Darin J. Saltzman

The microvasculature in skeletal muscle: VI. Adrenergic innervation of arterioles in normotensive and spontaneously hypertensive rats

A microanatomical study of the adrenergic nerve plexus on the arterioles in the spinotrapezius muscle of normotensive and spontaneously hypertensive rats was carried out. The spinotrapezius muscle was selected since its microvasculature has been reconstructed in previous studies of this series. A modified glyoxylic acid amine densification technique was used to visualize the major portion of the microvascular nerve plexus. The nerve plexus density was quantified in the form of fiber length per unit area of vascular smooth muscle media. The adrenergic innervation was found to be limited to the arterial/arteriolar side of the microcirculation and positioned in close vicinity to vascular smooth muscle, in line with previous reports. Substantial variations of the nerve plexus density could be detected along the arterioles. Arcade arterioles show a significant reduction of the adrenergic innervation compared to that of the thoracodorsal supply artery. There was a significant elevation of the nerve plexus density at the origin of the transverse arterioles at the arcade arterioles, a site that in the past has been shown to exhibit the highest microvascular tonus in all arterioles of this organ. Distal to this site, transverse arterioles exhibit a progressive reduction of adrenergic plexus density toward their capillary endings, in line with the termination of vascular smooth muscle in these small branches. Sporadic fiber extensions were encountered leading from some of the transverse arterioles into the capillary network per se, but no regular innervation was detected in capillaries or in venules. These results suggest that the transverse arterioles may play a central role in nervous control of blood flow to the capillaries of muscle. Compared with the Wistar and Wistar-Kyoto strain, the spontaneously hypertensive rats exhibit qualitatively a similar pattern, but show quantitatively a significantly higher plexus density in the thoracodorsal artery and the arcade arterioles, a factor that may contribute to the elevated arteriolar tone.

Microvascular Oxygen Delivery and Interstitial Oxygenation during Sodium Pentobarbital Anesthesia

Background Anesthesia may represent a considerable bias in experimental medicine, particularly in conditions of stress (such as hemorrhage). Sodium pentobarbital (PB), widely used for cardiovascular investigations, may impair oxygen delivery by hemodynamic and respiratory depression. The critical issue, however, is whether the microcirculation can still maintain tissue oxygenation during anesthesia. To answer this question, the authors studied the effect of PB anesthesia on subcutaneous microvascular oxygen delivery and interstitial oxygenation in Syrian golden hamsters. Methods Sodium pentobarbital anesthesia was induced by intravenous injection (30 mg/kg body weight) and maintained by a 15‐min infusion (2 mg [center dot] kg‐1 [center dot] min‐1), with animals breathing spontaneously (PB‐S) or ventilated with air (PB‐V). Systemic parameters evaluated were mean arterial pressure (MAP), heart rate, cardiac index (CI), arterial oxygen tension (PaO2), arterial carbon dioxide tension (PaCO2), base excess, and pH. Microvascular and interstitial oxygen tension (PO2), vessel diameter, red blood cell velocity (upsilonRBC), and blood flow (Qb) were measured in a dorsal skinfold preparation. Microcirculatory PO2 values were determined by phosphorescence decay. Results Sodium pentobarbital anesthesia significantly decreased CI, MAP, upsilonRBC, and Qb. During PB infusion, PaO2 values were 56 +/‐ 12.8 mmHg (PB‐S) and 115.9 +/‐ 14.6 mmHg (PB‐V) compared with 69.4 +/‐ 18.2 mmHg and 61.4 +/‐ 12.6 mmHg at baseline. However, microvascular PO2 was reduced by 25–55% in both groups, resulting in an interstitial PO2 decrease from 23.9 +/‐ 5.6 mmHg (control) to 13.1 +/‐ 9.1 mmHg (PB‐S) and 15.2 +/‐ 7 mmHg (PB‐V). Microcirculatory PO2 values were restored 30 min after PB infusion, even though hemodynamic depression and a light anesthetic plane were maintained. Conclusions Sodium pentobarbital anesthesia caused impairment of microvascular oxygen delivery and interstitial oxygenation, effects that were not prevented by mechanical ventilation. Although these effects were restricted to deep anesthetic planes, prolonged hemodynamic depression suggests that caution is warranted when using PB as an anesthetic in cardiovascular investigations.

