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

Prediction of Fluid Responsiveness Based on the External Jugular Vein Distensibility Index After Changes in Volume Status in Healthy, Anesthetized, and Mechanically Ventilated Dogs

OBJECTIVE

To investigate whether point-of-care ultrasound of the external jugular vein (EJV) can predict fluid responsiveness (FR) in healthy, anesthetized, mechanically ventilated dogs.

DESIGN

Prospective, nonrandomized experimental study.

SETTING

University-based small animal research facility.

ANIMALS

Six healthy Beagle dogs.

INTERVENTIONS

Dogs were investigated at six time points (TPs): baseline (TP1); 20 mL/kg of circulating blood was collected over 10 min (TP2); half of the collected blood was autotransfused for 10 min (TP3); remaining collected blood was autotransfused for 10 min (TP4); 0.9% normal saline (10 mL/kg for 10 min) was administered (TP5); and an additional dose of 0.9% normal saline (10 mL/kg for 10 min) was administered (TP6). Hemodynamic variables, Doppler images of the left ventricular outflow tract (LVOT), and M-mode images of the EJV were obtained at each TP. FR was evaluated during TP3-6. FR was defined as an increase of >15% in the LVOT velocity time integral following fluid challenge, while other results were defined as fluid nonresponsiveness (FNR). The external jugular vein distensibility index (EJVDI) was calculated as follows: [(maximal EJV diameter - minimal EJV diameter)/minimal EJV diameter] × 100%. The maximal EJV diameter was measured during inspiration, and the minimal EJV diameter was measured during expiration. In addition, gray zones indicating the range of diagnostic uncertainty were proposed in various indices for predicting FR.

MEASUREMENTS AND MAIN RESULTS

Among the 24 fluid challenges performed between TP3 and TP6, 11 FR and 13 FNR were identified. The area under the receiver operating characteristic curve for the EJVDI in predicting FR was 0.92, with a cut-ff value of 22.7%, and the gray zone was identified as 22.6%-27.3%.

CONCLUSIONS

The EJVDI could be used to predict FR in healthy, anesthetized, mechanically ventilated dogs. Further studies are required before point-of-care ultrasound of the EJV can be applied in various clinical settings.

Assessment of change in end-tidal CO2 after fluid challenge as a marker of fluid responsiveness as measured by the aortic velocity time integral in healthy anesthetized mechanically ventilated dogs

OBJECTIVE

To evaluate if variation in the end-tidal CO2 partial pressure (∆Petco2) after a fluid challenge could predict fluid responsiveness with a sensitivity of 75% and a specificity of 70% in healthy anesthetized and mechanically ventilated dogs.

DESIGN

Diagnostic accuracy study.

SETTING

University hospital.

ANIMALS

Twenty-seven dogs admitted for neutering.

INTERVENTIONS

To obtain a balanced sample between fluid responder and nonresponder dogs, a 10-mL/kg lactated Ringer's solution was administered over 15 minutes to half of the population before the baseline measurements. All animals then received a fluid challenge of 10 mL/kg lactated Ringer's solution in 5 minutes.

MEASUREMENTS AND MAIN RESULTS

The velocity-time integral of aortic blood flow (VTIAo) was evaluated with Doppler echocardiography before and after a fluid challenge to classify the included dogs as fluid responders or nonresponders. Fluid responsiveness was defined as an increase of ≥15% of the VTIAo after the fluid challenge. Petco2 was evaluated at 1, 5, and 10 (T1, T5, T10) minutes after fluid expansion. Area under the receiver operating characteristic curve (AUROC) analysis was used to assess the ability of ∆Petco2 to predict fluid responsiveness at different time points. A total of 13 dogs were fluid responders, and 14 were nonresponders. The best predictive capacity for ∆Petco2 was observed at T10. The AUROC with its 95% confidence interval (CI) for ∆Petco2 at T10 was 0.75 (0.56-0.93), with a sensitivity of 84.62% (95% CI, 54.60-98.10), a specificity of 64.29% (95% CI, 35.10-87.20), a positive predictive value of 68.80% (95% CI, 41.30-89.00), and a negative predictive value of 81.80% (95% CI, 48.20-97.70). The optimal cutoff was 1 mm Hg.

