Lecture 6 Respiratory Physiology, Pathophysiology and Anesthesia Management – Flashcards
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Which gas law explains the mechanics of breathing?
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Boyle's: contraction of the muscles? intra thoracic pressure and ?volume of thoracic cavity
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Which muscles contract during normal breathing?
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Diaphragm ; external intercostals
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How can only half the diaphragm become paralyzed?
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Two domes of the diaphragm separate the abdominal ; thoracic cavities, phrenic nerve injury results in paralysis on only that side.
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How far does the diaphragm descend during normal breathing? Forceful?
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Normal: 1-2 cm Forceful: 10 cm For air to move into the alveoli pressure must be less than atmospheric pressure.
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What is lung compliance?
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Defined as the change in volume divided by the change in pressure. V/P.
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What is static compliance?
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Pressure/volume relationship for a lung when air is not moving. ?: any condition making lungs difficult to inflate, fibrosis, ARDS, obesity, external compression ?: emphysema as elastic tissue is lost, problem will be DEflating lungs
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What is plateau pressure?
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Pressure at end-exhalation, can observe during inspiratory pause on ventilator.
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What is static compliance?
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TV/ (Plateau pressure-PEEP) Normal: 60-100 ml/cm H?O
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What is dynamic compliance?
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TV/ (PIP- PEEP) Compliance of the air in the lung while moving.
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What forces are responsible for emptying of the lung dying exhalation and have a large role in determination of lung compliance?
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lung elastic recoil, surfactant also causes elastic recoil
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What does LaPlace's Law state?
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If surface tension (T) is constant, pressure (P) would ? as radius (r) ?.
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Do the lungs follow LaPlace's Law?
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No, as alveolar radius ?, surface tension also ? so that pressure remains the same. This occurs because of surfactant.
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What is the role of surfactant in the lungs?
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Surfactant will ? the surface tension in the small alveoli, preventing alveolar collapse.
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What is the resting end-expiratory point?
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Outward recoil of the chest wall is balanced by the inward elastic recoil of the lungs.
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What is Reynold's number?
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Predicts when flow will be laminar or turbulent. 4000 turbulent Re= pvd/? (pg 567)
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Resistance to laminar flow follows what law?
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Pousielle's, viscosity, length, distance. Doubling radius decreases resistance 16 times.
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What amount of O? is utilized by ventilatory muscles in eupneic breathing?
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; 5%
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What are the two major categories of lung disease?
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Obstructive: expiratory flow rates ? Restrictive: ? lung volumes ; lung compliance
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The amount of air that enters ; leaves the body with each breath and contains ?500ml air is?
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Tidal volume Vt ? 500ml
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Equals the respiratory rate multiplied by Vt. RR x Vt= ?
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Minute volume MV
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What is the volume of air remaining in the lungs after maximum expiration called?
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Residual volume RV ? 1200ml
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What is the maximum volume of air inspired from the resting end-expiratory level called?
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Inspiratory reserve volume IRV?3000
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What is the maximum volume of air expired from the resting end-expiratory level called?
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Expiratory reserve volume IRV? 1100
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What is the sum of the four basic lung volumes? IRV+Vt+ERV+RV=
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Total Lung Capacity TLC? 5800 Volume of air in the lungs after maximum inspiration (the sum of all volume compartments)
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What is the maximum volume of air inspired from the end-expiratory level? IRV + Vt=
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Inspiratory Capacity IC? 3500
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What is the maximum volume of air expired from the maximum inspiratory level? IRV+Vt+ERV=
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Vital Capacity VC? 4500
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What is the maximum volume of air remaining in the lungs at the end expiratory level? RV+ERV=
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Functional Residual Capacity FRC ? 2300
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What is the normal respiratory pressure in eupneic breathing? Maximal inspiration ; expiration?
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-1 to +1 -90 to ;100
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What is the volume of conducting airways called?
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Dead space, no active gas exchange, ?2ml/kg
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What are alveoli that are ventilated but not perfused?
