CLINICIAN’S POCKET REFERENCE - PART 6 doc

18 Respiratory Care 361 Vital Capacity (VC): Maximum volume of air that can be exhaled from the lungs after a maximal inspiration Residual Volume (RV): The volume of air remaining in the lungs at the end of a maxi- mal exhalation DIFFERENTIAL DIAGNOSIS OF PFTS Table 18–1 shows the differential diagnosis of various PFT patterns When interpreting PFTs, remember that some patients may have combined restrictive and obstructive diseases such as emphysema and asbestosis OXYGEN AND HUMIDITY SUPPLEMENTS Table 18–2 describes various methods of oxygen and humidity supplementation TABLE 18–1 Differential Diagnosis of Pulmonary Function Tests Test Restrictive Disease Obstructive Disease FVC TLC FEV1/FVC FEV1 ↓ ↓ N or ↑ ↓ N or ↓ ↑ ↓ ↓ OBSTRUCTIVE AIRWAYS DISEASE (COPD) Test FEV1 (% of VC) RV (% of predicted) Normal Mild Moderate Severe >75 60–75 40–60 200 RESTRICTIVE LUNG DISEASE Test Normal Mild–Moderate Severe FVC (% of predicted) FEV1 (% of VC) RV (% of predicted) >80 >75 80–120 60–80 >75 80–120 50–60 >75 70–80 18 75 70 Abbreviations: N = normal; ↑ = increased, ↓ = decreased; FVC = forced vital capacity; TLC = total lung capacity; RV/FRC = residual volume/functional residual capacity; FEV1 = forced expiratory volume in 1s; VC = vital capacity 362 Clinician’s Pocket Reference, 9th Edition TABLE 18–2 Various Methods of Oxygen and Humidity Supplementation Device 02 Range Nasal cannula L/min Fi02 Low 1–6 0.24–0.5 Simple face mask Medium 6–8 0.5–0.6 Partial rebreathing face mask High 8–12 0.6–0.7 Nonrebreathing face mask High 8–12 0.7–0.95 Venturi mask Low–medium — 0.24–0.50 Uses COPD, general oxygen needs General oxygen needs High oxygen emergency needs High oxygen emergency needs COPD (can specify exact Fi02) Note: Fi02 may vary with fluctuations in the patient’s minute ventilation when using a nasal cannula This is not true when using the Venturi mask because it is a “high-flow oxygen enrichment system” that supplies three times the patient’s minute ventilation, thus providing an exact Fi02 Abbreviation: COPD = chronic obstructive pulmonary disease Humidity Therapy 18 Humidity generators are divided into humidifiers and nebulizers Patients with intact upper airways do not need as high a percentage of relative humidity (% RH) as do patients with artificial airways (endotracheal tubes or tracheostomy tubes) Artificial airways require higher humidity to prevent secretions from obstructing the tubes To bring the % RH of the inspired gas up to room humidity (30–40% RH) when using the nasal cannula, simple oxygen mask, partial rebreathing mask, or nonrebreathing mask, the bubble-diffuser humidifier is the device of choice To provide medium to high levels of % RH, aerosol devices such as the face tent, aerosol mask, aerosol T piece, and aerosol collar are the devices of choice The humidity generator for these devices is the aerosol-jet nebulizer, which can provide cool or heated mist The gas that powers the nebulizer may be blended to any desired inspired oxygen concentration (FiO2) BRONCHOPULMONARY HYGIENE The following is a listing of the modalities available through the respiratory care or nursing services of most hospitals All are designed to help patients with their bronchopulmonary hygiene, more commonly referred to as “pulmonary toilet.” Bronchopulmonary hygiene is defined as maintenance of clear airways and removal of secretions from the tracheo- 18 Respiratory Care 363 bronchial tree This is important for routine postoperative surgical patients, medical patients with obstructive pulmonary diseases, or any patient with excessive respiratory secretions Aerosol (Nebulizer) Therapy Aerosolized medications such as bronchodilators and mucolytic agents can be delivered via nebulizer for spontaneously breathing, awake patients or intubated patients Indications • Treatment of COPD, acute asthma, cystic fibrosis, and bronchiectasis • Help in inducing sputum for diagnostic tests Goals • Relief of bronchospasm • Help in decreasing the viscosity and in clearing of secretions To Order: Specify the following: • • • • • Frequency Heated or cool mist