Cardiovascular Effects of Anesthesia and Operation

Regional Anesthesia is Associated with Improved Mortality and Morbidity in Patients with Congestive Heart Failure Undergoing Lower Extremity Amputation

BACKGROUND

While existing literature reports variable results of general anesthesia (GA) and regional anesthesia (RA) in patients undergoing lower extremity amputation (LEA), the effect of RA on patients with congestive heart failure (CHF) has not been explored. This study aims to assess whether the choice of anesthesia plays a role in influencing outcomes within this vulnerable population.

METHODS

Using the American College of Surgeons National Surgical Quality Improvement Program files between 2005 and 2022, all patients receiving LEA were identified, and the subset of patients with CHF was included. Patient characteristics and 30-day outcomes were compared using χ2 or Fischer's exact test as appropriate for categorical variables and the independent t-test or Mann-Whitney U test as appropriate for continuous variables. The association between anesthesia modality and post-operative outcomes was studied using multivariable logistic regression analysis.

RESULTS

A total of 5,831 patients (4,779 undergoing GA, 1,052 undergoing RA) with a diagnosis of CHF undergoing LEA were identified. On multivariable logistic regression analysis, RA was associated with lower mortality (adjusted odds ratio [aOR] 0.79, 95% CI 0.65-0.97), pneumonia (aOR 0.76, 95% CI 0.58-0.99), septic shock (aOR 0.64, 95% CI 0.47-0.88), post-operative blood transfusion (aOR 0.82, 95% CI 0.70-0.97), and 30-day readmission (aOR 0.79, 95% CI 0.64-0.97).

CONCLUSIONS

This study demonstrates that RA for LEA in patients with CHF is associated with decreased morbidity and mortality compared to GA. While furthermore research is needed to confirm this association, RA should be at least considered in CHF patients undergoing LEA when feasible.

Clinical outcomes of percutaneous transforaminal endoscopic decompression for the treatment of degenerative lumbar scoliosis associated with spinal stenosis in elderly individuals: a matched comparison study

PURPOSE

This retrospective cohort study evaluated the efficacy and safety of percutaneous transforaminal endoscopic decompression (PTED) in elderly patients with degenerative lumbar scoliosis (DLS) associated with lumbar spinal stenosis (LSS).

STUDY DESIGN

A matched comparison study.

METHODS

In total, 97 patients with DLS associated with LSS who underwent PTED under local anesthesia between 2016 and 2021 were retrospectively analyzed. Using the inclusion and exclusion criteria, 24 patients aged ≥ 80 years were screened and included in the study group. Then, 24 patients aged 50-80 years were matched according to gender, date of surgery, and surgical levels were included in the control group. Clinical outcomes such as the visual analog scale (VAS) score, Oswestry Disability Index (ODI) score, modified MacNab criteria, radiological parameters, and complications were assessed. The independent sample t-test, Pearson's chi-square test and Fisher's exact test were used to compare the parameters between the study and control groups.

RESULTS

The study group had significantly higher mean American Society of Anesthesiologists classification and age-adjusted Charlson Comorbidity Index scores than the control group (2.42 ± 0.72) vs. 5.25 ± 1.03 and 1.67 ± 0.76 vs. 3.17 ± 2.10, respectively). The VAS scores for pain in two legs and back and ODI scores significantly improved at two weeks after surgery and at the final followup (p < 0.05). The study group had higher back pain VAS and ODI scores than the control group at the final followup (p < 0.05). In addition, the complication and patient satisfaction rates were similar between the two groups (p > 0.05). The overall radiological parameters were comparable between the two groups, and there was no significant deterioration in coronal imbalance or loss of disc height between the two groups.

CONCLUSION

Elderly patients (aged ≥ 80 years) with DLS associated with LSS are less fit and have a greater number of comorbidities. However, they can achieve satisfactory outcomes with PTED, which are comparable to those of patients < 80 years. PTED under local anesthesia can also be an efficient alternative to conventional open lumbar decompression surgery for treating elderly patients with comorbidities.

