Effects of Preoperative Respiratory Physical Therapy on Postoperative Respiratory Function After Bariatric Surgery
Condition: Morbid Obesity
MeSH terms: Obesity, Morbid
Study type: Interventional

Summary: 
      Background. Morbidly obese patients show an increased risk of hypoxemia and a higher
      incidence of postoperative pulmonary complications during the postoperative period resulting
      in prolonged hospital length of stay when compared with normal weight subjects. Preoperative
      respiratory physiotherapy including inspiratory muscle training (IMT) has been shown to
      reduce the incidence of post operative respiratory complications in some different settings.

      Objective. To determine wether a program of preoperative respiratory physical therapy could
      reduce the incidence and severity of postoperative hypoxemia in morbidly obese patients
      undergoing laparoscopic bariatric surgery.

      Setting. Hospital Clínico Universitario, Valencia, Spain.

      Design and Patients. A double-blind, randomized clinical trial. 50 patients (BMI≥40%)
      consecutively scheduled for laparoscopic bariatric surgery were included of whom 44 completed
      the study. Sample size was calculated using the repeated measures of the PaO2/FiO2 ratio
      along the postoperative period as the primary endpoint and considering an effect size of
      0.25.

      Interventions. Patients were randomly assigned to receive either preoperative respiratory
      physical therapy (n=23) or usual care (n=21) during a month just before the date of surgery.
      Both groups received the same postoperative physical therapy.

      Measures. Data on oxygenation (primary outcome, PaO2/Fio2 ratio) were obtained at 1hour and
      at 12 hours after surgery. Data on spirometry and maximum static respiratory pressures
      (secondary outcomes) were obtained before and after the training period, and in the
      postoperative period.
    

Detailed description: 
      Background. Morbidly obese patients show an increased risk of hypoxemia during the
      postoperative period resulting in a higher incidence of postoperative pulmonary complications
      and prolonged hospital length of stay when compared with normal weight subjects. Mechanisms
      involved in this predisposition of morbidly obese patients for develop this physiopathologic
      scheme include a greater impairment on the respiratory mechanics induced by general
      anesthesia and paralysis -greater reduction in pulmonary and chest compliances and higher
      airway resistance- and an increment in ventilatory requirements. That leads to an increased
      work of breathing (WOB) and oxygen consumption (VO2). These effects are exaggerated in
      patients undergoing laparoscopic surgery because the direct effects of the pneumoperitoneum
      on the pulmonary mechanics. In addition, in morbidly obese patients respiratory muscles show
      a reduction in both strength and endurance probably a cause of the fatty tissular
      infiltration and the exacerbated inflammatory response usually observed in these patients.

      Respiratory physical therapy has shown to be effective and reduce postoperative pulmonary
      complications both, as postoperative treatment and when given preoperatively. When applied
      postoperatively respiratory physiotherapy has proved to be able to expand pulmonary volumes
      and to improve arterial oxygenation, leading to decreases in postoperative pulmonary
      complications, specially after abdominal surgery. In the specific setting of morbidly obese
      patients submitted to bariatric surgery, postoperative inspiratory muscle training (IMT )
      improves inspiratory muscle strength and endurance allowing an earlier recovery of pulmonary
      airflows.

      There are scanty data about the results of applying respiratory physiotherapy on the
      preoperative period. However it has proved to be able to reduce the postoperative incidence
      of postoperative pulmonary complications in some different settings: (1) In patients after
      thoracic surgery, (2) In patients undergoing CABG surgery, specially in those considered at
      high risk for pulmonary complications and (3) after upper abdominal surgery.

      At our knowledge no studies aimed to determine wether preoperative respiratory physiotherapy
      could improve the postoperative respiratory function in morbidly obese patients have been
      published.

      The objective of this study was to evaluate the effects of a preoperative respiratory
      physical therapy program on the postoperative respiratory function in morbidly obese patients
      undergoing bariatric laparoscopic surgery.

      Fifty morbid obese patients (BMI≥40%) consecutively scheduled for laparoscopic bariatric
      surgery were considered eligible. All subjects were treated by the same surgical team and
      were submitted to the same anesthetic procedures. All the patients were informed about the
      objectives and interventions of the study and signed an informed consent form. The protocol
      was approved by the local Human Research Ethics Committee.

      The sample size was calculated using the repeated measures of the PaO2/FiO2 ratio in the
      postoperative period as the primary endpoint. Assuming that an increment of 25% or more in
      this parameter (effect size of 0.25) would be of clinical importance, with an alfa error
      probability of 0.05 and a power of 0.95, a required sample size of 44 patients was obtained.
      To account for attrition a proportion of 15% was added, reaching a total sample size of 50
      patients. The calculation was carried out by means of the GPower 3.1.5 application for
      statistics. After inclusion, the informed consent procedure, and evaluation of baseline
      characteristics, the study patients were randomly and blindly divided into two groups:
      control group (CG) and intervention group (RPT). Randomization was done with a computer
      generated randomization table and individual closed sealed envelopes. An investigator blinded
      to the allocation sequence picked consecutive allocation envelopes for consecutive
      participants.

