Maximal Inspiratory Pressure Is Not a Reliable Test of Inspiratory Muscle Strength in Mechanically Ventilated Patients

Multz, Alan S.; Aldrich, Thomas K.; Prezant, David J.; Karpel, Jill P.; Hendler, Jay M.

doi:10.1164/ajrccm/142.3.529

Cited by 90 publications

(47 citation statements)

References 7 publications

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“…In addition the degree of consciousness, respiratory drive, and lung volume can also affect measurement of PI max (34). Adult patients are often conscious or semiconscious when PI max is measured and their degree of mental alertness will directly affect their cooperation and ability to perform the test (35). The test is often applied in patients who are sufficiently awake to respond to commands, but their level of consciousness may prevent them from making truly maximal efforts (36).…”

Section: Discussionmentioning

confidence: 99%

Tension–Time Index as a Predictor of Extubation Outcome in Ventilated Children

Harikumar¹,

Egberongbe²,

Nadel³

et al. 2009

Am J Respir Crit Care Med

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Rationale: Indices that assess the load on the respiratory muscles, such as the tension-time index (TTI), may predict extubation outcome. Objectives: To evaluate the performance of a noninvasive assessment of TTI, the respiratory muscle tension time index (TTmus), by comparison to that of the diaphragm tension time index (TTdi) and other predictors of extubation outcome in ventilated children. Methods: Eighty children (median [range] age 2.1 yr [0.15-16]) admitted to pediatric intensive care units at King's College and St Mary's Hospitals who required mechanical ventilation for more than 24 hours were studied. Measurements and Main Results: TTmus, maximal inspiratory pressure, respiratory drive, respiratory system mechanics, and functional residual capacity using a helium dilution technique, the rapid shallow breathing and CROP indices (compliance, rate, oxygenation, and pressure) indexed for body weight were measured and standard clinical data recorded in all patients. TTdi was measured in 28 of the 80 children using balloon catheters. Eight children (three in the TTdi group) failed extubation. TTmus (0.199 vs. 0.09) and TTdi (0.157 vs. 0.07) were significantly higher in children who failed extubation. TTmus greater than 0.18 (n 5 80) and TTdi greater than 0.15 (n 5 28) had sensitivities and specificities of 100% in predicting extubation failure. The other predictors performed less well. Conclusions: Invasive and noninvasive measurements of TTI may provide accurate prediction of extubation outcome in mechanically ventilated children.Keywords: diaphragm; respiratory muscles; pediatric critical care; weaningPatients are extubated when assessed to be capable of sustaining spontaneous ventilation without respiratory support. Premature extubation leading to cardiorespiratory compromise necessitates reintubation and reinstitution of mechanical ventilation and increases mortality and morbidity (1), whereas prolonged ventilatory support exposes the child to increased risk of nosocomial infection and lung injury (2). Extubation failure has been reported to occur in 4 to 10% of children (3, 4), hence an accurate predictor of extubation outcome would be of significant clinical value (1).Univariate indices that examine a single aspect of physiological function often have poor predictive power probably because they do not fully reflect all the pathophysiological processes affecting extubation outcome (5). Accurate prediction is more likely using multivariate indices that integrate a number of physiological functions (6). Studies of multivariate indices in children, such as the rapid-shallow breathing index (RSB) (respiratory rate [RR] divided by tidal volume [VT]) (5) and the CROP index (compliance, RR, oxygenation, and inspiratory pressure [PI]), however, have been limited and yielded contradictory results. We (7) and others (8, 9) have shown that the predictive power of those indices in children is poor, whereas Baumeister and colleagues (10), demonstrated that the CROP index discriminated strongly between successful an...

