RCPs have made huge strides in optimizing the management
of artificially ventilated lungs through providing basic lung
function needs such as optimal temperature and humidity and
attempting to eliminate every possible source of nosocomial
infection.
The human lung is a mighty yet
fragile organ that constantly interacts with the surrounding
environment, while effectively transporting oxygen and carbon
dioxide into and out of the individual. When committed to a
mechanical ventilator, a necessary but unnatural marriage
occurs. It is the RCP's role to serve the lung by ensuring
proper temperature, humidity, and gas exchange. We must
simultaneously protect the lung from mechanical malfunctions,
human error, infections, and the onslaughts of volume and
pressure that can result in ventilator-induced lung
injury.
Maintaining the Airway
While focusing
attention on contemporary modes of ventilation and other
higher order patient care issues, it can be easy to overlook
the basics, including simple airway management. A secure
airway is essential to ventilator management, and without it,
all other issues become moot. “The rate of unplanned
extubation (accidental extubation or self-extubation) has been
reported as 2% to 13%.”1 Whether secured with
adhesive tape, twill tape, or commercially available devices,
it is essential that the endotracheal (ET) tube and cuff
pressures be evaluated routinely and repositioned periodically
to prevent tissue necrosis and sores. Securing and/or
repositioning the tube should never be undertaken
single-handedly; one clinician should perform the procedure
while another stabilizes the tube position. Optimal cuff
pressure to create an effective seal while minimizing
aspiration or tracheal wall injury is normally 25 to 35 cm
H2O.
The upper airway is the conduit between the lungs and the
lower respiratory tract. By substituting an artificial airway,
important functions are compromised or bypassed. These include
the jobs of providing warmth, humidification, filtration,
removal of debris, and facilitation of expectoration and
speech. The upper airway represents an essential component of
the immune system that is lost when ventilator support is
required—a significant factor when considering lung protection
strategies.
Ventilator-Associated
Pneumonia
Ventilator-associated pneumonia (VAP) is
a nosocomial infection occurring in patients after 48 hours of
mechanical ventilation. It is typically accompanied by fever,
increased leukocyte production, and purulent secretions.
Vastly differing rates of VAP are reported, principally
because there is not a consistent standard for diagnosis,
beyond the occurrence of a new infiltrate presenting (usually
after 48 hours) in a mechanically ventilated patient.
Identification of VAP typically includes:
- Appearance of a new infiltrate or consolidation that is
evident on chest x-ray.
- New onset of purulent secretions or change in the
character of the sputum.
- Pathogenic organisms isolated by blood culture and/or
transtracheal aspirate or bronchial lavage. Cultures are
best obtained via bronchoscopy, which produces the most
consistent results, but traditional acquisition via a
suction trap is also commonly used.
VAP rates can be determined by dividing the number of VAPs
identified and dividing this figure by the total ventilator
days times 1,000:
VAP
number |
|
Ventilator days X
1,000 |
Active or Passive Humidification?
Once
upon a time, RCPs spent considerable time draining wet
ventilator tubing into bedside buckets before the contents
blocked airflow or emptied into the patient’s lungs.
Eventually, inline water traps collected the condensate while
eliminating the need to disconnect the patient from the
ventilator when disposing of the water. Heat moisture
exchangers (HMEs) are passive systems and have more recently
become en vogue. They eliminate the need for a heated
humidifier and the associated condensation as well as many of
the other challenges previously associated with active
systems. They are also economical, efficient, convenient, and
dependable. Consequently, HMEs continue to provide an
attractive tool for use with short-term or postoperative
patients.
However, the policy of using HMEs for all patients all the
time is currently being challenged when applied to long-term
ventilatory support. When VAP becomes a concern, a recursion
from passive to active humidification is winning favor. Many
investigators believe the heat and moisture provided by HMEs
may be insufficient to promote optimal mucokinesis over a long
term, especially if high minute volumes are required.
