Intro to Vents – Part 2: Mechanical Ventilation Modes PDF

Intro to Vents – Part 2: Operating Modes of Mechanical Ventilation Chang’s Chapter 4 Lab: 1 and 1B Vent Graphics - Scalars Vent Graphics - Scalars  MODE Introduction Ventilator mode can be defined as a set of operating characteristics that control how the ventilator funct...

Intro to Vents – Part 2: Operating Modes of Mechanical Ventilation Chang’s Chapter 4 Lab: 1 and 1B Vent Graphics - Scalars Vent Graphics - Scalars  MODE Introduction Ventilator mode can be defined as a set of operating characteristics that control how the ventilator functions. Options for breath delivery are referred to as modes of ventilation.  MODE Introduction There are numerous modes of ventilation available in different ventilators. Two or more of these modes are often used together to achieve certain desired effects. For example, spontaneous plus PEEP is the same as CPAP.  MODE Introduction Operating mode can be described by the way a ventilator is triggered or cycled. That is, what variables are limited during inspiration, and whether or not the mode allows mandatory, supported, spontaneous breaths or both.  MODE Introduction BASIC Modes of operation: Controlled Mechanical Ventilation Assist Controlled Mech. Vent. (A/C) Intermittent Mandatory Vent. (older) (IMV) Synchronized Intermittent Mandatory Vent. (newer) (SIMV) Pressure Support Vent (PCV) Spontaneous (CPAP)  CONTROL Mode Ventilator delivers the preset tidal volume at a set time interval. Should only be used when the pt. is properly medicated with a combination of sedatives, respiratory depressants, and/or neuromuscular blockers. Patient is unable to spontaneously breathe.  Assist Control Mode Pt. always receives a mechanical breath, whether triggered by the vent or by the patient, i.e. the pt. can spontaneously breathe. Indicated when full ventilatory support is needed. Used when pt. has a stable respiratory drive (10-12 bpm spontaneous rate) Assisted & Machine  A/C (cont’d) The generally accepted set minimum rate is 2-4 breaths less than the pt.’s assist rate, (respiratory rate), or a minimum of 8 - 10 breaths.  A/C (cont’d) Advantages include a very small WOB when sensitivity and flow is set properly. This mode allows the pt. to control the RR. Disadvantage include alveolar  IMV Mode Pt. can breathe spontaneously at any tidal volume between the mechanical breaths. Primary disadvantage is chance for breath stacking; therefore, care should be taken to set the high-pressure limit properly to reduce risk of barotrauma.  SIMV Mode Mandatory breaths are synchronized with the pt.’s spontaneous efforts to avoid breath stacking. SIMV has basically replaced IMV to rectify “breath stacking.”  SIMV Mode (cont’d) “Synchronized Window” refers to the time just prior to time triggering in which the vent is responsive to the pt.’s effort (0.5 sec is typical). SPONTANEOUS & MACHINE  SIMV Mode (cont’d) Advantages include maintaining respiratory muscle strength, reduces V/Q mismatch, decreases mean airway pressure, and helps in weaning the patient from ventilation.  SIMV Mode (cont’d) Disadvantage usually has to do with trying to wean pt. too rapidly, leading to increased WOB and muscle fatigue.  PSV Mode / Adjunct Used to lower the WOB and augment a patient’s spontaneous tidal volume. When PSV is used with SIMV, it lowers the O2 consumption because of the decrease in WOB.  PSV adjunct (cont’d) PSV applies a preset pressure plateau to the pt. during a spontaneous breath. PSV breaths are patient triggered, pressure limited, and flow cycled. PSV helps to overcome resistance of the artificial airway.  Pressure-Controlled Ventilation The pressure-controlled breaths are time triggered by a preset respiratory rate. Once inspiration begins, a pressure plateau is created and maintained for a preset inspiratory time. Remember Volume = Flow x Time  PCV (Cont.) Typically used in ARDS where it takes excessive pressure in volume cycled modes to ventilate a pt., leading to barotrauma. In other words, very non-compliant “stiff” lungs. (Low compliance).  