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Evaluation of the knowledge base of French intensivists and anaesthesiologists as concerns the interpretation of respiratory arterial pulse pressure variation
Anaesth Crit Care Pain Med 34 (2015) 29–34
Original article
Evaluation of the knowledge base of French intensivists and anaesthesiologists as concerns the interpretation of respiratory arterial pulse pressure variation Marc-Olivier Fischer a,b,*, Fabien Dechanet a, Damien du Cheyron a, Jean-Louis Ge´rard a, Jean-Luc Hanouz a,b, Jean-Luc Fellahi a,b a b
Poˆle Re´animations Anesthe´sie Samu/Smur, CHU de Caen, avenue de la Coˆte-de-Nacre, CS 30001, 14000 Caen, France EA 4650, Universite´ de Caen Basse-Normandie, esplanade de la Paix, CS 14 032, 14000 Caen, France
A R T I C L E I N F O
A B S T R A C T
Article history: Available online 5 March 2015
Objective: The aims of the study were to assess the knowledge of intensivists and/or anaesthesiologists concerning respiratory arterial pulse pressure variation (PPV) and to define the criteria used to indicate a fluid challenge. Study design: A prospective observational study. Patients and methods: Intensivists and anaesthesiologists from one region of France were evaluated for their knowledge about the prerequisites (continuous arterial pressure monitoring, regular sinus rhythm, mechanical ventilation without spontaneous breathing) and confounding factors shifting the threshold value of PPV (low tidal volume, decreased pulmonary compliance, low heart rate/respiratory rate ratio, right ventricular dysfunction, and/or intra-abdominal hypertension) using clinical vignettes. Criteria used by physicians to indicate a fluid challenge were also collected. Results: One hundred and forty-five physicians were included in the study. Among them, 87 (60%) knew prerequisites but none of them had full knowledge of all confounding factors. Criteria used to perform a fluid challenge were mainly PPV and the passive leg-raising test for the residents and PPV, blood pressure, oliguria and hydric balance for the qualified physicians. Conclusions: PPV was widely employed to indicate a fluid challenge and 60% of the physicians knew the prerequisites. However, the physicians did not correctly interpret all confounding factors. ß 2015 Socie´te´ franc¸aise d’anesthe´sie et de re´animation (Sfar). Published by Elsevier Masson SAS. All rights reserved.
Keywords: Case vignettes Clinical vignettes Critical care Monitoring Predicting fluid responsiveness Pulse pressure variation
1. Introduction Fluid optimization is often used as a first-line therapy in patients with hemodynamic instability and represents a daily challenge for physicians managing critically ill patients in the intensive care unit (ICU) or high-risk surgical patients in the operating room [1,2]. The respiratory arterial pulse pressure variation (PPV) has been described as a simple, continuous and reliable means to predict fluid responsiveness [3], which could help optimize volemia and conduct early goal-directed therapy [4]. The ability to monitor PPV in a non-invasive manner has been recently reported [5] and could further promote a wider use of PPV.
* Corresponding author at: Poˆle Re´animations Anesthe´sie Samu/Smur, CHU de Caen, avenue de la Coˆte-de-Nacre, CS 30001, 14000 Caen, France. Tel.: +33 2 31 06 47 36; fax: +33 2 31 06 51 37. E-mail address: fi[email protected] (M.-O. Fischer).
However, three prerequisites are mandatory in order to use PPV reliably at the bedside: a continuous beat-to-beat arterial pressure monitoring; a regular sinus rhythm; controlled positive-pressure ventilation without spontaneous respiratory effort [3]. Furthermore, various hemodynamic, respiratory and abdominal confounding factors could limit the interpretation of the threshold value of PPV indicating fluid responsiveness. For example, the threshold value could be decreased in case of low tidal volume (Vt) [6], low pulmonary compliance [7] or low heart rate/respiratory rate ratio (HR/RR) [8]. In contrast, the threshold value could be increased when right ventricular dysfunction (RVD) [9] or intra-abdominal hypertension occur [10]. Although less described, other additional factors may also be involved, such as a
http://dx.doi.org/10.1016/j.accpm.2014.06.001 2352-5568/ß 2015 Socie´te´ franc¸aise d’anesthe´sie et de re´animation (Sfar). Published by Elsevier Masson SAS. All rights reserved.
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M.-O. Fischer et al. / Anaesth Crit Care Pain Med 34 (2015) 29–34
decreased left ventricular ejection fraction (LVEF) [11] or a decreased value of perfusion index [12]. Finally, taking into account the gray zone approach at the bedside could further decrease the proportion of patients for which PPV was usable [13]. One issue not yet assessed is whether or not PPV is fully understood and correctly interpreted by physicians involved in the management of critically ill and high-risk surgical patients on a daily basis. Therefore, we performed a prospective study in which residents and qualified intensivists and anaesthesiologists answered questions derived from two clinical vignettes. The aim of the study was to assess the proportion of physicians who interpreted PPV correctly regarding both prerequisites and confounding factors. Additionally, we studied the parameters used by clinicians to guide the decision for fluid loading.
