Pulse pressure variation is comparable with central venous pressure to guide fluid resuscitation in experimental hemorrhagic shock with endotoxemia

Use of infrared thermography to detect early alterations of peripheral perfusion: evaluation in a porcine model

This study aimed to evaluate the variations of infrared thermography according to rapid hemodynamic changes, by measuring the peripheral skin temperature in a porcine model. Eight healthy piglets were anesthetized and exposed to different levels of arterial pressure. Thermography was performed on the left forelimb to measure carpus and elbow skin temperature and their associated gradient with the core temperature. Changes in skin temperature in response to variations of blood pressure were observed. A negative correlation between arterial pressure and temperature gradients between peripheral and core temperature and a negative correlation between cardiac index and these temperature gradients were observed. Thermography may serve as a tool to detect early changes in peripheral perfusion.

Anesthesia-Associated Relative Hypovolemia: Mechanisms, Monitoring, and Treatment Considerations

Although the utility and benefits of anesthesia and analgesia are irrefutable, their practice is not void of risks. Almost all drugs that produce anesthesia endanger cardiovascular stability by producing dose-dependent impairment of cardiac function, vascular reactivity, and compensatory autoregulatory responses. Whereas anesthesia-related depression of cardiac performance and arterial vasodilation are well recognized adverse effects contributing to anesthetic risk, far less emphasis has been placed on effects impacting venous physiology and venous return. The venous circulation, containing about 65–70% of the total blood volume, is a pivotal contributor to stroke volume and cardiac output. Vasodilation, particularly venodilation, is the primary cause of relative hypovolemia produced by anesthetic drugs and is often associated with increased venous compliance, decreased venous return, and reduced response to vasoactive substances. Depending on factors such as patient status and monitoring, a state of relative hypovolemia may remain clinically undetected, with impending consequences owing to impaired oxygen delivery and tissue perfusion. Concurrent processes related to comorbidities, hypothermia, inflammation, trauma, sepsis, or other causes of hemodynamic or metabolic compromise, may further exacerbate the condition. Despite scientific and technological advances, clinical monitoring and treatment of relative hypovolemia still pose relevant challenges to the anesthesiologist. This short perspective seeks to define relative hypovolemia, describe the venous system’s role in supporting normal cardiovascular function, characterize effects of anesthetic drugs on venous physiology, and address current considerations and challenges for monitoring and treatment of relative hypovolemia, with focus on insights for future therapies.

Pulse pressure variation as a guide for volume expansion in dogs undergoing orthopedic surgery

OBJECTIVE

To investigate whether pulse pressure variation (PPV) can predict fluid responsiveness in healthy dogs during clinical surgery.

STUDY DESIGN

Prospective clinical study.

ANIMALS

Thirty-three isoflurane-anesthetized dogs with arterial hypotension during orthopedic surgery.

METHODS

Fluid challenge with lactated Ringer's solution (15 mL kg^-1 in 15 minutes) was administered in mechanically ventilated dogs (tidal volume 10 mL kg^-1) with hypotension [mean arterial pressure (MAP) < 65 mmHg]. The volume expansion was considered effective if cardiac output (CO; transesophageal Doppler) increased by ≥ 15%. Cardiopulmonary data were analyzed using two-way ANOVA, receiver operating characteristics (ROC) curves and Spearman coefficient; p < 0.05 was considered significant.

RESULTS

Effective volume expansion, mean ± standard deviation 42 ± 4% increase in CO (p < 0.0001) was observed in 76% of the dogs, resulting in a decrease in PPV (p < 0.0001) and increase in MAP (p < 0.0001), central venous pressure (CVP; p = 0.02) and ejection fraction (p < 0.0001) compared with before the fluid challenge. None of these changes occurred when volume expansion resulted in a nonsignificant CO increase of 4 ± 5%. No significant differences were observed in blood gas analysis between responsive and nonresponsive dogs. The increase in CO was correlated with the decrease in PPV (r = -0.65; p < 0.0001) but absolute values of CO and PPV were not correlated. The PPV performance (ROC curve area: 0.89 ± 0.06, p = 0.0011) was better than that of CVP (ROC curve area: 0.54 ± 0.12) and MAP (ROC curve area: 0.59 ± 0.13) to predict fluid responsiveness. The best cut-off for PPV to distinguish responders and nonresponders was 15% (50% sensitivity and 96% specificity).

CONCLUSIONS AND CLINICAL RELEVANCE

In mechanically ventilated, healthy, isoflurane-anesthetized dogs, PPV predicted fluid responsiveness to volume expansion, and MAP and CVP did not show such applicability.

The Use of Internal Jugular Vein Ultrasonography to Anticipate Low or High Central Venous Pressure During Mechanical Ventilation

BACKGROUND

Critically low or high central venous pressure (CVP) values, together with systemic hypotension, can indicate hypovolemia or acute heart failure. However, measuring CVP requires the insertion of a central venous catheter, a time-consuming procedure that can be associated with severe complications.

OBJECTIVE

We sought to evaluate the use of ultrasonography of the internal jugular vein (IJV) to estimate low or high CVP values in patients who were on ventilation.

METHODS

Ultrasonography of IJV dimensions and the collection of hemodynamic data was performed in 47 patients, and the ratio between IJV diameter in the 30° and 0° position was calculated (ratio(30/0)). The predictive value of ratio(30/0) for estimating low and high CVP levels was analyzed using receiver operating characteristic curves.

RESULTS

The median IJV diameter ratio(30/0) was 0.49. CVP ranged from 1 to 13 mm Hg (median 7 mm Hg). Seventeen patients had a CVP ≤ 5 mm Hg or lower (defined as "low"), and in 11 patients, values of ≥ 10 mm Hg were measured (defined as "high"). The corresponding IJV diameter ratios increased significantly from 0.34 (in the low CVP group) to 0.9 (in the high CVP group). Receiver operating characteristic analysis revealed a good predictive value of the ratio(30/0) for the prediction of low or high CVP values, respectively. A ratio(30/0) of < 0.45 optimally indicated a low CVP, while > 0.65 was the cutoff value to detect a CVP ≥ 10 mm Hg.

CONCLUSION

The estimation of low or high CVP values by IJV ultrasonography in different patient positions can be a helpful instrument for the rapid hemodynamic assessment of the critically ill patient.