Changes in stroke volume induced by lung recruitment maneuvr predict fluid responsiveness in mechanically ventilated patients in the operating room
Presented by: Dr C Williams
- Haemodynamic optimisation in the perioperative period can reduce morbidity and mortality
- Stroke volume (SV) and SV variation/pulse pressure (PP) and PP variation can be used as objective measures of fluid responsiveness.
- Reliability of SVV and PVV limited in patient receiving low tidal volume ventilation (Vt <8ml/kg predicted body weight)
- Lung protective ventilation is standard of care for ARDS patients. Also demonstrated to be beneficial in patients undergoing surgery.
- Lung recruitment manoeuvres (LRMs) are a key component of lung-protective ventilation strategies but as they increase intrathoracic pressure, lead to a decrease in venous return with a subsequent decrease in SV.
- Authors hypothesised that degree of decrease in SV during LRM could represent a functional test to predict fluid responsiveness.
Design & setting
- Single centre study
- No data on the centre – type of hospital etc.
- Nonconsecutive case series – low quality evidence
- Over 1 year twenty-eight mechanically ventilated patients studied
- Patients ventilated with low tidal volumes (6-8ml/kg) & PEEP 5
- All patients needed radial arterial cannula and cardiac output monitoring – unclear if this was standard for surgery or extra for study
- >18 years old
- Having neurosurgery
Exclusion criteria extensive:
- <18 years old
- Intracranial hypertension
- Co-morbidities that may affect dynamic waveform indices: arrhythmia, lung disease, EF <50%, possible RV dysfunction, sleep apnoea, COPD, pulmonary hypertension
- Extremes of body habitus (BMI <15 or >40)
- Lung recruitment manoeuvre (LRM) by applying continuous positive airway pressure of 30 cmH2O for 30 seconds
- Volume expansion with 250 ml 0.9% saline over more than 10 minutes
- Heart rate/MAP/SA/PPV measured before and after both LRM and volume expansion
Unclear exactly what the primary outcomes were. Aims of the study were:
- Assess ability of LRM induced decrease in SV to predict fluid responsiveness in mechanically ventilated patients in theatre
- Compare the ability of the LRM induced decrease in SV and PPV to predict fluid responsiveness
- Assess the relationship between LRM induced SV decrease and SV changes induced by volume expansion
- Sixteen (out of 28) patients were classified as responders (i.e. SV index increased by >10% after 250ml of fluid)
- LRM induced a significant decrease (p = 0.001) in MAP and SV in ALL patients
- Volume expansion caused a significant increase in SV (p = 0.001) in ALL patients
- The bigger the drop in SV with LRM, the bigger the change in SV after fluid expansion.
- Drop in SV with LRM was more sensitive and more specific at predicting fluid responsiveness than the change in PPV with LRM
- Fluid responsive patients had a bigger PPV
- A 30% decrease in SV during an LRM could predict the effect of infusing 250ml of fluid
- The SV change seen during LRM was a better indicator than PPV to predict fluid responsiveness
- The SV change during LRM and the SV change during volume expansion were strongly correlated (i.e. the bigger the SV drop with LRM the bigger the SV increase with fluid)
Authors recognise limitations of the study
- Nonconsecutive case series – definition of nonconsecutive case series is a clinical study that includes some but not all eligible patients identified during the research period. Why were not all eligible patients included? No comment made on this.
- Low sample size – 28 patients over 1 year period
- Unclear what primary outcomes were
- Neurosurgery patients?? Unsure if these are the most appropriate group of patients to carry this study out on! Why would you deliberately chose to carry out a manoeuvre that could alter intracranial pressure and drop blood pressure in this group of patients?
- Patient characteristics not split into responders vs non-responders – same types of patients in each group?
- 18 of the 28 patients were ASA III. Large numbers of comorbidities excluded therefore what made them ASA III?
- Co-morbidities excluded therefore cannot extrapolate results for patient with any kind of arrhythmia, preoperative lung disease or COPD, EF <50%, possible RV dysfunction, sleep apnoea, pulmonary hypertension, extremes of body habitus (BMI <15 or >40) or patients requiring vasopressors/inotropes
- LRM performed in the supine position during steady-state period and before skin incision – results cannot be extrapolated to positions other than supine or after knife-to-skin
- LRM performed shortly after induction of anaesthesia – haemodynamic effects may have been impacted by degree of vasoplegia due to anaesthetic drugs
- LRM consisted of applying continuous positive airway pressure of 30 cmH2O for 30 seconds – study authors say results cannot be extrapolated for other LRMs. Is this an adequate LRM? ARDS studies talk about LRM of 2 minutes – would 30 seconds be an adequate time in a clinical situation and how often would it need to be done?
- Change in SV was estimated using pulse contour analysis technology – accuracy in measuring exact SV disputable. Better for measuring trends over time than SV at a given point
More objective evidence is needed from a much larger and better designed study to be able to answer this clinical question. Flawed and poorly designed study with many limitations (admitted by the authors). A decrease in SV during LRM may indicate the need for volume expansion but realistically to be clinically effective how often would LRM need to be carried out? Therefore few clinical implications of this study.
Potential for impact
Whist no conclusive evidence is presented in this paper it does highlight that LRMs cause a decrease in SV which can be greater if the patient is hypovolaemic.
This is a good reminder to us all that care should be taken when performing LRMs in patients with cardiac dysfunction or those that are inadequately fluid resuscitated.