Postoperative hypoxaemia after major abdominal vascular surgery

Balanced Opioid-free Anesthesia with Dexmedetomidine versus Balanced Anesthesia with Remifentanil for Major or Intermediate Noncardiac Surgery

BACKGROUND

It is speculated that opioid-free anesthesia may provide adequate pain control while reducing postoperative opioid consumption. However, there is currently no evidence to support the speculation. The authors hypothesized that opioid-free balanced anesthetic with dexmedetomidine reduces postoperative opioid-related adverse events compared with balanced anesthetic with remifentanil.

METHODS

Patients were randomized to receive a standard balanced anesthetic with either intraoperative remifentanil plus morphine (remifentanil group) or dexmedetomidine (opioid-free group). All patients received intraoperative propofol, desflurane, dexamethasone, lidocaine infusion, ketamine infusion, neuromuscular blockade, and postoperative lidocaine infusion, paracetamol, nefopam, and patient-controlled morphine. The primary outcome was a composite of postoperative opioid-related adverse events (hypoxemia, ileus, or cognitive dysfunction) within the first 48 h after extubation. The main secondary outcomes were episodes of postoperative pain, opioid consumption, and postoperative nausea and vomiting.

RESULTS

The study was stopped prematurely because of five cases of severe bradycardia in the dexmedetomidine group. The primary composite outcome occurred in 122 of 156 (78%) dexmedetomidine group patients compared with 105 of 156 (67%) in the remifentanil group (relative risk, 1.16; 95% CI, 1.01 to 1.33; P = 0.031). Hypoxemia occurred 110 of 152 (72%) of dexmedetomidine group and 94 of 155 (61%) of remifentanil group patients (relative risk, 1.19; 95% CI, 1.02 to 1.40; P = 0.030). There were no differences in ileus or cognitive dysfunction. Cumulative 0 to 48 h postoperative morphine consumption (11 mg [5 to 21] versus 6 mg [0 to 17]) and postoperative nausea and vomiting (58 of 157 [37%] versus 37 of 157 [24%]; relative risk, 0.64; 95% CI, 0.45 to 0.90) were both less in the dexmedetomidine group, whereas measures of analgesia were similar in both groups. Dexmedetomidine patients had more delayed extubation and prolonged postanesthesia care unit stay.

CONCLUSIONS

This trial refuted the hypothesis that balanced opioid-free anesthesia with dexmedetomidine, compared with remifentanil, would result in fewer postoperative opioid-related adverse events. Conversely, it did result in a greater incidence of serious adverse events, especially hypoxemia and bradycardia.

EDITOR’S PERSPECTIVE

POFA trial study protocol: a multicentre, double-blind, randomised, controlled clinical trial comparing opioid-free versus opioid anaesthesia on postoperative opioid-related adverse events after major or intermediate non-cardiac surgery

INTRODUCTION

Reducing opioid consumption during and after surgery has been recommended for more than 10 years. Opioid-free anaesthesia (OFA) is a multimodal anaesthesia associating hypnotics, NMDA antagonists, local anaesthetics, anti-inflammatory drugs and α-2 agonists. Proofs of the effect of OFA on reducing opioid-related adverse effects after major or intermediate non-cardiac surgery are still scarce. We hypothesised that the reduced opioid consumption allowed by OFA compared with standard of care will be associated with a reduction of postoperative opioid-related adverse events.

METHODS/ANALYSIS

The POFA trial is a prospective, randomised, parallel, single-blind, multicentre study of 400 patients undergoing elective intermediate or major non-cardiac surgery. Patients will be randomly allocated to receive either a standard anaesthesia protocol or an OFA. The primary outcome measure is the occurrence of a severe postoperative opioid-related adverse event within the first 48 hours after extubation defined as: postoperative hypoxaemia or postoperative ileus or postoperative cognitive dysfunction. In addition, each component of the primary outcome measure will be analysed separately. Data will be analysed on the intention-to-treat principle and a per-protocol basis.

ETHICS AND DISSEMINATION

The POFA trial has been approved by an independent ethics committee for all study centres. Participant recruitment begins in November 2017. Results will be published in international peer-reviewed medical journals.

TRIAL REGISTRATION NUMBER

NCT03316339; Pre-results.

Perioperative hypoxemia is common with horizontal positioning during general anesthesia and is associated with major adverse outcomes: a retrospective study of consecutive patients

Background

Reported perioperative pulmonary aspiration (POPA) rates have substantial variation. Perioperative hypoxemia (POH), a manifestation of POPA, has been infrequently studied beyond the PACU, for patients undergoing a diverse array of surgical procedures.

Methods

Consecutive adult patients with ASA I-IV and pre-operative pulmonary stability who underwent a surgical procedure requiring general anesthesia were investigated. Using pulse oximetry, POH was documented in the operating room and during the 48 hours following PACU discharge. POPA was the presence of an acute pulmonary infiltrate with POH.

