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

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

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 in VT or rate (f)

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 VT Desired PaCO2

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 f Desired PaCO2

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 .

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)

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

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)

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

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

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

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)

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)

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)

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

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

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 .

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

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

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

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

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

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

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

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

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

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

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

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 .

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) .

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)

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?

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

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% _ _

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 _ _

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 _ _ _

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 _ _ _ _

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 _ _

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

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

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

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

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

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

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)

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

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

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

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

Optimized Lung Volume “Safe Window” Overdistension Edema fluid accumulation Surfactant degradation High oxygen exposure Mechanical disruption Derecruitment, Atelectasis Repeated closure / re-expansion Stimulation inflammatory response Inhibition surfactant Local hypoxemia Compensatory overexpansion Zone of Overdistention Injury “Safe” Window Volume Zone of Derecruitment and Atelectasis Injury Pressure

Application of PEEP

Improving Ventilation / Oxygenation Oxygenation Using FiO2 and PEEP Positive End Expiratory Pressure (PEEP) Application of PEEP Arterial PO2, FiO2, and PaO2/FiO2 The usual approach to the management of FiO2 and PEEP is to start with high FiO2 and incrementally decrease it as PEEP improves oxygenation

Improving Ventilation / Oxygenation Oxygenation Using FiO2 and PEEP Positive End Expiratory Pressure (PEEP) Application of PEEP Arterial to End-Tidal Carbon Dioxide Tension Gradient Normal P(a-et)CO2 gradient is 4.5 ± 2.5 (Pilbeam) Is lowest when gas exchange units are maximally recruited without being overdistended If P(a-et)CO2 gradient increases minimal acceptable values, it signifies that too much PEEP has been added and is producing a drop in cardiac output and in increase in VD/VT

Application of PEEP

Improving Ventilation / Oxygenation Oxygenation Using FiO2 and PEEP Positive End Expiratory Pressure (PEEP) Application of PEEP Arterial-to-Venous Oxygen Difference (C(a-v)O2) reflects O2 utilization by the tissues Normal value is 5 vol% Increases in C(a-v)O2 with increases in PEEP may indicate hypovolemia, cardiac malfunction, decreased venous return to the heart, and decreased cardiac output from PEEP

Application of PEEP

Improving Ventilation / Oxygenation Oxygenation Using FiO2 and PEEP Positive End Expiratory Pressure (PEEP) Application of PEEP Mixed Venous O2 Tension or Saturation Normal PvO2 = 35–40 mm Hg (minimal acceptable is 28 mm Hg) Normal SvO2 = 75% (minimal acceptable is 50%) PEEP usually improves PvO2 and SvO2 When PvO2 and/or SvO2 decrease, with a increase C(a-v)O2 increase, this indicates a decrease in cardiac output – TOO MUCH PEEP

Application of PEEP

Improving Ventilation / Oxygenation Oxygenation Using FiO2 and PEEP Positive End Expiratory Pressure (PEEP) Application of PEEP Cardiac Output Cardiac output provide key information about the body’s response to PEEP PEEP improves V/Q  Oxygenation  CO Too much PEEP  Overdistention  Venous return  CO

Application of PEEP

Improving Ventilation / Oxygenation Oxygenation Using FiO2 and PEEP Positive End Expiratory Pressure (PEEP) Application of PEEP Pulmonary Vascular Pressure Monitoring When using PEEP >15 cm H2O, it is important to closely evaluate the patient’s hemodyamic status, which may require the placement of a pulmonary artery catheter If pulmonary artery occluding pressure (PAOP), also known as “wedge pressure,” rises markedly as PEEP is increased, the lungs may be overinflated On the other hand, when PEEP rises, PAOP may be markedly decreased because of pulmonary blood flow is reduced as a result of decreased venous return to the right side of the heart

Application of PEEP

Improving Ventilation / Oxygenation Data From a Patient with ARDS on MV 24 Hours after Admission VT: 700 f: 6 VE: 6.6 FiO2: 0.8 PEEP BP HR PCWP CO CS PIP PaO2 PVO2 0 130/65 130 16 4.8 28 50 40 27 120/55 135 13 4.2 31 58 45 37 135/65 125 18 5.8 33 60 50 35 130/70 120 19 5.9 36 55 115 37 110/50 130 25 4.1 27 63 150 29 Can you find the optimal PEEP level?

Improving Ventilation / Oxygenation Oxygenation Using FiO2 and PEEP Positive End Expiratory Pressure (PEEP) Weaning From PEEP Patient should demonstrate an acceptable PaO2 on an FiO2 of <0.40 Must be hemodynamically stable and nonseptic Lung conditions should have improved CS, PaO2/FiO2 ratio Reduce PEEP in 5 cm H2O increments Evaluate SpO2 within 3 minutes to determine effect – if it falls <20% from previous PEEP level, the patient is ready to tolerate lower PEEP level. If SpO2 drops >20% place PEEP at previous level

Improving Ventilation / Oxygenation Oxygenation Using FiO2 and PEEP Positive End Expiratory Pressure (PEEP) Weaning From PEEP Wait between reductions in PEEP and reevaluate the initial criteria. If the patient is stable, reduce PEEP by another 5 cm H2O. This may take 1 hour or may require as long as 6 hours or more When the patient is at 5 cm H2O, an additional evaluation is necessary. If reducing the PEEP to zero result is a worsening of the patient, then it may be appropriate to leave the patient at 5 cm H2O until extubation