CONCLUSIONS

The current study showed that, although minimal, ∆Petco2 predicted fluid responsiveness in the dogs studied.

Feline caudal vena cava to aorta ratio reference interval

OBJECTIVES

The primary objective of this investigation was to ultrasonographically evaluate the caudal vena cava to aorta (CVC:Ao) ratio in healthy, conscious cats and to generate reference intervals. A secondary objective was to identify the site of examination with the least intra- and inter-observer variability. This investigation was undertaken to assess whether the CVC:Ao ratio holds promise as a technique to assess intravascular volume responsiveness in cats.

METHODS

In total, 42 healthy cats were included for reference interval generation. Ultrasound examinations were performed by two operators with each examination performed twice by each operator on the same occasion. Examinations were performed on conscious cats in left lateral recumbency. Ultrasound sites investigated were the subxiphoid, hepatic intercostal, hepatorenal and iliac bifurcation. Operators also assessed each site for 'ease of visualisation' on a scale of 0-3.

RESULTS

Reference intervals were generated for the CVC:Ao ratio at all four ultrasonographic sites. While each site demonstrated low variability around its mean ratio, all sites exhibited significant intra- and inter-observer variability. The hepatorenal and iliac bifurcation sites were found to be the easiest to visualise (score 3; well-defined visualisation of both vessels) and had reference intervals of 0.8-1.41 and 0.75-1.2, respectively.

CONCLUSIONS AND RELEVANCE

The ultrasonographic assessment of the CVC:Ao ratio was possible at four anatomical locations in the cat. The hepatorenal and iliac bifurcation may offer more readily assessable CVC:Ao ratios. Further studies are necessary to assess the utility of the CVC:Ao ratio in disease states, including in hypovolaemia and hypervolaemia.

Construction of nomogram prediction model using heart rate and pulse perfusion variability index as predictors for hypotension in cervical cancer patients with spinal epidural anesthesia

The prevention and treatment strategies for cervical cancer patients undergoing spinal epidural anesthesia have increasingly focused on early screening for high-risk factors associated with potential hypotension. We analyze the general conditions and preoperative examination results of 312 cervical cancer patients who received spinal epidural anesthesia, in order to identify independent risk factors for hypotension, assess their predictive efficacy, and construct a nomogram. 312 patients with cervical cancer received spinal epidural anesthesia were included in this study. Among them, 164 patients with hypotension after hysterectomy with spinal epidural anesthesia were in a hypotension group. Important risk predictors of hypotension after hysterectomy with spinal epidural anesthesia were identified using univariate and multivariate analyses, then a clinical nomogram was constructed. The predictive accuracy was assessed by unadjusted concordance index (C-index) and calibration plot. Univariate and multivariate regression analysis identified basal HR (≥95) (95% CI 0.831-0.900; P = 0.000) and basal PVI (95% CI 0.679-0.877; P = 0.000) were the independent risk factors for hypotension in cervical cancer patients with spinal epidural anesthesia. Those risk factors were used to construct a clinical predictive nomogram. The regression equation model based on the above factors was logit (P) = -6.820 + 0.216 * basal HR + basic PVI * 0.312. The calibration curves for hypotension risk revealed excellent accuracy of the predictive nomogram model. Decision curve analysis showed that the predictive model could be applied clinically when the threshold probability was 20 to 75%. We surmised that the basal HR values and PVI values are the independent risk factors for hypotension in cervical cancer patients with spinal epidural anesthesia. The construction of nomograms is beneficial in predicting the risk of hypotension in these patients.

