Evaluation of the biologic importance of various hemodynamic and oxygen transport variables: which variables should be monitored in postoperative shock?

Assessment of microcirculatory alteration by a vascular occlusion test using near-infrared spectroscopy in pediatric cardiac surgery: effect of cardiopulmonary bypass

OBJECTIVES

Cardiopulmonary bypass cause microcirculatory alterations. Near infrared spectroscopic measurement of tissue oxygen saturation and vascular occlusion test are novel technologies for assessing the microcirculatory function of peripheral tissue specifically in patients undergoing cardiac surgery with cardiopulmonary bypass.Our study aimed to evaluate dynamic microcirculatory function using the vascular occlusion testing during cardiac surgery in pediatric patients.

METHODS

120 pediatric patients were scheduled. Children had continuous regional oxygen saturation monitoring using near infrared spectroscopy and vascular occlusion test. Vascular occlusion test was performed five times; before induction (T1), after induction (T2), then during cardiopulmonary bypass with full flow (T3), after the termination of CPB (T4) and after sternum closure (T5).

RESULTS

Basal value was the lowest at T3 and this value was significantly different among measurements (p < 0,01).Values for maximum and minimum tissue oxygen saturation were the lowest at T3 (83,4 and 52,9%).The occlusion slope varied significantly among measurements (p < 0,01).Reperfusion slopes were significantly different among measurements (p < 0,01) with a further progressive decrease in reperfusion slope with duration of cardiopulmonary bypass.

CONCLUSION

Microcirculatory function can assessed using VOT with forearm Near-infrared spectroscopy derived variables during cardiopulmonary bypass in pediatric cardiac surgery. Noninvasive assessment of microcirculatory perfusion during cardiopulmonary bypass can further help evaluate and improve circulatory support techniques.

TRIAL REGISTRATION

The research Project was registered at ClinicalTrials.gov (NCT06191913).

The relationship between cardiopulmonary exercise test variables, the systemic inflammatory response, and complications following surgery for colorectal cancer

Background

Both preoperative cardiopulmonary exercise test (CPET)-derived measures of fitness and postoperative C-reactive protein (CRP) concentrations are associated with complications following surgery for colorectal cancer. The aim of the present pilot study was to examine the relationship between CPET and postoperative CRP concentrations in this patient group.

Methods

Patients who had undergone CPET prior to elective surgery for histologically confirmed colorectal cancer in a single centre between September 2008 and April 2017 were included. Preoperative VO₂ at the anaerobic threshold (AT) and peak exercise were recorded, along with preoperative modified Glasgow Prognostic Score (mGPS) and CRP on each postoperative day.

Results

Thirty-eight patients were included. The majority were male (30, 79%), over 65 years old (30, 79%), with colonic cancer (23, 61%) and node-negative disease (24, 63%). Fourteen patients (37%) had open surgery and 24 (63%) had a laparoscopic resection. A progressive reduction in VO₂ at peak exercise was significantly associated with both increasing American Society of Anesthesiology (ASA) grade (median, ml/kg/min: ASA 1 = 22, ASA 2 = 19, ASA 3 = 15, ASA 4 = 12, p = 0.014) and increasing mGPS (median, ml/kg/min: mGPS 0 = 18, mGPS 1 = 16, mGPS 2 = 14, p = 0.039) There was no significant association between either VO₂ at the AT or peak exercise and postoperative CRP.

Conclusions

The present pilot study reports a possible association between preoperative CPET-derived measures of exercise tolerance, and the preoperative systemic inflammatory response, but not postoperative CRP in patients undergoing surgery for colorectal cancer.

Microvascular Responsiveness to Pulsatile and Nonpulsatile Flow During Cardiopulmonary Bypass

BACKGROUND

Pulsatile perfusion may offer microcirculatory advantages over conventional nonpulsatile perfusion during cardiopulmonary bypass (CPB). Here, we present direct visual evidence of microvascular perfusion and vasoreactivity between perfusion modalities.

METHODS

A prospective, randomized cohort study of 20 high-risk cardiac surgical patients undergoing pulsatile (n = 10) or nonpulsatile (n = 10) flow during CPB was conducted. Changes in sublingual mucosal microcirculation were assessed with orthogonal polarization spectral imaging along with near-infrared spectroscopic indices of thenar muscle tissue oxygen saturation (StO₂) and its recovery during a vascular occlusion test at the following time points: baseline (T₀), 30 minutes on CPB (T₁), 90 minutes on CPB (T₂), 1 hour after CPB (T₃), and 24 hours after CPB (T₄).

RESULTS

On the basis of our scoring scale, a shift in microcirculatory blood flow occurred over time. The pulsatile group maintained normal perfusion characteristics, whereas the nonpulsatile group exhibited deterioration in perfusion during CPB (T₂: 74.0% ± 5.6% versus 57.6% ± 5.0%) and after CPB (T₃: 76.2% ± 2.7% versus 58.9% ± 5.2%, T₄: 85.7% ± 2.6% versus 69.8% ± 5.9%). Concurrently, no important differences were found between groups in baseline StO₂ and consumption slope at all time points. Reperfusion slope was substantially different between groups 24 hours after CPB (T₄: 6.1% ± 0.6% versus 3.7% ± 0.5%), indicating improved microvascular responsiveness in the pulsatile group versus the nonpulsatile group.

CONCLUSIONS

Pulsatility generated by the roller pump during CPB improves microcirculatory blood flow and tissue oxygen saturation compared with nonpulsatile flow in high-risk cardiac surgical patients, which may reflect attenuation of the systemic inflammatory response and ischemia-reperfusion injury.

A Review of Central Venous Pressure and Its Reliability as a Hemodynamic Monitoring Tool in Veterinary Medicine

OBJECTIVE

To review the current literature regarding central venous pressure (CVP) in veterinary patients pertaining to placement (of central line), measurement, interpretation, use in veterinary medicine, limitations, and controversies in human medicine.

