Optimal crystalloid volume ratio for blood replacement for maintaining hemodynamic stability and lung function: an experimental randomized controlled study

Comparison of the respiratory effects of commonly utilized general anaesthesia regimes in male Sprague-Dawley rats

Background: Respiratory parameters in experimental animals are often characterised under general anaesthesia. However, anaesthesia regimes may alter the functional and mechanical properties of the respiratory system. While most anaesthesia regimes have been shown to affect the respiratory system, the effects of general anaesthesia protocols commonly used in animal models on lung function have not been systematically compared. Methods: The present study comprised 40 male Sprague-Dawley rats divided into five groups (N = 8 in each) according to anaesthesia regime applied: intravenous (iv) Na-pentobarbital, intraperitoneal (ip) ketamine-xylazine, iv propofol-fentanyl, inhaled sevoflurane, and ip urethane. All drugs were administered at commonly used doses. End-expiratory lung volume (EELV), airway resistance (Raw) and tissue mechanics were measured in addition to arterial blood gas parameters during mechanical ventilation while maintaining positive end-expiratory pressure (PEEP) values of 0, 3, and 6 cm H2O. Respiratory mechanics were also measured during iv methacholine (MCh) challenges to assess bronchial responsiveness. Results: While PEEP influenced baseline respiratory mechanics, EELV and blood gas parameters (p < 0.001), no between-group differences were observed (p > 0.10). Conversely, significantly lower doses of MCh were required to achieve the same elevation in Raw under ketamine-xylazine anaesthesia compared to the other groups. Conclusion: In the most frequent rodent model of respiratory disorders, no differences in baseline respiratory mechanics or function were observed between commonly used anaesthesia regimes. Bronchial hyperresponsiveness in response to ketamine-xylazine anaesthesia should be considered when designing experiments using this regime. The findings of the present study indicate commonly used anaesthetic regimes allow fair comparison of respiratory mechanics in experimental animals undergoing any of the examined anaesthesia protocols.

Expiratory high-frequency percussive ventilation: a novel concept for improving gas exchange

Background

Although high-frequency percussive ventilation (HFPV) improves gas exchange, concerns remain about tissue overdistension caused by the oscillations and consequent lung damage. We compared a modified percussive ventilation modality created by superimposing high-frequency oscillations to the conventional ventilation waveform during expiration only (eHFPV) with conventional mechanical ventilation (CMV) and standard HFPV.

Methods

Hypoxia and hypercapnia were induced by decreasing the frequency of CMV in New Zealand White rabbits (n = 10). Following steady-state CMV periods, percussive modalities with oscillations randomly introduced to the entire breathing cycle (HFPV) or to the expiratory phase alone (eHFPV) with varying amplitudes (2 or 4 cmH₂O) and frequencies were used (5 or 10 Hz). The arterial partial pressures of oxygen (PaO₂) and carbon dioxide (PaCO₂) were determined. Volumetric capnography was used to evaluate the ventilation dead space fraction, phase 2 slope, and minute elimination of CO₂. Respiratory mechanics were characterized by forced oscillations.

Results

The use of eHFPV with 5 Hz superimposed oscillation frequency and an amplitude of 4 cmH₂O enhanced gas exchange similar to those observed after HFPV. These improvements in PaO₂ (47.3 ± 5.5 vs. 58.6 ± 7.2 mmHg) and PaCO₂ (54.7 ± 2.3 vs. 50.1 ± 2.9 mmHg) were associated with lower ventilation dead space and capnogram phase 2 slope, as well as enhanced minute CO₂ elimination without altering respiratory mechanics.

Conclusions

These findings demonstrated improved gas exchange using eHFPV as a novel mechanical ventilation modality that combines the benefits of conventional and small-amplitude high-frequency oscillatory ventilation, owing to improved longitudinal gas transport rather than increased lung surface area available for gas exchange.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02215-2.

Postpartum Hemorrhage Management and Blood Component Therapy

This article serves to highlight both the common nature and severity of postpartum hemorrhage (PPH). Identification of etiologies and management of each is reviewed. In addition, the evaluation and administration of proper blood component therapies and massive transfusion are also explained to help providers become comfortable with early administration and delivery of blood component therapies.

High-rise syndrome in cats and dogs

OBJECTIVE

To review the current literature pertaining to the pathophysiology, diagnosis, and treatment of injuries sustained from high-rise syndrome in cats and dogs.

ETIOLOGY

High-rise syndrome is defined as a fall from a height of 2 or more stories that results in a constellation of injuries, including thoracic, abdominal, orthopedic, and orofacial trauma. Animals often fall after slipping from windowsills, engaging in mating behavior, or chasing prey. Cats suffer less severe injuries than dogs due to their "righting reflex" and smaller body mass. Affected animals are younger, and the frequency of falls is higher in warmer months.

DIAGNOSIS

Physical examination coupled with radiographs, ultrasound, and computed tomography can diagnose a myriad of injuries that include pneumothorax, pleural or abdominal effusion, orthopedic fractures, and orofacial injuries. Bloodwork may identify anemia, thrombocytopenia, or increases in hepatic, renal, or pancreatic values consistent with trauma to these organs. Serial venous or arterial blood gas can help determine the severity of respiratory compromise and influence resuscitative efforts. Traditional coagulation tests and thromboelastography can assess trauma-induced coagulopathy and guide transfusion therapy.

