Role of Pv-aCO2 gradient and Pv-aCO2/Ca-vO2 ratio during Cardiac Surgery

Background. Arterial lactate, mixed venous O2 saturation and parameters derived from CO2 metabolism as the venous minus arterial CO2 partial pressure (Pv-aCO2) gradient and the ratio between this gradient and the arterial minus venous oxygen content (Pv-aCO2/Ca-vO2) were proposed as markers of tissue hypoperfusion and oxygenation. The main goals were to characterize their physiologic determinants of Pv-aCO2 difference, and the Pv-aCO2 /Ca-vO2 ratio and the interchangeability of the variables calculated from mixed and central venous samples. Methods. We made a sub-analysis of 35 cardiac surgery patients included in a previous investigation database. Parameters were measured or calculated: after anesthesia induction (T1), end of cardiac surgery (T2), and at 6-8 hours intervals after ICU admission (T3 and T4). Results. Macrohemodynamics was characterized by increased cardiac index and low systemic vascular resistances, after surgery (p<0.05). Hemoglobin, arterial pH, lactate, and systemic O2 metabolism showed significant but transient changes during the study (p<0.05). Pv-aCO2 remained high and without changes along the study, and Pv-aCO2/Ca-vO2 was also high and only decreased at T4 (p<0.05). A weak but significant correlation was observed both, globally and at each time interval, between Pv-aCO2 or Pv-aCO2/Ca-vO2 with factors that may affect the CO2 hemoglobin dissociation. Using a similar approach, a multilevel linear regression model with Pv-aCO2 and Pv-aCO2/Ca-vO2 as outcome variables showed a significant association for Pv-aCO2 with mixed venous O2 saturation (SvO2), and base excess (BE) (p<0.05), while Pv-aCO2/Ca-vO2 was significantly associated with Hb, SvO2 , and BE (p<0.05) but not with cardiac output. Measurements and calculations from mixed and central venous blood were not interchangeable. Conclusions. Since Pv-aCO2 and Pv-aCO2/Ca-vO2 could be influenced by different factors that affect the CO2 dissociation curve, these variables should be considered with caution during the hemodynamic management of cardiac surgery patients. Finally, central venous and mixed values were not interchangeable.

Correlation of Venous Oxygen Saturations from Noninvasive Hematocrit Monitoring Using Blood Gas Measured Oximetry in Chronic Pediatric Hemodialysis Patients

<b><i>Introduction:</i></b> Noninvasive hematocrit monitoring (NIVHM) during pediatric hemodialysis (pedHD) provides data in real time regarding changes in hematocrit and blood volume and also provides venous oxygen saturations. The latter has been proposed to indicate changes in tissue oxygen consumption. It is not known how well NIVHM oxygen saturations (O2sat) approximate blood gas measured oximetry saturation (mO2sat) in the course of pedHD. We aimed to assess the validity and reliability of NIVHM O2sat compared to mO2sat. <b><i>Methods:</i></b> This is a prospective study in 15 patients &#x3c;21 years old with &#x3e;90 days on hemodialysis (HD) without congenital heart disease. HD access was fistula (AVF) in 4 patients and tunneled catheters in the remainder. Pulse oximetry (spO2) was continuously monitored; mO2sat was measured via oximetry in a blood gas analyzer and NIVHM O2sat values collected at the start, middle, and end of HD treatment. <b><i>Results:</i></b> A total of 45 dyad measurements were obtained. NIVHM O2sat correlated well with mO2sat (<i>R</i> = 0.89, <i>p</i> &#x3c; 0.0001); the same was seen at pre, mid, and post HD time points (<i>R</i> = 0.86–0.95, <i>p</i> &#x3c; 0.001). NIVHM O2sat was lower than mO2sat; with catheter as access, the difference was 9.3 ± 8.6 (CI: 12.3–6.22, <i>p</i> &#x3c; 0.0001) and with AVF was 2.1 ± 0.78 (CI: 2.6–1.7, <i>p</i> &#x3c; 0.0001). Bland-Altman analysis demonstrated the difference but did not show any systematic bias. Continuous monitor of spO2 showed no hypoxia. <b><i>Discussion/Conclusion:</i></b> Intradialytic NIVHM O2sat correlates well with mO2sat but yield lower values. Future studies can include NIVHM O2sat changes as a surrogate for central venous O2 saturation changes and potentially yield useful information regarding tissue oxygen consumption in pedHD patients.

Management of septic shock in the critically ill

The management of septic shock is a medical emergency. Following prompt recognition, treatment priorities are haemodynamic resuscitation, empirical antimicrobials, urgent control of the source of infection and monitoring the response to therapy. Haemodynamic resuscitation is focused on maintaining an adequate macrocirculation, while also ensuring adequacy of microcirculatory blood flow to the cells. Intravenous fluids and catecholamines have been the mainstay of therapy. However, the amount and type of fluids, choice of vasoactive medications, and the appropriate resuscitation endpoints have been questioned. Greater awareness of the importance of resuscitating the microcirculation and cell function have led to endpoints such as venous O2 saturation and changes in lactate levels becoming resuscitation targets. Urgent definitive treatment of the infection is also crucial. This requires prompt broad-spectrum empirical antimicrobial therapy, draining infected collections and removing infected medical devices. Despite extensive research, no new therapies have improved survival from septic shock.