Results

The 500 consecutive, eligible patients had operative body-positions of prone 13%, decubitus 8%, sitting 1%, and supine/lithotomy 78%, with standard practice of horizontal recumbency. POH was found in 150 (30%) patients. Post-operative stay with POH was 3.7 ± 4.7 days and without POH was 1.7 ± 2.3 days (p < 0.0001). POH rate varied from 14% to 58% among 11 of 12 operative procedure-categories. Conditions independently associated with POH (p < 0.05) were acute trauma, BMI, ASA level, glycopyrrolate administration, and duration of surgery. POPA occurred in 24 (4.8%) patients with higher mortality (8.3%), when compared to no POPA (0.2%; p = 0.0065). Post-operative stay was greater with POPA (7.7 ± 5.7 days), when compared to no POPA (2.0 ± 2.9 days; p = 0.0001). Conditions independently associated with POPA (p < 0.05) were cranial procedure, ASA level, and duration of surgery. POPA, acute trauma, duration of surgery, and inability to extubate in the OR were independently associated with post-operative stay (p < 0.05). POH, gastric dysmotility, acute trauma, cranial procedure, emergency procedure, and duration of surgery had independent correlations with post-operative length of stay (p < 0.05).

Conclusions

Adult surgical patients undergoing general anesthesia with horizontal recumbency have substantial POH and POPA rates. Hospital mortality was greater with POPA and post-operative stay was increased for POH and POPA. POH rates were noteworthy for virtually all categories of operative procedures and POH and POPA were independent predictors of post-operative length of stay. A study is needed to determine if modest reverse-Trendelenburg positioning during general anesthesia has a relationship with reduced POH and POPA rates.

Ventilatory responses after major surgery and high dependency care

BACKGROUND

Disturbed breathing during sleep, with episodic upper airway obstruction, is frequent after major surgery. Ventilatory responses to hypercapnia and hypoxia during episodes of airway obstruction are difficult to investigate because the usual measure, that of ventilation, has been attenuated by the obstruction. We simulated the blood gas stimulus associated with obstruction to allow investigation of the responses.

METHODS

To assess ventilatory responses, we studied 19 patients, mean age 59 (19-79), first at discharge from high dependency care after major abdominal surgery and then at surgical review, ~6 weeks later. Exhaled gas was analysed and inspired gas adjusted to simulate changes that would occur during airway obstruction. Changes in ventilation were measured over the following 45-70 s. Studies were done from air breathing if possible, and also from an increased inspired oxygen concentration.

RESULTS

During simulated obstruction, hypercapnia developed similarly in all the test conditions. Arterial oxygen saturation decreased significantly more rapidly when the test was started from air breathing. The mean ventilatory response was 5.8 litre min(-2) starting from air breathing and 4.5 litre min(-2) with oxygen breathing. The values 6 weeks later were 5.9 and 4.3 litre min(-2), respectively (P=0.05, analysis of variance). There was no statistical difference between the responses starting from air and those on oxygen.

CONCLUSIONS

After major surgery, ventilatory responses to hypercapnia and hypoxaemia associated with airway obstruction are small and do not improve after 6 weeks. With air breathing, arterial oxygen desaturation during simulated rebreathing is substantial.

[Postoperative pulmonary complications: prophylaxis after noncardiac surgery]

Postoperative pulmonary complications are a major problem after upper abdominal or thoracoabdominal surgery. They lead to a prolonged ICU stay as well as increased costs and are one of the main causes of early postoperative mortality. Even after uncomplicated operations, postoperative hypoxemia occurs in 30-50% of patients. Acute respiratory failure involves a disturbance in gas exchange. The mortality ranges from 10 to 60% according to the severity of respiratory failure. The most important complications are interstitial and alveolar pulmonary edema, atelectasis, postoperative pneumonia, hypoventilation, and aspiration. Preoperative optimization, postoperative prophylaxis according to a stepwise approach, and early mobilization decrease the rate of complications.

Postoperative study of vital capacity and ventilation measurements following elective craniotomy

CONTEXT AND OBJECTIVE

Changes in pulmonary function commonly occur after general surgery. The aims were to evaluate vital capacity, tidal volume and respiratory frequency among patients undergoing elective craniotomy and to determine possible correlations of these parameters with surgery duration and etiology for neurosurgery.

DESIGN AND SETTING

Prospective, open study at a tertiary university hospital.

METHODS

Twenty-six patients underwent elective craniotomy for aneurysm clipping (11) or tumor resection (15). Vital capacity (VC), tidal volume (TV), minute volume (VE) and respiratory rate were determined before the operation and on the first to fourth postoperative days.

RESULTS

There were significant decreases of 25% in VC, 22% in TV and 12% in VE (p < 0.05) and no significant increase in respiratory frequency (5%) on the first postoperative day. VE returned to baseline on the second postoperative day and TV on the third postoperative day, while VC was 8% lower on the fourth postoperative day, compared with before the operation (p < 0.05). VC reduction was significantly greater in patients undergoing aneurysm clipping (43%) than in patients undergoing tumor resection (14%) when surgery duration was more than four hours (p < 0.05), with no significant change when surgery duration was less than four hours.

CONCLUSION

Reductions in VC, TV and VE were observed during the postoperative period in patients undergoing aneurysm clipping or tumor resection. The reductions in VC and TV were greater in patients undergoing craniotomy due to aneurysm and with longer surgery duration.

Influence de la stratégie analgésique sur la fonction respiratoire après chirurgie thoracique pour lobectomie

OBJECTIVE

To compare the influence of thoracic epidural analgesia (TEA) with intravenous patient-controlled analgesia with morphine (PCA) on the early postoperative respiratory function after lobectomy.

