The impact of inspiratory pressure on stroke volume variation and the evaluation of indexing stroke volume variation to inspiratory pressure under various preload conditions in experimental animals

Use of stepwise lung recruitment maneuver to predict fluid responsiveness under lung protective ventilation in the operating room

Recent research has revealed that hemodynamic changes caused by lung recruitment maneuvers (LRM) with continuous positive airway pressure can be used to identify fluid responders. We investigated the usefulness of stepwise LRM with increasing positive end-expiratory pressure and constant driving pressure for predicting fluid responsiveness in patients under lung protective ventilation (LPV). Forty-one patients under LPV were enrolled when PPV values were in a priori considered gray zone (4% to 17%). The FloTrac-Vigileo device measured stroke volume variation (SVV) and stroke volume (SV), while the patient monitor measured pulse pressure variation (PPV) before and at the end of stepwise LRM and before and 5 min after fluid challenge (6 ml/kg). Fluid responsiveness was defined as a ≥ 15% increase in the SV or SV index. Seventeen were fluid responders. The areas under the curve for the augmented values of PPV and SVV, as well as the decrease in SV by stepwise LRM to identify fluid responders, were 0.76 (95% confidence interval, 0.61-0.88), 0.78 (0.62-0.89), and 0.69 (0.53-0.82), respectively. The optimal cut-offs for the augmented values of PPV and SVV were > 18% and > 13%, respectively. Stepwise LRM -generated augmented PPV and SVV predicted fluid responsiveness under LPV.

Multimorbidity and Critical Care Neurosurgery: Minimizing Major Perioperative Cardiopulmonary Complications

With increasing prevalence of chronic diseases, multimorbid patients have become commonplace in the neurosurgical intensive care unit (neuro-ICU), offering unique management challenges. By reducing physiological reserve and interacting with one another, chronic comorbidities pose a greatly enhanced risk of major postoperative medical complications, especially cardiopulmonary complications, which ultimately exert a negative impact on neurosurgical outcomes. These premises underscore the importance of perioperative optimization, in turn requiring a thorough preoperative risk stratification, a basic understanding of a multimorbid patient’s deranged physiology and a proper appreciation of the potential of surgery, anesthesia and neurocritical care interventions to exacerbate comorbid pathophysiologies. This knowledge enables neurosurgeons, neuroanesthesiologists and neurointensivists to function with a heightened level of vigilance in the care of these high-risk patients and can inform the perioperative neuro-ICU management with individualized strategies able to minimize the risk of untoward outcomes. This review highlights potential pitfalls in the intra- and postoperative neuro-ICU period, describes common preoperative risk stratification tools and discusses tailored perioperative ICU management strategies in multimorbid neurosurgical patients, with a special focus on approaches geared toward the minimization of postoperative cardiopulmonary complications and unplanned reintubation.

The effect of positive-end-expiratory pressure on stroke volume variation: An experimental study in dogs

Stroke volume variation (SVV) may be affected by ventilation settings. However, it is unclear whether positive-end-expiratory pressure (PEEP) affects SVV independently of the effect of driving pressure. We aimed to investigate the effect of driving pressure and PEEP on SVV under various preload conditions using beagle dogs as the animal model. We prepared three preload model, baseline, mild and moderate haemorrhage model. Mild and moderate haemorrhage models were created in nine anaesthetized, mechanically ventilated dogs by sequentially removing 10 mL/kg, and then an additional 10 mL/kg of blood, respectively. We measured cardiac output, stroke volume (SV), SVV, heart rate, central venous pressure, pulmonary capillary wedge pressure and the mean arterial pressure under varying ventilation settings. Peak inspiratory pressure (PIP) was incrementally increased by 4 cmH₂ O, from 9 cmH₂ O to 21 cmH₂ O, under PEEP values of 4, 8, and 12 cmH₂ O. The driving pressure did not significantly decrease SV under each preload condition and PEEP; however, significantly increased SVV. In contrast, the increased PEEP decreased SV and increased SVV under each preload condition and driving pressure, but these associations were not statistically significant. According to multiple regression analysis, an increase in PEEP and decrease in preload significantly decreased SV (P < .05). In addition, an increase in the driving pressure and decrease in preload significantly increased SVV (P < .05). Driving pressure had more influence than PEEP on SVV.