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Section: Discussionmentioning

confidence: 99%

Tension–Time Index as a Predictor of Extubation Outcome in Ventilated Children

Harikumar¹,

Egberongbe²,

Nadel³

et al. 2009

Am J Respir Crit Care Med

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“…Maximum inspiratory pressure and vital capacity are dependent on patient comprehension and cooperation and are hindered by the endotracheal tube. As a result, many have questioned their ability to detect respiratory neuromuscular dysfunction that contributes to prolonged weaning [61][62][63]. Twitch transdiaphragmatic pressure in response to bilateral stimulation of the phrenic nerves can give an effort-independent measure of diaphragmatic contractility [64].…”

Section: Peripheral Dysfunctionmentioning

confidence: 99%

Weaning from mechanical ventilation

Boles

Bion

Connors³

et al. 2007

European Respiratory Journal

1,619

1,499

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“…However, the nature of volitional tests mean that objective quantification of muscle strength is not feasible when patients are sedated, and even when awake it is doubtful that critically ill patients are able to achieve maximum voluntary muscle activation. It is therefore not surprising that volitional tests of respiratory muscle strength, such as maximal mouth inspiratory pressure (PI,max), have been useful [94]. Viewed in this light, the ability to nonvolitionally assess muscle strength with magnetic stimulation appears to be particularly valuable on the ICU.…”

Section: Critical Illnessmentioning

confidence: 99%

Magnetic stimulation for the measurement of respiratory and skeletal muscle function

Man¹

2004

European Respiratory Journal

117

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Respiratory and skeletal muscle function is of interest in many areas of pulmonary and critical care medicine. The capacity of the respiratory muscle pump to respond to the load imposed by disease is the basis of an understanding of ventilatory failure. Over the last four decades, considerable progress has been made in quantifying the capacity of the respiratory muscles, in terms of strength, endurance and fatigue. With the development of magnetic stimulation, it has recently become possible to nonvolitionally assess the respiratory muscles in a clinically acceptable way. This is of particular interest in the investigation of patients receiving critical care, those with neuromuscular disease, and in children where volitional efforts are either not possible or likely to be sub-maximal. Furthermore, the adaptation of these techniques to quantify the strength of peripheral muscles, such as the quadriceps, has allowed the effects of muscle training or rehabilitation, uninfluenced by learning effect, to be assessed. This article focuses on the physiological basis of magnetic nerve stimulation, and reviews how the technique has been applied to measure muscle strength and fatigue, with particular emphasis upon the diaphragm. The translation of magnetic stimulation into a clinical tool is described, and how it may be of diagnostic, prognostic and therapeutic value in several areas of pulmonary medicine. In particular, the use of magnetic stimulation in neuromuscular disease, the intensive care setting, chronic obstructive pulmonary disease and paediatrics will be discussed. The nonvolitional assessment of skeletal musclesFor routine muscle strength measurements, the force generated from a maximum voluntary contraction (MVC) is often used. However volitional, effort-dependent manoeuvres for measuring strength are not always suitable for patients as the ability to perform a true MVC relies upon subject motivation and cooperation. This is particularly so in patients on intensive care units (ICU), children, patients with cognitive difficulties, and those patients prevented from performing a true MVC by pain (for example, following surgery). However, even in well-motivated subjects, sub-maximal muscle activation is common in routine clinical practice [1]. As volitional manoeuvres are influenced by a learning effect, the value of MVC is also limited in studies of training or rehabilitation. Consequently, there has been a need for nonvolitional methods to assess muscle strength. Skeletal muscle physiologySkeletal muscle is controlled by electrical impulses conducted by motor neurones that lead to the release of acetylcholine from the motor end plate, thus depolarising the muscle cell membrane. The force generated by muscle contraction is dependent upon a number of factors, including the number of muscle fibres stimulated, muscle length at the time of stimulation and the frequency of stimulation. The force-frequency curve of a muscle is of particular relevance in the understanding of nonvolitional techniques to asse...

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Maximal Inspiratory Pressure Is Not a Reliable Test of Inspiratory Muscle Strength in Mechanically Ventilated Patients

Cited by 90 publications

References 7 publications

Tension–Time Index as a Predictor of Extubation Outcome in Ventilated Children

Tension–Time Index as a Predictor of Extubation Outcome in Ventilated Children

Weaning from mechanical ventilation

Magnetic stimulation for the measurement of respiratory and skeletal muscle function

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