RT 230 Unit A- Indication, Setup and Monitoring of CMV
Indications for CMV • Apnea • Acute ventilatory failure: A PCO2 of more than 50mmHg with a pH of less than 7.25 • Impending acute ventilatory failure • Based on lab data and clinical findings indicating that pt is progressing towards ventilatory failure • Quick tip: acute hypercapnic failure ph drops 0.8 for every 10mm hg rise in co2 chronic hupercapnic ph drops 0.03 for every 10 mmhg rise in co2
Clinical problems often resulting in impending ventilatory failure • Pulmonary abnormalities • RDS=Respiratory Distress Syndrome • Pneumonia • Pulmonary emboli • Mechanical ability of lung to move air=muscle fatigue • Ventilatory muscle fatigue • Chest injury • Thoracic abnormalities=scoliosis, kyphoscoliosis • Neurologic disease=GB, MG • Pleural disease=pleurasy
Clinical evaluation • Vital signs: Pulse and BP increase • Ventilatory parameters • VT decreases • RR increases • Accessory muscle use increases • Paradoxical breathing (abdomen out, rib cage in) • Retractions may be noted • Development of impending acute vent failure may demonstrate • Progressive muscle weakness in pt with Neurologic disease • Increasing fatigue
ABGs demonstrating a trend toward failure • 9am 10am 11am 12pm 1pm • pH 7.58 7.53 7.46 7.38 7.35 • PCO2 22 28 35 42 48 • HCO3 21 22 23 24 24 • PO2 60 55 50 43 40
Non-responsive hypoxemia • PaO2 less than 50% on an FIO2 greater than 50% • PEEP is indicated • REFRACTORY HYPOXEMIA
Physiologic Effects of Positive Pressure Ventilation • Increased mean intrathoracic pressure • Decreased venous return • Thoracic pump is eliminated*** • Pressure gradient of flow to right side of heart is decreased • Right ventricular filling is impaired • Give fluid • Decreased cardiac output • Caused by decreased venous return • Give drugs and fluid • Monitor I and O. Normal urine output 1000-1500 cc/24 hours
THORACIC PUMP • The "thoracic pump" is the thoracic cavity, the diaphragm, the lungs, and the heart. • The diaphragm moves down, pressure in the cavity decreases and venous blood rushes through the vena cava via the right heart into the lungs. Pulmonary blood vessels expand dramatically, filling with blood, air and blood meeting across the very thin alveolar surface. The deeper the inhalation, the more negative the pressure, the more blood flows, and the fuller the lungs become.
THORACIC PUMP • As the diaphragm moves up the pressure in the thoracic cavity reverses. Pulmonary blood vessels shrink ejecting an equal volume of blood out of the pulmonary veins into the left heart. The left heart raises the pressure and checks and regulates the flow. The more complete the exhalation, the more positive the pressure becomes and the more blood is ejected from the lungs. • Decrease exhalation, more pressure in cavity decrease CO
Effects of ppv cont. • Increased intracranial pressure • Blood pools in periphery and cranium because of decreased venous return • Increased volume of blood in cranium increases intracranial pressure • Decreased urinary output • PPV could cause 30-50% decrease renal output • Decreased CO results in decreased renal blood flow • Alters filtration pressures and diminishes urine formation • Decreased venous return and decreased atrial pressure are interpreted as a decrease in overall blood volume • ADH is increased and urine formation is decreased
ADH=VASOPRESSIN • Roughly 60% of the mass of the body is water, and despite wide variation in the amount of water taken in each day, body water content remains incredibly stable. Such precise control of body water and solute concentrations is a function of several hormones acting on both the kidneys and vascular system, but there is no doubt that antidiuretic hormone is a key player in this process. • Antidiuretic hormone, also known commonly as arginine vasopressin
The single most important effect of antidiuretic hormone is to conserve body water by reducing the loss of water in urine. A diuretic is an agent that increases the rate of urine formation. • high concentrations of antidiuretic hormone cause widespread constriction of arterioles, which leads to increased arterial pressure. • Retention of fluids will cause EDEMA
Effects of ppv cont. • Decreased work of breathing • Force to ventilate is provided by the ventilator • Increased deadspace ventilation • Positive pressure distends conducting airways & inhibits venous return • The portion of VT that is deadspace increases • Greater percentage of ventilation goes to apices • Increased intrapulmonary shunt • Ventilation to gravity dependent areas is decreased • Perfusion to gravity dependent areas increase • Shunt fraction increases from 2-5% to 10%
A pulmonary shunt is a physiological condition which results when the alveoli of the lung are perfused with blood as normal, but ventilation (the supply of air) fails to supply the perfused region. In other words, the ventilation/perfusion ratio (the ratio of air reaching the alveoli to blood perfusing them) is zero.A pulmonary shunt often occurs when the alveoli fill with fluid, causing parts of the lung to be unventilated although they are still perfused.Intrapulmonary shunting is the main cause of hypoxemia (inadequate blood oxygen) in pulmonary edema and conditions such as pneumonia in which the lungs become consolidated. The shunt fraction is the percentage of blood put out by the heart that is not completely oxygenated. A small degree of shunt is normal and may be described as 'physiological shunt'. In a normal healthy person, the physiological shunt is rarely over 4%; in pathological conditions such as pulmonary contusion, the shunt fraction is significantly greater and even breathing 100% oxygen does not fully oxygenate the blood.
