WHAT ARE PRELOAD RESPONSIVE VENTILATOR TESTS?

Published on Friday, May 1st, 2020 by .

Are preload ventilator tests valid indicators of preload responsiveness?

            How are they clinically relevant?

 

Review hemodynamic effects of mechanical ventilation

In order to better understand the preload responsive ventilator tests, a review of the relationship between the effects of positive pressure mechanical ventilation and the cardiorespiratory cycle may be helpful. Briefly stated, the inspiratory phase of mechanical ventilation increases intrathoracic pressure, which in turn impedes venous return and squeezes pulmonary vessels. The net result is a decrease in left ventricular stroke volume. This is well illustrated by a model (see Figure. 1) provided by Michard & Teboul (2000).

 

Figure 1

The cardiorespiratory effects associated with mechanical ventilation produce measurable hemodynamic changes in stroke volume (SV), and “dynamic” measurements of stroke volume variation (SVV) and pulse pressure variation (PPV) which predict preload responsiveness (Marik et al., 2011). Here, dynamic tests are based on “inducing changes in the cardiac preload using heart-lung interactions” [and] to observe the resulting effect on cardiac output” (Monnet et al., 2016, p. 1).

 

SVV/PPV Inclusions

However, SVV and PPV are subject to inherent limitations. In fact, specific inclusion criteria for dynamic assessment includes mechanical ventilation without spontaneous effort, a set tidal volume of 8cc/kg, and a regular heart rhythm (Marik et al., 2011). Additionally, Monnet et al. (2016) summarised other conditions that effect the reliability of SVV/PPV testing (see Figure 2).

 

Figure 2

Monnet, X., Marik, P. E., & Teboul, J. (2016). Prediction of fluid responsiveness: An update. Annals of Intensive Care, 6(1), 1-11. doi:10.1186/s13613-016-0216-7

Protective Ventilation

The reason that these reliability factors deserve consideration is related to the current practice of “protective” ventilation. Here, low tidal volumes are used to decrease acute lung injury, as well as a treatment guideline for acute respiratory distress syndrome (ARDS; AHRQ, 2017). However, SVV and PVV measuring requires a set tidal volume (VT), and excludes states of low lung compliance (ARDS; Monnet et al., 2016). Therefore, protective ventilation would not be used to reliably predict preload responsiveness. Hence, SVV/PPV monitoring may not be a definitive tool to assess preload responsiveness during protective ventilation.

Alternate Methods

However, alternative tests to SVV or PVV do exist. These tests may include Tidal Volume Challenge (TVC), Lung Recruitment Manoeuvre (LRM), and End-Expiratory Occlusion Test (EEOT). Michard (2017) visually summarised these methods to determine preload responsiveness according to test, mechanism, and hemodynamic effect (see Figure 3). In general, this will require advanced hemodynamic monitoring that is capable of rapidly measuring changes in Stroke Volume (Myatra et al., 2017, a; Biais et al., 2017, a; Monnet, 2009; Marik et al., 2011).

 

Figure 3

 

Michard, F. (2017). Toward precision hemodynamic management. Critical Care Medicine, 45(8), 1421-1423. doi:10.1097/CCM.0000000000002458

Tidal Volume Challenge (TVC)

Increasing the TV to a prescribed 8cc/kg for a short period of time when clinically appropriate will fit the inclusion criteria for reliable SVV monitoring. Consequently, the physiological effect of the cardiorespiratory cycle during mechanical ventilation becomes clinically relevant (Figure 3). Research has shown TVC to be predictive for preload responsiveness (Myatra, 2017)

TEST

  • Obtain baseline PPV;
  • Increase TV to 8cc/kg PBW (predicted body weight);
  • At the completion of one (1) minute observe PPV/SVV change;
  • A change in PPV of greater than 3.5%; or in SVV of 2.5% suggest preload responsiveness; and
  • Increase of TV to 8cc/kg PBW predicted fluid responsiveness with Receiver Operator Curve (ROC) values of 0.96 for SVV; and 0.97 for PPV at (95% CIs; Myatra, 2017a).

This presents an easy, simple, and valid way to provide a more reliable dynamic assessment of SVV/PPV. However, the limitations of SVV/PPV monitoring including spontaneous breathing, cardiac arrhythmias, open chest, raised intra-abdominal pressure, high respiratory rate, and right heart failure still remain, and require clinical evaluation in this setting. Although, low compliance is usually considered to be a limitation for PPV predictability, the TVC remained accurate in one study by Myatra (2017a).

Lung Recruitment Maneuver (LRM)

Another ventilator test to predict fluid responsiveness includes lung recruitment maneuver (LRM). Historically, this procedure has been used to increase airway pressure with the overall goal of opening collapsed lung tissue (Hess, 2002). Clinically, this may have use in re-expanding lung tissue secondary to a protective low TV state (Hess, 2002), or as a treatment for ARDS (Goligher, 2017). However, LRM can be useful in predicting preload responsiveness (Biais, 2017). Here, due to the cardiorespiratory effects of mechanical ventilation, a reduction in SV may be expected (see Figure 3; Biais, 2017).

TEST

  • Application of continuous positive airway pressure of 30 cm H2O for 30 seconds;
  • If SV decreases by >30%, then the patient is likely fluid responsive; and
  • A 30% decrease in stroke volume during lung recruitment manoeuvre (LRM) predicted fluid responsiveness with a sensitivity of 88% and a specificity of 92% (95% CIs; Biais, 2017)

LRM has the advantage of being fast, valid, may be used in conjunction with protective ventilation protocol, and may not be subject to the specific limitations of SVV/PVV. However, current research has not included the variables of arrhythmia, heart failure, lung disease, obesity or vasopressor/inotrope support; and, only been conducted with participants in the supine position (Biais, 2017).