High positive end expiratory pressure levels affect hemodynamics in elderly patients with hypertension admitted to the intensive care unit: a prospective cohort study

Background

To study the effects of different positive end expiratory pressure (PEEP) on blood pressure and heart function in elderly patients with hypertension.

Methods

Forty elderly patients above 65 years of age treated with mechanical ventilation were divided into two groups: a control group of non-hypertensive subjects (n = 18) and a hypertension group (n = 22) patients with essential hypertension. Changes in blood pressure, central venous pressure (CVP), central venous oxygen saturation (ScvO₂), heart rate, and airway pressure were determined in response to different selected PEEP levels of 0, 2, 4, 6, 8, 10 and 12 cm H₂O under SIMV(PC) + PSV mode throughout the study.

Results

In both groups, the increase in PEEP led to an increase in CVP and airway pressure. When PEEP was above 4 cm H₂O in the hypertension group, a decrease in blood pressure and ScvO₂, and an increase of heart rate were observed. These results indicated that cardiac output significantly decreased.

Conclusion

High levels of PEEP can significantly influence changes in blood pressure and heart function in elderly patients with hypertension.

Trial registration

This trial was retrospectively registered, The Chinese trial registration number is ChiCTR-ROC-17012873. The date of registration is 10-2-2017.

Evaluation of pulse pressure variation and pleth variability index to predict fluid responsiveness in mechanically ventilated isoflurane-anesthetized dogs

OBJECTIVE

To evaluate whether pulse pressure variation (PPV) and pleth variability index (PVI) are more accurate than central venous pressure (CVP) for predicting fluid responsiveness in mechanically ventilated isoflurane-anesthetized dogs after premedication with acepromazine.

DESIGN

Prospective experimental trial.

SETTING

University teaching hospital.

ANIMALS

Twelve Harrier hound dogs.

INTERVENTIONS

Each dog was anesthetized and had a fluid challenge performed. This was repeated 4 weeks later for a total of 24 fluid challenges. After premedication with intramuscular acepromazine, anesthesia was induced with propofol and maintained with isoflurane. The dogs were mechanically ventilated with constant settings. The fluid challenge consisted of 10 mL/kg of 6% hydroxyethyl starch intravenously over 13 minutes.

MEASUREMENTS AND MAIN RESULTS

Before and after the fluid challenge, PPV, PVI, CVP, and other hemodynamics were recorded. Change in velocity time integral of pulmonary arterial blood flow by echocardiography was calculated as an indication of change in stroke volume. A fluid responder was defined as an increase in velocity time integral ≥ 15%. Receiver operator characteristic (ROC) curves were used to determine cutoff values. Areas under ROC curve were calculated and compared. Dogs responded on 14 fluid challenges and did not on 10. Cutoff values for PPV and PVI were 11% (sensitivity 79%; specificity 80%) and 9.3% (sensitivity 86%; specificity 70%), respectively. The areas under the ROC curve of PPV [0.85, 95% confidence interval (CI): 0.70-1.00, P = 0.038] and PVI (0.84, 95% CI: 0.68-1.00, P = 0.043) were significantly higher than CVP (0.56, 95% CI: 0.32-0.81).

CONCLUSIONS

PPV and PVI predicted fluid responsiveness more accurately than CVP and may be useful to guide fluid administration in mechanically ventilated isoflurane-anesthetized dogs after premedication with acepromazine.

