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Positive End-Expiratory Pressure to Increase Internal Jugular Vein Size Is Poorly Tolerated in Obese Anesthetized Adults

Downey, Laura A., MD; Blaine, Kevin P., MD, MPH; Sliwa, Jan, MD; Macario, Alex, MD, MBA; Brock-Utne, John, MD, PhD

doi: 10.1213/ANE.0000000000000347
Patient Safety: Brief Report
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BACKGROUND: Central venous cannulation is technically challenging in obese patients. We hypothesized that positive end-expiratory pressure (PEEP) increases the size of the internal jugular vein (IJV) in obese adults.

METHODS: The circumference and cross-sectional area of the IJV were measured in obese patients under general anesthesia at PEEP 0, 5, and 10 cm H2O. Results are reported as means ± SE.

RESULTS: PEEP at 10 cm H2O was tolerated by 18 of 24 obese patients. Each 5 cm H2O of PEEP increased the cross-sectional area by 0.16 ± 0.02 cm2 (P < 0.0001) and the circumference by 0.23 ± 0.03 cm (P < 0.0001).

CONCLUSIONS: PEEP modestly increases the size of the IJV in obese adults but was poorly tolerated because of hypotension.

From the Department of Anesthesiology, Pain, and Perioperative Medicine, Stanford University Medical Center, Stanford, California.

Laura A. Downey, MD, is currently affiliated with the Department of Anesthesia, Boston Childrens Hospital Boston, Boston, Massachusetts.

Kevin P. Blaine, MD, MPH, is currently affiliated with the Critical Care Medicine Department of the National Institutes of Health Clinical Center, Bethesda, Maryland.

Accepted for publication May 9, 2014.

Funding: This study was supported solely with departmental funds.

The authors declare no conflicts of interest.

This report was previously presented, in part, at the IARS Annual Meeting 2013.

Reprints will not be available from the authors.

Address correspondence to Laura A. Downey, MD, Department of Anesthesia, Boston Childrens Hospital, 300 Longwood Ave, Boston, MA 02115. Address e-mail to ladowney@gmail.com.

Catheterization of the internal jugular vein (IJV) is performed more than 5 million times annually in the United States.1 In obese patients, it is often difficult to place central venous catheters.2 In patients of normal body weight, previous work has shown that positive end-expiratory pressure (PEEP) in supine, mechanically ventilated patients can increase the cross-sectional area (CSA) of IJVs by 40%–76%3,4; those studies excluded obese patients because it is not clear that the IJV of obese patients would respond to PEEP due to the distorted anatomy and pressure alterations associated with obesity. We sought to quantify the effect of PEEP on right IJV CSA and circumference in anesthetized obese patients.

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METHODS

After receiving approval from the Stanford Medical Center IRB and with written informed patient consent, obese patients (body mass index >30 kg/m2) ASA physical class I–III undergoing elective surgery under general endotracheal anesthesia were enrolled in this study.

After induction of general anesthesia and endotracheal intubation, the patient was placed in a supine position on a level bed with the head in a neutral position. The circumference and CSA of the right IJV were measured at end inspiration from the midpoint between the mastoid process and sternal notch using minimal pressure from a 2D ultrasound 13–6-MHz linear transducer (M-Turbo, SonoSite, Bothell, WA). The circumference and CSA were calculated using the SonoSite planimetry software. CSA and circumference were measured incrementally from lowest to highest with PEEP 0, 5, and 10 cm H2O with 3 minutes between measurements to minimize the effect of abrupt changes. Data collection was terminated if arterial blood pressure decreased to <90/<60, heart rate increased to >100, peak airway pressures increased to >40 cm H2O, or oxygen saturation by pulse oximetry decreased to <94%. Demographic data are compared with descriptive statistics. The 2 reported P values have been Bonferroni-corrected for the 2 mixed-effects models. Data are presented as means ± SD for baseline characteristics and unadjusted CSA and circumference. Data are presented as means ± SD for demographics and unadjusted CSA and circumference. The effect of PEEP on CSA and circumference was determined by separate mixed-effects linear regression. Regression parameters are presented as ±SE. Regression coefficients and residual SE are presented to account for outliers. Analysis was performed with the statistical program R (R version 3.0.2, 2013, The R Foundation for Statistical Computing, Vienna, Austria).