In Patients with Heart Failure Undergoing Carotid Endarterectomy, Locoregional Anesthesia is Not Associated with Decreased Mortality, Stroke, or Myocardial Infarction Compared to General Anesthesia

BACKGROUND

While existing literature reports no benefit of locoregional anesthesia (LRA) over general anesthesia (GA) in patients undergoing carotid endarterectomy (CEA), the effect of LRA on patients with congestive heart failure (CHF) has not been explored. This study aims to assess whether the choice of anesthesia plays a role in influencing outcomes within this population.

METHODS

Using the American College of Surgeons National Surgical Quality Improvement Program (ACS-NSQIP) files between 2005 and 2022 and the procedural targeted ACS-NSQIP database for CEA between 2011-2022, all patients receiving CEA were identified, and the subset of patients with CHF was included. Patient characteristics and 30-day outcomes were compared using χ2 or Fischer's exact test as appropriate for categorical variables and the independent t-test or Mann-Whitney U test as appropriate for continuous variables. Mortality, stroke, myocardial infarction (MI), and major adverse cardiac events (MACE) were compared between patients receiving GA and LRA using univariate analysis.

RESULTS

A total of 3,040 patients (2,733 undergoing GA, 307 undergoing LRA) with a diagnosis of CHF undergoing CEA were identified. No difference in mortality (GA 3.1% vs. LRA 4.6%, P = 0.162), MI (GA 3.0% vs. LRA 2.3%, P = 0.478), stroke (2.4% vs. 2.6%, P = 0.805) or MACE (GA 7.4% vs. LRA 8.1%, P = 0.654) was observed. LRA patients had a significantly lower hospital stay compared to GA patients (1 day [interquartile range (IQR) 1-3] vs. 2 days [IQR 1-4], P < 0.001). Shunt was more commonly used in patients receiving GA (32.9% vs. 12.5%, P < 0.001) compared to LRA.

CONCLUSIONS

While utilizing LRA compared to GA during CEA in patients with CHF is associated with a shorter hospital stay and less intraoperative shunting, the choice of anesthesia did not impact the outcomes of mortality, MI or stroke. Further research is needed to determine the effect of LRA on the outcomes of CEA among patients with different stages of heart failure.

Single-center experience with the JETi Hydrodynamic Thrombectomy System for acute limb ischemia

OBJECTIVE

Acute limb ischemia (ALI) remains a vascular emergency with high morbidity and mortality. While the JETi Hydrodynamic Thrombectomy System (Abbott) offers a percutaneous approach to fragment and aspirate the thrombus in patients with arterial occlusions, data on its efficacy and safety are limited. This study reports our early experience using the JETi device to treat ALI at our institution.

METHODS

This is a single-center, retrospective review of patients with ALI treated with the JETi device between September 2020 and December 2022. Patients were included if the JETi device was used either as a primary intervention or as an adjunct procedure. The primary endpoint was technical success defined as <50% residual thrombus after intervention. Secondary endpoints included achieving complete resolution of the thrombus on angiogram, acute kidney injury (AKI), major bleeding, 30-day major amputation, and 30-day mortality.

RESULTS

A total of 59 JETi procedures for ALI (median age 62 years [interquartile range: 56-71 years]) were performed on 39 male and 20 female patients. The median time from onset of symptoms to hospitalization was 24 hours (interquartile range: 4-168 hours). Rutherford classifications were I (10), IIa (27), IIb (14), and undocumented (8). Etiology of ALI was native vessel thrombosis (27), embolism (16), graft/stent thrombosis (14), and iatrogenic (2). A total of 124 vessels were treated, with an average of 2.1 vessels per procedure. The primary outcome was achieved in 86% (107/124) of the arteries, with 82% (102/124) successfully opened using the JETi device alone without the need for any adjunctive therapy. Complete resolution of the thrombus using JETi was achieved in 81% (101/124) arteries, with or without the use of adjunctive therapy. A total of 6.7% (4/59) patients required a major limb amputation within 30 days despite successful recanalization, and one 30-day mortality was recorded. Complications included distal embolization (5), access site hematoma (2), and AKI (4). No major bleeding, hemolysis-induced AKI, or vessel dissection or perforation was observed.

