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Minimal occlusive volume cuff inflation: A survey of current practice
Intensive and Critical Care Nursing (2008) 24, 359—365
ORIGINAL ARTICLE
Minimal occlusive volume cuff inflation: A survey of current practice Louise Rose a,∗, Leanne Redl b,1 a
Lawrence S. Bloomberg Faculty of Nursing, University of Toronto, 155 College Street, Room 276, Toronto, ON M5T1P8, Canada b Intensive Care Unit, The Royal Melbourne Hospital, Grattan Street, Parkville, Melbourne, VIC 3050, Australia Accepted 14 May 2008
KEYWORDS Endotracheal intubation; Mechanical ventilation; Ventilator associated pneumonia; Cuff inflation; Minimal occlusive volume
Summary Objective: To describe the minimal occlusive volume (MOV) procedure used to monitor cuff inflation and identify practice variation. Research methodology: Self-administered questionnaire. Setting: Adult intensive care unit in an Australian university-affiliated hospital. Results: Survey response was 71% (80/113). Three methods of MOV were identified. Full cuff deflation, followed by reinflation, removal of 1 mL increments of air until a leak was detected, then restoration of cuff seal with 1 mL of air was the preferred method (47/80 respondents, 59%) (Method 1). Full cuff deflation followed by incremental addition of air until the MOV was established was used by 25/80 (31%) respondents (Method 2). Two (2.5%) nurses established MOV without full cuff deflation (Method 3), five (6.25%) used more than one method and one (1.25%) nurse did not perform cuff checks. Practice variation was identified for patient positioning, confirmation of cuff seal, and cuff leak management. Consistency of practice was noted in MOV procedure frequency, the number of nurses required, pre-oxygenation and oropharyngeal suctioning prior to cuff deflation. Conclusion: Substantial practice variation for certain aspects of cuff management was noted. Evidence to support the efficacy of MOV procedural elements is required to limit practice variation and reduce risk to patients. Crown Copyright © 2008 Published by Elsevier Ltd. All rights reserved.
Introduction ∗ Corresponding author. Tel.: +1 416 978 3492; fax: +1 416 978 0665. E-mail addresses: [email protected] (L. Rose), [email protected] (L. Redl). 1 Tel.: +61 3 9342 7209; fax: +61 3 9342 8812.
Endotracheal intubation is a life-saving procedure that enables the application of mechanical ventilation. In adults, endotracheal tubes have a balloon-like cuff that when inflated seals the airway
0964-3397/$ — see front matter. Crown Copyright © 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.iccn.2008.05.002
360 enabling delivery of positive pressure ventilation without loss of tidal volume or aspiration of pharyngeal contents (Pierce, 2007). Over the last four decades, cuff design has evolved from a rigid rubber structure that rapidly caused tracheal epithelial damage (Ganner, 2001) to high volume—low pressure cuffs that conform to tracheal contours at low pressures resulting in less ischaemic damage (Guyton, 1990). More recently, third generation polyurethane membrane cuffs have been developed that enable better prevention of aspiration while maintaining low cuff pressure (Crimlisk et al., 1996; Sengupta et al., 2004). To prevent complications associated with underinflation (aspiration of pharyngeal contents and risk of ventilator associated pneumonia [VAP]) or overinflation (tracheal ischaemic damage), the cuff is monitored intermittently. Minimal occlusive volume (MOV) is one of the four methods used to monitor cuff inflation. This method involves the addition of sufficient air to abolish an air leak on inspiration determined by auscultation over the trachea (Pierce, 2007). Other methods include the minimal leak technique that allows a small cuff leak on inspiration, cuff pressure manometry, and pilot balloon palpation. In the literature there is little consensus on the best method for monitoring ongoing cuff inflation, the frequency, or most appropriate patient position for monitoring to be performed (Crimlisk et al., 1996; Ganner, 2001; Sole et al., 2003). Certain aspects of the MOV technique also lack evidence or clear rationales. This lack of consensus may result in practice variation and uncertainty in clinical practice. Improper and inconsistent cuff management practices may increase the risk for complications associated with inappropriate cuff inflation including VAP and ischaemic damage to the trachea. The aim of the current study was to describe the application of the MOV procedure and identify practice variation in an intensive care unit (ICU) that uses MOV as the sole method of cuff inflation and ongoing monitoring.
Methods Participants and setting This survey was conducted at the ICU of The Royal Melbourne Hospital, Victoria, Australia. This ICU is a 24-bed adult, combined medical—surgical unit in a university-affiliated teaching hospital. Approximately, 100 patients per month receive treatment with mechanical ventilation in this ICU. All nursing
L. Rose, L. Redl staff employed in the ICU were eligible to participate.
Ethical considerations Approval for this survey was obtained from the Institutional Review Boards of Melbourne Health and RMIT University. The return of a completed questionnaire was considered indicative of consent.
Instrument To inform the study and generate questionnaire items, we conducted a detailed search of Medline, Proquest, PubMed, and CINAHL using the terms endotracheal cuff, cuff pressure, tracheal tube, airway management and ventilator associated pneumonia searched individually and in combination. Additionally, nursing clinicians with expertise in cuff management were consulted to identify procedures relevant to the MOV technique. A process of item reduction designed to minimise redundancy and completion time and maximise response rate resulted in a two-page questionnaire. This questionnaire was then tested for clinical sensibility to detect inappropriate, redundant items or important omissions and determine the clarity and face validity by a team of senior medical and nursing staff. The questionnaire sought information on nurse demographics, technical aspects of the MOV technique, the frequency of ongoing cuff monitoring, management of a cuff leak, and cuff management procedures prior to extubation. Questions relating to the participant’s conduct of the MOV technique were formatted using a three-item ordinal scale (always, sometimes, never). Participants were also asked to comment on perceived advantages and disadvantages of the MOV technique.
