) Gastrointestinal Considerations  Nutritional Considerations Malnutrition Excessive nutritional support Factors leading to ↑ CO2 production respiratory muscle fatigue ↑ Work of breathing (see next slide) Diaphragmatic dysfunction Ventilatory insufficiency and failure Nutritional Considerations  Nutritional Considerations Nutritional support – Preserve respiratory muscle strength – Prevent ventilatory failure due to fatigue – Resting energy expenditure (REE) Activity or stress factor (e.g., infection, burn) – Total parenteral nutrition (TPN) Dextrose-based TPN (↑O2 usage ↑CO2 production) Fat-based TPN (↑calorie ↓CO2 production)  Neurologic Considerations Hyperventilation – CO2 is a cerebral vasodilator – Hyperventilation causes vasoconstriction – Use of hyperventilation to lower ICP Closed-head injury Temporary effectiveness – Neurologic changes are noted on the next slide. Neurologic Considerations  Neurologic Considerations Ventilatory and oxygenation failure – Hypercapnia – Respiratory acidosis – Hypoxemia – Secondary polycythemia – Electrolyte changes – Neurologic impairment Neurologic Considerations Indicators of neurologic impairmen – Headache – Mental status changes – Motor disturbances – Ocular abnormalities  Neurologic Considerations