CONCLUSIONS

The JETi device appears to be a safe and effective percutaneous treatment option in the management of ALI. It provides definitive treatment with a high technical success rate of 86% and a good safety profile.

Guidelines for assessing maternal cardiovascular physiology during pregnancy and postpartum

Maternal mortality rates are at an all-time high across the world and are set to increase in subsequent years. Cardiovascular disease is the leading cause of death during pregnancy and postpartum, especially in the United States. Therefore, understanding the physiological changes in the cardiovascular system during normal pregnancy is necessary to understand disease-related pathology. Significant systemic and cardiovascular physiological changes occur during pregnancy that are essential for supporting the maternal-fetal dyad. The physiological impact of pregnancy on the cardiovascular system has been examined in both experimental animal models and in humans. However, there is a continued need in this field of study to provide increased rigor and reproducibility. Therefore, these guidelines aim to provide information regarding best practices and recommendations to accurately and rigorously measure cardiovascular physiology during normal and cardiovascular disease-complicated pregnancies in human and animal models.

Locoregional anesthesia is associated with decreased cardiac complications in symptomatic heart failure patients undergoing carotid endarterectomy

OBJECTIVE

Although the current literature reports no advantage for locoregional anesthesia (LRA) over general anesthesia (GA) in patients undergoing carotid endarterectomy (CEA), there remains a gap in understanding the impact of LRA on individuals with congestive heart failure (CHF). This study aims to assess whether the choice of anesthesia influences the rates of perioperative complications within this patient population.

METHODS

Using the Vascular Quality Initiative CEA module, all patients undergoing CEA between 2013 and 2023 were identified. The subset of patients with CHF was included, and patients were divided based on the type of anesthesia received. Patient characteristics and outcomes were compared using the χ2 or Fischer's exact test as appropriate for categorical variables and the independent t test or Mann-Whitney U test as appropriate for continuous variables. A sensitivity analysis was performed based on the symptomatic status of CHF, and the association between anesthesia modality and postoperative outcomes was studied using multivariable logistic regression analysis. The primary outcomes of this study included perioperative stroke, myocardial infarction (MI), acute HF, and the combination of MI and acute HF defined as major cardiac complications.

RESULTS

A total of 21,292 patients (19,730 receiving GA, 1562 receiving LRA) with a diagnosis of CHF undergoing CEA were identified. On multivariable logistic regression analysis, LRA was independently associated with lower MI (odds ratio [OR]; 0.35; 95% confidence interval [CI], 0.13-0.96), acute HF (OR, 0.27; 95% CI, 0.09-0.87), major cardiac complications (OR, 0.30; 95% CI, 0.13-0.67), hemodynamic instability (OR, 0.64; 95% CI, 0.53-0.78), cranial nerve injury (OR, 0.40; 95% CI, 0.19-0.81), shunt use (OR, 0.25; 95% CI, 0.20-0.31), and neuromonitoring device use (OR, 0.20; 95% CI, 0.17-0.24) compared with GA in patients with symptomatic CHF. No difference in MI, acute HF, and major cardiac complications was seen in patients with asymptomatic CHF.

CONCLUSIONS

CEA can be performed safely in patients with CHF. Using LRA is associated with a decreased incidence of perioperative cardiac complications in patients with symptomatic HF undergoing CEA.

Intra-cardiac motion detection catheter for the early identification of acute pericardial tamponade during invasive cardiac procedures

Objectives

To develop and test an intra-cardiac catheter fitted with accelerometers to detect acute pericardial effusion prior to the onset of hemodynamic compromise.

Background

Early detection of an evolving pericardial effusion is critical in ensuring timely treatment. We hypothesized that the reduction in movement of the lateral heart border present in developing pericardial effusions could be quantified by positioning an accelerometer in a lateral cardiac structure.

