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238 J. L. Johnson
“recruitment” maneuvers, strategic use of PEEP, optimal sedation/analgesia,
and optimal positioning (including prone).
• Fluid strategies that maintain euvolemia are optimal in a patient with ARDS.
• The only therapy proven to improve mortality in ARDS is an approach to
mechanical ventilation that limits stress (tidal volume) and strain (pressure)
on the lung.
• Prone ventilation consistently improves gas exchange and may improve
outcome in ARDS. The optimal frequency and duration of prone ventilation
is not clear.
• High frequency oscillation is ineffective as a ventilator strategy in adults
with ARDS.
Background
• ARDS is a life-threatening condition that affects about 5% of patients in a
surgical ICU. It was originally described as a constellation of symptoms and
signs, including dyspnea, hypoxia, and panlobar pulmonary infiltrates on
plain radiographs.
• Common risk factors for ARDS in surgical patients include shock, transfu-
sion, multiple trauma, infection, aspiration and pulmonary contusion.
• We now understand that ARDS represents an autotoxic injury to the pulmo-
nary capillary/alveolar interface. This results in flooding of alveoli, recruitment
of leukocytes, and loss of pulmonary epithelium. The inflammatory injury to
the lung in ARDS may be an engine for systemic inflammation and multiple
organ failure, promoting systemic injury, and subsequent damage to kidneys,
liver and other organs.
• Injury to the lung during ARDS occurs in a predictable, progressive phases
including the exudative phase (inflammation/injury/edema), proliferative
phase (inflammation/repair), and finally fibrosis.
• The modern (“Berlin”) definition of ARDS improves on the 1992 (AECC)
definition by standardizing the concept of “acute” onset, clarifying the importance of predisposing factors and acknowledging that volume overload and
ARDS can co-exist. It divides ARDS into three severities, by oxygenation,
using PO
• While the inflammatory nature of ARDS is widely acknowledged, pharmaco-
logic strategies to limit inflammation have been uniformly disappointing,
with the possible exception of systemic corticosteroids in select patients.
• Ventilator strategies historically used in ARDS to improve gas exchange
were recognized to produce barotrauma — both overt (such as pneumothorax/
to FiO2 ratio (P/F), namely < 100, 100–200, and 201–300.
2
Acute Respiratory Distress Syndrome 239
pneumomediastinum) and subtle (persistent or unremitting inflammation).
The existence of ventilator-induced lung injury (VILI) is now wellestablished. The main components are strain and stress. Strain is from overall airway pressure effects on the structure of the lung, and stress is from the
repetitive opening and closing of air units that are partially flooded.
• At the same time that VILI was being elucidated, the heterogeneous nature
of ARDS, with lung regions ranging from irreparably flooded to overdistended, promoted strategies that would both open collapsed alveoli
(“ recruitment maneuvers”) and keep them open with positive end-expiratory
pressure (PEEP).
• The current strategy for mechanical ventilation incorporates both the above
ideas: optimize the number of alveoli participating in gas exchange, but limit
the amount of damage produced by positive pressure ventilation. This lowstretch (tidal volume ≤6 cc/kg ideal body weight), limited pressure (plateau
airway pressure ≤30 mm H
O), moderate PEEP approach is the only proven
2
way to limit the mortality from ARDS.
• High frequency oscillation (HFO) seems attractive as an approach to ARDS,
since in some ways it represents an ultra-low tidal volume, limited pressure
moderate PEEP approach. Clinical trials have not borne this out as an effective strategy in adults, with the most recent trial being stopped early with
some evidence of harm. HFO cannot be recommended as a routine strategy
in adults with ARDS.
• Prone positioning has several promising features in terms of optimizing the
amount of lung participating in gas exchange. First, gravity helps to reverse
dependent (dorsal) flooding of the lungs. Second, the “weight of the heart”
may be taken off the basilar segments of the left lower lobe. Third, ventilation to dorsal lung regions is improved in the prone position, while
perfusion is maintained, producing better matching between ventilation
and perfusion.