Table 1 Expected answers to clinical cases. Item
Expected answer
PPV formula
100 [(PPmax-PPmin)/ ((PPmax + PPmin)/2)]
PPV physiological support
Respiratory variability of arterial pulse pressure
PPV threshold value
> 13%
Gray zone approach
Area of uncertainty without clinical application
PPV prerequisites
Sinus rhythm, controlled ventilation without spontaneous breathing and continuous arterial pressure monitoring
PPV confounding factors Respiratory conditions
2. Material and methods 2.1. Ethics Institutional approval was obtained from the local, independent Ethics Committee (Comite´ de Protection des Personnes Nord Ouest III: A11-D32-VOL.11) and written consent was obtained from all included physicians. Registered anaesthesiologists and intensivists of the Conseil de l’Ordre des Me´decins de Basse-Normandie (a northwest region of France) were initially contacted by phone to participate in an individual scheduled meeting. There was no a priori exclusion criteria. The study period went from January 2012 to November 2012. 2.2. Clinical vignettes and progression of the individual interviews We arranged a meeting with each included resident and qualified intensivist or anaesthesiologist. Interviews took place in an office, away from any noise or other disturbance or clinical activity. Demographic, professional and continuous medical education characteristics for all participants were collected. The criteria used to decide a fluid challenge, the availability of PPV monitoring and the clinical use of PPV by physicians were then assessed. Two critical care (Appendices 1 and 2) and two anaesthesia (Appendices 3 and 4) clinical vignettes were written by the investigators (FD and MOF) and validated by two independent hemodynamic experts (JLF and JLH). Cases consisted in histories based on realistic clinical scenarios and they were submitted as critical care or anaesthesia cases, at the convenience of each participant. The clinical vignettes had an open-ended response format, as previously described [14]. The physicians conducting the interview (MOF for the residents and FD for the qualified physicians) did not take any notes and did not help the physicians with their answers. Clinical vignettes included questions regarding the PPV formula, the PPV physiological concept, the threshold value of PPV, the gray zone approach, and the knowledge of participants about both prerequisites and confounding factors. 2.3. Assessment of the answers to clinical vignettes All individual interviews were recorded and listened to immediately after the meeting by MOF or FD in order to complete the evaluation checklist. The expected answers are presented in Table 1. They were similar for critical care and anaesthesia clinical vignettes. If an ambiguous response was noted, the two independent hemodynamic experts listened to the audio band again to definitely classify the answer as exact or inexact. The record was destroyed 7 days following the individual interview.
Cardiac conditions Abdominal conditions
Vt 8 mL/kg, HR/RR > 3.6, low respiratory system compliance (< 30 mL/ cmH2O) due to low pulmonary compliance Absence of RVD (TAPSE > 15 mm) Absence of intra-abdominal hypertension (< 16 mmHg)
HR/RR: heart rate/respiratory rate ratio; LVEF: left ventricular ejection fraction; PPmax: maximal pulse pressure; PPmin: minimal pulse pressure; PPV: arterial pulse pressure variation; RVD: right ventricular dysfunction; TAPSE: tricuspid annular plane systolic excursion; Vt: tidal volume.
2.4. Definitions 2.4.1. Prerequisites The prerequisites were defined as follows: patients having a continuous beat-to-beat arterial pressure monitoring, a regular sinus rhythm, and controlled positive-pressure ventilation without spontaneous respiratory efforts. 2.4.2. Confounding factors The confounding factors were defined as follows: clinical situations decreasing the threshold value of PPV that predicts fluid responsiveness (low Vt, low respiratory system compliance due to low pulmonary compliance, and low HR/RR ratio) or increasing the threshold value of PPV (RVD and intra-abdominal hypertension). Physicians included both residents in anaesthesiology and critical care, and qualified intensivists and anaesthesiologists. 2.5. Endpoints The primary endpoint was the proportion of physicians who correctly interpreted PPV as regards both prerequisites and confounding factors. The secondary endpoint was the criteria used by physicians to administer a fluid challenge. 2.6. Statistical analysis Data are expressed as means standard deviations (SD) for normally distributed variables, medians [25th–75th percentiles] for non-normally distributed variables (Kolmogorov-Smirnov test) or numbers (%), as appropriate. Continuous variables were analysed with the unpaired Mann-Whitney U test. Categorical variables were analysed with the Fisher exact test. A P value < 0.05 was considered to be statistically significant and all P values were two-tailed. Statistical analyses were performed using MedCalc1 Software bvba version 12.5.0. (Ostend, Belgium). 3. Results One hundred and one (55%) qualified intensivists and anaesthesiologists and 44 (92%) residents participated in the
M.-O. Fischer et al. / Anaesth Crit Care Pain Med 34 (2015) 29–34 Table 2 Demographic characteristics of physicians (n = 145). Residents (n = 44)
Qualified physicians (n = 101)
P value
Age (year)
28 3
46 11
< 0.001
Sex (M/F)
24/20
70/31
0.042
University hospital/tertiary hospital
43/1
45/56
< 0.001
Public/private health service
44/0
74/27
< 0.001
ICU/anesthesiology/both
9/5/30
24/57/20
< 0.001
Presence to medical meetings (per year)
1 [1,2]
2 [1,2]
0.003
Reading of scientific articles (per month)
4 [2–8]
2 [2–5]
0.013
ICU: intensive care unit; M: male; F: female; SD: standard deviation. Values are expressed as mean SD or number or median [25–75th].
31
study. Seven records were discussed with the independent hemodynamic experts. The characteristics of the two groups of physicians are listed in Table 2. The qualified intensivists and anaesthesiologists were more frequently male, worked in a tertiary hospital and had an exclusive anaesthesiology practice. Among participants, 87/145 (60%) identified the 3 prerequisites (Fig. 1). A significant difference in the knowledge of the 3 prerequisites was observed between residents and all qualified physicians (75% vs. 52%, P < 0.001). However, a significant difference in the knowledge of the 3 prerequisites was observed between qualified physicians who frequently used PPV and those who did not frequently use PPV (72% vs. 17%, P < 0.001). None of the physicians interpreted PPV adequately regarding the confounding factors (Fig. 1). The theoretical knowledge of confounding factors decreasing or increasing the threshold value of PPV is reported in Table 3. The knowledge of the residents and the qualified intensivists and anaesthesiologists for each evaluable
Physicians enrolled (n=230) Physicians who declined to participate (n=85) Physicians included (n=145) Physicians without the full knowledge of PPV prerequisites [n=58 (40%)] Physicians having the knowledge of PPV prerequisites [n=87 (60%)] Physicians without the full knowledge of confounding factors decreasing the PPV threshold value [n=86 (59%)]
Physicians without the full knowledge of confounding factors increasing the PPV threshold value [n=83 (57%)]
Physicians interpreting correctly PPV [n=0 (0%)] Fig. 1. Flowchart for the study. PPV: respiratory arterial pulse pressure variation.
