Accuracy of Anatomical Landmarks in Locating the Internal Jugular Vein Cannulation Site among Different Levels of Anesthesia Trainees

Abstract

Background

Internal jugular vein (IJV) cannulation is a common practice procedure employed by anesthesiologists to access large central veins. The purpose of this study is to examine the accuracy of the use of superficial anatomical landmarks to locate the IJV as well as to delineate differences in accuracy at various levels of anesthesiology trainees, and staff.

Methods

We prospectively evaluated the accuracy of locating the left and right IJV on the skin surface by anesthesiology residents and board certified anesthesiologists. Twenty-four patients with body mass index (BMI) <30 and 24 morbidly obese patients with BMI > 40 were employed across all groups. Ultrasound imaging of the actual IJV course was utilized as a reference.

Results

Experienced operators (Third year residents and faculty) achieved better accuracy in locating the IJV compared to first and second year residents. Higher accuracy was achieved when the carotid pulse was used as a landmark compared to the sternocleidomastoid muscle, particularly for experienced operators in morbidly obese patients. Overall, there was no difference in accuracy between the right and left IJV, although medial deviation was greater on the left side.

Conclusion

The accuracy of locating the IJV on the skin surface improved with operator experience in our anesthesiology training program. Experienced operators improved their accuracy using the carotid pulse as the external landmark. Ultrasound may be a useful tool to improve IJV localization early during training, and for cannulation of the left IJV.

Introduction

Central venous catheters are placed in the operating room by anesthesia providers for various indications which include intravascular volume resuscitation, vasoactive medications, hemodynamic monitoring, and when peripheral intravenous access is not adequate. ¹ The right internal jugular vein (IJV) is commonly used for access to the central circulation because: 1) it is accessible during surgery, 2) has a direct route to the right atrium and 3) has a low rate of complications. Previously reported studies have shown that the adoption of real-time ultrasound (US) to guide central venous line placement has the potential to improve the placement success rate. ^2,3,4 Reports also suggest that US decreases the incidence of complications and may detect anatomic variation as well as other pathologies (e.g. thrombosis). ²,³,⁵,⁶,⁷,⁸ Other work showed no improvement in cannulation success rate, including studies of operators with substantive, ⁹,¹⁰ and no prior experience ¹¹ with IJV cannulation. The aim of our investigation was to detect the effect of (a) operator experience, (b) IJV side (left vs. right), and (c) obesity (BMI <30 vs >40) on accuracy of skin surface identification of the IJV, as confirmed by ultrasound.

Methods

Approval was obtained from the Institutional Review Board of Saint Louis University Hospital. Four study groups were assembled. They included 3 groups of anesthesia trainees (1 ^st (CA−1), 2 ^nd (CA−2), and 3 ^rd (CA−3), year of clinical anesthesia training) and one group of board certified anesthesiologists (BCA). The study included 6 operators in each of the 4 groups; each operator was asked to locate the IJV on both sides after induction of general anesthesia in patients with body mass index (BMI) <30 and morbidly obese patients with BMI >40. Operators were asked to draw the course of the IJV by marking 3 points (A, B and C) on the patient’s neck (Figure 1). The intended cannulation site was marked as point C. Point A was to be chosen at a point 3 cm above and point B was to be 3 cm below the intended cannulation site, point C. We recorded the level of clinical experience of the operator locating the IJV, the BMI of the patient, and the anatomical landmarks used (sternocleidomastoid triangle [SCM] versus carotid pulse [CP]) by operators. While maintaining the head of the patient in the same position to minimize potential movement of the selected points, the principal investigator, using US, marked the actual course of the IJV by a second line. The distance of the operators’ points from the US line were then measured. The points were recorded as positive numbers if they were medial to the US line and negative numbers if they were lateral to it (Figure 1). The average adult IJV is 1.3 cm ¹² wide; if operators’ points were within 5 mm of the course of the IJV as determined by US, they were considered accurate. Actual cannulation of the IJV was not performed. CA−1 and CA−2 groups were combined into Group A (inexperienced operators) while CA−3 and BCA were combined into Group B (experienced operators). In our practice, US was available for at least 3 years prior to the initiation of the study. It continues to be available in our operating room but is not used routinely for central line placement.