Nursing strategies for the mechanically ventilated patient

The goal of this manuscript is to provide a comprehensive and multi-disciplinary review of the best nursing practices of caring for mechanically ventilated patients. By reviewing human medicine literature, the authors will extrapolate procedures that have been found to be most effective in reducing the risk of mechanical ventilation (MV) complications. Paired with review of the current standards in veterinary medicine, the authors will compile the best practice information on mechanically ventilated patient care, which will serve as a detailed resource for the veterinary nursing staff. Written from a nursing standpoint, this manuscript aims to consolidate the nursing assessment of a mechanically ventilated patient, addressing both systemic and physical changes that may be encountered during hospitalization. The goal of this review article is to present information that encourages a proactive approach to nursing care by focusing on understanding the effects of polypharmacy, hemodynamic changes associated with MV, complications of recumbent patient care, and sources of hospital acquired infections. When applied in conjunction with the more technical aspects of MV, this manuscript will allow veterinary technicians involved in these cases to understand the dynamic challenges that mechanically ventilated patients present, provide guidance to mitigate risk, address issues quickly and effectively, and create an up-to date standard of practice that can be implemented.

Development and comparison of an esophageal Doppler monitoring-based treatment algorithm with a heart rate and blood pressure-based treatment algorithm for goal-directed fluid therapy in anesthetized dogs: A pilot study

The objective of this pilot study was to determine the feasibility of a study comparing the efficacy of an esophageal Doppler monitor (EDM)-based fluid therapy algorithm with a heart rate (HR)- and mean arterial blood pressure (MAP)-based algorithm in reducing hypotension and fluid load in anesthetized dogs. Client-owned dogs undergoing general anesthesia for surgical procedures were randomized to two groups. An EDM probe for monitoring blood flow in the descending aorta was placed in each dog before receiving a crystalloid bolus (5 mL/kg) over 5 min. Fluids were repeated in case of fluid responsiveness defined by increasing Velocity Time Integral (VTI) ≥ 10% in group EDM and by decreasing HR ≥ 5 beats/min and/or increasing MAP ≥ 3 mmHg in group standard. The feasibility outcomes included the proportion of dogs completing the study and the clinical applicability of the algorithms. The clinical outcomes were the total administered fluid volume and the duration of hypotension defined as MAP < 60 mmHg. Data was compared between groups with Mann-Whitney U-test. p < 0.05 were deemed significant. Of 25 dogs screened, 14 completed the study (56%). There were no differences in the proportion of recorded time spent in hypotension in group standard [2 (0–39)% (median (range))] and EDM [0 (0–63) %, p = 1], or the total volume of fluids [standard 8 (5–14) mL/kg/h, EDM 11 (4–20) mL/kg/h, p = 0.3]. This study declined the feasibility of a study comparing the impact of two newly developed fluid therapy algorithms on hypotension and fluid load in their current form. Clinical outcome analyses were underpowered and no differences in treatment efficacy between the groups could be determined. The conclusions drawn from this pilot study provide important information for future study designs.

Effect of the respiratory rate on the pulse pressure variation induced by hemorrhage in anesthetized dogs

BACKGROUND

Studies on anesthetized dogs regarding pulse pressure variation (PPV) are increasing. The influence of respiratory rate (RR) on PPV, in mechanically ventilated dogs, has not been clearly identified.

OBJECTIVES

This study evaluated the influence of RR on PPV in mechanically ventilated healthy dogs after hemorrhage.

METHODS

Five healthy adult Beagle dogs were premedicated with intravenous (IV) acepromazine (0.01 mg/kg). Anesthesia was induced with alfaxalone (3 mg/kg IV) and maintained with isoflurane in 100% oxygen. The right dorsal pedal artery was cannulated with a 22-gauge catheter for blood removal, and the left dorsal pedal artery was cannulated and connected to a transducer system for arterial blood pressure monitoring. The PPV was automatically calculated using a multi-parameter monitor and recorded. Hemorrhage was induced by withdrawing 30% of blood (24 mL/kg) over 30 min. Mechanical ventilation was provided with a tidal volume of 10 mL/kg and a 1:2 inspiration-to-expiration ratio at an initial RR of 15 breaths/min (baseline). Thereafter, RR was changed to 20, 30, and 40 breaths/min according to the casting lots, and the PPV was recorded at each RR. After data collection, the blood was transfused at a rate of 10 mL/kg/h, and the PPV was recorded at the baseline ventilator setting.