When the patient is disconnected from the ventilator, some
machines generate significant flows through the circuit, which
may aerosolize contaminated fluids, increasing the risk of
lung infections. Consequently, a reduction or elimination of
ventilator circuit changes and a commitment not to break the
circuit have been successfully pursued.
When applied to VAP, ventilator circuit change frequency
has been one of the foremost topics of investigation. Frequent
ventilator circuit changes, once a standard practice, have
been reconsidered, with “the optimum protocol for ventilator
tubing changes ...still [considered to be] uncertain, but
evidence suggests that tubing-change intervals should be at
seven days, and accumulating evidence suggests that
ventilatory circuits need not be changed at any regular
interval.”1 Numerous studies have determined that
intervals of 7 days between circuit changes have shown no
difference in VAP rates. The practice is easy to implement,
cost-effective, and safe. Circuit change intervals
substantially longer than 7 days are currently being
investigated.
Gary Hospodar, MAOM, RRT, an independent consultant in
Santa Fe, NM, has studied the issue and presented his findings
at the 48th American Association for Respiratory Care
International Respiratory Congress in Tampa, Fla. He described
a 6-month investigative study, which embraced four components
intended to reduce VAP.
- Use of in-line suction catheters, which were changed
every 7 days. RCPs were allowed the option of changing the
catheters more frequently if they deemed it necessary, but
the 7-day standard replaced the former 24-hour frequency of
change. Suctioning was performed when clinically indicated,
not as a matter of thoughtless routine.
- Ventilator circuit changes every 30 days. This replaced
the former 7-day circuit change frequency. In addition to
dramatically decreasing the frequency of ventilator changes,
a policy of maintaining a closed, virtually unbroken system
was invoked.
- Implementation of active (heated) humidification
systems. The active systems were intended to enhance
mucociliary activity that may be compromised with passive
systems. The molecular water produced by modern heated
humidifiers is not thought to pose an important risk of
pneumonia in ventilated patients.
- Education of the entire clinical care team. Hospodar
emphasized this as a key element to the success of the
investigation. Revisiting the essential importance of hand
washing, double gloving, and use of personal protection
devices was stressed. Most important, all members of the
team, including physicians, nurses, infection control
specialists, and ancillary personnel, were indoctrinated
with the goals of the study.
Another commonly overlooked, but potential source of
infection may come from the ubiquitous oral suction tips that
are typically used and reused to remove oral secretions. While
these tools are useful for many patients and caregivers in a
variety of circumstances, their potential as a source for VAP
infections was considered. Hospodar eliminated the use of
these tools, favoring single-use alternatives for oral care
and suction.
Dean Hess, PhD, RRT, FAARC, is affiliated with the
Department of Respiratory Care, Massachusetts General
Hospital, Boston, and Harvard Medical School. He suggests,
“VAP is more likely the result of what is aspirated around the
cuff of the endotracheal tube than what is inhaled from the
ventilator circuit” and “rather than refer to these infections
as VAP, perhaps we should refer to them as ET associated
pneumonia.”2 Hospodar adds that VAP is likely a
result of numerous sources, and agrees that it is a mistake to
focus on any individual component, such as ventilator tubing
or suction catheters.
Hospodar’s investigation also demonstrated that improved
patient care could also be cost-effective. His investigation
showed a decrease from $17.81 to $7.79 in operational supply
expenses—a 56% reduction. In addition to the savings in supply
costs, staff labor time is naturally reduced.
When RCPs report for duty clearly suffering from a cold or
flu, perhaps even running a fever, there are often no
mechanisms to send the offender home to bed. This is
surprising in an industry that embraces quality improvement
and has policies and procedures to deal with virtually any
other event. The popular work ethic that often encourages
workers to “tough it out” when they are ill is in direct
conflict with everything else we value. Colds and flu can
admittedly be hard to quantify, but when RCPs report for duty
suffering from a contagious illness, they put everyone around
them at risk. Respiratory care departments should be
performing a careful self-examination with consideration as to
how employee illness may impact patient care.