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Alveolar dead space
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Alveolar dead space + anatomic dead space=
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Volume of dead space % VDS= (PaCo?-PECo?)/ PaCo?
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What is the respiratory quotient?
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Ratio of the amount CO? produced to quantity of O?
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What two sources supply the lungs with blood?
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1- bronchial arteries 2- pulmonary arteries
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What is the perfusion to zone 1?
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Dead space, ventilated but NOT perfused, upper part of lung, alveolar pressure is ;PAP
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What is the perfusion to zone 2?
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Variable flow between vasculature ; alveolar pressure.
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What is the perfusion to zone 3?
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Continuous blood flow, pulmonary ; venous pressure are ; alveolar pressure.
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Pulmonary Edema
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Capillary leak overcomes the compliance of interstitial space and fluid begins to pass to alveoli.
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How do you treat the occasional negative pressure pulmonary edema that occurs during emergence after extubation?
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O?, maintain patent airway, CPAP, fluid therapy to restore depleted intravascular volume.
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Ventilation is usually 4L/ minute and pulmonary blood flow is usually 5L/minute. What is the V/Q (ventilation/perfusion) ratio?
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0.8
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Which portion of the lungs are generally more compliant?
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Dependent regions, non-dependent portions are tented open and less compliant.
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What are some common causes of V/Q mismatch?
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Pulmonary embolus, very high airway pressure, very low cardiac output, airway obstruction, alveolar collapse, pneumonia.
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Effect of anesthesia on respiratory physiology
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-Moving from upright to supine ? FRC - 10% shunt from ? CO, atelectasis -inhaled anesthetics ? effectiveness of hypoxic pulmonary vasoconstriction, ? PaO? ?A-a gradient -Gases bronchodilate - GA ? ventilatory response to CO? ; hypoxia
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Diffusivity is?
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Solubility/ ?molecular weight CO? heavier but 24 times more soluble than O?
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What are the two ways oxygen can be transported in the blood?
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1-physical: dissolved in blood 2- chemical: bound to HGB
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What does hemoglobin do?
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HGB: rapidly ; reversibly binds oxygen, allowing oxygen to be released into the tissues
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What is hematocrit?
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Ratio of volume of blood cells: total volume of blood HGB level of 10g/100ml= 30% HCT Man: HCT 45%, HGB 15 Woman: HCT 39% HGB 13
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What does the oxyhemoglobin Dissociation Curve show?
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Relationship between the PO? of the plasma and the percentage of HGB saturation.
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What causes shifts to the LEFT of the oxyhemoglobin dissociation curve?
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-hypocapnia - ? temperature - alkalosis ?pH - ? 2,3 diphosphoglycerate Results i an increased affinity for HGB for O?
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What causes shifts to the RIGHT of the oxyhemoglobin dissociation curve?
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- hypercapnia - ? temperature -acidosis ? pH (? CO?) - ? 2,3 diphosphglycerate Results in a decreased affinity of HGB for O?
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What is the P???
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PaO? at which 50% of HGB is saturated
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What is the normal P?? in an adult?
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P??= 26-27 mmHG HGB curve to right= ? P?? HGB curve to left= ? P??
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What is methemoglobinemia? How is it treated?
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Iron in ferric, Fe³, instead of norma ferrous, Fe² state. HGB doesn't combine with O? in ferric state. Causes: nitrates, prilocaine Treat: O? therapy & methylene blue
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What are the three ways blood can transport CO??
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1- physical solution 5-10% 2- chemically combined with amino acids of blood proteins 5-10% 3- bicarbonate ions 80-90%
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What is the Haldane effect?
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Blood with oxygenated HGB: right shift Blood with deoxygenated HGB: shift left Allows blood to load more CO? at the tissues where more deoxygenated HGB is present and unload at the lungs.
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How does the respiratory system work to maintain body pH?