RESULTS

The data of PPV were analyzed using the Friedman test followed by the Wilcoxon signed-rank test (p < 0.05). Hemorrhage significantly increased PPV from 11% to 25% at 15 breaths/min. An increase in RR significantly decreased PPV from 25 (baseline) to 17%, 10%, and 10% at 20, 30, and 40 breaths/min, respectively (all p < 0.05).

CONCLUSIONS

The PPV is a dynamic parameter that can predict a dog's hemorrhagic condition, but PPV can be decreased in dogs under high RR. Therefore, careful interpretation may be required when using the PPV parameter particularly in the dogs with hyperventilation.

The Potential of Arterial Pulse Wave Analysis in Burn Resuscitation: A Pilot In Vivo Study

While urinary output (UOP) remains the primary endpoint for titration of intravenous fluid resuscitation, it is an insufficient indicator of fluid responsiveness. Although advanced hemodynamic monitoring (including arterial pulse wave analysis (PWA)) is of recent interest, the validity of PWA-derived indices in burn resuscitation extremes has not been established. The goal of this paper is to test the hypothesis that PWA-derived cardiac output (CO) and stroke volume (SV) indices as well as pulse pressure variation (PPV) and systolic pressure variation (SPV) can play a complementary role to UOP in burn resuscitation. Swine were instrumented with a Swan-Ganz catheter for reference CO and underwent a 40% total body surface area burns with varying resuscitation paradigms, and were monitored for 24 hours in an ICU setting under mechanical ventilation. The longitudinal changes in PWA-derived indices were investigated, and resuscitation adequacy was compared as determined by UOP versus PWA indices. The results indicated that PWA-derived indices exhibited trends consistent with reference CO and SV measurements: CO and SV indices were proportional to reference CO and SV, respectively (CO: post-calibration limits of agreement (LoA)=+/-24.7 [ml/min/kg], SV: post-calibration LoA=+/-0.30 [ml/kg]) while PPV and SPV were inversely proportional to reference SV (PPV: post-calibration LoA=+/-0.32 [ml/kg], SPV: post-calibration LoA=+/-0.31 [ml/kg]). The results also indicated that PWA-derived indices exhibited notable discrepancies from UOP in determining adequate burn resuscitation. Hence, it was concluded that the PWA-derived indices may have complementary value to UOP in assessing and guiding burn resuscitation.

Clinical Application of the Fluid Challenge Approach in Goal-Directed Fluid Therapy: What Can We Learn From Human Studies?

Resuscitative fluid therapy aims to increase stroke volume (SV) and cardiac output (CO) and restore/improve tissue oxygen delivery in patients with circulatory failure. In individualized goal-directed fluid therapy (GDFT), fluids are titrated based on the assessment of responsiveness status (i.e., the ability of an individual to increase SV and CO in response to volume expansion). Fluid administration may increase venous return, SV and CO, but these effects may not be predictable in the clinical setting. The fluid challenge (FC) approach, which consists on the intravenous administration of small aliquots of fluids, over a relatively short period of time, to test if a patient has a preload reserve (i.e., the relative position on the Frank-Starling curve), has been used to guide fluid administration in critically ill humans. In responders to volume expansion (defined as individuals where SV or CO increases ≥10–15% from pre FC values), FC administration is repeated until the individual no longer presents a preload reserve (i.e., until increases in SV or CO are <10–15% from values preceding each FC) or until other signs of shock are resolved (e.g., hypotension). Even with the most recent technological developments, reliable and practical measurement of the response variable (SV or CO changes induced by a FC) has posed a challenge in GDFT. Among the methods used to evaluate fluid responsiveness in the human medical field, measurement of aortic flow velocity time integral by point-of-care echocardiography has been implemented as a surrogate of SV changes induced by a FC and seems a promising non-invasive tool to guide FC administration in animals with signs of circulatory failure. This narrative review discusses the development of GDFT based on the FC approach and the response variables used to assess fluid responsiveness status in humans and animals, aiming to open new perspectives on the application of this concept to the veterinary field.