ETIOLOGY

CVP use in human medicine is a widely debated topic, as numerous sources have shown poor correlation of CVP measurements to the volume status of a patient. Owing to the ease of placement and monitoring in veterinary medicine, CVP remains a widely used modality for evaluating the hemodynamic status of a patient. A thorough evaluation of the veterinary and human literature should be performed to evaluate the role of CVP measurements in assessing volume status in veterinary patients.

DIAGNOSIS

Veterinary patients that benefit from accurate CVP readings include those suffering from hypovolemic or septic shock, heart disease, or renal disease or all of these. Other patients that may benefit from CVP monitoring include high-risk anesthetic patients undergoing major surgery, trending of fluid volume status in critically ill patients, patients with continued shock, and patients that require rapid or large amounts of fluids.

THERAPY

The goal of CVP use is to better understand a patient's intravascular volume status, which would allow early goal-directed therapy.

PROGNOSIS

CVP would most likely continue to play an important role in the hemodynamic monitoring of the critically ill veterinary patient; however, when available, cardiac output methods should be considered the first choice for hemodynamic monitoring.

A Comparison of Gastric and Rectal CO₂ in Cardiac Surgery Patients

Critical care nurses assess and treat clinical conditions associated with inadequate oxygenation. Changes in regional organ (gut) blood flow are believed to occur in response to a decrease in oxygenation. Although the stomach is a widely accepted monitoring site, there are multiple methodological and measurement issues associated with the gastric environment that limit the accuracy of P CO2 detection. The rectum may provide nurses with an alternative site for monitoring changes in PCO2 without the limitations associated with gastric monitoring. This pilot study used a repeated measures design to examine changes in gastric and rectal PCO2 during elective coronary artery bypass grafting with cardiopulmonary bypass (CPB) and in the immediate 4-hr postoperative period in 26 subjects. The systemic indicators explained little variation in the regional indicators during protocol. A comparison of rectal and gastric PCO2 revealed no statistically significant differences in the direction or magnitude of change over any phase of cardiac surgery (baseline, CPB, post-CPB). A reduction in both rectal and gastric PCO2 occurred during CPB, and both values trended upward during the post-CPB phase. However, poor correlation and agreement was found between the measures of PCO2 at the two sites. Although clinically important, the cause is unclear. Possible explanations include variation in CO2 production between the gastric and rectal site, differences in sensitivity of the two monitoring instruments, or the absence of hemodynamic complications, which limited the extent of change in PCO2. Further investigation using patients with more profound changes in oxygenation are needed to identify response patterns and possible mechanisms.

Do plasma catecholamines influence microcirculatory blood flow in cardiac surgery patients?

To investigate whether plasma catecholamines influence blood flow on the microcirculatory level, forehead and forearm skin blood flow was measured by a two-channel laser Doppler blood flux monitor in 50 patients undergoing aortocoronary bypass grafting. Macrohaemodynamics, plasma viscosity, and skin temperatures were additionally monitored. Plasma catecholamines (adrenaline [AD] and noradrenaline [NOR] ) were determined using high-pressure liquid chromatography (HPLC) from arterial blood samples.

In the prebypass period, blood concentrations of both catecholamines increased slightly showing a wide range of values (AD ranging from 3 to 955 pg/ml; NOR ranging from 27 to 5326 pg/ml). In spite of the tremendous increase in plasma catecholamines before and after bypass, laser Doppler flow (LDF) remained almost stable in this period. Neither LDF nor macrocirculatory parameters were correlated to plasma catecholamines. Cardiopulmonary bypass (CPB) resulted in a significant increase in catecholamines (AD ranging from 80 to 2480 pg/ml; NOR ranging from 188 to 9898 pg/ml). Although haematocrit and plasma viscosity were significantly reduced during CPB, LDF decreased in comparison to baseline values (LDF forehead: -25%; LDF forearm: -35%) ( p<0.05).

It is concluded that plasma catecholamine levels were markedly changed during cardiac surgery showing a wide range of concentrations. Microcirculatory flow assessed by laser Doppler remained almost unaffected by these alterations and was not correlated to AD or NOR plasma concentrations. However, during CPB a significant increase in catecholamines can contribute to the risk of microperfusion abnormalities which can be assessed by laser Doppler technique.

Less invasive methods of advanced hemodynamic monitoring: principles, devices, and their role in the perioperative hemodynamic optimization

The monitoring of the cardiac output (CO) and other hemodynamic parameters, traditionally performed with the thermodilution method via a pulmonary artery catheter (PAC), is now increasingly done with the aid of less invasive and much easier to use devices. When used within the context of a hemodynamic optimization protocol, they can positively influence the outcome in both surgical and non-surgical patient populations. While these monitoring tools have simplified the hemodynamic calculations, they are subject to limitations and can lead to erroneous results if not used properly. In this article we will review the commercially available minimally invasive CO monitoring devices, explore their technical characteristics and describe the limitations that should be taken into consideration when clinical decisions are made.

Perioperative increase in global blood flow to explicit defined goals and outcomes after surgery: a Cochrane Systematic Review

This systematic review and meta-analysis summarizes the clinical effects of increasing perioperative blood flow using fluids with or without inotropes/vasoactive drugs to explicit defined goals in adults. We included randomized controlled trials of adult patients (aged 16 years or older) undergoing surgery. We included 31 studies of 5292 participants. There was no difference in mortality at the longest follow-up: 282/2615 (10.8%) died in the control group and 238/2677 (8.9%) in the treatment group, RR of 0.89 (95% CI: 0.76-1.05; P=0.18). However, the results were sensitive to analytical methods and withdrawal of studies with methodological limitations. The intervention reduced the rate of three morbidities (renal failure, respiratory failure, and wound infections) but not the rates of arrhythmia, myocardial infarction, congestive cardiac failure, venous thrombosis, and other types of infections. The number of patients with complications was also reduced by the intervention. Hospital length of stay was reduced in the treatment group by 1.16 days. There was no difference in critical care length of stay. The primary analysis of this review showed no difference between groups but this result was sensitive to the method of analysis, withdrawal of studies with methodological limitations, and was dominated by a single large study. Patients receiving this intervention stayed in hospital 1 day less with fewer complications. It is unlikely that the intervention causes harm. The balance of current evidence does not support widespread implementation of this approach to reduce mortality but does suggest that complications and duration of hospital stay are reduced.

