A comparison of the cardiopulmonary effects of pressure controlled ventilation and volume controlled ventilation in healthy anesthetized dogs

Comparative study of ventilation techniques with supraglottic airway devices in cats: volume-controlled vs pressure-controlled techniques

OBJECTIVES

This study compared the effectiveness of a new supraglottic airway device (SGAD) in cats undergoing anaesthesia using two types of mechanical ventilation: volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV).

METHODS

A total of 13 healthy cats (five male, eight female; median age 2 years [range 1-3]) were randomly allocated to either VCV or PCV. Five tidal volumes (6, 8, 10, 12 and 14 ml/kg) and five peak inspiratory pressures (4, 5, 6, 7 and 8 cmH2O) were randomly applied with a minute ventilation of 100 ml/kg/min. Various parameters, such as blood pressure, gas leakage, end-tidal CO2 (ETCO2) and work of breathing (WOB), were measured while using VCV or PCV.

RESULTS

The occurrence of hypotension (mean arterial blood pressure <60 mmHg) was slightly less frequent with VCV (38 events, 65 ventilating sessions) than with PCV (40 events, 65 ventilating sessions), but this difference did not reach statistical significance (P = 0.429). The number of leakages did not differ between the VCV group (3 events, 65 ventilating sessions) and the PCV group (3 events, 65 ventilating sessions) (P = 1.000). Hypercapnia was identified when using VCV (10 events, 65 ventilating sessions) less frequently than when using PCV (17 events, 65 ventilating sessions), but this difference did not reach statistical significance (P = 0.194). The study found a significantly higher WOB in the PCV group compared with the VCV group (P <0.034).

CONCLUSIONS AND RELEVANCE

The present results suggested that both VCV and PCV can be used with an SGAD during anaesthesia, with VCV preferred for prolonged mechanical ventilation due to its lower workload. Adjusting tidal volume or inspiratory pressure corrects hypercapnia.

Comparison between mainstream (Capnostat 5) and a low-flow sidestream capnometer (Capnostream) in mechanically ventilated, sevoflurane-anesthetized rabbits using a Bain coaxial delivery system

OBJECTIVE

To evaluate agreement between end-tidal carbon dioxide (Pe'CO₂) and PaCO₂ with sidestream and mainstream capnometers in mechanically ventilated anesthetized rabbits, with two ventilatory strategies.

STUDY DESIGN

Prospective experimental study.

ANIMALS

A total of 10 New Zealand White rabbits weighing 3.6 ± 0.3 kg (mean ± standard deviation).

METHODS

Rabbits anesthetized with sevoflurane were intubated with an uncuffed endotracheal tube (3.0 mm internal diameter) and adequate seal. For Pe'CO₂, the sidestream capnometer sampling adapter or the mainstream capnometer was placed between the endotracheal tube and Bain breathing system (1.5 L minute^-1 oxygen). PaCO₂ was obtained from arterial blood collected every 5 minutes. A time-cycled ventilator delivered an inspiratory time of 1 second and 12 or 20 breaths minute^-1. Peak inspiratory pressure was initially set to achieve Pe'CO₂ normocapnia of 35-45 mmHg (4.6-6.0 kPa). A total of five paired Pe'CO₂ and PaCO₂ measurements were obtained with each ventilation mode for each capnometer. Anesthetic episodes were separated by 7 days. Agreement was assessed using Bland-Altman analysis and linear mixed models; p < 0.05.

RESULTS

There were 90 and 83 pairs for the mainstream and sidestream capnometers, respectively. The mainstream capnometer underestimated PaCO₂ by 12.6 ± 2.9 mmHg (proportional bias 0.44 ± 0.06 mmHg per 1 mmHg PaCO₂ increase). With the sidestream capnometer, ventilation mode had a significant effect on Pe'CO₂. At 12 breaths minute^-1, Pe'CO₂ underestimated PaCO₂ by 23.9 ± 8.2 mmHg (proportional bias: 0.81 ± 0.18 mmHg per 1 mmHg PaCO₂ increase). At 20 breaths minute^-1, Pe'CO₂ underestimated PaCO₂ by 38.8 ± 5.0 mmHg (proportional bias 1.13 ± 0.10 mmHg per 1 mmHg PaCO₂ increase).

