Ventilation and ED Ventilation and ED MonitoringMonitoring

for Dummies…for Dummies…

Todd RingTodd Ring

July 24/03July 24/03

ObjectivesObjectives

Invasive (IPPV) vs. Non Invasive Positive (NPPV) Pressure VentilationThe different modes of IPPV and typical ventilator settingsCPAP vs. BPAPClinical scenarios requiring mechanical ventilationPulse oximetry, non-invasive BP monitoring and capnography

Case 1: “Dumb” Motor-Case 1: “Dumb” Motor-BikerBiker

28 yo male, riding in Calgary, no helmet, crashes, unconscious, EMS scoop and run, in ED no spontaneous respirations, bag and mask ventilation.

What to do?

Indications for Mechanical Ventilation?

Indications for Indications for Mechanical VentilationMechanical Ventilation

1. Apnea2. Acute ventilatory failure (2/4)

• Acute dyspnea• RA PO2 < 50• PaCO2 > 50• Significant respiratory acidemia

3. Impending acute ventilatory failure4. Acute hypoxemic respiratory failure5. +/- Airway compromise

Case 1: Cont’dCase 1: Cont’d

The patient was successfully intubated. The RT is now “bagging” the patient manually and asks you to give orders for mechanical ventilation.

What mode to choose?

Where do you set your ventilator parameters?

Invasive Mechanical Invasive Mechanical VentilationVentilation

Volume vs. Pressure control

Spontaneous, controlled or combined ventilation

Invasive Mechanical Invasive Mechanical VentilationVentilation

Modes used in the ED:

Assist Control (A/C)

Pressure Support (PSV)

Simulated Intermittent Mechanical Ventilation (SIMV)

+/- Pressure Control (PCV)

Assist Control Ventilation (Volume Control)

In volume control ventilation (VCV) the mechanically ventilated patient receives a preset volume of gas with every breath.

VCV is frequently administered in an assist control (A/C) environment If the patient is apneic the ventilator will deliver a

preset rate If the patient is breathing they are able to initiate or

trigger a greater then the preset number of breaths.

A/C VentilationA/C Ventilation

Parameters for A/CParameters for A/C

TV 6 – 8 mls/kg IBW

Freq 10 – 18 bpm

FiO2 .4 – .6

PEEP 5 cm H2O

Other parameters set in A/C are:

Flow

Trigger Sensitivity

Disadvantages of A/C

Patients receive a mandatory breath every time they trigger the ventilator therefore hypocapnia with respiratory alkalemia may occurUncomfortable for patient Receive mandatory breath every time patient triggers

ventilator Patient unable to vary volume and flow

Results in patient-ventilator asynchronyHeavy sedation required which delays weaning

Observations to make when using A/C

Is the patient triggering the ventilator? If the objective of ventilation is to rest the patient, frequent

triggering may require significant work by the patient patient component of the inspiratory work in the A/C mode

can be significant (30 to 50%)

When delivering a preset volume of gas, the pressure in the lungs varies with changes in lung stiffness (compliance) and airway resistance airway pressures should be closely monitored and when

they consistently exceed 35 cm H2O a change in ventilating strategy should generally occur.

Case 2: Mrs. SeizureCase 2: Mrs. Seizure

35 yo female, former EtOH abuse, known EtOH seizure x’s 2, seizure free for 5 years, no meds, presents to Olds seizes in EDstatus epilepticus x’s 1h, STARS RSI intubation. Arrives @ FMC ED, GCS (E=1, M=5), spontaneous respirations.

What mode of MV would you choose?

Pressure Support Pressure Support VentilationVentilation

In pressure support ventilation (PSV) the patient receives a preset pressure of gas with every breath

The patient initiates every breath

The preset pressure is rapidly achieved and maintained throughout inspiration

Volume, flow and duration of inspiration are variable and change according to patient demand.

Pressure Support Pressure Support VentilationVentilation

PSV was originally introduced as a spontaneous mode that gave a small amount of pressure support designed to overcome the work of breathing imposed by endotracheal tube resistance. The amount of pressure required to overcome

the resistance of an 8mmID endotracheal tube is between 5 and 10 cmH2O.