STUDY DESIGN

Prospective and comparative observational study.

PATIENTS AND METHODS

Fourty-four patients scheduled for lobectomy (n=22 per group) were studied on the evolution of the postoperative respiratory function assessed by the forced vital capacity (FVC) and the forced expired volume (FEV(1)) during the first two postoperative days and the analysis of noctural arterial desaturation during the three first postoperative nights.

RESULTS

The use of TEA resulted in fewer decrease both in FEV(1) (1.01+/-0.34 versus 1.31+/-0.51 l/s for Day 1, P=0.03; 1.13+/-0.37 versus 1.53+/-0.59 l/s for Day 2, P=0.01) and in FVC (1.23 [1.05-1.51] versus 1.57 [1.38-2.53] l for day 1, P=0.008; 1.33+/-0.43 versus 2.24+/-0.87 l for day 2, P<0.001). Moreover, the duration of arterial desaturation<90% were longer in the PCA group during the first (8.6 [0.8-28.2] versus 1.3 [0-2.6] min, P=0.02) and the second postoperative night (13.5 [3.5-54] versus 0.4 [0-2.6] min, P=0.025).

CONCLUSION

The results of this study suggest that the use of TEA is associated with a better preservation of respiratory function assessed by spirometric data and noctural arterial desaturation recording after thoracic surgery for lobectomy.

Nocturnal episodic hypoxemia after ambulatory breast cancer surgery: comparison of sevoflurane and propofol-fentanyl anesthesia

PURPOSE

To study the incidence and severity of nocturnal episodic hypoxemia after ambulatory breast cancer surgery and its differences with sevoflurane and propofol anesthesia.

METHODS

Sixty-one adult female patients (ASA PS I-II; age, 32-77 years) without an apparent history of sleep apnea and respiratory disease undergoing major breast cancer surgery on an outpatient basis and with planned overnight admission were randomized to one of two anesthesia maintenance groups: sevoflurane anesthesia (SEV, n = 31) or intravenous propofol, fentanyl, and vecuronium anesthesia (TIVA, n = 30). All patients were administered propofol 2 mg x kg(-1) intravenously for anesthesia induction, had a laryngeal mask airway placed, and received rectal diclofenac and local infiltration anesthesia for pain relief. No opioid analgesic or oxygen was administered after discharge from the postanesthesia care unit (PACU). Oxygen saturation (Sp(O) (2)) was recorded continuously during the first postoperative night. Sp(O) (2) <90% that lasted >10 s was regarded as hypoxemia, and the percentage of effective recording time with Sp(O) (2) <90% (%time with Sp(O) (2) <90) was evaluated.

RESULTS

Six patients (SEV3/TIVA3) had >1% of %time with Sp(O) (2) <90 (S-hypoxemia group), 17 (SEV7/TIVA10) had >0% and <or=1% (M-Hypoxemia group), and 38 (SEV21/TIVA17) had 0% (no-hypoxemia group). There were no statistical differences in age, ASA PS, anesthesia technique, and duration of anesthesia among groups. The S-hypoxemia group had higher body mass index (BMI) and incidence of oxygen supplementation in the PACU than the no-hypoxemia group. No patient had major complications.

CONCLUSION

Nocturnal episodic hypoxemia occurs frequently after ambulatory breast cancer surgery. The incidence was not different between SEV and TIVA. Hypoxic patients had a higher BMI and needed oxygen therapy in PACU more frequently.

Nocturnal Hypoxemia After Lobectomy for Lung Cancer

BACKGROUND

Although nocturnal episodic hypoxemia after major abdominal surgery has been reported, the condition of nocturnal oxygen saturation after lung surgery is largely unknown. We evaluated nocturnal oxygen saturation during the perioperative period after lobectomy for lung cancer. This study also compared the postoperative course of nocturnal oxygen saturation after standard lobectomy with posterolateral thoracotomy and lobectomy with video-assisted thoracic surgery.

METHODS

Twenty-one consecutive patients who had undergone lobectomy for lung cancer by either the posterolateral thoracotomy approach (n = 11) or the video-assisted thoracic surgery approach (n = 10) were studied. Fifteen consecutive patients who had undergone gastrectomy for gastric cancer were also studied. Overnight oxygen saturation was measured on the third and 14th postoperative days.

RESULTS

The frequency of hypoxemia in the lobectomy group was higher than that in the gastrectomy group (p = 0.043). The frequency of hypoxemia on the 14th postoperative day (p = 0.009) and the severity of hypoxemia on the third and 14th postoperative days (p = 0.041, 0.046) for the video-assisted thoracic surgery approach were lower than those for the posterolateral thoracotomy approach. In terms of mean arterial oxygen saturation, heart rate, forced vital capacity, and forced expiratory volume in 1 second, there were no statistically significant differences between the video-assisted thoracic surgery group and the posterolateral thoracotomy group.

CONCLUSIONS

Video-assisted thoracic surgery lobectomy was superior in terms of early postoperative nocturnal oxygen saturation. We conclude that the video-assisted thoracic surgery approach is more beneficial than the posterolateral thoracotomy approach for high-risk patients.