Methods

A "motion detection" catheter was created by implanting a 3-axis accelerometer at the distal tip of a cardiac catheter. The pericardial space of 5 adult sheep was percutaneously accessed, and pericardial tamponade was created by infusion of normal saline. The motion detection catheter was positioned in the coronary sinus. Intracardiac echocardiography was used to confirm successful creation of pericardial effusion and hemodynamic parameters were collected.

Results

Statistically significant reduction in acceleration from baseline was detected after infusion of only 40 ml of normal saline (p < 0.05, ANOVA). In comparison, clinically significant change in systolic blood pressure (defined as >10% drop in baseline systolic blood pressure) occurred after infusion of 80 ml of normal saline (107 ± 22 mmHg vs. 90 ± 12 mmHg p = 0.97, ANOVA), and statistically significant change was recorded only after infusion of 200 ml (107 ± 22 mmHg vs. 64 ± 5 mmHg, p < 0.05, ANOVA).

Conclusions

An intra-cardiac motion detection catheter is highly sensitive in identifying acute cardiac tamponade prior to clinically and statistically significant changes in systolic blood pressure, allowing for early detection and treatment of this potentially life-threatening complication of all modern percutaneous cardiac interventions.

Characterization of Anesthesia in Rats from EEG in Terms of Long-Range Correlations

Long-range correlations are often used as diagnostic markers in physiological research. Due to the limitations of conventional techniques, their characterizations are typically carried out with alternative approaches, such as the detrended fluctuation analysis (DFA). In our previous works, we found EEG-related markers of the blood-brain barrier (BBB), which limits the penetration of major drugs into the brain. However, anesthetics can penetrate the BBB, affecting its function in a dose-related manner. Here, we study two types of anesthesia widely used in experiments on animals, including zoletil/xylazine and isoflurane in optimal doses not associated with changes in the BBB. Based on DFA, we reveal informative characteristics of the electrical activity of the brain during such doses that are important for controlling the depth of anesthesia in long-term experiments using magnetic resonance imaging, multiphoton microscopy, etc., which are crucial for the interpretation of experimental results. These findings provide an important informative platform for the enhancement and refinement of surgery, since the EEG-based DFA analysis of BBB can easily be used during surgery as a tool for characterizing normal BBB functions under anesthesia.

A cross-species validation of single-beat metrics of cardiac contractility

The assessment of left ventricular (LV) contractility in animal models is useful in various experimental paradigms, yet obtaining such measures is inherently challenging and surgically invasive. In a cross-species study using small and large animals, we comprehensively tested the agreement and validity of multiple single-beat surrogate metrics of LV contractility against the field-standard metrics derived from inferior vena cava occlusion (IVCO). Fifty-six rats, 27 minipigs and 11 conscious dogs underwent LV and arterial catheterization and were assessed for a range of single-beat metrics of LV contractility. All single-beat metrics were tested for the various underlying assumptions required to be considered a valid metric of cardiac contractility, including load-independency, sensitivity to inotropic stimulation, and ability to diagnose contractile dysfunction in cardiac disease. Of all examined single-beat metrics, only LV maximal pressure normalized to end-diastolic volume (EDV), end-systolic pressure normalized to EDV, and the maximal rate of rise of the LV pressure normalized to EDV showed a moderate-to-excellent agreement with their IVCO-derived reference measure and met all the underlying assumptions required to be considered as a valid cardiac contractile metric in both rodents and large-animal models. Our findings demonstrate that single-beat metrics can be used as a valid, reliable method to quantify cardiac contractile function in basic/preclinical experiments utilizing small- and large-animal models KEY POINTS: Validating and comparing indices of cardiac contractility that avoid caval occlusion would offer considerable advantages for the field of cardiovascular physiology. We comprehensively test the underlying assumptions of multiple single-beat indices of cardiac contractility in rodents and translate these findings to pigs and conscious dogs. We show that when performing caval occlusion is unfeasible, single-beat metrics can be utilized to accurately quantify cardiac inotropic function in basic and preclinical research employing various small and large animal species. We report that maximal left-ventricular (LV)-pressure normalized to end-diastolic volume (EDV), LV end-systolic pressure normalized to EDV and the maximal rate of rise of the LV pressure waveform normalized to EDV are the best three single-beat metrics to measure cardiac inotropic function in both small- and large-animal models.