Data collection The survey was distributed to staff on each nursing shift over 2 weeks. Surveys were hand delivered to staff members by senior nursing clinicians not directly involved in the study. This method of survey distribution was selected as nurses were known to check hospital mail (both paper and electronic) infrequently. All surveys were returned to a sealed box located in the ICU to maintain the confidentiality of responses.
Data analysis Categorical data (including demographic and procedural information) were expressed as proportions.
Minimal occlusive volume cuff inflation
361
For analytical purposes, participants were categorised as senior clinicians (those with more than five years ICU experience) and junior clinicians (those with less than five years ICU experience). Responses for cuff check procedures by these two groups were then compared using chi square or Fisher’s exact tests as appropriate. A p-value of <0.05 was considered statistically significant and all tests were two-tailed. All analyses were performed using Minitab 14 (Minitab, 2003). Comments on the perceived advantages and disadvantages of the MOV technique were analysed using content analysis to identify themes (Burns and Grove, 2001). The data were coded initially for key phrases such as ‘minimise tracheal damage’ or ‘increased risk of aspiration and ventilator associated pneumonia’ and then examined for repetition, characteristics and dimensions that identified and confirmed categories. Two reviewers coded the data independently. Discrepancies in coding were discussed until a consensus was reached. Percentages were then calculated for the number of responses to each identified theme.
Results Demographics Of the 113 surveys distributed, 80 were returned (response rate 71%). Table 1 shows the demographic
Table 1 (N = 80)
Status and experience of nurse respondents
Characteristic
n (%)
Position held Senior management (associate nurse manager, nurse educator) Clinical nurse specialist Critical care nursea Student critical care nurse Registered nurse
30 (37.5) 27 (33.5) 7 (9) 7 (9)
Years of ICU experience ≤2 years >2 years to ≤5 years >5 years to ≤10 years >10 years
8 (10) 22 (27.5) 27 (33.5) 23 (29)
Years of employment in participating ICU ≤2 years >2 years to ≤5 years >5 years to ≤10 years >10 years
11 44 12 13
a
9 (11)
(14) (55) (15) (16)
RN with postgraduate level critical care specialty qualification.
characteristics of the nursing respondents. Fifty percent of the nurses surveyed had greater than five years experience in the ICU specialty.
Cuff check procedure Participants were given three options to best describe the method they used to ascertain MOV. The majority of respondents (47/80, 59%) always determined MOV by full cuff deflation to establish the volume of air in the cuff, followed by reinflation with the volume of air removed. Air was then removed in 1 mL increments until a leak was detected. The MOV was then restored with the addition of 1 mL of air (Method 1). An alternative method (Method 2), used by 25 (31%) of respondents was full deflation of the cuff to establish the volume of air followed by incremental addition of air until the MOV was established. Two (2.5%) respondents established MOV by incremental removal of air without performing full cuff deflation (Method 3). Five (6.5%) respondents reported they used a variety of methods, and one respondent did not perform cuff checks. More junior nurses stated they always used Method 1 compared to experienced nurses (p = 0.004). Choice of MOV method was not associated with prior employment in another ICU (p = 0.4).
Frequency of procedure Of the 79 respondents who performed cuff checks, 69/80 (87%) performed a MOV procedure once per nursing shift (both 8 and 12 h shifts are available in this ICU). No nurses reported conducting more frequent cuff checks. Six (8%) nurses reported cuff checks were performed once per 24 h and four (5%) nurses only checked the cuff based on an assessed cuff leak.
Patient positioning The MOV technique was performed in the semirecumbent position (defined as 30—45◦ head of bed elevation) by 36/79 (46%) respondents, though a number of other patient positions were considered acceptable (Fig. 1).
Associated procedures All 79 respondents suctioned the oropharynx prior to cuff deflation. Other aspects of the procedure, performed by the majority of respondents, included use of two nurses to perform the technique, and pre-oxygenation prior to cuff deflation (Table 2). The majority of nurses did not perform aspiration
362
L. Rose, L. Redl
Audible cuff leak
Figure 1 Patient positioning during MOV procedure. No change indicates the cuff check procedure was performed without changing the patient’s position. ‘Other’ was selected by three respondents though the alternative position was not described.
of the nasogastric tube prior to cuff deflation routinely. Aspiration of the nasogastric tube prior to cuff deflation was not associated with the nurse’s level of ICU experience (p = 0.3) or prior employment in another ICU (p = 0.7). Few nurses reported using a manual inspiration when confirming a cuff seal during the MOV technique.
Cuff seal To assess adequacy of cuff seal between MOV procedures, auscultation over the trachea as the sole method (23/79, 29%), or in combination with assessment of expired tidal volume measured by the ventilator (27/79, 34%) were used most frequently. Other methods included manual inspiration via the ventilator (14/79, 18%) or palpation of the pilot balloon in combination with other methods (15/79, 19%). No respondent used balloon palpation exclusively.