Hemoglobin measurement patterns during noninvasive diffuse optical spectroscopy monitoring of hypovolemic shock and fluid replacement

The purpose of this study is to demonstrate the feasibility of broadband diffuse optical spectroscopy (DOS) for noninvasive optical monitoring of differentiating patterns of total tissue hemoglobin (THC), oxy- (OxyHb), and deoxyhemoglobin (DeOxyHb) concentrations during hypovolemic shock and subsequent fluid replacement with saline and whole blood. The goal of this DOS application is to determine the efficacy of resuscitation efforts at the tissue level rather than currently available indirect and invasive measurements of hemodynamic parameters. 16 New Zealand white rabbits are hemorrhaged 20% of their total blood volume. In resuscitated animals, shed blood volume is replaced with equal volume of crystalloid or whole blood (five animals each). Physiological variables (cardiac output, mean arterial pressure, systemic vascular resistance, hematocrit) are measured invasively, while (OxyHb) and (DeOxyHb) are measured during the interventions using broadband DOS. During the pure hypovolemic hemorrhages, the decrease in THC is mainly due to the decrease in (OxyHb), since the decrease in THC due to blood loss results in decreased tissue perfusion, with a resultant increased tissue extraction of oxygen. The hemorrhage with the whole blood resuscitation model shows significant changes in (OxyHb) during resuscitation phases due to the higher oxygen carrying capacity of whole blood, as opposed to the limited volume replacement effects and the decreased tissue oxygen content from the euvolemic anemia of the saline resuscitation. Broadband DOS noninvasive optical monitoring reveals distinct patterns of total tissue hemoglobin, oxy-, and deoxyhemoglobin during hemorrhage. Further studies are needed to confirm potential clinical utility and accuracy under more complex clinical conditions in animal models and patients.

Postoperative Thrombotic Thrombocytopenic Purpura After Open Heart Operations

BACKGROUND Postoperative thrombotic thrombocytopenic purpura (pTTP) after cardiovascular operations has an alarmingly high mortality rate if untreated. Five patients after coronary artery bypass graft (CABG) procedure were diagnosed with pTTP when they were observed to have a persistent thrombocytopenia associated with symptoms of fever, renal insufficiency, thromboembolic events, or altered mental status in conjunction with a microangiopathic hemolytic anemia (MAHA). A guideline for early diagnosis, followed by timely treatment in these cases, is reviewed. METHODS A retrospective record review of postoperative patients with thrombocytopenia identified 5 patients that met the criteria for pTTP from 2004 to 2008. We examined these 5 cardiovascular surgical patients in terms of clinical presentation, laboratory data, and outcomes. RESULTS All patients had the combination of an unexplained thrombocytopenia (platelets < 50,000 mm(3)) in conjunction with a MAHA as determined by the presence of schistocytes. Symptoms of neurologic dysfunction and renal insufficiency developed in all patients. Thromboembolic events were noted in 1 patient. All patients underwent plasmapheresis. In 3 patients, response time to clinical recovery and normalization of hematologic laboratory values after plasmapheresis was 3, 4, and 8 days. Two patients did not recover and died. One patient had a clinical and laboratory recovery after 19 days of plasmapheresis; however, after 11 days, thrombocytopenia with MAHA developed and he died on day 53 from complications related to the operation. CONCLUSIONS Postoperative TTP should be recognized as a possible pathophysiologic mechanism for unexplained postoperative thrombocytopenia and treatment should be initiated once the diagnosis is established.

Antibiotics-First Versus Surgery for Appendicitis: A US Pilot Randomized Controlled Trial Allowing Outpatient Antibiotic Management

Study objective Randomized trials suggest that nonoperative treatment of uncomplicated appendicitis with antibiotics‐first is safe. No trial has evaluated outpatient treatment and no US randomized trial has been conducted, to our knowledge. This pilot study assessed feasibility of a multicenter US study comparing antibiotics‐first, including outpatient management, with appendectomy. Methods Patients aged 5 years or older with uncomplicated appendicitis at 1 US hospital were randomized to appendectomy or intravenous ertapenem greater than or equal to 48 hours and oral cefdinir and metronidazole. Stable antibiotics‐first‐treated participants older than 13 years could be discharged after greater than or equal to 6‐hour emergency department (ED) observation with next‐day follow‐up. Outcomes included 1‐month major complication rate (primary) and hospital duration, pain, disability, quality of life, and hospital charges, and antibiotics‐first appendectomy rate. Results Of 48 eligible patients, 30 (62.5%) consented, of whom 16 (53.3%) were randomized to antibiotics‐first and 14 (46.7%) to appendectomy. Median age was 33 years (range 9 to 73 years), median WBC count was 15,000/&mgr;L (range 6,200 to 23,100/&mgr;L), and median computed tomography appendiceal diameter was 10 mm (range 7 to 18 mm). Of 15 antibiotic‐treated adults, 14 (93.3%) were discharged from the ED and all had symptom resolution. At 1 month, major complications occurred in 2 appendectomy participants (14.3%; 95% confidence interval [CI] 1.8% to 42.8%) and 1 antibiotics‐first participant (6.3%; 95% CI 0.2% to 30.2%). Antibiotics‐first participants had less total hospital time than appendectomy participants, 16.2 versus 42.1 hours, respectively. Antibiotics‐first‐treated participants had less pain and disability. During median 12‐month follow‐up, 2 of 15 antibiotics‐first‐treated participants (13.3%; 95% CI 3.7% to 37.9%) developed appendicitis and 1 was treated successfully with antibiotics; 1 had appendectomy. No more major complications occurred in either group. Conclusion A multicenter US trial comparing antibiotics‐first to appendectomy, including outpatient management, is feasible to evaluate efficacy and safety.