M.-O. Fischer et al. / Anaesth Crit Care Pain Med 34 (2015) 29–34
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Table 3 Theoretical knowledge regarding confounding factors and physiological and mathematical definitions of respiratory arterial pulse pressure variation (n = 145). Residents (n = 44)
Qualified physicians (n = 101)
P value
Decreasing PPV threshold value Pulmonary compliance < 30 mL/cmH2O Tidal volume < 8 mL/kg HR/RR < 3.6
2 (4) 14 (32) 3 (7)
2 (2) 17 (17) 2 (2)
0.683 0.021 0.170
Increasing PPV threshold value RV dysfunction (TAPSE < 15 mm) Intra-abdominal hypertension
1 (2) 12 (27)
3 (3) 29 (29)
1.000 0.875
PPV formula
17 (39)
31 (31)
0.299
Physiological concept
31 (70)
62 (61)
0.234
Threshold value of PPV
34 (77)
35 (35)
< 0.001
Gray zone approach
29 (66)
41 (41)
< 0.001
Fig. 3. Graduate level of theoretical knowledge for all physicians. Level (1) defined physicians who knew the three prerequisites of PPV, Level (2) defined the physicians in level 1 who knew tidal volume as well, and Level (3) defined physicians in level 2 who knew others confounding factors.
4. Discussion
to predict fluid responsiveness but only 60% were aware of the mandatory prerequisites for its use and none had a full theoretical knowledge of all potential confounding factors. We used clinical vignettes as the reference method to evaluate the knowledge base of physicians concerning PPV interpretation. A previous study suggested that clinical vignettes may be a useful way to assess physicians’ practices in an outpatient setting [14]. The clinical relevance of this method in a wide panel of clinical situations such as trauma triage, antibiotic prescriptions in neonatal ICUs, crisis-oriented anaesthesia events, regional anaesthesia or ethical considerations has been recently suggested [15– 19]. This modern method seems suited for evaluating the knowledge of a group and subsequently well adapted to the present study. As previously reported with the use of the pulmonary artery catheter two decades ago [20,21], the major risk emphasized by our study is PPV misinterpretation and misuse. The respiratory and cardiac conditions were clearly not fully assimilated and the growing emergence of new confounding factors increasing or decreasing the PPV threshold value in the recent literature could explain such a disappointing result. Indeed, although the
The main findings of the present study conducted among residents and qualified intensivists and anaesthesiologists from the northwest of France were that physicians frequently used PPV
Table 4 Declared criteria used to decide fluid challenge at the bedside (n = 145).
HR/RR: heart rate/respiratory rate ratio; LVEF: left ventricular ejection fraction; PPV: arterial pulse pressure variation; RV: right ventricle; TAPSE: systolic value of excursion of tricuspid annulus. Values are expressed as number (%).
item is depicted on Fig. 2. None of the physicians were able to identify all respiratory conditions, as reported in Table 1. A single qualified physician presented all cardiac conditions for the validity of PPV. Moreover, knowledge of both PPV threshold values and the gray zone concept was significantly better among residents when compared with qualified physicians (Table 3). Fig. 3 demonstrated a graduate level of knowledge for physicians. The criteria described by all participants for proceeding with a fluid challenge are depicted in Table 4 and on Fig. 4. PPV and passive leg-raising test were more frequently used by residents in contrast to qualified physicians who more frequently used blood pressure, diuresis and hydric balance. PPV was never declared as being used as part of a local hemodynamic algorithm at the bedside.
Residents (n = 44)
Qualified physicians (n = 101)
P value
PPV
43 (98)
65 (64)
< 0.001
PVI
6 (14)
Exact answers (%) 100 90 80 70
* *
60
Stroke volume variation
50
Passive leg-raising
40
*
7 (7)
0.165
3 (7)
11 (11)
0.459
20 (45)
26 (26)
0.008
End-expiratory occlusion test
2 (4)
20
Tachycardia
7 (16)
10
Central venous pressure
2 (4)
Blood pressure Diuresis
30
0
Hydric balance
Fig. 2. Theoretical knowledge of residents (dark gray) and qualified intensivists and anaesthesiologists (light gray) regarding respiratory arterial pulse pressure variation prerequisites and confounding factors (see material and methods). * P < 0.05 residents vs. qualified intensivists and anaesthesiologists. HR/RR: heart rate/respiratory rate ratio; IA: intra-abdominal; RV: right ventricular.
0 (0)
0.121
22 (22)
0.368
7 (7)
0.537
6 (14)
34 (34)
0.001
0 (0)
29 (29)
< 0.001
2 (4)
15 (15)
0.014
Ultrasound
15 (34)
27 (27)
0.357
Thermodilution
23 (52)
37 (37)
0.046
2 (4)
4 (4)
1.000
Oesophageal Doppler
PPV: respiratory arterial pulse pressure variation; PVI: plethysmographic variability index; SVV: stroke volume variations. Values are expressed as number (%).
M.-O. Fischer et al. / Anaesth Crit Care Pain Med 34 (2015) 29–34
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Declared criteria used to decide fluid challenge (%) 100
*
90 80 70 60 50
* *
40
* *
30 20
*
*
10 0
Fig. 4. Declared criteria used to decide fluid challenge implementation at the bedside for the residents (dark gray) and qualified intensivists and anaesthesiologists (light gray). *P < 0.05 residents vs. qualified intensivists and anaesthesiologists. PPV: pulse pressure variation; PLR: passive leg-raising; PVI: plethysmographic variability index; SVV: stroke volume variation; TTE: transthoracic echocardiography; CVP: central venous pressure.