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RESULTS

Twenty-four patients were enrolled, of whom 6 patients (25%) did not tolerate PEEP at 10 cm H2O due to systemic hypotension and were treated as missing data for the regression analysis. Patient demographics are included in Table 1. Unadjusted CSA and circumference measurements are presented in Table 2. There was no significant difference in slope between 2 separate regression lines from 0 to 5 and 0 to 10 cm H2O for either CSA (P = 0.682) or circumference (P = 0.739), and PEEP was therefore included as a single-ranked parameter in the mixed-model linear regression. The regression for CSA (adjusted r2 = 0.8927, residual SE ±0.1816) reported an increase of 0.16 ± 0.02 cm2 (P < 0.0001) for each 5 cm H2O of PEEP; the regression for circumference (adjusted r2 = 0.8984, residual SE ±0. 2899) returned an increase of 0.23 ± 0.03 cm (P < 0.0001) for each 5 cm H2O of PEEP.

Table 1

Table 1

Table 2

Table 2

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DISCUSSION

Obesity presents challenges for IJV catheterization. Subcutaneous tissue increases the depth of the target vessel and hides anatomic landmarks, such as the sternocleidomastoid muscle and carotid artery pulsation. The pressure necessary to pierce redundant tissue may compress the vessel in hypovolemic patients. Adipose tissue may require an excessively acute angle for needle insertion or a suboptimal position of an ultrasound probe. Techniques to improve the safety margin include the Trendelenburg position and valsalva maneuvers, both of which increase the CSA of the IJV. Our study suggests that PEEP can increase the size of the IJV in obese patients. Prior studies of nonobese patients demonstrated that PEEP can increase the IJV by approximately half with the combination of 10 cm H2O PEEP and the Trendelenburg position.5–7 Interestingly, one previous study6 also demonstrated a subset of patients with higher body mass index that did not increase CSA beyond 20%, despite PEEP and dynamic maneuvers. Similar to this work, we found an increment in CSA at PEEP 10 cm H2O of approximately 25%, which may be too small to justify the risk of hypotension. Abdominal compression from greater mass in obese patients may contribute to baseline venous distention pressure that PEEP may only add to modestly.

It is important to recognize that 6 of 24 patients (25%) did not tolerate 10 cm H2O PEEP without hypotension. A recent study in a predominantly nonobese population also demonstrated hypotension after induction, although with PEEP >20 cm H2O.8 Contributing factors may include recent use of induction drugs, relative hypovolemia from preoperative fast, and transiently increased intrathoracic pressure from experimentally higher PEEP. Solo practitioners especially may be concerned about arterial blood pressure management of unstable patients after donning sterile barriers for central venous cannulation. It may be advisable to attempt other maneuvers to optimize IJV cannulation in obese patients unless those techniques are contraindicated or logistically impractical.

Limitations to this study include variability in ultrasound measurements and small sample size. We did not perform measurements in the Trendelenburg position to isolate the effect of PEEP, although most practitioners would probably combine PEEP with a head-down position. In summary, while we demonstrated an increase in size for the IJV in obese patients from higher PEEP, we do not recommend using PEEP ≥10 cm H2O solely to facilitate IJV cannulation in obese patients because of hemodynamic instability.

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DISCLOSURES

Name: Laura A. Downey, MD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: Laura A. Downey has seen the original study data, reviewed the analysis of the data, approved the final manuscript, and is the author responsible for archiving the study files.

Name: Kevin P. Blaine, MD, MPH.

Contribution: This author helped analyze the data and write the manuscript.

Attestation: Kevin P. Blaine reviewed the analysis of the data and approved the final manuscript.

Name: Jan Sliwa, MD.

Contribution: This author helped design the study, conduct the study, and write the manuscript.

Attestation: Jan Sliwa has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

Name: Alex Macario, MD, MBA.

Contribution: This author helped design the study, analyze the data, and write the manuscript.

Attestation: Alex Macario reviewed the analysis of the data and approved the final manuscript.

Name: John Brock-Utne, MD, PhD.

Contribution: This author helped design the study, conduct the study, analyze the data, and write the manuscript.

Attestation: John Brock-Utne has seen the original study data, reviewed the analysis of the data, and approved the final manuscript.

This manuscript was handled by: Sorin J. Brull, MD, FCARCSI (Hon).

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REFERENCES

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