Anesth Analg 2008; 107:938-940
© 2008 International Anesthesia Research Society
doi: 10.1213/ane.0b013e31817f0e06
CRITICAL CARE AND TRAUMA
Adaptive Support Ventilation with Percutaneous Dilatational Tracheotomy: A Clinical Study
Denise P. Veelo, MD* ,
Dave A. Dongelmans, MD*,
Pauline Middelhoek, RN*,
Johanna C. Korevaar, PhD , and
Marcus J. Schultz, MD, PhD*
From the Departments of *Intensive Care Medicine; Anesthesiology; Clinical Epidemiology, Biostatistics and Bioinformatics, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands; and HERMES Critical Care Group, Amsterdam, The Netherlands.
 |
Abstract
|
|---|
We determined the need for changes in minute ventilation with adaptive support ventilation after percutaneous dilatational tracheotomy under endoscopic guidance in 34 intensive care unit patients. During the procedure, minute ventilation was not changed; only maximum pressure limits were adjusted, if necessary. After insertion of the tracheotomy, cannula minute ventilation was adjusted only if Paco2-values changed  0.5 kPa from baseline. In 74% of patients, adaptive support ventilation was unable to maintain minute ventilation during the use of the endoscope, mandating pressure limitation adjustments. In a minority of patients (26%), minute ventilation had to be adjusted to achieve similar Paco2 values.
|
Introduction
|
|---|
Adaptive support ventilation (ASV) is a microprocessor- controlled mode of mechanical ventilation (MV) that is able to maintain preset minute ventilation. ASV is characterized by automatic breath-by-breath adaptation of the respiratory rate (RR) and the level of inspiratory pressures (Pinsp) to adjust tidal volumes (VT),1–5 resulting in the least work of breathing as calculated from the Otis equation 6. Although Pinsp, RR and Vt are not adjusted by the operator, minute ventilation can be manipulated by adjusting the percentage of the ideal minute ventilation (%-MinVol) based on patient's height.
During percutaneous dilatational tracheotomy (PDT), especially when a bronchoscope is used, respiratory system mechanics rapidly change.7–10 With the use of conventional pressure-controlled (PC) modes, there is a realistic risk of under-ventilation during the procedure. After PDT, due to the use of a shorter cannula there is a small reduction of dead-space. With the use of conventional volume-controlled modes, patients may be over-ventilated when MV-settings are not adequately adjusted.11–13
It is uncertain how ASV behaves with these changes in resistance and dead-space. The aims of this study were to determine the need for change in %-MinVol during and after PDT in intensive care unit patients.
|
METHODS
|
|---|
The study protocol was approved by the local ethics committee; informed consent was not deemed necessary because of the observational nature of this study.
PDT was performed under bronchoscopic guidance with a Ciaglia Blue Rhino (Cook, Son, The Netherlands). Patients received anesthesia with propofol and fentanyl; muscle relaxation was obtained by rocuronium bromide. MV was maintained throughout the procedure with a Galileo ventilator (Hamilton Medical AG, Rhäzüns, Switzerland) set in the ASV-mode. The fraction of inspired oxygen was kept at 1.0 during the procedure.
At the start of the procedure, ASV was set to achieve minute ventilation similar to that with either PC or pressure support (PS)-MV before the procedure ("pre-PDT"). This was achieved by setting the %-MinVol between a minimum of 100 and a maximum of 200%. After muscle relaxation, lungs were recruited by performing an inspiratory hold (20 s without changing maximum airway pressure) twice and an arterial blood gas analysis was performed. During the procedure, %-MinVol was not changed. After insertion of the trachea cannula and repeating an inspiratory hold, arterial blood gas analysis was repeated ("post-PDT"). %-MinVol was adjusted (to a minimum of 90% at the most) to reach pre-PDT Paco2-values ("ASV-adjusted") only if Paco2-values changed 0.5 kPa.
In each patient, minute ventilation, Vt, RR and Pinsp (which equals maximum airway pressure level minus positive end-expiratory pressure level) were collected with the Hamilton data-logger version 3.27.1 (Hamilton). These variables were recorded 2 min before each arterial blood gas analysis. Other data were retrieved from the patient data management system (Metavision, iMDsoft, Sassenheim, the Netherlands, version 5.41.72).