Nocturnal Arterial Oxygen Desaturation and Episodic Airway Obstruction After Ambulatory Surgery

Some patients experience disordered breathing during sleep and arterial oxygen desaturation after major inpatient surgery. We performed this study to determine whether similar events occur after ambulatory surgery. Forty-five ambulatory surgery patients received an unrestricted anesthetic. Continuous unattended nocturnal recordings of breathing pattern and oxygen saturation were made in the patients' homes before surgery and during the first and second postoperative nights. Nine patients had a respiratory disturbance index >10 and/or >1% of recording time with oxygen saturation <90% on at least one study night. These nine patients had a significantly older median age and a significantly larger median body mass index. Their median respiratory disturbance index and median percentage of time with oxygen saturation <90% were significantly higher on the first postoperative night than on the preoperative night.

The automatic lung parameter estimator (ALPE) system: non-invasive estimation of pulmonary gas exchange parameters in 10-15 minutes

OBJECTIVE

Clinical measurements of pulmonary gas exchange abnormalities might help prevent hypoxaemia and be useful in monitoring the effects of therapy. In clinical practice single parameters are often used to describe the abnormality e.g., the "effective shunt." A single parameter description is often insufficient, lumping the effects of several abnormalities. A more detailed picture can be obtained from experiments where FiO2 is varied and two parameters estimated. These experiments have previously taken 30-40 minutes to complete, making them inappropriate for routine clinical use. However with automation of data collection and parameter estimation, the experimental time can be reduced to 10-15 minutes.

METHODS

A system has been built for non-invasive, Automatic, Lung Parameter Estimation (ALPE). This system consists of a ventilator, a gas analyser with pulse oximeter, and a computer. Computer programs control the experimental procedure, collect data from the ventilator and gas analyser, and estimate pulmonary gas exchange parameters. Use of the ALPE system, i.e. in estimating gas exchange parameters and reducing experimental time, has been tested on five normal subjects, two patients before and during diuretic therapy, and on 50 occasions in patients before and after surgical intervention.

RESULTS

The ALPE system provides estimation of pulmonary gas exchange parameters from a simple, clinical, non-invasive procedure, automatically and quickly. For normal subjects and in patients receiving diuretic therapy, data collection by clinicians familiar with ALPE took (mean +/- SD) 13 min 40 sec +/- 1 min 23 sec. For studies on patients before and after surgery, data collection by an intensive care nurse took (mean +/- SD) 10 min 47 sec +/- 2 min 14 sec. Parameter estimates were: for normal subjects, shunt = 4.95% +/- 2.64% and fA2 = 0.89 +/- 0.01; for patients with heart failure prior to diuretic therapy, patient 1, shunt = 11.50% fA2 = 0.41, patient 2 shunt = 11.61% fA2 = 0.55; and during therapy: patient 1, shunt = 11.51% fA2 = 0.71, patient 2, shunt = 11.22% fA2 = 0.49.

CONCLUSIONS

The ALPE system provides quick, non-invasive estimation of pulmonary gas exchange parameters and may have several clinical applications. These include, monitoring pulmonary gas exchange abnormalities in the ICU, assessing post-operative gas exchange abnormalities, and titrating diuretic therapy in patients with heart failure.

Modelling of hypoxaemia after gynaecological laparotomy

BACKGROUND

Late postoperative arterial hypoxaemia is common after major surgery, and may contribute to cardiovascular, cerebral or wound complications. This study investigates the time course of hypoxaemia following gynaecological laparotomy, and estimates parameters of mathematical models of pulmonary gas exchange to describe hypoxaemia.

METHODS

Twelve patients were studied on four occasions; preoperatively, 2, 8 and 48 h after surgery. On each occasion inspired oxygen fraction (FIO2) was varied, changing end-expired oxygen fraction (FEO2) to achieve arterial oxygen saturations (SaO2) ranging from 90% to 100%. Measurements of ventilation and blood gases were taken. Oxygenation was characterized plotting FEO2 against SaO2. The shape and position of the FEO2/SaO2 curve was described using two mathematical models including parameters describing gas exchange: either shunt and resistance to oxygen diffusion (Rdiff); or shunt and asymmetry of ventilation-perfusion (fA2).

RESULTS

Two hours after surgery SaO2 was reduced from 97.5%+/-1.2% (mean+/-SD) to 93.8%+/-2.7% (mean+/-SD) (P<0.001). Values of shunt, Rdiff and fA2 were significantly changed at 2 and 8 h postoperatively. Forty-eight hours postoperatively Rdiff and fA2 were still significantly changed.

CONCLUSION

Oxygenation in 12 patients preoperatively, 2, 8 and 48 h after gynaecological laparotomy is described. Two patients were hypoxaemic (SaO2 <92%) 48 h postoperatively. When two different models of oxygen transport are fitted to patient data, high values of Rdiff or low values of fA2 describe the right shift in the FEO2/SaO2 curve seen in patients with oxygenation problems. These models fit patient data identically, and may be useful in quantifying postoperative hypoxaemia.

Adult hypoxaemia in the perioperative period: a review of the literature

As a group of academic skills, learning to search for, obtain, read and critically review literature represents a considerable achievement. For the many perioperative nurses who may never be able to pursue their own research project, reading literature reviews is an excellent alternative which enables individuals to become better and more critically informed. A review of the available literature may provide answers to questions or indicate where a subject is in need of further research. In this article by Denise O'Reilly, perioperative hypoxaemia is defined and a range of literature about the subject is critically reviewed.