CONCLUSIONS AND CLINICAL RELEVANCE

Both capnometers underestimated PaCO₂. The sidestream capnometer underestimated PaCO₂ more than the mainstream capnometer, and was affected by ventilation mode.

A Survey on the Use of Spirometry in Small Animal Anaesthesia and Critical Care

Simple Summary

Spirometry can be used to monitor airway pressures, flows, and volumes. Its relevance in small animal anaesthesia is documented. The way the Veterinary Anaesthesia and Intensive Care communities use spirometry was not found in the literature. The objective was to document the use of spirometry and ventilation settings in small animal anaesthesia and intensive care through a descriptive, open, online, anonymous survey. The survey was advertised on social media and via email. Participation was voluntary. The google forms platform was used. It consisted of eight sections in English. Simple, descriptive analyses were applied. There were 128 respondents. Respondents used spirometry more when dogs were mechanically ventilated as opposed to spontaneously breathing. Over 3/4 of the respondents considered spirometry essential in “selected” (43%) or “most” cases (33%). Multiple devices and technologies were used. The majority of the respondents were not directly involved in or informed about the calibration of their equipment. More information on variables monitored and technical background on spirometers is required.

Abstract

The objective was to document the use of spirometry and ventilation settings in small animal anaesthesia and intensive care through a descriptive, open, online, anonymous survey. The survey was advertised on social media and via email. Participation was voluntary. The google forms platform was used. It consisted of eight sections in English: demographic information, use of spirometry in spontaneously ventilating/mechanically ventilated dogs, need for spirometry, equipment available and calibration status, ventilation modes, spirometry displays, compliance (C_RS) and resistance (R_RS) of the respiratory system. Simple descriptive analyses were applied. There were 128 respondents. Respondents used spirometry more in ventilated dogs than during spontaneous breathing. Over 3/4 of the respondents considered spirometry essential in “selected” (43%) or “most” cases (33%). Multiple devices and technologies were used. The majority of the respondents were not directly involved in or informed about the calibration of their equipment. Of all displays, pressure-volume loops were the most common. Values of C_RS and R_RS were specifically monitored in more than 50% of cases by 44% of the respondents only. A variety of ventilation modes was used. Intensivists tend to use smaller VT than anaesthetists. More information on reference intervals of C_RS and R_RS and technical background on spirometers is required

Effects of pressure- and volume-controlled ventilation on the work of breathing in cats using a cuffed endotracheal tube

Background and Aim:

Mechanical ventilation is essential for supporting patients’ respiratory function when they are under general anesthesia. For cats with limited lung capacity, the different effects of volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) on respiratory function remain elusive. The objective of the present study was to compare the efficacy of VCV and PCV in cats under general anesthesia using a cuffed endotracheal tube (ETT).

Materials and Methods:

Twelve healthy cats were randomly allocated to either a VCV or PCV group. Five tidal volumes (6, 8, 10, 12, and 14 mL/kg) were randomly applied to assess the efficacy of VCV, and respiratory rates were adjusted to achieve a minute ventilation of 100 mL/kg/min. Peak inspiratory pressures (4, 5, 6, 7, and 8 mmHg) were randomly applied to assess the efficacy of PCV, and respiratory rates were adjusted to achieve a minute ventilation of 100 mL/kg/min. Blood pressure, gas leakages, and end-tidal CO₂ were recorded from 60 trials for airway control during the use of VCV or PCV. Data were compared using Fisher’s exact test with a significance level of p<0.05.