Ventilator-Induced Lung
Injury
Ventilator-induced lung injury may result
from oxygen toxicity, biotrauma, atelectrauma, and volutrauma.
Acute lung injury (ALI) is caused by alveolar overdistention
caused by high peak inflation volume (volutrauma), and high
peak alveolar pressures.1
- Oxygen Toxicity. High oxygen
concentrations can result in oxygen toxicity, which can
create acute respiratory distress syndrome (ARDS)-like
changes in the lungs. Consequently, the fractional inspired
oxygen (Fio2) should be set as low as possible, while
maintaining oxygen saturations above 90%. Positive
end-expiratory pressure (PEEP) can enhance alveolar
recruitment while simultaneously enhancing oxygenation and
permitting an Fio2 of below 60% to maintain acceptable
oxygenation levels.
- Biotrauma. Biotrauma is an inflammatory
process that can result from ventilating the lungs in a
manner that promotes alveolar overdistention. “Inflammatory
mediators such as cytokines and chemokines may translocate
into the pulmonary circulation, causing systemic
inflammation. The manner in which the lungs are ventilated
therefore may play a role in systemic
inflammation.”1
- Atelectrauma. The implementation of
lung protection strategies for patients with acute lung
injury and ARDS has been an important step in optimizing
patient outcomes; however, while the application of low VT
ventilation is clearly beneficial, “it will not prevent
injury from repetitive alveolar opening and closing, and may
promote alveolar collapse,”3 or atelectrauma.
Consequently, investigators are taking a close look at
maneuvers intended to recruit alveoli into useful service.
Plateau pressure is reflective of alveolar pressure and
should be kept below 30 cm H2O, while PEEP is used to
enhance alveolar recruitment.
- Volutrauma. The overdistention of
alveoli caused by high peak inflation volume is also
associated with high peak alveolar pressures. “The main
determinant of volutrauma seems to be the end-inspiratory
volume (the overall lung distension), rather than the VT or
FRC (which depends on PEEP). Consequently, a consensus has
emerged as to the importance of monitoring and limiting
inspiratory plateau pressure (which reflects end-inspiratory
volume better than does peak pressure).”4
ARDSnet
ARDS is an inflammatory lung
condition that usually occurs in conjunction with catastrophic
medical conditions, such as pneumonia, shock, sepsis, and
trauma. Approximately 150,000 Americans are affected each
year, and more than 40% die.5 The ARDSnet (Acute
Respiratory Distress Syndrome Clinical Network) is a
monumental national trial, federally funded by the National
Institutes of Health (NIH) and the National Heart, Lung, and
Blood Institute (NHLBI). It is currently studying the effects
of numerous treatment modalities to optimize care for patients
with ARDS and ALI. ARDSnet has 10 clinical centers composed of
23 hospitals, and one clinical coordinating center. Several
studies have been concluded, and information about these as
well as ongoing studies can be accessed at www.ardsnet.org.
The information gathered by the investigators is evaluated
even as the studies are conducted. Fran Piedalue, RRT,
clinical coordinator for respiratory care at University of
Colorado Hospital, Denver, says, “Statisticians perform an
interim analysis on a predetermined enrollment number to
consider the efficacy versus futility for each study.”
Consequently, some studies are concluded early, when the
effectiveness (or lack of it) has been determined.
