Incidence of postoperative pulmonary congestion as diagnosed by lung ultrasound in surgeries performed under general anaesthesia: A prospective, observational study

ABSTRACT

Background and Aims:

Administering liberal fluid raises concerns about pulmonary congestion postoperatively. Bedside ultrasonography is a valuable tool for the early detection of pulmonary congestion. In this study, we have used it to ascertain the impact of the duration of surgery and intraoperative fluid volume on the causation of pulmonary congestion. Our objective was to determine the incidence of pulmonary congestion as diagnosed by lung ultrasound in patients undergoing general anaesthesia with varied fluid administration.

Methods:

Seventy participants of American Society of Anesthesiologists physical status I and II, aged between 18 and 60 years, undergoing elective extrathoracic surgeries of over 3 h under general anaesthesia were included. Preoperative lung ultrasound was carried out in all patients, and a postoperative lung ultrasound was carried out at 1 h after extubation. The appearance of three or more “B”-lines was considered positive for lung congestion.

Results:

Significant differences (P < 0.001) were found in the duration of surgery and the appearance of B-lines in the postoperative period. Participants who developed B lines received, on average, 150% more fluid (1148.16 ± 291.79 ml) than those who did not (591.29 ± 398.42 ml) (P = 0.0240). Net fluid balance was also significantly different in patients who developed B lines (P = 0.0014). None of the patients developed symptoms of lung congestion postoperatively.

Conclusion:

Long duration of surgery under general anaesthesia (>3 h) with the administration of large volumes of intraoperative fluid and a large net fluid balance are associated with lung congestion as diagnosed by lung ultrasound.

INTRODUCTION

Pulmonary oedema is fluid collection in the lungs’ interstitial tissue and air spaces.[1] It is a known complication in the postoperative period.[2,3] No perioperative predictors can successfully warn against the development of postoperative pulmonary oedema. Various aetiologies are implicated in the causation of postoperative pulmonary congestion or oedema, namely, the presence of preexisting cardiac disease, fluid overload, anaphylaxis in the intraoperative period, acute lung injury (as in blood transfusion–associated lung injury, sepsis, trauma burns), post-extubation negative pressure pulmonary oedema and excessive fluid administration during surgery.[1] Pulmonary congestion or oedema leads to impaired gas exchange, respiratory failure and significant morbidity; if left undiagnosed or untreated, it can be fatal. The guidelines for intraoperative intravenous (IV) fluid administration are poorly defined, and fluid administration varies from restrictive to liberal fluid administration.[2] The goals of intraoperative fluid administration should be to maintain proper volume in the circulation to maintain adequate tissue perfusion. Traditionally, a large volume of fluid is infused intraoperatively[3] with the belief that overnight fasting and the effect of anaesthesia on ongoing blood loss during surgery lead to hypovolemia that results in reduced circulatory volume and diminished tissue perfusion.[4,5] In contrast, inadequate fluid administration may lead to circulatory instability, compromised tissue perfusion and complications such as prerenal acute renal failure.[5-7] Liberal fluid administration has concerns about pulmonary congestion or oedema, decreased wound healing, decreased tissue oxygenation and delayed recovery.[2] Lung ultrasonography (LUS) is a valuable and fast bedside technique for detecting pulmonary congestion/oedema. Point-of-care ultrasound is an important tool in the intensive care unit setting for the rapid and reliable assessment of the lungs. Moreover, it can be performed rapidly and very easily. In the present study, we planned to evaluate the impact of intraoperative fluid administration strategy on the incidence of pulmonary congestion or oedema using LUS. We aimed to determine the incidence of pulmonary congestion in patients undergoing general anaesthesia for surgeries lasting more than 3 h with varied fluid administration.

METHODS

After obtaining clearance from the institute ethics committee (763/IEC/-AIIMSRPR/2019, dated 23.09.2019), 70 patients of the American Society of Anesthesiologists (ASA) physical status I and II, aged between 18 and 60 years, undergoing elective extrathoracic surgeries under general anaesthesia lasting for three or more hours were recruited for the study. Informed and written consent was obtained for participation in the study and use of the patient data for research and educational purposes from all patients before recruiting them. The study was conducted in accordance with the principles of the Declaration of Helsinki, 2013. Selected patients were screened during a preanaesthetic check-up for preexisting cardiac and pulmonary illnesses. Patients with preexisting B lines on LUS were not included in the study. Preexisting cardiac/pulmonary disease increases the susceptibility to pulmonary congestion or oedema; such patients were excluded from the study. We also excluded pregnant women and patients who did not consent to participate in the study. The study was a prospective, observational, feasibility study conducted from December 2019 to December 2020 in a tertiary care hospital.

Vital parameters, laboratory parameters such as haemoglobin (Hb), serum total protein and albumin, and IV fluid administration in the last 12 h, if any, were noted. Patients were cannulated with an IV cannula of appropriate size. Preoperative lung ultrasound was conducted by a standard technique using a SonoSite Edge II (Fujifilm Sonosite, WA, USA) 6–13 MHz linear and 3–5 MHz curvilinear ultrasound probe. In the operating room, ASA standard monitors were connected. The induction time was noted and considered as the commencement of general anaesthesia. The total volume of intraoperative IV fluid (crystalloids, colloids, blood and blood products) administered was recorded. Ringer lactate was the crystalloid used. The fluids, blood and blood products were administered in a goal-directed manner guided by dynamic indices, namely, pulse pressure variation (PPV) and stroke volume variation (SVV). The total blood loss and urine output during the surgery were recorded [Figure 1].