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Works along with the kidneys and the buffer systems to balance the acids & bases of the blood. Respiratory system can rapidly compensate for metabolic acidosis or alkalosis by changing alveolar ventilation. -Changes in the blood H ion content affect chemoreceptors - Chemoreceptors ? or ? alveolar ventilation - PaCO? is altered within minutes.
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What are volatile acids?
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-Exhaled CO? from lungs - 24,000 mEq/day, excreted through lungs -50 mEq from food, excreted by kidneys
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How is respiratory alkalosis or acidosis treated in the mechanically ventilated patient?
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? rate for alkalosis ? rate for acidosis
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Why shouldn't you give bicarbonate in respiratory acidosis?
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Bicarbonate can dissociate to CO? worsening acidosis.
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What generate the spontaneous respiratory rhythm?
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Medullary respiratory center (under floor of 4th ventricle)
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What centers does the pons contain?
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Apneustic: lower pons Pneumotaxic: upper pons
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What are three respiratory reflexes elicited by stretch receptors?
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Hering Breur inflation: large ; small airways- cease respiration, Hering Breur deflation: J receptors, hyperpnea Paradoxical reflex of Head: stretch receptors in lung, inspiration (newborn)
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What are J receptors?
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Vascular receptors that initiate lung responses "Juxtapulmonary capillary"
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What two important inputs are the primary chemical control of breathing?
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Arterial Cerebral Spinal Fluid: not directly exposed to arterial blood due to BBB, but CO? is rapidly diffusible through BBB, so changes transmitted in ?2 minutes
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What physical findings are found in the COPD patient?
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-Pulsus paradoxus in 2/3 -? in CO from ?catecholamine release - Enhanced HR response -? GFR, renal plasma flow
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What are the hallmark signs of COPD?
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-Exercise limitation - Chronic productive cough
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What are the characteristics of someone with chronic bronchitis AKA "blue bloater"?
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- overweight, dusky extremities - PaO? 45 -cor pulmonale - copious sputum ; cough - cardiomegaly
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What are the characteristics of someone with chonic emphysema AKA "pink puffer"?
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- thin, emaciated, anxious - PaO? ;60 - PaCO? normal - dyspnea - small heart, low flat diaphragm
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Preoperative Evaluation of the COPD patient
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- Supplemental O? if PaO² ; 60 or cor pulmonale - Assess for ? respiratory effort, altered breathing, abnormal heart sounds, productive cough -B agonists are mainstay treatment
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Anesthesia management ; COPD
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- Regional Anesthesia: may be safer than GA, do not use above T6, risk of ? expiratory reserve volume -GA ? A:a difference -Muscle relaxant ?20% FRC
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What are some respiratory considerations when COPD patient under GA?
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- If N?O is used bullae may enlarge ; rupture, contraindicated - Slower diffusion times cause longer induction ; emergence - Require ? Vt -Use caution with PEEP, PEEPe ; PEEPi decreases work of breathing - May require longer mechanical ventilation
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Postoperative care in COPD
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- Encourage ambulation - IS with peak inflation for 3-5 seconds reexpands alveoli
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Asthma is defined as...
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chronic inflammation disorder of the airways. - bronchoconstriction - hyper-irritability of tracheobronchial tree - air-way remodeling - immune mediated inflammatory response
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Key hallmarks of asthma are..
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- Recurrent wheezing - Dyspnea/tachypnea -Cough -Chest tightness -Symptoms worse with exercise
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What is status asthmaticus?
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Severe obstruction lasting for day or weeks.
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What will diagnostic testing for asthma show?
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- ? in FEV? of more than 15% p bronchodilator - Respiratory alkalosis -Eosinophilia
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What will you see in an anesthetized asthmatic patient during an attack?
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Wheezing, mucous, high inspiratory pressures, blunted CO? waveform, hypoxemia
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What are 3 risk reduction strategies used in the asthmatic patient?
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1- review meds ; control 2- provide meds to improve lung function possibly oral systemic corticosteroids 3- If on high dose steroids, give 100mg hydrocortisone every 8 hours IV during surgical period the wean within 24 hours postop.
