Influence of body position, PEEP and intra-abdominal pressure on the catheter positioning for neurally adjusted ventilatory assist

Abstract

PurposeNeurally adjusted ventilatory assist (NAVA) relies on the patient’s electrical activity of the diaphragm (EAdi) for actuating the ventilator. Thus a reliable positioning of the oesophageal EAdi catheter is mandatory. We aimed to evaluate the effects of body position (BP), positive end-expiratory pressure (PEEP) and intra-abdominal pressure (IAP) on catheter positioning.MethodsTwenty-one patients were enrolled in this study. In six different situations [supine or 45° head of bed elevation (HBE) at PEEP 5 and 15 cmH2O; left lateral anti-decubitus at PEEP 5 cmH2O; supine at PEEP 5 cmH2O with abdominal surgical belt (ASB)] the catheter position was evaluated for the stability of the EAdi signal and information provided by a catheter positioning tool (highlighted electrical activity in central leads, absence of p waves in the distal lead).ResultsWith an optimal catheter position EAdi signals were stable for all tested situations. During “45° PEEP 15” and “supine PEEP 15” absence of p waves in the distal lead revealed a difference compared with “supine PEEP 5” (p = 0.03), suggesting a caudal shift of the diaphragm relative to the oesophagus. The analysis of the highlighted electrical activity in the central leads supports this finding, revealing an influence of PEEP, BP and IAP on EAdi catheter position (p < 0.01).ConclusionPEEP, BP and IAP may affect the EAdi catheter position, although not compromising a stable signal. Additional information as provided by the catheter positioning tool is needed to ensure an optimal EAdi catheter position.

Clinical review: Update on neurally adjusted ventilatory assist - report of a round-table conference

“…Barwing and colleagues therefore enrolled 20 patients in order to evaluate the effects of these factors on catheter position [52]. They evaluated six different situations regarding the PEEP, body position and intra-abdominal pressure.…”

Hot Topics in Noninvasive Ventilation: Report of a Working Group at the International Symposium on Sleep-Disordered Breathing in Leuven, Belgium

“…The operator must be experienced in placing the catheter in a conscious subject to acquire a diaphragm EMG signal, and there are also concerns that the signal may be affected by a cardiac artifact, changes in body position, and lung volume. 178,179 The second intercostal space parasternal intercostal muscles are obligate inspiratory muscles that contract in concert with diaphragm muscles during inspiration to stabilize the upper chest wall. [180][181][182] Adjacent to the sternum, second intercostal space parasternal intercostal muscles have inspiratory mechanical advantage with little postural artifact, and mapping the neural respiratory drive of the chestwall muscles has confirmed this to be the point of maximum inspiratory neural respiratory drive.…”

“…However, this is prone to interference with crosstalk from abdominal muscle groups. 130,178,182 Alternative markers of inspiratory effort include respiratory inductance plethysmography. However, respiratory inductance plethysmography may underestimate the prevalence of patient-ventilator asynchrony if neural respiratory drive is insufficient to result in chest-wall expansion or if there is a delay between onset of neural respiratory drive and chest-wall excursion.…”

Effort-adapted modes of assisted breathing

“…The ventilator delivers synchronized assist linearly proportional to the electrical activation of the diaphragm (EAdi) during inspiration, assessed via esophageal electrodes mounted on a gastric tube [104]. Capturing representative tracings of the EAdi signal is mandatory and requires reliable catheter positioning [110,111]. Capturing representative tracings of the EAdi signal is mandatory and requires reliable catheter positioning [110,111].…”

“…Capturing representative tracings of the EAdi signal is mandatory and requires reliable catheter positioning [110,111]. Accentuation of the electromyographic signal with the highest amplitude and the position of the electrodes in relation to the heart (presence/absence of P wave and QRS complex in different leads) can provide information that facilitates catheter placement [110,111,113,114]. A monitoring tool is incorporated in the ventilator that displays four raw leads representing cranial to caudal arranged electrode pairs.…”