Effects of ppv cont. • Respiratory rate, VT, Inspiratory time, and flow rate can be controlled • May cause stress ulcers and bleeding in GI tract
Complications of Mechanical Ventilation Complications related to pressure Ventilator-associated lung injury (VALI) High pressures are associated with barotrauma Pneumothorax, pneumomediastinum, pneumopericardium, subcutaneous emphysema Pneumothorax has decreased chest movement, hyperresonance to percussion, on affected side If tension pneumothorax: medical emergency Relieved by needle insertion, then chest tube Use 100% oxygen to speed reabsorption.
Placing patient on CMV • Establish airway • Select VT 8‑12ml/kg of ideal body weight • Select mode ‑ a/c sensitivity at minimal to not self cycle • Set pressure limit 10cmH2O above delivery pressure • Set sigh volume 1‑1/2 to 2 times VT • Sigh pressure 10cmH2O above sigh delivery pressure • Rate as ordered • PEEP as ordered: exp. resist, insp. hold, etc. • Set spirometer 100 cc less than patient volume • check for function (turn on)
Modes • Control • All of WOB is taken over by ventilator • Sedation is required • Control mode is useful • During ARDS, especially if high PEEP is required or inverse I:E ratio • Assist • Patient is able to control ventilatory rate • Should not be used for continuous mechanical ventilation if pt is apneic
Assist/control • Pt able to control vent rate as long as spontaneous rate > backup rate • Machine performs majority of WOB • Sedation is often required to prevent hyperventilation • Is useful during early phase of vent support where rest is required • Useful for long term for pt not ready to wean • SIMV • In between positive press breaths pt can breathe spontaneously • Useful for long term for pt not ready to wean • Used as weaning technique for short-term vent dependent pt
PS • Vent functions as constant pressure generator • Positive pressure is set • Pt initiates breath, a predetermined pressure is rapidly established • Pt ventilates spont, establishes own rate, VT, peak flow and I:E • Can be used independently/CPAP/SIMV • Indicated to reduce work imposed by ETT, 5 to 20cm H2O • Can be used for weaning • A set IPS (12ml/kg VT) achieved by adjusting IPS level then slowly reducing as clinical status improves • To overcome resistance of ETT, IPS should meet Raw • To determine amount of PS needed: [(PIP – Plateau pressure) / Ventilatoryinspiratory flow] x spontaneous peak inspiratory flow
IBWEstimated ideal body weight in (kg)Males: IBW = 50 kg + 2.3 kg for each inch over 5 feet.Females: IBW = 45.5 kg + 2.3 kg for each inch over 5 fee. • 1 Kilogram = 2.20462262 Pounds
Monitoring CMV • Observation • Look at patient! • Make a good visual assessment • Start with patient, trace circuit back to ventilator • Check and drain tubing • Check connections • Check patient • Suctioning, position, etc. • BP • Spontaneous RR • Heart rate and all vital signs
Check machine settings • VT (set, exhaled, corrected) • f (assisted, set, spontaneous) • Pressure limit: 10 above delivery pressure • PEEP if applicable: Check BP! • Peak Insp. Pressure (PIP): Keep as low as possible • I:E ratio for proper flow • FiO2: Keep as low as possible to prevent Oxygen Toxicity yet keep them adequately oxygenated • Check all apnea alarms and settings. • Check set VT to exhaled VT for any lost volumes • If difference is greater than 100 cc, check for leak.
