This chapter reviews assessment and documentation of patient-ventilator interactions after a patient has been placed on a mechanical ventilator. The first step in this process involves the respiratory therapist verifying the physician’s orders (Box 8-1).² Once the physician’s orders have been verified, the respiratory therapist ensures that the designated ventilator has passed an operational verification procedure (OVP). The OVP process usually is described in the respiratory therapy department’s policies and procedures manual.

Box 8-1

Physician’s Orders for Mechanical Ventilation

The orders written by the physician for mechanical ventilation settings vary between institutions. In some cases the physician’s orders may be very specific, with little flexibility for respiratory therapist involvement. More commonly, the physician orders simply request a particular protocol for mechanical ventilation, which is then followed by the respiratory therapist, nurse, and other staff members involved with the care of the patient.²

The orders or protocol should include at least one (and preferably both) of the following:

• Desired range for the arterial carbon dioxide partial pressure (PaCO₂), transcutaneous carbon dioxide partial pressure (PtcCO₂), or end-tidal carbon dioxide partial pressure (P_ETCO₂) and/or for the arterial oxygen partial pressure (PaO₂), oxygen saturation as measured by pulse oximetry (SpO₂), transcutaneous oxygen partial pressure (PtcO₂), or arterial oxygen saturation (SaO₂).

• Ventilator variables to be initiated or manipulated to achieve the desired arterial blood gases (e.g., mode, tidal volume [V_T], respiratory rate [f], set pressure, and fractional inspired oxygen [F_IO₂]) while protecting the lung.

It is important that the respiratory therapy department maintains records showing the OVP history for each ventilator. In addition, a label or form should be attached to each ventilator showing when the OVP was performed, by whom, and whether the ventilator passed the multiple-part test. Newer microprocessor-controlled ventilators perform a series of automated self-tests when the operator initiates the self-test process. This self-test record may be part of the OVP.

The equipment evaluation process should also involve checking the integrity of the ventilator circuit and humidifier system and ensuring that related equipment has been correctly attached and tested to make sure the system is free of leaks (Box 8-2).²

Box 8-2

Simple Verification of Ventilator Operation

A simple ventilator check should be performed:

• Before connecting a patient to a ventilator for the first time.

• Before reconnecting the patient to a ventilator if the circuit has been changed or disassembled for any reason.

The operational verification procedure should also include checking the system for leaks before the patient is connected to the ventilator. To check for leaks, the operator should:

• Set the tidal volume (V_T) at 500 mL, the gas flow low (e.g., 20 L/min), the maximum pressure limit high (e.g., 100-120 cm H₂O), and an inspiratory pause of 1 to 2 seconds.

• Occlude the Y-connector, cycle the ventilator, and observe the airway pressure rise and pause on the pressure manometer; if no leak is present, the circuit will hold the pressure steady.

• Change the ventilator settings to those appropriate for the patient before connecting the patient to the ventilator.

• Newer microprocessor-controlled ventilators automatically perform a test to check for leaks in the patient-ventilator circuit. This test can be performed at anytime but the patient must be disconnected from the ventilator to perform the test.

Documentation of the Patient-Ventilator System

In addition to documentation of the OVP, patient information and ventilator settings should be documented regularly when a patient is receiving ventilatory support. These data can be recorded on a computer software program with specific entry fields or kept as a paper record. Regardless of the form it takes, the document often is called a ventilator flow sheet.

The frequency of patient-ventilator system checks depends on the institution’s policy. They generally are performed every 1 to 4 hours.3 In addition to this schedule, patient-ventilator system checks are performed:

• Before an arterial blood gas (ABG) sample is drawn

• When the physician has entered new orders

• Before hemodynamic data or bedside pulmonary function data are measured

• When a ventilator change has been made

• When an acute change occurs in the patient’s condition (such changes should be documented as soon as possible after the event)

• When a patient returns from testing (e.g., x-ray, magnetic resonance imaging, or MRI)

• When the ventilator’s performance is questionable

It is important to recognize that these patient-ventilator system checks represent a documented evaluation of the ventilator’s function and the patient’s response to ventilatory support. The American Association for Respiratory Care (AARC) has developed clinical practice guidelines for recording patient-ventilator system checks.2 Several points regarding these guidelines should be emphasized:

• Data relevant to the patient-ventilator system check are recorded on the appropriate hospital form and are part of the patient’s medical record.