Figure 1.

Diagram showing the 3 points required for marking the course of the internal jugular vein.

Statistical Analysis: SPSS V. 11 for Macintosh (SPSS Inc., Chicago, IL) was used to tabulate and analyze data. Fisher’s Exact test and chi-square were used to compare groups where appropriate. Analysis of Variance (ANOVA) was used to perform multiple comparisons between groups.

Results

1. Operator Experience: Overall, fifty-two (52/96, 54%) of the operator-marked points were marked within 5 mm of the actual course of the IJV on both sides. One way analysis of variance showed that group B was able to better identify the actual location of the IJV (32/48, 67%) compared to group A (20/48, 42%). Independent of all other variables, these findings are statistically significant ANOVA, p=0.014, Table 1 summarizes the deviation distances of the 4 groups on each side. Figure 2 plots the 95% confidence intervals.

Table 1:

The effect of greater experience on accuracy locating the IJ vein.

Level of training	RIJV*	Mean deviation**	LIJV*	Mean deviation**
CA-1(n=12)	3(25%)	−3.8±10.4 mm	7(58%)	+2.6±12.9 mm
CA-2(n=12)	6(50%)	−0.6±9.0 mm	4(33%)	+3.4 ±14.0 mm
CA-3(n=12)	9(75%)	+0.4±6.8 mm	9(75%)	+2.1 ±6.8 mm
BCA(n=12)	8(67%)	−0.25±6.9 mm	6(50%)	+1.6 ±5.6 mm
Total	26 (54%)		26 (54%)

^*Percent of mark placement within 5 mm of the IJV identified by ultrasound. Negative values lateral and positive values are medial to ultrasound reference point.

^**Mean deviation ±SD from ultrasound reference point

Figure 2.

Operators’ deviation from US identified right and left IJVs, by experience level. Mean deviation from actual cannulation site in both the left and right IJV. Note operators’ tendency to deviate medially when locating the IJV on the left side across all groups.

2. Side of the IJV: Group A identified the actual location of the right IJV with 38% (9/24) accuracy compared to 71% (17/24) in group B which was statistically significant (p=0.02). Group A accurately identified the location of the left IJV in 46% (11/24) of patients compared to 63% (15/24) in Group B (p=0.2). Overall accuracy locating the right IJV was 71% (17/24) compared to 63% (15/24) in group B (p=0.3). In both groups, operator marked points deviated medially to a greater extent for the left compared to the right IJV (p=0.024; see also table 1 and figure 3.

Figure 3.

Overall operators’ accuracy in locating right and left IJVs reflecting operators with 5 mm or more deviation from the actual course of the IJV on both sides.

3. BMI: Sixty percent (29/48) of IJVs were accurately identified in patients with BMI <30 compared to 48% (23/48) in patients with BMI >40 (p=0.8). The effect of BMI was not statistically significant regardless of operator experience

4. External Landmark Used: Group A utilized SCM as a landmark in 54% of patients compared to 63% by Group B. Overall, accuracy of locating the IJV ws not affected by selection of external landmarks (SCM vs CP; p=0.4). In patients with BMI >40, use of the CP landmark contributed to accurate IJV identification in 71% (17/24) versus 42% (10/24) when SCM was used. As shown in figure 4, for patients with BMI < 30 the use of SCM as a landmark located the IJV in 18/32 (56%) and in 10/24 (42%), when CP was used In Group A, the SCM and the CP provided similar accuracy in locating the IJV (p=0.5). The CP landmark was superior to SCM when used by Group B, (p= 0.01) particularly in morbidly obese patients (p=0.007).

Figure 4.