“The prognosis of ARDS seems to have improved over the
years for reasons that are yet unclear, but may be related in
part to the lower VT used in most intensive care units at
present.”4 Indeed, one of the most significant ARDSnet studies
that has been concluded showed that limiting tidal volume to 6
mL/kg or less (typically 4 to 6 mL/kg) can minimize the
undesirable effects of larger tidal volumes. The test study
was intended to enroll 1,000 patients, but was concluded early
because the results were overwhelmingly clear. “The decision
[to conclude the study] was recommended by the study's Data
Safety and Monitoring Board (DSMB)…based on data on the first
800 patients, which showed approximately 25% fewer deaths
among patients receiving small, rather than large, breaths of
air from a mechanical ventilator.”5
The resulting lower minute volumes create an increasingly
acidic state, and clinicians have traditionally been
uncomfortable with resulting arterial blood gas values that
fall outside the “normal” range; however, rather than risk
increased injury to the lungs from the effects of volume and
pressure, an elevated partial pressure of arterial carbon
dioxide (Paco2) was accepted. With this resulting “permissive
hypercapnea, the clinical concern generally is related to pH,
not Paco2 [and] most investigators agree that a pH above 7.25
is acceptable.”1
Current studies under way by the ARDSnet clinical trials
include:
- Late Steroid Rescue (LSR study). While
it has already been determined that corticosteroids are not
effective in treating early ARDS, the study is designed to
determine if the administration of cortico-steroids, in the
form of methylprednisolone sodium succinate, in severe
late-phase (after 7 days) ARDS will reduce mortality and
morbidity.
- Pulmonary Artery Catheter (PAC study).
Evaluating the use of a pulmonary artery catheter
vs a less invasive alternative, the central venous catheter,
for management of patients with ALI and ARDS. The study is
combined with a concurrent study evaluating a “Fluid
Conservative” vs “Fluid Liberal” management strategy in
patients with ALI or ARDS.
Studies concluded by the ARDSnet clinical trial due to lack
of efficacy included:
- Ketoconazole Study. Tested whether the
administration of ketoconazole early after the onset of ALI
or ARDS will reduce mortality and morbidity. It was
concluded early due to lack of efficacy.
- Lisofylline Study. Tested whether the
administration of lisofylline early after the onset of ALI
or ARDS would reduce mortality and morbidity. It was
concluded early due to lack of efficacy.
- ALVEOLI Study. Investigated the
hypothesis that mortality from ALI and ARDS would be reduced
with a mechanical ventilation strategy designed to prevent
lung injury from repeated collapse of bronchioles and
alveoli at end-expiration. It compared clinical outcomes of
patients with acute ALI and ARDS treated with a higher
end-expiratory lung volume/lower Fio2 vs a lower
end-expiratory lung volume/higher Fio2 ventilation strategy.
It was concluded early due to a lack of efficacy.
Conclusion
Lung protection strategies
for providing life-sustaining ventilator support while
minimizing morbidity and mortality continue to evolve and
improve. The introduction of new methods combined with a
continued willingness to challenge and question long-accepted
notions has led to dramatically improved patient outcomes. The
optimal management of ARDS continues to be evolving, most
notably as a result of the comprehensive ARDSnet studies, with
implications that will undoubtedly benefit other ventilator
management challenges as well. By providing basic lung
function needs, including optimal temperature and humidity,
minimizing the effects of volume and pressure, and attempting
to eliminate every possible source of nosocomial infection, we
have made huge strides in optimizing the management of
artificially ventilated lungs. RCPs are leading the way in the
process, as investigators, inventors, and instigators of
positive change and evolution.
John A. Wolfe, RRT, CPFT, is a contributing writer
for RT Magazine.
References
1. Hess DR, MacIntyre NR,
Mishoe SC, Galvin WF, Adams AB, Saposnich AB. Respiratory Care
Principles and Practice. Philadelphia: WB Saunders Co;
2002.
2. Hess DR. Mechanical ventilation strategies: what’s
new and what’s worth keeping? Respir Care.
2002;47:1008-1009.
3. Hess DR, Bigatello LM. Lung
recruitment: the role of recruitment maneuvers. Respir Care.
2002;47:308-318.
4. Dreyfuss D, Saumon G.
Ventilator-induced lung injury. Am J Respir Crit Care Med.
1998;157:294-323.
5. National Institutes of Health;
National Heart, Lung, and Blood Institute. News Release; March
15, 1999.