Continuous positive airway pressure effect on functional residual capacity, vital capacity and its subdivisions

Nasal continuous positive airway pressure: A method to avoid endotracheal reintubation in postoperative high-risk patients with severe nonhypercapnic oxygenation failure

OBJECTIVES

To study whether nasal continuous positive airway pressure (nCPAP) improves pulmonary oxygen transfer and avoids reintubation in patients with severe nonhypercapnic oxygenation failure after major cardiac, vascular, or abdominal surgery.

DESIGN

Prospective interventional study.

SETTING

Surgical ICU of a university hospital.

PATIENTS

Twenty consecutive patients after thoracic, abdominal, or combined thoracoabdominal operations, in whom pulmonary oxygen transfer deteriorated continuously following elective extubation after initial mechanical ventilation. Respiratory failure was due to atelectasis and/or left heart failure, and all patients met predefined criteria for reintubation.

INTERVENTIONS

nCPAP therapy (8 to 10 cm H(2)O) was initiated if PaO(2) had decreased to < 80 mm Hg despite application of 100% oxygen (flow, 25 L/min), intermittent mask continuous positive airway pressure, and maximum conventional therapy.

MEASUREMENTS AND RESULTS

nCPAP treatment was started 24.1 +/- 3.4 h after elective extubation. PaO(2) was < 80 mm Hg in all patients, in 13 patients it was < 60 mm Hg, and in 3 patients it was < 50 mm Hg. Mean PaO(2)/fraction of inspired oxygen (FIO(2)) ratio had decreased to 60 +/- 2.6, and increased within the first hour of nCPAP to 136 +/- 12 (p < 0.001). The clinical condition in all patients improved further, and after 35.2 +/- 6.3 h, all patients were well oxygenated by face mask at ambient pressure (PaO(2)/FIO(2) ratio, 146 +/- 14). Two patients were reintubated for reasons unrelated to oxygenation or ventilation (data are presented as mean +/- SEM).

CONCLUSIONS

nCPAP is safe, easy to apply, and effective to improve arterial blood oxygenation in < 1 h in postoperative patients with severe nonhypercapnic oxygenation failure. In these patients, who otherwise would have been reintubated, nCPAP can avoid endotracheal reintubation and mechanical ventilation.

Effects of conventional physiotherapy, continuous positive airway pressure and non-invasive ventilatory support with bilevel positive airway pressure after coronary artery bypass grafting

BACKGROUND

Coronary artery bypass graft (CABG) surgery with the use of mammary arteries is associated with severe alteration of lung function parameters. The purpose of the present study was to compare the effect on lung function tests of conventional physiotherapy using incentive spirometry (IS) with non-invasive ventilation on continuous positive airway pressure (CPAP) and with non-invasive ventilation on bilevel positive airway pressure (BiPAP or NIV-2P), METHODS: Ninety-six patients were randomly assigned to 1 of 3 groups: NIV-2P (1 h/3 h), CPAP (1 h/3 h) and IS (20/2 h). Pulmonary function tests and arterial blood gases analyses were obtained before surgery. On the 1st and 2nd postoperative days, these parameters were collected together with cardiac output and calculation of venous admixture.

RESULTS

For the 3 groups a severe restrictive pulmonary defect was observed during the 1st postoperative day. On the 2nd postoperative day, in opposition to IS, intensive use of CPAP and NIV-2P reduced significantly the venous admixture (P<0.001) and improved VC, FEV1 and PaO2 (P<0.01).

CONCLUSION

We conclude that preventive use of NIV can be considered as an effective means to decrease the negative effect of coronary surgery on pulmonary function.

Effect of bi-level positive airway pressure (BiPAP) nasal ventilation on the postoperative pulmonary restrictive syndrome in obese patients undergoing gastroplasty

STUDY OBJECTIVE

Upper abdominal surgery results in a postoperative restrictive pulmonary syndrome. Bi-level positive airway pressure (BiPAP System; Respironics Inc; Murrysville, Pa), which combines pressure support ventilation and positive end-expiratory pressure via a nasal mask, could allow alveolar recruitment during inspiration and prevent expiratory alveolar collapse, and therefore limit the postoperative pulmonary restrictive syndrome. This study investigated the effect of BiPAP on postoperative pulmonary function in obese patients after gastroplasty.

DESIGN

Prospective controlled randomized study.

SETTING

GI surgical ward in a university hospital.

PATIENTS

Thirty-three morbidly obese patients scheduled for gastroplasty were studied.