Table 2
To manage an audible cuff leak, 28/79 (35%) respondents continued cuff inflation to obtain a seal irrespective of the volume of air required. A further 13/79 (16.5%) respondents continued cuff inflation and also notified medical staff. Twentythree (29%) respondents would attempt a range of troubleshooting techniques including assessment and manipulation of endotracheal tube insertion length and patient position. Notification of medical staff was the first course of action for 12/79 (15%) respondents. Two (2.5%) nurses assessed cuff pressure using a manometer. Only one respondent accepted an ongoing cuff leak. Participants were asked to identify the maximum volume of air acceptable for MOV. The most frequent response was 12 mL (34/79, 43%). Fifteen milliliter was the maximum volume accepted by 22/79 (28%) nurses, 10 mL by 15/79 (19%) nurses and 20 mL by 3/79 (4%) nurses. A further five respondents did not answer this question.
Extubation Prior to extubation, 57/79 (72%) participants routinely checked cuff volume to assess airway oedema. This procedure was not restricted to senior nurses (p = 0.9) or to those nurses whose ICU experience was limited to the participating institution (p = 0.6). Detection of a reduced cuff volume was considered an appropriate reason to defer the decision to extubate by 50/79 (63%) respondents.
Advantages and disadvantages Of the 79 respondents, 73 made comment on the perceived advantages and disadvantages of regular cuff monitoring using MOV. Five advantages were identified: to minimise damage to the tracheal wall (56% of respondents), to detect airway oedema
Minimal occlusive volume technique (N = 79)
Technique
Always, n (%)
Suction oropharynx prior to cuff deflation Two nurses to perform procedure Pre-oxygenation prior to cuff deflation Aspirate nasogastric tube prior to cuff deflation Manual inspiration to confirm cuff seal
79 (100)
0 (0)
0 (0)
0 (0)
76 (96)
3 (4)
0 (0)
0 (0)
74 (94)
4 (5)
1 (1)
0 (0)
11 (14)
36 (46)
31 (39)
1 (1)
17 (21.5)
59 (75)
2 (2.5)
1 (1)
Sometimes, n (%)
Never, n (%)
Did not answer, n (%)
Minimal occlusive volume cuff inflation (49%), to provide an adequate seal to prevent aspiration (15%), to facilitate pressure area care for the trachea (13%) and to enable delivery of mechanical ventilation (4%). Perceived disadvantages of the MOV procedure included: increased risk of aspiration and VAP due to full cuff deflation during the procedure (93% of respondents), loss of positive end expiratory pressure (PEEP) and interference with mechanical ventilation (21%), increased risk of tube migration or extubation (12%), patient discomfort (12%) and inaccuracy of the technique (5%). The MOV procedure was considered resource intensive compared to cuff pressure manometry by 15% of respondents.
Discussion To our knowledge, this survey is the first to provide an in-depth description of the MOV procedure and associated clinical processes in an ICU setting. The results of this survey indicate considerable practice variation. Substantial differences were noted in the method used to achieve MOV, patient positioning during the procedure, the most appropriate method for confirming cuff seal, and management of a cuff leak. Practice differences were only partially explained by the level of ICU experience. Junior nursing staff were more likely to use Method 1, a technique which theoretically decreases the risk of aspiration as the cuff is deflated for a shorter time. This method is advocated by the unit’s nurse educators whose role is to provide clinical education to junior staff members completing a postgraduate diploma in the critical care specialty. Other practice variation was not associated with nurse seniority or exposure to other ICU clinical environments. Little evidence is available that identifies the most appropriate method for ongoing monitoring of cuff inflation. Moreover detailed description of methods, associated processes, and evidence of efficacy are lacking. Step-by-step description of how to ascertain MOV in a cuff that is already inflated is required. Mechanical ventilation and critical care texts primarily describe the MOV technique for initial cuff inflation with cuff pressure monitoring (CPM) recommended for ongoing cuff monitoring (AACN, 2005; Pilbeam and Cairo, 2006; Pierce, 2007). However, practice surveys conducted in the United Kingdom suggest CPM is used infrequently (Spittle and Beavis, 2001; Vyas et al., 2002). Currently, there are no studies that confirm the superiority of CPM over the MOV technique for ongoing monitoring of cuff inflation. Disadvantages associated with the MOV technique include interruption of positive pressure
363 ventilation resulting in loss of PEEP and hypoxaemia, risk of aspiration and hyperinflation on cuff reinflation, and damage to the pilot valve through repetitive use (St John, 1999). Disadvantages of CPM include a sensitivity to changes in head, patient and tube position, coughing, lung compliance, airway and intrathoracic pressures (Crimlisk et al., 1996; Vyas et al., 2002; Pierce, 2007). Pressure readings taken prior to a position change or altered lung compliance may not accurately reflect cuff pressure. Additionally, patients with high intrathoracic or airway pressures require increased cuff pressure to maintain an adequate seal and may be at increased risk of ischemic injury. Alternatively, maintenance of pressure within the recommended range will predispose these patients to aspiration (Bouvier, 1981; Guyton et al., 1997). In this survey, the maximum frequency of monitoring cuff inflation was once per shift. This practice is congruent with recommendations in mechanical ventilation texts (MacIntyre and Branson, 2001; AACN, 2005; Pilbeam and Cairo, 2006) and practice survey reports (Sole et al., 2002, 2003; Rose and Redl, in press). Failure to monitor cuff inflation at least once per nursing shift may place the patient at increased risk of aspiration and subsequent ventilator associated pneumonia due to underinflation or tracheal mucosal damage in the presence of overinflation. Patients at increased risk of complications associated with cuff inflation include those with airway oedema, variable lung compliance and airway pressures (Guyton et al., 1997), and hypotension due to low perfusion pressure in the trachea (Pilbeam and Cairo, 2006). Cuff monitoring procedures should be performed in the semi-recumbent position to reduce stimulation of the gag reflex and risk of aspiration (AACN, 2005; Metheny et al., 2006). Though the majority of respondents in the current survey used this position, some practice variation was noted. During cuff monitoring procedures, the ability of the cuff to seal the airway is decreased while aspiration risk is increased due to stimulation of gag and cough reflexes associated with oropharyngeal and tracheal suctioning. Large residual volumes within the gut further increase the risk of aspiration (Metheny et al., 2006). Aspiration of nasogastric contents prior to cuff deflation is another intervention that may reduce the risk of aspiration of gastric contents. Surprisingly this procedure was routinely performed by only 14% of the survey respondents. During the inspiratory phase of a positive pressure breath the airways expand resulting in a drop in pressure (St John, 1999). To ensure appropriate cuff inflation, the cuff seal should be assessed during inspiration using a positive pressure breath prefer-