Anatomical landmarks and IJV localization accuracy. Figure (4a) shows the effect of the anatomical landmarks used on accuracy of locating the IJV in patients with BMI < 30 while Figure (4b) depicts the same in patients with BMI >40.

Within = < 5 mm of the actual IJV location

Outside = > 5 mm of the actual IJV location

Discussion

The routine use of real-time US guidance during central line insertion has been advocated by many authors to improve success rate and decrease complications. ¹¹,¹³ Evidence to suggest that ultrasound use confers any advantage in the hand of the experienced anesthesiologists is lacking. ¹³,¹⁴ Our results show that experienced operators achieved greater accuracy of locating IJV on the skin surface. Our findings are consistent with the opinion voiced by Rothschild that experienced anesthesiologist may continue to place most central lines without US guidance. In his opinion, immediate availability, the nature of emergency cases anesthesiologists usually deal with and the high number of central lines placed by anesthesiologists may justify such practice. ¹⁴

Right IJV cannulation is the most commonly used central venous access procedure in the operating room. In our study, experienced operators located the IJV fairly well on both sides. However, there was a greater tendency to deviate medially on the left side risking potential carotid artery puncture, which was statistically significant. This may be due lesser experience in cannulation of left IJV compared to the right. IJV location is highly consistent in relation to the carotid artery with rare exceptions, which make using this anatomical landmark rational. In a study of 188 patients, only one IJV was located medial to the carotid artery. ¹⁵ In our study, experienced operators used this landmark to achieve better accuracy. Morbid obesity did not affect the accuracy of locating the IJV on either side. However, utilizing CP as an anatomical landmark improved experienced operators’ accuracy of locating the IJV in morbidly obese patients.

Published data reports inadvertent carotid puncture during IJV cannulation as the most common complication which ranges from 3 to 10% without US guidance; it is 1 % if ultrasound is used. ¹⁶,¹⁷ While carotid puncture is significantly lower with US use, it is unknown if carotid puncture increases overall procedure morbidity or changes patient outcome. In this study, medial deviation of operator marked points decreased progressively with operator experience. This likely decreases the risk of carotid artery puncture if the actual procedure is to be performed. However, the observed greater medial deviation in locating for left IJV cannulation may warrant US use for left-sided approaches.

Anesthesiologists face emergencies that require quick insertion of large bore central lines for resuscitation. It is the view of the authors that thorough knowledge of the anatomical landmarks of the different approaches is a requisite for safe and timely insertion, as US equipment may not be immediately available, may make the procedure more complex and delay the resuscitation. The additional equipment and manipulation associated with real-time US guidance for central venous catheters (CVCs) insertion may increase the rate of catheter-related infections, but published studies have not included these complications. ¹⁸ Placing CVCs with US guidance added 30 seconds to several minutes which may result in an unacceptable delay in emergency resuscitation. ¹⁶

This study is limited by the small number of subjects in each group. Although statistical analysis used was tailored to detect difference among small groups clinically significant differences might have been missed in some comparisons due to small sample size and heterogeneity of operators. Actual insertion of IJV was not required for the study purpose. Interpretation of our results should take into account that our results relate to localization but not cannulation success.

The greatest benefit of US guidance may apply to operators in training and for high-risk cases, such as patients requiring mechanical ventilation, hemodialysis, or who are coagulopathic. On the other hand, routine US use may make the trainees depend solely on this technology for CVC insertion and lessen their skills in the use of the anatomical landmarks. Incorporating real-time US-guided techniques with an approach that uses traditional anatomical landmarks may provide additional valuable learning benefits to new operators. ¹⁵

Conclusion

We found that operator experience improved the accuracy of locating the IJV using standard anatomical landmarks. For experienced operators, carotid pulse may prove to be a better landmark than SCM in locating the IJV in morbidly obese patients. Operators tended to err medially more often on the left than on the right side of the neck. Ultrasound may be a useful tool early during training and for cannulation of the left internal jugular vein.