INTERVENTION

The patients were assigned to one of three techniques of ventilatory support during the first 24 h postoperatively: O2 via a face mask, BiPAP System 8/4, with inspiratory and expiratory positive airway pressure set at 8 and 4 cm H2O, respectively, or BiPAP System 12/4 set at 12 and 4 cm H2O. Pulmonary function (FVC, FEV1, and peak expiratory flow rate [PEFR]) were measured the day before surgery, 24 h after surgery, and on days 2 and 3. Oxygen saturation by pulse oximeter (SpO2) was also recorded during room air breathing.

RESULTS

Three patients were excluded. After surgery, FVC, FEV1, PEFR, and SpO2 significantly decreased in the three groups. On day 1, FVC and FEV1 were significantly improved in the group BiPAP System 12/4, as compared with no BiPAP; SpO2 was also significantly improved. After removal of BiPAP System 12/4, these benefits were maintained, allowing faster recovery of pulmonary function. No significant effects were observed on PEFR. BiPAP System 8/4 had no significant effect on the postoperative pulmonary restrictive syndrome.

CONCLUSION

Prophylactic use of BiPAP System 12/4 during the first 24 h postoperatively significantly reduces pulmonary dysfunction after gastroplasty in obese patients and accelerates reestablishment of preoperative pulmonary function.

Noninvasive positive-pressure ventilation in patients with acute respiratory failure

This article provides a systematic review of the literature on the application of noninvasive ventilation in various forms of hypercapnic and hypoxemic respiratory failures. A description of the underlying pathophysiology is followed by a review of physiologic data explaining the mechanisms of action of noninvasive ventilation. A critical review of clinical studies is presented with specific suggestions. The methodology of correctly implementing and monitoring noninvasive ventilation in patients with acute respiratory failure, critical to success, is detailed.

Benefits of nocturnal nasal CPAP in patients with cystic fibrosis

Patients with cystic fibrosis (CF) often hypoventilate during sleep with marked falls in oxygen saturation (SaO2%). This occurs most commonly during REM sleep, when there is a reduction in rib cage excursion and a fall in end-expiratory lung volume (EELV). The aim of this study was to examine the effect of nocturnal nasal continuous positive airway pressure (nCPAP) on SaO2 and the respiratory disturbance index (RDI) during sleep in patients with CF and severe lung disease. Seven patients (FEV1% pred, 23 +/- 5; range, 14 to 28%) were evaluated during sleep on two nights, control and nCPAP (11 +/- 2 cm H2O; range, 8 to 16 cm H2O), with four patients breathing room air and three patients breathing supplemental oxygen on both nights. Mean awake SaO2 was 91 +/- 1% (range, 89 to 93%). All patients showed significant oxyhemoglobin desaturation and respiratory disturbance in the control study. The maximal falls in SaO2 (15 +/- 10%) were most often associated with phasic eye movements, and a decline in rib cage excursion and the sum signal (Respitrace) during REM sleep. Nasal CPAP resulted in a significant improvement in the mean minimum oxygen saturation (MMOS) during both NREM (nCPAP 91 +/- 3% vs control 88 +/- 2%, p < 0.05) and REM sleep (nCPAP 89 +/- 6% vs control 83 +/- 6%, p < 0.05). Transcutaneous CO2 measurements were not significantly different between the control and the nCPAP studies. The RDI was also significantly reduced with nCPAP especially during REM sleep (9 +/- 7 events per hour vs control 25 +/- 11 events per hour, p < 0.05). Nasal CPAP caused no change in total sleep time or sleep efficiency yet significantly reduced the RDI and improved baseline SaO2 during both NREM and REM sleep.

Continuous positive airway pressure by mask in patients after coronary surgery

Thirty patients who underwent coronary artery bypass grafting were randomized to receive 30% oxygen by mask either with an ambient airway pressure or with 7.4 mmHg (1 kPa) continuous positive airway pressure (CPAP) for 8 h after extubation. Arterial blood oxygen tension (PaO2) decreased remarkably in the control group after extubation (from 19.2 +/- 5.3 kPa to 12.4 +/- 2.7 kPa) but less in the CPAP group (from 16.4 +/- 3.3 kPa to 14.0 +/- 2.1 kPa). On the second postoperative morning PaO2 was equally low in both groups (control: 8.4 +/- 1.5 kPa, CPAP: 8.9 +/- 1.9 kPa). Atelectatic areas were seen with similar frequency in both groups, 17% (whole material) on the first and 50% on the second postoperative morning. Atelectasis was more common in patients with internal thoracic artery grafting and/or pleural drainage. In conclusion, CPAP therapy was well tolerated, and minimized the decrease in PaO2 after extubation, but could not prevent the poor oxygenation or the late development of atelectatic areas on the second postoperative day.