364 ably via the ventilator using either a sigh breath or manual inspiration function (AACN, 2005). In the current survey few respondents used this technique to confirm cuff seal during the MOV procedure, or to ascertain cuff seal between cuff checks. Similarly, few ICUs identified this practice in a recent survey of cuff management in Australia and New Zealand (Rose and Redl, in press). Loss of cuff volume and/or pressure is a common occurrence that increases the risk of aspiration of pharyngeal contents and VAP (Rello et al., 1996; Valencia et al., 2007). Notably, there is an absence of information in the literature to guide management of an audible cuff leak once the recommended volume or pressure has been reached. In the current study, the majority of nurses stated they would continue cuff inflation to obtain a seal irrespective of the volume of air required indicating greater concern for the risk of aspiration than tracheal damage. Nurses cited maximal acceptable cuff inflation volumes ranging from 10 to 20 mL. Manufacturers of modern high volume, low-pressure cuffs do not provide guidelines as to the recommended maximum cuff volume. Severe consequences of cuff overinflation including tracheal rupture, tracheo-carotid artery erosion and tracheal innominate artery fistulas are now rare due to widespread use of these cuffs (Sengupta et al., 2004). Nurses, however, need to remain mindful of the consequences of overinflation when large volumes of air are used. Conversely, VAP remains an important cause of morbidity and mortality in the critically ill (ATS, 2005). Respondents also perceived full cuff deflation during the MOV procedure increased the risk of aspiration and VAP. Currently there are no studies to demonstrate an increased risk of aspiration with MOV compared to other methods of cuff monitoring such as cuff pressure manometry or the minimal leak technique.
Limitations This survey has limitations. First, despite a reasonable response rate, the results may not represent the practice of non-responding nurses. Second, survey findings are the result of a self-report questionnaire and as such may reflect nurses’ best or intended practice rather than clinical reality. Third, this survey represents practice of a single ICU in which MOV was the sole method of cuff inflation and ongoing monitoring. As such, the described practice may not be generalised to other ICU settings. A recent survey of cuff inflation practices in Australia and New Zealand (Rose and Redl, in press) found MOV was used either in combination with cuff pres-
L. Rose, L. Redl sure manometry, or as the sole method of ongoing cuff monitoring, in 50% of ICUs surveyed indicating widespread use of this technique.
Conclusion Within the literature, evidence to support various aspects of the MOV procedure is limited. The results of our survey suggest, within this single ICU setting, substantial practice variation for certain aspects of cuff management exists. Despite concern for the risk of aspiration associated with cuff deflation during the MOV technique, procedures such as semi-recumbent positioning, aspiration of gastric contents prior to cuff deflation and manual inspiration to confirm cuff seal were not uniformly employed. As a result of the findings of this survey, unit guidelines for ongoing cuff monitoring have been revised to standardise practice. Additionally, a study has been initiated that examines the rate of gross aspiration using blue dye inserted into the oral cavity prior to cuff monitoring with both the MOV and cuff pressure monitoring techniques.
Role of funding source This study was supported by a research grant from RMIT University.
Conflict of interest None declared.
Acknowledgement The authors would like to thank the staff of the intensive care unit of The Royal Melbourne Hospital.
References AACN. AACN procedure manual for critical care. St. Louis: Elsevier Saunders; 2005. ATS. Guidelines for the management of adults with hospitalacquired, ventilator associated, and healthcare associated pneumonia. Am J Respir Crit Care Med 2005;171:388—416. Bouvier J. Measuring tracheal tube cuff pressures- tool and technique. Heart Lung 1981;10:686—90. Burns N, Grove SK. The practice of nursing research: conduct, critique and utilization. 4th ed. Philadelphia: Saunders; 2001. Crimlisk J, Horn M, Wilson D, Marino B. Artificial airways: a survey of cuff management practices. Heart Lung 1996;25:225—35.
Minimal occlusive volume cuff inflation Ganner C. The accurate measurement of endotracheal tube cuff pressures. Br J Nurs 2001;10:1127—34. Guyton D. Endotracheal and tracheotomy tube cuff design: influence on tracheal damage. Crit Care Updates 1990;1:1—10. Guyton D, Barlow M, Besselievre T. Influence of airway pressure on minimum occlusive endotracheal tube cuff pressure. Crit Care Med 1997;25:91—4. MacIntyre N, Branson R. Mechanical ventilation. Philadelphia: Saunders; 2001. Metheny N, Clouse R, Chang Y, Stewart B, Oliver D, Kollef M. Tracheobronchial aspiration of gastric contents in critically ill tube-fed patients: frequency, outcomes, and risk factors. Crit Care Med 2006;34:1007—15. Pierce L. Management of the mechanically ventilated patient. St. Louis: Saunders Elsevier; 2007. Pilbeam S, Cairo J. Mechanical ventilation: physiological and clinical applications. St. Louis: Mosby Elsevier; 2006. Rello J, Sonara R, Jubert P, Artigas A, Rue M, Valles J. Pneumonia in intubated patients: role of respiratory airway care. Am J Respir Crit Care Med 1996;154:111—5. Rose L, Redl L. Survey of cuff management practices within Australia and New Zealand. Am J Crit Care; in press.
