Prone position (PP) is a postural therapy capable of influencing patient oxygenation. This goal is obtained by improving the balance between lung ventilation and perfusion, recruiting dependent lung tissue, and promoting drainage of pulmonary secretions.1-3 Using lung protective strategies in adult respiratory distress syndrome (ARDS) patients, with low tidal volumes and plateau pressures (<6 mL/kg of ideal body weight and plateau pressure < 28 cm H2O), can lead to poorly ventilated areas in dependent lung regions and result in alterations of ventilation/perfusion ratio.4,5 According to Guérin and colleagues,3 prone positioning, when compared with supine positioning, markedly reduces the overinflated lung areas while promoting alveolar recruitment. Several multicenter studies and meta-analysis have shown that the application of long sessions of PP, together with a namely lower tidal volume targeting 6 mL/kg of ideal body weight, and a continuous intravenous infusion of cisatracurium for 48 hours are the most important strategies that lead to an overall mortality reduction in patients having ARDS.4-6 The PROSEVA study indicated that PP therapy in addition to standard care reduced mortality by 26%.3 The benefit was seen in severe hypoxemic patients (PO2/FiO2 < 100 mm Hg) who were left prone for at least 16 hours, and early initiation of prone therapy seems to be an important factor for success.
An international prospective epidemiological study conducted in 459 intensive care units (ICUs) across the world in 2014 that analyzed the treatment of 2377 ARDS patients7 has shown that the PP was adopted only for 16% of patients with severe ARDS.8 Recently, the APRONET study (6723 patients) demonstrates that PP was used on 32.9% of patients with severe ARDS.9 This study has shown that a reduction in complication rate is achieved when the procedure is performed in experienced and specialized centers. The authors reported the onset of complications in 12 patients (11.9%) for whom prone positioning was used (pressure sores in 5 patients, hypoxemia in 2 patients, unplanned extubation in 2 patients, ocular injuries in 2 patients, and a transient increase in intracranial pressure in 1 patient). Similar rates of complications are reported by other authors. Sud and colleagues2 report these complications related to PP: unplanned removal of central or arterial lines (6.6%), pneumothorax (5.7%), cardiac arrest (13.8%), dislodgement of thoracostomy tube (1.9%), and pressure sores (46.4%). Furthermore, the incidence of pressure sores in a study by Girard and colleagues10 was 56.9%. Moreover, PP was related to the development of edema and pressure sores of the anterior body regions, including the face.11
Aims of the Study
The primary aim of this study is to observe the incidence of pressure sores and other complications caused by prone positioning in a population of patients having ARDS and treated with PP in a general ICU. The secondary aim was to investigate the modifications of the PaO2/FiO2 mm Hg ratio induced by PP.
Study Design and Observed Variables
An observational retrospective study was performed. The study was developed between January 2008 and December 2018 in a general ICU of a university hospital in the north of Italy, being part of the National ECMO (extracorporeal membrane oxygenation) Network. In the study period, we enrolled all patients with ARDS undergoing invasive mechanical ventilation (both with endotracheal tube or tracheostomy) who were treated with PP, even with veno-venous ECMO support.12 Patients in PP but treated with noninvasive ventilation were excluded.13 During the study, criteria for PP were as follows: fulfilled the diagnostic criteria of ARDS8 and PaO2/FiO2 ratio equal to or lower than 200 mm Hg. The observed variables, described by previous literature as complications of PP, were as follows: pressure sores (face, thorax, trochanters, knees, other sites), vomiting, unplanned extubations, airway obstruction, unplanned removal of vascular catheters, and thoracic drainages. An antidecubitus mattress with alternate pressure was routinely applied to all patients (Proficare, ArjoHuntleigh, United Kingdom).
Instruments and Data Collection
Our current in-hospital protocol for PP is the following: mandatory filling of a dedicated electronic chart where the typologies of potential complications related to PP have to be recorded (eg, vascular catheter's dislodgement, development of skin ulcers). In addition, monitoring of a patient's skin status has to be recorded before and after every cycle of PP maneuver, focusing on the detection of early-stage edema or pressure sores. Pronation of patients involves a complex and coordinated effort, involving physicians and nurses. Every prone positioning maneuver was performed according to our ICU protocol and policy10,13,14:
- - A total of 5 health care professionals must be involved: 4 operators performing the positioning of the patient and 1 responsible for the overall coordination and protection of the endotracheal tube. While 2 operators are ensuring the stability and patency of the endotracheal tube, a nurse looks after the intravenous lines and at least 2 members of staff roll the patient. It is advisable for a senior physician to be always available at the bedside in case of emergency reintubation need.