Medications: In sterile water or NS FiO2 Example Albuterol 2.5 mg in 3 mL of sterile saline, FiO2 0.28 Chest Physiotherapy This technique uses P&PD along with coughing and deep breathing exercises (TC&DB) P&PD is performed by positioning the patient so that the involved lobes of the lung are placed in a dependent drainage position and then using a cupped hand or vibrator to percuss the chest wall Nasotracheal suctioning is quite uncomfortable for the patient but is still useful in the appropriate clinical setting in the absence of significant coagulopathy Indication • Treatment of pneumonia, atelectasis, and diseases resulting in weak or ineffective coughing To Order 1 P&PD: Specify the following: • Frequency • Segments or lobes involved (RUL, etc) • Duration • Drainage only 2 TC&DB: Ordered on a timed schedule or as needed • Example P&PD qid of RUL and RML 5 min/lobe or TC&DB q4h Incentive Spirometry This method encourages patients to make a maximal and sustained inspiratory effort to help reinflate the lungs or prevent atelectasis Indications • Treatment of patients at risk for developing postoperative pulmonary complications • Treatment and prevention of atelectasis, especially in postoperative setting 18 364 Clinician’s Pocket Reference, 9th Edition Goals Set for the patient depending on the device available: • Lighting lights • Moving Ping-Pong balls • Moving colored fluids in “blow bottles” To Order Specify the following: • Frequency (such as 10 min q1–2h while awake) • Device (if you have a preference) Example Incentive spirometry 10 min every hour with blow bottle TOPICAL MEDICATIONS The following agents can be added to aerosol therapy to prevent or treat pulmonary complications caused by bronchoconstriction, mucosal congestion, or inspissated secretions Remember, even though these are primarily topical agents, some systemic absorption can often occur Acetylcysteine (Mucomyst): A mucolytic agent useful for treating retained mucoid secretions; inspissated secretions; and impacted mucoid plugs seen in diseases such as COPD, cystic fibrosis, and pneumonia A bronchodilator should be given along with Mucomyst Usual Adult Dosage 1–3 mL of 20% acetylcysteine in 0.5 mL (2–10 mg) of Bronkosol Albuterol (Ventolin, Proventil): A short-acting selective bronchodilator with principally beta-2 activity; can cause tachycardia Onset 15 min Peak effect at 0.5–1 h, duration 3–5 h Usual Dosage 2.5 mg in 3 mL NS q4h Metaproterenol (Alupent, Metaprel): A short-acting bronchodilator with both beta1 and beta-2 activity; can cause tachycardia Peak effect at 0.5–1 h, duration 3–5 h Usual Dosage 0.3 mL (10–15 mg) of a 5% solution in 2.5 mL NS bid–qid Racemic Epinephrine: Contains both d and l forms of epinephrine Useful because the alpha effects result in mucosal vasoconstriction that reduces mucosal engorgement and the bronchodilation lessens the risk of hypoxemia Most useful for laryngotracheobronchitis and immediately after extubation in children Usual Dosage 0.125–0.5 mL (3–10 mg) in 2.5 mL NS 18 Ipratropium Bromide (Atrovent): A parasympatholytic bronchodilating agent that causes bronchodilation and a decrease in secretions with “drying” of the respiratory mucosa This is minimally absorbed and rarely results in tachycardia Onset 45 min, duration 4–6 h Usual Dosage 0.5 mg in 3 mL NS qid Atropine: A parasympatholytic agent that causes bronchodilation and a decrease in secretions with “drying” of the respiratory mucosa This is readily absorbed and, therefore has cardiac effects (tachycardia) Usual Dosage 0.025–0.05 mg/kg of a 1% solution 18 Respiratory Care 365 METERED-DOSE INHALERS All bronchodilating agents can be effectively delivered by metered-dose inhaler as long as proper technique is used For these devices to be successful, in-patients must be well trained or have the assistance of a nurse or respiratory therapist Albuterol and ipratropium bromide (Atrovent) can each be delivered two puffs q4h A combination bronchodilator (Combivent) containing the equivalent of one puff of each is also available and provides synergistic bronchodilatation 18 This page intentionally left blank 