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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5537_Библиотеки_им_академика_М_И_Перельмана.pdf
384
U.S. Ayyala
Table 2. Glossary of Respiratory Parameters
Respiratory Parameter Description
Respiratory rate (RR) Normally set at 12–16. I↑RR to ↑ventilation.
↓RR used in “permissive hypercapnia” strategy.
Fraction of inspired oxygen Range 21%–100%. Initial ventilator settings
(FiO
2
) should begin with 100% and titrate down to
maintain PaO
2
of >60, O2sat >90%.
Positive end-expiratory pressure Positive pressure during expiration.
(PEEP) Normal ventilator settings — physiologic PEEP
of 3–5 mmHg.
PEEP→↑functional residual capacity (FRC) —
prevents atelectasis and improves oxygenation.
Side effects: ↑intrathoracic pressure ◊↓venous
return →↓preload.
Inspiratory flow rate Usually set at 60 L/min.
↑flow to ↑expiratory time.
↑flow will ↑P
peak
.
Inspiratory time Set in pressure-cycled ventilation. Can alter
inspiratory time to change I:E ratio.
I:E ratio Normally 1:2. Change to 1:3–1:5 for
obstructive lung disease. May increase
inspiratory time in ARDS.
Peak inspiratory pressure Highest pressure during respiratory cycle.
(PIP) Function of both airway resistance and lung/
chest wall/abdominal muscle compliance↑.
↓PIP → air leak in system.
↑PIP → either ↑airway resistance (mucus
plugging, bronchospasm, occluded ETT) or
↑ P
plat
(ARDS, pneumonia, pulmonary
edema, pneumothorax, atelectasis).
Plateau pressure (P
plat
) Measured at end of inspiration when airway
resistance = 0.
↑P
plat
→↓compliance of lung or chest wall.
pressure during respiration, reflecting two components: airway resistance
and intrinsic compliance of the lung, chest wall, and abdomen.
2
P
plat
is
measured at end inspiration, when airway resistance is absent (zero flow),
and is therefore a static measurement of lung, chest wall, and abdominal
compliance.2PIP and P
plat
become important when one is evaluating
distress on the mechanical ventilator.
Monitoring and Supportive Care
Monitoring
Patients who are mechanically ventilated require daily clinical, radiological, and laboratory monitoring. In addition to a complete physical examination, clinical evaluation of patients should include observation for
ventilator synchrony by assessing chest and abdominal movements.
Radiographic monitoring after intubation is important, especially for confirming placement of the endotracheal tube. However, the frequency with
which subsequent chest radiographs should be obtained is not yet defined,
with some evidence supporting on-demand radiographs instead of daily
chest radiographs.
3
Continuous pulse oximetry should be part of hemodynamic monitoring but can be inaccurate in patients who are hypothermic or
hypotensive,
4
and should not replace arterial blood gas determinations of
arterial oxygen tension (PaO
2
). Daily arterial blood gases should be
obtained to measure not only adequacy of oxygenation but also ventilation.
Supportive Care
Supportive care of the mechanically ventilated patient should encompass
that of the critically ill patient, including sedation, stress ulcer prophylaxis, deep venous thrombosis prophylaxis, enteral nutrition, and measures to prevent nosocomial infections.
5
Of critical importance for these
patients is adequate pain control. Pain may be due to the primary process
requiring intubation (i.e. the surgical procedure and underlying medical
condition) or from routine management, including placement of invasive
catheters, suctioning of secretions, and turning to prevent decubitus
ulcers. Pain can lead to increase in catecholamines, increase in oxygen
consumption, and myocardial ischemia, and can manifest as impairment
of vital signs as well as patient–ventilator dyssynchrony. No one sedative
385
Management of the Mechanically Ventilated Patient
or analgesic has been proven to be superior to another in the critically ill
population, and selection should be tailored individually. Sedatives commonly used include opiates, benzodiazapenes, propofol, neuroleptics, and
dexmedetomidine. In specific instances, patients with ventilator dyssynchrony may require neuromuscular blocking agents to safely oxygenate
and ventilate them. These drugs should be used with caution and always
in conjunction with adequate sedation. Daily interruption of sedative infusions in addition to a daily spontaneous breathing trial has been proven to
be of benefit in reducing days on the ventilator, ICU length of stay, and
one-year mortality.
7
Disease-Specific Conditions and Ventilator Management
The overall management of mechanical ventilation regardless of disease
state includes: (1) titration of FiO
2
to the minimum required, (2) maintenance of low pressures to reduce barotrauma, (3) utilization of appropriate tidal volumes to reduce volutrauma, and (4) use of adequate PEEP to
facilitate oxygenation. Initial ventilator settings for the majority of
patients requiring invasive mechanical ventilation involve the ACV volume-controlled mode with a target TV of 8 ml/kg ideal body weight.
Initially FiO
2
is set to 100% and PEEP is preset to 3–5 cmH2O.