365 Sengupta P, Sessler D, Maglinger P, Wells S, Vogt A, Durrani J, et al. Endotracheal tube cuff pressure in three hospitals and the volume required to produce an appropriate cuff pressure. BMC Anesthesiol 2004;4:4—8. Sole M, Byers J, Ludy J, Ostrow L. Suctioning techniques and airway management practices: pilot study and instrument evaluation. Am J Crit Care 2002;11:363—8. Sole M, Byers J, Ludy J, Zhang Y, Banta C, Brummel K. A multisite survey of suctioning techniques and airway management practices. Am J Crit Care 2003;12:220—30. Spittle C, Beavis S. Do you measure tracheal cuff pressure? A survey of clinical practice. Br J Anaesthesiol 2001;87: 344—5. St John R. Advances in artificial airway management. Crit Care Nurs Clin N Am 1999;11:7—17. Valencia M, Ferrer M, Farre R, Navajas D, Badia J, Nicolas J, et al. Automatic control of tracheal tube cuff pressure in ventilated patients in semirecumbent position: a randomized trial. Crit Care Med 2007;35:1543—9. Vyas D, Inweregbu K, Pittard A. Measurement of tracheal tube cuff pressure in critical care. Anaesthesia 2002;57: 275—7.
Available online at www.sciencedirect.com
ORIGINAL ARTICLE
Minimal occlusive volume cuff inflation: A survey of current practice Louise Rose a,∗, Leanne Redl b,1 a
Lawrence S. Bloomberg Faculty of Nursing, University of Toronto, 155 College Street, Room 276, Toronto, ON M5T1P8, Canada b Intensive Care Unit, The Royal Melbourne Hospital, Grattan Street, Parkville, Melbourne, VIC 3050, Australia Accepted 14 May 2008
KEYWORDS Endotracheal intubation; Mechanical ventilation; Ventilator associated pneumonia; Cuff inflation; Minimal occlusive volume
Summary Objective: To describe the minimal occlusive volume (MOV) procedure used to monitor cuff inflation and identify practice variation. Research methodology: Self-administered questionnaire. Setting: Adult intensive care unit in an Australian university-affiliated hospital. Results: Survey response was 71% (80/113). Three methods of MOV were identified. Full cuff deflation, followed by reinflation, removal of 1 mL increments of air until a leak was detected, then restoration of cuff seal with 1 mL of air was the preferred method (47/80 respondents, 59%) (Method 1). Full cuff deflation followed by incremental addition of air until the MOV was established was used by 25/80 (31%) respondents (Method 2). Two (2.5%) nurses established MOV without full cuff deflation (Method 3), five (6.25%) used more than one method and one (1.25%) nurse did not perform cuff checks. Practice variation was identified for patient positioning, confirmation of cuff seal, and cuff leak management. Consistency of practice was noted in MOV procedure frequency, the number of nurses required, pre-oxygenation and oropharyngeal suctioning prior to cuff deflation. Conclusion: Substantial practice variation for certain aspects of cuff management was noted. Evidence to support the efficacy of MOV procedural elements is required to limit practice variation and reduce risk to patients. Crown Copyright © 2008 Published by Elsevier Ltd. All rights reserved.
Introduction ∗ Corresponding author. Tel.: +1 416 978 3492; fax: +1 416 978 0665. E-mail addresses: [email protected] (L. Rose), [email protected] (L. Redl). 1 Tel.: +61 3 9342 7209; fax: +61 3 9342 8812.
Endotracheal intubation is a life-saving procedure that enables the application of mechanical ventilation. In adults, endotracheal tubes have a balloon-like cuff that when inflated seals the airway
0964-3397/$ — see front matter. Crown Copyright © 2008 Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.iccn.2008.05.002
360 enabling delivery of positive pressure ventilation without loss of tidal volume or aspiration of pharyngeal contents (Pierce, 2007). Over the last four decades, cuff design has evolved from a rigid rubber structure that rapidly caused tracheal epithelial damage (Ganner, 2001) to high volume—low pressure cuffs that conform to tracheal contours at low pressures resulting in less ischaemic damage (Guyton, 1990). More recently, third generation polyurethane membrane cuffs have been developed that enable better prevention of aspiration while maintaining low cuff pressure (Crimlisk et al., 1996; Sengupta et al., 2004). To prevent complications associated with underinflation (aspiration of pharyngeal contents and risk of ventilator associated pneumonia [VAP]) or overinflation (tracheal ischaemic damage), the cuff is monitored intermittently. Minimal occlusive volume (MOV) is one of the four methods used to monitor cuff inflation. This method involves the addition of sufficient air to abolish an air leak on inspiration determined by auscultation over the trachea (Pierce, 2007). Other methods include the minimal leak technique that allows a small cuff leak on inspiration, cuff pressure manometry, and pilot balloon palpation. In the literature there is little consensus on the best method for monitoring ongoing cuff inflation, the frequency, or most appropriate patient position for monitoring to be performed (Crimlisk et al., 1996; Ganner, 2001; Sole et al., 2003). Certain aspects of the MOV technique also lack evidence or clear rationales. This lack of consensus may result in practice variation and uncertainty in clinical practice. Improper and inconsistent cuff management practices may increase the risk for complications associated with inappropriate cuff inflation including VAP and ischaemic damage to the trachea. The aim of the current study was to describe the application of the MOV procedure and identify practice variation in an intensive care unit (ICU) that uses MOV as the sole method of cuff inflation and ongoing monitoring.