Sample size calculation revealed that a sample size of 34 patients would have 80% power to detect a 10% difference in %-MinVol (at which pre-PDT Paco2- values were reached) assuming a standard deviation of 20%, using a two-sided t-test with a 0.05 two-sided significance level.
Comparisons are made with Wilcoxon signed ranks test and Mann-Whitney U-test or independent samples T-test and paired samples T-test for continuous data. The  2 test was used for categorical data.
|
RESULTS
|
|---|
Demographics, reason for initiation of MV and reason for tracheotomy for 34 patients are shown in Table 1. Thirty-one patients received PS-MV before start of the procedure, four patients received PC-MV. In four patients (included in the analysis) the procedure proceeded too fast to collect data before start of ASV. No apneas or decreased oxygen saturation were seen during PDT.
Time from start of ASV to initiating muscle relaxation was 4.0 (2.0–11.0) min. Time from initiation of muscle relaxation to start of PDT (incision) was 6.0 (4.8–7.5) min. Average PDT-time (from start of PDT to a patent tracheal cannula) was 22.1 ± 6.4 min.
Figure 1 shows Vt, RR and Pinsp for all patients. Minute ventilation at pre-PDT and post-PDT was similar (P = 0.08).
View larger version (9K):
[in this window]
[in a new window]
|
Figure 1. Box plots of tidal volume, respiratory rate and inspiratory pressure (Pinsp) during 1) pressure-controlled/pressure support mechanical ventilation 2); adaptive support ventilation (ASV) pre-percutaneous dilatational tracheotomy (PDT) 3); ASV post-PDT 4); ASV-adjusted. Minute ventilation at pre-PDT and post-PDT was similar, 9.5 ± 2.6 and 9.6 ± 2.6 L/min (P = 0.08). With start of ASV, tidal volume increased from 6.5 ± 1.9 to 8.8 ± 1.3 mL/kg ideal body weight (P < 0.01). This was accompanied by a decrease of respiratory rate from 25 ± 9 to 16 ± 3 breath/min (P < 0.01) and an increase of inspiratory pressure (Pinsp) from 12 ± 6 to 23 ± 8 cm H2O (P < 0.01).
|
|
In 25 cases (74%), ASV was unable to maintain minute ventilation during the use of the bronchoscope because of pressure limitation, which had to be increased (from 40 to 60 cm H2O). In two cases, maximum pressure limitation was already preset (at 70 cm H2O) before start of the procedure.
In 25 patients, Paco2-values remained stable during the procedure (mean difference 0.04 ± 0.22 kPa, NS). In nine patients, Paco2 values changed more than 0.5 kPa (mean decrease of 0.63 ± 0.10 kPa, P < 0.01), mandating a change in minute ventilation from 10.0 ± 3.4 to 7.8 ± 2.9 L/min to reach pre-PDT Paco2 values. To achieve this, %-MinVol was reduced from 142% ± 30% to 118% ± 36% (Fig. 2). In one patient, pre-PDT Paco2-values were not reached, because the protocol did not allow reduction of %-MinVol beyond 90%.
View larger version (13K):
[in this window]
[in a new window]
|
Figure 2. Box plots of Paco2 (left), set percentage of ideal minute ventilation (%-MinVol) (middle) and measured minute ventilation (right) during 1) pressure-controlled/pressure support mechanical ventilation 2); adaptive support ventilation (ASV) pre-percutaneous dilatational tracheotomy 3); ASV post-PDT 4); ASV-adjusted, for patients who needed adjustment of minute ventilation to achieve iso-Paco2 (white boxes) and those that did not (gray boxes).
|
|
|
DISCUSSION
|
|---|
In most patients, ASV did not adequately maintain minute ventilation during PDT without increasing pressure limits during use of the bronchoscope. This is an expected limitation of pressure-limited ventilation modes with large changes in airway resistance. However, hypoventilation has also been described during the use of conventional modes,11–13 which was accompanied by significant hypercarbia. Accordingly, at this point, ASV presents no advantage over other modes of MV during PDT. The potential high distending pressures that are created by increasing the pressure limits, might have an effect on patient safety. Additional mechanical and physiological measurements are necessary to better evaluate the safety of ASV in these circumstances.