• Since alveolar flooding is central to the pathogenesis of ARDS, it makes
intuitive sense that limiting fluid administration/promoting diuresis is of
benefit. That being said, it is not necessarily hydrostatic forces that
underpin pulmonary edema in ARDS, and there may be some risk to hypovolemia, particularly in surgical patients. The best trial examining the
benefits of limiting volume in patients with ARDS suggests there are modest benefits in terms of ventilator days and length of ICU stay, but no
mortality benefit. For the surgical intensivist, this can be incorporated
as yet another reason to maintain euvolemia and avoid overzealous administration of fluids.
240 J. L. Johnson
Main Body
• The Berlin definition can be recommended as a standard way of defining
whether an individual patient has ARDS. Recognition of ARDS in its early
phases promotes early application of “lung-protective” ventilator strategies, a
reminder to use fluids judiciously, and an expectation of a difficult course.
• It is critical to make a best determination about the cause of the ARDS; in
surgical patients, in particular, one must be diligent about searching for sepsis
(pneumonia? Intra-abdominal complication?). Since there is no definitive
therapy — only best supportive care — reversing the underlying cause of
ARDS is of utmost importance. Furthermore, since surgical patients may
need secondary insults (subsequent operations including fracture fixation),
optimal timing of these interventions are worthy of some discussion so as not
to exacerbate the underlying condition.
• Initial patient care should include the following:
{ Analgesia and anxiolysis that promotes excellent interface with the venti-
lator. Since many of these patients will have prolonged courses of
mechanical ventilation, the advantage of very short acting agents would
appear less. Neuroleptics or atypical antipsychotics can be recommended
for patients with agitated delirium. Our practice is to use standing doses
of quetiapine with haloperidol for acute agitation. Medications that produce reliable effects with minimal hemodynamic compromise are
preferred. For that reason, our practice is to use infusions of lorazepam
and fentanyl.
{ Neuromuscular blockers should be considered for patients with severe
hypoxemia (p/f <100), or who continue to interface poorly with the ventilator despite the above. Routine use of neuromuscular blockers cannot
be recommended.
{ While there are advantages to sedation “holidays” in many patients, those
with severe ARDS should be considered outliers in whom even transient
loss of participating lung units may be undesirable. Simply put, it is hard
to get back “lost” alveoli in these parts, and the approach must be individualized.
{ Avoidance of factors that exacerbate intraabdominal hypertension, includ-
ing gastric overdistension, colonic pseudo-obstruction, volume overload,
uncontrolled ascites, and Trendelenburg position. Intraabdominal hypertension increases the pressures (read “strain”) needed to inflate the lungs.
{ Drainage of substantial pleural effusions. Simply put, this can quickly pro-
vide some additional functional residual capacity for the lungs. If diuresis
Acute Respiratory Distress Syndrome 241
can promote resolution of effusions, this is a reasonable initial approach
to the patient with mild disease.
{ Empiric administration of antimicrobials when infection is suspected as
an underlying cause and after appropriate culture material is sent.
• Initial ventilator management in the patient with ARDS should approximate:
{ Pick a ventilator mode that achieves full ventilator support with a predict-
able tidal volume, minute volume and plateau pressure, since these are the
critical variables you will need to follow. In particular, modes that are
machine triggered, volume cycled and flow limited tend to be quite practical; Assist/Control has many advantages in this regard and has no
clinical disadvantage over other modes.
{ Tidal volumes ≤6 cc/kg ideal body weight. This should be decreased in
small increments if plateau pressures remain >30; increase respiratory rate
to maintain minute volume. Respiratory rates >32 tend to promote autoPEEP due to inadequate exhalation time and cannot be recommended. In
these circumstances, permissive hypercapnia should be utilized.
Remove as much dead space between the ventilator circuit and the trachea
as possible (e.g. minimal length adaptor between circuit and endotracheal
tube). At extremely low tidal volumes (< 4 cc/kg IBW or about 300 cc),
even a small amount of dead space (30 cc) can be a significant part of
each breath (10%). This may get you 2–3 Torr in improved PCO
.
2
Ignore PCO2 per se; allow it to rise.
Shift focus to management of arterial pH. Tolerance to acidosis varies
widely. Elderly patients and patients with other organ dysfunctions
may be at higher risk. If pH < 7.20 OR patient exhibits organ dysfunction in association with acidemia (e.g. bradycardia, hypotension,
oliguria), use the following strategies to maintain pH:
Ö Infusion of bicarbonate (2 ampules of sodium bicarbonate in
1 liter of D5w, with initial rate of 100 cc/hr).
