Establishing the Need for Mechanical Ventilation Flashcards
-Acute respiratory failure
-The purpose of ventilation, be it spontaneous or artificial, is to assist in the maintenance of homeostasis
-Any condition in which respiratory activity is completely absent or is inadequate to maintain oxygen uptake and carbon dioxide clearance is referred to as acute respiratory failure
respiratory insufficiency
-If adequate gas exchange is being maintained, but at a great expense to the breathing mechanism of the subject, this is referred to as respiratory insufficiency
-This condition can eventually lead to acute respiratory failure -Clinically, acute RF may be defined as the inability of the pt to maintain the arterial pressure of oxygen (PaO2), carbon dioxide (PaCO2), and Ph at acceptable levels
-Acute respiratory failure and respiratory insufficiency
-Generally considered to be :
-A PaO2 below the predicted normal range for the PT age under ambient air conditions
-A PaCO2 levels above 50 m HG and raising -A falling PH of 7.25 or less
-Two forms of acute failure
-Hypoxic RF, acte life threatening or vital organ threatening tissue hypoxia
-Ca be treated with supplemental oxygen or in comh=bination with PEEP, CPAP -Mechanical ventilation may be necessary -Hypercapnic RF, occurs when a person cannot achieve adequate ventilation to maintain a normal PaCO2 -Known as acute ventilatory failure -It is important to be able to recognize these conditions quickly i the clinical setting. They Identify the need for mechanical ventilatory support
-There are certain types of disorders and situations that make individuals more likely to develop RF
-These generally fall into three categories
-Disorders of the Central nervous system -Problems with neuromuscular function -Increased WOB
-Disorders of the CNS associated with reduced Drive to breathe
-Depressant drugs (barbiturates, tranquilizers, narcotics, ect._
-Brain or brainstem lesions (stroke, trauma to the head or neck, cerebral hemorrhaging, tumor spinal cord injury) -Pickwickian syndrome or sleep apnea syndrome -Inappropriate oxygen therapy
-Disorders Associated with Neuromuscular Function
-Myasthenia gravis
-Tetanus -Botulism -Guillain Barre syndrome -Polio -muscular Dystrophy -Drugs
-Disorders that result in increased WoB
-Pleural effusions, hemothorax
-Pneumothorax, fail chest, rib fracture -Kyphoscoliosis, chest wall deformity, obesity -Increased airway resistance, athma, emphysema, chronic bronchitis, croup, epiglottis, -Apoiration, ARDS, Cardiogenic pulmonary edema -Pulmonary emboli -Airway emergencies -postoperative pulmonary complications
-There are specific physiological measurements, which indicate the need for MV regardless of the cause
-These measurements and their values are generally grouped into 3 categories
-Ventilatory mechanics
-Ventilation -Oxygenation
Ventilatory Mechanics
Ventilatory mechanics Normal Adult Range Critical Values
Maximal INspiratory Pressure -100-50 -20 to 0 Maximal expiratory pressure 100 <40 Vital Capacity(ML/KG) 65-75 <10-15 Tidal Volume (ml/kg) 5-8 <5 Respiration Rate (f) 12-20 >35 Forced expiratory Volume @ 1 sec 50-60 <10 Peak expiratory flow(l/min) 350-600 75-100
-Maximal Inspiratory pressure (MIP) or negative inspiratory force (NIF)
-Lowest, most negative pressure generated during a forceful inspiratory effort against an occluding airway
-Used to assess respiratory muscle strength
-Maximal expiratory pressure
-Used to assess the ability to couch and clear secretions
-Vital Capacity
-Volume of air that can be maximally exhaled following a maximum inspiration
-PT must be able to take in a large volume of air to produce a cough strong enough to clear the airway -Used to assess respiratory muscle strength
-Tidal volume
-Volume of air moved in and out of the lungs during normal breaths
-Respiratory Rate or frequency (f)
-Number of breaths taken per minute, usually at rest
-Elevated RR is an indication of increased WOB and eventually leads to respiratory muscle fatigue
-Forced Expired Volume at 1 second (FEV1)