Respiratory function in the elderly

Aging reduces the reserve capacity of virtually all pulmonary functions. Age-related alterations in the respiratory system are based on structural changes that lead to functional impairment of gas exchange. Pulmonary complications during anesthesia and the postoperative period are significantly increased in elderly patients with pre-existing diseases. The physiologic changes in the aged respiratory system and their anesthetic implications are reviewed in this article.

PaO2 during anaesthesia and years of smoking predict late postoperative hypoxaemia and complications after upper abdominal surgery in patients without preoperative cardiopulmonary dysfunction

BACKGROUND

The incidence of late postoperative hypoxaemia and complications after upper abdominal surgery is 20-50% among cardiopulmonary healthy patients. Atelectasis development during anaesthesia and surgery is the main hypothesis to explain postoperative hypoxaemia. This study tested the predictive value of PaO2<19 kPa during combined general and thoracic epidural anaesthesia and the preoperative functional residual capacity (FRC) reduction in the 30 degree head tilt-down position for the development of late prolonged postoperative hypoxaemia, PaO2<8.5 kPa for a minimum of 3 out of 4 days, and other complications. Forty patients without cardiopulmonary morbidity, assessed by ECG, spirometry, FRC and diffusion capacity preoperatively, underwent upper abdominal surgery. PaO2 during anaesthesia and preoperative FRC reduction were compared to known risk factors for the development of hypoxaemia and complications: age, pack-years of smoking and duration of operation. The effect of optimizing pulmonary compliance with peroperative positive end-expiratory pressure (PEEP) on postoperative hypoxaemia and complications was evaluated in a blinded and randomized manner.

RESULTS

Late prolonged postoperative hypoxaemia and other complications were found in 37% and 38% of the patients, respectively. Patients with PaO2>19 kPa during anaesthesia with F(I)O2=0.33 exhibited a risk, irrespective of PEEP status, of suffering late prolonged hypoxaemia of 0% (0;23) and patients with PaO2<19 kPa a risk of 52% (32;71), P<0.005. Having smoked more than 20 pack-years was associated with a 47% (19;75) higher incidence of postoperative complications than having smoked less than 20 pack-years, P<0.006.

CONCLUSIONS

PaO2 during anaesthesia and smoked pack-years provide new tools evaluating patients undergoing upper abdominal surgery in order to predict the patients who develop late postoperative hypoxaemia and complications.

Nocturnal oxygenation during patient-controlled analgesia

Patient-controlled analgesia (PCA) has become a standard modality for the management of postoperative pain, although anecdotal reports of excessive sedation and respiratory depression impugn its safety. To study the prevalence and severity of nocturnal hypoxemia, we measured arterial oxygen saturation (SpO2) continuously overnight in 32 postoperative patients who were receiving morphine via PCA. To evaluate the potential benefit of providing concurrent supplemental oxygen, the patients breathed oxygen-enriched air the night of surgery and room air the next night. Patients experienced more pain and consumed twice as much morphine the first night. However, breathing supplemental oxygen that night, the nocturnal mean SpO2 was 99%+/-1%, 94%+/-4% (P<0.001), and only four patients had periods of hemoglobin desaturation <90%. In contrast, breathing room air the subsequent night, the mean SpO2 was lower (94%+/-4%; P<0.001), and hypoxemia occurred more frequently and was more severe: 18 patients experienced episodes of SpO2 <90%, 7 patients experienced episodes of SpO2 <80%, and 3 patients experienced episodes of SpO2 <70%. One patient required resuscitation for profound bradypnea and cyanosis, but none suffered permanent sequelae. We conclude that when postoperative patients use PCA at night, hypoxemia can be substantial and oxygenation can be improved by providing supplemental oxygen.

IMPLICATIONS

Oxygen saturation was measured postoperatively in patients using morphine patient-controlled analgesia. Substantial nocturnal hypoxemia occurred in half of the patients while they breathed room air. The severity of the hypoxemia was reduced when patients received supplemental oxygen.

Prediction of hypoxemia and mechanical ventilation after lung resection for cancer

BACKGROUND

Hypoxemia usually occurs after thoracotomy, and respiratory failure represents a major complication.

METHODS

To define predictive factors of postoperative hypoxemia and mechanical ventilation (MV), we prospectively studied 48 patients who had undergone lung resection. Preoperative data included, age, lung volume, force expiratory volume in one second (FEV1), predictive postoperative FEV1 (FEV1ppo), blood gases, diffusing capacity, and number of resected subsegments.

RESULTS

On postoperative day 1 or 2, hypoxemia was assessed by measurement of PaO2 and alveolar-arterial oxygen tension difference (A-aDO2) in 35 nonventilated patients breathing room air. The other patients (5 lobectomies, 9 pneumonectomies) required MV for pulmonary or nonpulmonary complications. Using simple and multiple regression analysis, the best predictors of postoperative hypoxemia were FEV1ppo (r = 0.74, p < 0.001) in lobectomy and tidal volume (r = 0.67, p < 0.01) in pneumonectomy. Using discriminant analysis, FEV1ppo in lobectomy and tidal volume in pneumonectomy were also considered as the best predictive factors of MV for pulmonary complications.