Ö Infusion of THAM. This can provide excellent buffering with
lower volumes and avoidance of further CO2 production but is not
universally available.
Ö Continuous renal replacement therapy, particularly in the part with
volume overload or oliguria.
{ Plateau pressures ≤ 30. This is dependent on a number of other variables
including ventilator modes, flow rates, flow waveforms, I:E ratios and
patient factors.
242 J. L. Johnson
{ PEEP ≥ 5. Subsequent PEEP should be adjusted either to a predetermined
scale based on FiO2 requirements (ARDS Net approach), or individualized to the physiology of a particular patient. The latter requires
experience and close observation, and is practiced by our group. The
overall approach is as follows:
Perform a recruitment maneuver. Conceptually, this is “opening up” gas
exchange units that are temporarily flooded. In mild disease and with
experienced hands, this might be something as simple as hand ventilation with a bag-valve, or transient ventilation at higher tidal volumes.
For more advanced disease, we can recommend the following:
Ö Use a time-cycled, machine triggered mode with the frequency set
at 12 and an I:E of 1:1 (often called a “pressure control” mode).
Conceptually this provides long, slow breaths.
Ö Set the PEEP at 10–20 above current PEEP, and use a pressure
limit that produces a tidal volume of about 12 cc/kg IBW
(approaching one liter for an adult). This may be as little pressure
as 10 or as much as 40, depending on the pulmonary and chest
wall compliance.
Ö Keep in mind that during this maneuver, the minute volume deliv-
ered is likely to be substantially less than what the patient requires.
Expect the patient to become acutely more hypercapneic and
acidemic. This may be unwise in patients with intracranial hypertension or marginal hemodynamics. In any event, should the
patient’s heart rate or blood pressure drop substantially, it is time
to stop the maneuver.
Ö Also bear in mind that the mean airway pressure being delivered
is probably substantially higher than baseline. Patients who are
hypovolemic may develop hypotension that requires cessation of
the maneuver. A modest volume challenge followed by a repeat
attempt might be in order.
Ö It is not uncommon for patients to have transient desaturation dur-
ing the early part of the maneuver followed by substantial
improvement. Be prepared for this by deciding what level of
desaturation you are willing to tolerate in an individual patient.
Patients who do not respond within three minutes are unlikely to
respond.
Patients who respond to recruitment should be placed on baseline
PEEP +2.5 additional cm H
O. Conceptually, this is “keeping open”
2
Acute Respiratory Distress Syndrome 243
air units that have been recruited. Most patients with ARDS have an
optimal PEEP in the range of 10–15.
Recruitment should be repeated in patients who respond, until they no
longer respond. Conceptually, this is when the lungs have been optimally recruited, and the main goal is to keep them recruited through
PEEP (now higher and presumably optimal) and adjunct measures.
• For patients with severe ARDS in whom the required FIO
is ≥ 0.80 despite
2
pleural drainage, neuromuscular blockade and recruitment, we would recommend ventilation in the prone position.
{ It is very possible that some patients with less severe ARDS benefit from
earlier prone positioning, yet predicting who will respond to prone positioning remains difficult.
{ Whenever possible, place the patient prone BEFORE they are desaturat-
ing on 100% FIO2. In this circumstance, it becomes a dangerous,
desperation maneuver as opposed to a planned therapeutic intervention.
{ Before placing the patient in the prone position, consider the following:
Do I have the right equipment? (padding for torso, pillow for face/
ventilator tubing, appropriate bed; table for the head if desired) ICU
beds designed specifically for prone positioning are helpful but do not
eliminate this step.
Are there any lines or tubes that should be put in or removed PRIOR
to placing the patient prone?
Any wound care or appliance problems that can be anticipated?
Do I have enough people? This is a team effort. And in the unusual
circumstances where patients respond poorly, it is best to have plenty
of enthusiastic helpers.
{ If prone positioning seems ineffective, perform a recruitment maneuver in
the prone position.
{ If the patient responds, leave them prone for 8–12 hours, then supinate.
This limits facial/tongue/corneal edema which can be both unpleasant for
visitors and problematic for the patient. In general, try to execute changes
in position during times of high staff availability (read “daytime”), as
these tend to be periods of high lability for the patient.