Pressure Support Pressure Support VentilationVentilation

Parameters in PSVParameters in PSV

PS: 5 – 35 cm H20

FI02: 0.40 – 0.60

PEEP: 5 cm H20

Other parameters set in PSV are:

Trigger Sensitivity (pressure or flow)

Ramp – PSV has no flow control and typically

delivers high initial flows.

PSVPSV

PSV is usually used during the recovery phase of respiratory failure as a weaning mode.Levels are set at values < 15 cmH20 and titrated down as toleratedPatients are typically extubated at PSV levels of between 5 and 10 cmH20The lack of mandatory breaths when using PSV can result in lower mean airway pressures which can result in a decrease in a patient’s PaO2

Disadvantages of PSVDisadvantages of PSV

Potential for increased work of breathing at lower levels of PSVReduction in mean airway pressure with decreased patient oxygenation

ObservationsObservations

Patient tidal volume should be above 250 – 350 mls (5 mls/kg) as a minimum. When the level of PSV is inadequate the VT will drop

below this range.

Patient rate (f) When low-level PSV is not being tolerated the VT

falls and the f rises. Rates greater than 35 bpm are generally undesirable and signal the need for higher levels of PSV or a switch to a mandatory mode (VCV, A/C or PCV).

Case 1: The sequale…Case 1: The sequale…

The RT from case one comes up to you annoyed and states “we need more sedation/paralysis for the motor-biker who hit his head. He is starting to fight the ventilator.”

Do you tell the nurse to give more sedation/paralytic or is there something else you can do?

SIMVSIMV

The patient gets a preset number of mandatory breaths (A/C) volume-controlled and they are synchronized with the patient’s breathing Synchronization means that the mandatory breath will

be delivered when triggered by the patient. The patient will only get the set number of mandatory breaths per minute.

If the patient’s rate exceeds the set rate the additional breaths will be spontaneous breaths Usually pressure supported

SIMVSIMV

TODD’S RULE: SIMV = A/C + PSTODD’S RULE: SIMV = A/C + PS

Parameters in SIMVParameters in SIMV

Freq: 8 to 12 bpmVT: 6 – 8 mls/kg IBWPS: 5 – 20 cmH20FIO2: 0.40 to 0.60PEEP: 5 cm H20

Additional Parameters in SIMV:FlowSensitivity

Disadvantages of SIMVDisadvantages of SIMV

Mandatory support can be set inappropriately low when SIMV is used as the vehicle for VCV or PCV.

Observations in SIMVObservations in SIMV

Patients total rate

Tidal volume during spontaneous breaths

Airway pressures during VCV mandatory breaths

Careful assessment of adequate mandatory support

Pressure Control Pressure Control Ventilation (PCV)Ventilation (PCV)

A mode in which the patient receives a preset system pressure, which is rapidly achieved by high flow and this pressure is maintained throughout inspirationAdministered in an assist control (A/C) environment In the apneic patient a preset rate is delivered Patients who are breathing are able to initiate or trigger at

greater than the preset number of breaths

With pressure set instead of volume, the volume the patient receives will vary as a function of the respiratory system compliance and resistance

PCVPCV

Parameters in PCVParameters in PCV

Level of pressure control: 20 to 35 cmH20Freq: 10 – 18 bpmI:E ratio: 1:2 to 1:3FIO2: 0.40 to 0.60PEEP: 5 cmH20Additional parameters in PCV:Trigger Sensitivity (pressure or flow)Inspiratory time - determined by the rate and I:E ratio control settingsRamp adjustment

PCVPCV

PCV is the ideal mandatory mode to use when ventilating patients who have high airway pressures using VCV Because the pressure is preset, a safe upper limit can be

adjusted

PCV is often considered for a lung protective strategy centered on regulation of peak, mean and end expiratory pressuresIt is often considered as the mode of choice for patients with acute lung injury or ARDS

Disadvantages of PCVDisadvantages of PCV

Inability to maintain a constant tidal volume and PaCO2When compliance decreases and resistance increases, tidal volume falls and PaCO2 may rise (hypercapnia)The set I: E ratios are not maintained when the patient rate exceeds set rate (when in A/C mode) resulting in shortening expiratory time which leads to increasing Auto PEEP, decreasing tidal volumes and increasing asynchrony.