CONCLUSIONS

These results suggest that the degree of chronic obstructive pulmonary disease in lobectomy and impairment of preoperative breathing pattern in pneumonectomy are the main factors of respiratory failure after lung resection.

Ventilatory pattern and associated episodic hypoxaemia in the late postoperative period in the general surgical ward

Episodic oxygen desaturation is frequent in the late postoperative period and seems most pronounced on the second and third postoperative nights. However, the ventilatory pattern has not been described systematically during this period. We studied the ventilatory pattern and associated arterial oxygenation using the Edentrace II equipment (impedance pneumography and pulse oximetry) on the second and third postoperative nights in 28 patients undergoing major abdominal surgery. Ventilatory disturbances were common and included periods of hypopnoea, and obstructive, central and mixed apnoeas. Overall, the median (range) respiratory disturbance index (apnoeas + hypopnoeas per h) was 12 (0-121), with the patients spending 6% (0-65%) of the night in some kind of ventilatory disturbance. It was not possible from pre-operative snoring habits to predict patients who developed postoperative ventilatory disturbances. Overall, 23% (0-100) of the hypopnoeas and 7% (0-100) of the apnoeas were associated with episodic hypoxaemia. In conclusion, ventilatory disturbances were common in the late postoperative period in the general surgical ward and often associated with episodes of oxygen desaturation.

Postoperative oxygen therapy

Much has been published in the medical literature concerning adverse events relating to the surgical patient. Among the notable disorders requiring the expertise of the postanesthesia care unit nurse are the diagnosis and management of respiratory dysfunction acutely attributable to the effects of surgery and anesthesia. Inhalational and/or intravenous anesthetic agents contribute to pathophysiological alterations that lend to the development of hypoxemia in the postoperative period. When patients present with preexisting respiratory disease, their care is frequently more complex and challenging. This review session will address the oxygenation component of respiration and the perioperative influences that alter it as well as treatment considerations for normalizing oxygenation.

Artefactual episodic hypoxaemia during postoperative respiratory monitoring

PURPOSE

To determine the reliability of continuous pulse oximetry in the detection of episodic hypoxaemia in total hip joint replacement patients. Episodic hypoxaemia has been described in postoperative patients and is associated with analgesic technique. This study compared the incidence of hypoxaemic episodes identified solely by pulse oximetry and then subsequently where additional monitoring, as indicated for sleep-related breathing disorders, was also utilised.

METHODS

Eight patients were studied on the night before and for three nights after surgery. Pulse oximetry, ECG, chest impedance, nasal and oral airflow and transcutaneous CO2 were recorded. Sudden episodic hypoxaemia was defined as a decrease in oxygen saturation of > or = 5% within two minutes, for > five seconds and with a nadir of < 90%. Artefacts were identified by noise signals on the ECG and impedance recordings and by a motion annotation wave superimposed on the oximetry trace.

RESULTS

Using these criteria 172 (79%) of 219 desaturation events were classified as artefactual. The median duration of genuine events was greater (P < 0.001 Mann Whitney U test) than artefactual events; 21 sec (range, 6-443) vs 11 sec (5-63). Genuine desaturations reached a median nadir of SpO2 87% (range 83-89%) compared with 81% (61-88%) for the artefactual. These differences were statistically significant (P < 0.001).

CONCLUSION

Previous studies utilising unobserved pulse oximetry data alone may have overestimated the incidence of episodic hypoxaemic events in postoperative patients.

The dose-response pharmacology of intrathecal sufentanil in female volunteers

The pharmacologic effects of intrathecal sufentanil (ITS) beyond what is clinically administered (10 microg) are not known. We observed 18 healthy, young, adult female volunteers who received 12.5, 25, or 50 microg of ITS in a randomized, double-blind fashion for 11 h. Analgesia was assessed by pressure algometry at the tibia. Respiratory function was assessed by pulse oximetry, respiratory rate, arterial blood gas, the ventilatory response to CO2, and a respiratory intervention score (RIS). The incidence and severity of side effects also were documented. Serum sufentanil levels were measured for 4 h after ITS administration. We found that ITS produced statistically significant changes in algometry, doubling the pressure required to produce moderate pain. However, doses of ITS greater than 12.5 microg failed to produce proportionate increases in the duration or intensity of analgesia. All doses of ITS produced significant respiratory depression, but only the RIS was significantly related to ITS dose. Neither respiratory rate nor sedation reliably predicted hypoxemia. Supplemental oxygen by nasal cannula consistently prevented pulse oximeter readings below 90%. Serum sufentanil concentrations were related to ITS dose in a statistically significant manner, reached clinically significant concentrations, and followed a time course similar to analgesia and measures of respiratory depression. However, there was no significant increase in measured analgesia associated with the increases in serum sufentanil concentrations. We conclude that in our volunteer model of lower extremity pain, administering ITS in doses larger than 12.5 microg does not improve the speed of onset, magnitude, or duration of analgesia and only causes dose-related increases in serum sufentanil concentrations, which may augment respiratory depression.

