Mechanical Ventilation: Usage and Requirements

• Mechanical ventilation is used to manage patients
• Mechanical ventilation facilitates the ventilation of airways and lungs but cannot cause diffusion of gases
• We put ADULT patients on ventilators

Ventilator vs Respirator

• A ventilator is a device to assist breathing, while a respirator is a broader term
• Ventilation is defined as the gross movement of air in and out of the lungs which is necessary to maintain normal arterial blood gas levels
• Respiration: the exchange of oxygen and carbon dioxide across a simipermeable membrance occuring in both the lungs and tissues

Determining the Need for Ventilatory Support

• The most common indication to use a ventilator is acute ventilatory failure
• This requires rapid intubation and mechanical support for breathing
• Acute ventilatory failure can be diagnosed when acute respiratory acidosis is present
• Etiology is often neuromuscular dysfunction or drug-induced CNS depression
• Hypoxemia is another major indication
• It can be caused by a low ventilation-perfusion ratio
• Shunting can occur when pulmonary capillary perfusion is normal, but alveolar ventilation is lacking
• Asthma, pneumonia, COPD, and atelectasis can cause hypoxemia
• Pulmonary function tests can help decide if mechanical ventilation is needed, including vital capacity, tidal volume, respiratory rate, and ABGs

Special Considerations: Elderly

• Age-related changes in elderly patients can put them at risk for pulmonary failure
• These changes can cause increased work of breathing, decreased oxygenation, decreased lung volumes and strength, and reduced sensitivity to hypoxia and carbon dioxide
• Use of mechanical ventilation in the elderly is controversial, outcomes and predictability of survival are questioned, and the patient's wishes should be considered

Commonly Monitored Ventilator Settings

• Tidal volume is the amount of air that moves in and out of lungs in a normal breath
• Normal ranges are 7-9 mL/kg (500-800 mL in adult)
• In a volume-cycled ventilator, the tidal volume needs to be set
• Selection of tidal volume range can be from 7-9 mL/kg depending on patient's lung status; some physicians prefer a 6-8 range
• Plateau pressure should be maintained at less than 30 cm H₂O
• FiO2 is the fraction of inspired oxygen, expressed as a decimal but discussed in percentage of oxygen concentrations
• It can deliver from 0.21 (room air) to 1.0 (100 percent) oxygen concentration, based on patient need and clinical picture
• FIO2 is generally kept < 0.60 oxygen concentration

Ventilation Mode

• The most common ventilation modes are Assist-Control (AC), Intermittent mandatory ventilation (IMV), and Synchronized IMV (SIMV)
• Peak airway pressure is the amount of pressure required to deliver the volume, which varies according to airway resistance and lung compliance
• Peak airway pressure is also called Peak Inspiratory Pressure (PIP) and should be at a normal value of less than 40 cm H₂O
• Increasing PIP is caused from increased airway resistance or decreased lung compliance
• Decreasing PIP can arise from less pressure needed to deliver tidal volume or improvement in airway resistance or lung compliance

Example Ventilator Settings

• Tidal Volume 6-8 mL/kg (ideal wt)
• Rate 8-12 bpm
• Mode Assist-Control
• FiO2 0.5-1.0
• Any adjuncts such as PEEP, CPAP, PS

Noninvasive Positive Pressure Ventilation

• A relatively new means of providing ventilatory support without intubation
• Requires a positive pressure ventilator and a mask
• Advantages of this technique include being easier to apply and remove, with lower incidence of nosocomial infections
• A disadvantage of this technique is air leaks
• Contraindications include patients with unstable hemodynamic status, cardiac dysrhythmias, apnea, and inability to clear own secretions or attain a proper mask
• Indications for use include patients who cannot fully support their own ventilatory effort for prolonged periods of time and to avoid intubation in ICU patients
• May be used for immunocompromised patients so as not to increase risk of infection or bleeding
• Continuous Positive Airway Pressure (CPAP) does not provide assisted ventilation on inspiration but improves oxygenation by opening alveoli
• CPAP is most commonly used at home to treat obstructive sleep apnea by keeping the airway open
• CPAP is used in acute settings for pulmonary edema
• Complications of CPAP include hypoventilation, conjunctivitis, gastric distention, nasal-related complaints, skin irritation, and aspiration