Results:

Leakages did not differ between VCV (1/60 events) and PCV (0/60 events; p=0.500). Hypercapnia was identified when using VCV (6/60 events) less frequently than when using PCV (7/60 events; p=0.762), but did not reach statistical significance. Hypotension (mean arterial blood pressure <60 mmHg) occurred less frequently with VCV (0/60 events) than with PCV (9/60 events; p=0.003). Moreover, VCV provided a significantly lower work of breathing (151.10±65.40 cmH₂O mL) compared with PCV (187.84±89.72 cmH₂O mL; p<0.05).

Conclusion:

VCV in cats using a cuffed ETT causes less hypotension than PCV. It should be noted that VCV provides a more stable tidal volume compared with PCV, resulting in a more stable minute volume. Nonetheless, VCV should not be used in patients with an airway obstruction because higher peak airway pressure may occur and lead to lung injury.

The effects of different ventilatory modes in female adult rats submitted to mechanical ventilation

This study aimed to analyze the effects of volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) modes in female Wistar rats. 18 Wistar female adult rats were divided into three groups: control (CG), pressure-controlled ventilation (PCVG), and volume-controlled ventilation (VCVG). PCVG and VCVG were submitted to MV for one hour with a tidal volume (TV) of 8 mL/Kg, respiratory rate of 80 breaths/min, and positive end-expiratory pressure of 0 cmH₂O. At the end of the experiment, all animals were euthanized. The neutrophils and lymphocytes influx to lung were higher in VCVG and PCVG compared to CG. The activities of superoxide dismutase, catalase and myeloperoxidase were higher in PCVG compared to CG. There was an increase in lipid peroxidation and protein oxidation in PCVG compared to CG. The levels of CCL3 and CCL5 were higher in PCVG compared to CG. In conclusions, the PCV mode promoted structural changes in the lung parenchyma, redox imbalance and inflammation in healthy adult female rats submitted to MV.

Efeito de frações inspiradas de oxigênio e modalidades ventilatórias diferentes sobre a idade de cães

RESUMO Objetivou-se avaliar diferentes modalidades ventilatórias em cães de diferentes idades submetidos à fração inspirada de oxigênio (FiO2) de 40% e 100%. Foram utilizados 36 cães de três grupos etários (GJ: 0-5; GA: 5-10 e GG: 10-15 anos), sem padronização de peso, sexo, raça e procedimento cirúrgico. Foram pré-medicados com acepromazina e morfina (0,02 e 0,5mg/kg), induzidos à anestesia geral com propofol dose-efeito, manutenção do plano anestésico com isoflurano em 1,3 V% e fornecimento de oxigênio conforme a FiO2 estabelecida para o grupo. Os animais foram submetidos a quatro diferentes modalidades ventilatórias: ventilação espontânea (VE), ventilação ciclada a volume (VCV), ventilação ciclada a pressão (VCP) e ventilação ciclada a pressão com PEEP (VCPP), e permaneceram 30 minutos em cada modalidade. Os parâmetros cardiovasculares mantiveram-se estáveis para todas as FiO2, modalidades ventilatórias e idades. Com relação aos parâmetros ventilatórios, na FiO2 100%, foram observados PaCO2 de 45mmHge e 29% de shunt, enquanto a FiO2 40% apresentou PaCO2 de 43 mmHg e 13% de shunt. Em relação às diferentes idades, os animais adultos e geriátricos apresentaram maiores valores de shunt (26% e 22%) e PaCO2 (44mm/Hg e 46mm/Hg). Conclui-se que a fração inspirada de 40% e a modalidade ventilatória ciclada a volume mostraram-se mais eficientes.

Factors affecting respiratory system compliance in anaesthetised mechanically ventilated healthy dogs: a retrospective study

OBJECTIVES

To determine the influence of several factors on respiratory system compliance in volume-controlled mechanically ventilated healthy anaesthetised dogs.

MATERIALS AND METHODS

Review of 100 dogs anaesthetised for elective surgeries between 2015 and 2016. Dogs were mechanically ventilated with a respiratory rate adjusted to maintain normocapnia and a fraction of inspired oxygen of 50%. Body weight, body condition score, age, thoracic shape, time in spontaneous ventilation before volume-controlled ventilation, time with a fraction of inspired oxygen of 100% until starting mechanical ventilation, type of surgery and patient position were recorded. Respiratory system compliance, expressed per kg of bodyweight, was recorded every 15 minutes following initiation of volume-controlled ventilation.