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Preoperative evaluation of asthmatic patient
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- atropine or robinul exhibit mild bronchodilating effects and are effective 20-30 minutes before surgery
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Intraoperative management of asthmatic
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-Regional safer -Propofol or ketamine for induction -Avoid atracurium (histamine release), B blockers (bronchoconstrict such as esmolol or labetalol -caution with emergence ; extubation
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Pregnancy ; astham
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- Treat, albuterol is preffered -Inhaled steroids are safer - don't use H? blockers -ephedrine for vasopressor
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Pulmonary Artery Hypertension
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- Caused by ?in vascular tone and the growth & proliferation of pulmonary vascular smooth muscle - 90% small vessel obliterated in lungs - ECG enlarged R atrium, R ventricle hypertrophy - Anesthesia management: vasodilator agents
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Cor Pulmonale or Pulmonary Heart Disease
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- PAH advanced into R ventricle hypertrophy, dilation and cardiac decompensation - Hypertrophy of smooth muscle in tunica media= irreversible ? in PVR - R sided cath for diagnosis (usually also has COPD)
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What are some clinical signs of cor pulmonale?
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-? JVD -Cardiac heave - widely split S?, S? gallop & presence of S? -Pulmonic or tricuspid murmur - hepatomegaly, ascites - large, hypertrophic R heart
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Treatment & anesthesia management in cor pulmonale?
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Goals: ? workload of heart, reduce PVR, prevent ? in PAP, avoid major hemodynamic changes Anesthesia: keep well oxygenated, avoid acidosis, avoid vasoconstrictors, avoid ? sympathetic tone, avoid hypothermia
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Pulmonary embolism
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PE is the impaction of a dislodged thrombus into the pulmonary vascular bed. - contributing factors: stasis of blood flow, venous injury, hyper coagulation (Virchow triad) - moderate hypoxemia without CO? retention
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What are some S/S of PE?
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- Dyspnea of sudden onset -tachypnea, tachycardia - hypotension - cyanosis - neck vein distention - chest pain, syncope - cough, hemoptysis
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Surgery with PE
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-Usually to place umbrella filter -use high FIO? -may need continuos catecholamines - Induction with etomidate or ketamine (hemodynamically stable) -Detection under GA: decreasing PETCO? and tachycardia followed by ? in SaO? and arterial hypoxemia -ECG: right axis deviation, R BBB, peaked T waves
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Pulmonary edema
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-Excess fluid in interstitial and air-filled spaces of lung -High pressure & ? permeability (Starling) -Nearly always accompanied by preexisting disease - Upper airway obstruction, laryngospasm after extubation (observe longer than 60-90 mins) - Pink, frothy expectorations - Basilar crackles on auscultation - Rapid, shallow breathing - Pleural effusion, "whited out", "butterfly" CXR
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Anesthesia Management of Pulmonary Edema
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- high FiO? - PEEP or CPAP or intubation - Vasodilators, diuretics, inotropes, steroids - Morphine frequently used , preload reducer & venodilatory -Furosemide, ?left atrial pressure, diuresis
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Aspiration Pneumonitis
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- Adds 15 days to hospital stay, $22,000 1:3000 anesthetics - stomach contents into lung -induction,intubation or emergence -chemical, mechanical or bacterial - arterial hypoxemia, tachypnea, tachycardia, HTN, cyanosis - ABG & CXR
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Anesthesia Management in Aspiration Pneumonitis
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-bicitra 15-30 minutes preop -famotidine or other H? blocker 45-60 mins prep - if aspiration during induction, tilt head to side, rapid suction of mouth & pharynx -early PEEP - condition of patient 2 hours post aspiration is prognostic of eventual course
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ARDS
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- history or noxious event? interval of hours to days of normal lung function post event? rapid onset and progression to dyspnea, severe hypoxia, stiff non-compliant lungs - 50-70% mortality 90% in gram negative septic shock - Risk factors: shock, trauma, pulmonary infection, inflammatory disease, exposure to narcs/barbs, CNS disease, aspiration, metabolic events -cytokines & phospholipids - treat, O?, antibiotics, replace fluids, help heart