19 BASIC ECG READING Introduction Basic Information Axis Deviation Heart Rate Rhythm Cardiac Hypertrophy Myocardial Infarction Electrolyte and Drug Effects Miscellaneous ECG Changes INTRODUCTION The formal procedure for obtaining a readable ECG is given in Chapter 13, page 266 Every electrocardiogram should be approached in a systematic, stepwise fashion Many automated ECG machines can give a preliminary interpretation of a tracing; however, all automated interpretations require analysis and sign-off by a physician Determine each of the following: • Standardization With the ECG machine set on 1 mV, a 10-mm standardization mark (0.1 mV/mm) is evident (Figure 19–1) • Axis If the QRS is upright (more positive than negative) in leads I and aVF, the axis is normal The normal axis range is –30 degrees to +105 degrees • Intervals Determine the PR, QRS, and QT intervals (Figure 19–2) Intervals are measured in the limb leads The PR should be 0.12–0.20 s, and the QRS, 11 mm in aVL or R in I + S in aVF >25 mm • Infarction or Ischemia Check for the presence of ST-segment elevation or depression, Q waves, inverted T waves, and poor R-wave progression in the precordial leads 19 A more detailed discussion of each of these categories is presented in the following sections 367 Copyright 2002 The McGraw-Hill Companies, Inc Click Here for Terms of Use 368 1 mV 10 mm 1 mm Clinician’s Pocket Reference, 9th Edition 0.04 s 0.20 s FIGURE 19–1 Examples of a 10-mm standardization mark and time marks and standard electrocardiogram paper running at 25 mm/s BASIC INFORMATION Equipment Bipolar Leads • Lead I: Left arm to right arm • Lead II: Left leg to right arm • Lead III: Left leg to left arm Precordial Leads: V1 to V6 across the chest, as shown in the section on electrocardiograms in Chapter 13 (see Figure 13–9, page 267) ECG Paper: With the ECG machine set at 25 mm/s, each small box represents 0.04 s and each large box 0.2 s (see Figure 19–1, above) Most ECG machines automatically print a standardization mark 19 Normal ECG Complex Note: A small amplitude in the Q, R, or S wave is represented by a lowercase letter; a large amplitude by an uppercase letter The pattern shown in Figure 19–2 could also be noted as qRs • P Wave Caused by depolarization of the atria With normal sinus rhythm, the P wave is upright in leads I, II, aVF, V4, V5, and V6 and inverted in aVR 369 19 Basic ECG Reading R VAT 10 mm = 1 mV Voltage (mV) PR segment ST segment T P P U J PR interval Q S Isoelectric line QRS interval 1 mm QT interval QU interval 0 0.2 0.4 0.6 0.8 0.04 s Time (s) FIGURE 19–2 Diagram of the electrocardiographic complexes, intervals, and segments The U wave is normally not well seen (Reprinted, with permission, from: Goldman MJ [ed]: Principles of Clinical Electrocardiography, 12th ed Lange Medical Publications, Los Altos CA, 1986.) • QRS Complex Represents ventricular depolarization • Q Wave The first negative deflection of the QRS complex (not always present and, if present, may be pathologic) • R Wave The first positive deflection (R) is the positive deflection that sometimes occurs after the S wave) • S Wave The negative deflection following the R wave • T Wave Caused by repolarization of the ventricles and follows the QRS complex Normally upright in leads I, II, V3, V4, V5, and V6 and inverted in aVR AXIS DEVIATION The term axis, which represents the sum of the vectors of the electrical depolarization of the ventricles, gives some idea of the electrical orientation of the heart in the body In a healthy person, the axis is downward and to the left, as shown in Figure 19–3 19 370 Clinician’s Pocket Reference, 9th Edition I I AVF AVF –90∞ LAD 180∞ AVL Extreme RAD 0∞I I I Normal AVF +120∞ III +90∞ AVF +60∞ II AVF FIGURE 19–3 Graphic representation of the “axis deviation.” Electrocardiographic representations of each type of axis are shown in each quadrant The large arrow is the normal axis The QRS axis is midway between two leads that have QRS complexes of equal amplitude, or the axis is 90 degrees to the lead in which the QRS is isoelectric, that is, the amplitude of the R wave equals the amplitude