Arterial blood gases, electrolytes, and metabolic indices associated with hemorrhagic shock: inter- and intrainbred rat strain variation

We have previously shown interstrain variation (indicating a genetic basis), and intrastrain variation in survival time after hemorrhage (STaH) among inbred rat strains. To assist in understanding physiological mechanisms associated with STaH, we analyzed various arterial blood measures (ABM; pH, Paco2, oxygen content, sodium, potassium, glucose, bicarbonate, base excess, total CO2, and ionized calcium) in inbred rats. Rats from five inbred strains (n = 8-10/strain) were catheterized and, ≈ 24 h later, subjected to a conscious, controlled, 47% hemorrhage. ABM were measured at the start (initial) and end (final) of hemorrhage. Inter- and intrainbred strain variations of ABM were quantified and compared, and correlations of ABM with STaH were determined. All final ABM values and some initial ABM values were different among strains. Most ABM changed (Δ) during hemorrhage, and these changes differed among strains (P <0.03). Some strain-dependent correlations (r ≥ 0.7; P ≤ 0.05) existed between ΔABM and STaH (e.g., BN/Mcwi, ΔK(+), r = -0.84). Dark Agouti rats (longest STaH) had the smallest ΔPaco2, ΔHCO3(-), and Δbase excess, and the highest final glucose. High coefficients of variation (CVs, >10%), strain-specific CVs, and low intraclass correlation coefficients (rI < 0.5) defined the large intrastrain ABM variation that exceeded interstrain variation for most ABM. These results suggest that some ABM (K(+), Paco2, glucose, oxygen content) could predict subsequent STaH in an inbred rat strain-dependent manner. We speculate that whereas genetic differences may be responsible for interstrain variation, individual-specific epigenetic processes (e.g., DNA methylation) may be partly responsible for both inter- and intrastrain ABM variation.

Perioperative increase in global blood flow to explicit defined goals and outcomes following surgery

BACKGROUND

Studies have suggested that increasing whole body blood flow and oxygen delivery around the time of surgery reduces mortality, morbidity and the expense of major operations.

OBJECTIVES

To describe the effects of increasing perioperative blood flow using fluids with or without inotropes or vasoactive drugs. Outcomes were mortality, morbidity, resource utilization and health status.

SEARCH METHODS

We searched CENTRAL (The Cochrane Library 2012, Issue 1), MEDLINE (1966 to March 2012) and EMBASE (1982 to March 2012). We manually searched the proceedings of major conferences and personal reference databases up to December 2011. We contacted experts in the field and pharmaceutical companies for published and unpublished data.

SELECTION CRITERIA

We included randomized controlled trials with or without blinding. We included studies involving adult patients (aged 16 years or older) undergoing surgery (patients having a procedure in an operating room). The intervention met the following criteria. 'Perioperative' was defined as starting up to 24 hours before surgery and stopping up to six hours after surgery. 'Targeted to increase global blood flow' was defined by explicit measured goals that were greater than in controls, specifically one or more of cardiac index, oxygen delivery, oxygen consumption, stroke volume (and the respective derived indices), mixed venous oxygen saturation (SVO(2)), oxygen extraction ratio (0(2)ER) or lactate.

DATA COLLECTION AND ANALYSIS

Two authors independently extracted the data. We contacted study authors for additional data. We used Review Manager software.

MAIN RESULTS

We included 31 studies of 5292 participants. There was no difference in mortality: 282/2615 (10.8%) died in the control group and 238/2677 (8.9%) in the treatment group, RR of 0.89 (95% CI 0.76 to 1.05, P = 0.18). However, the results were sensitive to analytical methods and the intervention was better than control when inverse variance or Mantel-Haenszel random-effects models were used, RR of 0.72 (95% CI 0.55 to 0.95, P = 0.02). The results were also sensitive to withdrawal of studies with methodological limitations. The rates of three morbidities were reduced by increasing global blood flow: renal failure, RR of 0.71 (95% CI 0.57 to 0.90); respiratory failure, RR of 0.51 (95% CI 0.28 to 0.93); and wound infections, RR of 0.65 (95% CI 0.51 to 0.84). There were no differences in the rates of nine other morbidities: arrhythmia, pneumonia, sepsis, abdominal infection, urinary tract infection, myocardial infarction, congestive cardiac failure or pulmonary oedema, or venous thrombosis. The number of patients with complications was reduced by the intervention, RR of 0.68 (95% CI 0.58 to 0.80). Hospital length of stay was reduced in the treatment group by a mean of 1.16 days (95% CI 0.43 to 1.89, P = 0.002). There was no difference in critical care length of stay. There were insufficient data to comment on quality of life and cost effectiveness.

AUTHORS' CONCLUSIONS

It remains uncertain whether increasing blood flow using fluids, with or without inotropes or vasoactive drugs, reduces mortality in adults undergoing surgery. The primary analysis in this review (mortality at longest follow-up) showed no difference between the intervention and control, but this result was sensitive to the method of analysis, the withdrawal of studies with methodological limitations, and is dominated by a single large RCT. Overall, for every 100 patients in whom blood flow is increased perioperatively to defined goals, one can expect 13 in 100 patients (from 40/100 to 27/100) to avoid a complication, 2/100 to avoid renal impairment (from 8/100 to 6/100), 5/100 to avoid respiratory failure (from 10/100 to 5/100), and 4/100 to avoid postoperative wound infection (from 10/100 to 6/100). On average, patients receiving the intervention stay in hospital one day less. It is unlikely that the intervention causes harm. The balance of current evidence does not support widespread implementation of this approach to reduce mortality but does suggest that complications and duration of hospital stay are reduced.