Compliance • Measures distensibility of lung – how much does the lung resist expansion. • Relationship between Volume and Pressure • High compliance equals lower PIP thus easier ventilation and less side effects of CMV
Disease states resulting in low compliance include the Adult Respiratory Distress Syndrome (ARDS), pulmonary edema, pneumonectomy, pleural effusion, pulmonary fibrosis, and pneumonia among others. • Emphysema is a typical cause of increased lung compliance.
You must know • Dynamic = VT (corrected or exhaled) PIP – PEEP • Always subtract out PEEP • Consistently use exhaled or corrected VT • Used to assess volume/pressure relationships during breathing – any changes in RR will effect it • CDYN decreases as RR increases which may cause V/Q mismatch which may cause hypoxemia • May reflect change due to change in flow due to turbulence instead of compliance • Normal = 30 – 40 cmH2O
Very important • Static = VT (corrected or exhaled) Plateau – PEEP • Always subtract out PEEP • Always consistently use either VT exhaled or VT corrected • Will not change due to change in flow, more accurate • Measured pressure to keep airways open with no gas flow. • Normal values very with pt, but usually above 80 cmh2o will show lung overdistention
Importance • to follow trends in patient compliance • Decreased C = stiffer lung = less compliant = higher ventilating pressures = you need a ventilator with high internal resistance to deliver volumes using square wave. • High compliance = possible Emphysema
Static vs Dynamic Compliance • Decrease in CDYN with no change in CST indicates worsening airway resistance • Causes • Bronchospasm • Secretions • Kinked/Occluded ETT • Inappropriate flow and/or sensitivity settings • If both CDYN and CST worsen, not likely to be an airway problem • Causes • Pulmonary Edema • ARDS • Tension Pneumothorax • Atelectasis • Fibrosis • Pneumonia • Obesity • Patient Position
RAW = PIP – Pplat Flow (L/sec.) • Airway Resistance • Impedance to ventilation by movement of gas through the airways thus the smaller the airway the more resistance which will increase WOB (causing respiratory muscle and patient fatigue) • Example: ETT, Ventilator Circuit, Bronchospasm
Airway Resistance & Compliance • Decreased Compliance + Increased Airway • Resistance = High PIP, Decreased Volumes and significant increase in WOB • Very difficult to wean a patient until problems are resolved
Patient stability • Vital signs • Pulse – normal, weak, thready, bounding, rate, etc. • BP – hypo/hypertensive – directly related to CO • Respirations – tachypnea, bradypnea, hyperpnea, hypopnea, rate, etc. • Color – dusky, pale, gray, pink, cyanotic • Auscultation ‑ bilateral, etc. • Are they bilateral, amount of air moving, rales, rhonchi or wheezing • Are they Vesicular (normal) or Adventitious (abnormal) • Describe what you hear: fine, course, high-pitched, low-pitched, etc. • And the location where you heard it: bilateral bases, posterior bases, right upper anterior lobe, laryngeal, upper airway, etc.