prerequisites for the use of PPV have been clearly stated in numerous publications, the confounding factors we evaluated in the current study have been scarcely reported. This last point could explain the actual low level of theoretical knowledge regarding these factors. However, physicians indicated in a previous survey that basic science information had a positive impact on their clinical practice [22]. They also indicated that basic science information was most frequently applied during practice-based learning and improvement [22]. The absence of clinical guidelines for PPV interpretation and use at bedside could also have contributed in the disappointing results we report in the present study. Finally, the absence of hemodynamic protocols for daily routine practice could also explain the misuse of PPV in the clinical vignettes [23]. In contrast, a recent study using PPV associated with a standardized hemodynamic protocol reported a decrease in perioperative morbidity [24]. A checklist was recently suggested to validate the use of PPV before performing volume expansion [25]. The current study showed that PPV was much more frequently used at the bedside to predict fluid responsiveness than previously reported in ICUs [26,27]. The purely declarative information we deal with could be responsible for an information bias during the interviews and partially explain such a difference. Interestingly, thermodilution was often used to decide a fluid challenge, whereas cardiac output monitoring has been scarcely reported in recent studies [23,26]. Again, an information bias could explain this result. Other dynamic tools were also mentioned by physicians when considering a fluid challenge, such as PLR or echocardiographic data. This last point suggests that a multiple-index approach could be more appropriate than using PPV alone for a consistent fluid challenge strategy at the bedside. We found significant differences between residents and qualified anaesthesiologists or intensivists for prerequisites, certain confounding factors and both for the interpretation of the threshold value and the gray zone concept. A plausible hypothesis is that residents have more updated readings and medical education as compared to
qualified physicians. Another explanation may be that qualified physicians who do not frequently use PPV have less knowledge of PPV than those who frequently use PPV. The limitations associated with our study should be highlighted. First, only 55% of qualified physicians were included, in contrast with 92% of residents. This can be explained by the fact that residents principally work at the university hospital and were subsequently easier to interview. Second, neither the differences between physicians nor the information-based measure of disagreement were explored with an objective method [28]. However, objective and quantitative criteria were easily recorded, although these same criteria could be considered as arbitrary and modifying the knowledge of physicians in the present study. Finally, the impact of the low level of theoretical knowledge of physicians regarding the confounding factors of PPV described in the present study was not assessed in terms of outcomes. To date, as previously reported with the pulmonary artery catheter [20,21], no relationship has been found between the level of knowledge on PPV and patient outcomes. 5. Conclusion This study demonstrated that 60% of physicians know the prerequisites for using PPV to guide fluid challenge implementation at the bedside. However, none of them correctly interpreted PPV regarding numerous recently described confounding factors. The low rate of scientific medical readings, the absence of local hemodynamic protocols and established guidelines may explain these results. Disclosure of interest The authors declare that they have no conflicts of interest concerning this article.
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Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.accpm.2014.06.001. References [1] Rivers E, Nguyen B, Havstad S, Ressler J, Muzzin A, et al. Early goal-directed therapy in the treatment of severe sepsis and septic shock. N Engl J Med 2001;345:1368–77. [2] Hamilton M, Cecconi M, Rhodes A. A systematic review and meta-analysis on the use of preemptive hemodynamic intervention to improve postoperative outcomes in moderate and high-risk surgical patients. Anesth Analg 2011;112:1392–402. [3] Michard F, Boussat S, Chemla D, Anguel N, Mercat A, Lecarpentier Y, et al. Relation between respiratory changes in arterial pulse pressure and fluid responsiveness in septic patients with acute circulatory failure. Am J Respir Crit Care Med 2000;162:134–8. [4] Lopes MR, Oliveira MA, Pereira VO, Lemos IP, Auler JO, Michard F. Goal-directed fluid management based on pulse pressure variation monitoring during highrisk surgery: a pilot randomized controlled trial. Crit Care 2007;11:R100. [5] Lansdorp B, Ouweneel D, de Keijzer A, van der Hoeven JG, Lemson J, Pickkers P. Non-invasive measurement of pulse pressure variation and systolic pressure variation using a finger cuff corresponds with intra-arterial measurement. Br J Anaesth 2011;107:540–5. [6] De Backer D, Heenen S, Piagnerelli M, Koch M, Vincent JL. Pulse pressure variations to predict fluid responsiveness: influence of tidal volume. Intensive Care Med 2005;31:517–23. [7] Monnet X, Bleibtreu A, Ferre A, Dres M, Gharbi R, Richard C, et al. Passive leg-raising and end-expiratory occlusion tests perform better than pulse pressure variation in patients with low respiratory system compliance. Crit Care Med 2012;40:152–7. [8] De Backer D, Taccone FS, Holsten R, Ibrahimi F, Vincent JL. Influence of respiratory rate on stroke volume variation in mechanically ventilated patients. Anesthesiology 2009;110:1092–7. [9] Mahjoub Y, Pila C, Friggeri A, Zogheib E, Lobjoie E, Tinturier F, et al. Assessing fluid responsiveness in critically ill patients: false-positive pulse pressure variation is detected by Doppler echocardiographic evaluation of the right ventricle. Crit Care Med 2009;37:2570–5. [10] Renner J, Gruenewald M, Quaden R, Hanss R, Meybohm P, Steinfath M, et al. Influence of increased intra-abdominal pressure on fluid responsiveness predicted by pulse pressure variation and stroke volume variation in a porcine model. Crit Care Med 2009;37:650–8. [11] Mesquida J, Kim HK, Pinsky MR. Effect of tidal volume, intrathoracic pressure, and cardiac contractility on variations in pulse pressure, stroke volume, and intrathoracic blood volume. Intensive Care Med 2011;37:1672–9. [12] Fischer MO, Pelissier A, Bohadana D, Ge´rard JL, Hanouz JL, Fellahi JL. Prediction of responsiveness to an intravenous fluid challenge in patients after cardiac surgery with cardiopulmonary bypass: a comparison between arterial pulse pressure variation and digital plethysmographic variability index. J Cardiothorac Vasc Anesth 2013;27:1087–93.