Assessment of Volume Status and Fluid Responsiveness in Small Animals

Intravenous fluids are an essential component of shock management in human and veterinary emergency and critical care to increase cardiac output and improve tissue perfusion. Unfortunately, there are very few evidence-based guidelines to help direct fluid therapy in the clinical setting. Giving insufficient fluids and/or administering fluids too slowly to hypotensive patients with hypovolemia can contribute to continued hypoperfusion and increased morbidity and mortality. Similarly, giving excessive fluids to a volume unresponsive patient can contribute to volume overload and can equally increase morbidity and mortality. Therefore, assessing a patient's volume status and fluid responsiveness, and monitoring patient's response to fluid administration is critical in maintaining the balance between meeting a patient's fluid needs vs. contributing to complications of volume overload. This article will focus on the physiology behind fluid responsiveness and the methodologies used to estimate volume status and fluid responsiveness in the clinical setting.

Intraoperative Assessment of Fluid Responsiveness in Normotensive Dogs under Isoflurane Anaesthesia

The aim of this study was to evaluate the incidence of fluid responsiveness (FR) to a fluid challenge (FC) in normotensive dogs under anaesthesia. The accuracy of pulse pressure variation (PPV), systolic pressure variation (SPV), stroke volume variation (SVV), and plethysmographic variability index (PVI) for predicting FR was also evaluated. Dogs were anaesthetised with methadone, propofol, and inhaled isoflurane in oxygen, under volume-controlled mechanical ventilation. FC was performed by the administration of 5 mL/kg of Ringer's lactate within 5 min. Cardiac index (CI; L/min/m²), PPV, (%), SVV (%), SPV (%), and PVI (%) were registered before and after FC. Data were analysed with ANOVA and ROC tests (p < 0.05). Fluid responsiveness was defined as 15% increase in CI. Eighty dogs completed the study. Fifty (62.5%) were responders and 30 (37.5%) were nonresponders. The PPV, PVI, SPV, and SVV cut-off values (AUC, p) for discriminating responders from nonresponders were PPV >13.8% (0.979, <0.001), PVI >14% (0.956, <0.001), SPV >4.1% (0.793, <0.001), and SVV >14.7% (0.729, <0.001), respectively. Up to 62.5% of normotensive dogs under inhalant anaesthesia may be fluid responders. PPV and PVI have better diagnostic accuracy to predict FR, compared to SPV and SVV.

Terms, Definitions, Nomenclature, and Routes of Fluid Administration

Fluid therapy is administered to veterinary patients in order to improve hemodynamics, replace deficits, and maintain hydration. The gradual expansion of medical knowledge and research in this field has led to a proliferation of terms related to fluid products, fluid delivery and body fluid distribution. Consistency in the use of terminology enables precise and effective communication in clinical and research settings. This article provides an alphabetical glossary of important terms and common definitions in the human and veterinary literature. It also summarizes the common routes of fluid administration in small and large animal species.

Caudal vena cava collapsibility index as a tool to predict fluid responsiveness in dogs

OBJECTIVE

To evaluate the use of the caudal vena cava collapsibility index (CVCCI) as a predictor of fluid responsiveness in hospitalized, critically ill dogs with hemodynamic or tissue perfusion abnormalities.

DESIGN

Retrospective observational study.

SETTING

Private referral center.