Observations in PCVObservations in PCV

Careful monitoring of tidal volume

Actual patient rateWhen patient rate significantly exceeds set rate

I: E ratios will inverse.

Potential Adverse Potential Adverse Effects of Effects of IPPVIPPV

Increased mean intrathoracic pressureDecreased venous return and cardiac outputIncreased ventilation/perfusion ratioDecreased renal blood flow and glomerular filtration rate with fluid retentionAir trapping and intrinsic positive end-expiratory pressure (iPEEP, auto-PEEP)BarotraumaNosocomial infections of the lungs and sinusesRespiratory alkalosisAgitation and increased respiratory distressIncreased work of breathing

Ventilator SettingsVentilator Settings

Rule of 10’sVT 10ml/kg IBWFreq 10 bpmFiO2 100%

FiO2: start high and wean down

VT: Between 5 – 10 ml/kg; be aware of lung compliance

More Ventilator More Ventilator Settings…Settings…

Respiratory Rate: wide range; increase or decrease according to ventilatory parametersInspiratory Pressure: < 35 cm H2O; generally 10 – 30 Pressure Support: 5 – 30 cm H2O; when weaning pressures should be < 10 cmTrigger Sensitivity: amount of negative pressure that the patient must establish for the machine to sense patient effort and thus deliver a breath; generally −1 to −2 cm H2O

Even More Ventilator Even More Ventilator Settings…Settings…

PEEP: the level of positive pressure that is maintained in the airways at the end of expiration; range from 5–20 mm H2O

I:E ratio: generally set at 1:2; may increase to facilitate complete expiration in obstructive lung disease

PEEPPEEP

Preprogrammed level of positive pressure maintained at the end of exhalation

Improvement in oxygenation with increased PEEP

The advantages of PEEP are balanced by its potential detrimental effects A worsening of gas exchange is possible if an

increase in dead space ventilation occurs

Auto-PEEPAuto-PEEP

A phenomenon that is seen most often in patients with airflow limitation or with high respiratory rates combined with a shortened expiratory time. In this situation, expiration to functional residual capacity is not accomplished before the next inspiratory cycle begins, resulting in dynamic hyperinflation.

Case 3: Mrs. FailureCase 3: Mrs. Failure

80 yo female, CAD, MI, CHF, CRF on dialysis (missed today’s run). Presents to PLC ED via EMS acutely SOB (“wants to die breathing so bad”). SaO2 88 % 5L O295% 15 L NRB. Clinically no failure. CXR bilateral effusions, CHF. ABG 7.30/65/60/28.

What to do?

CPAP vs. BPAP?

Non-Invasive Positive Non-Invasive Positive Pressure Ventilation Pressure Ventilation

(NPPV)(NPPV)Positive pressure is delivered by way of a tightly fitting maskIn 1938 continuous positive airway pressure (CPAP) shown to be effective for the treatment of acute pulmonary edema Nasal CPAP mask for the treatment of obstructive sleep apnea in the 1980sIn the 1990’s an alternative to endotracheal intubation in acute respiratory failure

Advantages of NPPVAdvantages of NPPV

Avoids complications that are related to endotracheal intubation and mechanical ventilation and the loss of airway defenses caused by endotracheal intubation

NPPV is not as invasive as endotracheal intubation; it offers a means of temporarily supporting some patients who do not wish to have aggressive or prolonged ventilatory means used in their care.

Evidence?Evidence?

A case-controlled study by Girou et al found the use of NPPV in critically ill patients with acute COPD and CHF exacerbations was associated with a lower risk for pulmonary infections, lower antibiotic use, shorter length of stay, and lower mortality

Girou E, Schortgen F, Delclaux C, et al. Association of noninvasive ventilation with nosocomial infections and survival in critically ill patients.