Use of continuous positive airway pressure in the management of community acquired pneumonia

Three cases of severe community acquired pneumonia requiring ventilatory support are presented. Continuous positive airway pressure (CPAP) applied via a tightly fitting face mask was used and was successful in two cases; the third required intermittent positive pressure ventilation. More extensive use of CPAP in these circumstances should be considered.

Effect of continuous positive airway pressure applied by face mask on right ventricular function after cardiac surgery

The effect of respiratory therapy with continuous positive airway pressure (CPAP) on right ventricular function 24 hours after elective cardiac surgery was evaluated in patients with or without severe coronary artery disease. The first group included 10 patients following coronary artery bypass graft (CABG) surgery, and the second group included 10 patients following aortic valve replacement (AVR) without preexisting coronary artery disease. Patients of both groups had preoperative left ventricular ejection fractions above 40%. CPAP was applied by face mask at a flow rate of 20 L/min with 40% oxygen in nitrogen and with a positive end-expiratory pressure of 12 cmH2O. Right ventricular function was estimated at end-expiration by a fast-response thermodilution cardiac output catheter. The results demonstrate that in both groups of patients, CPAP did not significantly modify right ventricular indices, ejection fraction, end-systolic and end-diastolic volume indices, and stroke volume index, indicating that CPAP can safely be applied after elective cardiac surgery in patients with or without severe coronary artery disease and preoperative left ventricular ejection fractions above 40%. Furthermore, the concomitant postoperative intravenous infusion of nitroglycerin (to all 10 patients of the CABG group and to 4 patients of the AVR group) counteracted the expected beneficial effect of CPAP therapy on arterial oxygenation.

What is the value of preoperative pulmonary function testing?

This article reviews the current information regarding the value of different tests of lung function in patients undergoing abdominal or thoracic surgery. Risk factors as well as the pathophysiology of postoperative pulmonary complications are also discussed. Finally, a rational approach synthesizing clinical features with pulmonary function test results to estimate risk and minimize complication is presented.

[Postoperative respiratory function and cholecystectomy by laparoscopic approach]

Open cholecystectomy is associated with characteristic changes in pulmonary function showing a restrictive pattern. Laparoscopic cholecystectomy without opening of the peritoneal cavity could be an alternative in reducing postoperative respiratory dysfunction. Having given their informed consent, 13 healthy ASA1 patients (age: 41 +/- 18 yrs) undergoing laparoscopic cholecystectomy were enrolled in this study, in order to assess their postoperative pulmonary function tests (forced vital capacity [FRC], forced expiratory volume [FEV1], functional residual capacity [FRC]) before operation (T0) and 4 h (T4), 24 h (T24), 48 h (T48) after surgery. Anaesthesia technique was the same associating propofol-atracurium-fentanyl, 50% N2O/O2. Ventilation was adapted to maintain end-tidal carbon dioxide pressure up to 30-35 mmHg. Postoperative analgesic regimen consisted of paracetamol-ketoprofen. Mean length of surgery was 84 +/- 15 min; mean duration of anaesthesia was 110 +/- 24 min. An immediate and harmonious restrictive breathing pattern developed postoperatively. Postoperative FVC measured 65% (T4), 63% (T24), 72% (T48) of preoperative function (p < 0.025); postoperative FEV1 measured respectively 60, 66 and 75% of preoperative function (p > 0.001), without change in FEV1/CV and FRC; a significant hypoxia occurred (T0: 86 mmHg, T4: 80 mmHg, T24: 75 mmHg, T48: 81 mmHg [p < 0.05]). Laparoscopic cholecystectomy resulted in less postoperative respiratory dysfunction than conventional cholecystectomy, as previously reported; this restrictive pattern observed without changes in FRC was similar to that following lower abdominal surgery.

Chest physiotherapy for the surgical patient

This article reviews the evidence that chest physiotherapy is effective in the prevention and treatment of pulmonary complications after major abdominal and thoracic surgery. There is some evidence that regular chest physiotherapy significantly decreases the incidence of pulmonary complications, although the mechanism of this effect is uncertain. It is not known whether chest physiotherapy is effective in the treatment of postoperative pulmonary complications after they have developed.