Low-Concentration Norepinephrine Infusion for Major Surgery: A Safety and Feasibility Pilot Randomized Controlled Trial

BACKGROUND

Prevention of hypotension during the intra- and postoperative period is an important goal. Peripheral administration of low-concentration norepinephrine may be a safe and effective strategy to reduce the risk of hypotension.

METHODS

We conducted a 2-center, randomized pilot feasibility trial, with a target of 60 adult patients undergoing major noncardiac surgery. We randomized patients to receive a peripheral low-concentration (10 µg/mL) norepinephrine or placebo (saline 0.9%) infusion. The study drug infusion was titrated to achieve a minimum systolic blood pressure target, preselected within 10% of baseline value and within the range limit 100 to 120 mm Hg during surgery and for up to 4 or 24 hours postoperatively.

RESULTS

We achieved a high consent rate (84%), successful study drug administration throughout surgery (98% of patients) and absence of unblinding. There were no important study drug-related adverse events. The average intraoperative systolic blood pressure was 120 ± 12.6 mm Hg in the norepinephrine group and 115 ± 14.9 mm Hg in the placebo group. The mean difference between the intraoperative systolic blood pressure achieved less the preselected minimum systolic blood pressure target was 10.0 ± 12.7 mm Hg in the norepinephrine group and 2.9 ± 14.7 mm Hg in the placebo group; difference in means, 7.1 (95% confidence interval, 0.2-14.0) mm Hg.

CONCLUSIONS

A future large trial evaluating the effectiveness and safety of peripheral administration of low-concentration norepinephrine during the perioperative period is feasible, and likely to achieve a minimum systolic blood pressure threshold.

General Anesthesia Leads to Underestimation of Regurgitation Severity in Patients With Secondary Mitral Regurgitation Undergoing Transcatheter Mitral Valve Repair

OBJECTIVES

To evaluate the effect of general anesthesia (GA) on severity of mitral regurgitation (MR) in patients undergoing transcatheter mitral valve repair (TMVR).

DESIGN

Retrospective cohort study.

SETTING

Tertiary care university hospital.

PARTICIPANTS

Fifty consecutive patients with symptomatic severe MR and extremely high surgical risk.

INTERVENTION

TMVR under GA.

MEASUREMENTS AND RESULTS

Transesophageal echocardiography was performed during the preprocedural workup under conscious sedation and during TMVR under GA. After the parameters of MR were assessed, color-flow jet area (CJA), vena contracta (VC), effective regurgitant orifice area (EROA), regurgitant volume (RVOL), three-dimensional (3D) vena contracta area (VCA), and severity of MR were compared between the two examinations. In patients with primary MR (n = 11), there were no significant differences in CJA, VC, EROA, RVOL, or 3D-VCA between pre- and intraprocedural transesophageal echocardiography. In patients with secondary MR (n = 39), GA led to significant decreases of CJA (10 ± 7 v 7 ± 3 cm², p < 0.001), VC (5.5 ± 1.6 v 4.7 ± 1.5 mm, p = 0.002), EROA (30 ± 11 v 24 ± 10 mm², p < 0.001), and RVOL (47 ± 17 v 34 ± 13 mL/beat, p < 0.001). Consequently, GA led to a downgrade of regurgitation severity classification in 44% of patients when assessed by two-dimensional analysis. When evaluated by 3D analysis, GA also led to a significant but less extensive decrease of MR (3D-VCA: 66 ± 27 v 60 ± 29 mm², p = 0.002), and subsequent downgrade of MR classification in 20% of patients.

CONCLUSIONS

GA underestimates regurgitation severity in patients with secondary, but not primary MR, undergoing TMVR. This effect must be considered when evaluating the immediate result of the procedure.