• The patient-ventilator system check includes observations of ventilator settings at the time of the check.

• The record should include the physician’s order for mechanical ventilator settings.

• The patient-ventilator system check includes a brief narrative of the clinical observations of the patient’s response to mechanical ventilation at the time of the check.

Figure 8-1 shows the information that may be included on a ventilator flow sheet.² The top of the form contains basic patient information:

• Medical record number

• Ventilator start date

• Age

• Weight

• Height

• Ideal body weight (IBW)

• Body surface area (BSA)

• Physician’s orders

• Endotracheal tube (ET) size and the centimeter marking at the teeth, corner of the mouth, or nares

• Date of intubation

• Date mechanical ventilation was initiated

• Ventilator day (number of days on the ventilator)

Spaces are also provided for current information and measurements of patient and ventilator parameters. These may include the following:

• Date

• Time

• Mode of ventilation

• Minute ventilation ()

• Respiratory rate (f)

• Tidal volume (V_T)

• Peak inspiratory pressure (PIP)

• Plateau pressure (P_plateau)

• Static compliance (C_s)

• Airway resistance (Raw)

• Fractional inspired oxygen (F_IO₂)

• Temperatures of inspired gases

• Inspiratory-to-expiratory (I : E) ratio

• Continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP)

• Inspiratory and end-expiratory positive airway pressures (IPAP/EPAP)

• Arterial blood gases (ABGs)

• Alveolar-to-arterial partial pressure of oxygen (P[A-a]O₂) or ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO₂/F_IO₂)

• Vital capacity (VC)

• Maximum inspiratory pressure (MIP)

• Vital signs

• Alarm settings

Volumes, pressures, temperature, vital signs, and F_IO₂ are measured during each patient-ventilator system check. Please note that although F_IO₂ may be measured intermittently for adults, it should be continuously monitored for infants receiving mechanical ventilation.2 Most of the current intensive care unit (ICU) ventilators have oxygen analyzers that provide continuous monitoring of F_IO₂. Alarms should be regularly checked to ensure that they have been set appropriately. ABGs, shunt, P(A-a)O₂, and PaO₂/F_IO₂ are determined when the patient’s condition or the ventilator settings change significantly.

Despite the importance of regular, accurate documentation, many respiratory therapy departments do not follow the AARC’s clinical practice guideline for patient-ventilator system checks or a similar model.^3,4 Case Study 8-1 provides a clinical scenario illustrating the important of maintaining accurate patient-ventilator records.⁵

Case Study 8-1

The Importance of Documentation

A 38-year-old woman is intubated for respiratory failure secondary to severe pneumonia. After 24 hours her status improves. The endotracheal tube is kept in place to allow suctioning, because she has large amounts of secretions. On the third day after intubation, her respiratory status declines. She has a cardiac arrest and is resuscitated but suffers brain injury as a result. She dies several weeks later.

The family hires an attorney. At issue is the fact that in the medical record, the respiratory therapist’s notes with the ventilator flow sheet indicate that the patient had been suctioned about every 2 hours for large amounts of thick, yellow secretions. However, during the 8 hours before the arrest, nowhere did the notes state that the patient had been suctioned. The therapist states that he had suctioned the patient but had not recorded it in the chart. Was the therapist negligent and did his actions lead to the wrongful death of the patient?

See Appendix A for the answer.

