Assessing lung recruitability

Assessment should be the starting point

Zones of collapsed and consolidated alveoli in the most dependent lung frequently require airway opening pressures of more than 35–40 cmH2O to recruit (Borges JB, Okamoto VN, Matos GF, et al. Reversibility of lung collapse and hypoxemia in early acute respiratory distress syndrome. Am J Respir Crit Care Med. 2006;174(3):268-278. doi:10.1164/rccm.200506-976OC1).

Knowledge of the percentage of potentially recruitable lung may be important for establishing the therapeutic efficacy of PEEP. Setting levels of PEEP independently of that knowledge may reduce the possible benefits of PEEP, while use of high PEEP levels in patients with a low percentage of potentially recruitable lung provides little benefit and may actually be harmful (Gattinoni L, Caironi P, Cressoni M, et al. Lung recruitment in patients with the acute respiratory distress syndrome. N Engl J Med. 2006;354(17):1775-1786. doi:10.1056/NEJMoa0520522).

Assessing lung recruitability before changing the patient’s position from supine to prone helps you predict the outcome of the prone positioning and determine the strategy. If the assessment shows low recruitability, the patient can be changed to the prone position and no recruitment maneuver is performed. If the assessment shows high recruitability, the patient remains in the supine position and a recruitment maneuver is performed.

The P/V Tool available as a standard or optional feature on HAMILTON-G5/S1 (Standard on the HAMILTON-S1A) and HAMILTON-C3/C6 ventilators can be used to assess lung recruitability (Maggiore SM, Jonson B, Richard JC, Jaber S, Lemaire F, Brochard L. Alveolar derecruitment at decremental positive end-expiratory pressure levels in acute lung injury: comparison with the lower inflection point, oxygenation, and compliance. Am J Respir Crit Care Med. 2001;164(5):795-801. doi:10.1164/ajrccm.164.5.20060713, Grasso S, Fanelli V, Cafarelli A, et al. Effects of high versus low positive end-expiratory pressures in acute respiratory distress syndrome. Am J Respir Crit Care Med. 2005;171(9):1002-1008. doi:10.1164/rccm.200407-940OC4).

Step 1

Use the following settings to generate a low-flow P/V curve:

Parameter	Setting
Pstart	0 cmH2O
Ptop	40 cmH2O
End PEEP	0 cmH2O Note: When prompted whether to change the PEEP setting after the maneuver, touch No.
Ramp speed	2 cmH2O
Tpause	0 s

Step 2

Use the following criteria to help you assess the patient‘s potential for lung recruitment.

a. Determine the shape of the inspiratory curve.

Upward convexity means there is low potential for recruitment
Upward concavity means there is high potential for recruitment

b. Assess the volume difference at 20 cmH2O. The difference must be > 500 ml (Demory D, Arnal JM, Wysocki M, et al. Recruitability of the lung estimated by the pressure volume curve hysteresis in ARDS patients. Intensive Care Med. 2008;34(11):2019-2025. doi:10.1007/s00134-008-1167-85). A difference of less than 500 ml means there is low potential for recruitment.

Screenshot showing upward convexity of inspiratory curve — Figure 1: Upward convexity - low potential for recruitment

Screenshot showing upward concavity of inspiratory curve — Figure 2: Upward concavity - high potential for recruitment

Screenshot showing volume difference at 20cmH20 less than 500 ml — Figure 3: Difference < 500 ml - low potential for recruitment

Screenshot showing volume difference at 20cmH20 greater than 500 ml — Figure 4: Difference > 500 ml - high potential for recruitment

Steps 3 and 4

Step 3: If either one or both of these two criteria is met, a recruitment maneuver is warranted.

Step 4: If neither criteria is met, the patient‘s lung is not recruitable. In this case:

Keep PEEP < 10 cmH2O
Consider prone positioning

Footnotes

A. Standard on the HAMILTON-S1

References

1. Borges JB, Okamoto VN, Matos GF, et al. Reversibility of lung collapse and hypoxemia in early acute respiratory distress syndrome. Am J Respir Crit Care Med. 2006;174(3):268-278. doi:10.1164/rccm.200506-976OC
2. Gattinoni L, Caironi P, Cressoni M, et al. Lung recruitment in patients with the acute respiratory distress syndrome. N Engl J Med. 2006;354(17):1775-1786. doi:10.1056/NEJMoa052052
3. Maggiore SM, Jonson B, Richard JC, Jaber S, Lemaire F, Brochard L. Alveolar derecruitment at decremental positive end-expiratory pressure levels in acute lung injury: comparison with the lower inflection point, oxygenation, and compliance. Am J Respir Crit Care Med. 2001;164(5):795-801. doi:10.1164/ajrccm.164.5.2006071
4. Grasso S, Fanelli V, Cafarelli A, et al. Effects of high versus low positive end-expiratory pressures in acute respiratory distress syndrome. Am J Respir Crit Care Med. 2005;171(9):1002-1008. doi:10.1164/rccm.200407-940OC
5. Demory D, Arnal JM, Wysocki M, et al. Recruitability of the lung estimated by the pressure volume curve hysteresis in ARDS patients. Intensive Care Med. 2008;34(11):2019-2025. doi:10.1007/s00134-008-1167-8

Reversibility of lung collapse and hypoxemia in early acute respiratory distress syndrome.