Review of Current Literature with References
• For an outstanding description of the rationale behind the Berlin defi nition of
ARDS, and its advantages over the American-European Concensus Confer-
244 J. L. Johnson
ence defi nition, the practitioner will want to review the paper by Ferguson
et al.1 In brief, it crystallizes the concept that ARDS is a spectrum of a disease,
and eliminates the idea that acute lung injury is a separate entity. It clarifi es
the defi nition of acute, and provides for situations where left atrial hyperten-
sion and ARDS may coexist.
• The pathophysiology of pulmonary infl ammation in ARDS is nicely described
in two recent papers, that describe the interaction between endothelium, alve-
olar e pithelium, and the leukocytes which are thought to deliver the autotoxic
2,3
insult.
Understanding the four different potential zones in the lung injured
by ARDS is pivotal for optimal ventilator management. With this in mind, the
strategy of prone positioning may improve gas exchange by providing better
aeration to dorsal regions of the lung without signifi cantly impacting perfusion, thus improving v/q mismatch.
4
• For an overview of the concepts of VILI, the reader is referred to a paper
by Gattinoni et al.,5 which outlines the concept of stress and strain, with
their biomechanical underpinnings. Lastly, it is clearly worth reviewing
the ARDSnet papers which solidifi ed the survival advantage of a minimal
pressure, low stretch strategy.
6
1. Ferguson ND, Fan E, Camporota L et al. The Berlin defi nition of ARDS: an expanded
rationale, justifi cation, and supplementary material. Intensive Care Med.
2012; 38(10): 1573–1582. doi:10.1007/s00134-012-2682-1.
2. Matthay MA, Ware LB, Zimmerman GA. The acute respiratory distress
syndrome. J Clin Invest. 2012; 122(8): 2731–2740. doi:10.1172/JCI60331.
3. Lucas R, Verin AD, Black SM, Catravas JD. Regulators of endothelial and
epithelial barrier integrity and function in acute lung injury. Biochem Phar-
macol. 2009; 77(12): 1763–1772. doi:10.1016/j.bcp.2009.01.014.
4. Guérin C, Reignier J, Richard J-C et al. Prone positioning in severe acute
respiratory distress syndrome. N Engl J Med. 2013; 368(23): 2159–2168.
doi:10.1056/NEJMoa1214103.
5. Gattinoni L, Carlesso E, Caironi P. Stress and strain within the lung. Curr
Opin Crit Care 2012; 18(1): 42–47. doi:10.1097/MCC.0b013e32834f17d9.
6. Kallet R. What is the legacy of the national institutes of health acute
respiratory distress syndrome network? Respir Care 2009; 54(7): 912–924.
Available at: http://www.ingentaconnect.com/content/jrcc/rc/2009/00000054/
00000007/art00010. Accessed on January 27, 2013.
Chapter 6-(vi)
Pleural Space and Mediastinum
Daine T. Bennett, MD* Robert A. Meguid, MD, MPH†
John D. Mitchell, MD
*Surgical Resident, University of Colorado School of Medicine
†
Assistant Professor of Surgery, University of Colorado School of Medicine
‡
Professor of Surgery, University of Colorado School of Medicine
§
Associate Professor of Surgery, University of Colorado School of Medicine
‡
and Michael J. Weyant, MD
§
Take Home Points
• Not all pleural effusions require drainage. Dependent effusions less than
10 mm by ultrasound frequently resolve without intervention.
• In management of a complex pleural effusion, any of the three following criteria
mandate decortication: (1) Purulent fluid at the initial thoracentesis;
(2) Multiloculated fluid collection with evidence of a pleural peel; or (3) Failure
to improve with fibrinolytic therapy.
• Retained hemothorax after trauma, not adequately drained after initial tube
thoracostomy, should be managed with thoracoscopic/video-assisted
thoracic surgery (VATS) drainage in patients who can tolerate surgery.
Contact information: University of Colorado Denver, Anschutz Medical Campus, Division of Cardiothoracic Surgery, 12631 East 17
daine.bennett@ucdenver.edu, robert.meguid@ucdenver.edu, john.mitchell@ucdenver.edu,
michael.weyant@ucdenver.edu
th
Ave, MS 310, Aurora, CO 80045; Email:
245
246 D. T. Bennett et al.
• Early VATS drainage has been shown to reduce cost, hospital length of stay and
duration of tube drainage when compared to second tube thoracostomy for
retained hemothorax.
