2IntroductionSpecially designed pumps that support Ventilatory functions of RS and improve oxygenation through high O2 and positive pressure.
3Indications for MV Hypercarbic resp failure: Hypoxemic Resp Failure: Basically decreased Min Ventilation or increased Physiologic dead space.Neuromuscular disease:M. Gravis, Ascending polyradiculopathy, MyopahtyMuscle fatigue diseases: Asthma, COPD, restrictive lung diseasePco2 >50mm Hg and Ph <7.3Hypoxemic Resp Failure:Basically a V/Q mismatch and shunt problemPneumonia, Pulm edema, ARDS, Pulm hemorrhageSao2 <90 despite >60% fio2.
4Other indications for MV Increased ICP – controlled Hyperventilation to reduce cerebral blood flowPost Op pulmonary HTN: to improve pulmonary hemodynamicsCHF in presence of Myocardial ischemia: To reduce preload and afterload and to reduce work of breathingPrevent aspiration of Gastric contents: unstable patients needing Lavage for drug overdose and EGD
5Physiologic aspects of MV Hypoxia : fio2Hypercarbia: TV x RR = Min VentilationPEEP helps maintain patency of alveoli – reverses hypoxemia and atelectasis by improving V/Q matchingNormal is Can be increased if refractory hypoxemia needing Fio2 >0.6
6Modes of ventilation O2 by Nasal cannula, ventimask, Nonrebreather Non Invasive Positive pressure ventilation: CPAP and BIPAPInvasive ventilation:Assist controlSIMV
7Establishing and maintaining airway Cuffed ETT is used to maintain Positive pressure and prevent aspirationMedications used:Sedatives – avoid long acting benzos. Use Propofol or etomidateAnalgesics – Avoids morphine – can worsen bronchospasm. Use fentanyl.Paralyzing agents – Succinylcholine should be avoided in renal failure, Tumor lysis, Hyperkalemia.
9TerminologyModes:refers to the manner in which ventilator breaths are triggered,cycled and limited. SIMV, ACTrigger: defines what the ventilator senses to initiate an assisted breath -an inspiratory effort or time based signalCycle: refers to factors that determine the end of inspiration – volume, pressure or flow or time cycled.Limiting factors: are operator specific values: ex Airway pressure.
10Assist control modeInspiratory cycle is initiated by inspiratory effort of pt or by timer signal ( back up rate)Every breath delivered consists of operator specified TV.Vent rate is determined by either by pt or Operator specified backup rate – which ever is higher
11ACMVAdvantages:Often used for initiation of MV – to ensure backup min Ventilation and synchronization of vent cycle with pts insp effort.Disadvantages:-Respiratory Alkalemia:leading to myoclonus and seizures-Dynamic hyperinflation – auto PEEP and barotrauma, decreased Cardiac output.
12SIMV Pt is allowed to breath spontaneously Preferred in pts with intact resp driveFixed mandatory breaths are delivered in addition to pts RR.Only the preset number of breaths are ventilator assisted.Total respiratory rate is Pts RR + Preset rate
13SIMV Advantages: Exercise respiratory muscles Easy to wean Disadvantages:-difficult to use in tachypnea- as dysynchrony might occur-cannot be used paralyzed pts.
14CPAP and BiPAP Non invasive ventilation Used early stages of respiratory distressPt should be alert and cooperativeCPAP can also be used to assess extubation potential in intubated pts.
15General support in ventilated patients Sedation – Propofol or etomidateAnalgesia - fentanyl is bestGI prophylaxis: H2 receptor blockers/ carafate/antacids – carafate is preferred as it doesn’t change gastric Ph – so less colonization by nosocomial organismsNutrition support: Early feeding is encouraged.Delayed Gastric emptying: Consider Reglan
16Complications of MV Pulmonary: Barotrauma ( if Pr >50cm H2O )Vent Associated Pneumonia –( If intubated >72 hrs) – G –ve rods, S.Aureus, Anaerobes.O2 toxicityTracheal stenosisRespiratory deconditioningHypotension – almost always responsive to Volume supportGI:Stress ulceration– H2 receptor blockers / sucralfateCholestasis – Total bilirubin < 4 mg/dl
17Weaning criteria - MVUpper airway functioning should intact – stridor or aspiration.Intact cough – mobilizes secretionsAlveolar ventilation: Ph 7.35 – 7.45, Sao2 >90 %,Fio2 <0.5, PEEP <5.Respiratory drive and chest wall function should be assessed ( TV, Insp Pressure, RR, VC)Weaning index: breathing frequency/ TV <105.VC >10 ml/kg, Insp Pr> -30 cm H2O.
18Methods of weaningShort term ventilated pts: 5 min/ hr. Gradually increased every hour.T Piece ( on O2)CPAPLong term ventilated pts:SIMV – decrease mandatory backup rate 2-4 breaths/min and reasses each time( if >25 or worsening PH indicates difficulty in weaning)PSV - Gradually reduce the pressure to below Peak insp pressures by 5cm H2O until the pressures Just equal to ET tube pressure (5-10 normally)