Head Trauma in the Cat: 1. Assessment and Management of Craniofacial Injury

Practical relevance Feline trauma is commonly seen in general practice and frequently involves damage to the head.

Clinical challenges While craniofacial injuries following trauma vary widely in severity, affected cats can often be severely compromised in terms of their neurological, respiratory and cardiovascular status, and their management can be challenging in both the short and long term. They need prompt stabilisation and careful monitoring in the initial period to maximise prospects of a successful outcome. Many cats with severe facial trauma will require surgery to stabilise skull fractures or address injuries to the eyes, with its inherent issues surrounding pain management, ensuring adequate nutrition and the necessity for ongoing hospitalisation.

Diagnostics Cats with head trauma benefit from imaging of the injured areas as well as thoracic radiography. Imaging the skull can be challenging and is best performed under general anaesthesia. In unstable patients this can be delayed to prevent any associated morbidity.

Evidence base The clinical evidence base relating to injury to the feline head is limited, despite its relative frequency in general practice. This review focuses on the initial approach to craniofacial (in particular, ocular and jaw) trauma, and outlines simple techniques for management of soft tissue and bone injuries. Much of the information is based on the authors' clinical experience, as there is a paucity of well-described clinical case material.

Life or death? A physiogenomic approach to understand individual variation in responses to hemorrhagic shock

Severe hemorrhage due to trauma is a major cause of death throughout the world. It has often been observed that some victims are able to withstand hemorrhage better than others. For decades investigators have attempted to identify physiological mechanisms that distinguish survivors from nonsurvivors for the purpose of providing more informed therapies. As an alternative approach to address this issue, we have initiated a research program to identify genes and genetic mechanisms that contribute to this phenotype of survival time after controlled hemorrhage. From physiogenomic studies using inbred rat strains, we have demonstrated that this phenotype is a heritable quantitative trait, and is therefore a complex trait regulated by multiple genes. Our work continues to identify quantitative trait loci as well as potential epigenetic mechanisms that might influence survival time after severe hemorrhage. Our ultimate goal is to improve survival to traumatic hemorrhage and attendant shock via regulation of genetic mechanisms and to provide knowledge that will lead to genetically-informed personalized treatments.

Early physiologic responses to hemorrhagic hypotension

The identification of early indicators of hemorrhagic hypotension (HH) severity may support early therapeutic approaches and bring insights into possible mechanistic implications. However, few systematic investigations of physiologic variables during early stages of hemorrhage are available. We hypothesized that, in certain subjects, early physiologic responses to blood loss are associated with the ability to survive hemorrhage levels that are lethal to subjects that do not present the same responses. Therefore, we examine the relevance of specific systemic changes during and after the bleeding phase of HH. Stepwise hemorrhage, representing prehospital situations, was performed in 44 rats, and measurements were made after each step. Heart and respiratory rates, arterial and venous blood pressures, gases, acid-base status, glucose, lactate, electrolytes, hemoglobin, O(2) saturation, tidal volume, and minute volume were measured before, during, and after bleeding 40% of the total blood volume. Fifty percent of rats survived 100 min (survivors, S) or longer; others were considered nonsurvivors (NS). Our findings were as follows: (1) S and NS subjected to a similar hemorrhage challenge showed significantly different responses during nonlethal levels of bleeding; (2) survivors showed higher blood pressure and ventilation than NS; (3) although pH was lower in NS at later stages, changes in bicarbonate and base excess occurred already during the hemorrhage phase and were higher in NS; and (4) plasma K(+) levels and glucose extraction were higher in NS. We conclude that cardiorespiratory and metabolic responses, essential for the survival at HH, can differentiate between S and NS even before a lethal bleeding was reached.

Rat strains bred for low and high aerobic running capacity do not differ in their survival time to hemorrhage

Hemorrhagic shock reflects low tissue perfusion that is inadequate to maintain normal metabolic functions. Often associated with this condition are impairments in cellular oxygen delivery and utilization. Rat strains divergent in their running endurance have been artificially selected over 12 generations. As these rats bred for high (HCR) vs low (LCR) aerobic running capacity have greater tissue O(2) utilization capacity and improved cardiovascular function, we hypothesized that HCR would be more tolerant (i.e., have greater survivability) to the global ischemia of hemorrhagic shock than LCR. To address this hypothesis, survival time to a severe-as substantiated by dramatic changes in plasma lactate, HCO(3), and base deficit-controlled hemorrhage was measured. Male rats were catheterized and, approximately 24 h later, an estimated >35% of the calculated blood volume was removed during a 26-min period while the rats were conscious and unrestrained. Rats were observed for 6 h or until death. Contrary to our hypothesis, survival time in HCR (220 +/- 63 min; n = 6) did not differ statistically (P = 0.46) from that in LCR (279 +/- 53 min; n = 7). Similarly, there were no statistical differences (P >or= 0.08) between rat lines in blood pH, lactate, HCO(3), and base deficit pre- or post-hemorrhage. In addition, few significant differences between lines in response to hemorrhage were detected by measures of cellular antioxidant status in heart, liver, or lung. Since animals with genetically greater tissue oxygen utilization capacity failed to show longer survival times, our results suggest that other mechanisms must play a more dominant role in determining survivability to hemorrhage under conditions of this hemorrhage.

Indirect calorimetry can be used to measure cardiac output in septic patients?