[13] Cannesson M, Le Manach Y, Hofer CK, Goarin JP, Lehot JJ, Vallet B, et al. Assessing the diagnostic accuracy of pulse pressure variations for the prediction of fluid responsiveness: a ‘‘gray zone’’ approach. Anesthesiology 2011;115:231–41. [14] Peabody JW, Luck J, Glassman P, Dresselhaus TR, Lee M. Comparison of vignettes, standardized patients, and chart abstraction. A prospective validation study of 3 methods for measuring quality. JAMA 2000;283:1715–22. [15] Mohan D, Fischhoff B, Farris C, Switzer GE, Rosengart MR, Yealy DM, et al. Validating a vignette-based instrument to study physician decision making in trauma triage. Med Decis Making 2014;34:242–52. [16] Patel S, Landers T, Larson E, Zaoutis T, Delamora P, Paul DA, et al. Clinical vignettes provide an understanding of antibiotic prescribing practices in neonatal intensive care units. Infect Control Hosp Epidemiol 2011;32:597– 602. [17] McLain NE, Biddle C, Cotter JJ. Anesthesia clinical performance outcomes: does teaching method make a difference? AANA J 2012;80:S11–6. [18] Sites BD, Antonakakis JG. Ultrasound guidance in regional anesthesia: state of the art review through challenging clinical scenarios. Reg Loc Anesth 2009;2:1–14. [19] Ruppe MD, Feudtner C, Hexem KR, Morrisson WE. Family factors affect clinician attitudes in pediatric end-of-life decision making: a randomized vignette study. J Pain Sympt Manage 2013;45:832–40. [20] Iberti T, Daily E, Leibowitz A, Schecter C, Fischer E, Silverstein J, The Pulmonary Artery Catheter Study Group. Assessment of critical care nurses’ knowledge of the pulmonary artery catheter. Crit Care Med 1994;22:1674–8. [21] Gnaegi A, Feihl F, Perret C. Intensive care physicians’ insufficient knowledge of right-heart catheterization at the bedside: time to act? Crit Care Med 1997;25:213–20. [22] Fischer JA, Muller-Weeks S. Physician perceptions of the role and value of basic science knowledge in daily clinical practice. Med Teach 2012;34: 744–7. [23] Cannesson M, Pestel G, Ricks C, Hoeft A, Perel A. Hemodynamic monitoring and management in patients undergoing high-risk surgery: a survey among North American and European anesthesiologists. Crit Care 2011;15:R197. [24] Salzwedel C, Puig J, Carstens A, Bein B, Molnar Z, Kiss K, et al. Perioperative goal-directed hemodynamic therapy based on radial arterial pulse pressure variation and continuous cardiac index trending reduces postoperative complications after major abdominal surgery: a multi-center, prospective, randomized study. Crit Care 2013;17:R191. [25] Sondergaard S. Pavane for a pulse pressure variation defunct. Crit Care 2013;17:327. [26] Fischer M-O, et al. Arterial pulse pressure variation suitability in critical care: a French national survey. Anaesth Crit Care Pain Med 2015. http://dx.doi.org/ 10.1016/j.accpm.2014.08.001. [27] Mahjoub Y, Lejeune V, Muller L, Perbet S, Zieleskewicz L, Bart F, et al. Evaluation of pulse pressure variation validity criteria in critically ill patients: a prospective observational multicentre point-prevalence study. Br J Anaesth 2014;112:681–5. [28] Henriques T, Antunes L, Bernardes J, Matias M, Sato D, Costa-Santos C. Information-based measure of disagreement for more than two observers: a useful tool to compare the degree of observer disagreement. BMC Med Res Methodol 2013;13:47.
Original article
Evaluation of the knowledge base of French intensivists and anaesthesiologists as concerns the interpretation of respiratory arterial pulse pressure variation Marc-Olivier Fischer a,b,*, Fabien Dechanet a, Damien du Cheyron a, Jean-Louis Ge´rard a, Jean-Luc Hanouz a,b, Jean-Luc Fellahi a,b a b
Poˆle Re´animations Anesthe´sie Samu/Smur, CHU de Caen, avenue de la Coˆte-de-Nacre, CS 30001, 14000 Caen, France EA 4650, Universite´ de Caen Basse-Normandie, esplanade de la Paix, CS 14 032, 14000 Caen, France
A R T I C L E I N F O
A B S T R A C T
Article history: Available online 5 March 2015
Objective: The aims of the study were to assess the knowledge of intensivists and/or anaesthesiologists concerning respiratory arterial pulse pressure variation (PPV) and to define the criteria used to indicate a fluid challenge. Study design: A prospective observational study. Patients and methods: Intensivists and anaesthesiologists from one region of France were evaluated for their knowledge about the prerequisites (continuous arterial pressure monitoring, regular sinus rhythm, mechanical ventilation without spontaneous breathing) and confounding factors shifting the threshold value of PPV (low tidal volume, decreased pulmonary compliance, low heart rate/respiratory rate ratio, right ventricular dysfunction, and/or intra-abdominal hypertension) using clinical vignettes. Criteria used by physicians to indicate a fluid challenge were also collected. Results: One hundred and forty-five physicians were included in the study. Among them, 87 (60%) knew prerequisites but none of them had full knowledge of all confounding factors. Criteria used to perform a fluid challenge were mainly PPV and the passive leg-raising test for the residents and PPV, blood pressure, oliguria and hydric balance for the qualified physicians. Conclusions: PPV was widely employed to indicate a fluid challenge and 60% of the physicians knew the prerequisites. However, the physicians did not correctly interpret all confounding factors. ß 2015 Socie´te´ franc¸aise d’anesthe´sie et de re´animation (Sfar). Published by Elsevier Masson SAS. All rights reserved.
Keywords: Case vignettes Clinical vignettes Critical care Monitoring Predicting fluid responsiveness Pulse pressure variation
1. Introduction Fluid optimization is often used as a first-line therapy in patients with hemodynamic instability and represents a daily challenge for physicians managing critically ill patients in the intensive care unit (ICU) or high-risk surgical patients in the operating room [1,2]. The respiratory arterial pulse pressure variation (PPV) has been described as a simple, continuous and reliable means to predict fluid responsiveness [3], which could help optimize volemia and conduct early goal-directed therapy [4]. The ability to monitor PPV in a non-invasive manner has been recently reported [5] and could further promote a wider use of PPV.