      Surgery was scheduled on the day 32 to 36 from the baseline day for all patients. Anesthetic
      management was standardized. Patients received no premedication. In the operating room
      patients were placed in reverse trendelemburg (RTDL) position (30º). Continuous positive
      airway pressure (CPAP) at 10 cmH2O was applied to all patients during the administration of
      oxygen in air (FiO2 0.8) for 5 minutes. After preoxygenation anesthesia was induced with
      propofol, 3 mg.kg-1 based on ideal body weight (IBW= X + 0.91* height (cm) - 152,4-1; X = 50
      for men; X= 45 for women) and fentanyl 0,1 microg.kg-1, followed by rocuronium 0.6 mg. kg-1.
      Then all the patients were ventilated using pressure support ventilation (PSV) with a
      inspiratory pressure of 10 cmH2O, PEEP 10 cmH2O and a minimum respiratory rate of 10
      breaths.min-1 (Ventilator Engström CS, GE Healthcare, Finland). When neuromuscular blockade
      was complete tracheal intubation was performed maintaining the RTDL position at 30º. The
      radial artery was cannulated for continuous monitoring of arterial blood pressure and
      arterial blood gas measurements. Anesthesia was maintained by continuous infusion of propofol
      and remifentanil to target a bispectral index ™ (XP version 3.0, Aspect Medical Inc. Norwood,
      MA) between 40 and 50. Neuromuscular blockade was maintained with rocuronium and continuously
      monitored (TOF Watch, Bluestar Enterprises, Inc., Chanhassen, MN). Remifentanil was
      discontinued at the time of the removal of the laparoscope. Residual neuromuscular blockade
      was reversed with neostigmine, 0.05 mg/kg IV (IBW). Normothermia was maintained
      intraoperatively using a forced warm air system (Bair Hugger®, Arizant Healthcare Inc., Eden
      Prairie, MN, USA).

      Intraoperative mechanical ventilation was the same for both groups of patients. The lungs
      were ventilated with volume controlled ventilation (VCV) with a mixture of 50% oxygen in air,
      and a tidal volume of 6 mL.kg-1 (IBW), inspiratory to expiratory ratio 1:2, and PEEP 10
      cmH2O. Respiratory rate was adjusted to maintain end-tidal carbon dioxide partial pressure
      (etCO2) between 30 and 35 mmHg. An alveolar recruitment strategy (ARS) was applied after the
      onset of pneumoperitoneum. ARS was performed by increasing PEEP in increments of 5 cmH2O from
      0 to 20 cmH2O using pressure controlled ventilation with a driving pressure similar to the
      airways plateau pressure obtained during VCV. Once PEEP reached 20 cmH2O the driving pressure
      was augmented to reach 45 cmH2O. After 10 breaths at maximal airways pressure, PEEP was
      decreased in steps of 2 cmH2O and static compliance of the respiratory system was measured at
      each step in order to determine the lung's closing pressure. Then a second ARS was applied
      and PEEP was set at 2 cm H2O higher than the closing pressure. At the end of surgery a new
      ARS was applied, before the extubation. In this case PEEP after the ARS was kept in 10 cmH2O
      until the extubation.

      Tracheal extubation was performed in the RTDL position (30º). Fully monitored patients were
      then transferred to the PACU in a semi-sitting position, while receiving a high flow of
      oxygen in air at a FiO2 of 0.5.

      Postoperative analgesia in the first 12 h was intravenous paracetamol (1 g every 6 h) and
      intravenous dexketoprofen (50 mg every 8 h) for all patients.

      In order to know the training effects we recorded the patient follow-up to the physical
      therapy program and measured forced vital capacity (FVC), forced expiratory volume in 1
      second (FEV1), maximal inspiratory pressure (PiMAX), and maximal expiratory pressure (PeMAX)
      (Datospir-600D, SIBEL SA Spain) before and at the end of the 30 days of training. All the
      patients were also instructed and trained about these measurements, aiming to avoid any
      learning effect during the study. The measurements were performed with the patients on a
      sitting position and wearing a nasal clip. PiMAX was measured from residual volume and PeMAX
      from total lung capacity. Five maneuvers were performed for each patient, and the three most
      acceptable were registered. The highest value obtained was considered for calculations.

      Spirometry was performed according to American Thoracic Society (ATS) recommendations,
      employing the above mentioned spirometer (Datospir-600D) previously calibrated . Three
      acceptable curves and two replicable ones were considered, allowing a maximum of eight
      attempts to each patient. The choices of the best values were done according to ATS criteria
      . The obtained values were expressed as percentage of normal values calculated according to
      Knudson et al.

      All the functional data were obtained by the same investigator, namely, the physical
      therapist.
    

Intervention name(s): Respiratory Physical Therapy
Intervention type(s): Procedure
Intervention description(s): Patients were randomly assigned to receive either a preoperative respiratory physiotherapy program (Intervention group, RPT) which included lung re-expansion (Incentive Spirometer, Voldyne5000, Teleflex medical USA) and respiratory muscle training (Threshold IMT, Respironics Inc. Pittsburgh, PA, USA) or usual care (Control group). Immediately after randomization the RPT group patients received detailed instructions about the training program and how correctly use the IMT and incentive spirometer devices. The patients trained daily, for 30 consecutive days. Each session consisted in 20 minutes of IMT and incentive spirometer. The patients adherence to the program was evaluated weekly by the physical therapist. Postoperative physical therapy was the same for both groups and consisted in lung re-expansion exercise with the aid of the incentive spirometer. Besides, patients were placed in sitting position rather than lying and early mobilization was stimulated.
Other intervention name(s): Inspiratory muscle training; Incentive spirometer
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Double (Care Provider, Outcomes Assessor)
Primary purpose: Supportive Care
Keywords: Obesity, Morbid; Hypoxemia; Postoperative complications; Bariatric surgery; Respiratory physical therapy; Preoperative care.