PURPOSE

The aim of this study was to compare two different cardiac output (CO) monitoring systems based on the thermodilution principle (Thermo-CO) and indirect calorimetry (Fick mixed-CO) in septic patients.

METHODS

Prospective study in septic patients admitted in an intensive care unit of a university hospital. Nineteen patients aged on average 45.4 +/- 21.5 years were enrolled in the study. Four series of hourly measurements by the two techniques were carried out simultaneously.

RESULTS

No significant differences were observed between Thermo-CO and Fick mixed-CO (7.0 +/- 1.8 L.min-1 and 6.4 +/- 1.7 L.min-1.). Parallel analysis of Fick mixed-CO and Fick atrial-CO was performed introducing a correction factor for the eight atrial samples in order to adjust the values of oxygen saturation obtained from atrial blood (Fick corrected atrial-CO) to those obtained from mixed venous blood. No significant differences could be detected between Fick mixed-CO and Fick corrected atrial-CO. The correlation coefficients of Thermo CO/Fick mixed-CO and Fick mixed-CO/Fick corrected atrial-CO were 0.84 and 0.94, respectively.

CONCLUSION

We observed that the agreement between the two methods was satisfactory on the basis of the decisions made for treatment. Indirect calorimetry is useful to measure CO in patients with septic shock.

[Arteriovenous difference in O2 content, pulmonary venous O2 saturation, cardiac index: are they equivalent in cardiac surgery?]

OBJECTIVE

To study the concordance of cardiac index (CI), mixed venous oxygen saturation (SvO(2)) and the arterial-mixed venous O(2) content difference, i.e.: C(a-v)O(2), postoperatively to cardiac surgery. We hypothesized that significant discrepancies would be measurable between C(a-v)O(2) and SvO(2), and CI, because the latter two indices encompass less metabolic components than the former.

DESIGN

Analysis of variables collected as part of routine care.

PATIENTS

Eighty anesthetized patients receiving mechanical ventilation after heart surgery.

MEASUREMENTS AND RESULTS

Using linear regression of SvO(2) versus C(a-v)O(2) (Reg 1) and CI versus C(a-v)O(2) (Reg 2), respectively we found that CI=2.2 L min(-1)m(-2) and SvO(2)=70% were equivalent to C(a-v)O(2)=5 ml/100ml. The error reflected by the vertical scatter of points around the regression line, once normalized was 3.24 times greater in Reg 2 than in Reg 1.

CONCLUSIONS

The correspondence of CI, SvO(2) and C(a-v)O(2) values observed in a population of patients studied immediately after scheduled heart surgery match those reported in critically ill patients. SvO(2) and furthermore CI induced a sizeable scatter of points around regression line. Accordingly, they appear as a lesser estimate of the flow/metabolism balance that may at best be inferred from C(a-v)O(2).

Hemodynamic Characteristics of Vasopressin in Dogs with Severe Hemorrhagic Shock

The effect of vasopressin was compared with that of the established vasopressor epinephrine in experimentally induced hemorrhagic shock. After rapid crystalloid resuscitation in a ratio of three volumes of 0.9% saline to one volume of blood (3:1 crystalloid resuscitation), six dogs were given 0.4 IU/kg vasopressin and another six dogs were given 0.1 mg/kg epinephrine. Five dogs in the control group were given fluid resuscitation in the same manner as above without administration of any drugs. Administration of vasopressin increased diastolic arterial pressure (DAP) from 45.0 +/- 4.9 to 91.2 +/- 9.6 mmHg within 5 min, compared with epinephrine from 46 +/- 4.0 to 51.8 +/- 7.7, and control from 47.3 +/- 7.5 to 46.3 +/- 7.3. Systolic arterial pressure (SAP) did not increase significantly following vasopressin compared with epinephrine and control group. Results of DAP and systemic vascular resistance index (SVRI) suggested that vasopressin administration was vasoconstrictive after fluid resuscitation in decompensatory hemorrhagic shock in dogs, whereas epinephrine did not compared with control. In addition, epinephrine did not affect the cardiac index (CI) and SVRI, while a significant decrease in CI and increase in SVRI were observed in vasopressin group. The pressor effect of epinephrine in the vascular system was abrupt and only lasted a short period of time (within 5 min), while that of vasopressin was steady and lasted for more than 1 hr, especially regard to in DAP. When compared with epinephrine, vasopressin can be a more effective and safer choice in patients with severe hemorrhagic shock.

Bench-to-bedside review: oxygen debt and its metabolic correlates as quantifiers of the severity of hemorrhagic and post-traumatic shock

Evidence is increasing that oxygen debt and its metabolic correlates are important quantifiers of the severity of hemorrhagic and post-traumatic shock and and may serve as useful guides in the treatment of these conditions. The aim of this review is to demonstrate the similarity between experimental oxygen debt in animals and human hemorrhage/post-traumatic conditions, and to examine metabolic oxygen debt correlates, namely base deficit and lactate, as indices of shock severity and adequacy of volume resuscitation. Relevant studies in the medical literature were identified using Medline and Cochrane Library searches. Findings in both experimental animals (dog/pig) and humans suggest that oxygen debt or its metabolic correlates may be more useful quantifiers of hemorrhagic shock than estimates of blood loss, volume replacement, blood pressure, or heart rate. This is evidenced by the oxygen debt/probability of death curves for the animals, and by the consistency of lethal dose (LD)_25,50 points for base deficit across all three species. Quantifying human post-traumatic shock based on base deficit and adjusting for Glasgow Coma Scale score, prothrombin time, Injury Severity Score and age is demonstrated to be superior to anatomic injury severity alone or in combination with Trauma and Injury Severity Score. The data examined in this review indicate that estimates of oxygen debt and its metabolic correlates should be included in studies of experimental shock and in the management of patients suffering from hemorrhagic shock.