The First 30 Minutes

Immediately after the patient is connected to a mechanical ventilator, the clinician should perform auscultation of the patient’s chest to confirm adequate volume delivery and proper placement of the ET. The patient’s vital signs are checked, making particular note of heart rate and blood pressure, because ventilation may affect these parameters (Key Point 8-1). The alarms (e.g., apnea, low pressure, low V_T, and high pressure limit) are activated.⁶ An arterial blood sample is obtained about 15 minutes after mechanical ventilation is initiated for evaluation of the effectiveness of ventilation and oxygenation.^3,7 If not already done, a chest radiograph is obtained to confirm proper placement of the ET. Box 8-3 lists other clinical laboratory tests a physician might order to assess the patient’s status when mechanical ventilation is initiated.³

Key Point 8-1

Positive-pressure ventilation can reduce venous return to the heart, cardiac output, and blood pressure. (See Chapter 16 for more information on the cardiovascular effects of mechanical ventilation.)

Box 8-3

Clinical Laboratory Tests for Initial Assessment

The following clinical laboratory tests may be included in the initial evaluation of the patient:

• Complete blood count (CBC)

• Blood chemistries (glucose, sodium, potassium, chloride, carbon dioxide [CO₂], blood urea nitrogen, creatinine, phosphate, magnesium)

• Prothrombin time, partial thromboplastin time, and platelet count

• Blood, sputum, and urine cultures

Once the patient assessment shows the individual is stable, the respiratory therapist then performs the first ventilator check.

Mode

The mode of ventilation is recorded in the appropriate space on the ventilator flow sheet. It may be recorded as follows:

• Volume-controlled continuous mandatory ventilation (VC-CMV) or assist/control (A/C) ventilation.

• Pressure-controlled continuous mandatory ventilation (PC-CMV)

• Synchronized intermittent mandatory ventilation (SIMV), using either volume-controlled ventilation (VC-SIMV) or pressure-controlled ventilation (PC-SIMV), with or without pressure support ventilation (PSV)

• Pressure-regulated volume control (PRVC)

• Airway pressure release ventilation (APRV)

• PSV, volume support (VS), CPAP, unsupported spontaneous ventilation (these are spontaneous modes)

• Bilevel positive airway pressure (bilevel PAP; noninvasic positive-pressure ventilation [NIV]).

Sensitivity

If a patient-triggered mode is used (i.e., inspiration is initiated by patient effort), the pressure or flow required to trigger the ventilation should be checked; no more than −1 or −2 cm H₂O should be required. If the ventilator is flow triggered, the sensitivity should be set so that the ventilator will trigger at a flow change of 2 to 3 L/min. The ventilator should be checked for auto-triggering, and the patient’s ability to trigger a breath should be assessed. Adjustments are made as needed.

As discussed previously, when auto-PEEP is present, the patient has more difficulty triggering breaths. The presence of auto-PEEP should be suspected if the patient is using his accessory muscles of inspiration or demonstrates labored breathing. Ventilator graphics that show failure of the expiratory flow to return to zero before the next breath also is an indicator of auto-PEEP (see Chapter 9).⁸

If auto-PEEP is present, a number of strategies can be used to reduce its effects, including increasing the flow (reducing the inspiratory time [T_I]), reducing V_T, or reducing the rate (i.e., reducing ), suctioning the patient, or changing modes to allow for more spontaneous breaths. It is important to recognize that it might not always be possible to eliminate auto-PEEP, particularly in patients with increased flow resistance and airway closure. The addition of extrinsic PEEP (PEEP_E) in these patients may make triggering easier (see Fig. 7-1). PEEP_E is increased progressively during VC-CMV until the patient’s use of accessory muscles diminishes or until PIP and P_plateau begin to rise. (Additional information about treatment of auto-PEEP can be found in Chapter 17.)

Tidal Volume, Rate, and Minute Ventilation

Usually, V_T, f, and are displayed digitally on the front panel of the ventilator in the data display window. Most ventilators display the set V_T (V_Tset) and the exhaled V_T (V_Texh). Newer microprocessor-controlled ventilators provide excellent, reliable flow and pressure monitoring. If this information is not available, V_T can be measured using a handheld bedside pulmonary function device or other volume-measuring device (e.g., respirometer) and a watch or clock with a sweep second hand. Although this technique generally is used only with older ventilators, it can also be used to verify digital readouts if a question arises about the machine’s reliability (Fig. 8-2 and Box 8-4).