THERAPY

Animals presenting in shock require hemodynamic stabilization. Initial resuscitation may incorporate crystalloids, colloids, blood products, and analgesics. Thoracic injuries may require oxygen, thoracocentesis, chest tube placement, and mechanical ventilation. Fractures and wounds are decontaminated and splinted/bandaged, with definitive fixation pursued after stabilization. Abdominal injuries are managed medically unless there is severe ongoing bleeding, sepsis, or injury to the urinary tract.

PROGNOSIS

In feline high-rise syndrome, the prognosis is generally excellent following treatment, with survival exceeding 90%. Canine literature is sparse. The largest retrospective study reported a >90% survival to discharge and a greater need for surgical stabilization in this species. There are no prognostic factors identified that are associated with survival for either species.

Blood loss estimation during posterior spinal fusion for adolescent idiopathic scoliosis

PURPOSE

Blood loss (BL) during posterior spinal fusion for adolescent idiopathic scoliosis (AIS) may be estimated using a variety of unproven techniques. Patient care and research on BL are likely impacted by a lack of standardization. A novel FDA-approved blood volume (BV) analysis system (BVA-100 Blood Volume Analyzer) allows rapid processing with > 97% accuracy. The purpose of this study was to investigate common methods for BL estimation.

METHODS

BV assessment was performed with the BVA-100. After obtaining a baseline sample of 5 mL of blood, 1 mL of I-131-labeled albumin was injected intravenously over 1 min. Five milliliter blood samples were then collected at 12, 18, 24, 30, and 36 min post-injection. Intravenous fluid was minimized to maintain euvolemia. Salvaged blood was not administered during surgery. BL was estimated using several common techniques and compared to the BV measurements provided by the BVA-100 (BVABL).

RESULTS

Thirty AIS patients were prospectively enrolled with major curves of 54° and underwent fusions of 10 levels. BL based on the BVA-100 (BVABL) was 519.2 [IQR 322.9, 886.2] mL. Previously published formulas all failed to approximate BVABL. Multiplying the cell saver volume return by 3 (CS3) approximates BVABL well with a Spearman correlation coefficient and ICC of 0.80 and 0.72, respectively. An extrapolated cell salvage-based estimator also showed high intraclass correlation coefficient (ICC) and Spearman coefficients with less bias than CS3.

CONCLUSION

Published formulaic approaches do not approximate true blood loss. Multiplying the cell saver volume by 3 or using the cell salvage-based estimator had the highest correlation coefficient and ICC.

LEVEL OF EVIDENCE

Prospective cohort Level 2.

Fluid Therapy in Pulmonary Disease: How Careful Do We Need to Be?

Intravenous fluid therapy is a vital and life-saving therapeutic in veterinary medicine. In the absence of heart or lung disease, trauma or sepsis there is limited evidence that fluid therapy will have a detrimental effect on lung function. In healthy dogs there is a reasonable level of experimental evidence that supraphysiologic rates of fluid are required before signs of fluid overload are made evident. In cats, however, this may not be the case. There are higher rates of asymptomatic myocardial disease, but even in the absence of that it seems that some cats may be susceptible to fluid overload. Where systemic inflammation already exists the careful homeostatic and protective mechanisms within the lung are deranged and increases in hydrostatic pressure are more likely to result in fluid movement into the lung tissues. Strategies including restricting the use of intravenous crystalloid fluid administration and using blood products for management of severe hemorrhage are of increasing importance in human trauma and seem to be associated with fewer pulmonary complications, and lower mortality. Managing dogs and cats with sepsis and acute respiratory distress syndrome is already challenging, but ensuring adequate vascular expansion needs to be balanced with avoiding excessive volume administration which may negatively impact pulmonary function. While fluids remain crucial to management of these conditions, there will be an ongoing requirement to balance need without providing excess. The use of point of care ultrasound may provide clinicians with a non-invasive and accessible way to do this.

Immune response in fluid therapy with crystalloids of different ratios or colloid for rats in haemorrhagic shock

This study investigated the association between different ratios of balanced salt based-crystalloid (PLASMA SOLUTION-A [CJ HealthCare, Seoul, Korea]) (the ratios of crystalloid for blood loss, 1:1, 1:2 and 1:3) or balanced salt-based colloid (VOLULYTE 6% [Fresenius Kabi, Germany]) (the ratio of colloid for blood loss, 1:1) to restore blood loss and immune response in rats with haemorrhagic shock. About 50% of total estimated blood volume was removed after anaesthesia. The fluid was administered for resuscitation after exsanguination, according to the type of fluid and the ratios of exsanguinated volume and fluid volume for resuscitation. After sacrifice, expression of immune cells in blood and tissues was evaluated. Histological analyses and syndecan-1 immunohistochemistry assays were performed on tissues. Endothelial damage according to syndecan-1 and cytokine levels in blood was also assessed. Fluid resuscitation with same, two-fold, or three-fold volumes of crystalloid, or same volume of colloid, to treat haemorrhagic shock in rats resulted in a similar increase in blood pressure. The expression of neutrophils in blood decreased significantly after colloid administration, compared to before exsanguination. Syndecan-1 expression increased after exsanguination and fluid resuscitation in all groups, without any significant difference. In conclusion, same volume of balanced salt-based crystalloid for blood loss was enough to restore BP at the choice of fluid for the management of haemorrhagic shock in the rats, compared with different ratios of crystalloid or same volume of colloid, on the aspect of immune response.