Clinical Year Review

:Critical Care

By

Gamal Rabie Agmy , MD , FCCP Professor of Chest Diseases ,Assiut University

Early tracheostomy versus Late Tracheostomy

◙ A 2005 meta-analysis of 5 studies (n=406) concluded

that early tracheostomy reduced need for mechanical

ventilation and ICU days.

◙ The Timing of Tracheotomy in Critically Ill Patients

Undergoing Mechanical Ventilation:A Systematic

Review and Meta-analysis of Randomized Controlled

Trials

Chest December 2011, Vol 140, No. 6

The timing of the tracheotomy did not significantly

alter important clinical outcomes in critically ill

patients

Novel Modes of Mechanical Ventilation Mashael Al-Hegelan, Neil R. MacIntyre

Semin Respir Crit Care Med. 2013; 34(4):499-507.

Novel Strategies Addressing the Challenge

of Balancing Gas Exchange versus VILI

Airway Pressure Release Ventilation Airway pressure release ventilation (APRV, also known as Bi-

Level (Covidien, Boulder, CO) and Bi-phasic (CareFusion,

Yorba Linda, CA), among other trade names) is a time-cycled,

pressure-targeted form of ventilatory support. APRV is

actually a variation of pressure-targeted SIMV that allows

spontaneous breathing (with or without pressure support) to

occur during both the inflation and the deflation phases. APRV

uses a prolonged inspiratory time producing so-called inverse

ratio ventilation (IRV with I:E ratios of up to 4 or 5:1).

Spontaneous breaths thus now occur during this prolonged

inflation period.

Novel Strategies Addressing the Challenge

of Balancing Gas Exchange versus VILI

High-frequency Oscillatory Ventilation High-frequency oscillatory ventilation (HFOV) uses very high

breathing frequencies (120 to 900 breaths per minute [bpm] in

the adult) coupled with very small tidal volumes (usually less

than anatomical dead space and often less than 1 mL/kg at

the alveolar level) to provide gas exchange in the lungs.

The putative advantages to HFOV are twofold. First, the very

small alveolar tidal pressure swings minimize cyclical

overdistension and derecruitment. Second, a high mean

airway pressure can also prevent derecruitment.

Novel Strategies Addressing the Challenge

of Balancing Gas Exchange versus VILI

Adaptive Support Ventilation Adaptive support ventilation (ASV) is an assist-control,

pressure-targeted, time-cycled mode of ventilation that

automatically sets the frequency-tidal volume pattern

according to respiratory system mechanics to minimize the

ventilator work. Conceptually, this minimal ventilator work may

translate into minimal stretching forces on the lungs, which

may, in turn, reduce VILI.

.

Novel Modes Addressing Improved

Patient Ventilator Interactions

Volume Feedback Control of Pressure-Targeted Breaths As noted previously, pressure-targeted breaths with variable flow features

often synchronize with patient flow demands better than fixed flow, volume-

targeted breaths. A drawback to pressure targeting, however, is that a tidal

volume cannot be guaranteed. The most common approach is to use a

measured volume input to manipulate the applied pressure level of

subsequent pressure-targeted breaths.When these breaths are exclusively

supplied with time cycling, the mode is commonly referred to as pressure-

regulated volume control (PRVC), although there are several proprietary

names (e.g., Autoflow [Draeger, Andover, MA], VC+ [Covidien], Adaptive

Pressure Ventilation [Hamilton Medical Inc., Reno, NV]). When these breaths

are supplied exclusively with patient-triggered, flow-cycling characteristics,

the mode is commonly referred to as volume support (VS). Some ventilators

will switch between these two breath types depending on the number of

patient efforts. Both animal and human studies have shown that these

feedback algorithms function as designed

Novel Modes Addressing Improved

Patient Ventilator Interactions

Enhancements on Volume Feedback Control of Pressure-targeted Breaths Airway occlusion pressure (P0.1), oxygen saturation (SpO2) and end-tidal

CO2concentration have been incorporated into PRVC and VS mode-control

algorithms to adjust either the target VT or the breath-delivery pattern.

The one system that is commercially available uses end tidal CO2 and

respiratory rate along with the tidal volume to adjust the applied inspiratory

pressure.[76] Known by the proprietary trade name SmartCare

Novel Modes Addressing Improved

Patient Ventilator Interactions

Proportional Assist Ventilation Proportional assist ventilation (PAV) is a novel

approach to assisted ventilation that uses a clinician-

set "gain" on patient-generated flow and volume.PAV

uses intermittent controlled "test breaths" to calculate

resistance and compliance.