Postoperative pulmonary complications. When are preventive and therapeutic measures necessary?

Relevant clinical and physiologic data are available to help guide decision making in the management of patients who are at risk for or already have postoperative pulmonary complications. Prophylactic measures should be simple and focused. Inexpensive treatment methods should be tried before resorting to more individual-intensive and expensive measures. Proper treatment of postoperative atelectasis requires adequate patient assessment and knowledge of the therapeutic options. Costs, measured in dollars as well as in patient morbidity and mortality, are substantially greater when physicians fail to recognize and treat reversible disease before elective surgery and when effective postoperative therapy is not provided in accordance with individual needs.

Continuous positive airway pressure ventilation for respiratory failure associated with Pneumocystis carinii pneumonia

The value of continuous positive airway pressure (CPAP) ventilation via a tight fitting face mask was assessed in eight HIV-1 antibody-positive patients with Pneumocystis carinii pneumonia who were in hypoxaemic respiratory failure. All patients were conscious, able to protect their airway and not hypercapnic. Treatment was effective in seven patients. Prior to CPAP, mean (range) arterial oxygen tension was 6.7 (4.7-10.5) kPa in seven patients breathing oxygen via a face mask (FiO2 = 0.6), 6.1 kPa in one patient breathing room air and rose to 9.9 (6.8-12.8) kPa with CPAP (FiO2 = 0.6 and PEEP = 1.3 kPa in six patients and 2.6 kPa in one patient); the mean increase in PaO2 was 3.1 kPa (P less than 0.02). These seven patients experienced a rapid reduction in dyspnoea and their respiratory rate fell from a mean of 40 breaths min-1 to 32 breaths min-1 (P less than 0.001). One patient deteriorated rapidly on CPAP and died: no other complications were seen with this technique. CPAP was continued for a mean of 4.5 days and the seven responders all survived the episode of P. carinii pneumonia. We conclude that mask CPAP provides an effective means of improving oxygenation in severely hypoxaemic patients with P. carinii pneumonia.

Postoperative pulmonary complications and lung function in high-risk patients: a comparison of three physiotherapy regimens after upper abdominal surgery in general anesthesia

The effect of three postoperative regimens of respiratory therapy on pulmonary complications and lung function was compared in high-risk patients. Fifty-one patients were randomized to: 1) conventional chest physiotherapy alone (PHYS), 2) chest physiotherapy and positive expiratory pressure (PEP), or 3) chest physiotherapy with both positive expiratory pressure and inspiratory resistance (RMT). Treatments were given twice daily by a physiotherapist and self-administered. The incidence of postoperative pulmonary complications (PPC) was respectively, 71%, 76% and 65% in the PHYS-, PEP- and RMT-groups. The incidence of PPC requiring treatment with antibiotic, bronchodilator or supplementary oxygen according to the existing clinical practice was 47%, 47% and 29%. The incidence of atelectasis was 65%, 64% and 60% and of pneumonia 29%, 35% and 6%. There was no difference between the groups, except for a tendency to a lower frequency of pneumonia in the RMT-group. Postoperatively forced vital capacity (FVC) decreased to mean 54%, forced expired volume in 1 s to 48% and functional residual capacity to 76% of preoperative values. Arterial oxygen tension (PaO2) declined to mean 8.1 kPa and arterial saturation (SaO2) to 89%. There was no difference between the groups except for FVC, PaO2 and SaO2 (P = 0.008, P = 0.008 and P = 0.002), which showed the least decrease in the RMT-group. None of the regimens could be considered as satisfactory concerning the prevention of PPC, but RMT seemed to be the most efficient. Insufficient self-administration of treatment was probably one of the causes of the overall high incidence of PPC in this study.

Lung function during anesthesia and respiratory insufficiency in the postoperative period: physiological and clinical implications

This review covers the physiological and clinical implications of lung function during anesthesia and respiratory insufficiency in the postoperative period. We have divided it into 3 main sections: 1) lung function changes induced by anesthesia and surgery, in which the impact on pulmonary mechanics, ventilation/perfusion changes and gas exchange are examined; 2) physiological implications of postoperative respiratory function secondary to decreased alveolar ventilation, development of atelectasis, and interstitial lung edema; and 3) clinical implications of postoperative respiratory failure. In this last section we analyze the current therapeutic modalities available to reduce the incidence of postoperative respiratory failure, as well as related morbidity and mortality.