Obstructive Lung Disease
Mechanical ventilation initiated for acute exacerbations of asthma or
chronic obstructive lung disease (COPD) requires careful attention, due
to the potential for complications. In particular, patients with obstructive
lung disease are at risk for high peak pressures, mainly from increased
airway resistance. These pressures can lead to barotrauma manifesting
as pneumothorax or pneumomediastinum. In addition, patients with
obstructive lung disease can develop dynamic hyperinflation, where
exhalation is not completed before initiation of the next breath. This
leads to auto-PEEP, which can result in barotrauma as well as hemodynamic compromise (hypotension). A ventilatory strategy of “permissive
386
U.S. Ayyala
hypercapnia” can prevent dynamic hyperinflation.8It employs a lower
RR(8–10) and a higher flow rate (80–100 L/min) to allow for increased
time for exhalation (I:E ratio of 1:3–1:5). The consequence of this lower
RR is decreased minute ventilation leading to hypercapnia. Any patient
with evidence of auto-PEEP and hemodynamic instability should be disconnected from the ventilator and allowed to fully exhale before altering
parameters and reconnecting.
Acute Respiratory Distress Syndrome/ Acute Lung Injury
In patients who meet criteria for acute respiratory distress syndrome
(ARDS)/acute lung injury (ALI), a lung-protective strategy is utilized. In
a landmark trial, this approach of using a low TV (6 ml/kg IBW or less)
compared to traditional TVs of 12 ml/kg to minimize volumtrauma from
overdistension of alveoli and to limit airway pressures (goal plateau pressure <30) conferred an absolute mortality benefit of 8.8%.
9
Increasing levels of PEEP are used to prevent atelectasis and improve oxygenation. This
ventilatory strategy results in hypercapnia which can be managed by
increasing the RR.
Evaluation of Respiratory Distress in the Mechanically Ventilated Patient
Respiratory distress that develops in the mechanically ventilated patient can
be a life-threatening emergency and must be attended to immediately.
Clinically, such patients often have abnormal vital signs with evidence of
tachycardia, tachypnea, or desaturation. Patients may be agitated, “bucking”
the ventilator with dyssynchronous movements of the chest wall and
abdominal musculature. There is a broad differential for respiratory distress
in these patients that includes endotracheal tube or ventilator malfunction,
inappropriate ventilator settings, inadequate sedation, intrinsic pulmonary
pathology (e.g. bronchospasm, secretions, pneumothorax), or extrapulmonary processes (e.g. arrhythmias, sepsis).
387
Management of the Mechanically Ventilated Patient
Evaluation of respiratory distress in these patients should begin with
determination of hemodynamic stability. If the patient is hemodynamically unstable, then he or she should be disconnected from the ventilator
and manually ventilated with 100% oxygen. Close attention should be
given to the ease with which ventilation can be provided. If resistance is
met with each breath, the endotracheal tube may be obstructed and suctioning or even replacement of the tube may improve the patient’s condition. If air is audible with each manually delivered breath, an air leak may
be present and the endotracheal cuff may need to be inflated or the tube
replaced to correct this problem. Other life-threatening conditions that
must be addressed in the deteriorating patient include evaluation for tension pneumothorax and auto-PEEP. If clinical suspicion exists for tension
pneumothorax (unilateral breath sounds, tracheal deviation, hemodynamic instability), then needle decompression needs to be performed.
In the stabilized patient, a more complete assessment can be performed (Fig. 1). This includes focused physical examination, chest radiography to evaluate tube placement and lung parenchyma, arterial blood
gas to determine gas exchange, and an electrocardiogram to look for
arrhythmia. Examination of the ventilator circuit and any triggered alarms
can be helpful in localizing a cause for respiratory distress. The most common ventilator alarm activated is PIP. As discussed earlier, PIP, P
plat,
and
the difference (PIP-P
plat
) are values that can help identify the underlying
cause of respiratory distress (Fig. 1).
Liberation from the Mechanical Ventilator
Liberation from the mechanical ventilator is a process that gradually transitions a patient from full ventilator support to spontaneous breathing. A
patient’s readiness to maintain spontaneous breathing is the first step in
liberation from the ventilator (Table 3). Once the conditions are met, a
spontaneous breathing trial can be initiated. In randomized controlled trials, both PSV and T-tube trials have been shown to be superior to SIMV
as weaning modalities.
10,11
Coordinated efforts with the nurses, respiratory
therapist, and physicians are integral to successful extubations.
388
U.S. Ayyala
389
Management of the Mechanically Ventilated Patient
Fig. 1. Distress in the mechanically ventilated patient.
Table 3. Assessing Patient Readiness for a Spontaneous Breathing Trial
Clinical criteria:
• Underlying cause of respiratory failure has improved.
• Hemodynamic stability with HR 50–140, SBP 90–180 mmHg.
• SpO
2
>92% on FiO2< or = 40%.
• PEEP <5 cmH
2
O.
• Patient can initiate his own breaths.
• Patient is alert and can follow simple commands.
