Head-Up Tilt Rapidly Compromises Hemodynamics in Healthy Anesthetized Swine

Abstract

The aims were to explore the effect of head-up tilt (HUT) to 30 and 60 degrees on hemodynamics and tissue oxygenation in anesthetized healthy swine. The data serve as a reference for a study of resuscitation efficacy at HUT such as during transport. Nine healthy swine (49±4 kg) were anesthetized and multiple sensors including myocardial pressure-volume loops catheter, carotid flow probe, blood pressure catheters, near infrared spectroscopy (NIRS) tissue oximetry and mixed venous oximetry (SVO2) catheter were introduced and parameters continuously recorded. Experimental protocol consisted of baseline in supine position (15 min), 30 degrees HUT (15 min), recovery at supine position (15 min) and 60 degrees HUT (5 min). Vacuum mattress was used for body fixation during tilts. We found that 30 and 60 degrees inclination led to significant immediate reduction in hemodynamic and oximetry parameters. Mean arterial pressure (mm Hg) decreased from 98 at baseline to 53 and 39, respectively. Carotid blood flow dropped to 47 % and 22 % of baseline values, end diastolic volume to 49 % and 53 % and stroke volume to 47 % and 45 % of baseline. SVO2 and tissue oximetry decreased by 17 and 21 percentage points. The values are means. In conclusions, within minutes, both 30 and 60 degrees head-up tilting is poorly tolerated in anesthetized swine. Significant differences among individual animals exist.

Assessment of the benefits of head-up preoxygenation using near-infrared spectroscopy with pulse oximetry in a swine model

“…| Significant difference vs. supine position at apnea 60 s (P = 0.0459). § Significant difference vs. supine, head-down, and head-up to supine at apnea 60 s (P = 0.035, P = 0.0096, and P = 0.0039) normovolemia, decreased cerebral oxygenation in animals [10] and healthy adult humans [23]. The present study has uniquely evaluated the benefits of head-up preoxygenation during normal and hypovolemic conditions using both pulse oximetry and NIRS.…”

“…Patients requiring emergency tracheal intubation frequently suffer from major bleeding and/or hypovolemia. The head-down position is advantageous for increasing the preload despite decreasing the FRC, whereas the head-up position decreases preload despite high oxygen storage and might decrease cerebral tissue oxygenation [10]. The efficacy of positioning for maintaining oxygenation after preoxygenation has not been examined during hypovolemia or when using cerebral oxygenation.…”