Fig. 8-2 Measurement of tidal volume (V_T) at the endotracheal tube (ET). The respirometer is attached to the ET so that the patient’s actual exhaled air can be measured. The respirometer can also be attached at the exhalation valve, but those readings would include compressible volume from the ventilator circuit in addition to volume from the patient’s lungs.

Box 8-4

Respirometer Technique for Measuring Tidal Volume (V_T) and Minute Ventilation (V_E)

Modern microprocessor controlled ventilators provide digital displays for the clinician to monitor a patient’s tidal volume and minute ventilation. Before the introduction of these devices, clinicians typically relied on handheld respirometers to measure these variables. The procedure for measuring V_T and with a respirometer is relatively easy to accomplish.

• The respirometer is connected directly to the patient’s endotracheal tube and to the Y-connector of the ventilator circuit (see Fig. 8-2). This allows easy measurement of the V_T that do not have to be corrected for compressible volume from the ventilator circuit. (NOTE: In cases where the V_T was measured at the expiratory port, the compressible volume [volume lost to C_T] must be subtracted from the V_T reading on the respirometer.)

• Gas exhaled from the lungs is measured for 1 minute and the f is simultaneously counted. can be calculated ( = V_T × f) or measured directly. If the patient is on intermittent mandatory ventilation/synchronized intermittent mandatory ventilation (IMV/SIMV), the total is measured. Mandatory V_T and f can be measured separately, and mandatory can be subtracted from the total to determine a patient’s spontaneous .

Correcting Tubing Compliance

Accurate reporting of volumes requires correction for volume loss within the patient circuit due to the effects of tubing compliance (also called compressible volume). Tubing compliance (C_T) for most ventilator circuits ranges from about 1.5 to 2.5 mL/cm H₂O.9 Box 8-5 presents a sample calculation of volume loss associated with C_T (also see Chapter 6).

Box 8-5

Calculation of Compressible Volume (Volume Lost to Tubing Compliance)

If the positive inspiratory pressure (PIP) is 25 cm H₂O, the tidal volume (V_T) at the exhalation port is 600 mL during performance of the C_T calculation, and tubing compliance (C_T) is 3 mL/cm H₂O. The volume lost to the tube is calculated as follows:

PIP×CT

25cm H2O×3mL/cm H2O=75mL

The volume actually delivered to the patient’s lungs is found by subtracting 75 mL from the V_T measured at the exhalation port:

600−75=525mL

Most microprocessor-controlled ventilators (e.g., Puritan Bennett 840 [Covidien-Nellcor and Puritan Bennett, Boulder, Colo.] Servoi [Maquet Inc, Wayne, N.J.]) do not require calculation of tubing compliance because these machines automatically compensate for this factor. As discussed previously, ventilators that perform this function typically increase the delivered volume so that the set volume is the amount provided to the patient (i.e., the digital readout indicates the V_T actually delivered to the patient’s airway). With older ventilators, the operator can set the value for the circuit’s C_T and the ventilator will add volume to the set V_T to compensate for volume loss due to tubing compliance.

Alveolar Ventilation

Monitoring of alveolar ventilation () has declined in popularity in recent years because many acute care facilities do not include this variable on the ventilator flow sheet. Unfortunately, its importance often is overlooked when using low V_T strategies. In-line heat and moisture exchangers (HMEs), closed suction systems, and other circuit adapters and equipment can add mechanical dead space (V_Dmech) to the ventilator circuit and affect the V_D/V_T. Knowledge of the effect of dead space on alveolar volume delivery can be particularly important in infants, children, and smaller adults with ARDS.

Two factors must be considered in determining alveolar ventilation:

1 Anatomic dead space

2 Mechanical dead space.

Dead Space

Normal anatomic dead space (V_Danat) is about 1 mL/lb IBW.* Bypassing the upper airway with an artificial airway reduces V_Danat by about one half. Using a Y-connector, additional flex tubing between the Y-connector and the ET, or a HME adds mechanical dead space.