Nursing Considerations

• Select proper mask size and allow patient to feel airflow
• Hold mask to patient's face without straps/hose and let patient breathe through mask briefly
• Connect tubing to mask and set IPAP low: <8
• Connect straps/hose, continue to hold mask in place, and adjust head straps as patient becomes more comfortable
• As patient continues with comfort, gradually increase the pressure to desired level
• Teaching is needed for home use of CPAP, including signs and symptoms of complications, circumstances to call MD, proper use/maintenance/troubleshooting of equipment
• BiPAP may be delivered with face mask or nasal devices similar to CPAP
• CPAP provides continuous positive airway pressure throughout the respiratory cycle, BiPAP divides cycle into IPAP and EPAP. Pressure can vary with each phase
• The inspiratory PAP (IPAP) increases TV and minute ventilation to decrease PaC02
• Expiratory PAP (EPAP) increases the FRC (Functional Residual Capacity), keeping alveoli more inflated during expiration to improve oxygenation

Major Complications of Mechanical Ventilation

• Cardiovascular: As intrathoracic pressure increases, major vessels may become compressed
• These complications can include increasing central venous pressure (CVP), reduced venous return decreasing right preload and stroke volume, and left ventricular output falls leading to decreased cardiac output
• Pulmonary: Altered Ventilation and Perfusion
• PPV increases ventilation to healthy lung areas while flow decreases to diseased areas, increasing lung resistance
• Increased shunting can occur, reflected by deteriorating PaO2 levels
• Barotrauma/Volutrauma: Barotrauma is excessive alveolar pressure and volutrauma is ecessive alveolar volume
• Risk of trauma increases with a higher pressure or volume
• Suspect if a patient has sudden onset of agitation or coughing, BP and ABG rapidly decline, Breath sounds are suddenly diminished or absent, and Subcutaneous emphysema can be palpated
• Oxygen Toxicity: Associated with oxygen concentrations > 60 percent for > 48 hours or 100 percent for > 6 hours
• Can damage the endothelial lining of lungs and decreases alveolar macrophage activity/surfactant production
• Nosocomial Infection: Ventilator-Associated Pnueumonia (VAP) is a major complication which occurs as result of contamination
• Failure to follow strict aseptic technique during suctioning or contaminated equipment can result in VAP
• Neurovascular: Two Major Mechanisms
• Increased intracranial pressure
• Decreased cerebral perfusion pressure
• Increased Intrathoracic Pressure decreases venous return from the head
• Renal
• Decreased Urinary Output (Decreased cardiac output, reduced renal perfusion and glomerular filtration rate)
• Causes changes in kidney function - 40% percent decrease in urinary output
• Hormonal alterations stimulate release of ADH, renin, aldosterone, atrial natriuretic factor, and catecholamines
• May affect renal blood flow and function, with observed effects varying with patient's clinical status, hydration, and underlying disease
• GI Complications: PPV can decrease blood flow into intestinal viscera, resulting in tissue ischemia and increased permeability of mucosal lining, resulting in ulcers and GI bleeds
• Prevention includes prophylactic use of H2 blockers such as Famotidine

Artificial Airway Complications

• Trauma to Nasal Mucous Membranes can occur during intubation. Ischemia and Necrosis of nares may result from pressure caused by tube
• Pressure or infection can cause inner ear poblems
• Excessive Cuff Pressure may lead to Tracheal and laryngeal injuries and Fistulas in the vocal cords may form, rarely
• Preventing injuries from excessive cuff pressure requires the Minimum occluding pressure technique

Goals of Mechanical Ventilation

• Supporting Physiologic Needs
• Promote optimal oxygenation
• Provide adequate ventilation
• Protect airway
• Support tissue perfusion
• Provide adequate nutrition
• Supporting Psychological Needs
• Reduce anxiety
• Provide a balance of sleep and activity
• Promote communication
• Support family

Nursing Management

• Ineffective Airway Clearance:
• ABCs, ensure patent airway by hyperoxygenating / hyperventilating, suctioning and returning to ventilator
• Manage thick secretions with Fluid intake 2-2.5 L per day and Pooled secretions by Turning q 2 hours
• Impaired Gas Exchange:
• Monitor ABGs and ventilator settings, adjusting TV or RR to treat CO2 levels and Fi02 or PEEP to treat O2 levels
• Ineffective Breathing Pattern:
• Assess for causes of breathing pattern change via medications, ventilator settings, and other causes
• Protect the airway by maintaining sufficient slack on ventilator tubing and manually ventilating the patient when transferring them in and out of bed
• Alteration in Cardiac Output (as seen in diagram on slide): Monitor hemodynamic effects of mechanical ventilation
• Alteration in Nutrition:
• Elevate head of bed greater than 30 degrees
• Start nasogastric or nasoenteric feedings within three days of artificial airway placement
• Begin a bowel regimen to avoid constipation
• Anxiety and Pain:
• Explain invasive and painful procedures and manage fear of dying
• Monitor signs and symptoms of pain and anxiety, implementing ways to decrease them
• Maintain restful environment and assess effects of treatments
• Sleep Pattern Disturbance:
• Clustering of activities and providing for uninterrupted rest periods. Minimize interruptions at night
• Impaired Verbal Communication:
• Devise alternative method of communication. Writing pad, Picture board, Letter board, and Lip reading
• Family Support:
• Assess family concern and understanding and assist them in communicating with the patient