ASV did a reasonable job of maintaining minute ventilation after PDT. In most patients, MV-settings did not have to be adjusted. Although earlier studies showed a lower work of breathing and improved effectiveness of respiratory function after PDT without a significant change in minute ventilation,8,9 in our cohort desired minute ventilation had to be decreased in a minority of patients. There were no determinants that could explain this occurrence, other than higher pre-PDT Paco2 values. In all patients, Vt substantially increased from PC/PS-MV to ASV, which is in line with earlier reports.5,14 It might be that some patients are more sensitive to tidal recruitment. However, a quarter of patients had high Pinsp after switching to ASV. Consequently, one can wonder if, in these patients, the use of ASV is really safe.
In conclusion, ASV did not adequately maintain minute ventilation in most patients during PDT without adjustment of the maximum pressure limits to high levels. ASV did a reasonable job of maintaining minute ventilation after PDT when the patient was recovering.
|
Footnotes
|
|---|
Accepted for publication April 25, 2008.
Address correspondence and reprint requests Denise P. Veelo, Mail stop: G3-228, Department of Intensive Care Medicine, Academic Medical Center, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam. Address e-mail to d.p.veelo{at}amc.uva.nl.
|
REFERENCES
|
|---|
- Weiler N, Eberle B, Heinrichs W. Adaptive lung ventilation (ALV) during anesthesia for pulmonary surgery: automatic response to transitions to and from one-lung ventilation. J Clin Monit Comput 1998;14:245–52[Web of Science][Medline]
- Brunner JX, Iotti GA. Adaptive Support Ventilation (ASV). Minerva Anestesiol 2002;68:365–8[Medline]
- Sulzer CF, Chiolero R, Chassot PG, Mueller XM, Revelly JP. Adaptive support ventilation for fast tracheal extubation after cardiac surgery: a randomized controlled study. Anesthesiology 2001;95:1339–45[Web of Science][Medline]
- Petter AH, Chiolero RL, Cassina T, Chassot PG, Muller XM, Revelly JP. Automatic "respirator/weaning" with adaptive support ventilation: the effect on duration of endotracheal intubation and patient management. Anesth Analg 2003;97:1743–50[Abstract/Free Full Text]
- Cassina T, Chiolero R, Mauri R, Revelly JP. Clinical experience with adaptive support ventilation for fast-track cardiac surgery. J Cardiothorac Vasc Anesth 2003;17:571–5[Web of Science][Medline]
- Otis AB, Fenn WO, Rahn H. Mechanics of breathing in man. J Applied Physiology 1950;2:592–607
- Davis K Jr, Campbell RS, Johannigman JA, Valente JF, Branson RD. Changes in respiratory mechanics after tracheostomy. Arch Surg 1999;134:59–62[Abstract/Free Full Text]
- Diehl JL, El Atrous S, Touchard D, Lemaire F, Brochard L. Changes in the work of breathing induced by tracheotomy in ventilator-dependent patients. Am J Respir Crit Care Med 1999;159:383–8[Abstract/Free Full Text]
- Amygdalou A, Dimopoulos G, Moukas M, Katsanos C, Katagi A, Mandragos C, Constantopoulos SH, Behrakis PK, Vassiliou MP. Immediate post-operative effects of tracheotomy on respiratory function during mechanical ventilation. Crit Care 2004;8:R243–R247[Web of Science][Medline]
- Cavo J, Ogura JH, Sessions DG, Nelson JR. Flow resistance in tracheotomy tubes. Ann Otol Rhinol Laryngol 1973;82:827–30[Web of Science][Medline]
- Reilly PM, Sing RF, Giberson FA, Anderson HL III, Rotondo MF, Tinkoff GH, Schwab CW. Hypercarbia during tracheostomy: a comparison of percutaneous endoscopic, percutaneous Doppler, and standard surgical tracheostomy. Intensive Care Med 1997;23:859–64[Web of Science][Medline]
- Reilly PM, Anderson HL III, Sing RF, Schwab CW, Bartlett RH. Occult hypercarbia. An unrecognized phenomenon during percutaneous endoscopic tracheostomy. Chest 1995;107:1760–3[Web of Science][Medline]
- Ferraro F, Capasso A, Troise E, Lanza S, Azan G, Rispoli F, Anello CB. Assessment of ventilation during the performance of elective endoscopic-guided percutaneous tracheostomy: clinical evaluation of a new method. Chest 2004;126:159–64[Web of Science][Medline]
- Arnal J. Utilization of Adaptive Support Ventilation (ASV) in a polyvalent intensive care unit. Intensive Care Med 2004; 30:84S–131S
|
Top
Abstract
Introduction