Adjuncts to modes Add the following parameters to many different types of modes: 1. Pressure Support (PS) 2. Positive End Expiration Pressure (PEEP)  SPONTANEOUS Not an actual mode since rate and tidal volume during spontaneous breathing are determined by patient. SPONTANEOUS With PEEP ZEEP  SPONTANEOUS (cont’d.) Apnea ventilation is a safety feature used for spontaneous mode. In the event the patient becomes apneic, the vent will kick on delivering breaths as pre-set.  PEEP PEEP increases the end-expiratory or baseline airway pressure to a value greater than atmospheric and is often used to improve the pt.’s O2 status, especially if refractory. PEEP is not a stand-alone mode but is used in conjunction with other  PEEP When PEEP is applied to a spontaneously breathing pt., then it is CPAP. Two major indication for PEEP are: Intrapulmonary shunt leading to refractory hypoxemia; Decreased functional residual capacity and lung compliance.  Positive End-Expiratory Pressure Alveolar pressure at end-expiration is above atmospheric pressure. The set PEEP is aka Extrinsic PEEP Not the same as Auto PEEP (aka Intrinsic PEEP) Vent Graphics  Complications of PEEP Complications and hazards associated with PEEP include: (1) decreased venous return and cardiac output, (2) barotrauma, (3) increased intracranial pressure, and (4) alterations of renal functions and water metabolism.  Barotrauma Barotrauma is lung injury that results from the hyperinflation of alveoli past the rupture point. Although each patient is different, a PEEP greater than 10 cmH20 (or mean airway pressure >30 cm H20, or a peak inspiratory pressure >50 cm H20) is associated with an increased incidence of alveolar rupture or  Increased Intracranial Pressure In patients with normal lung compliance, PEEP may raise the intracranial pressure (ICP) (normal 8 to 12 cmH20) due to an impedance of venous return from cerebral perfusion. However, in patients with ARDS or noncompliant lungs, transmission of the excessive pressure generated by PEEP is minimal and it does not cause as much adverse effect on a patient's ICP.  Renal response to PEEP : Fluid retention, :  urine output :  ADH :  mean renal arterial perfusion pressure :  urine flow, and redistribution of blood flow from the cortex :  creatine clearance  INVERSE RATIO VENTILATION (lRV) The ratio of inspiratory time (I time) to expiratory time (E time) is known as the I:E ratio. Inverse ratio ventilation (IRV) improves oxygenation by: (1) reduction of intrapulmonary shunting, (2) improvement of V/Q matching, and (3) decrease of deadspace ventilation.  INVERSE RATIO VENTILATION (lRV) Two notable changes are observed during IRV. They are: (1) Increase of mean airway pressure. (2) presence of auto-PEEP. These two changes are likely the reason for the improvement of shunting and hypoxemia in ARDS patients.  Increase of Mean Airway Pressure To achieve the same degree of ventilation and oxygenation, IRV requires a lower peak airway pressure and PEEP, but a higher mean airway pressure (mPaw) than conventional mechanical ventilation. The increase in mPaw during IRV helps to reduce shunting and improve oxygenation in ARDS patients.  Adverse Effects of IRV Potential hazards of IRV: A higher rate of transvascular fluid flow or flooding induced by an increased alveolar pressure. This condition may induce or worsen pre-existing pulmonary edema. Patients receiving IRV are often agitated. They may require sedation and neuromuscular blocking agents to facilitate ventilation.  Alarms Alarms may be audible, visual or both. Visual alarms can be colored lights or messages. Audible alarms normally pertain to input/output.  Alarms Input Alarms: Power, electrical, or pneumatic. Control alarms: Those alarms when a set variable will not function properly; ( I:E ratio, rate or flow).  Alarms Output Alarms: Pressure (set 10 to 15 cmH2O above) Volume = exhaled volume Time = (f) respiratory rate Minute Volume = RR x Vt  Alarms Inspired Gas Temperature of aerosol FiO2 high or low Importance of Alarms (Sentinel Events)  Alarms Alarm Fatigue Throughout the hospital, there are numerous alarms from doorways, to IV pumps, to vents, to every piece of equipement we use. Healthcare workers can become "immune" to the sounding of alarms. Always be perceptive of alarms and respond to them appropriately.