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Anesthesia Management of ARDS
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- PIP, PEEP (barotrauma from prolonged high PEEP) - in general lower PEEP 6-8ml/kg and lower Vt - A-line for ABG's, lactic acid level -hypovolemic/ hemodynamically unstable - CO, filling pressures of heart -consider drug metabolism (multiple organs struggling) -continual precordial breath sounds
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Noncytotoxic Drug Induced Pulmonary Disease
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- Over 100 drugs produce adverse effects on lungs - Amiodarone- severe pulmonary toxicity, accumulates in lung, non-productive cough, weight loss, dyspnea, fever, hypoxemia, usually after 2 months of administration - Gold salts used in RA, hypersensitivity in lungs, 6hr to 1month post administration
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Cytotoxic Drug Induced Pulmonary Disease
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- Chronic pneumonitis ; fibrosis: direct cytotoxic effect on endothelial, interstitial or alveolar epithelial cells ?inflammatory response? deposits fibrin?interstitial inflammation - Hypersensitivity Lung disease: bleomycin, methotrexate, procarbazine -Noncardiogenic Pulmonary Edema: anti-neoplastic agents, bleomycin (lowest possible O?)
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Pulmonary Oxygen Toxicity
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-Prolonged duration of O?, ;50% for 24 hours - Excessive production of free O? radicals -? O?, antineoplastic agents, age, previous radiotherapy of thorax, combination chemotherapy -Acute: type 1 cells, Chronic: type 2 cells - substernal chest pain, tachypnea, non productive cough
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Sarcoidosis
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-Multisystemic disorder non-caseating epithelioid-cell granulomas, 90% involves lungs - cor pulmonale - lymph node involvement - treat with corticosteroids
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Flail chest
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- chest trauma, multiple rib fractures -paradoxical movement of the chest wall at the site of fracture -hypoventilation, hypercapnia, alveolar collapse - pain control, intercostal nerve block, IS, PEEP - no wide swings in pleural pressure with vented patient
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Simple Pneumothorax
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- no communication with the atmosphere - no shift of mediastinum or hemidiaphragm - catheter aspiration or tube thoracotomy - observe
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Communicating Pneumothorax
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- communcation with atmosphere "sucking chest wound" - cover with occlusive dressing - tension pneumo possible - O?, thoracotomy, intubate ; ventilate
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Tension Pneumothorax
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- Air progressively accumulates under pressure within the pleural cavity - Mediastinum shifts to opposite side - ?CO, ? BP, ?CVP - hypotension, hypoxemia tachycardia, ? airway pressures - Lethal, decompression of chest to treat, 16-18g angiocath into 2nd or 3rd intercostal space
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Hemothorax
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- accumulation of blood in pleural cavity - evacuate blood, thoracostomy - spontaneous (rupture of alveoli), traumatic (rib fracture) or iatrogenic (line placement, barotrauma, high airway pressures) - no nitrous unless chest tube is present, never in closed pneumo
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Atelectasis
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- collapse of pulmonary tissue, no gas exchange - first few minutes of GA, lasts hours to days due to loss of diaphragmatic tone - use Vt 6-10 ml/kg, PEEP and vital capacity maneuvers (30 cm H?O held for 10 seconds in alveoli)
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Pleural Effusion
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- abnormal accumulation of fluid in the pleural space - Causes: block lymph drainage, cardiac failure, reduced plasma colloid osmotic pressure, infection -thoracostomy, thoracentesis, pleurodesis - tetracyline through chest tube= adhesion formation and fusion of membranes
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Pectus Excavatum
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- funnel chest, depression of sternum - Reduced TLC
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Pectus Carinatum
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-longitudinal protrusion of the sternum -displaced sternum, corrected surgically
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Kyphoscoliosis
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-accentuated posterior curvature of spine - lateral bending and rotation of vertebral column - cervical scoliosis= difficult airway - ;60° curve = ? pulmonary function - ? lung volumes ; chest wall compliance, V/Q mismatch, hypoxemia, ?PAP, ?work of breathing, abnormal response to CO?