Weaning the Patient from the Mechanical Ventilator

• Weaning is withdrawing a pt from mechanical ventilator support and attaining total independence from the ventilator, using a multidisciplinary approach
• Patient Categories for Weaning:
• Removal is rapid when reason for mechanical ventilation is resolved
• Removal is slow and gradual, requiring deliberate planning
• Unweanable patients require long-term ventilatory support
• The Weaning process consists of a Determination of Readiness (Physiologic and Psychologic Readiness), Initial Patient Screening, and a Weaning Process

Weaning Process

• Initial Patient Screening:
• Cause of respiratory failure is resolving or improving
• Adequate oxygenation
• Hemodynamic stability
• Spontaneous ventilatory effort
• Rapid Weaning Process:
• For patients with short-term needs for ventilation and correction of underlying problem is resolved
• Evaluate for weaning with a Spontaneous breathing trial like CPAP or removed ventilator and placed on T-piece for 30 to 120 minutes
• Monitor for comfort, cardiac rhythm, and ABG status
• If criteria remain within acceptable ranges, patient can be extubated
• Slow Weaning Process:
• For patients with chronic lung disease complicated by an acute problem or a prolonged illness. Generally poorer state of health overall
• Problems associated with difficult weaning include Excessive respiratory muscle work of breathing, Respiratory muscle fatigue, Anemia, Malnutrition, Excessive secretions, Infection, and Unstable hemodynamic state
• Requires retraining and strengthening and multiple weaning methods such as IMV/SIMV, mandatory minute ventilation (MMV), PSV, manual weaning, and spontaneous breathing trials
• Close multisystem monitoring of patients is needed
• During a Comprehensive Patient Screening, if any “No” answers result from screening, quit the process and reevaluate patient in 48 hours (as seen on list on slide)

Methods of Weaning

• Manual Weaning which follows a schedule of removal from ventilator for increasing periods of time, during which the patient is taken off ventilator and placed on T-piece with humidified oxygen
• Signs of respiratory are Respiratory rate > 30, increased BP and pulse, Cyanosis, Decreased SaO2, Diaphoresis, Use of accessory muscles, abdominal paradox
• This process is individualized for each patient, strengthening respiratory muscles with good nutrition and hydration.
• Manual Weaning: Ex T-piece is associated with Disadvantages (Frightening experience for patient, Time-consuming for nurse), and Spontaneous Breathing Trials result in the patient being placed on CPAP & or PS (pressure support). Length of time on CPAP &/or PS increases with increased tolerance
• Ventilator Weaning: More common and less traumatic to patient than manual weaning
• Variety of alternative modes are used (IMV/SIMV, PSV, and CPAP). Monitor 02 saturation, RR & quality
• HR & BP should not increase more than 10-20%
• Pulmonary Function Tests are used to Decide if Extubating is Possible, with tests including RSBI- f/Vt (Rapid Shallow Breathing Index), Vital capacity, Respiratory rate, ABGs, and Maximal Inspiratory Capacity

Parameters for Weaning and Extubation (cont)

• Rapid Shallow Breathing Index: target is <105 spontaneous breathing (obtain ≥ 1 min after disconnecting from vent)
• Vital Capacity: target is > 10mL/kg (alert enough to cooperate, not a consistent predictor)
• RR or f (frequency): target is <bpm (Rapid, shallow breathing nonsustainable off vent)
• Maximal Inspiratory Pressure (MIP) or Negative Inspiratory Force (NIF): target is <-20 to -30 cm H2O (Indicates ability to adequately breath deep when needed. Stop weaning/ no extubation if desat or have arrhythmias)
• Minute Ventilation: target is < 10L/min (Over 10 L/min, patient will fatigue, may have to re-intubate)
• A Cuff leak test is a simple method to predict post-extubation stridor among those at risk