Weaning parameter:
• Rapid shallow breathing index (RSBI): RR/TV (L)
– To be performed while patient is spontaneously breathing. A value >105
breath/min/L predicts that a patient will fail a spontaneous breathing trial.
12
References
1. Koh SO. (2007) Mode of mechanical ventilation: Volume controlled
mode. Crit Care Clin 23: 161–167.
2. Tobin, MJ. (1990) Respiratory monitoring. JAMA 264: 244–251.
3. Hejblum G, Chalumeau-Lemoine L, Loos V, et al. (2009) Comparison
of routine and on-demand prescription of chest radiographs in
Respiratory Distress on Mechanical Ventilator
Hemodynamically Unstable Patient
Disconnect from ventilator and manually provide 100 Fio
Increased
Check P
Increased
Reduced Compliance
- atelectasis
- pneumonia/pulmonary edema
- pneumothorax
2
plateau
Hemodynamically Stable Patient
Focused Physical Examination
- Check ventilation and circulation
Normal
Airway Obstruction
- mucus plug
- bronchospasm
- ventilator tubing
- CXR
- ABG
Check PIP
Normal
Decreased
Check for air leak
mechanically ventilated adults: A multicentre, cluster-randomised,
two-period crossover study. Lancet 374(9702): 1687–1693.
4. Hinkelbein J, Genzwuerker HV, Fielder F. (2005) Detection of a systolic pressure threshold for reliable readings in pulse oximetry.
Resuscitation 64: 315–319.
5. Dellinger RP, Levy MM, Carlet JM, Bion J, Parker MM, Jaeschke R,
Reinhart K, Angus DC, Brun-Buisson C, Beale R, Calandra T,
Dhainaut JF, Gerlach H, Harvey M, Marini JJ, Marshall J, Ranieri M,
Ramsay G, Sevransky J, Thompson BT, Townsend S, Vender JS,
Zimmerman JL, Vincent JL. International Surviving Sepsis Campaign
Guidelines Committee; American Association of Critical-Care Nurses;
American College of Chest Physicians; American College of
Emergency Physicians; Canadian Critical Care Society; European
Society of Clinical Microbiology and Infectious Diseases; European
Society of Intensive Care Medicine, et al. (2008) Surviving Sepsis
Campaign: International guidelines for management of severe sepsis
and septic shock. Crit Care Med 36: 296–327.
6. Epstein J, Breslow MJ. (1999) The stress response of critical illness.
Crit Care Clin 15: 17–33.
7. Girard, TD, Kress JP, Fuchs BD, et al. (2008) Efficacy and safety of
a paired sedation and ventilator weaning protocol for mechanically
ventilated patients in intensive care (Awake and Breathing Controlled
trial): A randomized controlled trial. Lancet 371: 126.
8. Oddo M, Feihl F, Schaller MD, Perret C. (2006) Management of
mechanical ventilation in acute severe asthma: Practical aspects.
Intensive Care Med 32(4): 501–510.
9. The Acute Respiratory Distress Syndrome Network. (2000) Ventilation
with lower tidal volumes as compared with traditional tidal volumes
for acute lung injury and the acute respiratory distress syndrome.
N Engl J Med 342(18): 1301–1308.
10. Esteban, A, Fructos F, Tobin MJ, et al. (1995) A comparison of four
methods of weaning from mechanical ventilation. Spanish Lung
Failure Collaborative Group. N Engl J Med 332(6): 345–350.
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11. Brochard L, Rauss A, Benito S, et al. (1994) Comparison of three
methods of gradual withdrawal from ventilatory support during weaning from mechanical ventilation. Am J Respir Crit Care Med 150(4):
896–903.
12. Meade M, Guyatt G, Cook D, et al. (2001) Predicting success in
weaning from mechanical ventilation. Chest 120(6S): 400S–424S.
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Management of the Mechanically Ventilated Patient
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Glycemic Management in Critically
IIl Patients
Maria Skamagas*
Key Pearls
• Glucose goals in the critically ill patient: 140–180 mg/dL.
• A validated intravenous insulin protocol which incorporates current
glucose, rate of glucose change, and current insulin infusion rate into
adjustments of insulin infusion should be used. A hypoglycemia protocol should be incorporated.
• Glucose should be monitored every one hour after initiation of insulin
infusion.
• HbA1c in the hyperglycemic critically ill patient should be measured to
determine if there is pre-existing diabetes or whether elevated glucose
is due to stress hyperglycemia.
• Intravenous insulin should be converted to subcutaneous insulin as
the patient improves clinically. Patients with stress hyperglycemia on
low dose insulin drip may only require correction insulin scale.
Critically ill patients are at risk for hyperglycemia, even if they do not
carry a prior diagnosis of diabetes. Hyperglycemia is likely related to a
host of factors, including counter-regulatory hormones such as cortisol
and catecholamines; inflammatory cytokines; nutritional support
(enteral and parenteral); and medications including glucocorticoids.
1
393
*Mount Sinai School of Medicine, New York, NY, USA.
33
Chapter