82
Correspondence
types of anesthesia machines used in this study employed piston-driven compliance-compensated ventilators, the ability to maintain a steady delivered volume is achieved when a breathing circuit compliance check is performed each time the circuit configuration changes. For example, when using “accordion-type” circuits, the delivered VTs can vary by as much as 25% if the circuit is extended after the compliance check. Importantly, the VTs reported by the ventilator’s display may not correlate with the volume realized by the airway under these circumstances [2]. Thus, the type of circuit (collapsible vs noncollapsible), when and how often compliance checks were performed, and some data regarding the accuracy of the values displayed on the monitor compared with similar measurements taken at the patient’s airway should be provided. Depth of anesthesia may increase over time, rendering ventilation by facemask more efficient. This is of particular importance in the absence of administered neuromuscular blocking drugs. Apnea induced by intravenous (IV) administration of fentanyl and propofol does not ensure adequate depth of anesthesia to blunt motor responses or upper airway reflex activation in response to a vigorous jaw thrust in all patients [3]. Further, it is unclear from the reported methods whether volatile anesthetic gas was started during mask ventilation, as would be done routinely following IV induction. If so, documentation and control by study design or statistical methodology of the end-tidal gas concentration would be an important factor for consideration. The fact that significant improvements in VTs occurred only when a patient started with the E-C clamp (EC) grip technique and crossed over to the TE grip technique, but did not worsen when going from TE to EC grip techniques, suggests that the outcome was dependent on other factors aside from the grip. This “sequence effect” was noted by the authors in their discussion, but no consideration was given to how these factors might have confounded their main results. Finally, the size, type, and management of the oropharyngeal airway were not described. Incorrectly inserted or malpositioned devices hinder mask ventilation. Progressive anterior displacement from a fully seated position with the proximal end deep in the hypopharynx may limit the efficiency of ventilation and be of particular importance in patients with obstructive sleep apnea [4]. In summary, it very well may be that the technique the authors propose is superior to the traditional E-C clamp technique, but their study, as described, limits the ability of the reader to agree with that conclusion. Aaron M. Joffe DO (Associate Professor of Anesthesiology) University of Washington Harborview Medical Center Seattle, WA 98104, USA E-mail address: [email protected]
Richard E. Galgon MD, MS (Assistant Professor of Anesthesiology) University of Wisconsin School of Medicine and Public Health, Madison, WI 53792, USA http://dx.doi.org/10.1016/j.jclinane.2013.07.010
References [1] Gerstein NS, Carey MC, Braude DA, et al. Efficacy of facemask ventilation techniques in novice providers. J Clin Anesth 2013;25:193-7. [2] Bachiller PR, McDonough JM, Feldman JM. Do new anesthesia ventilators deliver small tidal volumes accurately during volumecontrolled ventilation? Anesth Analg 2008;106:1392-400. [3] Townsend R, Brimacombe J, Keller C, Wenzel V, Herff H. Jaw thrust as a predictor of insertion conditions for the proseal laryngeal mask airway. Middle East J Anesthesiol 2009;20:59-62. [4] Hillman DR, Platt PR, Eastwood PR. The upper airway during anaesthesia. Br J Anaesth 2003;91:31-9.
Reply We welcome the interest and critique of Joffe and Galgon regarding our study, “Efficacy of facemask ventilation techniques in novice providers” [1]. They raise a number of insightful points and concerns regarding various facets of our study. We appreciate the opportunity to respond. Drs. Joffe and Galgon suggest that the use of a pneumotachograph (PNT) would increase the study validity and power (by decreasing random error), with reference to PNT as the gold standard for accurately measuring pressures and flows versus the use of the anesthesia machine’s sensors. However, due to the sequencing and crossover design, any error introduced by measurements would not be systematically biased in one direction. Any effect in measurements should affect both groups equally. There is no reason to suspect bias toward higher volumes in the thenar eminence (TE) group. There are a number of other contemporary mask ventilation studies that do not utilize a PNT or specify that a PNT is used for flow or volume measurements, as this does not represent the typical monitoring at many centers [2–5]. Using standard anesthesia machine-generated measurements lends face validity to our study, as this represents the manner in which ventilatory indices are typically assessed. The concern about increasing depth of anesthesia over time is similarly obviated by our crossover design and contradicted by the results themselves. Joffe and Galgon contend that an initially light anesthesia level may be responsible for the poor performance of the E-C clamp technique (EC) in the EC-first group. However, one would then need to explain why the TE technique was superior when used first, as shown in their Figure 4 and specifically tested in the Results and reiterated in the Discussion [1]. This makes it less likely that anesthesia depth was a confounder and perhaps progression of anesthesia depth may permit the EC grip as a fair reasonable second technique option.