End-Expiratory Occlusion Test (EEOT)

Finally, End-Expiratory Occlusion Test (EEOT) may be useful in predicting fluid responsiveness (Biais, 2017a; Monnet, 2009). This is a common test used in Respiratory Therapy to measure intrinsic PEEP (positive end-expiratory pressure) experienced during mechanical ventilation. Physiology, a familiar pattern in which positive pressure ventilation impedes venous return and reduces cardiac preload is presumed (see Figure 3). Consequently, holding mechanical ventilation for a prescribed period stops this impediment to venous return, and should be expected to increase cardiac preload; much like a defacto fluid bolus (Biais, 2017a; Monnet 2009).

TEST

  • Simply stop mechanical ventilation;
  • End-Expiratory Occlusion for 15 seconds;
  • Responders will show in increase in SV/CI of greater than 5% (Biais, 2017a); and
  • Monnet (2009), recorded that a cardiac index of greater or equal to five percent (5%) change during the End-Expiratory Occlusion identified preload responsiveness with a sensitivity of 91% and a specificity of 100% (95% CIs; Monnet, 2009).

The advantages of EEOT include that it is easy, short, valid, and may not be subject to any of the limitations of SVV/PPV dynamic testing (Marik, 2011).  However, it may be limited to patients that can clinically tolerate withholding ventilation for at least fifteen (15) seconds.

 

Conclusion

Ventilator tests such as TVC, LRM, and EEOT are valid indicators of preload responsiveness. Although each ventilator test may have certain limitations, they provide an easy, quick, and versatile alternative to traditional SVV/PPV monitoring. However, the requirement of an advanced rapid acting hemodynamic monitoring capability is necessitated.

 

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References

Agency for Healthcare Research and Quality (AHRQ). (2017). Low Tidal Volume (Lung Protective) Ventilation Literature Review. Retrieved from Content last reviewed January        2017Retrieved from https: //www.ahrq.gov/professionals/quality-patient safety/hais/tools/mvp/modules/technical/ltvv-litreview.html

Biais, M., Lanchon, R., Sesay, M., Le Gall, L., Pereira, B., Futier, E., & Nouette-Gaulain, K. (2017). Changes in stroke volume induced by lung recruitment maneuver predict fluid responsiveness in mechanically ventilated patients in the operating room. Anesthesiology, 126(2), 260-267. doi:10.1097/ALN.0000000000001459

Biais, Matthieu & Larghi, Mathilde & Henriot, Jeremy & de Courson, Hugues & Sesay, Musa & Nouette-Gaulain, Karine. (2017). End-Expiratory Occlusion Test Predicts Fluid Responsiveness in Patients with Protective Ventilation in the Operating Room. Anesthesia and analgesia. 125. 10.1213/ANE.0000000000002322.

Goligher, E. C., Hodgson, C. L., Adhikari, N. K. J., Meade, M. O., Wunsch, H., Uleryk, E., Fan, E. (2017). Lung recruitment maneuvers for adult patients with acute respiratory distress syndrome. A systematic review and meta-analysis. Annals of the American Thoracic Society, 14(Supplement_4), S304-S311. doi:10.1513/AnnalsATS.201704-340OT

Hess, D. R., & Bigatello, L. M. (2002). Lung recruitment: The role of recruitment maneuvers. Respiratory Care, 47(3), 308.

Marik, P. E., Monnet, X., & Teboul, J. (2011). Hemodynamic parameters to guide fluid therapy. Annals of Intensive Care, 1(1), 1-9. doi:10.1186/2110-5820-1-1

Michard, F., & Teboul, J. L. (2000). Using heart-lung interactions to assess fluid responsiveness during mechanical ventilation. Critical Care (London, England), 4(5), 282-289. doi:10.1186/cc710

Michard, F. (2017). Toward precision hemodynamic management. Critical Care Medicine, 45(8), 1421-1423. doi:10.1097/CCM.0000000000002458

Monnet, X. (2009). Predicting volume responsiveness by using the end-expiratory occlusion in mechanically ventilated intensive care unit patients. Critical Care Medicine, 37(3),951-   6.2)

Monnet, X., Marik, P. E., & Teboul, J. (2016). Prediction of fluid responsiveness: An update. Annals of Intensive Care, 6(1), 1-11. doi:10.1186/s13613-016-0216-7

Myatra, S. N., Prabu, N. R., Divatia, J. V., Monnet, X., Kulkarni, A. P., & Teboul, J. (2017). The changes in pulse pressure variation or stroke volume variation after a “tidal volume challenge” reliably predict fluid responsiveness during low tidal volume ventilation. Critical Care Medicine, 45(3), 415-421. doi:10.1097/CCM.0000000000002183

Myatra, S. N., Monnet, X., & Teboul, J. (2017). Use of ‘tidal volume challenge’ to improve the reliability of pulse pressure variation. Critical Care (London, England), 21(1), 60. doi:10.1186/s13054-017-1637-x

Written by Gary Martinez

Gary Martinez is a registered nurse in the US with many years of critical care clinical experience with a background in education. Gary is a clinical specialist working for LiDCO in Houston, Texas and enjoys golf and learning new things.

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