JAMA 2000;284:2361

CPAPCPAP

Delivers a constant level of positive pressure throughout the respiratory cycle

Main use is for hypoxemic respiratory failure

Improve oxygenation by: increasing the mean airway pressure, increasing

functional residual capacity, and opening underventilated and collapsed alveoli, enhancing gas exchange and oxygenation

CPAPCPAP

Initiated between 0 – 15 cm H2O

Level is set low initially and slowly increased to allow adequate oxygenation with as low an FIO2 as

possible

Important to check the mask for leaks

BPAPBPAP

Two different pressure levels are cycled between inspiration and expirationInspiratory pressure (IPAP) > expiratory pressure (EPAP) The primary benefit of this mode over CPAP is in patients with ventilatory fatigue or failure increases airway pressure in expiration and

decreases WOB by aiding inspiration

Inspiratory pressure set at 8 – 20 cm H2O and expiratory pressure is set at 0 – 15 cm H2O

Complications of NPPVComplications of NPPV

Often minor: nasal congestion, eye irritation, discomfort, and

pressure necrosis caused by the tight mask fit

Airway protection must be addressed in patients with altered sensorium especially with tight fitting mouth mask

Gastric distension is uncommon unless pressures exceed 20–25 cm H2O

NPPVNPPVThe most common reason for failure of NPPV is patient intoleranceKey to success is adequate patient preparation and acclimatization to the deviceChoice of mask depends on familiarity and availability Nasal masks allow patients to communicate verbally,

but they suffer from air leaks unless the patient keeps his or her mouth closed.

Full-face masks offer the tightest seal but can be hazardous in patients who cannot completely protect their airway or who are at risk for vomiting

CPAP vs. BPAPCPAP vs. BPAP

In patients with hypoventilatory respiratory failure, BPAP should be the preferred mode because of its theoretic advantage in providing ventilatory assistance and therefore decreasing the work of breathing. With hypoxemic ventilatory failure, CPAP and BPAP should be similarly efficacious given that both improve oxygenation Though BPAP has theoretic advantages over CPAP,

the choice of modes should be based on familiarity with and patient tolerance of a given mode

Case 4: Mr. PuffCase 4: Mr. Puff

76 yo male, known COPD, seen at PLC ED 3 times in prior week for SOB. Dx: COPD exacerbation. Presents SOB SaO2 90 % RA, 95 % 10 L O2. Working ++ hard to breath. Initial ABG 7.30/65/70/30

What ventilation strategy would you employ?

COPDCOPD

1st line = consideration of NPPV

Good evidence that NPPV decreases incidence of the need for intubation and invasive ventilation

Bott J, Carroll MP, Conway JH, et al. Randomised controlled trial of nasal ventilation in acute ventilatory failure due to chronic obstructive airways disease. Lancet 1993;341:1555

Celikel T, Sungur M, Ceyhan B, et al. Comparison of noninvasive positive pressure ventilation with standard medical therapy in hypercapnic acute respiratory failure. Chest 1998;114:1636 

Case 4: Mr. Puff Case 4: Mr. Puff Breath’s on…Breath’s on…

You initiate BPAP. One hour later Mr. Puff is beginning to tire despite continuous ventolin and atrovent, and 4 mg IV MgSO4. You repeat the ABG: 7.15/60/138/30

What is your next step?

COPD: Goals of IPPVCOPD: Goals of IPPVGradually correct respiratory acidosis (over hours)Normalization of lung volumeDecrease auto-PEEP by: higher flow rates (eg, 100 L/min) during inspiration increasing I:E ratio (1:3 to 1:4) occasionally disconnecting the patient from the

ventilator to allowing complete exhalation use of bronchodilators and steroids adding extrinsic PEEP (no more than auto-PEEP) to

decrease work required to maintain auto-PEEP

AsthmaAsthma

Asthmatics with impending respiratory failure demonstrate some of the most difficult management issues with regard to mechanical ventilation

Asthma is predominantly a problem with expiration with increased airway resistance resulting in pulmonary hyperinflation

AsthmaAsthma

Mechanical ventilation can help decrease the work of breathing BUT intubation exaggerates expiratory obstruction by the fixed diameter of the endotracheal tubePotential for significant auto-PEEP and decreased venous return Therefore, all attempts should be made to avoid the initiation of mechanical ventilation in asthmatic patients except as a last resort

NPPV in AsthmaticsNPPV in Asthmatics

NPPV has not been studied prospectively

Meduri described the use of BPAP in 17 patients with severe asthma and impending respiratory failure. Intubation was averted in all but two patients and no complications were observed.