Methods Participants and setting This survey was conducted at the ICU of The Royal Melbourne Hospital, Victoria, Australia. This ICU is a 24-bed adult, combined medical—surgical unit in a university-affiliated teaching hospital. Approximately, 100 patients per month receive treatment with mechanical ventilation in this ICU. All nursing
L. Rose, L. Redl staff employed in the ICU were eligible to participate.
Ethical considerations Approval for this survey was obtained from the Institutional Review Boards of Melbourne Health and RMIT University. The return of a completed questionnaire was considered indicative of consent.
Instrument To inform the study and generate questionnaire items, we conducted a detailed search of Medline, Proquest, PubMed, and CINAHL using the terms endotracheal cuff, cuff pressure, tracheal tube, airway management and ventilator associated pneumonia searched individually and in combination. Additionally, nursing clinicians with expertise in cuff management were consulted to identify procedures relevant to the MOV technique. A process of item reduction designed to minimise redundancy and completion time and maximise response rate resulted in a two-page questionnaire. This questionnaire was then tested for clinical sensibility to detect inappropriate, redundant items or important omissions and determine the clarity and face validity by a team of senior medical and nursing staff. The questionnaire sought information on nurse demographics, technical aspects of the MOV technique, the frequency of ongoing cuff monitoring, management of a cuff leak, and cuff management procedures prior to extubation. Questions relating to the participant’s conduct of the MOV technique were formatted using a three-item ordinal scale (always, sometimes, never). Participants were also asked to comment on perceived advantages and disadvantages of the MOV technique.
Data collection The survey was distributed to staff on each nursing shift over 2 weeks. Surveys were hand delivered to staff members by senior nursing clinicians not directly involved in the study. This method of survey distribution was selected as nurses were known to check hospital mail (both paper and electronic) infrequently. All surveys were returned to a sealed box located in the ICU to maintain the confidentiality of responses.
Data analysis Categorical data (including demographic and procedural information) were expressed as proportions.
Minimal occlusive volume cuff inflation
361
For analytical purposes, participants were categorised as senior clinicians (those with more than five years ICU experience) and junior clinicians (those with less than five years ICU experience). Responses for cuff check procedures by these two groups were then compared using chi square or Fisher’s exact tests as appropriate. A p-value of <0.05 was considered statistically significant and all tests were two-tailed. All analyses were performed using Minitab 14 (Minitab, 2003). Comments on the perceived advantages and disadvantages of the MOV technique were analysed using content analysis to identify themes (Burns and Grove, 2001). The data were coded initially for key phrases such as ‘minimise tracheal damage’ or ‘increased risk of aspiration and ventilator associated pneumonia’ and then examined for repetition, characteristics and dimensions that identified and confirmed categories. Two reviewers coded the data independently. Discrepancies in coding were discussed until a consensus was reached. Percentages were then calculated for the number of responses to each identified theme.
Results Demographics Of the 113 surveys distributed, 80 were returned (response rate 71%). Table 1 shows the demographic
Table 1 (N = 80)
Status and experience of nurse respondents
Characteristic
n (%)
Position held Senior management (associate nurse manager, nurse educator) Clinical nurse specialist Critical care nursea Student critical care nurse Registered nurse
30 (37.5) 27 (33.5) 7 (9) 7 (9)
Years of ICU experience ≤2 years >2 years to ≤5 years >5 years to ≤10 years >10 years
8 (10) 22 (27.5) 27 (33.5) 23 (29)
Years of employment in participating ICU ≤2 years >2 years to ≤5 years >5 years to ≤10 years >10 years
11 44 12 13
a
9 (11)
(14) (55) (15) (16)
RN with postgraduate level critical care specialty qualification.
characteristics of the nursing respondents. Fifty percent of the nurses surveyed had greater than five years experience in the ICU specialty.
Cuff check procedure Participants were given three options to best describe the method they used to ascertain MOV. The majority of respondents (47/80, 59%) always determined MOV by full cuff deflation to establish the volume of air in the cuff, followed by reinflation with the volume of air removed. Air was then removed in 1 mL increments until a leak was detected. The MOV was then restored with the addition of 1 mL of air (Method 1). An alternative method (Method 2), used by 25 (31%) of respondents was full deflation of the cuff to establish the volume of air followed by incremental addition of air until the MOV was established. Two (2.5%) respondents established MOV by incremental removal of air without performing full cuff deflation (Method 3). Five (6.5%) respondents reported they used a variety of methods, and one respondent did not perform cuff checks. More junior nurses stated they always used Method 1 compared to experienced nurses (p = 0.004). Choice of MOV method was not associated with prior employment in another ICU (p = 0.4).
Frequency of procedure Of the 79 respondents who performed cuff checks, 69/80 (87%) performed a MOV procedure once per nursing shift (both 8 and 12 h shifts are available in this ICU). No nurses reported conducting more frequent cuff checks. Six (8%) nurses reported cuff checks were performed once per 24 h and four (5%) nurses only checked the cuff based on an assessed cuff leak.
Patient positioning The MOV technique was performed in the semirecumbent position (defined as 30—45◦ head of bed elevation) by 36/79 (46%) respondents, though a number of other patient positions were considered acceptable (Fig. 1).