Borges JB, Okamoto VN, Matos GF, et al. Reversibility of lung collapse and hypoxemia in early acute respiratory distress syndrome. Am J Respir Crit Care Med. 2006;174(3):268-278. doi:10.1164/rccm.200506-976OC

Link to article

RATIONALE

The hypothesis that lung collapse is detrimental during the acute respiratory distress syndrome is still debatable. One of the difficulties is the lack of an efficient maneuver to minimize it.

OBJECTIVES

To test if a bedside recruitment strategy, capable of reversing hypoxemia and collapse in > 95% of lung units, is clinically applicable in early acute respiratory distress syndrome.

METHODS

Prospective assessment of a stepwise maximum-recruitment strategy using multislice computed tomography and continuous blood-gas hemodynamic monitoring.

MEASUREMENTS AND MAIN RESULTS

Twenty-six patients received sequential increments in inspiratory airway pressures, in 5 cm H(2)O steps, until the detection of Pa(O(2)) + Pa(CO(2)) >or= 400 mm Hg. Whenever this primary target was not met, despite inspiratory pressures reaching 60 cm H(2)O, the maneuver was considered incomplete. If there was hemodynamic deterioration or barotrauma, the maneuver was to be interrupted. Late assessment of recruitment efficacy was performed by computed tomography (9 patients) or by online continuous monitoring in the intensive care unit (15 patients) up to 6 h. It was possible to open the lung and to keep the lung open in the majority (24/26) of patients, at the expense of transient hemodynamic effects and hypercapnia but without major clinical consequences. No barotrauma directly associated with the maneuver was detected. There was a strong and inverse relationship between arterial oxygenation and percentage of collapsed lung mass (R = - 0.91; p < 0.0001).

CONCLUSIONS

It is often possible to reverse hypoxemia and fully recruit the lung in early acute respiratory distress syndrome. Due to transient side effects, the required maneuver still awaits further evaluation before routine clinical application.

Lung recruitment in patients with the acute respiratory distress syndrome.

Gattinoni L, Caironi P, Cressoni M, et al. Lung recruitment in patients with the acute respiratory distress syndrome. N Engl J Med. 2006;354(17):1775-1786. doi:10.1056/NEJMoa052052

Link to article

BACKGROUND

In the acute respiratory distress syndrome (ARDS), positive end-expiratory pressure (PEEP) may decrease ventilator-induced lung injury by keeping lung regions open that otherwise would be collapsed. Since the effects of PEEP probably depend on the recruitability of lung tissue, we conducted a study to examine the relationship between the percentage of potentially recruitable lung, as indicated by computed tomography (CT), and the clinical and physiological effects of PEEP.

METHODS

Sixty-eight patients with acute lung injury or ARDS underwent whole-lung CT during breath-holding sessions at airway pressures of 5, 15, and 45 cm of water. The percentage of potentially recruitable lung was defined as the proportion of lung tissue in which aeration was restored at airway pressures between 5 and 45 cm of water.

RESULTS

The percentage of potentially recruitable lung varied widely in the population, accounting for a mean (+/-SD) of 13+/-11 percent of the lung weight, and was highly correlated with the percentage of lung tissue in which aeration was maintained after the application of PEEP (r2=0.72, P<0.001). On average, 24 percent of the lung could not be recruited. Patients with a higher percentage of potentially recruitable lung (greater than the median value of 9 percent) had greater total lung weights (P<0.001), poorer oxygenation (defined as a ratio of partial pressure of arterial oxygen to fraction of inspired oxygen) (P<0.001) and respiratory-system compliance (P=0.002), higher levels of dead space (P=0.002), and higher rates of death (P=0.02) than patients with a lower percentage of potentially recruitable lung. The combined physiological variables predicted, with a sensitivity of 71 percent and a specificity of 59 percent, whether a patient's proportion of potentially recruitable lung was higher or lower than the median.

CONCLUSIONS

In ARDS, the percentage of potentially recruitable lung is extremely variable and is strongly associated with the response to PEEP.

Alveolar derecruitment at decremental positive end-expiratory pressure levels in acute lung injury: comparison with the lower inflection point, oxygenation, and compliance.