ANIMALS

Twenty-seven critically ill, spontaneously breathing dogs with compromised hemodynamics or tissue hypoperfusion.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

The electronic medical records were searched for dogs admitted for any cause, from August 2016 to December 2017. We included dogs with ultrasound measurements of: CVCCI, performed at baseline; and velocity time integral (VTI) of the subaortic blood flow, carried out before and after a fluid load. CVCCI was estimated as: (maximum diameter-minimum diameter/maximum diameter) × 100. Dogs in which VTI increased ≥15% were considered fluid responders. The CVCCI accurately predicted fluid responsiveness with an area under the receiver operating characteristic curve of 0.96 (95% CI, 0.88 to 1.00). The optimal cut-off of CVCCI that better discriminated between fluid responders and nonresponders was 27%, with 100.0% sensitivity and 83.3% specificity. At baseline, fluid responders had lower VTI (5.48 [4.26 to 7.40] vs 10.61 [7.38 to 13.23] cm, P = 0.004) than nonresponders. The basal maximum diameter of the caudal vena cava adjusted to body weight was not different between responders and nonresponders (0.050 [0.030 to 0.100] vs 0.079 [0.067 to 0.140] cm/kg, P = 0.339). The increase in VTI was related to basal CVCCI (R = 0.60, P = 0.001). Bland-Altman analysis showed narrow 95% limits of agreement between measurements of CVCCI and VTI performed by different observers or by the same observer.

CONCLUSIONS

The results of this small cohort study suggest that CVCCI can accurately predict fluid responsiveness in critically ill dogs with perfusion abnormalities. Further research is necessary to extrapolate these results to larger populations of hospitalized dogs.

Evaluation of the caudal vena cava diameter to abdominal aortic diameter ratio and the caudal vena cava respiratory collapsibility for predicting fluid responsiveness in a heterogeneous population of hospitalized conscious dogs

Fluid responsiveness, defined as the response of stroke volume to fluid loading, is a tool to individualize fluid administration in order to avoid the deleterious effects of hypovolemia or hypervolemia in hospitalized patients. To evaluate the accuracy of two ultrasound indices, the caudal vena cava to abdominal aorta ratio (CVC/Ao) and the respiratory collapsibility of the caudal vena cava (cCVC), as independent predictors of fluid responsiveness in a heterogeneous population of spontaneously breathing, conscious, hospitalized dogs. A prospective, multicenter, observational, cross-sectional study was designed in twenty-five dogs. The accuracy of CVC/Ao and cCVC in predicting fluid responsiveness was evaluated by the area under the receiver operating characteristic curve (AUROC) in a group of hospitalized dogs after receiving a mini-fluid bolus of 4 ml/kg of Hartmann's solution. Dogs with an increased aortic velocity time integral >15% were classified as fluid responders. Twenty-two dogs were finally included. Ten were classified as responders and 12 as non-responders. The AUROC curves were 0.88 for the CVC/Ao ratio (95% confidence interval, CI, 0.67-0.98; P=0.0001) and 0.54 for cCVC (95% CI 0.32-0.75; P=0.75). The CVC/Ao threshold optimized for best sensitivity (SE) and specificity (SP) values was 0.83 (SE 100%; SP 75%). In spontaneously breathing hospitalized dogs, the CVC/Ao measurement predicted stroke volume increase after a fluid bolus, while the respiratory variations in the cCVC did not discriminate between fluid responders and non-responders.

Dynamic prediction of fluid responsiveness during positive pressure ventilation: a review of the physiology underlying heart-lung interactions and a critical interpretation

OBJECTIVE

Cardiovascular responses to hypovolemia and hypotension are depressed during general anesthesia. A considerable number of anesthetized and critically ill animals may not benefit hemodynamically from a fluid bolus; therefore, it is important to have measures for accurate prediction of fluid responsiveness. Static measures of preload, such as central venous pressure, do not provide accurate prediction of fluid responsiveness, whereas dynamic measures of cardiovascular function, obtained during positive pressure ventilation, are highly predictive. This review describes key physiological concepts behind heart-lung interactions during positive pressure ventilation, factors that can modify this relationship and provides the basis for a rational interpretation of the information obtained from dynamic measurements, with a focus on pulse pressure variation (PPV).

DATABASE USED

PubMed. Search items used were: heart-lung interaction, positive pressure ventilation, pulse pressure variation, dynamic index of fluid therapy, goal-directed hemodynamic therapy, dogs, cats, pigs, horses and rabbits.