of the S wave 19 • Normal Axis QRS positive in I and aVF (0–90 degrees) Normal axis is actually –30 to 105 degrees • LAD QRS positive in I and negative in aVF, –30 to –90 degrees • RAD QRS negative in I and positive in aVF, +105 to +180 degrees • Extreme Right Axis Deviation QRS negative in I and negative in aVF, +180 to +270 or –90 to –180 degrees Clinical Correlations • RAD Seen with RVH, RBBB, COPD, and acute PE (a sudden change in axis toward the right), as well as in healthy individuals (occasionally) • LAD Seen with LVH, LAHB (–45 to –90 degrees), LBBB, and in some healthy individuals 20 Critical Care 423 Alveolar-to-Arterial Gradient [P(A–a)O2] Provides an assessment of alveolar–capillary gas exchange • Alveolar PO2 (PAO2) minus calculated • Arterial PO2 (PaO2) minus measured Calculating the A–a Gradient To calculate the alveolar-to-arterial gradient: 1 Place the patient on 100% oxygen (FiO2) for 20 min 2 Next obtain a peripheral ABG measurement 3 Calculate the alveolar PO2 After breathing 100% oxygen for 20 min, the only gases other than oxygen within the alveoli are H2O and excreted CO2 from tissue metabolism PaO 2 [(713) × FiO 2 − ( PaCO 2 )] − 0.8 INDICATIONS FOR INTUBATION The decision to intubate a patient for prolonged ventilator support is one of the most difficult decisions for clinicians It is easy for the physician to be lulled into a false sense of security by marginal blood gases The following indications can be used as a basic checklist for respiratory support: • Inability to adequately ventilate (eg, chest trauma, sedation, paralyzed or fatigued respiratory muscles) • Inability to adequately oxygenate (eg, pulmonary edema, ARDS) • Excessive work of breathing (eg, prophylaxis for impending collapse) • Protection of airway (eg, unconscious, altered mental status, massive resuscitation, facial trauma) These basic indications should be used in conjunction with clinical judgment in the final decision for mechanical ventilation The decision to intubate, if made in a timely and appropriate fashion, can turn an otherwise traumatic intubation into a controlled and elective procedure Table 20–7 lists some common parameters used to evaluate the need for respiratory support in adults MECHANICAL VENTILATORS Classes of Ventilators The two classic types of ventilator are the pressure-limited and the volume-limited ventilators Although newer ventilators combine many of the qualities of both classes, it is conceptually advantageous to discuss the two types separately Additionally, several other types of ventilators are occasionally used Pressure Limited: These ventilators deliver a volume of air until a preset pressure is reached They are used in some neonatal units They are not generally used to ventilate adult patients, because changes in airway pressure and in lung and chest wall compliance may result in an inadequate minute ventilation This technique is reserved for patients who fail to respond to traditional modes of ventilation Volume Limited: A preset volume of air is delivered regardless of the opposing pressure This is the most common class of ventilator used (Note: A pressure limit setting usually allows the venting of excessive pressure to prevent barotrauma.) 20 424 Clinician’s Pocket Reference, 9th Edition TABLE 20–7 Indicators of Respiratory Failure Condition PaCO2 >60 mm Hg PaO2 30 breaths/min Altered mental status such that the patient is unable to protect the airway against aspiration Normal Range (adults) 35–45 mm Hg 80–100 mm Hg on room air 10–20 breaths/min High-Frequency Ventilation: Rapid oscillations of breath (60–1200 cycles) used with or without the bulk delivery of gases to the lung Several forms of this type of ventilation exist, including high-frequency jet ventilation, high-frequency positive pressure ventilation, and high-frequency oscillation Ventilator Modes Ventilator modes are represented in Figure 20–20 Controlled Ventilation: The patient gets a breath only when it is delivered by the machine The patient cannot initiate any of his or her own breaths Used in the past on patients who were intentionally paralyzed by drugs Assist