- - Application of thin hydrocolloid dressing for pressure ulcer prevention on the risk areas: face, thorax, iliac crests, and tibial plateau.11,15,16
- - Application of a double sutureless device to preserve central venous lines and prevent their displacement.
- - Use of double sheets for turning. Using the bottom sheet, 2 nurses pull the patient toward them on the edge of the bed. If rolling is performed on the right side, the right arm of the patient should be placed under his right side, whereas the opposite is true for left-sided rolls. Only when the endotracheal tube and vascular lines are secured, the team can gently roll the patient into PP.
- - The standard monitoring during the entire procedure is as follows: pulse oximetry, continuous mixed venous oxygen saturation, end-tidal carbon dioxide, and invasive arterial blood pressure.
- - Placing the head of the patient on a C-letter–shaped pad to prevent facial pressure ulcers. Face rotation at a regular interval is not scheduled. Face rotation on the left side and, afterward, on the right side every pronation session or every time redness on the skin is observed.
- - Placement of the head over the upper edge of the patient's bed, using customized facial padding if the patient had a tracheostomy.
- - Limbs are positioned so as to prevent abnormal extension or flexion against the shoulders and elbows. Pillows can be added to provide additional support to the hips, shoulders, and face (Figure).
- - Positioning of transversal rolls placed under the pelvis and the chest in patients with poor neck flexibility (in those patients, rolls improve a better facial repositioning) and/or with tracheostomy.11,17
Occurrence of known complications related to PP applications (ie, displacement of indwelling catheters, facial edema, second-degree pressure sores or higher, pressure neuropathies, compression of nerves and retinal vessels, vomiting, and intolerance to the maneuver) was reported as recorded in the medical and nursing charts. The European Pressure Ulcer Advisory Panel (EPUAP) score was used to classify the pressure sores.18 The Braden score was used for predicting pressure ulcer risk (range, 9-23).19 The nursing workload was measured using the Nursing Activities Score (range, 0%-177%).20,21
To calculate the PO2/FiO2 ratio for each patient, PaO2 and ventilator FiO2 values were collected during 4 different time steps: before pronation (PRE-supine step), 1 hour after pronation (1 h-PP step), at the end of pronation (END-PP step), and 1 hour after supination (POST-supine step).
The study protocol was evaluated by the local ethics committee that waived written informed consent because of the following reasons: the retrospective study design and the fact that prone positioning represents an integral part of care provided routinely to patients with ARDS. The local ethics committee approved the study in 2018 (decreto numero: 874-15/05/2018).
Statistical analysis was performed using SPSS version 22.0 (SPSS Inc, Chicago, Illinois). Continuous variables were expressed as mean (SD) or median and interquartile range (IQR). Nonparametric test was performed for the difference between groups (Mann-Whitney U test for 2 samples or Kruskal-Wallis test for k sample). Unpaired Student t test and 1-way repeated-measures analysis of variance were used to evaluate the differences at the different time points of the PO2/FiO2 ratio values. A P value less than .05 was considered statistically significant.
A total of 170 patients were included in the study. The median age was 55 years (IQR, 41-66; range, 2-87). The median ICU length of stay was 20 days (IQR, 12-40; range, 2-158). Fifty-eight percent (n = 98) of patients survived and were discharged from ICU. At ICU admission, patients presented a median Braden score of 11 (IQR, 10-14) and, during their ICU stay, a median Nursing Activities Score of 80 (IQR, 73-89).
All the patients were mechanically ventilated with a tidal volume less than 6 mL/kg of ideal body weight. During the first session of PP, the median positive end-expiratory pressure (PEEP) observed was 15 (IQR, 12-16) cm H2O. In 57 patient cases (34%), PP was adopted while the patient was connected to veno-venous ECMO.
The median of the pronation cycles per patient was 2 (IQR, 1-3; range, 1-56); the median time spent in PP for each cycle was 9 hours (IQR, 7-12; range, 1-22), whereas the median total time in PP per patient was equal to 18 hours (IQR, 9-39; range, 1-429). The total pronation maneuvers investigated were 526. The total number of patients who developed a pressure sore was 23 (14%). The anatomical positions were as follows: face/chin, 5% (n = 8); face/cheekbones, 6% (n = 11); thorax, 2% (n = 3); trochanter, 1% (n = 1); and other sites, 5% (n = 8). In total, we identified 31 pressure sores related to PP on 23 patients. According to the EPUAP pressure sores classification, 14 pressure sores (44%) were at stage I, 15 (48%) were at stage II, and the remaining 2 pressure sores (6%) were at stage IV. No stage III pressure sores were recorded.