Assessment and treatment of perfusion abnormalities in the emergency patient

Many patients presented to the emergency veterinarian are suffering from global or local tissue hypoperfusion. Global or systemic hypoperfusion can occur secondary to a reduction in the effective circulating intravascular volume (hypovolemic shock) or reduced ability of the heart to pump blood around the body secondary to reduced cardiac function (cardiogenic shock),obstruction to blood flow (obstructive shock), or maldistribution of the circulating intravascular volume (distributive shock). Initial assessment involving physical examination supplemented by measurement of hemodynamic and metabolic parameters allows the clinician to recognize and treat patients with severe global hypoperfusion. Use of techniques like sublingual capnometry and measurement of central venous oxygen saturation may aid recognition and evaluation of early hypoperfusion. Treatment decisions are made based on an assessment of the severity of the hypoperfusion and its probable underlying cause. Early effective treatment of hypoperfusion is likely to lead to a better outcome for the patient.

Minimally Invasive Optimization of Organ Donor Resuscitation: Case Reports

Increased use of expanded donors requires optimal organ perfusion to prevent graft damage. In this regard, pulmonary artery catheters have been advocated to monitor hemodynamic status. Cost, catheter placement, and inconsistent management preclude broad use of pulmonary artery catheters. Esophageal Doppler monitoring also monitors hemodynamic status and can be instituted in minutes by an organ procurement coordinator. Concomitant assessment of acid-base balance using base excess and/or anion gap can help determine resuscitation efficacy. Esophageal Doppler monitoring is described to help salvage 2 hemodynamically deteriorating donors. Anion gap and corrected base excess identified poor resuscitation status in both donors and normalized after improvement in hemodynamic status. Compared to pulmonary artery catheters, esophageal Doppler monitoring may provide a more accessible means to assess and improve hemodynamic status. Base deficit and/or anion gap may determine resuscitation efficacy by exposing acid-base imbalance resulting from poor tissue perfusion. The full efficacy of this approach remains to be determined.

Systemic responses to prolonged hemorrhagic hypotension

Studies are needed to provide a rigorous examination of the relevance of monitored variables during prolonged hemorrhagic hypotension (HH). This study was designed to investigate the parameters that describe biochemical and O2 transport patterns in animals subjected to HH. Systemic parameters that could differentiate survivors from nonsurvivors were identified. An aortic flow probe was implanted in rats ( n = 21) for continuous measurement of cardiac output. Experiments were performed 6–9 days after surgery. Rats were bled to a mean arterial pressure of 40 mmHg and kept at that level using Ringer-lactate solution. Arterial and venous blood pressures, gases, acid-base status, glucose, lactate, electrolytes, hemoglobin, O2 saturation, heart and respiratory rates, total peripheral resistance, and O2 delivery and consumption were measured before hemorrhage, soon after 40 mmHg was reached, and 0.5, 1, 2, 3, and 4 h later. Fifty-three percent of rats survived ≥3 h (survivors); others were considered nonsurvivors. Nonsurvivors showed a significantly greater degree of metabolic acidosis than survivors. Arterial Po2, respiratory rate, O2 saturation, O2 content, glucose, and pH were significantly higher in survivors. The rate of Ringer-lactate infusion, arterial K+, and Pco2 were lower in survivors. Arterial K+ and respiratory rate were the only parameters significantly different between survivors and nonsurvivors at all time points during HH. Arterial levels of K+ showed the clearest distinction between survivors and nonsurvivors and may explain the sudden death experienced by animals during HH. The data suggest that early respiratory and metabolic compensations are essential for survival of prolonged HH.

Thoracic epidural anesthesia increases tissue oxygenation during major abdominal surgery

Intraoperative surgical stress may markedly increase adrenergic nerve activity and plasma catecholamine concentrations, which causes peripheral vasoconstriction and decreased tissue oxygen partial pressure possibly leading to tissue hypoxia. Tissue hypoxia is associated with an increased incidence of surgical wound infections. Thoracic epidural anesthesia blocks afferent neural stimuli and inhibits efferent sympathetic outflow in response to painful stimuli. Consequently, we tested the hypothesis that supplemental thoracic epidural anesthesia during major abdominal surgery improves tissue perfusion and subcutaneous oxygen tension. Thirty patients were randomly assigned to two groups: general (n = 15) or combined general and epidural anesthesia (n = 15). Anesthesia technique and fluid management were standardized. Subcutaneous tissue oxygen tension was measured continuously in the upper arm with a Clark type electrode. Data were compared with unpaired, two-tailed t-tests, Wilcoxon's ranked sum test, or repeated-measures analysis of variance and Scheffé F tests as appropriate; P < 0.05 was considered statistically significant. After 60 min, intraoperative tissue oxygen tension was significantly larger during combined anesthesia than during general anesthesia (54.3 +/- 7.4 mm Hg versus 42.1 +/- 8.6 mm Hg; P = 0.0002). Subcutaneous tissue oxygen tension remained significantly higher in the combined general/epidural anesthesia group throughout the observation period. Hemodynamic responses and global oxygen variables were similar in the groups. Thoracic epidural anesthesia improved intraoperative tissue oxygen tension outside the area of the epidural block. Thus, our results give evidence that supplemental neural nociceptive block blunts generalized vasoconstriction caused by surgical stress and adrenergic responses.

IMPLICATIONS

Thoracic epidural anesthesia blunts the decrease of subcutaneous tissue oxygen tension caused by surgical stress and adrenergic vasoconstriction during major abdominal surgery. Consequently, combined general and epidural anesthesia helps to provide sufficient tissue oxygenation.