Meduri G, Cook T, Turner R, et al. Noninvasive positive pressure ventilation in status asthmaticus. Chest 1996;110:767

Mechanical Ventilation Mechanical Ventilation and Asthmaand Asthma

Limit the negative effects of positive pressureAllow maximal expiratory time to minimize the chances of auto-PEEP and resultant dynamic pulmonary hyperinflationWhen pulmonary pressures remain elevated, deep sedation and neuromuscular blockade should be considered in an effort to minimize ventilator asynchrony In severe cases controlled hypoventilation with permissive hypercapnea should be considered

Case 3: Mrs. Failure continues to fail…

Despite BPAP for 45 min Mrs. Failure shows no signs of improvement. Her O2 sat has slowly been decreasing (now 85%) on 15 L and she is starting to become obtunded. You repeat her ABG 7.25/55/65/30

What is your next step?

Cardiogenic Pulmonary Cardiogenic Pulmonary EdemaEdema

A systematic review of CPAP in CHF revealed a pooled decrease in need for intubation of 26% and a trend toward decreased mortality

Pang D, Keenan SP, Cook DJ, et al. The effect of positive pressure airway support on mortality and the need for intubation in cardiogenic pulmonary edema: a systematic review. Chest 1998;114:1185

One randomized trial compared CPAP with BPAP in a total of 27 patients and found a more rapid improvement in ventilatory parameters (PaCO2, pH) and vital signs with BPAP than CPAP in acute pulmonary edema

Mehta S, Jay GD, Woolard RH, et al. Randomized, prospective trial of bilevel versus continuous positive airway pressure in acute pulmonary edema. Crit Care Med 1997;25:620

Mechanical Ventilation Mechanical Ventilation in CHFin CHF

In mechanically ventilated patients PEEP can help to reduce extravascular lung water and thus can result in improved oxygenation

However, PEEP can have an adverse effect in patients with CHF who are in cardiogenic shock by decreasing pulmonary venous return

Compromise is to use only enough PEEP to decrease FiO2 to less than 60 %

Acute Lung Injury (ALI) Acute Lung Injury (ALI) and Acute Respiratory and Acute Respiratory

Distress Syndrome Distress Syndrome (ARDS)(ARDS)

One small study looked at the use of NPPV in 10 hemodynamically stable patients with ALI/ARDS and averted intubation in 6 of the 10 patients

Rocker GM, Mackenzie MG, Williams B, et al. Noninvasive positive pressure ventilation: successful outcome in patients with acute lung injury/ARDS. Chest 1999;115:173

Most cases of ALI and ARDS require invasive mechanical ventilation

ALI/ARDSALI/ARDS

Indication for PCVUse small tidal volumes (6 mL/kg)

Keep plateau pressure ≤30 cm H2O. Increase PEEP and RR to help decrease tidal volumesWatch for significant amounts of auto-PEEP with the increase in respiratory rate

Physiologic Changes in Pregnancy

Mother has reduced oxygen reserve (decreased FRC) and increased oxygen consumption (15 – 20 %)The fetus is very vulnerable to any reduction in oxygen delivery 30% decrease in uterine blood flow with maternal

hypoxia

Higher risk of aspiration in pregnancyPregnant patient = difficult airway

Physiologic respiratory alkalosis (PaCO2 of 30 mm Hg) in the last stage of pregnancy

Mechanical Ventilation in Pregnancy

Rapid sequence induction is recommended for intubation

Increase tidal volumes when ventilating

Hyperventilate to maintain physiologic respiratory alkalosis

ED MonitoringED Monitoring

Clinical observationRoutine vital sign measurementElectrocardiographic monitoring Pulse oximetry

End-tidal carbon dioxide (CO2 ) measurementNoninvasive blood pressure (BP) measurement

Non-Invasive Blood Non-Invasive Blood Pressure MonitoringPressure Monitoring

Use a detection system based on auscultatory, oscillometric, or Doppler principlesAutomatic oscillometric devices determine BP by electronically determining the pulse amplitude Cuff inflated at predetermined intervals to a preset level Cuff deflated sensing the amplitude of oscillations Abrupt

increase in the magnitude of the oscillation is the systolic pressure.

The point where there is no longer an alteration in the magnitude of the oscillation is the diastolic pressure.

