Medline ® Abstracts for References 9-12
of 'Assessment of respiratory distress in the mechanically ventilated patient'
Mechanical effects of airway humidification devices in difficult to wean patients.
Girault C, Breton L, Richard JC, Tamion F, Vandelet P, Aboab J, Leroy J, Bonmarchand G
Crit Care Med. 2003;31(5):1306.
OBJECTIVE: To evaluate the influence of airway humidification devices on the efficacy of ventilation in difficult to wean patients.
DESIGN: A prospective, randomized, controlled physiologic study.
SETTING: A 22-bed medical intensive care unit in a university hospital.
PATIENTS: Chronic respiratory failure patients.
INTERVENTIONS: Performances of a heated humidifier and a heat and moisture exchanger were evaluated on diaphragmatic muscle activity, breathing pattern, gas exchange, and respiratory comfort during weaning from mechanical ventilation by using pressure support ventilation. Eleven patients with chronic respiratory failure were submitted to four pressure support ventilation sequences by using the heated humidifier and the heat and moisture exchanger at two different levels of pressure support ventilation (7 and 15 cm H(2)O).
MEASUREMENT AND MAIN RESULTS: Compared with the heated humidifier and regardless of the pressure support ventilation level used, the heat and moisture exchanger significantly increased all of the inspiratory effort variables (inspiratory work of breathing expressed in J/L and J/min, pressure time product, changes in esophageal pressure, and transdiaphragmatic pressure; p<.05) and dynamic intrinsic positive end-expiratory pressure (p<.05). Similarly, the heat and moisture exchanger produced a significant increase in Paco(2) (p<.01) responsible for severe respiratory acidosis (p<.05), which was insufficiently compensated for despite a significant increase in minute ventilation (p<.05). This resulted in respiratory discomfort for all patients with the heat and moisture exchanger (p<.01). Adverse effects were partially counterbalanced by increasing the pressure support ventilation level with the heat and moisture exchanger by>or=8 cm H(2)O.
CONCLUSIONS: The type of airway humidification device used may negatively influence the mechanical efficacy of ventilation and, unless the pressure support ventilation level is considerably increased, the use of a heat and moisture exchanger should not be recommended in difficult or potentially difficult to wean patients with chronic respiratory failure.
Medical Intensive Care Department, Rouen University Hospital-Charles Nicolle, France.
Effect of the humidification device on the work of breathing during noninvasive ventilation.
Lellouche F, Maggiore SM, Deye N, TailléS, Pigeot J, Harf A, Brochard L
Intensive Care Med. 2002;28(11):1582.
OBJECTIVE: Heat and moisture exchangers (HME) increase circuitry deadspace compared to heated humidifiers (HH). This study compared the effect of HH and HME during noninvasive ventilation (NIV) on arterial blood gases and patient's effort assessed by respiratory muscles pressure-time product and by work of breathing (WOB).
DESIGN AND SETTING: Randomized cross-over study in a medical intensive care unit.
PATIENTS: Nine patients receiving NIV for moderate to severe acute hypercapnic respiratory failure.
MEASUREMENTS: HME was randomly compared to HH during periods of 20 min. Each device was studied without (ZEEP) and with a PEEP of 5 cmH(2)O. At the end of each period arterial blood gases, ventilatory parameters, oesophageal and gastric pressures were recorded and indexes of patient's effort calculated.
RESULTS: Minute ventilation was significantly higher with HME than with HH (ZEEP: 15.8+/-3.7 vs. 12.8+/-3.6 l/min) despite a similar PaCO(2) (60+/-16 vs. 57+/-16 mmHg). HME was associated with a greater increase in WOB (ZEEP: 15.5+/-7.7 vs. 8.4+/-4.5 J/min and PEEP: 11.3+/-5.7 vs. 7.3+/-3.8 J/min) and indexes of patient effort. NIV with HME failed to decrease WOB compared to baseline. Addition of PEEP reduced the level of effort, but similar differences between HME and HH were observed.
CONCLUSIONS: In patients receiving NIV for moderate to severe acute hypercapnic respiratory failure, the use of HME lessens the efficacy of NIV in reducing effort compared to HH.