To identify the major risk factors for pressure sore development, patients were divided into 2 groups: those with and those without pressure sores developed from prone positioning. The risk factors investigated were reported in Table 1. In the comparison of the 2 groups, there was a statistically significant difference for the following risk factors: length of the PP session, total number of PP sessions, and, consequently, the total time spent in PP.
Complications due to the maneuver of prone positioning occurred in 1% of cases, with the following incidence: episodes of vomit in 1% (n = 5) and displacement of the respiratory device in 0.2% (n = 1). No displacement of central venous, arterial or, Swan Ganz catheters was observed, nor of thoracic drainages. One hundred sixty-four patients (96%) underwent PP with an endotracheal tube, whereas the remaining 6 patients (4%) had a tracheostomy. The total number of pronation maneuvers performed on patients with tracheostomy was 17 (3%).
Collected data were classified by year, as reported in Table 2. There was a progressive increasing of median prone positioning time per cycle, without any significant changes in pressure sore incidence.
The median value of PO2/FiO2 mm Hg ratio in all the 526 cycles before PP (PRE-supine step) was 109 (IQR, 80-148), then reached 144 (IQR, 96-200) after 1 hour from the beginning of the session (1 h-PP step), then 158 (IQR, 110-213) before the patient was placed supine again (END-PP step), and, finally, achieved 131 (IQR, 95-175) when the patient was in the supine position for 1 hour (POST-supine step). There was a statistically significant difference in the PaO2/FiO2 ratios observed in the 4 time frames (P < .0001). Data related to ventilator setup and oxygenation are reported in Table 3.
The rate of overall complications attributed to PP in this study was very low (1%), and the rate of pressure sores was similar to the results from other studies previously published.2,9,10 The physiological response to PP confirms the finding of significant improvement in oxygenation. Median time spent in PP had a progressive increase to reach the time recommended by literature.3,9 Time spent in a PP was, on average, around 9 hours from 2008 to 2013. This pronation time was linked to study protocols used in previous studies that involved our ICU.14,22 After the study by Guérin and colleagues, in 2013, we tried to implement the pronation time to reach at least 12 hours. Only in the last year, this time reached an average of 17 hours, as summarized in our introduction, by PROSEVA trial.
The overall complications associated with PP in the observed sample are lower in comparison with other previous literature reports. In a meta-analysis summarizing 11 Randomized controlled trials, the total percentage of airway-related complications described for PP was 20%: a 9.1% occurrence of unplanned extubation and/or selective intubation (211 events in 2309 patients) and a 10.8% occurrence of endotracheal tube obstruction (200 events in 1847 patients).2 In our sample, only 1 unplanned extubation was recorded (0.4% of overall PP maneuvers). In all the included patients, the artificial airway was secured with a 5-cm canvas tape placed upon a thin hydrocolloid.23 Conventionally, the tape is changed every 8 hours giving the opportunity to relocate the tube from one side to the other side of the mouth. Before every procedure of pronation, the tape was replaced to guarantee better stability. Moreover, before pronation, the tube was displaced on the side of the mouth not leaning on the pillow (eg, when the head was rotated on the right side, the tube was fixed on the left one, and vice versa). For the 6 patients carrying a tracheostomy, an ulcer prevention facial mask was used. This position prevented a higher pressure to be applied on the cannula and provided nurses with a good access for endotracheal suctioning.
The review conducted by Sud and colleagues2 reports other kinds of complications related to PP: unplanned removal of central or arterial lines (6.6%), pneumothorax (5.7%), and cardiac arrest (13.8%). There was no occurrence of these complications in our study. When looking at the unplanned removal of central and arterial lines, we hypothesize that the local procedure of placing 2 sutureless devices for each catheter used on the patient could have been protective. The first sutureless device is applied to ensure the correct device's placement (Grip-Lock, Vygon, Italy). The second one is applied to prevent any unplanned traction that can occur while nursing interventions are performed to the patients (ie, bathing the patient, sheet changing, mobilization).