Correspondence There is the possibility that the described sequence-effect indicates some sort of confounding; something is occurring beyond grip quality. We reviewed these possibilities in our discussion. The TE technique also may make it easier to position the head correctly, and without a protocoled step of repositioning the head to a neutral position, switching to EC would provide the benefit of a well-positioned head and neck. We believe (and our findings support) that some of these factors are inherent in the grips' ergonomics, especially for novices. The existence of confounding by the only other factor mentioned (increasing anesthesia depth) is contradicted by the study results. Finally, the concern regarding our oropharyngeal airway use is also mitigated by crossover design. If the oropharyngeal airway was incorrectly sized, it was incorrectly sized when the patient was ventilated with the TE grip and the EC grip. If inaccurate sizing or improper insertion was a factor in our findings, one would expect that the second technique would also produce a worse result. Neither group’s ventilation quality became significantly worse with time. Neal Stuart Gerstein MD (Associate Professor) Timothy Randal Petersen PhD (Research Coordinator, Adjunct Assistant Professor) Isaac Tawil MD, FCCM (Assistant Professor) Darren Alan Braude MD (Professor) Department of Anesthesiology and Critical Care University of New Mexico School of Medicine Albuquerque, NM 87131,USA E-mail address: [email protected] http://dx.doi.org/10.1016/j.jclinane.2013.09.004
References [1] Gerstein NS, Carey MC, Braude DA, et al. Efficacy of facemask ventilation techniques in novice providers. J Clin Anesth 2013;25:193-7. [2] Otten D, Liao MM, Wolken R, et al. Comparison of bag-valve-mask hand-sealing techniques in a simulated model. Ann Emerg Med 2014;63:6-12.e3. [3] Davidovic L, LaCovey D, Pitetti RD. Comparison of 1- versus 2-person bag-valve-mask techniques for manikin ventilation of infants and children. Ann Emerg Med 2005;46:37-42. [4] Dörges V, Ocker H, Hagelberg S, Wenzel V, Schmucker P. Optimisation of tidal volumes given with self-inflatable bags without additional oxygen. Resuscitation 2000;43:195-9. [5] Wagner-Berger HG, Wenzel V, Voelckel WG, et al. A pilot study to evaluate the SMART BAG: a new pressure-responsive, gas-flow limiting bag-valve-mask device. Anesth Analg 2003;97:1686-9.
83
Fig. 1
View of typical tourniquet placement, with no veins seen.
eral venous catheter placement may be difficult, especially at the extremes of age or if the patient is obese, dark skinned, an IV drug abuser, hypotensive, or has multiple injuries limiting the number of limbs available [1]. Various methods have been used to obtain IV access, including use of warming devices, ultrasound, and Doppler and blood pressure cuffs. The Esmarch bandage is a common device used in orthopedic surgery for exsanguination of the extremities. It is an elastic pressure bandage that compresses the vessel in the direction applied. It is inexpensive and commonly available. Using an Esmarch bandage in a reverse fashion is effective for pooling of blood temporarily, and hence, makes veins prominent, which may help in obtaining difficult IV access. A 61 year old woman was scheduled for lumbar epidural steroid injection with sedation. Veins were noticeably frail, thin, and deep [Fig. 1]. Intravenous access was attempted at two different sites in both upper limbs using standard tourniquet technique. An Esmarch bandage [latex-free, 10 cm × 270 cm (4 in × 9 ft); De Royal, Powell, TN, USA] was wrapped tightly around the left arm in a reverse fashion (proximal to distal), from arm to forearm [2]. This
Difficult intravenous access: reverse Esmarch bandaging in the ambulatory setting To the Editor: Difficult intravenous (IV) access may be a concern encountered by anesthesiologists in everyday practice. Periph-
Fig. 2 View of a reverse-wrapped Esmarch bandage (De Royal, Powell, TN, USA), showing the prominent engorged veins.