• Descending necrotizing mediastinitis is a rare entity typically presenting after
oropharyngeal/cervical infections or cervical trauma. It must be considered in
patients with neck swelling and elevated inflammatory markers.
• Delay in diagnosis and inadequate drainage are the main causes of mortality
from descending necrotizing mediastinitis.
• Diagnosis of descending necrotizing mediastinitis is confirmed by presence
of fluid collections/abscesses on computed tomography (CT) scan. Treatment
is with immediate administration of broad-spectrum antibiotic coverage and
surgical debridement of the neck and mediastinum. Delay in diagnosis and
treatment can have disastrous effects.
Background
• Under normal physiologic conditions, each pleural space produces approxi-
mately 5–10 ml/kg of body weight per day of fluid which is easily resorbed.
• 40% of pneumonia cases are accompanied by pleural effusion with 5%
of these resulting in a complex effusion or empyema frequently requiring
surgical intervention.
• Complicated pleural effusion develops in three phases: (1) Sterile effusion
due to inflammation; (2) Fibropurulent phase with bacterial contamination;
and (3) Organizational phase with fibroblasts creating a thick lining. Once the
effusion has reached the organizational phase, surgical debridement will be
necessary.
• Retained hemothorax can result in empyema or fibrothorax if not evacuated
promptly or adequately.
• Descending necrotizing mediastinitis is diagnosed by neck swelling, elevated
inflammatory markers and radiologic evidence. The diagnosis is confirmed
by necrotizing tissue identified intraoperatively.
Main Body
Complex pleural effusion/empyema
• Not all effusions require drainage. The first step in management is evaluation of
the size of the pleural effusion by ultrasound. Dependent effusions <10 mm by
ultrasound frequently resolve spontaneously and should be managed expectantly.
Pleural Space and Mediastinum 247
• If larger than 10 mm, the effusion should be drained by thoracentesis. Pleural
fluid with pH <7.2 or glucose <60 ng/dL is considered infected. If infected by
these criteria, a tube thoracostomy is necessary with bacterial cultures of the
effusion obtained and antibiotics started.
• If the initial thoracentesis reveals frank purulence, the patient should be taken
to the operating room for decortication.
• If the effusion is not adequately drained within 24 hours of tube thoracostomy,
a CT scan is obtained to evaluate the thoracic cavity. Imaging demonstrating
an established pleural peel or multiloculated empyema mandates immediate
decortication.
• For retained effusions less than 3 days old and without a pleural peel, fibrino-
lytic therapy is indicated with tPA and DNase administration twice daily for
three days through the thoracostomy tube (see review of current literature
below). However, failure to improve the effusion within 24 hours of starting
fibrinolytic therapy necessitates decortication.
• Decortication is indicated for the following scenarios: (1) Frank purulence at
the time of initial thoracentesis; (2) Evidence of a pleural peel with associated
multiloculated empyema; and (3) Failure to improve with fibrinolytic therapy.
• VATS approach is preferred to open decortication when feasible. If open decor-
tication is necessary, a posterolateral muscle-sparing thoracotomy is preferred.
Hemothorax
• Traumatic hemothorax is initially treated with tube thoracostomy at the time
of presentation to the hospital. Patients with initial evacuation of >1500 mL of
blood or >200 mL/hr for 4 hours should be considered for immediate thoracotomy for management of ongoing bleeding.
• Retained hemothorax in the stable patient after initial management with tube
thoracostomy can result in empyema or fibrothorax, prolonging hospital stay
and complicating patient management.
• Retained hemothorax can initially be treated with a second tube thoracos-
tomy. However, the failure rate of this management strategy is high: about
50% of patients will require surgical evacuation. This management approach
should be reserved for small hemothoraces and patients unfit for surgery.
• In patients with larger retained hemothoraces who are acceptable surgical candi-
dates, evacuation of the hemothorax with VATS is preferred. VATS technique is
less invasive than open thoracotomy and allows for faster recovery. Management
of retained hemothorax with VATS, instead of second tube thoracostomy, has
been shown to reduce drainage duration, hospital length of stay and cost.