ECG changes after non-cardiac surgery: a prospective observational study in intermediate-high risk patients

BACKGROUND

Efforts to mitigate the risk for perioperative cardiac events focus on both patient's and operation's risk and often include a preprocedural electrocardiogram (ECG). The merits of postprocedural ECG for detection of occult cardiac events occurring during surgery are unknown. We aim to explore the incidence of pre, and new postprocedural ECG pathologies in an intermediate-high risk population undergoing non-cardiac surgery.

METHODS

This single-center, prospective, observational study, included patients older than 18 years with at least two cardiovascular risk factors who were scheduled for non-cardiac surgery. All patients had pre, and postprocedural ECG. The ECG was analyzed and coded according to the Minnesota criteria. A multivariable logistic regression analysis was performed for indices associated with new postoperative ECG pathologies.

RESULTS

A total of 217 patients were enrolled. Preoperative pathologic ECG changes were recorded in 62.2% of the patients. Postoperatively, new ECG pathologies were documented in 49.8% of patients, most commonly T-wave changes (36.4% of changes). Pathologic ECG changes at baseline (OR 3.15, 95% CI [1.61-6.17]; P<0.01), diabetes (OR 1.93, 95% CI [1.02-3.64]; P=0.04), history of ischemic heart disease (OR 2.14, 95% CI [1.03-4.47]; P=0.04), higher volumes of fluid replacement (OR 1.70, 95% CI [1.10-2.61]; P=0.01) and higher levels of preoperative hemoglobin (OR 1.24, 95% CI [1.04-1.47]; P=0.01) were all independently associated with postoperative ECG changes.

CONCLUSIONS

Pre-, but most importantly, postoperative ECG changes are common in intermediate-high risk surgical patients. Postoperative ECG may be valuable to disclose silent cardiovascular events that occurred during surgery.

Hyperthermia-Induced Controlled Local Anesthesia Administration Using Gelatin-Coated Iron-Gold Alloy Nanoparticles

The lack of optimal methods employing nanoparticles to administer local anesthesia often results in posing severe risks such as non-biocompatibility, in vivo cytotoxicity, and drug overdose to patients. Here, we employed magnetic field-induced hyperthermia to achieve localized anesthesia. We synthesized iron-gold alloy nanoparticles (FeAu Nps), conjugated an anesthetic drug, Lidocaine, and coated the product with gelatin to increase the biocompatibility, resulting in a FeAu@Gelatin-Lidocaine nano-complex formation. The biocompatibility of this drug-nanoparticle conjugate was evaluated in vitro, and its ability to trigger local anesthesia was also evaluated in vivo. Upon exposure to high-frequency induction waves (HFIW), 7.2 ± 2.8 nm sized superparamagnetic nanoparticles generated heat, which dissociated the gelatin coating, thereby triggering Lidocaine release. MTT assay revealed that 82% of cells were viable at 5 mg/mL concentration of Lidocaine, indicating that no significant cytotoxicity was induced. In vivo experiments revealed that unless stimulated with HFIW, Lidocaine was not released from the FeAu@Gelatin-Lidocaine complex. In a proof-of-concept experiment, an intramuscular injection of FeAu@Gelatin-Lidocaine complex was administered to the rat posterior leg, which upon HFIW stimulation triggered an anesthetic effect to the injected muscle. Based on our findings, the FeAu@Gelatin-Lidocaine complex can deliver hyperthermia-induced controlled anesthetic drug release and serve as an ideal candidate for site-specific anesthesia administration.