Medical Intensive Care Unit, Hôpital Henri Mondor, AP-HP, UniversitéParis 12 et INSERM U492, 51 av du Maréchal de Lattre de Tassigny, 94010 Créteil, France.
Effects of heat and moisture exchangers on minute ventilation, ventilatory drive, and work of breathing during pressure-support ventilation in acute respiratory failure.
Pelosi P, Solca M, Ravagnan I, Tubiolo D, Ferrario L, Gattinoni L
Crit Care Med. 1996;24(7):1184.
OBJECTIVES: To evaluate the effect of two commonly used heat and moisture exchangers on respiratory function and gas exchange in patients with acute respiratory failure during pressure-support ventilation.
DESIGN: Prospective, randomized trial.
SETTING: Intensive care unit of a university hospital.
PATIENTS: Fourteen patients with moderate acute respiratory failure, receiving pressure-support ventilation.
INTERVENTIONS: Patients were assigned randomly to two treatment groups, in which two different heat and moisture exchangers were used: Hygroster (DAR S.p.A., Mirandola, Italy) with higher deadspace and lower resistance (group 1, n = 7), and Hygrobac-S (DAR S.p.A.) with lower deadspace and higher resistance (group 2, n = 7). Patients were assessed at three pressure-support levels: a) baseline (10.3 +/- 2.4 cm H2O for group 1, 9.3 +/- 1.3 cm H2O for group 2); b) 5 cm H2O above baseline; and c) 5 cm H2O below baseline. Measurements obtained with the heat and moisture exchangers were compared with those values obtained using the standard heated hot water humidifier.
MEASUREMENTS AND MAIN RESULTS: At baseline pressure-support ventilation, the insertion of both heat and moisture exchangers induced in all patients a significant increase in the following parameters: minute ventilation (12.4 +/- 3.2 to 15.0 +/- 2.6 L/min for group 1, and 11.8 +/- 3.6 to 14.2 +/- 3.5 L/min for group 2); static intrinsic positive end-expiratory pressure (2.9 +/- 2.0 to 5.1 +/- 3.2 cm H2O for group 1, and 2.9 +/- 1.7 to 5.5 +/- 3.0 cm H2O for group 2); ventilatory drive, expressed as P41 (2.7 +/- 2.0 to 5.2 +/- 4.0 cm H2O for group 1, and 3.3 +/- 2.0 to 5.3 +/- 3.0 cm H2O for group 2); and work of breathing, expressed as either power (8.8 +/- 9.4 to 14.5 +/- 10.3 joule/ min for group 1, and 10.5 +/- 7.4 to 16.6 +/- 11.0 joule/min for group 2) or work per liter of ventilation (0.6 +/- 0.6 to 1.0 +/- 0.7 joule/L for group 1, and 0.8 +/- 0.4 to 1.1 +/- 0.5 joule/L. for group 2). These increases also occurred when pressure-support ventilation was both above and below the baseline level, although at high pressure support the increase in work of breathing with heat and moisture exchangers was less evident. Gas exchange was unaffected by heat and moisture exchangers, as minute ventilation increased to compensate for the higher deadspace produced in the circuit by the insertion of heat and moisture exchangers.
CONCLUSIONS: The tested heat and moisture exchangers should be used carefully in patients with acute respiratory failure during pressure-support ventilation, since these devices substantially increase minute ventilation, ventilatory drive, and work of breathing. However, an increase in pressure-support ventilation (5 to 10 cm H2O) may compensate for the increased work of breathing.
Istituto di Anestesia e Rianimazione, Universita' degll Studi di Milano, IRCCS Ospedale Maggiore, Italy.
Hidden hazards and dangers associated with the use of HME/filters in breathing circuits. Their effect on toxic metabolite production, pulse oximetry and airway resistance.
Br J Anaesth. 2003;91(2):249.
Shackleton Department of Anaesthesia, Southampton University Teaching Hospitals, Tremona Road, SO16 6YD, UK. firstname.lastname@example.org