Microvascular changes following four‐hour single arteriole occlusion

Free tissue transplantations are lengthy procedures that result in prolong tissue ischemia. Restoral of blood flow is essential for free flap recovery; however, upon reperfusion tissue that is viable may continue to be nonperfused. To further elucidate this pathophysiology skeletal muscle microcirculation was investigated during reperfusion following 4‐hour single arteriole occlusion.

Broadband diffuse optical spectroscopy assessment of hemorrhage- and hemoglobin-based blood substitute resuscitation

Hemoglobin-based oxygen carriers (HBOCs) are solutions of cell-free hemoglobin (Hb) that have been developed for replacement or augmentation of blood transfusion. It is important to monitor in vivo tissue hemoglobin content, total tissue hemoglobin [THb], oxy- and deoxy-hemoglobin concentrations ([OHb], [RHb]), and tissue oxygen saturation (S(t)O(2)=[OHb][THb]x100%) to evaluate effectiveness of HBOC transfusion. We designed and constructed a broadband diffuse optical spectroscopy (DOS) prototype system to measure bulk tissue absorption and scattering spectra between 650 and 1000 nm capable of accurately determining these tissue hemoglobin component concentrations in vivo. Our purpose was to assess the feasibility of using DOS to optically monitor tissue [OHb], [RHb], S(t)O(2), and total tissue hemoglobin concentration ([THb]=[OHb]+[RHb]) during HBOC infusion using a rabbit hypovolemic shock model. The DOS prototype probe was placed on the shaved inner thigh muscle of the hind leg to assess concentrations of [OHb], [RHb], [THb], as well as S(t)O(2). Hemorrhagic shock was induced in intubated New Zealand white rabbits (N=6) by withdrawing blood via a femoral arterial line to 20% blood loss (10-15 cckg). Hemoglobin glutamer-200 (Hb-200) 1:1 volume resuscitation was administered following the hemorrhage. These values were compared against traditional invasive measurements, serum hemoglobin concentration (sHGB), systemic blood pressure, heart rate, and blood gases. DOS revealed increases of [THb], [OHb], and tissue hemoglobin oxygen saturation after Hb-200 infusion, while blood total hemoglobin values continued did not increase; we speculate, due to hyperosmolality induced hemodilution. DOS enables noninvasive in vivo monitoring of tissue hemoglobin and oxygenation parameters during shock and volume expansion with HBOC and potentially enables the assessment of efficacy of resuscitation efforts using artificial blood substitutes.

Association of Admission Laboratory Values and the Timing of Endoscopic Retrograde Cholangiopancreatography With Clinical Outcomes in Acute Cholangitis

Importance Acute cholangitis (AC), particularly severe AC, has historically required urgent endoscopic decompression, although the timing of decompression is controversial. We previously identified 2 admission risk factors for adverse outcomes in AC: total bilirubin level greater than 10 mg/dL and white blood cell count greater than 20 000 cells/µL. Objectives To validate previously identified prognostic factors in AC, evaluate the effect of timing of endoscopic retrograde cholangiopancreatography on clinical outcomes, and compare recent experience with AC vs an historical cohort. Design, Setting, and Participants A retrospective analysis (2008-2015) of patients with AC (validation cohort, n = 196) was conducted at 2 academic medical centers to validate predictors of adverse outcome. Timing of endoscopic retrograde cholangiopancreatography and outcome were stratified by severity using the Tokyo Guidelines for acute cholangitis diagnosis. Outcomes for the validation cohort were compared with the derivation cohort (1995-2005; n = 114). Data analysis was conducted from July 1, 2015, to September 9, 2015. Main Outcomes and Measures Death and a composite outcome of death or organ failure. Results The median age of patients in the derivation cohort was 54 years (interquartile range, 40-65 years) and in the validation cohort was 59 years (45-67 years). Multivariate logistic regression analysis of the validation cohort confirmed white blood cell count of more than 20 000 cells/µL (odds ratio, 3.4; 95% CI, 1.2-9.5; P = .02) and total bilirubin level of more than 10 mg/dL (odds ratio, 5.4; 95% CI, 1.8-16.4; P = .003) as independent risk factors for poor outcomes. In the validation cohort, timing of endoscopic retrograde cholangiopancreatography was not significantly different between those with and without an adverse outcome, even when stratified by AC severity (moderate: median, 0.6 hours [interquartile range (IQR), 0.5-0.9] vs 1.7 hours [IQR, 0.7-18.0] and severe: median, 10.6 hours [IQR, 1.2-35.1] vs 25.5 hours [IQR, 15.5-58.5] for those with and without adverse events, respectively). Patients in the validation cohort had a shorter hospital length of stay (median, 7 days [IQR, 4-10 days] vs 9 days [IQR, 5-16 days]) and lower rate of intensive care unit admission (26% vs 82%), despite a higher rate of severe cholangitis (n = 131 [67%] vs n = 29 [25%]). There were no significant differences in the composite outcome between the validation and derivation cohorts (22 [18.6%] vs 44 [22.4%]; P = .47). Adjusted analysis demonstrated decreased mortality in the validation cohort (odds ratio, 0.3; 95% CI, 0.1-0.7; P = .01). Conclusions and Relevance White blood cell count greater than 20 000 cells/µL and total bilirubin level greater than 10 mg/dL are independent prognostic factors for adverse outcomes in AC. Consideration should be given to include these criteria in the Tokyo Guidelines severity assessment. Timing of endoscopic retrograde cholangiopancreatography does not appear to affect clinical outcomes in these patients. Management of AC has improved with time, with an overall shorter hospital length of stay, lower rate of intensive care unit admission, and a decreased adjusted mortality, demonstrating improvements in care efficiency and delivery.