Total intravenous anaesthesia with propofol or inhalational anaesthesia with isoflurane for major abdominal surgery. Recovery characteristics and postoperative oxygenation--an international multicentre study

Two hundred and ten adult patients undergoing open cholecystectomy, vagotomy or gastrectomy were included in a randomised multicentre study to compare postoperative nausea and vomiting, oxygen saturations for the first three postoperative nights, time to return of gastrointestinal function, mobilisation, and discharge from the hospital following induction and maintenance of anaesthesia with propofol and alfentanil or with thiopentone, nitrous oxide, isoflurane and alfentanil. Recovery from anaesthesia was significantly faster in the propofol group (mean (SD) times to eye opening and giving correct date of birth of 14.0 (SD 13.8) and 25.5 (SD 29.5) minutes, and 18.5 (SD 14.8) and 35.5 (SD 37.2) minutes in the propofol and isoflurane groups respectively). There was significantly less nausea in the propofol group (15.4%) than in the isoflurane group (33.7%) in the first two postoperative hours (p < 0.003) but not thereafter. There were no significant differences between the groups in any other recovery characteristics. The incidence of hypoxaemia (arterial oxygen saturation less than 93%) was close to 70% in both groups for the first three postoperative nights, indicating the need for oxygen therapy after major abdominal surgery.

Intraoperative ventilation with air and oxygen during laparoscopic cholecystectomy decreases the degree of postoperative hypoxaemia

We studied the effects of intraoperative use of air in oxygen (O2) (FiO2 = 0.33) versus nitrous oxide (N2O) in O2 (FiO2 = 0.33) on the degree of postoperative hypoxaemia in 30 patients undergoing laparoscopic cholecystectomy. Patients were randomly allocated to receive either general anaesthesia with air (Group A, n = 15) or with N2O (Group N, n = 15). Arterial gas tensions were measured before, 24 h and 48 h after surgery while breathing room air. The mean PaO2 24 h and 48 h postoperatively decreased significantly in both groups compared with the preoperative values. The mean PaO2 24 h postoperatively in Group N (74.6 +/- 6.4 mmHg) tended to be lower than that in Group A (78.1 +/- 8.3 mmHg). The mean PaO2 48 h postoperatively in Group N (75.0 +/- 7.8 mmHg) was significantly lower than that in Group A (83.5 +/- 7.9 mmHg) (P < 0.05). On the contrary, the mean PaCO2 did not show any significant change during 48 h postoperatively in either group. Our results suggest that ventilation with N2O and O2 during laparoscopic cholecystectomy is associated with a lower degree of postoperative hypoxaemia.

Influence of anesthetic technique on early postoperative hypoxemia

In the present study we have compared the incidence and degree of hypoxemia during the early postoperative period and for the first 3 nights after operation occurring after the administration of total intravenous anesthesia with propofol versus inhalation anesthesia with nitrous oxide and isoflurane. We studied 50 consecutive non-obese patients, ages 25-65, ASA I-II, who were scheduled for elective cholecystectomy. Patients received randomly either total intravenous anesthesia with propofol (24 patients) or inhalation anesthesia with nitrous oxide and isoflurane (26 patients). Oxygen saturation was continuously recorded on the night before surgery, for 8 hours after extubation (early postoperative period) and during the first, second and third nights after operation. In the early postoperative period we found statistically significant higher values of mean (P<0.05) and minimum (P<0.01) SpO2 in patients who received total intravenous anesthesia compared to patients in whom inhalation anesthesia was used. Moreover, in the early postoperative period, 4 (16.7%) patients of the intravenous anesthesia group versus 11 (42.3%) patients of the inhalation anesthesia group had at least 1 hypoxemic event (P<0.05). We conclude that the incidence and degree of hypoxemia in the early postoperative period is significantly less when total intravenous anesthesia with propofol is used.

Enhancement of postoperative desaturation in heavy snorers

The risk of postoperative decreases of arterial saturation in oxygen (SpO2) could be enhanced in patients with previous history of sleep-induced respiratory impairment. To test this hypothesis, patients scheduled for orthopedic surgery were classified preoperatively as heavy snorers, light snorers, and nonsnorers, according to their answers to a questionnaire. During the first postoperative night, the patients were breathing room air and both the arterial saturation and the tracheal sounds were monitored. Although the cumulated duration of snore was similar in the three groups, the number of desaturations (decrease in SpO2 > or = 4%) was more in the heavy snorers (14.9 +/- 27.9) than in the light snorers (0.1 +/- 0.3) and the nonsnorers (0.2 +/- 0.3) (P < 0.05). The percent duration of recording at SpO2 < 90% was longer in the heavy snorers (52.0% +/- 41.9% of the recording time) than in the two other groups: 9.3% +/- 12.4% (light snorers) and 17.5% +/- 21.8% (nonsnorers) (P < 0.05). Patients with a previous history of sleep-disordered breathing risked postoperative desaturation and could be detected preoperatively by the answers to certain questions.

Oxygen therapy reduces postoperative tachycardia

Concomitant hypoxaemia and tachycardia in the postoperative period is unfavourable for the myocardium. Since hypoxaemia per se may be involved in the pathogenesis of postoperative tachycardia, we have studied the effect of oxygen therapy on tachycardia in 12 patients randomly allocated to blinded air or oxygen by facemask on the second or third day after major surgery. Inclusion criteria were arterial hypoxaemia (oxygen saturation < or = 92%) and increased heart rate (> 90 beat.min-1). Each patient responded similarly to oxygen therapy: an increase in arterial oxygen saturation and a decrease in heart rate (p < 0.002). Thus, postoperative supplementary oxygen has a positive effect on the cardiac oxygen delivery and demand balance.

