Brian K. Parker, MD, MS; Sara Manning, MD; Michael E. Winters, MD, MBA

Disclosures

Western J Emerg Med. 2019;20(2):323-330. 

In This Article

Alterations in Circulatory Physiology

Similar to the respiratory system, the physiology of the circulatory system is altered in obese people. Alterations in circulatory physiology were first reported in 1964 by Alexander, who described the linear relationship between a patient's weight and total blood volume.[45] Greater total blood volume increases stroke volume, which ultimately leads to an increase in preload and myocardial wall tension. Ferraro and colleagues demonstrated that these physiologic changes cause an eccentric left ventricular hypertrophy, impaired ventricular relaxation, and diastolic dysfunction.[46] Diastolic dysfunction eventually leads to systolic dysfunction, pulmonary hypertension, and right ventricular hypertrophy. Together, these physiologic changes have been termed the "obesity cardiomyopathy syndrome."[47]

For the majority of ED patients, initial assessment of the circulatory system begins with a noninvasive blood pressure measurement. Importantly, standard blood pressure cuffs are often too narrow and too short for the obese patient. In many cases, this leads to an overestimation of blood pressure.[48,49] If the obese patient appears moribund, demonstrates signs of poor perfusion (i.e., cool and mottled skin), or is critically injured, the EP should consider early placement of an invasive arterial line to accurately determine the mean arterial blood pressure.[50]

Intravenous (IV) fluid administration is one of the most common interventions in critically ill ED patients. Unfortunately, obesity has been shown to be an independent risk factor for difficult IV access.[51–53] The causes of difficult IV access in the obese patient are likely multifactorial and include increased adipose tissue, increased tissue edema, and smaller vein caliber. Alternatives to peripheral IV access include the intraosseous route and central venous access. Importantly, these alternatives also have limitations and complications in the obese patient. Kehrl and colleagues demonstrated that a standard 25 millimeter (mm)-intraosseous needle might not be long enough for patients with a BMI greater than 43 kg/m2.[54] In these severely obese patients, the EP should consider using an extended 45-mm intraosseous needle.[54] However, in a study of out-of-hospital cardiac arrest, Kawano and colleagues demonstrated worse patient outcomes in those who had intraosseous vascular access compared with those who had IV access.[55]

Ultrasound guidance is rapidly becoming an essential tool in scenarios involving difficult IV access.[56] The use of longer catheters reduces the rate of IV dislodgement,[56] and ultrasound guidance during cannulation has a higher successful rate than the standard blind approach.[57] Additionally, Au et al. demonstrated that the use of ultrasound guidance for IV access reduced the need for central venous access.[58]

Placement of a central venous line in an obese patient can be problematic. Risks associated with central venous access in the obese patient include inability to place the line, the need to use extended-length needles to assist with cannulation, and higher infection rates.[59–61] Although many physicians use a landmark approach to central venous access, this method is not reliable in obese patients.[62,63] Furthermore, traditional depths of insertion are often too shallow in the obese patient.[61,64] Although EPs are trained in ultrasound-guided cannulation of the central veins, up to 40% of EDs in the U.S. do not have bedside ultrasound available.[65] Whenever possible, the EP should use ultrasound to guide central venous cannulation of the femoral, internal jugular, and subclavian veins.[65]

For patients in cardiac arrest, the delivery of high-quality cardiopulmonary resuscitation (CPR) is crucial to achieve return of spontaneous circulation. Critical components of high-quality CPR are compressions delivered at the proper rate and depth and allowing full recoil of the chest between compressions.[66] Current international guidelines for the resuscitation of adult patients in cardiac arrest recommend placement of the hands on the lower half of the sternum during CPR.[66–68] Given the increased adipose tissue of the chest wall and a more cephalad displacement of the diaphragm in obese patients, this hand location might not be the optimal position for CPR in obesity. Lee and colleagues found that the optimal hand position for CPR in obese patients might be slightly more cephalad than in non-obese patients.[67]

processing....