The most frequent complication reported in the literature was the onset of pressure sores (43.4% in a review conducted by Sud and colleagues,2 56.9% in a study by Girard and colleagues,10 and 36% by Gattinoni and colleagues14). In our population, the development of 14% of pressure sores (23 patients) is given using the PP. These pressure sores mainly occurred on the face of the patient and, in a lesser extent, on the trochanters and thorax. These data are similar to the ones reported by Girard and colleagues.10 The study is the only one exploring in detail the incidence of pressure sores given by the PP alone. The pressure sores were observed as follows: 29% on the face, 18% on the anterior part of the thorax, 20% on the sacrum, 12% on the heels, and 25% in other anatomical regions. In our study population, the results in terms of pressure sores are very encouraging, especially when considering the occurrence of sores on the face and chin (6% and 5%, respectively) and on the anterior part of the thorax (2%).10 In our study, as a first choice for prone positioning, there was no application of cylindrical cushions under the thorax and trochanters. Chiumello and colleagues17 demonstrated that the patient can be placed prone directly on the antidecubitus surface usually applied, without any impact on gas exchange. Our first choice, combined with an extensive use of hydrocolloids to protect the skin surface, could have led to a reduction of the occurrence of pressure sores. Moreover, the rotation of the head of the patient at every single PP session could have had an additional benefit in decreasing the pressure sore onset. The application of cylindrical cushions under the thorax and the iliac crests had been limited to patients with limited neck mobility or with a tracheostomy.
The main variables associated with an increased occurrence of pressure sores in our population were as follows: the length of time spent in PP (single cycle and overall time) and the repetition of PP sessions. The median length of PP for each session was higher in the group with pressure sores (11; IQR, 1-8) compared with the other group (9; IQR, 7-12; P = .04), just like the median number of sessions applied (3 vs 2; P = .03). Our results highlight an increase in oxygenation within the use of the PP. PaO2/FiO2 ratio measured with the patient in the supine position before and after the first PP session increased from 108 (80-148) to 144 (96-200) mm Hg (P = .001). It is crucial to remember that the improvement of the PO2/FiO2 mm Hg ratio value on its own does not represent a reliable parameter to evaluate the possible benefits of PP. Guérin and colleagues3 have shown how the PP compared with the supine position markedly reduces the overinflated lung areas while promoting alveolar recruitment. These effects may contribute to prevent the well-known ventilator-induced lung injury by homogenizing the distribution of stress and strain within the lung. Guérin and colleagues3 also suggest sessions not shorter than 16 hours. Other articles suggest that the PP maneuver should be performed by not less than 5 trained and skilled operators.11,14,22 Moreover, to guarantee the defined length pronation session and to ensure the simultaneous presence of 5 health professionals (generally 1 physician and 4 nurses) during the study, the procedure was generally performed in the late afternoon with the restoration of supine position in the following morning, according to patients' clinical conditions. This decision limited any position modification during night shifts, characterized by a reduction of the health care personnel. Despite dedicated beds being made available in the past years (Rotoprone, Arjo Huntleigh), all PP maneuvers in the study were performed with a manual technique.
This is a retrospective single-center study, so our conclusions have some biases related to the individual center. In fact, the physicians were free to decide whether to implement the PP, selecting only patients suitable to improve their oxygenation and able to tolerate the repositioning. Furthermore, in several patients, the mechanical ventilation setup (PEEP, tidal volume) was modified during the PP. Physicians were free to modify FiO2, PEEP, and tidal volume according to blood gas analysis and respiratory mechanics modification. Finally, the small sample size does not allow a proper evaluation of the effect of PP on clinical outcomes, mortality, or length of ICU stay.
This retrospective study has shown that the PP in ARDS patients, as previously suggested by literature, can be applied in an experienced center using a specific protocol to limit the occurrence of complications. As recommended by recent studies, the length for any PP session should be at a minimum of 16 hours.
RECOMENDATIONS FOR PRACTICE
Literature recommends prone positioning for patients with severe ARDS (PO2/FiO2 < 150 mm Hg). Each session should last at least 16 hours. Prolonged time of application leads to better outcomes. To limit complications, the pronation protocol should include strategies for skin protection, primary and secondary methods for central line fixation, pillow utilization and displacement, and the correct position of patients' face. As suggested by published literature, the maneuver should be performed by at least 5 trained and skilled health care operators.
The authors would like to thank Mrs Patrizia Procopio, MSN, RN; Mrs Elena Dettori, MSN, RN; Mrs Luisa Katherine Barreda, MSN, RN; and Mr Angelo Taraddei, MSN, RN, for their support and assistance during data collection. The authors also thank all the local ICU physicians, nurses, residents, and students for their continuous, extraordinary efforts in caring for these complex patients.
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