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Anesthetic Management for Kyphoscoliosis
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-Assess -Labs, PFT -Blood type ; screen - MAC of 1, opioid infusion ; N?O - possible deliberate hypotension
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Ankylosing Spondylitis
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- Rheumatoid spondylitis - fusion of spinal vertebrae and costovertebral joints - atypical fibrosis of lungs, fixation of thoracic cage
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Anesthesia Management for Ankylosing Spndylitis
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- Upper airway is priority, potential for obstruction - Cervical spine involvement may limit movement -Awake intubation with fiberoptic scope
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Airway Management M ; M
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-Improper face mask technique can cause continued deflation of anesthesia reservoir when APL is closed, indicating leak around mask. Mimimal chest movement ; minimal breath sounds = obstructed airway
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What does the laryngeal airway protect?
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Partially protects the larynx from pharyngeal secretions. Should remain in place until return of airway reflexes.
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What is done with the ETT cuff after insertion?
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-Cuff is inflated with least amount of air necessary to create positive pressure ventilation (minimize pressure transmitted to tracheal mucosa)
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What is the earliest indicator of bronchial intubation?
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? in positive inspiratory pressure
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What can cause postoperative hoarseness and increase the risk of extubation?
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Cuff above the level of the cricoid cartilage.
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How can you prevent esophageal intubation?
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-Direct visualization of the tip of tube through the vocal cords. - Ausculate bilateral breath sounds - No gastric gurgling - ETCO? - CXR
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What are some indications of bronchial intubation?
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- Unilateral breath sounds - hypoxia - inability to palpate cuff in sternal notch - decreased bag compliance - high inspiratory pressures
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What can large negative intrathoracic pressures in struggling patient with laryngospasm result in?
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- Negative pressure pulmonary edema
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How is the length for a nasal airway determined?
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-Measure nares to meatus of ear, should be about 2-4cm longer than oral airway
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What is the maximum amount of positive pressure ventilation to avoid stomach inflation?
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20 cm H?O
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Why are uncuffed tubes used in children?
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Minimize risk of pressure injury ; postintubation croup
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What are oral tracheal tube size guidelines?
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Infant: 3.5 mm 12 cm Child: 4+ (Age/4 )= diameter 14+ (Age/2) = cm EG: 12 year old child 4+ (12/4)= 7mm 4+ (12/2)= 20cm Adult: Female: 7-7.5mm 24cm Male: 7.5-9.0mm 24c
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In general when is the best time to extubate a patient?
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-Either deeply anesthetized or - Fully awake
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How can you tell if a patient is lightly anesthetized or deeply anesthetized?
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Light: any reaction to pharyngeal suctioning Deep: no reaction to pharyngeal suctioning
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How many mmHG is the ETT cuff inflated to?
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- About 20mmHG, higher pressures can lead to necrosis, inflammation, ulceration
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How can you break a patient out of laryngospasm?
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-Gentle positive pressure ventilation - 100% O? - IV lidocaine or succinylcholine
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Why do we use uncuffed tubes in peds?
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Minimize pressure injury and postintubation croup
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Anatomy of mouth and nose
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Warms and humidifies air, resistance 2x compared to exercise
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Anatomy of Pharynx
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Connects nasal/oral cavity to larynx Nasopharygnx separated by nasopharynx Oropharynx C2-C3 Hypopharynx ends at cricoid cartilage C4-C6 (food and respiration mix)
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Anatomy of Larynx
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C3-C6 separates trachea from esophagus, reflexes exaggerated causes laryngospasm 3 paired (6) cartligages 3 unpaired thyroid, cricoid, aretynoid and epiglottis
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What is the narrowest part of the adult airway?
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Vocal cords