Hemodynamic monitoring • BTFDC • Also known as • Balloon Tipped Flow Directed Catheter • Swan-Ganz Catheter • Pulmonary Artery Catheter • Done by inserting a BTFDC into R atrium, thru R ventricle, and into pulmonary artery • SvO2 is drawn from the distal port of a BTFDC • Used to monitor tissue oxygenation and the amount of O2 consumed by the body
CVP • Monitors fluid levels, blood going to the right side of heart • Normal = 2 – 6 mmHg (4 – 12 cmH2O) • Increased CVP = right sided heart failure (cor pulmonale), hypervolemia (too much fluid) • Decreased CVP = hypovolemia (too little fluid), hemorrhage, vasodilation (as occurs with septic shock)
PAP • Pulmonary Artery Pressure = B/P lungs • Monitors blood going to lungs via Swan-Ganz catheter (BTFDC) • Normal 25/8 (mmHg) • Increased PAP= COPD, Pulmonary Hypertension, or Pulmonary Embolism • PCWP • Pulmonary Capillary Wedge Pressure monitors blood moving to the L heart • Balloon is inflated to cause a wedge • Normal PCWP = 8 mmHg • Range is 4 – 12 mmHg • Increased PCWP = L heart failure, CHF • Measure backflow resistance
Cardiac Output • Expressed as QT or CO (QT= Greek alphabet, 1050 BC scientist used qt had cardiac output expression) • Normal = 5 LPM • Range 4 – 8 LPM • Decreased CO = CHF, L heart failure, High PEEP effects • I & O • Needs to be monitored closely to prevent fluid imbalance due to increased ADH production and decreased renal perfusion • Fluid imbalance can develop into pulmonary edema and hypertension
Cardiac Output (CO) The amount of blood pumped out of the left ventricle in 1 minute is the CO A product of stroke volume and heart rate Stroke volume: amount of blood ejected from the left ventricle with each contraction Normal stroke volume: from 60 to 130 ml Normal CO: from 4 to 8 L/min at rest Fick CO: Vo2/Cao2-Cvo2 C(a-v)O2 could decrease if CO is increased due to less oxygen needs to be extracted from each unit of blood that passes
Fick MethodThe Fick method requires that you be able to measure the A-V oxygen content difference and requires that you be able to measure the oxygen consumption. An arterial blood gas from a peripheral artery provides the blood for the CaO2 measurement or calculation while blood from the distal PA port of a Swan-Ganz catheter provides the blood for the CvO2 measurement or calculation Dilution methods mathematically calculate (using calculus) the cardiac output based on how fast the flowing blood can dilute a marker substance introduced into the circulation normally via a pulmonary artery catheter. (injecting a dye in prox port of Swanz. Not really used anymore due to infections
Measures of Cardiac Output and Pump Function • Cardiac index (CI) • Determined by dividing the CO by body surface area • Normal CI is 2.5 to 4.0 L/min/m2 • CI measurement allows a standardized interpretation of the cardiac function • True cardiac output compared to each persON
Measures of Cardiac Output and Pump Function (cont’d) • Cardiac work • A measurement of the energy spent ejecting blood from the ventricles against aortic and pulmonary artery pressures • It correlates well with the amount of oxygen needed by the heart • Normally cardiac work is much higher for the left ventricle
Measures of Cardiac Output and Pump Function (cont’d) • Ventricular stroke work • A measure of myocardial work per contraction • It is the product of stroke volume times the pressure across the vascular bed • Ventricular volume • Estimated by measuring end-diastolic pressure
Measures of Cardiac Output and Pump Function (cont’d) • Ejection fraction • The fraction of end-diastolic volume ejected with each systole; normally 65% to 70%; drops with cardiac failure
Determinants of Pump Function Preload • Created by end-diastolic volume • The greater the stretch on the myocardium prior to contraction the greater the subsequent contraction will be • When preload is too low, SV and CO will drop • This occurs with hypovolemia • Too much stretch on the heart can also reduce SV
Determinants of Pump Function Afterload • Two components: peripheral vascular resistance and tension in the ventricular wall • Created by end systolic volume • Increases with ventricular wall distention and peripheral vasoconstriction • As afterload increases, so does the oxygen demand of the heart • Decreasing afterload with vasodilators may help improve SV but can cause BP to drop if the blood volume is low
Ventilation Patient Parameters • Spontaneous VT • Is it adequate for patient? • Spontaneous volumes should be between 5 – 8 ml/Kg of Ideal Body Weight (IBW) • Spontaneous VC • 10 – 15 ml/Kg IBW • NIF/MIP/MIF/NIP • -20 to -25 cmH2O within 20 seconds
ABGs • PaO2 represents oxygenation – adjust with PEEP or FiO2 • PaCO2 represents ventilation – adjust with VT or RR • pH represents Acid/Base status • pH acid: High CO2 (respiratory cause) or low HCO3 (Metabolic cause) • pH alkaline: Low CO2 (respiratory cause) or high HCO3 (Metabolic cause)
Draw ABGs • To stabilize • With any change in ventilator settings change only one vent setting at a time • With any change in patient condition