CONCLUSIONS

The veterinary literature suggests that targeting specific PPV thresholds should guide fluid therapy in lieu of conventional assessments. Understanding the physiology of heart-lung interactions during intermittent positive pressure ventilation provides a rational basis for interpreting the literature on dynamic indices of fluid responsiveness, including PPV. Clinical trials are needed to evaluate whether goal-directed fluid therapy based on PPV results in improved outcomes in veterinary patient populations.

Investigation of percentage changes in pulse wave transit time induced by mini-fluid challenges to predict fluid responsiveness in ventilated dogs

OBJECTIVE

To investigate whether percentage changes in pulse wave transit time (PWTT%Δ) induced by mini-fluid challenges predict fluid responsiveness in mechanically ventilated anesthetized dogs.

DESIGN

Prospective experimental trial.

SETTING

University teaching hospital.

ANIMALS

Twelve Harrier hounds.

INTERVENTION

Each dog was anesthetized with propofol and isoflurane after premedication with acepromazine, mechanically ventilated, and had a fluid challenge. This was repeated 4 weeks later. The fluid challenge, 10 mL/kg of colloid administration over 13 minutes, consisted of 3 intermittent mini-fluid challenges (1 mL/kg of each over a minute) with a minute interval, and the remaining colloid administration (7 mL/kg) over 7 minutes.

MEASUREMENTS AND MAIN RESULTS

Percentage change in velocity time integral of pulmonary arterial flow by echocardiography was calculated as an indication of change in stroke volume. Fluid responsiveness was defined as percentage change in velocity time integral ≥ 15% after 10 mL/kg colloid. Dogs responded on 14 fluid challenges and did not on 10. After 1, 2, 3, and 10 mL/kg of fluid challenge, PWTT%Δ_{1, 2, 3, 10} were measured. Receiver operator characteristic (ROC) curves were generated and areas under ROC curve were calculated for PWTT%Δ_{1, 2, 3} . A gray zone approach was used to identify the clinically inconclusive range. The area under the ROC curve for PWTT%Δ₃ was 0.91 (P = 0.001). Cutoff value for PWTT%Δ₃ was -2.5% (sensitivity: 86%, specificity: 90%). The gray zone for PWTT%Δ₃ was identified as between -2.9% to -1.9% for which fluid responsiveness could not be predicted reliably in 6 out of 24 fluid challenges.

CONCLUSIONS

In mechanically ventilated anesthetized dogs given a mini-fluid challenge of 3 mL/kg of colloid, PWTT%Δ could predict fluid responsiveness although the gray zone should be considered.

Pulse Pressure Variation Can Predict the Hemodynamic Response to Pneumoperitoneum in Dogs: A Retrospective Study

Pneumoperitoneum may induce important hemodynamic alterations in healthy subjects. Pulse pressure variation (PPV) is a hemodynamic parameter able to discriminate preload dependent subjects. Anesthesia records of dogs undergoing laparoscopy were retrospectively evaluated. The anesthetic protocol included acepromazine, methadone, propofol and isoflurane administered with oxygen under mechanical ventilation. The hemodynamic parameters were considered five minutes before (BASE) and ten minutes after (P10) the pneumoperitoneum. Based on the cardiac index (CI) variation, at P10, dogs were classified as sensitive (S group, CI ≤ 15%) and non-sensitive (NO-S group). Data were analyzed with the ANOVA test and the ROC curve (p < 0.05). Fifty-five percent of dogs (S) had a reduction of CI ≥ 15% at P10 (2.97 ± 1.4 L/min/m²) compared to BASE (4.32 ± 1.62 L/min/m²) and at P10 in the NO-S group (4.51 ± 1.41 L/min/m²). PPV at BASE was significantly higher in the S group (22.4% ± 6.1%) compared to the NO-S group (10.9% ± 3.3%). The ROC curve showed a threshold of PPV > 16% to distinguish the S and NO-S groups. PPV may be a valid predictor of the hemodynamic response to pneumoperitoneum in dogs. A PPV > 16% can identify patients that may require fluid administration before the creation of pneumoperitoneum.