A propensity score-matched analysis indicates screening for asymptomatic coronary artery disease does not predict cardiac events in kidney transplant recipients

Screening for asymptomatic coronary artery disease prior to kidney transplantation aims to reduce peri- and post-operative cardiac events. It is uncertain if this is achieved. Here, we investigated whether pre-transplant screening with a stress test or coronary angiogram associated with any difference in major adverse cardiac events (MACE) up to five years post-transplantation. We examined a national prospective cohort recruited to the Access to Transplant and Transplant Outcome Measures study who received a kidney transplant between 2011-2017, and linked patient demographics and details of cardiac screening investigations to outcome data extracted from the Hospital Episode Statistics dataset and United Kingdom Renal Registry. Propensity score matched groups were analyzed using Kaplan-Meier and Cox survival analyses. Overall, 2572 individuals were transplanted in 18 centers; 51% underwent screening and the proportion undergoing screening by center ranged from 5-100%. The incidence of MACE at 90 days, one and five years was 0.9%, 2.1% and 9.4% respectively. After propensity score matching based on the presence or absence of screening, 1760 individuals were examined (880 each in screened and unscreened groups). There was no statistically significant association between screening and MACE at 90 days (hazard ratio 0.80, 95% Confidence Interval 0.31-2.05), one year (1.12, 0.51-2.47) or five years (1.31, 0.86-1.99). Age, male sex and history of ischemic heart disease were associated with MACE. Thus, there is no association between screening for asymptomatic coronary artery disease and MACE up to five years post-transplant. Practices involving unselected screening of transplant recipients should be reviewed.

Respiratory pump maintains cardiac stroke volume during hypovolemia in young, healthy volunteers

Spontaneous breathing has beneficial effects on the circulation, since negative intrathoracic pressure enhances venous return and increases cardiac stroke volume. We quantified the contribution of the respiratory pump to preserve stroke volume during hypovolemia in awake, young, healthy subjects. Noninvasive stroke volume, cardiac output, heart rate, and mean arterial pressure (Finometer) were recorded in 31 volunteers (19 women), 19–30 yr old, during normovolemia and hypovolemia (approximating 450- to 500-ml reduction in central blood volume) induced by lower-body negative pressure. Control-mode noninvasive positive-pressure ventilation was employed to reduce the effect of the respiratory pump. The ventilator settings were matched to each subject’s spontaneous respiratory pattern. Stroke volume estimates during positive-pressure ventilation and spontaneous breathing were compared with Wilcoxon matched-pairs signed-rank test. Values are overall medians. During normovolemia, positive-pressure ventilation did not affect stroke volume or cardiac output. Hypovolemia resulted in an 18% decrease in stroke volume and a 9% decrease in cardiac output ( P < 0.001). Employing positive-pressure ventilation during hypovolemia decreased stroke volume further by 8% ( P < 0.001). Overall, hypovolemia and positive-pressure ventilation resulted in a reduction of 26% in stroke volume ( P < 0.001) and 13% in cardiac output ( P < 0.001) compared with baseline. Compared with the situation with control-mode positive-pressure ventilation, spontaneous breathing attenuated the reduction in stroke volume induced by moderate hypovolemia by 30% (i.e., −26 vs. −18%). In the patient who is critically ill with hypovolemia or uncontrolled hemorrhage, spontaneous breathing may contribute to hemodynamic stability, whereas controlled positive-pressure ventilation may result in circulatory decompensation.

NEW & NOTEWORTHY Maintaining spontaneous respiration has beneficial effects on hemodynamic compensation, which is clinically relevant for patients in intensive care. We have quantified the contribution of the respiratory pump to cardiac stroke volume and cardiac output in healthy volunteers during normovolemia and central hypovolemia. The positive hemodynamic effect of the respiratory pump was abolished by noninvasive, low-level positive-pressure ventilation. Compared with control-mode positive-pressure ventilation, spontaneous negative-pressure ventilation attenuated the fall in stroke volume by 30%.