The mean arterial pressure (MAP) is the cuff pressure at the point of largest oscillation

Noninvasive BP Noninvasive BP MonitoringMonitoring

More accurate, precise, and reliable than auscultation in patients with very low or high BPLimitations common to regular BP measurement obese arms, uncooperative moving patients, and

those with very high or very low BP

Cycle length of the inflation-deflation sequence in the older machines was exceedingly long and led to frequent failure; resolved in newer machines

Indications for Invasive Indications for Invasive MonitoringMonitoring

1. Exceedingly high (>250 mm Hg systolic) or low (<80 mm Hg systolic) pressures

2. Patients who are rapidly going into shock best chance to insert an arterial line may be in

the ED while the arterial pulse is still palpable

3. Anatomic indications in critically ill patients with either has no limb or no suitable limb (e.g., too obese) to undertake conventional measurement

4. Frequent arterial sampling is required

Pulse OximetryPulse OximetryNoninvasive and continuous means of rapidly determining arterial oxygen saturation and its changesBased on differences in the optical transmission spectrum of oxygenated and deoxygenated hemoglobinUses Beer Lambert Law = relates the concentration of a solute to the intensity of light transmitted through a solutionLight absorption is divided into a pulsatile (AC) component (arterial blood) and a non-pulsatile (venous and capillary)

Limitations of Pulse Limitations of Pulse OximetryOximetry

Severe vasoconstriction (e.g., shock, hypothermia)

Excessive movement

Synthetic fingernails and nail polish

Severe anemia

Presence of abnormal hemoglobinsCarboxy and Methemoglobin

COHgb and MetHgbCOHgb and MetHgb

Pulse oximeter senses COHgb as oxyhemoglobin and therefore gives an erroneously high SaO2

MetHgb absorbs light at both red and IR wavelengths therefore the net effect is a reading of 85 %

Caution with Pulse Caution with Pulse OximetryOximetry

Does not give any information with regards to adequate ventilation

Capnography/Capnography/CapnogramCapnogram

The measurement and display of CO2

concentrations on a visual display

CapnogramCapnogramA. Normal tracing

A-B: inspiratory phase; B-C: transnition of inspiration to expiration; C-D: alveloar plateua; D-A: inspiratory downstroke; D: end tidal point

C. Pt.-vent asynchrony

-curare cleft = spontaneous breath

B. Obstructive lung disease

D. Endotracheal cuff leak

CapnometersCapnometers

Either sidestream (ED) or mainstream in designSidestream capnometers aspire a sample of gas through a small catheter into a measuring chamber lightweight and can be used in intubated and non-

intubated patients disadvantages include plugging by secretions, 2-or

3-second delays in response time, and air leaks, which can dilute the sample

CapnometersCapnometers

Colorimetric capnometers use pH-sensitive filter paper impregnated with metacresol purple, which changes color from purple (<4 mm Hg CO2 ) to tan (4 to 15 mm Hg CO2 ) to yellow (>20 mm Hg CO2 ) depending on the concentration of CO2 Yellow = yes (in the right place) Purple = poor (wrong tube)

The indicator is inserted between the endotracheal tube and the ventilator bag detects changes on a breath-by-breath basis

Uses of CapnographyUses of Capnography

Confirm endotracheal tube placement in non-arrest settings the ETCO2 approaches

100% sensitivity and specificity in confirming correct tube placement; it is also useful to monitor for accidental extubation

Estimate PaCO2

Monitor effectiveness of cardiopulmonary resuscitation (CPR), mechanical ventilation, and conscious sedation

Limitations of Limitations of CapnographyCapnography

ETCO2 falsely elevated after

esophageal intubation following bag/mask ventilation in the following: ingestion of carbonated beverages or

antacids: these tracings usually resolve after six breaths and look abnormal

injection of bicarbonate: falsely elevated for about 5 minutes after

ETCOETCO22 as Surrogate for as Surrogate for

PaCO2PaCO2Can estimate PaCO2 in

hemodynamically stable patients who do not have rapidly progressive lung pathology

Pa-ETCO2 gradient is usually 2 to 5 mm

Hg, but this may increase to 15 mm Hg in patients with hemodynamic instability and pulmonary complications

Review…

Three main ventilation strategies A/C, PSV, SIMV

Rule of 10’s Consider NPPV in respiratory failure Hypoxemic = CPAP or BPAP Hypoventilatory = BPAP

NIBP, pulse oximetry and capnography are important monitoring tools in the ED but have limitations