Added Mechanical Dead Space

Because HMEs or other adapters attached to the ET (Fig. 8-3) add to mechanical dead space (V_Dmech), the volume of these devices, along with the V_Danat, must be subtracted from the V_T to determine actual alveolar ventilation (Box 8-6). For example, if a 150-lb adult has a V_T of 500 mL and the added V_Dmech is 100 mL, the alveolar ventilation for each breath would be:

VT−VDmech−VDanat=500mL−100mL−150mL=250mL

(Key Point 8-2)

Fig. 8-3 Airway pressure waveform during volume-control ventilation. An end-inspiratory breath hold and an end-expiratory breath hold are applied to measure the plateau pleasure and the auto-PEEP, respectively. Note the difference between the peak inspiratory pressure (PIP) and the plateau pressure (P_plateau); this is the transairway pressure (P_TA), which is produced by the interaction of the set flow and airway resistance. The V_T is the product of the pressure difference between P_plateau and total PEEP (set PEEP and auto-PEEP) and lung compliance. (From Hess DR, MacIntyre NR, Mishoe SC, et al: *Respiratory care principles and practice,* Philadelphia, 2002, WB Saunders.)

Box 8-6

Added Mechanical Dead Space

Some patient situations require the addition of a small amount of mechanical dead space. For example, in Fig. 7-3 a small circuit has been added at the Y-connector to allow for intermittent use of a metered-dose inhaler (MDI) without removing the heat and heat-moisture exchanger (HME) or disconnecting the circuit. This adds V_Dmech to the ventilator circuit.

Excessive turbulence at the upper airway and Y-connector sometimes can produce a pressure spike at the beginning of a breath during pressure-targeted ventilation. This has been noted with CareFusion (Pulmonetics) LTV-1000 ventilator (CareFusion, Yorba Linda, Calif.) in a clinical situation.¹² Auto-triggering occasionally occurs in this same ventilator. These two phenomena can be prevented in most cases by adding about 2 in. of corrugated tubing between the Y-connector and the endotracheal tube (or between the HME and the endotracheal tube) but must be accounted for as additional V_Dmech.

Key Point 8-2

The volume of mechanical dead space can be easily measured for any device added to a ventilator circuit. The device is simply filled with water and then emptied into a graduated container; the volume measured is the volume of mechanical dead space for the device. (A piece of equipment [i.e., tubing] similar to that being placed on the patient should be used for this type of measurement.)

Final Alveolar Ventilation

During VC-CMV (A/C), is calculated by multiplying the number of breaths counted for 1 minute by the corrected V_T: = (V_T − V_Danat − Added V_Dmech) × f. When a patient is on VC-SIMV, the mandatory rate and volume delivery must be calculated separately from the patient’s spontaneous rate and volume; these values then are added to determine the total minute ventilation (Box 8-7).

Box 8-7

Calculation of Alveolar Ventilation in VC-SIMV

Calculations are made using the following data:

• Synchronized intermittent mandatory ventilation (SIMV) rate = 5 breaths/min

• Tidal volume (V_T) = 600 mL

• Anatomic dead space (V_Danat) = 100 mL

• Added mechanical dead space (V_Dmech) = 50 mL

• Mandatory alveolar ventilation per minute () = 5 × [600 − 100 − 50] = 2250 mL or 2.25 L/min

• Patient spontaneous rate = 10 breaths/min

• Spontaneous V_T = 350 mL

• Spontaneous alveolar ventilation = 10 × [350 − 100 − 50] = 2000 mL or 2 L

• Total alveolar ventilation = 2.25 + 2 = 4.25 L/min

Monitoring Airway Pressures

All positive-pressure ventilators have a pressure monitor or display that continuously shows the upper airway pressure. The pressure monitor is probably most accurate when it shows pressures measured very near the patient’s upper airway because this eliminates the effects of the humidifying device and the breathing circuit on the measurement. Proximal pressure measurements are obtained by connecting the monitor tubing (usually a small-diameter plastic tube) to the Y-connector of the patient circuit. If the tubing is not visible on the circuit, pressures are detected through the main patient circuit and not at the upper airway. Although these values are not measured at the proximal airway, ICU ventilators are generally very accurate and clinically useful 1 (Key Point 8-3).