Leaky ryanodine receptors contribute to diaphragmatic weakness during mechanical ventilation

Ventilator-induced diaphragmatic dysfunction (VIDD) refers to the diaphragm muscle weakness that occurs following prolonged controlled mechanical ventilation (MV). The presence of VIDD impedes recovery from respiratory failure. However, the pathophysiological mechanisms accounting for VIDD are still not fully understood. Here, we show in human subjects and a mouse model of VIDD that MV is associated with rapid remodeling of the sarcoplasmic reticulum (SR) Ca(2+) release channel/ryanodine receptor (RyR1) in the diaphragm. The RyR1 macromolecular complex was oxidized, S-nitrosylated, Ser-2844 phosphorylated, and depleted of the stabilizing subunit calstabin1, following MV. These posttranslational modifications of RyR1 were mediated by both oxidative stress mediated by MV and stimulation of adrenergic signaling resulting from the anesthesia. We demonstrate in the murine model that such abnormal resting SR Ca(2+) leak resulted in reduced contractile function and muscle fiber atrophy for longer duration of MV. Treatment with β-adrenergic antagonists or with S107, a small molecule drug that stabilizes the RyR1-calstabin1 interaction, prevented VIDD. Diaphragmatic dysfunction is common in MV patients and is a major cause of failure to wean patients from ventilator support. This study provides the first evidence to our knowledge of RyR1 alterations as a proximal mechanism underlying VIDD (i.e., loss of function, muscle atrophy) and identifies RyR1 as a potential target for therapeutic intervention.

The effect of surgery (Ovariohysterectomy) on the plasma disposition of meloxicam following intravenous administration in dogs

Background

Meloxicam (MLX) is a nonsteroidal anti-inflammatory drug used in the relief of postoperative pain for human and veterinary medicine. This study was designed to investigate the effect of surgery on the plasma disposition of MLX in dogs undergoing ovariohysterectomy following a single intravenous injection at a dose of 0.2 mg/kg bodyweight. Eight crossbred bitches were used in the study. A two-phase experimental design with a 10-day washout period was used. Pre-operative MLX was administered intravenously to 8 bitches about 10 days before surgery (Phase I, control) at a dose of 0.2 mg/kg bodyweight and peri-operative MLX was administered intravenously after anaesthesia and 15 min before the start of surgery (Phase II). Blood samples were collected from all animals at various times between 1 and 96 h after the drug administrations in both phases. The drug concentrations were analysed using high performance liquid chromatography.

Results

The volume of plasma MLX distribution at steady-state (Vd_ss) of the control group (Vd_ss: 263.0 ml/kg) was significantly greater (P < 0.05) compared to that of the surgery group (Vd_ss: 149.3 ml/kg). The AUC values were higher (29.5 vs. 23.0 μg.h²/ml) and the CL values were lower (7.7 vs. 10.5 ml.h/kg) in the surgery group compared to the control group, respectively, but differences were not significant.

Conclusions

The results of the present study indicated that surgery could alter the plasma disposition of MLX and thus the drug efficacy and side effects such as gastrointestinal ulceration, unusual bleeding and loss of kidney function/failure when repeated doses are used.

Change in circulating blood volume following craniotomy

OBJECT

The importance of monitoring circulating blood volume (CBV) during perioperative management is widely recognized in critically ill patients. The purpose of this study was to investigate the change in CBV following craniotomy by using indocyanine-green pulse spectrophotometry.

METHODS

Circulating blood volume and plasma hormones related to stress and fluid regulation were measured five times: preoperatively, immediately postoperatively, and 1, 2, and 7 days after craniotomy was performed in 17 patients with a brain tumor or an unruptured aneurysm. The mean value of CBV preoperatively was 82 ml/kg, which decreased to 64 ml/kg (78%) immediately postoperatively and gradually recovered to 82 ml/kg on Day 7 postsurgery (p = 0.0069). The mean values of adrenaline, noradrenaline, arginine vasopressin, renin, and aldosterone were highest immediately postoperatively. The mean intraoperative balances of water and sodium were 1,090 ml and 113 mEq, respectively. Partial correlation coefficients of CBV to noradrenaline and serum sodium during the entire study were -0.430 (p = 0.0036) and 0.418 (p = 0.0048), respectively.

CONCLUSIONS

Attention should be paid to decreased CBV following craniotomy, which is caused by the shift of fluid to interstitial spaces due to surgical stress. Hypovolemia can be suspected from a postoperative decrease in serum sodium.