Controlled: The patient gets a full mechanical tidal volume each time he or she attempts an inspiratory effort The respiratory frequency is determined by the patient, although a backup rate is set to ensure a minimum minute ventilation • Advantages of AC is that patients can easily increase their minute ventilation even if they are weak and have a poor inspiratory effort • Disadvantage is the predisposition to hyperventilation if the patient becomes agitated or has an altered respiratory drive because of neurologic injury Agitation may also lead to “breath stacking,” in which the ventilator delivers a second tidal volume before completing the expiratory phase of the first breath Fortunately, this is rarely a clinical problem because the patient often feels more comfortable and consequently less agitated because of the decreased work of breathing on AC Synchronous IMV: 20 The respirator delivers a set number of breaths each minute and allows the patient to supplement ventilation with his or her own inspiratory efforts between machine breaths This allows the patient to use the respiratory muscles As the ventilator rate decreases progressively, the patient assumes more of the work of breathing The ventilator also senses when the patient is taking a breath and will not deliver the mandatory breath until after the patient’s own breath is completed This was developed to prevent the patient’s working against the ventilator or receiving a double tidal volume (ie, a mechanical tidal volume on top of a spontaneous breath) This is the most commonly used type of ventilatory mode in conjunction with pressure support and PEEP 425 20 Critical Care Controlled ventilation (CV) Mechanical ventilation 0 Rate is fixed by ventilator Patient is not allowed to breathe spontaneously in between mechanical breaths Assist-controlled ventilation (AC) 0 Volume Each inspiratory attempt triggers a mechanical breath Synchronous intermittent mandatory ventilation (SIMV) 0 Patient is allowed to breathe spontaneously in between synchronized mechanical breaths Pressure support ventilation (PSV) + SIMV 0 Patient triggers positive pressure support during inspiration of spontaneous breath - in between SIMV mechanical breaths Time FIGURE 20–20 Representation of different ventilator modes 20 426 Clinician’s Pocket Reference, 9th Edition Pressure Support Ventilation: A preset level of positive pressure is turned on only during the inspiratory phase and is turned off during expiration The patient controls the rate and inspiratory time while augmenting tidal volume and inspiratory flow The higher the pressure support, the less work the patient expends to take a breath Thus, PSV is comfortable because the patient has more control of his or her ventilation PSV serves as an ideal weaning mode because the pressure can be turned down slowly, with changes as small as 1 cm H2O This allows the patient to assume the workload of breathing in small increments PSV is often integrated with SIMV as a backup to ensure a minimum minute ventilation Positive End-Expiratory Pressure: Positive pressure applied during expiration It represents the supraatmospheric pressure remaining in the airways at the end of expiration PEEP increases alveolar ventilation by preventing small airway collapse, thereby increasing FRC PEEP also is often used prophylactically against atelectasis, particularly in the postoperative period It has become a standard modality to treat pulmonary edema Increasing levels of PEEP is typically used to decrease the FiO2, in an attempt to limit oxygen toxicity One disadvantage of PEEP, however, is that it may decrease the cardiac index by decreasing left ventricular end-diastolic volume and should be used cautiously in patients at risk for myocardial ischemia Pressure Regulated Volume Control: This mode of ventilation is used in the setting of increased airway pressure A microprocessor in the ventilator adjusts the pressure needed to achieve the proper tidal volume Continuous Positive Airway Pressure: Positive pressure throughout inspiration and expiration without mechanical assistance during ventilation This is