Cardiac output, wedge pressure, and oxygen delivery

The primary goal of the intensive care clinician can be said to be to optimize global DO2. This approach is the primary means by which the greatest killers of the critically ill patient (sepsis, SIRS, multiple organ dysfunction syndrome) may be addressed at present. Optimizing DO2 means delivering just enough to meet the patient's needs, because therapeutic measures taken to increase DO2 are all associated with some degree of risk. When used correctly, the PAC can allow the clinician to determine if DO2 is optimal and, if not, what steps might be best suited to improve on it. Newer generations of PACs are becoming available and can provide valuable additional insights into a patient's cardiovascular status. Nearly all attempts to increase DO2 address one or more of a relatively short list of variables. The specific endpoints of therapy need to be tailored to the individual patient but include clinical, metabolic, organ function, and hemodynamic markers. As clinicians expand our understanding of the key elements found in survivors of critical illness, it is hoped that this knowledge translates into better outcomes.

Prognostic factors in intensive care

Predicting the outcome of critical illness remains an evolving art despite many recent advances. This review article describes the tools currently employed, appraising each in turn. The subject is viewed from the perspective that physiological reserve and inflammatory response are the essential elements in assessing prognosis in patients with multi-organ dysfunction/failure, the most commonly encountered syndrome in intensive care practice.

Intraoperative and Early Postoperative Gastric Intramucosal pH Predicts Morbidity and Mortality after Major Abdominal Surgery

The present study was undertaken to investigate the correlation between the intraoperative and postoperative gastric intramucosal pH (pHi) with important perioperative variables and to explore any potential relationship of the measured pHi with the patients’ postoperative course. A prospective study was carried out in a group of 48 patients who underwent major abdominal operations over an 8-month period at St. John Hospital and Medical Center. An automated air tonometer was used for gastric pHi monitoring. Twenty-eight elective and 20 emergency abdominal operations were performed in 23 men and 25 women. Twenty-six patients (54%) required postoperative hospitalization in the Intensive Care Unit (ICU). Seventeen patients (35%) developed early postoperative complications. The non-ICU and ICU mortality rates were 4.5 and 19.2 per cent respectively. The mean intraoperative pHi (pHiOR) and postoperative pHi (pHiPO) ranged between 7.03 and 7.58 (7.38 ± 0.12) and 6.89 and 7.56 (7.35 ± 0.12) respectively (mean ± standard deviation). There was a significant decrease of the gastric pHi at the first hour intraoperatively compared with the pHi after induction to anesthesia (7.44 vs 7.38 ± 0.14, P < 0.001). Patients who underwent emergent abdominal procedures were characterized by lower pHiOR and pHiPO values (7.43 ± 0.08 vs 7.30 ± 0.13 and 7.39 ± 0.84 vs 7.30 ± 0.15, P < 0.001 and P < 0.05). Similarly patients who required surgical ICU admission had significantly lower pHiOR and pHiPO measurements (7.3 ± 0.12 and 7.28 ± 0.12) compared with the rest (7.46 ± 0.06 and 7.43 ± 0.06; P < 0.001). Overall, lower pHiOR and pHiPO values were associated with the occurrence of postoperative complications ( P < 0.001), the postoperative mortality ( P < 0.001), the requirement for postoperative mechanical ventilator ( P < 0.001) and its duration ( P < 0.001), longer ICU stay ( P < 0.001), and prolonged hospitalization ( P < 0.05). Evidence of intraoperative and early postoperative gastric mucosal ischemia (pHiOR and pHiPO ≤ 7.32) was observed in 12 (25%) and 15 (31%) patients respectively. The incidence of postoperative complications and the mortality rate were higher in this group of patients ( P < 0.001). At a cutoff point of 7.32 gastric pHiOR gave a sensitivity of 69 per cent and specificity of 97 per cent for predicting postoperative complications as well as a sensitivity and specificity of 67 per cent and 81 per cent for predicting death. Intraoperative and early postoperative gastric pHi is a reliable predictor of patient outcome after major abdominal operations. Splanchnic ischemia may play an important role in determining early complications and survival; therapy guided by the gastric pHi might improve outcome.

Initial severity of metabolic acidosis predicts the development of acute lung injury in severely traumatized patients

OBJECTIVES

First, to determine whether the severity of shock, as measured by systemic hypotension and metabolic acidosis, is significantly associated with a higher risk of acute lung injury in patients with severe trauma. Second, to determine whether the volumes of blood and crystalloid solutions administered in the early posttrauma period are independent risk factors for acute lung injury in severely traumatized patients.

DESIGN

Prospective observational study.

SETTING

Level I urban trauma center in a university hospital.

PATIENTS

A total of 102 severely injured, mechanically ventilated trauma patients with an Injury Severity Score > or =16 and aged between 18 and 75 yrs.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Initial clinical and laboratory data were collected in the emergency department, and on a daily basis thereafter during the patient's intensive care unit stay. Of the 102 severely injured patients enrolled, 42 developed acute lung injury (41%) and 60 did not (59%). A total of 93% of the trauma patients who developed acute lung injury during the 17-month study period were included in the study. Initial base deficit was significantly lower in patients who developed acute lung injury than in those who did not (-8.8+/-4.5 vs. -5.6+/-5.1, p<.01). The difference in systolic blood pressure between the two groups was not significant.

CONCLUSIONS

In this group of severely injured trauma patients, the degree of metabolic acidosis at the time of admission identified those patients with the highest probability of developing acute lung injury. In addition, the volume of crystalloid solution administered during the first 24 hrs was significantly greater in patients who later developed acute lung injury. Finally, there was a significantly higher morbidity in patients who developed acute lung injury, whereas mortality did not differ between the two groups.

Maternal oxygen transport variables during the third trimester of normal pregnancy

OBJECTIVE

The aim of this study was to measure and calculate oxygen transport variables in uncomplicated term pregnancies.

STUDY DESIGN

Ten normotensive primiparous women between 36 and 38 weeks' gestation underwent pulmonary and radial arterial catheterization as part of a larger study. Seven women had studies repeated at approximately 12 weeks post partum. Measurements were made with patients in the left lateral recumbent position after a 30-minute stabilization period. Cardiac output was measured with the thermodilution technique. Blood samples were obtained simultaneously from the pulmonary and radial arteries and analyzed in duplicate for oxygen content with a blood gas analyzer.