* Corresponding author at: Poˆle Re´animations Anesthe´sie Samu/Smur, CHU de Caen, avenue de la Coˆte-de-Nacre, CS 30001, 14000 Caen, France. Tel.: +33 2 31 06 47 36; fax: +33 2 31 06 51 37. E-mail address: fi[email protected] (M.-O. Fischer).
However, three prerequisites are mandatory in order to use PPV reliably at the bedside: a continuous beat-to-beat arterial pressure monitoring; a regular sinus rhythm; controlled positive-pressure ventilation without spontaneous respiratory effort [3]. Furthermore, various hemodynamic, respiratory and abdominal confounding factors could limit the interpretation of the threshold value of PPV indicating fluid responsiveness. For example, the threshold value could be decreased in case of low tidal volume (Vt) [6], low pulmonary compliance [7] or low heart rate/respiratory rate ratio (HR/RR) [8]. In contrast, the threshold value could be increased when right ventricular dysfunction (RVD) [9] or intra-abdominal hypertension occur [10]. Although less described, other additional factors may also be involved, such as a
http://dx.doi.org/10.1016/j.accpm.2014.06.001 2352-5568/ß 2015 Socie´te´ franc¸aise d’anesthe´sie et de re´animation (Sfar). Published by Elsevier Masson SAS. All rights reserved.
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M.-O. Fischer et al. / Anaesth Crit Care Pain Med 34 (2015) 29–34
decreased left ventricular ejection fraction (LVEF) [11] or a decreased value of perfusion index [12]. Finally, taking into account the gray zone approach at the bedside could further decrease the proportion of patients for which PPV was usable [13]. One issue not yet assessed is whether or not PPV is fully understood and correctly interpreted by physicians involved in the management of critically ill and high-risk surgical patients on a daily basis. Therefore, we performed a prospective study in which residents and qualified intensivists and anaesthesiologists answered questions derived from two clinical vignettes. The aim of the study was to assess the proportion of physicians who interpreted PPV correctly regarding both prerequisites and confounding factors. Additionally, we studied the parameters used by clinicians to guide the decision for fluid loading.
Table 1 Expected answers to clinical cases. Item
Expected answer
PPV formula
100 [(PPmax-PPmin)/ ((PPmax + PPmin)/2)]
PPV physiological support
Respiratory variability of arterial pulse pressure
PPV threshold value
> 13%
Gray zone approach
Area of uncertainty without clinical application
PPV prerequisites
Sinus rhythm, controlled ventilation without spontaneous breathing and continuous arterial pressure monitoring
PPV confounding factors Respiratory conditions
2. Material and methods 2.1. Ethics Institutional approval was obtained from the local, independent Ethics Committee (Comite´ de Protection des Personnes Nord Ouest III: A11-D32-VOL.11) and written consent was obtained from all included physicians. Registered anaesthesiologists and intensivists of the Conseil de l’Ordre des Me´decins de Basse-Normandie (a northwest region of France) were initially contacted by phone to participate in an individual scheduled meeting. There was no a priori exclusion criteria. The study period went from January 2012 to November 2012. 2.2. Clinical vignettes and progression of the individual interviews We arranged a meeting with each included resident and qualified intensivist or anaesthesiologist. Interviews took place in an office, away from any noise or other disturbance or clinical activity. Demographic, professional and continuous medical education characteristics for all participants were collected. The criteria used to decide a fluid challenge, the availability of PPV monitoring and the clinical use of PPV by physicians were then assessed. Two critical care (Appendices 1 and 2) and two anaesthesia (Appendices 3 and 4) clinical vignettes were written by the investigators (FD and MOF) and validated by two independent hemodynamic experts (JLF and JLH). Cases consisted in histories based on realistic clinical scenarios and they were submitted as critical care or anaesthesia cases, at the convenience of each participant. The clinical vignettes had an open-ended response format, as previously described [14]. The physicians conducting the interview (MOF for the residents and FD for the qualified physicians) did not take any notes and did not help the physicians with their answers. Clinical vignettes included questions regarding the PPV formula, the PPV physiological concept, the threshold value of PPV, the gray zone approach, and the knowledge of participants about both prerequisites and confounding factors. 2.3. Assessment of the answers to clinical vignettes All individual interviews were recorded and listened to immediately after the meeting by MOF or FD in order to complete the evaluation checklist. The expected answers are presented in Table 1. They were similar for critical care and anaesthesia clinical vignettes. If an ambiguous response was noted, the two independent hemodynamic experts listened to the audio band again to definitely classify the answer as exact or inexact. The record was destroyed 7 days following the individual interview.
Cardiac conditions Abdominal conditions
Vt 8 mL/kg, HR/RR > 3.6, low respiratory system compliance (< 30 mL/ cmH2O) due to low pulmonary compliance Absence of RVD (TAPSE > 15 mm) Absence of intra-abdominal hypertension (< 16 mmHg)
HR/RR: heart rate/respiratory rate ratio; LVEF: left ventricular ejection fraction; PPmax: maximal pulse pressure; PPmin: minimal pulse pressure; PPV: arterial pulse pressure variation; RVD: right ventricular dysfunction; TAPSE: tricuspid annular plane systolic excursion; Vt: tidal volume.