Anesthesia-Associated Relative Hypovolemia: Mechanisms, Monitoring, and Treatment Considerations

Although the utility and benefits of anesthesia and analgesia are irrefutable, their practice is not void of risks. Almost all drugs that produce anesthesia endanger cardiovascular stability by producing dose-dependent impairment of cardiac function, vascular reactivity, and compensatory autoregulatory responses. Whereas anesthesia-related depression of cardiac performance and arterial vasodilation are well recognized adverse effects contributing to anesthetic risk, far less emphasis has been placed on effects impacting venous physiology and venous return. The venous circulation, containing about 65–70% of the total blood volume, is a pivotal contributor to stroke volume and cardiac output. Vasodilation, particularly venodilation, is the primary cause of relative hypovolemia produced by anesthetic drugs and is often associated with increased venous compliance, decreased venous return, and reduced response to vasoactive substances. Depending on factors such as patient status and monitoring, a state of relative hypovolemia may remain clinically undetected, with impending consequences owing to impaired oxygen delivery and tissue perfusion. Concurrent processes related to comorbidities, hypothermia, inflammation, trauma, sepsis, or other causes of hemodynamic or metabolic compromise, may further exacerbate the condition. Despite scientific and technological advances, clinical monitoring and treatment of relative hypovolemia still pose relevant challenges to the anesthesiologist. This short perspective seeks to define relative hypovolemia, describe the venous system’s role in supporting normal cardiovascular function, characterize effects of anesthetic drugs on venous physiology, and address current considerations and challenges for monitoring and treatment of relative hypovolemia, with focus on insights for future therapies.

Physiologic Considerations in Trauma Patients Undergoing Resuscitative Endovascular Balloon Occlusion of the Aorta

Resuscitative endovascular balloon occlusion of the aorta is a new procedure for adjunctive management of critically injured patients with noncompressible torso or pelvic hemorrhage who are in refractory hemorrhagic shock, ie, bleeding to death. The anesthesiologist plays a critical role in management of these patients, from initial evaluation in the trauma bay to definitive care in the operating room and the critical care unit. A comprehensive understanding of the effects of resuscitative endovascular balloon occlusion of the aorta is essential to making it an effective component of hemostatic resuscitation.

Stroke volume variation (SVV) and pulse pressure variation (PPV) as indicators of fluid responsiveness in sevoflurane anesthetized mechanically ventilated euvolemic dogs

Changes in stroke volume variation (SVV) and pulse pressure variation (PPV) in response to fluid infusion were experimentally evaluated during vecuronium infusion and sevoflurane anesthesia in 5 adult, mechanically ventilated, euvolemic, beagle dogs. Sequential increases in central venous pressure (CVP; 3-7[baseline], 8-12, 13-17, 18-22 and 23-27 mmHg) were produced by infusing lactated Ringer's solution and 6% hydroxyethyl starch solution. Heart rate (beats/min), right atrial pressure (RAP, mmHg), pulmonary arterial pressure (PAP, mmHg), pulmonary capillary wedge pressure (PCWP, mmHg), transpulmonary thermodilution cardiac output (TPTDCO, l/min), stroke volume (SV, ml/beat), arterial blood pressure (ABP, mmHg), extravascular lung water (EVLW, ml), pulmonary vascular permeability index (PVPI, calculated), SVV (%), PPV (%) and systemic vascular resistance (SVR, dynes/sec/cm⁵) were determined at each predetermined CVP range. Heart rate (P=0.019), RAP (P<0.001), PAP (P<0.001), PCWP (P<0.001), TPTDCO (P=0.009) and SV (P=0.04) increased and SVR (P<0.001), SVV (P<0.001) and PPV (P<0.001) decreased associated with each stepwise increase in CVP. Arterial blood pressure, EVLW, PVPI and the arterial partial pressures of oxygen and carbon dioxide did not change. The changes in SVV and PPV directly reflected the fluid load and the minimum threshold values for detecting fluid responsiveness were SVV ≥11% and PPV ≥7% in dogs.