RESULTS

Baseline respiratory system compliance was 1.3 ± 0.3 mL/cmH₂ O/kg and was reduced by high body condition score and barrel-shaped thorax but not by age, type of surgery or patient position, time in spontaneous ventilation nor time with a fraction of inspired oxygen of 100%.

CLINICAL SIGNIFICANCE

Respiratory system compliance is lower in overweight and barrel-chested dogs and should be taken into account during monitoring of lung function and ventilation management under general anaesthesia.

Parâmetros hemodinâmicos e ventilatórios em coelhos anestesiados com isoflurano, submetidos à ventilação controlada à pressão com ou sem PEEP

RESUMO Foi comparada a ventilação controlada à pressão com ou sem pressão positiva expiratória final (PEEP), em coelhos, distribuídos em três grupos, denominados GP (grupo ventilação ciclada à pressão), GPP (grupo ventilação ciclada à pressão com PEEP) e GE (grupo ventilação espontânea - grupo controle). Os animais foram anestesiados com isoflurano, em circuito com reinalação de gases, durante duas horas. As médias de pressão arterial média (PAM) e pressão arterial sistólica (PAS) permaneceram discretamente abaixo dos valores normais em todos os grupos. Houve diminuição significativa da PAM e da PAS no grupo submetido à PEEP (GPP) ao longo do tempo. A pressão parcial de dióxido de carbono arterial (PaCO2) foi maior no GPP quando comparado aos outros grupos no último momento, gerando acidemia respiratória após uma hora de procedimento. A concentração de dióxido de carbono ao final da expiração (ETCO2) apresentou médias discretamente elevadas no grupo não tratado com PEEP (GP) e no grupo controle, enquanto o GPP apresentou maiores médias, possivelmente, relacionadas à diminuição do volume corrente neste grupo. Com base nesses resultados, foi possível concluir que a utilização da PEEP levou à acidemia, que se agravou ao longo do tempo anestésico. Ademais, a anestesia prolongada com isoflurano promove depressão cardiorrespiratória, independentemente do modo ventilatório empregado.

Comparative effects of open-lung positive end-expiratory pressure (PEEP) and fixed PEEP on respiratory system compliance in the isoflurane anaesthetised healthy dog

This study was performed to assess the effects of open-lung positive end-expiratory pressure (OL-PEEP) following stepwise recruitment manoeuvre (RM) and those of a fixed PEEP of 5 cm H₂O without previous RM on respiratory system compliance (Crs) and selected cardiovascular variables in healthy dogs under general anaesthesia. Forty-five healthy client-owned dogs undergoing surgery were anaesthetised and mechanically ventilated (tidal volume, VT = 10-12 mL/kg; PEEP = 0 cm H₂O) for 1 min (baseline) and randomly allocated into zero positive end-expiratory pressure (ZEEP), PEEP (5 cm H₂O) and OL-PEEP treatment groups. In the OL-PEEP group, a stepwise RM was performed and the individual OL-PEEP was subsequently applied. The Crs, heart rate (HR) and non-invasive mean arterial pressure (NIMAP) were registered at baseline and then every 10 min during 60 min. In the ZEEP group, Crs decreased from baseline. In the PEEP group, Crs was not different from either baseline or ZEEP group values. In the OL-PEEP group, Crs was higher than both baseline and ZEEP group values at all time points as well as of those in the PEEP group during at least 20 min after RM. There were no differences for HR and NIMAP between groups. A clinically relevant hypotension following RM was observed in 40% of dogs. Therefore, an individually set OL-PEEP following stepwise RM improved Crs in anaesthetised healthy dogs, although transient but clinically relevant hypotension was observed during RM in some dogs. Fixed PEEP of 5 cm H₂O without previous RM did not improve Crs, although it prevented it from decreasing.