2.4. Definitions 2.4.1. Prerequisites The prerequisites were defined as follows: patients having a continuous beat-to-beat arterial pressure monitoring, a regular sinus rhythm, and controlled positive-pressure ventilation without spontaneous respiratory efforts. 2.4.2. Confounding factors The confounding factors were defined as follows: clinical situations decreasing the threshold value of PPV that predicts fluid responsiveness (low Vt, low respiratory system compliance due to low pulmonary compliance, and low HR/RR ratio) or increasing the threshold value of PPV (RVD and intra-abdominal hypertension). Physicians included both residents in anaesthesiology and critical care, and qualified intensivists and anaesthesiologists. 2.5. Endpoints The primary endpoint was the proportion of physicians who correctly interpreted PPV as regards both prerequisites and confounding factors. The secondary endpoint was the criteria used by physicians to administer a fluid challenge. 2.6. Statistical analysis Data are expressed as means standard deviations (SD) for normally distributed variables, medians [25th–75th percentiles] for non-normally distributed variables (Kolmogorov-Smirnov test) or numbers (%), as appropriate. Continuous variables were analysed with the unpaired Mann-Whitney U test. Categorical variables were analysed with the Fisher exact test. A P value < 0.05 was considered to be statistically significant and all P values were two-tailed. Statistical analyses were performed using MedCalc1 Software bvba version 12.5.0. (Ostend, Belgium). 3. Results One hundred and one (55%) qualified intensivists and anaesthesiologists and 44 (92%) residents participated in the
M.-O. Fischer et al. / Anaesth Crit Care Pain Med 34 (2015) 29–34 Table 2 Demographic characteristics of physicians (n = 145). Residents (n = 44)
Qualified physicians (n = 101)
P value
Age (year)
28 3
46 11
< 0.001
Sex (M/F)
24/20
70/31
0.042
University hospital/tertiary hospital
43/1
45/56
< 0.001
Public/private health service
44/0
74/27
< 0.001
ICU/anesthesiology/both
9/5/30
24/57/20
< 0.001
Presence to medical meetings (per year)
1 [1,2]
2 [1,2]
0.003
Reading of scientific articles (per month)
4 [2–8]
2 [2–5]
0.013
ICU: intensive care unit; M: male; F: female; SD: standard deviation. Values are expressed as mean SD or number or median [25–75th].
31
study. Seven records were discussed with the independent hemodynamic experts. The characteristics of the two groups of physicians are listed in Table 2. The qualified intensivists and anaesthesiologists were more frequently male, worked in a tertiary hospital and had an exclusive anaesthesiology practice. Among participants, 87/145 (60%) identified the 3 prerequisites (Fig. 1). A significant difference in the knowledge of the 3 prerequisites was observed between residents and all qualified physicians (75% vs. 52%, P < 0.001). However, a significant difference in the knowledge of the 3 prerequisites was observed between qualified physicians who frequently used PPV and those who did not frequently use PPV (72% vs. 17%, P < 0.001). None of the physicians interpreted PPV adequately regarding the confounding factors (Fig. 1). The theoretical knowledge of confounding factors decreasing or increasing the threshold value of PPV is reported in Table 3. The knowledge of the residents and the qualified intensivists and anaesthesiologists for each evaluable
Physicians enrolled (n=230) Physicians who declined to participate (n=85) Physicians included (n=145) Physicians without the full knowledge of PPV prerequisites [n=58 (40%)] Physicians having the knowledge of PPV prerequisites [n=87 (60%)] Physicians without the full knowledge of confounding factors decreasing the PPV threshold value [n=86 (59%)]
Physicians without the full knowledge of confounding factors increasing the PPV threshold value [n=83 (57%)]
Physicians interpreting correctly PPV [n=0 (0%)] Fig. 1. Flowchart for the study. PPV: respiratory arterial pulse pressure variation.
M.-O. Fischer et al. / Anaesth Crit Care Pain Med 34 (2015) 29–34
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Table 3 Theoretical knowledge regarding confounding factors and physiological and mathematical definitions of respiratory arterial pulse pressure variation (n = 145). Residents (n = 44)
Qualified physicians (n = 101)
P value
Decreasing PPV threshold value Pulmonary compliance < 30 mL/cmH2O Tidal volume < 8 mL/kg HR/RR < 3.6
2 (4) 14 (32) 3 (7)
2 (2) 17 (17) 2 (2)
0.683 0.021 0.170
Increasing PPV threshold value RV dysfunction (TAPSE < 15 mm) Intra-abdominal hypertension
1 (2) 12 (27)
3 (3) 29 (29)
1.000 0.875
PPV formula
17 (39)
31 (31)
0.299
Physiological concept
31 (70)
62 (61)
0.234
Threshold value of PPV
34 (77)
35 (35)
< 0.001
Gray zone approach
29 (66)
41 (41)
< 0.001
Fig. 3. Graduate level of theoretical knowledge for all physicians. Level (1) defined physicians who knew the three prerequisites of PPV, Level (2) defined the physicians in level 1 who knew tidal volume as well, and Level (3) defined physicians in level 2 who knew others confounding factors.
4. Discussion
to predict fluid responsiveness but only 60% were aware of the mandatory prerequisites for its use and none had a full theoretical knowledge of all potential confounding factors. We used clinical vignettes as the reference method to evaluate the knowledge base of physicians concerning PPV interpretation. A previous study suggested that clinical vignettes may be a useful way to assess physicians’ practices in an outpatient setting [14]. The clinical relevance of this method in a wide panel of clinical situations such as trauma triage, antibiotic prescriptions in neonatal ICUs, crisis-oriented anaesthesia events, regional anaesthesia or ethical considerations has been recently suggested [15– 19]. This modern method seems suited for evaluating the knowledge of a group and subsequently well adapted to the present study. As previously reported with the use of the pulmonary artery catheter two decades ago [20,21], the major risk emphasized by our study is PPV misinterpretation and misuse. The respiratory and cardiac conditions were clearly not fully assimilated and the growing emergence of new confounding factors increasing or decreasing the PPV threshold value in the recent literature could explain such a disappointing result. Indeed, although the
The main findings of the present study conducted among residents and qualified intensivists and anaesthesiologists from the northwest of France were that physicians frequently used PPV
Table 4 Declared criteria used to decide fluid challenge at the bedside (n = 145).