Novel Modes Addressing Improved

Patient Ventilator Interactions

Neurally Adjusted Ventilatory Assistance Neurally adjusted ventilatory assistance (NAVA) utilizes a

diaphragmatic electromyographic (EMG) signal to trigger and

govern the flow and cycle of ventilatory assistan] The EMG

sensor is an array of electrodes mounted on an esophageal

catheter that is positioned in the esophagus at the level of the

diaphragm. Ventilator breath triggering is thus virtually

simultaneous with the onset of phrenic nerve excitation of the

inspiratory muscles, and breath cycling is tightly linked to the

cessation of inspiratory muscle contraction. Flow delivery is

driven by the intensity of the EMG signal.

Transthoracic Chest Sonography in Critical Care

Ultrasound profiles.

Lichtenstein D A , Mezière G A Chest 2008;134:117-125

http://radiographics.rsnajnls.org/cgi/content/full/20/3/653/F6B

Tissue pattern representative of Alveolar

Consolidation

Presence of hyperechoic punctiform images representative of air bronchograms

Pleural effusion

Lower lobe

Updates in ARDS

Berlin definition: ―Acute lung injury‖ no longer exists. Under the Berlin

definition, patients with PaO2/FiO2 200-300 would now have

―mild ARDS.‖

Onset of ARDS (diagnosis) must be acute, as defined as

within 7 days of some defined event, which may be sepsis,

pneumonia, or simply a patient’s recognition of worsening

respiratory symptoms. (Most cases of ARDS occur within 72

hours of recognition of the presumed trigger.)

Bilateral opacities consistent with pulmonary edema

must be present but may be detected on CT or chest X-

ray.

There is no need to exclude heart failure in the new ARDS

definition

The new criterion is that respiratory failure simply be

―not fully explained by cardiac failure or fluid overload

An ―objective assessment―– meaning an

echocardiogram in most cases — should be performed

if there is no clear risk factor present like trauma or

sepsis

Updates in ARDS

ARDS Severity PaO2/FiO2* Mortality**

Mild 200 – 300 27%

Moderate 100 – 200 32%

Severe < 100 45%

*on PEEP 5+; **observed in cohort

Mechanical Ventilation in ARDS: 2012 Review

The protocol from the ARMA trial can serve as a guide to

performing low tidal volume ventilation for mechanically

ventilated patients with ARDS:

Start in any ventilator mode with initial tidal volumes of 8

mL/kg predicted body weight in kg, calculated by: [2.3

*(height in inches - 60) + 45.5 for women or + 50 for men].

Set the respiratory rate up to 35 breaths/min to deliver

the expected minute ventilation requirement (generally, 7-9 L

/min)

Set positive end-expiratory pressure (PEEP) to at least 5 cm

H2O (but much higher is probably better), and FiO2 to

maintain an arterial oxygen saturation (SaO2) of 88-95%

(paO2 55-80 mm Hg). Titrate FiO2 to below 70% when

feasible (though ARDSNet does not specify this).

Over a period of less than 4 hours, reduce tidal volumes to

7 mL/kg, and then to 6 mL/kg.

Ventilator adjustments are then

made with the primary goal of keeping plateau

pressure (measured during an inspiratory hold of 0.5

sec) less than 30 cm H2O, and preferably as low as

possible, while keeping blood gas parameters

―compatible with life.‖ High plateau pressures vastly

elevate the risk for harmful alveolar distension (a.k.a.

ventilator-associated lung injury, volutrauma).

Mechanical Ventilation in ARDS: 2012 Review

If plateau pressures remain elevated after following the

above protocol, further strategies should be tried:

Further reduce tidal volume, to as low as 4 mL/kg by 1

mL/kg stepwise increments.

Sedate the patient (heavily, if necessary) to minimize

ventilator-patient dyssynchrony.

Consider other mechanisms for the increased plateau

pressure besides the stiff, noncompliant lungs of ARDS.

Mechanical Ventilation in ARDS: 2012 Review

Permissive hypercapnia

Permissive hypoxaemia

Mechanical Ventilation in ARDS: 2012 Review

Obesity — may have higher plateau pressures

at baseline and during ARDS than non-obese

patients.

Esophageal manometry is considered superior

to plateau pressures through its measurement

of transpulmonary pressure, considered a

more precise measure of potentially injurious

pressures in the lung. Because it is invasive and

the probes are prone to migration, esophageal

manometry is not widely used.

Limitations in Use of Plateau Pressure for

ARDS

A strategy employing higher PEEP along with low tidal

volume ventilation should be considered for patients

receiving mechanical ventilation for ARDS. This

suggestion is based on a 2010 meta-analysis of 3

randomized trials (n=2,229) testing higher vs. lower PEEP

in patients with acute lung injury or ARDS, in which ARDS

patients receiving higher PEEP had a strong trend toward

improved survival.

However, patients with milder acute lung injury

(paO2/FiO2 ratio > 200) receiving higher PEEP had a

strong trend toward harm in that same meta-analysis.

Higher PEEP can conceivably cause ventilator-induced

lung injury by increasing plateau pressures, or cause

pneumothorax or decreased cardiac output.

