Principles of Mechanical Ventilation

1. Principles of Mechanical Ventilation RET 2284 Module 6.0 Ventilator Management - Improving Ventilation/Oxygenation

2. Improving Ventilation / Oxygenation The first 30 – 60 minutes following initiation of ventilation are generally spent evaluating vital signs, breath sounds, ventilator parameters, lung compliance and resistance, the artificial airway, and documenting patient response to therapy After that initial phase, the RT is often concerned with improving ventilation and oxygenation and managing the patient-ventilator system

3. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • A change in will often be needed when a patient is first placed on mechanical ventilation to correct for respiratory alkalosis or acidosis; this is facilitated by making a change inVT or rate (f)

4. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Methods of Changing Ventilation Based on PaCO2 and pH If it is appropriate to keep rate (f) constant and change VT, the equations is as follows: Desired VT = Known PaCO2 x Known VTDesired PaCO2

5. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Methods of Changing Ventilation Based on PaCO2 and pH If it is appropriate to keep VT the same and change rate (f), then the equations is as follows: Desired f = Known PaCO2 x Known fDesired PaCO2

6. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Respiratory Acidosis • Volume and Pressure Ventilation Changes • When PaCO2 is elevated (>45 mm Hg) and pH is decreased (<7.35), respiratory acidosis is present and VA is not adequate • Causes • PE, Pneumonia • Airway disease (e.g., severe asthma attack) • Pleural abnormalities (e.g., effusions) • Chest wall abnormalities • Neuromuscular disease • CNS problems .

7. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Respiratory Acidosis • Volume and Pressure Ventilation Changes Guideline: • VT to 8 – 12 mL/kg ideal body weight (based on patient’s pulmonary problem) • Maintain plateau pressure <30 cm H2O • If VT is already high and/or Pplateau are already high, then f should be increased • Read example 1, 2 and 3: Respiratory Acidosis, Increasing VT, page 259 – 260 (Pilbeam)

8. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Respiratory Alkalosis • Volume and Pressure Ventilation Changes • When PaCO2 is decreased (<35 mm Hg) and pH increases (>7.35), then respiratory alkalosis is present and alveolar ventilation is excessive • Causes • Hypoxia with compensatory hyperventilation • Parenchymal lung disease • Medications • Mechanical ventilation • CNS disorders • Anxiety • Metabolic disorders

9. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Respiratory Alkalosis • Volume and Pressure Ventilation Changes Guideline: • Volume ventilation: f, and if necessary, VT • Pressure ventilation: f, and if necessary, pressure • Read example 1 and 2: Respiratory Alkalosis, Decreasing the rate, page 261 (Pilbeam)

10. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Metabolic Acidosis and Alkalosis • Treatment of metabolic acidosis and alkalosis should focus on identifying those metabolic factors that can cause these acid-base disturbances

11. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Metabolic Acidosis and Alkalosis • Metabolic Acidosis • Causes • Ketoacidosis (alcoholism, starvation, diabetes) • Uremic acidosis (renal failure to excrete acid) • Loss of bicarbonate (diarrhea) • Renal loss of base following administration of carbonic anhydrase inhibitors (e.g., Diamox) • Overproduction of acid (lactic acidosis) • Toxin ingest that produce acidosis (salicylate, ethylene glycol [antifreeze], methanol

12. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Metabolic Acidosis and Alkalosis • Metabolic Acidosis • Treatment should first deal with the cause of the acidosis • Secondly, assess the need to reverse the acidemia with some form of alkaline agent

13. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Metabolic Acidosis and Alkalosis • Metabolic Acidosis • These patients are often struggling to lower their PaCO2 to compensate for the metabolic acidemia. As a consequence, these patients are at risk for developing respiratory muscle fatigue • If the patient is losing the struggle to maintain high with spontaneous breathing, assisted ventilation may be necessary to avoid respiratory failure. It is then appropriate to keep the pH (7.35 – 7.45)

14. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Metabolic Acidosis and Alkalosis • Metabolic Alkalosis • Causes • Loss of gastric fluid and stomach acids (vomiting, nasogastric suctioning) • Acid loss in the urine (diuretic administration) • Acid shift into the cells (potassium deficiency) • Lactate, acetate, citrate administration • Excessive bicarbonate loads (bicarbonate administration)

15. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Metabolic Acidosis and Alkalosis • Metabolic Alkalosis • Treatment involves correcting the underlying cause and reversing those factors leading to the alkalosis. In severe cases, carbonic anhydrate inhibitors, acid infusion, and low bicarbonate dialysis my be required • Only in rare circumstances does partial respiratory compensation of metabolic alkalosis occur – PaCO2 will usually not rise higher than 55 mm Hg (Remember that as the CO2 rises, the PaO2 falls)

16. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Mixed Acid – Base Disturbances • Combined Respiratory Alkalosis and Metabolic Acidosis • Read case studies: Pilbeam, pg. 262 – 263 • Combined Respiratory Acidosis and Metabolic Alkalosis • Read case study: Pilbeam, pg. 263

17. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Increased Physiological Dead Space • If pure respiratory acidosis persists even after alveolar ventilation has been increased, the patient may have a problem with increased dead space • Causes • Pulmonary emboli • Low cardiac output  low pulmonary perfusion • High alveolar pressure (PEEP)   pulmonary blood flow • Air trapping   pulmonary perfusion

18. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Increased Metabolism and Increased CO2 Production • Read case study: Pilbeam, pg. 264 • Metabolic rate and VCO2 are increased in the following patients: • Fever • Sepsis • Burns • Multiple trauma and multiple surgical procedures • Hyperthyroidism • Seizures .

19. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Increased Metabolism and Increased CO2 Production • In these patients is increased and WOB is elevated Treatment Options • Increase machine rate to WOB: may cause auto-peep • Add pressure support for spontaneous breaths to WOB through ET and circuit • Switch to PC-CMV, use sedation to WOB

20. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Intentional Iatrogenic Hyperventilation • Definition • Deliberate hyperventilation in patients with acute head injury and increased intracranial pressure (ICP) • Hyperventilation reduces PaCO2 which causes vasoconstriction of cerebral blood vessels and decreases blood flow to the brain and is believed to lower increased intracranial pressure ICP

21. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Intentional Iatrogenic Hyperventilation • Current therapy guideline for head injuries with increased ICP do not recommend prophylactic hyperventilation (PaCO2 <25 mm Hg) during the first 24 hours - may cause cerebral ischemia and cerebral hypoxemia

22. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Intentional Iatrogenic Hyperventilation • Hyperventilation may be needed for brief periods when acute neurological deterioration is present and ICP elevated • Mild hyperventilation (PaCO2 30 – 35 mm Hg) may be used for longer periods in a situation in which increased ICP is refractory to standard treatment The practice of iatrogenic hyperventilation still remains controversial

23. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Permissive Hypercapnia (PHY) • Definition • Deliberate limitation of ventilatory support to avoid lung overdistention and injury of lung • ARDS • Status asthmaticus • PaCO2 values are allowed to rise above normal • ≥50 – 150 mm Hg • pH values are allowed to fall below normal • ≥7.10 – 7.30 • Most researchers agree pH ≥7.25 is acceptable

24. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Permissive Hypercapnia (PHY) • PaCO2 accompanied PaO2 • O2 administration must be provided and monitored closely • PaCO2 stimulates the drive to breath • Appropriate to provide sedation to patients in whom PHY is being employed

25. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Permissive Hypercapnia (PHY) • Procedures for Managing PHY • Allow PaCO2 to rise and pH to fall without changing mandatory rate or volume • Sedate the patient • Avoid high ventilating pressures • Maintain oxygenation • Reduce CO2 production • Paralyze • Cool • Restrict glucose

26. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Permissive Hypercapnia (PHY) • Procedures for Managing PHY • Keep pH >7.25 • Sodium bicarbonate • Tris-hydroxiaminomethane (an amino buffer) • Carbicarb (mixture of sodium carbonate and bicarbonate

27. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Permissive Hypercapnia (PHY) • Contraindications and Effects of PHY • Head trauma • Intracranial disease • Intracranial lesions

28. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Permissive Hypercapnia (PHY) • Relatively contraindicated in the following • Cardiac ischemia • Left ventricular compromise • Pulmonary hypertension • Right heart failure

29. Improving Ventilation / Oxygenation • Correcting PaCO2 Abnormalities • Permissive Hypercapnia (PHY) The use of PHY is restricted to situations in which the target airway pressure is at its maximum and the highest possible rates are being used The risks of hypercapnia are considered by some to be preferable to the high Pplat required to achieve normal CO2 levels Read Case Study: Pilbeam, pg. 265 – 266

30. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Adjusting FiO2 • Every attempt should be made to maintain the FiO2 <0.40 to 0.50 to prevent the complications of O2 toxicity while keeping the PaO2 between 60 and 90 mm Hg • This goal is not always possible and sometimes a higher FiO2 is required • The SpO2 can be used to titrate FiO2, with the goal of maintaining the SpO2 >90% • The SaO2 on an ABG is used to establish the relationship with the current SpO2 .

31. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Adjusting FiO2 • ABGs are obtained after mechanical ventilation is initiated and compared with FiO2 being delivered and the SpO2 to establish their relationships • A linear relationship exists between PaO2 and FiO2 as long as VE, CO, Shunt, VD/VT remain fairly constant (cardiopulmonary status) .

32. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Adjusting FiO2 • Because of the linear correlation between PaO2 and FiO2 the following equation can be used to select the desired FiO2 to achieve a desired PaO2: Desired FiO2 = PaO2 (desired) x FiO2 (known) PaO2 (known)

33. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Adjusting FiO2 Exercise After being supported on a ventilator for 30 minutes, a patient’s PaO2 is 40 mm Hg on an FiO2 of 0.50. Acid-base status is normal and all other ventilator parameters are within the acceptable range. What FiO2 is required to achieve a desired PaO2 of 60 mm Hg?

34. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Adjusting FiO2 Desired FiO2 = PaO2 (desired) x FiO2 (known) PaO2 (known) Desired FiO2 = (60 mm Hg) (0.50 FiO2) 40 mm Hg Desired FiO2 = 0.75

35. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Selection of FiO2 or Adjustment of Paw • Maintaining an FiO2 >60 may lead to: • O2 toxicity • Absorption atelectasis • Lower limits of target PaO2 is 60 mm Hg • Lower limits of target SpO2 is 90% _ _

36. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Selection of FiO2 or Adjustment of Paw • When PaO2 remains very low on high FiO2, significant shunting, V/Q abnormalities , and/or diffusion defects are present - other methods to improve oxygenation, besides increasing FiO2, must be considered • Paw • PEEP • HFOV • APRV _ _

37. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Selection of FiO2 or Adjustment of Paw • Paw can be used to increase the PaO2 • Factors that affect Paw during PPV • PIP • PEEP • Auto-PEEP • I:E ratio • Respiratory rate • Inspiratory flow patterns _ _ _

38. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Selection of FiO2 or Adjustment of Paw • Paw is a major determinant of oxygenation in patients with ARDS • Mean alveolar pressure  oxygenation • Alveolar recruitment  oxygenation • Typical method to increase Paw • PEEP • Other methods to increase Paw • HFOV • APRV _ _ _ _

39. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Selection of FiO2 or Adjustment of Paw • Paw must be monitored closely to prevent: • Air trapping • Overdistention • Barotrauma (e.g. pneumothorax) • Venous return • CO _ _

40. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Goals of PEEP • Enhance tissue oxygenation • Maintain a PaO2 above 60 mm Hg, and SpO2 ≥90% at an acceptable pH • Restore FRC • These goals my be accompanied by the opportunity to reduce the FiO2 to safer levels (<0.50) as PEEP becomes effective • Must maintain cardiovascular function and avoid lung injury

41. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Minimum or Low PEEP • PEEP at 3 – 5 cm H2O to help preserve a patient’s normal FRC • Therapeutic PEEP • PEEP >5cm H2O • Used in the treatment of refractory hypoxemia caused by increased intrapulmonary shunting and V/Q mismatching accompanied by a decreased FRC and pulmonary compliance

42. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Optimal PEEP • The level of PEEP at which the maximum beneficial effects of PEEP occur • O2 transport • FRC • Compliance • Shunt

43. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Optimal PEEP • The level of PEEP is considered optimum because it is not associated with profound cardiopulmonary side effects • Venous return • CO • BP • Shunting • VD/VT • Barotrauma • Volutrauma • Accompanied by safe levels of FiO2

44. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Indications for PEEP Therapy • Bilateral infiltrates on chest radiograph • Recurrent atelectasis • Reduced CL • PaO2 <60 mm Hg on high FiO2 of >0.5 • PaO2/FiO2 ratio <200 for ARDS and <300 for ALI • Refractory hypoxemia: PaO2 increases <10 with FiO2 increase of 0.2

45. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Specific clinical disorders that may benefit from PEEP • ALI • ARDS • Cardiogenic PE • Bilateral, diffuse pneumonia

46. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Application of PEEP • Increased in increments of 3 – 5 cm H2O in adults, 2 – 3 cm H2O in infants • Target acceptable PaO2/FiO2 ratio at a safe FiO2 • >300 (e.g., PaO2 = 100, with FiO2 = 0.33 (optimal, but not always realistic)

47. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Application of PEEP • Patient Appearance • Color, level of consciousness, anxiety – a sudden deterioration may indicate cardiovascular collapse or pneumothorax • Blood Pressure • BP of 20 mm Hg systolic drop is significant • Breath Sounds • Barotrauma, e.g., pneumothorax

48. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Application of PEEP • Ventilator Parameters • VT, Flow, PIP, plateau pressure, VE

49. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Application of PEEP • Static Compliance (CS) • As PEEP progressively restores FRC, compliance should increase

50. Improving Ventilation / Oxygenation • Oxygenation Using FiO2 and PEEP • Positive End Expiratory Pressure (PEEP) • Application of PEEP • Static Compliance (CS) • Too Much PEEP  Overdistention  CS