Intraoperative use of low volume ventilation to decrease postoperative mortality, mechanical ventilation, lengths of stay and lung injury in patients without acute lung injury
Abstract
Background
During the last decade, there has been a trend towards decreasing tidal volumes for positive pressure ventilation during surgery. It is not known whether this new trend is beneficial or harmful for patients.
Objectives
To assess the benefit of intraoperative use of low tidal volume ventilation (< 10 mL/kg of predicted body weight) to decrease postoperative complications.
Search methods
We searched the Cochrane Central Register of Controlled Trials (CENTRAL 2014, Issue 9), MEDLINE (OvidSP) (from 1946 to 5 September 2014) and EMBASE (OvidSP) (from 1974 to 5 September 2014).
Selection criteria
We included all parallel randomized controlled trials (RCTs) that evaluated the effect of low tidal volumes (defined as < 10 mL/kg) on any of our selected outcomes in adult participants undergoing any type of surgery. We did not retain studies with participants requiring one‐lung ventilation.
Data collection and analysis
Two authors independently assessed the quality of the retained studies with the Cochrane 'Risk of bias' tool. We analysed data with both fixed‐effect (I2 statistic < 25%) or random‐effects (I2 statistic > 25%) models based on the degree of heterogeneity. When there was an effect, we calculated a number needed to treat for an additional beneficial outcome (NNTB) using the odds ratio. When there was no effect, we calculated the optimal size information.
Main results
We included 12 studies in the review. In total these studies detailed 1012 participants (499 participants in the low tidal volume group and 513 in the high volume group). All studies included were at risk of bias as defined by the Cochrane tool. Based on nine studies including 899 participants, we found no difference in 0‐ to 30‐day mortality between low and high tidal volume groups (risk ratio (RR) 0.79, 95% confidence interval (CI) 0.40 to 1.54; I2 statistic 0%; low quality evidence). Based on four studies including 601 participants undergoing abdominal or spinal surgery, we found a lower incidence of postoperative pneumonia in the lower tidal volume group (RR 0.44, 95% CI 0.20 to 0.99; I2 statistic 19%; moderate quality evidence; NNTB 19, 95% CI 14 to 169). Based on two studies including 428 participants, low tidal volumes decreased the need for non‐invasive postoperative ventilatory support (RR 0.31, 95% CI 0.15 to 0.64; moderate quality evidence; NNTB 11, 95% CI 9 to 19). Based on eight studies including 814 participants, low tidal volumes during surgery decreased the need for postoperative invasive ventilatory support (RR 0.33, 95% CI 0.14 to 0.80; I2 statistic 0%; NNTB 36, 95% CI 27 to 202; moderate quality evidence). Based on three studies including 650 participants, we found no difference in the intensive care unit length of stay (standardized mean difference (SMD) ‐0.01, 95% CI ‐0.22 to 0.20; I2 statistic = 42%; moderate quality evidence). Based on eight studies including 846 participants, we did not find a difference in hospital length of stay (SMD ‐0.16, 95% CI ‐0.40 to 0.07; I2 statistic 52%; moderate quality evidence). A meta‐regression showed that the effect size increased proportionally to the peak pressure measured at the end of surgery in the high volume group. We did not find a difference in the risk of pneumothorax (RR 2.01, 95% CI 0.51 to 7.95; I2 statistic 0%; low quality evidence).
Authors' conclusions
Low tidal volumes (defined as < 10 mL/kg) should be used preferentially during surgery. They decrease the need for postoperative ventilatory support (invasive and non‐invasive). Further research is required to determine the maximum peak pressure of ventilation that should be allowed during surgery.
PICOs
Plain language summary
Use of small volumes of breath insufflation for intraoperative mechanical ventilation during surgery
Background: Inspiration (breathing in) is produced by the shortening of various muscles that stretch the lungs to increase their size like rubber balloons. During this phase, oxygen enters the lungs. When these muscles stop their contractions, the lungs go back to their initial size. During this phase, carbon dioxide goes out. When patients are cared for under general anaesthesia, some of the drugs used will stop the movements of the muscles controlling lung size. Insufflation is the act of mechanically forcing air into a patient's respiratory system. A machine is required to replace the effects of the muscles. A mixture of gas containing oxygen is blown into the lungs. It is actually not known whether is better to blow small volumes of gas at a higher rate or bigger volumes at a lower rate. In this review we tried to determine whether this volume should be lower or higher than 10 millilitres per kilogram of body weight.
Study characteristics: We searched the literature up to 5 September 2014. We included 12 studies with 1012 adult participants of both sexes. These participants had operations on the abdomen, the heart, the back or the lower limbs. Financial support from the pharmaceutical industry or from medical equipment manufacturers was mentioned in two studies. We do not think that this had an effect on the results as high or low volumes may be administered with any machine.
Key results: We found that using a volume lower than 10 millilitres per kilogram of body weight increases the chances that the patients will be able to get back to their normal respiratory status immediately after surgery. Low tidal volumes should be used preferentially during surgery. For every 1000 patients operated on, 136 patients will subsequently need additional non‐invasive ventilatory support (through a mask applied to the face of the patient) if high volumes are used during surgery. If volumes lower than 10 millilitres per kilogram of body weight are used during surgery, then only 42 patients will require non‐invasive ventilatory support. For every 1000 patients operated on, 44 patients will subsequently need invasive ventilatory support (through a tube inserted in the patient's windpipe) if high volumes are used during surgery. If volumes lower than 10 millilitres per kilogram of body weight are used during surgery, only 14 patients will require invasive ventilatory support. We did not find differences in 0‐ to 30‐day mortality and hospital length of stay. We did not identify any possible harmful effects of using low volumes.
Quality of evidence: We judged the quality of the evidence as moderate for these two outcomes (need for non‐invasive or invasive ventilatory support).