High vs. Low PEEP in ARDS

Predicting Survival and Outcomes After ARDS

A ―high risk‖ patient profile with a 52% mortality was

identified of severe ARDS (PaO2/FiO2 ratio <

100) with either a high corrected expired volume >=

13 L/min, or a low static compliance < 20 mL/cm

H2O.

Reviews of ARDS outcomes suggest that most

people who survive ARDS recover pulmonary function,

but may remain impaired for months or years in other

domains, both physically and psychologically.

Alternative / Rescue Ventilator Modes &

ECMO in ARDS

Some patients with severe ARDS develop severe

hypoxemia or hypercarbia with acidemia despite optimal

treatment with low-tidal volume mechanical ventilation. In

these situations, alternative, salvage or ―rescue‖

ventilator strategies are often employed. Their common

goal is to maintain high airway pressures to maximize

alveolar recruitment and oxygenation, while minimizing

alveolar stretch or shear stress. The most commonly

used alternative ventilatory strategies are high-frequency

oscillatory ventilation (HFOV) or airway pressure release

ventilation (APRV or ―bilevel‖).

Surviving Sepsis Campaign: International

Guidelines for Management of Severe

Sepsis and Septic Shock: 2013 Critical Care Medicine, February 2013 • Volume 41 • Number 2

(http://links.lww.com/CCM/A615)

1-early quantitative resuscitation of the septic

patient during the first 6 hrs after recognition (1C);

2-blood cultures before antibiotic therapy (1C);

imaging studies performed promptly to confirm a

potential source of infection (UG);

3-administration of broad-spectrum antimicrobials

therapy within 1 hr of recognition of septic shock

(1B) and severe sepsis without septic shock (1C)

as the goal of therapy;

4-reassessment of antimicrobial therapy daily

for de-escalation, when appropriate (1B);

5-infection source control with attention to the

balance of risks and benefits of the chosen

method within 12 hrs of diagnosis (1C);

6-initial fluid resuscitation with crystalloid (1B)

and consideration of the addition of albumin in

patients who continue to require substantial

amounts of crystalloid to maintain adequate

mean arterial pressure (2C) and the avoidance

of hetastarch formulations (1C)

7-initial fluid challenge in patients with sepsis-induced

tissue hypoperfusion and suspicion of hypovolemia to

achieve a minimum of 30 mL/kg of crystalloids (more rapid

administration and greater amounts of fluid may be

needed in some patients) (1C);

8- norepinephrine as the first-choice vasopressor to

maintain mean arterial pressure ≥ 65 mm Hg (1B);

epinephrine when an additional agent is needed to

maintain adequate blood pressure (2B); vasopressin (0.03

U/min) can be added to norepinephrine to either raise

mean arterial pressure to target or to decrease

norepinephrine dose but should not be used as the initial

vasopressor (UG);

10- dopamine is not recommended except in highly

selected circumstances (2C); dobutamine infusion

administered or added to vasopressor in the presence

of a) myocardial dysfunction as suggested by elevated

cardiac filling pressures and low cardiac output or b)

ongoing signs of hypoperfusion despite achieving

adequate intravascular volume and adequate mean

arterial pressure (1C);

11-avoiding use of intravenous hydrocortisone in adult

septic shock patients if adequate fluid resuscitation and

vasopressor therapy are able to restore hemodynamic

stability (2C);

12-avoiding use of intravenous hydrocortisone in adult

septic shock patients if adequate fluid resuscitation and

vasopressor therapy are able to restore hemodynamic

stability (2C);

13-low tidal volume (1A) and limitation of inspiratory

plateau pressure (1B) for acute respiratory distress

syndrome (ARDS); application of at least a minimal amount

of positive end-expiratory pressure (PEEP) in ARDS (1B);

higher rather than lower level of PEEP for patients with

sepsis-induced moderate or severe ARDS (2C); recruitment

maneuvers in sepsis patients with severe refractory

hypoxemia due to ARDS (2C)

14-prone positioning in sepsis-induced ARDS patients with

a Pao2/Fio2 ratio of ≤ 100 mm Hg in facilities that have

experience with such practices (2C); head-of-bed elevation

in mechanically ventilated patients

15-avoidance of neuromuscular blockers if possible in the

septic patient without ARDS (1C); a short course of

neuromuscular blocker (no longer than 48 hrs) for patients

with early ARDS and a Pao2/Fio2 < 150 mm Hg (2C);

16-a protocolized approach to blood glucose management

commencing insulin dosing when two consecutive blood

glucose levels are > 180 mg/dL, targeting an upper blood

glucose ≤ 180 mg/dL

17-prophylaxis for deep vein thrombosis (1B); use of

stress ulcer prophylaxis to prevent upper

gastrointestinal bleeding in patients with bleeding risk

factors (1B);

18-oral or enteral (if necessary) feedings, as tolerated,

rather than either complete fasting or provision of only

intravenous glucose within the first 48 hrs after a

diagnosis of severe sepsis/ septic shock (2C);