5 Lecture 5-Ventilation of critically ill patients.pptx

Educative

1. Mechanical Ventilation Irene Bandoh

2. Introduction Mechanical ventilation is one of the most common interventions made in intensive care. It is often life saving, but there are life threatening side effects associated with its use. Mechanical Ventilation refers to the use of Life-Support Technology to perform the work of breathing for patients who are unable to do so on their own A mechanical ventilator is a device used to replace or assist breathing in order to move air into the lungs and permit spontaneous deflation of the lungs The decision to ventilate a patient should be considered early, should be planned and shouldn’t be delayed until it becomes an emergency

3. Origins of mechanical ventilation Negative-pressure ventilators (“iron lungs”) Non-invasive ventilation first used in Boston Children’s Hospital in 1928 Used extensively during polio outbreaks in 1940s – 1950s Positive-pressure ventilators Invasive ventilation first used at Massachusetts General Hospital in 1955 Now the modern standard of mechanical ventilation The era of intensive care medicine began with positive-pressure ventilation The iron lung created negative pressure in abdomen as well as the chest, decreasing cardiac output. Iron lung polio ward at Rancho Los Amigos Hospital in 1953.

4. Indications Established or imminent respiratory failure from any cause Helps to reduce the work of breathing and myocardial oxygen consumption in patients who have compromised myocardial function and muscle fatigue e.g. shock Controlled hyperventilation in patients with closed head injury to help reduce intracranial pressure Inability to protect airway as a result of trauma, neurological dysfunction, Anaesthesia or drug overdose Cardiopulmonary arrest

5. GOALS OF VENTILATION Treat hypoxemia/hypercapnia Relieve respiratory distress/reverse fatigue Decrease Myocardial O2 demand Prevention or reversal of atelectasis Breath for the sedated/ paralysed patient

6. Types of ventilators

7. Ventilatory modes A ventilator mode describes how each breath is delivered to a patient by the ventilator A ventilator mode may provide A partial ventilatory support e.g. SIMV, CPAP, BiPAP Total ventilatory support e.g. IPPV (or CMV) Each breath delivered may either be; pressure-controlled (pressure-targeted ventilation) volume controlled (volume-targeted ventilation) dual-controlled mode

8. Common settings on the ventilator FiO2 Frequency of breath I:E ratio Extrinsic PEEP Pressure support Tidal volume Inspiratory pressure Alarm set ups Patient type; adult/pediatric/neonate

9. Definitions FiO2: Fraction of inspired oxygen. It’s the percentage oxygen delivered to the patient. The FiO2 range is from 0.21 (room air) to 1 (100% O2). PEEP: Positive end expiratory pressure is the amount of pressure in the lungs at the end of exhalation. The initial PEEP for patients admitted to ICU is usually between 5 and 10 cm H2O. I:E ratio: refers to the ratio of inspiratory time: expiratory time. In normal spontaneous breathing, the expiratory time is about twice as long as the inspiratory time. This gives an I:E ratio of 1:2

10. Tidal volume: is the amount of air delivered with each breath. Frequency : set respiratory rate based on patient’s age and needs Tinsp

11. Ventilation modes To deliver inspiratory volume, the operator most commonly sets either a volume or a pressure The primary variable the ventilator adjusts to achieve inspiration is called the control variable

12. CONTROL VARIABLES The primary variable the ventilator adjusts to achieve inspiration Mechanical ventilators can control 3 variables, but only one at a time Pressure- Pressure Controlled Volume- Volume Controlled Flow- Flow Controlled Pressure control and volume control are the commonest modes

13. Volume Control Refers to modes of ventilation where the volume of the tidal breath is set . E.g. we set the ventilator to deliver a breath of 500 ml. Setting the rate is normally mandatory for this method of controlling ventilation. E.g. we set the tidal volume ( Vt ) at 500 ml to be delivered at a rate of 14 bpm (breath per minute). The ventilator in this example is set to deliver a minute volume of 500 x 14 = 7 litres. The airway pressure in this mode of ventilation will depend on the lung and chest wall compliance.