Associated procedures All 79 respondents suctioned the oropharynx prior to cuff deflation. Other aspects of the procedure, performed by the majority of respondents, included use of two nurses to perform the technique, and pre-oxygenation prior to cuff deflation (Table 2). The majority of nurses did not perform aspiration
362
L. Rose, L. Redl
Audible cuff leak
Figure 1 Patient positioning during MOV procedure. No change indicates the cuff check procedure was performed without changing the patient’s position. ‘Other’ was selected by three respondents though the alternative position was not described.
of the nasogastric tube prior to cuff deflation routinely. Aspiration of the nasogastric tube prior to cuff deflation was not associated with the nurse’s level of ICU experience (p = 0.3) or prior employment in another ICU (p = 0.7). Few nurses reported using a manual inspiration when confirming a cuff seal during the MOV technique.
Cuff seal To assess adequacy of cuff seal between MOV procedures, auscultation over the trachea as the sole method (23/79, 29%), or in combination with assessment of expired tidal volume measured by the ventilator (27/79, 34%) were used most frequently. Other methods included manual inspiration via the ventilator (14/79, 18%) or palpation of the pilot balloon in combination with other methods (15/79, 19%). No respondent used balloon palpation exclusively.
Table 2
To manage an audible cuff leak, 28/79 (35%) respondents continued cuff inflation to obtain a seal irrespective of the volume of air required. A further 13/79 (16.5%) respondents continued cuff inflation and also notified medical staff. Twentythree (29%) respondents would attempt a range of troubleshooting techniques including assessment and manipulation of endotracheal tube insertion length and patient position. Notification of medical staff was the first course of action for 12/79 (15%) respondents. Two (2.5%) nurses assessed cuff pressure using a manometer. Only one respondent accepted an ongoing cuff leak. Participants were asked to identify the maximum volume of air acceptable for MOV. The most frequent response was 12 mL (34/79, 43%). Fifteen milliliter was the maximum volume accepted by 22/79 (28%) nurses, 10 mL by 15/79 (19%) nurses and 20 mL by 3/79 (4%) nurses. A further five respondents did not answer this question.
Extubation Prior to extubation, 57/79 (72%) participants routinely checked cuff volume to assess airway oedema. This procedure was not restricted to senior nurses (p = 0.9) or to those nurses whose ICU experience was limited to the participating institution (p = 0.6). Detection of a reduced cuff volume was considered an appropriate reason to defer the decision to extubate by 50/79 (63%) respondents.
Advantages and disadvantages Of the 79 respondents, 73 made comment on the perceived advantages and disadvantages of regular cuff monitoring using MOV. Five advantages were identified: to minimise damage to the tracheal wall (56% of respondents), to detect airway oedema
Minimal occlusive volume technique (N = 79)
Technique
Always, n (%)
Suction oropharynx prior to cuff deflation Two nurses to perform procedure Pre-oxygenation prior to cuff deflation Aspirate nasogastric tube prior to cuff deflation Manual inspiration to confirm cuff seal
79 (100)
0 (0)
0 (0)
0 (0)
76 (96)
3 (4)
0 (0)
0 (0)
74 (94)
4 (5)
1 (1)
0 (0)
11 (14)
36 (46)
31 (39)
1 (1)
17 (21.5)
59 (75)
2 (2.5)
1 (1)
Sometimes, n (%)
Never, n (%)
Did not answer, n (%)
Minimal occlusive volume cuff inflation (49%), to provide an adequate seal to prevent aspiration (15%), to facilitate pressure area care for the trachea (13%) and to enable delivery of mechanical ventilation (4%). Perceived disadvantages of the MOV procedure included: increased risk of aspiration and VAP due to full cuff deflation during the procedure (93% of respondents), loss of positive end expiratory pressure (PEEP) and interference with mechanical ventilation (21%), increased risk of tube migration or extubation (12%), patient discomfort (12%) and inaccuracy of the technique (5%). The MOV procedure was considered resource intensive compared to cuff pressure manometry by 15% of respondents.