Correspondence
types of anesthesia machines used in this study employed piston-driven compliance-compensated ventilators, the ability to maintain a steady delivered volume is achieved when a breathing circuit compliance check is performed each time the circuit configuration changes. For example, when using “accordion-type” circuits, the delivered VTs can vary by as much as 25% if the circuit is extended after the compliance check. Importantly, the VTs reported by the ventilator’s display may not correlate with the volume realized by the airway under these circumstances [2]. Thus, the type of circuit (collapsible vs noncollapsible), when and how often compliance checks were performed, and some data regarding the accuracy of the values displayed on the monitor compared with similar measurements taken at the patient’s airway should be provided. Depth of anesthesia may increase over time, rendering ventilation by facemask more efficient. This is of particular importance in the absence of administered neuromuscular blocking drugs. Apnea induced by intravenous (IV) administration of fentanyl and propofol does not ensure adequate depth of anesthesia to blunt motor responses or upper airway reflex activation in response to a vigorous jaw thrust in all patients [3]. Further, it is unclear from the reported methods whether volatile anesthetic gas was started during mask ventilation, as would be done routinely following IV induction. If so, documentation and control by study design or statistical methodology of the end-tidal gas concentration would be an important factor for consideration. The fact that significant improvements in VTs occurred only when a patient started with the E-C clamp (EC) grip technique and crossed over to the TE grip technique, but did not worsen when going from TE to EC grip techniques, suggests that the outcome was dependent on other factors aside from the grip. This “sequence effect” was noted by the authors in their discussion, but no consideration was given to how these factors might have confounded their main results. Finally, the size, type, and management of the oropharyngeal airway were not described. Incorrectly inserted or malpositioned devices hinder mask ventilation. Progressive anterior displacement from a fully seated position with the proximal end deep in the hypopharynx may limit the efficiency of ventilation and be of particular importance in patients with obstructive sleep apnea [4]. In summary, it very well may be that the technique the authors propose is superior to the traditional E-C clamp technique, but their study, as described, limits the ability of the reader to agree with that conclusion. Aaron M. Joffe DO (Associate Professor of Anesthesiology) University of Washington Harborview Medical Center Seattle, WA 98104, USA E-mail address: [email protected]
Richard E. Galgon MD, MS (Assistant Professor of Anesthesiology) University of Wisconsin School of Medicine and Public Health, Madison, WI 53792, USA http://dx.doi.org/10.1016/j.jclinane.2013.07.010
References [1] Gerstein NS, Carey MC, Braude DA, et al. Efficacy of facemask ventilation techniques in novice providers. J Clin Anesth 2013;25:193-7. [2] Bachiller PR, McDonough JM, Feldman JM. Do new anesthesia ventilators deliver small tidal volumes accurately during volumecontrolled ventilation? Anesth Analg 2008;106:1392-400. [3] Townsend R, Brimacombe J, Keller C, Wenzel V, Herff H. Jaw thrust as a predictor of insertion conditions for the proseal laryngeal mask airway. Middle East J Anesthesiol 2009;20:59-62. [4] Hillman DR, Platt PR, Eastwood PR. The upper airway during anaesthesia. Br J Anaesth 2003;91:31-9.
Reply We welcome the interest and critique of Joffe and Galgon regarding our study, “Efficacy of facemask ventilation techniques in novice providers” [1]. They raise a number of insightful points and concerns regarding various facets of our study. We appreciate the opportunity to respond. Drs. Joffe and Galgon suggest that the use of a pneumotachograph (PNT) would increase the study validity and power (by decreasing random error), with reference to PNT as the gold standard for accurately measuring pressures and flows versus the use of the anesthesia machine’s sensors. However, due to the sequencing and crossover design, any error introduced by measurements would not be systematically biased in one direction. Any effect in measurements should affect both groups equally. There is no reason to suspect bias toward higher volumes in the thenar eminence (TE) group. There are a number of other contemporary mask ventilation studies that do not utilize a PNT or specify that a PNT is used for flow or volume measurements, as this does not represent the typical monitoring at many centers [2–5]. Using standard anesthesia machine-generated measurements lends face validity to our study, as this represents the manner in which ventilatory indices are typically assessed. The concern about increasing depth of anesthesia over time is similarly obviated by our crossover design and contradicted by the results themselves. Joffe and Galgon contend that an initially light anesthesia level may be responsible for the poor performance of the E-C clamp technique (EC) in the EC-first group. However, one would then need to explain why the TE technique was superior when used first, as shown in their Figure 4 and specifically tested in the Results and reiterated in the Discussion [1]. This makes it less likely that anesthesia depth was a confounder and perhaps progression of anesthesia depth may permit the EC grip as a fair reasonable second technique option.