14. Pressure Control Refers to modes of ventilation where the pressure of the tidal breath is set . E.g. we set the ventilator to deliver a breath pressure of 30 cm H20. Setting the rate is normally mandatory for this method of controlling ventilation. E.g. we set the breath pressure at 30 cm H20 to be delivered at a rate of 14 bpm (breath per minute). The tidal volume in this mode of ventilation will depend on the lung and chest wall compliance. Indeed the tidal volume might change from breath to breath depending on many factors.

15. Pressure or Volume Controlled The choice between these two modes of ventilation is often a matter of clinician preference, as there is no evidence that either mode is superior to the other in relation to any clinically important outcome. If pressure controlled mode is chosen, the inspiratory pressure is set . You have to then note what Vt is being delivered to the patient to make sure that it is the Vt that you want to deliver. If Volume controlled mode is used, the Vt is set . Here the effect on airway pressures has to be noted to make sure that the airway pressures are within safe limits.

16. Non- invasive ventilation Advantages: 1.allows speech 2.ideal for patients with nocturnal hypoventilation 3.complications of intubation –avoided 4. does not require heavy sedation 5. Provides flexibility in initiating and removing mechanical ventilation

17. Disadvantages of NIV 1. Mask leakage 2. lack of airway protection 3. patient should be alert with normal respiratory drive 4. Claustrophobia 5. slower correction of blood gas abnormalities 6. facial pain and skin pressure ulcerations 7. gastric distention 8. apparatus uncomfortable for patients

18. Non invasive ventilation Absolute contraindications; Respiratory arrest, cardiovascular instability, patient with tracheoesophageal fistula, inability to protect the airway or high risk of aspiration scenarios, uncooperative patient, facial trauma, severe head injury Relative contraindications; Copious secretions, facial abnormalities, extreme obesity

19. 1.CPAP: Patient continuously receives a set air pressure, during both inspiration and expiration. Best suited for: patients with obstructive sleep apnea cardiac patients requiring ventilatory assistance but not requiring immediate intubation 2.BiPAP This provides a set inspiratory pressure and a different set expiratory pressure Patient has full control over the respiratory rate, inspiratory time and depth of inspiration

20. Modes IMV Modes : intermittent mandatory ventilation modes –ventilator breaths only. Patient not allowed to breath Assist Control Ventilation- Ventilator breath is given at intervals based on respiratory rate/frequency. If patient makes an effort, ventilator takes over and makes it a machine breath. So patient is allowed to initiate the breath. Pressure Support Ventilation -The patient controls the respiratory rate and does most of the breathing. The model provides pressure support to overcome the increased work of breathing imposed by the disease process, the endotracheal tube, the inspiratory valves and other mechanical aspects of ventilatory support.

21. SIMV - Most commonly used mode, Spontaneous breaths and mandatory breaths can both be taken. If patient initiates a breath, the ventilator allows the patient to breath fully and breaths are synchronizes that with the machine breaths. BIPAP- CPAP-

22. Complications of Mechanical Ventilation Pulmonary Barotrauma/ volutrauma Tension Pneumothorax Respiratory muscle atrophy Pneumomediastinum / Pneumopericardium Pneumoperitoneum Ventilator induced lung injury(VILI) Ventilator associated pneumonia Psychological Effects Inability to communicate

23. Cardiovascular Effects Decreased Venous Return Decreased Cardiac Output Increased Pulmonary Vascular Resistance Removal of natural defence mechanisms with intubation: Contamination of ventilator circuits Contamination through suctioning Others Patient-ventilator asynchrony (“fighting the ventilator”) Difficulty weaning after prolonged mechanical ventilation Accidental ventilator disconnection/leak/failure

24. Indications for weaning Clinical parameters Resolution/Stabilization of disease process Hemodynamically stable Intact cough/gag reflex Spontaneous respirations No need for frequent suctioning Acceptable vent settings FiO 2 < 50%, PEEP < 8, P a O 2 > 75, pH > 7.25 General approaches SIMV Weaning Pressure Support Ventilation (PSV) Weaning Spontaneous breathing trials T-Piece weaning No weaning parameter completely accurate when used alone Numerical Parameters Normal Range Weaning Threshold P/F > 400 > 200 Tidal volume 5 - 7 ml/kg 5 ml/kg Respiratory rate 14 - 18 breaths/min < 40 breaths/min Vital capacity 65 - 75 ml/kg 10 ml/kg Minute volume 5 - 7 L/min < 10 L/min