equivalent to PS plus PEEP at a constant pressure level The patient does all the breathing on his or her own Often used as a last step before extubation A CPAP trial may be performed at room air or an FiO2 of 40% (See the discussion on extubation-weaning trials page 427.) High-Frequency Ventilation: The physiologic explanation of HFV defies conventional teaching and is under current study Despite the marked reduction in flow rates, oxygenation and CO2 exchange are still achieved HFV may be ideally suited to treat such conditions as bronchopleural fistulas or may serve as a more desirable form of ventilation during surgeries requiring a minimum of lung movement Ventilator Management Ventilator Orders Once the decision has been made to place a patient on a ventilator, the patient must be intubated with an appropriate endotracheal tube (see Chapter 13, page 268) The following is a sample of typical initial ventilator orders for an adult: 20 • • • • • • Mode (ie, AC, SIMV) FiO2 30–100% Rate 8–12/min Tidal volume 5–7 mL/kg Pressure support (level depends on the clinical situation) PEEP (5 cm H2O or higher, if needed) Ventilator Setting Changes The following four basic respiratory parameters can be changed to improve ventilation, oxygenation, and compliance, and to prevent ventilator induced lung injury: 20 Critical Care • • • • 427 FiO2 Minute volume (tidal volume X rate) Pressure support PEEP 1 FiO2 Initially, an FiO2 that ensures a saturation (SaO2) >90% is set on the ventilator Once adequate oxygenation is established, the FiO2 is decreased to avoid oxygen toxicity Because of the danger of oxygen toxicity, an FiO2 >50% is to be avoided Increasing the level of PEEP is often a helpful means of decreasing the FiO2 requirement while maintaining adequate oxygenation 2 Minute volume Adjust to maintain PCO2 within a normal range (35–45 mm Hg) Usually done by increasing tidal volume Changes in rate are usually limited by a decrease in PCO2, with a resultant respiratory alkalosis 3 Pressure support After the patient’s respiratory pattern is established on SIMV, pressure support may be added initially at a level of 5–8 cm H2O Pressure support may then be turned up to a level that allows the patient to breathe at a comfortable rate (eg, 70 mm Hg PCO2 7.35 • Vital capacity >15 mL/kg • Tidal volume in adults (50–70 kg) >400 mL • Inspiratory force > –30 cm H2O Weaning Modes Modern respirators are designed to facilitate weaning Once the preceding criteria have been met, a ventilator mode appropriate to the clinical situation, such as SIMV or PSV, is usually selected SIMV and PSV are considered weaning modes because the patient is allowed to assume more of the workload of breathing as mechanical support is withdrawn Extubation Trials Once weaning has achieved minimal ventilatory settings, various trials off mechanical support (while still intubated) may be attempted CPAP trials with 5 cm of positive pressure is the most commonly used For example, a 5-cm CPAP trial with TABLE 20–8 Criteria for Weaning from Mechanical Ventilation Parameter 20 Pulmonary mechanics Vital capacity Resting minute ventilation (tidal volume × rate) Spontaneous respiratory rate Lung compliance Negative inspiratory forces (NIF) Oxygenation A-a gradient Shunt fraction PO2 (on 40% FiO2) PCO2 Value >10–15 mL/kg −25 cm H20 90–92% or PaO2 >70 mm Hg 2 Sequentially reduce the IMV rate to a level of 4 breaths per minute Add pressure support to maintain adequate minute volume ABGs as well as capnography are used to monitor for hypercarbia 3 Sequentially reduce PEEP in 2- to 3-cm H2O increments while maintaining SaO2 >90%, until a level of 5 cm H2O is achieved Follow FiO2 If a PA catheter is present, mixed venous saturation information will allow for calculation of the shunt equation Qs/Qt should be kept below 0.25 4 Sequentially reduce pressure support by 2- to 3-cm H2O increments, maintaining minute volume until a pressure support of 5 cm H2O is met Monitor respiratory rate, work of breathing, and PCO2 Essential Tips in Ventilator Management • Avoid changing more than one ventilator parameter at a time • A PO2 70, a PCO2