Maggiore SM, Jonson B, Richard JC, Jaber S, Lemaire F, Brochard L. Alveolar derecruitment at decremental positive end-expiratory pressure levels in acute lung injury: comparison with the lower inflection point, oxygenation, and compliance. Am J Respir Crit Care Med. 2001;164(5):795-801. doi:10.1164/ajrccm.164.5.2006071

Link to article

We examined the hypothesis that recording multiple elastic pressure-volume (Pel/V) curves and calculating alveolar derecruitment (V(DER)) induced by decreasing positive end-expiratory pressure (PEEP) may allow determination of alveolar closing pressures, thus helping to select the optimal PEEP level. V(DER) measured in 16 patients with acute lung injury (ALI) was compared with the lower inflection point (LIP) and oxygenation changes. A modified automated method was used to record multiple Pel/V curves at low constant flow. PEEP was decreased in 5-cm H(2)O steps, from 20 or 15 cm H(2)O to 0 cm H(2)O (ZEEP). V(DER) was the volume loss between the curves recorded from PEEP and from ZEEP at the same Pel. Derecruitment occurred at each PEEP decrement, being spread almost uniformly over the 20/15 to 0 cm H(2)O range. V(DER) was not correlated with LIP. V(DER) changes correlated with Pa(O(2))/FI(O(2)) changes (rho = 0.6, p = 0.02). Linear compliance at ZEEP was correlated to V(DER) at PEEP 15 cm H(2)O (rho = 0.9, p = 0.001), suggesting that compliance above LIP may reflect the amount of recruitable lung. Thus, alveolar closure in ALI occurs over a wide range of pressures, and LIP is a poor predictor of alveolar closure.

Effects of high versus low positive end-expiratory pressures in acute respiratory distress syndrome.

Grasso S, Fanelli V, Cafarelli A, et al. Effects of high versus low positive end-expiratory pressures in acute respiratory distress syndrome. Am J Respir Crit Care Med. 2005;171(9):1002-1008. doi:10.1164/rccm.200407-940OC

Link to article

A recent study by the Acute Respiratory Distress Syndrome Network compared the traditional lower end-expiratory pressure strategy with a higher end-expiratory pressure strategy in patients with the acute respiratory distress syndrome ventilated with low tidal volumes. Clinical outcomes were similar whether lower or higher positive end-expiratory pressure (PEEP) levels were used. We applied both the lower (9 +/- 2 cm H2O) and higher (16 +/- 1 cm H2O) PEEP strategy in 19 patients. In nine recruiters, the higher end-expiratory pressure strategy resulted in significant alveolar recruitment (587 +/- 158 ml), improvement in arterial oxygen partial pressure/inspired oxygen fraction ratio (from 150 +/- 36 to 396 +/- 138), and reduction in static lung elastance (from 23 +/- 3 to 20 +/- 2 cm H2O/L). In 10 nonrecruiters, alveolar recruitment was minimal, oxygenation did not improve, and static lung elastance significantly increased (from 26 +/- 5 to 28 +/- 6 cm H2O/L). The increase in oxygenation, the reduction in static lung elastance, and the shape of the volume-pressure curve during the lower PEEP strategy were independently associated with alveolar recruitment. In conclusion, the protocol proposed by the Acute Respiratory Distress Syndrome Network, lacking solid physiologic basis, frequently fails to induce alveolar recruitment and may increase the risk of alveolar overinflation.

Recruitability of the lung estimated by the pressure volume curve hysteresis in ARDS patients.

Demory D, Arnal JM, Wysocki M, et al. Recruitability of the lung estimated by the pressure volume curve hysteresis in ARDS patients. Intensive Care Med. 2008;34(11):2019-2025. doi:10.1007/s00134-008-1167-8

Link to article

OBJECTIVE

To assess the hysteresis of the pressure-volume curve (PV curve) as to estimate, easily and at the bedside, the recruitability of the lung in ARDS patients.

DESIGN

Prospective study.

SETTING

Twelve medico-surgical ICU beds of a general hospital.

PATIENTS

Twenty-six patients within the first 24 h from meeting ARDS criteria.

INTERVENTION

A Quasi-static inflation and deflation PV curve from 0 to 40 cmH(2)O and a 40 cmH(2)O recruitment maneuver (RM) maintained for 10 s were successively done with an interval of 30 min in between. RECORDINGS AND CALCULATION: Hysteresis of the PV curve (H(PV)) was calculated as the ratio of the area enclosed by the pressure volume loop divided by the predicted body weight (PBW). The volume increase during the RM (V(RM)) was measured by integration of the flow required to maintain the pressure at 40 cmH(2)O and divided by PBW, as an estimation of the volume recruited during the RM.

RESULTS

A positive linear correlation was found between H(PV) and V(RM) (r = 0.81, P < 0.0001).

CONCLUSIONS

The results suggest using the hysteresis of the PV curve to assess the recruitability of the lung.