Effect of general anesthesia and major versus minor surgery on late postoperative episodic and constant hypoxemia

STUDY OBJECTIVE

To evaluate the relative contribution of general anesthesia alone and in combination with the surgical procedure to the pathogenesis of late postoperative hypoxemia.

DESIGN

Open, controlled study.

SETTING

University hospital.

PATIENTS

60 patients undergoing major abdominal surgery and 16 patients undergoing middle ear surgery, both with comparable general anesthesia.

MEASUREMENTS AND MAIN RESULTS

Patients were monitored with continuous pulse oximetry on one preoperative night and the second postoperative night. Significant episodic or constant hypoxemia did not occur on the second postoperative night following middle ear surgery and general anesthesia, but severe episodic and constant hypoxemia did occur on the second postoperative after major abdominal surgery and general anesthesia.

CONCLUSIONS

General anesthesia in itself is not an important factor in the development of late postoperative constant and episodic hypoxemia, which instead may be related to the magnitude of trauma and/or opioid administration.

Intranasal fentanyl titration for postoperative pain management in an unselected population

A randomized, double-blind study was undertaken to investigate the suitability of intranasally administered fentanyl for postoperative pain management under routine conditions in an unselected population. For postoperative pain relief, patients received either 0.027 mg fentanyl intranasally and sodium chloride 0.9% intravenously (intranasal group, n = 53) or sodium chloride 0.9% intranasally and 0.027 mg fentanyl intravenously (intravenous group, n = 59). These doses were repeated every 5 min until the patients were free of pain or refused further analgesia. Pain severity was evaluated before beginning opioid titration and 5, 10, 15, 20, 30, 40, 50, 60, 70 and 80 min thereafter. Adequate pain relief was achieved in 52 of 53 patients in the intranasal and in all patients in the intravenous group. Pain intensities evaluated on a 101-point numerical rating scale as well as on a verbal rating scale decreased significantly in both study groups within 5 min. At the 15 min measurement point, numerical rating scale pain intensity and at the 10 and 20 min point, verbal rating scale pain intensity was significantly lower in the intravenous group. The incidence of side effects was low in both groups and no patient complained of intranasal pain. Intranasally administered fentanyl would appear to be suitable for the management of postoperative pain.

A comparison of epidural tramadol and epidural morphine for postoperative analgesia

The present study compared epidural tramadol with epidural morphine for postoperative analgesia in 20 patients undergoing major abdominal surgery. Intraoperatively, the patients were anaesthetized by a balanced technique of general anaesthesia combined with lumbar epidural lidocaine. In ten of the patients 100 mg tramadol diluted in 10 ml normal saline was also injected epidurally, while 4 mg epidural morphine was used in the other ten patients. In all patients, the visual analogue pain score, PaO2, PaCO2 and respiratory rate were monitored every hour for the first 24 hr postoperatively. In both the tramadol and morphine groups, the mean hourly pain scores ranged from 0.2 +/- 0.6 to 1.4 +/- 2.5 throughout the period of observations. However, the mean PaO2 was decreased postoperatively in the epidural morphine group, while no change was observed in the epidural tramadol group. The maximal decrease of PaO2 in the epidural morphine group was observed at the tenth hour postoperatively, when it decreased to 72.8 +/- 10.3 mmHg. This was not associated with any increase in PaCO2 or a decrease of respiratory rate, suggesting that hypoxaemia rather than hypercarbia or decreased respiratory rate may be an earlier indicator of respiratory rate, suggesting that hypoxaemia rather than hypercarbia or decreased respiratory rate may be an earlier indicator of respiratory depression in patients breathing room air without oxygen supplementation. The absence of clinically relevant respiratory depression following epidural tramadol compared with epidural morphine may be attributed to the different mechanisms of their analgesic action. The results suggest that epidural tramadol can be used to provide prolonged postoperative analgesia without serious side effects.

Postoperative oxygenation in the elderly following general or local anaesthesia for ophthalmic surgery

Peripheral oxygen saturation was recorded on the pre-operative night (between 2400 and 0600 h), the immediate postoperative period (first 60 min) and the first postoperative night (2400 to 0600 h) in 18 elderly patients aged 70 years or over presenting for elective ophthalmic surgery. Nine patients had surgery performed under general anaesthesia employing muscle relaxants and controlled ventilation and nine under local anaesthesia using a peribulbar block. The median (interquartile range) percentage of time during which the patients had an oxygen saturation of less than 90% was 0 (0-0.2) and 0.04 (0-0.4) on the pre-operative night, 0.7 (0-1.4) and 0.3 (0-1.2) in the immediate postoperative period, and 0.05 (0-0.16) and 0 (0-0.3) on the postoperative night in the general and local anaesthesia patients respectively. There were no significant differences between general and local anaesthesia in respect of these data and the overall incidence of significant desaturation was low. The present study could not demonstrate any adverse effect of general anaesthesia on oxygen saturation in patients undergoing minimally invasive surgery.