HR/RR: heart rate/respiratory rate ratio; LVEF: left ventricular ejection fraction; PPV: arterial pulse pressure variation; RV: right ventricle; TAPSE: systolic value of excursion of tricuspid annulus. Values are expressed as number (%).
item is depicted on Fig. 2. None of the physicians were able to identify all respiratory conditions, as reported in Table 1. A single qualified physician presented all cardiac conditions for the validity of PPV. Moreover, knowledge of both PPV threshold values and the gray zone concept was significantly better among residents when compared with qualified physicians (Table 3). Fig. 3 demonstrated a graduate level of knowledge for physicians. The criteria described by all participants for proceeding with a fluid challenge are depicted in Table 4 and on Fig. 4. PPV and passive leg-raising test were more frequently used by residents in contrast to qualified physicians who more frequently used blood pressure, diuresis and hydric balance. PPV was never declared as being used as part of a local hemodynamic algorithm at the bedside.
Residents (n = 44)
Qualified physicians (n = 101)
P value
PPV
43 (98)
65 (64)
< 0.001
PVI
6 (14)
Exact answers (%) 100 90 80 70
* *
60
Stroke volume variation
50
Passive leg-raising
40
*
7 (7)
0.165
3 (7)
11 (11)
0.459
20 (45)
26 (26)
0.008
End-expiratory occlusion test
2 (4)
20
Tachycardia
7 (16)
10
Central venous pressure
2 (4)
Blood pressure Diuresis
30
0
Hydric balance
Fig. 2. Theoretical knowledge of residents (dark gray) and qualified intensivists and anaesthesiologists (light gray) regarding respiratory arterial pulse pressure variation prerequisites and confounding factors (see material and methods). * P < 0.05 residents vs. qualified intensivists and anaesthesiologists. HR/RR: heart rate/respiratory rate ratio; IA: intra-abdominal; RV: right ventricular.
0 (0)
0.121
22 (22)
0.368
7 (7)
0.537
6 (14)
34 (34)
0.001
0 (0)
29 (29)
< 0.001
2 (4)
15 (15)
0.014
Ultrasound
15 (34)
27 (27)
0.357
Thermodilution
23 (52)
37 (37)
0.046
2 (4)
4 (4)
1.000
Oesophageal Doppler
PPV: respiratory arterial pulse pressure variation; PVI: plethysmographic variability index; SVV: stroke volume variations. Values are expressed as number (%).
M.-O. Fischer et al. / Anaesth Crit Care Pain Med 34 (2015) 29–34
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Declared criteria used to decide fluid challenge (%) 100
*
90 80 70 60 50
* *
40
* *
30 20
*
*
10 0
Fig. 4. Declared criteria used to decide fluid challenge implementation at the bedside for the residents (dark gray) and qualified intensivists and anaesthesiologists (light gray). *P < 0.05 residents vs. qualified intensivists and anaesthesiologists. PPV: pulse pressure variation; PLR: passive leg-raising; PVI: plethysmographic variability index; SVV: stroke volume variation; TTE: transthoracic echocardiography; CVP: central venous pressure.
prerequisites for the use of PPV have been clearly stated in numerous publications, the confounding factors we evaluated in the current study have been scarcely reported. This last point could explain the actual low level of theoretical knowledge regarding these factors. However, physicians indicated in a previous survey that basic science information had a positive impact on their clinical practice [22]. They also indicated that basic science information was most frequently applied during practice-based learning and improvement [22]. The absence of clinical guidelines for PPV interpretation and use at bedside could also have contributed in the disappointing results we report in the present study. Finally, the absence of hemodynamic protocols for daily routine practice could also explain the misuse of PPV in the clinical vignettes [23]. In contrast, a recent study using PPV associated with a standardized hemodynamic protocol reported a decrease in perioperative morbidity [24]. A checklist was recently suggested to validate the use of PPV before performing volume expansion [25]. The current study showed that PPV was much more frequently used at the bedside to predict fluid responsiveness than previously reported in ICUs [26,27]. The purely declarative information we deal with could be responsible for an information bias during the interviews and partially explain such a difference. Interestingly, thermodilution was often used to decide a fluid challenge, whereas cardiac output monitoring has been scarcely reported in recent studies [23,26]. Again, an information bias could explain this result. Other dynamic tools were also mentioned by physicians when considering a fluid challenge, such as PLR or echocardiographic data. This last point suggests that a multiple-index approach could be more appropriate than using PPV alone for a consistent fluid challenge strategy at the bedside. We found significant differences between residents and qualified anaesthesiologists or intensivists for prerequisites, certain confounding factors and both for the interpretation of the threshold value and the gray zone concept. A plausible hypothesis is that residents have more updated readings and medical education as compared to
qualified physicians. Another explanation may be that qualified physicians who do not frequently use PPV have less knowledge of PPV than those who frequently use PPV. The limitations associated with our study should be highlighted. First, only 55% of qualified physicians were included, in contrast with 92% of residents. This can be explained by the fact that residents principally work at the university hospital and were subsequently easier to interview. Second, neither the differences between physicians nor the information-based measure of disagreement were explored with an objective method [28]. However, objective and quantitative criteria were easily recorded, although these same criteria could be considered as arbitrary and modifying the knowledge of physicians in the present study. Finally, the impact of the low level of theoretical knowledge of physicians regarding the confounding factors of PPV described in the present study was not assessed in terms of outcomes. To date, as previously reported with the pulmonary artery catheter [20,21], no relationship has been found between the level of knowledge on PPV and patient outcomes. 5. Conclusion This study demonstrated that 60% of physicians know the prerequisites for using PPV to guide fluid challenge implementation at the bedside. However, none of them correctly interpreted PPV regarding numerous recently described confounding factors. The low rate of scientific medical readings, the absence of local hemodynamic protocols and established guidelines may explain these results. Disclosure of interest The authors declare that they have no conflicts of interest concerning this article.
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M.-O. Fischer et al. / Anaesth Crit Care Pain Med 34 (2015) 29–34
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