Right ventricular end-diastolic stiffness heralds right ventricular failure in monocrotaline-induced pulmonary hypertension

Recent studies suggest right ventricular (RV) stiffness is important in pulmonary hypertension (PH) prognosis. Smaller stroke volume (SV) variation after a certain RV end-diastolic pressure (EDP) respiratory variation as assessed by spectral transfer function (STF) may identify RV stiffness. Our aim was to evaluate RV stiffness in monocrotaline (MCT)-induced PH progression and to validate STF gain between EDP and SV as marker of stiffness. Seven-week-old male Wistar rats randomly injected with 60 mg/kg MCT or vehicle were divided into three groups ( n = 12 each) according to cardiac index (CI): controls (Ctrl), preserved CI (MCT pCI), and reduced CI (MCT rCI). All underwent RV pressure-volume (PV) evaluation 24–34 days after MCT, under halogenate anesthesia and constant positive-pressure ventilation. End-diastolic stiffness (βi), end-systolic elastance (Eesi), arterial elastance for indexed volumes (Eai), and preload recruitable stroke work (PRSW) were obtained and beat-to-beat fluctuations during ventilation assessed by STF. Eai was the strongest determinant of CI, alongside βi but not PRSW. MCT rCI showed impaired ventricular-vascular coupling (VVC) and higher βi, along with low end-diastolic pressure (EDP) and stroke volume index (SVi) STF gain, denoting impaired preload reserve. On multivariate analysis βi and not Eesi correlated with EDP-SVi STF gain ( P < 0.001). Receiver-operating characteristics (ROC) curve analysis of EDP-SVi STF gain showed an area under curve of 0.84 for βi prediction ( P = 0.002). Afterload, impaired VVC and RV stiffness are major players in RV failure. RV stiffness can be assessed by STF gain analysis of respiratory fluctuations between EDP and SVi, which may constitute a prognostic tool in PH.

Spectral transfer function analysis of respiratory hemodynamic fluctuations predicts end-diastolic stiffness in preserved ejection fraction heart failure

Preserved ejection fraction heart failure (HFpEF) diagnosis remains controversial, and invasive left ventricular (LV) hemodynamic evaluation and/or exercise testing is advocated by many. The stiffer HFpEF myocardium may show impaired stroke volume (SV) variation induced by fluctuating LV filling pressure during ventilation. Our aim was to investigate spectral transfer function (STF) gain from end-diastolic pressure (EDP) to indexed SV (SVi) in experimental HFpEF. Eighteen-week-old Wistar-Kyoto (WKY) and ZSF1 lean (ZSF1 Ln) and obese rats (ZSF1 Ob) randomly underwent LV open-chest (OC, n = 8 each group) or closed-chest hemodynamic evaluation (CC, n = 6 each group) under halogenate anesthesia and positive-pressure ventilation at constant inspiratory pressure. Beat-to-beat fluctuations in hemodynamic parameters during ventilation were assessed by STF. End-diastolic stiffness (βi) and end-systolic elastance (Eesi) for indexed volumes were obtained by inferior vena cava occlusion in OC (multibeat) or single-beat method estimates in CC. ZSF1 Ob showed higher EDP spectrum (P < 0.001), higher STF gain between end-diastolic volume and EDP, and impaired STF gain between EDP and SVi compared with both hypertensive ZSF1 Ln and normotensive WKY controls (P < 0.001). Likewise βi was only higher in ZSF1 Ob while Eesi was raised in both ZSF1 groups. On multivariate analysis βi and not Eesi correlated with impaired STF gain from EDP to SVi (P < 0.001), and receiver-operating characteristics analysis showed an area under curve of 0.89 for higher βi prediction (P < 0.001). Results support further clinical testing of STF analysis from right heart catheterization-derived EDP surrogates to noninvasively determined SV as screening/diagnostic tool to assess myocardial stiffness in HFpEF.