Key Point 8-3

Proximal pressure and flow monitor lines must be free of moisture and secretions to provide accurate readings.

Pressure monitoring allows the clinician to assess pressure delivery to the upper airway. It ensures that a minimal pressure is maintained (low-pressure limit) and that high-pressure limits are not exceeded during mechanical ventilation. Intermittent readings of PIP, P_plateau, set pressure (for pressure-targeted modes such as PC-CMV and pressure support [PS]), transairway pressure (P_TA = PIP − P_plateau), mean airway pressure (), and end-expiratory pressure (EEP) can provide valuable information about the patient’s condition.

Peak Inspiratory Pressure

PIP (or P_Peak), which is the highest pressure observed during inspiration, can be used to calculate dynamic compliance (C_D; also called dynamic characteristic). A fairly constant V_T with an increasing P_peak may indicate a reduction in lung compliance (C_L) or an increase in airway resistance (Raw). Conversely, a declining PIP may indicate a leak or may be a sign of improvement in compliance or resistance.

Plateau Pressure

A P_plateau reading can be obtained by using the ventilator’s inspiratory pause control or by setting a pause time of about 0.5 to 1.5 seconds. Remember that the static pressure is read when no gas flow is occurring. Traditionally, P_plateau was determined by occluding the ventilator’s expiratory port at the end of inspiration and reading the pressure registered on the ventilator’s pressure manometer. After PIP is reached, the manometer needle or pressure indicator shows a drop of a few centimeters from peak and then briefly remains in a plateau (static) position before dropping to zero (Fig. 8-3). It is important to remember that P_plateau cannot be measured accurately if the patient makes active respiratory efforts, has a high f, or resists extending T_I; therefore measurement of P_plateau is difficult, if not impossible, to obtain in spontaneously breathing individuals.

P_plateau most often is used to calculate C_S, which reflects the elastic recoil of the alveolar walls and thoracic cage against the volume of air in the patient’s lungs. Current practice strongly recommends keeping P_plateau below 30 cm H₂O (Key Point 8-4). Notice that during either pressure or volume ventilation, if a condition of no gas flow occurs near the end of inspiration (i.e., the flow-time waveform graphic shows a reading of zero), the corresponding pressure on the pressure-time curve is an indicator of P_plateau (Fig. 8-4 and Key Point 8-5).

Key Point 8-4

Current practice strongly recommends keeping P_plateau below 30 cm H₂O to avoid ventilator induced lung injury.

Fig. 8-4 A, VC-CMV with an inspiratory pause set. *Top curve,* Flow-time curve. *Middle curve,* Volume-time curve. *Bottom curve,* Pressure-time curve. After PIP, P_max is reached, the pressure drops to a plateau (begins at P₁ and ends at P₂). At the same time, inspiratory flow delivery ends and the flow drops to zero. The exhalation valve does not open until the end of the pause time. Expiratory flow does not occur until then. B, PC-CMV in which flow drops to zero during inspiration before the exhalation valve opens. The pressure measured during the no-flow period is an indicator of P_plateau. (NOTE: For a plateau to be visible in PC-CMV, T_I must be long enough to allow ventilator pressure and lung pressure to equilibrate. If no pressure difference exists, no flow occurs.). (A from Pelosip P, Cereda M, Foti G, et al: *Am J Resp Crit Care Med,* 152:531-537, 1995. B from MacIntyre NR, Branson RD: *Mechanical ventilation,* ed 2, Philadelphia, 2009, Saunders/Elsevier.)

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Aug 7, 2016 | Posted by admin in RESPIRATORY | Comments Off

Thoracic Key

Fastest Thoracic Insight Engine

Initial Patient Assessment

Initial Patient Assessment

Learning Objectives

Key Terms

Documentation of the Patient-Ventilator System

The First 30 Minutes