Embedded Files
Page 20
number is likely to be small, it is probably not zero, and this needs to be considered when dealing with patients who repeatedly fail an SBT. The criteria used to define SBT “tolerance” are often integrated indexes since, as noted above, single parameters alone perform so poorly. These integrated indexes usually include several physiologic parameters as well as clinical judgment, incorporating such difficult-to-quantify factors as “anxiety,” “discomfort,” and “clinical appearance.” The criteria that have been used in several large trials are given in Table 6. A potential concern about the SBT is safety. Although unnecessary prolongation of a failing SBT conceivably could precipitate muscle fatigue, hemodynamic instability, discomfort, or worsened gas exchange,19,50,117,126,127 there are no data showing that SBTs contribute to any adverse outcomes if terminated promptly when failure is recognized. Indeed, in a cohort of 1,000 patients in whom SBTs were routinely administered and properly monitored as part of a protocol, only one adverse event was thought to be even possibly associated with the SBT.104 There is evidence that the detrimental effects of ventilatory muscle overload, if it is going to occur, often occurs early in the SBT.73,108,110,128 Thus, the initial few minutes of an SBT should be monitored closely, before a decision is made to continue (this is often referred to as the “screening” phase of an SBT). Thereafter, the patient should continue the trial for at least 30 min, but for not 120 min,102 to assure maximal sensitivity and safety. It also appears that whether the SBT is performed with low levels of CPAP (eg, 5 cm H2O), low levels of pressure support (eg, 5–7 cm H2O), or simply as “T-piece” breathing has little effect on outcome.101,129–131 CPAP, however, conceivably could enhance breath triggering in patients with significant auto-PEEP.132,133 Recommendation 4. The removal of the artificial airway from a patient who has successfully been discontinued from ventilatory support should be based on assessments of airway patency and the ability of the patient to protect the airway. Rationale and Evidence (Grade C) Extubation failure can occur for reasons distinct from those that cause discontinuation failure. Examples include upper airway obstruction or inability to protect the airway Table 6. Criteria Used in Several Large Trials* to Define Tolerance of an SBT Objective measurements indicating tolerance/success Gas exchange acceptability (SpO2 85–90%; PO2 50–60 mm Hg; pH 7.32; increase in PaCO2 10 mm Hg) Hemodynamic stability (HR 120–140 beats/min; HR not changed 20%; systolic BP 180–200 mm Hg and 90 mm Hg; BP not changed 20%, no pressors required) Stable ventilatory pattern (eg, RR 30–35 breaths/min, RR not changed 50%) Subjective clinical assessments indicating intolerance/failure Change in mental status (eg, somnolence, coma, agitation, anxiety) Onset or worsening of discomfort Diaphoresis Signs of increased work of breathing (use of accessory respiratory muscles, thoracoabdominal paradox) SBT spontaneous breathing trial SpO2 oxygen saturation measured by pulse oximetry PO2 partial pressure of oxygen PaCO2 arterial partial pressure of carbon dioxide HR heart rate RR respiratory rate *References 101, 102, 105, 108–110, 119, and 120. EVIDENCE-BASED GUIDELINES FOR WEANING AND DISCONTINUING VENTILATORY SUPPORT 76 RESPIRATORY CARE • JANUARY 2002 VOL 47 NO 1 and clear secretions. The risk of postextubation upper airway obstruction increases with the duration of mechanical ventilation, female gender, trauma, and repeated or traumatic intubation.106 The detection of an air leak during mechanical ventilation when the endotracheal tube balloon is deflated can be used to assess the patency of the upper airway (cuff leak test).134 In a study of medical patients,135 a cuff leak 110 mL (ie, average of 3 values on 6 consecutive breaths) measured during assist control ventilation within 24 hours of extubation identified patients at high risk for postextubation stridor. Although others have not confirmed the utility of the cuff leak test for predicting postextubation stridor,136 many patients who develop this can be treated
Google Sites
Report abuse