Correspondence There is the possibility that the described sequence-effect indicates some sort of confounding; something is occurring beyond grip quality. We reviewed these possibilities in our discussion. The TE technique also may make it easier to position the head correctly, and without a protocoled step of repositioning the head to a neutral position, switching to EC would provide the benefit of a well-positioned head and neck. We believe (and our findings support) that some of these factors are inherent in the grips' ergonomics, especially for novices. The existence of confounding by the only other factor mentioned (increasing anesthesia depth) is contradicted by the study results. Finally, the concern regarding our oropharyngeal airway use is also mitigated by crossover design. If the oropharyngeal airway was incorrectly sized, it was incorrectly sized when the patient was ventilated with the TE grip and the EC grip. If inaccurate sizing or improper insertion was a factor in our findings, one would expect that the second technique would also produce a worse result. Neither group’s ventilation quality became significantly worse with time. Neal Stuart Gerstein MD (Associate Professor) Timothy Randal Petersen PhD (Research Coordinator, Adjunct Assistant Professor) Isaac Tawil MD, FCCM (Assistant Professor) Darren Alan Braude MD (Professor) Department of Anesthesiology and Critical Care University of New Mexico School of Medicine Albuquerque, NM 87131,USA E-mail address: [email protected] http://dx.doi.org/10.1016/j.jclinane.2013.09.004
References [1] Gerstein NS, Carey MC, Braude DA, et al. Efficacy of facemask ventilation techniques in novice providers. J Clin Anesth 2013;25:193-7. [2] Otten D, Liao MM, Wolken R, et al. Comparison of bag-valve-mask hand-sealing techniques in a simulated model. Ann Emerg Med 2014;63:6-12.e3. [3] Davidovic L, LaCovey D, Pitetti RD. Comparison of 1- versus 2-person bag-valve-mask techniques for manikin ventilation of infants and children. Ann Emerg Med 2005;46:37-42. [4] Dörges V, Ocker H, Hagelberg S, Wenzel V, Schmucker P. Optimisation of tidal volumes given with self-inflatable bags without additional oxygen. Resuscitation 2000;43:195-9. [5] Wagner-Berger HG, Wenzel V, Voelckel WG, et al. A pilot study to evaluate the SMART BAG: a new pressure-responsive, gas-flow limiting bag-valve-mask device. Anesth Analg 2003;97:1686-9.
83
Fig. 1
View of typical tourniquet placement, with no veins seen.
eral venous catheter placement may be difficult, especially at the extremes of age or if the patient is obese, dark skinned, an IV drug abuser, hypotensive, or has multiple injuries limiting the number of limbs available [1]. Various methods have been used to obtain IV access, including use of warming devices, ultrasound, and Doppler and blood pressure cuffs. The Esmarch bandage is a common device used in orthopedic surgery for exsanguination of the extremities. It is an elastic pressure bandage that compresses the vessel in the direction applied. It is inexpensive and commonly available. Using an Esmarch bandage in a reverse fashion is effective for pooling of blood temporarily, and hence, makes veins prominent, which may help in obtaining difficult IV access. A 61 year old woman was scheduled for lumbar epidural steroid injection with sedation. Veins were noticeably frail, thin, and deep [Fig. 1]. Intravenous access was attempted at two different sites in both upper limbs using standard tourniquet technique. An Esmarch bandage [latex-free, 10 cm × 270 cm (4 in × 9 ft); De Royal, Powell, TN, USA] was wrapped tightly around the left arm in a reverse fashion (proximal to distal), from arm to forearm [2]. This
Difficult intravenous access: reverse Esmarch bandaging in the ambulatory setting To the Editor: Difficult intravenous (IV) access may be a concern encountered by anesthesiologists in everyday practice. Periph-
Fig. 2 View of a reverse-wrapped Esmarch bandage (De Royal, Powell, TN, USA), showing the prominent engorged veins.