RESULTS

The oxygen contents of both arterial and mixed venous blood are significantly lower (P <.05) in the third trimester of pregnancy (15.96 and 11.97 mL/dL, respectively) than in the postpartum period (18.00 and 13.54 mL/dL). The fall in oxygen content during pregnancy prevents any significant increase in oxygen delivery in the third trimester (867. 59 mL/min) relative to the postpartum period (806.50 mL/min, P not significant).

CONCLUSION

This is the first report of directly measured oxygen transport variables in healthy pregnant women.

The effects of thoracic epidural anesthesia on intraoperative visceral perfusion and metabolism

After institutional approval and informed consent, we studied the effect of epidural bupivacaine 0.5% on visceral perfusion and metabolism by using gastric mucosal tonometry in 30 patients in a placebo-controlled fashion. The maximal intramucosal pH (pHi) decrease was significantly (P < 0.001) greater in the control group (0.16 +/- 0.04) than in the thoracic epidural anesthesia (TEA) group (0.07 +/- 0.05). There were 10 patients in the control group and 2 patients in the TEA group who had evidence of gastric mucosal ischemia (pHi <7.32) at the end of the study (P< 0.01). The differences in pHi and intramucosal CO2 (PiCO2) became statistically significant between the groups after 180 and 240 min. The study data show that TEA prevents the decrease of pHi during major abdominal surgery, perhaps as an effect of stable visceral perfusion. We conclude that TEA may be a valuable method for intra- and postoperative treatment of surgical stress.

IMPLICATIONS

The present study shows that thoracic epidural anesthesia prevents a decrease of intramucosal pH during major abdominal surgery, which suggests that thoracic epidural anesthesia may be a valuable tool for the treatment of surgical stress.

Muscle lactate concentration during experimental hemorrhagic shock

PURPOSE

Blood lactate concentration does not correspond well to oxygen transport variables during circulatory shock. Prolonged washout of lactate from tissues during shock has been reported. This study was designed to test the hypothesis that the discrepancy between serum lactate and oxygen metabolism is caused by the failure of lactate to wash out from the tissues and that tissue lactate may reflect the oxygen metabolism better.

METHODS

Using a canine model of hemorrhagic shock, lactate concentration measured in a muscle biopsy specimen and in arterial blood was compared with the cumulative deficit in oxygen consumption.

RESULT

The cumulative deficit in oxygen consumption correlated with the concentration of lactate in muscle (r= 0.67,P<0.01) but not with that in blood. During shock, all muscle lactate levels were greater than those in serum, and a linear relationship was demonstrated between arterial(X) and muscle(Y) lactate levels (Y=2.45X-2.72,r=0.82,P<0.001). The muscle/serum lactate concentration ratio increased from 1 to 2.5 as the blood volume decreased.

CONCLUSION

In the setting of experimental hemorrhagic shock, only tissue lactate levels reflected the true deficit in oxygen metabolism. The difference between lactate levels in muscle and serum represented the severity of the shock.

Emergency department cardiopulmonary bypass in the treatment of human cardiac arrest

OBJECTIVE

To study the use of emergency department (ED) femoro-femoral cardiopulmonary bypass (CPB) in the resuscitation of medical cardiac arrest patients.

DESIGN

Prospective, uncontrolled trial.

SETTING

Urban academic ED staffed with board-certified emergency physicians (EPs).

PARTICIPANTS

Ten patients with medical cardiac arrest unresponsive to standard therapy.

INTERVENTIONS

Femoro-femoral CPB instituted by EPs.

RESULTS

The time of cardiac arrest prior to CPB (mean+/-SD) was 32.0+/-13.6 min. The cardiac output while on CPB was 4.09+/-1.03 L/min with an average of 229+/-111 min on bypass. All 10 patients had resumption of spontaneous cardiac activity while on CPB. Seven of these were weaned from CPB with intrinsic spontaneous circulation. Of these, six patients were transferred from the ED to the operating room for cannula removal and vessel repair while the other patient died in the ED soon after discontinuing CPB. Mean survival was 47.8+/-44.7 h in the six patients leaving the ED. Although these patients had successful hemodynamic resuscitation, there were no long-term survivors.

CONCLUSION

CPB instituted by EPs is feasible and effective for the hemodynamic resuscitation of cardiac arrest patients unresponsive to advanced cardiac life support therapy. Future efforts need to focus on improving long-term outcome.

Bedside assessment of myocardial performance in the critically ill

No measurement of myocardial performance currently available in the ICU can be regarded is ideal. Table 2 summarises the main features of the major monitoring techniques. As many of the indices of myocardial performance are interdependent, quantifying the contribution of each component to overall cardiac function is not possible currently, and the clinical utility of monitoring each individually is not therefore established. Bedside measurements of LV dimensions, volumes and ejection fraction, and the other indices of systolic and diastolic function can now be made, but the case for their routine use in influencing clinical practice remains unproven. Transoesophageal echocardiography has an important and established diagnostic role and has been used successfully for continuous monitoring during surgery, but practical considerations seriously limit its potential for routine use. Radionuclide techniques allow the measurement of many of the same parameters and have the potential for continuous use, but practical problems and the additional risk of radiation exposure may limit this application in the critical care environment. Doppler techniques are non-invasive, provide continuous data and are simple to operate, but the data provided has important limitations. Although the pulmonary artery catheter has been in use for over twenty years, questions regarding the information is provides concerning myocardial function remain and the extent to which it should influence therapeutic decisions is still controversial. However with the development of additional facilities, particularly the continuous measurement of cardiac output the pulmonary artery catheter seems likely to remain the mainstay of bedside monitoring of myocardial performance in the critically ill in the immediate future.