#### What We Already Know about This Topic

#### What This Article Tells Us That Is New

^{1}Commonly used airway management techniques include bag-and-mask ventilation and laryngoscopic orotracheal intubation. Learning curves for various anesthesia procedures have been evaluated using various statistical approaches,

^{2–8}but few studies have investigated learning curves for bag-and-mask ventilation.

^{9}Cusum charts have been used for surgical skill assessment.

^{10}The control chart is especially sensitive to short runs of failures and identifies them quickly. Hence, the trainee who has difficulty in a particular technique can be detected, and immediate corrective measures can be taken.

#### Materials and Methods

##### Protocol and Measurements

##### Data Analysis

##### Standard Cusum.

Equation (Uncited) Image Tools |
Equation (Uncited) Image Tools |
Equation (Uncited) Image Tools |

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Equation (Uncited) Image Tools |

^{11,12}But considering that our interns were nonanesthesiologists rotating in anesthesia for only 3 months and that we did not permit physical assistance from instructors to facilitate mask ventilation, we set the acceptable failure rate (p0) for mask ventilation at 20% (

*i.e.*, four times the reported failure rate among experienced anesthesiologists). As is customary for cusum analysis, the unacceptable failure rate (p1) was set at twice p0 or 40%. The probability of type I (α) and II (β) errors were each set to 0.1.

*e.g.*, Cormack and Lehane grade 3 and 4) has been reported to be as high as 10%.

^{11–14}Again considering the inexperience of our interns, we set the acceptable failure rate (p0) for laryngoscopic tracheal intubation at 20% and unacceptable failure rate (p1) at twice p0 (40%) and type I and II errors at 0.1. These parameters were identical to those used in a similar study by de Oliveira Filho.

^{2}

##### Risk-adjusted Cusum.

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Table 3 Image Tools |

^{15}A risk score for each patient was first calculated as the estimated probability of failure predicted as a function of traditional difficult mask ventilation and intubation risk factors

^{14,16,17}(tables 2 and 3) using logistic regression. The risk-adjusted cusum chart was then formed by adding 1 minus the individual patient risk score to the cumulative score for each failure and subtracting the risk score for each failed attempt. The cusum at time t is, thus, c

_{t}= c

_{t − 1}+ (x

_{t}− x

_{0}), where c

_{t − 1}is the cusum through the previous attempt, x

_{t}is 1 for failure and 0 for success (observed), and x

_{0}is the estimated risk for the patient being intubated or ventilated at time t (expected). Interns whose accumulated observed rate of failure is generally consistent with the expected values for the patients they intubated will have scores near the zero line, whereas those performing better or worse than expected will have scores below and above the zero line, respectively.

#### Results

##### Mask Ventilation

Table 4 Image Tools |
Fig. 2 Image Tools |

*P*< 0.001).

^{2}, Mallampati 3 or 4 (

*vs.*1, 2), age more than 57 yr, and Mandibular protrusion (severely limited), which have been shown to be associated with difficult mask ventilation. In the risk-adjusted observed − expected learning curves for mask ventilation (fig. 1B), 10 interns (66%) finished their attempts below the zero line and, thus, on average performed better than expected, given the level of difficulty of the patients they encountered. This figure is quite different in shape to the standard cusum in figure 1A for most interns, reflecting the distinct cusum formulae (and interpretations) and the varying levels of patient difficulty experienced across interns.

##### Orotracheal Intubation

*P*< 0.001). Under a more stringent specification of p0 = 10%, only one intern crossed the intubation acceptable failure rate decision limit.

*P*= 0.025 (McNemar's test).

#### Discussion

*et al.*

^{6}suggested that 20 consecutive, successful tracheal intubations might be appropriate for a student to perform solo anesthesia. However, this approach does not allow statistical inference. Three additional studies examined the learning process for tracheal intubation using statistical approaches. Kopacz

*et al.*,

^{5}using the pooled cumulative success rate at groups of five attempts, demonstrated that a 91% tracheal intubation success rate was achieved after 45 attempts. Konrad

*et al.*,

^{4}using a least-square fit model and Monte Carlo procedures, demonstrated that 90% success rates for tracheal intubation were achieved after 57 attempts. However, these studies did not report the number of attempts at procedures corresponding to certain percentiles of the subjects attaining acceptable failure rate on a time-to-event curve. de Oliveira Filho,

^{2}using the same statistical approach as our study, demonstrated that four of seven participants attained a 20% acceptable failure rate at intubation, and they did so after mean of 43 attempts.

^{2}who required successful intubation after a single laryngoscopy without any physical assistance, or Konrad

*et al.*,

^{4}who required a successful procedure within two attempts without physical assistance. However, we consider it appropriate for interns to request external laryngeal pressure to optimize the laryngoscopic view and regard it as a reflection of their understanding of upper airway anatomy. Thus, we consider our criteria of successful intubation to be clinically relevant. Furthermore, even experienced intubators sometimes require a second attempt; we, thus, do not consider a second attempt to be an overall failure to intubate.

^{3,4,7,18}In this study, acceptable failure rate for tracheal intubation was set at twice the maximum reported incidence of suboptimal laryngoscopic view for intubation (

*i.e.*, Cormack and Lehane grades 3 and 4).

^{11–14}This rather generous acceptable failure rate was chosen because our interns were nonanesthesiologists and presumably would only occasionally be required to manage airways. This acceptable failure rate is also used in a previously performed similar study by de Oliveira Filho,

^{2}making it possible to directly compare our interns' performances with anesthesia residents from another site.

*a priori*chosen 20% limit, but would have been underpowered for a stricter 10% limit.

^{2}This may be explained by the difference in the criteria of successful intubation between the two studies. De Oliveira Filho

^{2}allowed only one attempt at laryngoscopy with no physical assistance for intubation to be considered successful; in contrast, we allowed two laryngoscopy attempts and physical assistance in the form of external laryngeal pressure, which perhaps better reflects how intubation is normally approached.

*i.e.*, h0) with mask and intubation. We nonetheless observed a difference in the proportion of interns who crossed the decision limit for the respective methods: with mask ventilation, 93% of our interns crossed the lower decision limit after 27 ± 13 procedures, which was significantly greater than the proportion for intubation, which was 60%. Median time to cross h0 with a 20% acceptable failure rate was similar between mask ventilation and intubation, but intubation can be a technique associated with more interindividual variability in initial skill acquisition than mask ventilation. Although the higher proportion of interns crossed the acceptable failure rate decision limit for mask ventilation than intubation, for those infrequently managing the patient's airway, not only ease of skill acquisition but also ease of skill maintenance is of clinical importance. A previous report showed occasional performance of intubation does not ensure skill maintenance.

^{19}No comparable reports for mask ventilation are available, and the evaluation of skill maintenance in mask ventilation is warranted. In the current study, many patients were paralyzed, which facilitates mask ventilation. Per protocol, patients who had difficult airways were excluded because they would have been designated for awake intubation. Therefore, caution needs to be used to apply these data to the urgent floor airway situation where patients are not fasting, bed position is suboptimal, and an efficient respiratory circuit of an anesthesia machine is not available.

^{20}where a baseline probability of failure is specified for particular patients or groups of patients, and the curve monitors

*a priori*reduction or increase from baseline.