-Pulmonary function parameter used too assess airway resistance
-Not an appropriate measurement to perform on a PT who is severely short of breath and in acute respiratory distress
-Peak Expiratory Flow
-Good indicator of airway resistance and a PTs ability to maintain airway patency
-Part of an effective asthma treatment plan -Low values are cause for alarm and indicate severe airflow obstruction
Ventilation
Ventilation adult normal range critical Values
pH 7.35-7.45 <7.25 PaCO2 35-45 >50 and rising Ve 5-6 >10 VD/VT 0.3-0.4 >0.6
-Ve
-Volume of air a person breaths out per minute
-Minute ventilation or minute volume is the product of tidal volume and respiratory rate -Ve= Vt * f -f is also RR -Example: calculate the minute ventilation Vt 500ml and f 123/min -500 * 12 = 6000 or 6.0 L/min
-VD/VT
-% of PT Vt that is Dead Space (wasted) ventilation, does not go through gas exchange, ventilation without perfusion
-VD/VT= PaCO2-PECO2/ PaCO2 -E= Exhaled -Alveolar Dead Space- Air reaches the alveoli but does not take part in gas exchange and results from lack of perfusion to air-filled alveoli, for example pulmonary embolism -Deadspace volume is = 1 ml per 1lb of their ideal body weight -Alveolar minute ventilation = Vd/Vt = (Vt-Vd) * f
-VD/VT
-Example:
-You are ask to calculate the Vd/Vt of a PT whose PaCO2 is 50mmHg and whose expired carbon dioxide tension is 31 mmHG
-PaCO2-PECO2/ PaCO2 50-31/50= .38 or 38%
-Example
-What is the alveolar ventilation under the following conditions
VT 950
F 14bpm PaCO2 42 mmHg P(A-a) O2 40 mmHg Vd/ Vt 40% Weight 166lbs (950-166) * 14 = 10976ml 0r 10.9L
-Example: What is the alveolar ventilation under the following conditions?
Vt 820ml
F 17 bpm
PaCO2 33mmHg
Vd 230 ml
FiO2 40%
(820-230) * 17 =10.03
Oxygenation
Oxygenation Normal Adult Range Critical Values
PaO2 80-100 >70(on O2> .6) P(A-a)O2 or (A-a DO2) 5-20 >450 (on O2) PaO2/ PAO2 .75 <.15 PaO2/FiO2 475 <200
-A-a Gradient P(A-a) O2
-Measures the difference (gradient) Between alveolar and arterial P02
-Smaller the gradient = Better -Normal Range up to 300 can corrected with conventional oxygen therapy -Above 300 shunt problem (blood flow in excess of ventilation= Shunt) - treatment has to be more than O2 therapy
-Ratio of arterial to alveolar PO2 (PaO2/PAO2)
-PaO2/PAO2 normally is about .75-.95 this range indicates that 75% to 95% of the oxygen available in the alveoli is diffusing into the pulmonary capillaries
-For example a normal PaO2 of 90,mmHg divided by a normal PAO@ on room air (100MMHg) gives a ratio of .90 A value of .15 or less is critical (i:e only 15% of available oxygen is getting into the artery)
-P/F ratio or PaO2/FiO2 ratio
-Ratio of the partial pressure of arterial oxygen to the inspired fractional concentration of oxygen
-Used to determination of acute lung injury or acute respiratory distress syndrome -Measures the efficiency of oxygen transferred across the lung -A ratio less than 300 torr signifies ALI -A ratio less than 200 torr signifies ARDS
-The standard criteria for the institution of mechanical ventilatory support are as follows
-Apnea or absence of breathing when reversible disease is present
-Acute respiratory failure -Impending respiratory failure -PaCO2 best indication of ventilation, PaO2 best indication of oxygenation -Severe hypoxemia attributed to increase work of breathing or ineffective breathing pattern -It should be kept in ind that no single parameter should determine the decision for treatment -History physical assessment, arterial blood gas evaluation, lung mechanics, and prognosis should be considered -The goals for therapy for the mechanically ventilated PT should always be remembered while caring for the PT
Goals
-To provide the pulmonary system with the support needed to maintain an adequate level of alveolar ventilation
-To reduce the work of breathing until the cause of respiratory failure van be removed
-To restore normal acid base balance to the arterial and systemic areas
-To increase oxygen transfer and oxygenation to the body organs and tissue