Comparison of volume-controlled ventilation mode and pressure-controlled ventilation with volume-guaranteed mode in the prone position during lumbar spine surgery

Background

During lumbar spine surgery, patients are placed in the prone position for surgical access. The prone position has various effects on cardiac and pulmonary function, including a decreased cardiac index (CI), decreased dynamic lung compliance (Cdyn), and increased peak inspiratory pressure (Ppeak). In this study, we compared the volume-controlled ventilation mode (VCV) and pressure-controlled ventilation with volume guaranteed mode (PCV-VG) based on hemodynamic and pulmonary variables in the prone position during lumbar spine surgery.

Methods

Thirty-six patients scheduled for lumbar spine surgery in the prone position were enrolled in this prospective, randomized clinical trial. The patients were randomly assigned to receive VCV or PCV-VG. Hemodynamic variables, respiratory variables, and arterial blood gases were measured in the supine position 15 min after the induction of anesthesia, 15 min after placement in the prone position, 30 min after placement in the prone position, and 15 min after placement in the supine position at the end of anesthesia.

Results

The hemodynamic variables and arterial blood gas results did not differ significantly between the two groups. Lower Ppeak values were observed in the PCV-VG group than in the VCV group (p = 0.045). The Cdyn values in the VCV group were lower than those in the PCV-VG group (p = 0.040).

Conclusion

PCV-VG led to lower Ppeak and improved Cdyn values compared with VCV, showing that it may be a favorable alternative mode of mechanical ventilation for patients in the prone position during lumbar spine surgery.

Trial registration

The study was retrospectively registered at ClinicalTrials.gov (NCT 03571854). The initial registration date was 6/18/2018.

Ventilation distribution assessed with electrical impedance tomography and the influence of tidal volume, recruitment and positive end-expiratory pressure in isoflurane-anesthetized dogs

OBJECTIVE

To examine the intrapulmonary gas distribution of low and high tidal volumes (V_T) and to investigate whether this is altered by an alveolar recruitment maneuver (ARM) and 5 cmH₂O positive end-expiratory pressure (PEEP) during anesthesia.

STUDY DESIGN

Prospective randomized clinical study.

ANIMALS

Fourteen client-owned bitches weighing 26 ± 7 kg undergoing elective ovariohysterectomy.

METHODS

Isoflurane-anesthetized dogs in dorsal recumbency were ventilated with 0 cmH₂O PEEP and pressure-controlled ventilation by adjusting the peak inspiratory pressure (PIP) to achieve a low (7 mL kg^-1; n = 7) or a high (12 mL kg^-1; n = 7) V_T. Ninety minutes after induction (T90), an ARM (PIP 20 cmH₂O for 10 seconds, twice with a 10 second interval) was performed followed by the application of 5 cmH₂O PEEP for 35 minutes (RM35). The vertical (ventral=0%; dorsal=100%) and horizontal (right=0%; left=100%) center of ventilation (CoV), four regions of interest (ROI) (ventral, central-ventral, central-dorsal, dorsal) identified in electrical impedance tomography images, and cardiopulmonary data were analyzed using two-way repeated measures anova.

RESULTS

The low V_T was centered in more ventral (nondependent) areas compared with high V_T at T90 (CoV: 38.8 ± 2.5% versus 44.6 ± 7.2%; p = 0.0325). The ARM and PEEP shifted the CoV towards dorsal (dependent) areas only during high V_T (50.5 ± 7.9% versus 41.1 ± 2.8% during low V_T, p = 0.0108), which was more distributed to the central-dorsal ROI compared with low V_T (p = 0.0046). The horizontal CoV was centrally distributed and cardiovascular variables remained unchanged throughout regardless of the V_T, ARM, and PEEP.

CONCLUSIONS AND CLINICAL RELEVANCE

Both low and high V_T were poorly distributed to dorsal dependent regions, where ventilation was improved following the current ARM and PEEP only during high V_T. Studies on the role of high V_T on pulmonary complications are required.