Discussion To our knowledge, this survey is the first to provide an in-depth description of the MOV procedure and associated clinical processes in an ICU setting. The results of this survey indicate considerable practice variation. Substantial differences were noted in the method used to achieve MOV, patient positioning during the procedure, the most appropriate method for confirming cuff seal, and management of a cuff leak. Practice differences were only partially explained by the level of ICU experience. Junior nursing staff were more likely to use Method 1, a technique which theoretically decreases the risk of aspiration as the cuff is deflated for a shorter time. This method is advocated by the unit’s nurse educators whose role is to provide clinical education to junior staff members completing a postgraduate diploma in the critical care specialty. Other practice variation was not associated with nurse seniority or exposure to other ICU clinical environments. Little evidence is available that identifies the most appropriate method for ongoing monitoring of cuff inflation. Moreover detailed description of methods, associated processes, and evidence of efficacy are lacking. Step-by-step description of how to ascertain MOV in a cuff that is already inflated is required. Mechanical ventilation and critical care texts primarily describe the MOV technique for initial cuff inflation with cuff pressure monitoring (CPM) recommended for ongoing cuff monitoring (AACN, 2005; Pilbeam and Cairo, 2006; Pierce, 2007). However, practice surveys conducted in the United Kingdom suggest CPM is used infrequently (Spittle and Beavis, 2001; Vyas et al., 2002). Currently, there are no studies that confirm the superiority of CPM over the MOV technique for ongoing monitoring of cuff inflation. Disadvantages associated with the MOV technique include interruption of positive pressure
363 ventilation resulting in loss of PEEP and hypoxaemia, risk of aspiration and hyperinflation on cuff reinflation, and damage to the pilot valve through repetitive use (St John, 1999). Disadvantages of CPM include a sensitivity to changes in head, patient and tube position, coughing, lung compliance, airway and intrathoracic pressures (Crimlisk et al., 1996; Vyas et al., 2002; Pierce, 2007). Pressure readings taken prior to a position change or altered lung compliance may not accurately reflect cuff pressure. Additionally, patients with high intrathoracic or airway pressures require increased cuff pressure to maintain an adequate seal and may be at increased risk of ischemic injury. Alternatively, maintenance of pressure within the recommended range will predispose these patients to aspiration (Bouvier, 1981; Guyton et al., 1997). In this survey, the maximum frequency of monitoring cuff inflation was once per shift. This practice is congruent with recommendations in mechanical ventilation texts (MacIntyre and Branson, 2001; AACN, 2005; Pilbeam and Cairo, 2006) and practice survey reports (Sole et al., 2002, 2003; Rose and Redl, in press). Failure to monitor cuff inflation at least once per nursing shift may place the patient at increased risk of aspiration and subsequent ventilator associated pneumonia due to underinflation or tracheal mucosal damage in the presence of overinflation. Patients at increased risk of complications associated with cuff inflation include those with airway oedema, variable lung compliance and airway pressures (Guyton et al., 1997), and hypotension due to low perfusion pressure in the trachea (Pilbeam and Cairo, 2006). Cuff monitoring procedures should be performed in the semi-recumbent position to reduce stimulation of the gag reflex and risk of aspiration (AACN, 2005; Metheny et al., 2006). Though the majority of respondents in the current survey used this position, some practice variation was noted. During cuff monitoring procedures, the ability of the cuff to seal the airway is decreased while aspiration risk is increased due to stimulation of gag and cough reflexes associated with oropharyngeal and tracheal suctioning. Large residual volumes within the gut further increase the risk of aspiration (Metheny et al., 2006). Aspiration of nasogastric contents prior to cuff deflation is another intervention that may reduce the risk of aspiration of gastric contents. Surprisingly this procedure was routinely performed by only 14% of the survey respondents. During the inspiratory phase of a positive pressure breath the airways expand resulting in a drop in pressure (St John, 1999). To ensure appropriate cuff inflation, the cuff seal should be assessed during inspiration using a positive pressure breath prefer-
364 ably via the ventilator using either a sigh breath or manual inspiration function (AACN, 2005). In the current survey few respondents used this technique to confirm cuff seal during the MOV procedure, or to ascertain cuff seal between cuff checks. Similarly, few ICUs identified this practice in a recent survey of cuff management in Australia and New Zealand (Rose and Redl, in press). Loss of cuff volume and/or pressure is a common occurrence that increases the risk of aspiration of pharyngeal contents and VAP (Rello et al., 1996; Valencia et al., 2007). Notably, there is an absence of information in the literature to guide management of an audible cuff leak once the recommended volume or pressure has been reached. In the current study, the majority of nurses stated they would continue cuff inflation to obtain a seal irrespective of the volume of air required indicating greater concern for the risk of aspiration than tracheal damage. Nurses cited maximal acceptable cuff inflation volumes ranging from 10 to 20 mL. Manufacturers of modern high volume, low-pressure cuffs do not provide guidelines as to the recommended maximum cuff volume. Severe consequences of cuff overinflation including tracheal rupture, tracheo-carotid artery erosion and tracheal innominate artery fistulas are now rare due to widespread use of these cuffs (Sengupta et al., 2004). Nurses, however, need to remain mindful of the consequences of overinflation when large volumes of air are used. Conversely, VAP remains an important cause of morbidity and mortality in the critically ill (ATS, 2005). Respondents also perceived full cuff deflation during the MOV procedure increased the risk of aspiration and VAP. Currently there are no studies to demonstrate an increased risk of aspiration with MOV compared to other methods of cuff monitoring such as cuff pressure manometry or the minimal leak technique.
Limitations This survey has limitations. First, despite a reasonable response rate, the results may not represent the practice of non-responding nurses. Second, survey findings are the result of a self-report questionnaire and as such may reflect nurses’ best or intended practice rather than clinical reality. Third, this survey represents practice of a single ICU in which MOV was the sole method of cuff inflation and ongoing monitoring. As such, the described practice may not be generalised to other ICU settings. A recent survey of cuff inflation practices in Australia and New Zealand (Rose and Redl, in press) found MOV was used either in combination with cuff pres-
L. Rose, L. Redl sure manometry, or as the sole method of ongoing cuff monitoring, in 50% of ICUs surveyed indicating widespread use of this technique.
Conclusion Within the literature, evidence to support various aspects of the MOV procedure is limited. The results of our survey suggest, within this single ICU setting, substantial practice variation for certain aspects of cuff management exists. Despite concern for the risk of aspiration associated with cuff deflation during the MOV technique, procedures such as semi-recumbent positioning, aspiration of gastric contents prior to cuff deflation and manual inspiration to confirm cuff seal were not uniformly employed. As a result of the findings of this survey, unit guidelines for ongoing cuff monitoring have been revised to standardise practice. Additionally, a study has been initiated that examines the rate of gross aspiration using blue dye inserted into the oral cavity prior to cuff monitoring with both the MOV and cuff pressure monitoring techniques.
Role of funding source This study was supported by a research grant from RMIT University.
Conflict of interest None declared.
Acknowledgement The authors would like to thank the staff of the intensive care unit of The Royal Melbourne Hospital.
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