Analysis of Exhaled Volatile Compounds Following Acute Superior Mesenteric Artery Occlusion in a Pilot Rat Study

BACKGROUND Prompt diagnosis and treatment of acute mesenteric ischemia (AMI) requires a high index of suspicion for timely management. Poor clinical outcomes and delays in surgical treatment are demonstrated even in modern clinical series. Recognition of exhaled volatile organic compounds (VOCs) specific to AMI may facilitate early detection and diagnosis and improve patient outcomes. METHODS Adult Wistar rats (n = 5) were intubated and anesthetized, and control tracheostomy breath samples were collected using Tedlar gas sample bags. Intestinal ischemia was induced by placing an occlusive clip across the superior mesenteric artery, and breath samples were collected after 1 hour of intestinal ischemia and after 15 minutes of intestinal reperfusion. Gas chromatography was used to identify and measure levels of VOCs obtained, and measured retention indices were compared with known values in the Kovats retention index database. RESULTS Multiple retention indices (n = 41) were noted on gas chromatography, representing a variety of VOCs detected. Z,Z-farnesol (C15H26O), an isoprenoid, was the only compound detected that was undetectable during the control phase (median = 0 cts/sec) but which significantly elevated during the ischemic (median = 34 cts/sec, range = 25-37) and reperfusion (median = 148 cts/sec, range = 42-246) phases. Three other isoprenoid compounds (E,E-alpha-farnesene, germacrene A, and Z,Z-4,6,8-megastigmatriene) were also detected in all five animals, but their levels did not differ significantly between control, ischemic, and reperfusion phases. CONCLUSIONS This pilot study demonstrates the feasibility of analyzing exhaled VOCs using a novel rat model for AMI. These findings may be useful for the development and identification of similar assays for the rapid diagnosis of AMI.

Nonoperative Management of Appendicitis: Avoiding Hospitalization and Surgery

The meta-analysis of studies of nonoperative management of acute appendicitis by Findlay and colleagues concluded that surgery more often led to successful treatment, defined as lack of appendicitis recurrence, and found “no convincing evidence” that an antibiotics-first approach reduced complications. This conclusion comes from a medical perspective of eliminating disease as opposed to minimizing the impact of that disease on the patient. The results could be interpreted alternatively as favoring antibiotics because, during 1 year, only about 25% of antibiotics-first treated participants had surgery, compared with 100% of those getting traditional urgent appendectomy. Many laypersons would view surgery itself as among the major complications to avoid. Alternatively, other major complications could have been portrayed as rare and, as of yet, found to be no more frequent among antibiotic-treated participants. Minor complications, such as wound infections, particularly with open procedures, have been found to be substantially less frequent with an antibiotic strategy. That antibiotics were associated with a slightly longer hospitalization ignores that all studies required a minimal hospital stay for those treated with antibiotics as opposed to earliest discharge based on standard postoperative milestones, such as clinical stability, oral intake, and pain control. We recently conducted an NIH-sponsored pilot study among patients with clinically and CT-confirmed acute uncomplicated appendicitis and found that approximately 90% of antibiotic-randomized patients initially treated with a long-acting parenteral antibiotic (ie ertapenem) reached stability and were discharged straight from the emergency department. This is akin to treatment of acute uncomplicated diverticulitis, and the minority of antibiotic-treated patients with recurrent appendicitis could similarly be offered the option of antibiotic retreatment. That none of our participants had early antibiotic failure as opposed to approximately 10% observed in past trials suggests that many operations might have been done prematurely out of caution and the greater opportunity afforded by hospitalization,