Figure 1.

Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) diagram showing the flow of patients

At the end of the surgery, the tracheal extubation time was recorded as the time of the end of general anaesthesia (T), and patients were transferred to the post-anaesthesia care unit (PACU). LUS was performed in the postoperative period, 1 h after extubation in the PACU (T + 1 h).

LUS was performed by the consultant anaesthesiologist by the technique described by Miller,[8] with the patient in the supine position. First, the anterior thorax was divided into three parts using a two-hand method:

1. Upper anterior point- This is the base of the middle and ring fingers of the upper hand. It corresponds to the upper lobe.

2. Lower anterior point- This is the middle of the palm of the lower hand (close to the nipple in a male). It corresponds to the middle or lingular lobe.

3. Posterolateral point- From the lower anterior end, the ultrasonography probe is moved laterally and posteriorly as far as possible behind the posterior axillary line (limited by the bed), which finally lies over the lower lobe.

The appearance of numerous (>3) and closely spaced B lines between two adjacent ribs was considered as the presence of lung congestion. B lines are defined as hyperechogenic, vertical comet tail artefacts with a narrow base, spreading from the pleural line to the border of the screen. A single investigator performed LUS to avoid intervariability. Intraoperative parameters like mode of ventilation, tidal volume delivered, airway pressures, fluid intake and output, and any adverse event were also obtained from the intraoperative anaesthesia record.

The study’s primary outcome measures were calculating the incidence of pulmonary congestion detected by LUS. The secondary outcome measures included correlating net fluid balance, the total duration of surgery, real IV fluids administered intraoperatively, and blood and product administration with the incidence of pulmonary congestion.

In this study, with a 95% confidence level, anticipated population proportion of 0.05 and a 5% margin of error for population size (N) of 1000, we would require 69 subjects. Hence, a sample size of 70 was considered to be adequate.

Data was entered in the Microsoft Excel (Office 365). The statistical analysis was performed using International Business Machines (IBM) statistical package for the social sciences (SPSS) Statistics for Windows, version 21.0 (IBM Corp., Armonk, NY, USA). Data were expressed as mean and standard deviation (SD). Demographic data were analysed using Student’s t-test. A P value less than 0.05 was considered statistically significant. F-test was used to compare the variance of data distribution. Finally, t-test or Welch t-test was used to compare the data.

RESULTS

In this study, 74 participants were enroled, of whom four were excluded [Figure 1]. Preoperative LUS revealed less than three B lines in all the recruited patients. Among the 70 patients, six were found to have significant numbers of B lines during examination in the 1 h postoperative period. There was no significant difference in the distribution of age, gender, height, weight, and body mass index between the two groups of study participants [Table 1]. In addition, there was no significant difference in the distribution of values of laboratory parameters, haemoglobin and serum albumin [Table 1]. Similarly, no significant difference was noted in ventilatory parameters, positive end-expiratory pressure and peak inspiratory pressure [Table 2]. However, a significant difference (P < 0.05) was found between the groups when the overall duration of surgery was compared [Table 2]. The duration of surgery was taken as a surrogate for the total duration under positive pressure ventilation. Duration of surgery (in hours) and net balance (in ml) had a statistically significant role as predictors, and the duration of surgery showed an odds ratio of 6.74 [Table 3]. The area under the receiver operating characteristic curve was 0.984 with a 95% confidence interval of 0.921 to 0.999 showing excellent discrimination in predicting the role of net fluid balance and duration of surgery in causing pulmonary oedema. There were no incidents of postoperative adverse events. The overall prevalence of pulmonary congestion was found to be 8.5%.

Table 1.

Demographic variables and preoperative laboratory parameters

	All patients (n=70) (Mean±SD)	Congestion (n=6) (Mean±SD)	No congestion (n=64) (Mean±SD)	P
Age (years)	38.37±13.50	37.16±17.65	38.48±13.21	0.821
Height (cm)	158.91±8.45	157.83±7.11	159.01±8.60	0.745
Weight (kg)	59.90±9.84	59.66±9.99	59.92±9.91	0.951
BMI (kg/m2)	23.37±2.89	23.48±2.86	23.36±2.92	0.920
Haemoglobin (g/dl)		13.08±1.56	12.83±1.92	0.761
Total serum protein (mg/dl)		7.04±0.79	7.18±0.80	0.673
Serum albumin (mg/dl)		4.09±0.37	4.10±0.46	0.936

BMI=body mass index, SD=standard deviation

Table 2.

Intraoperative parameters

	Congestion (n=6) (Mean±SD)	No congestion (n=64) (Mean±SD)	P
Total duration of surgery (h)	8.25±2.40	4.92±1.52	<0.001
PEEP, median (IQR)	4 (3–5)	4 (3–5)	0.718
Crystalloids (ml)	2133.3±656.2	1408.2±741.4	0.024
Blood and blood products (ml)	229.8±278.9	31.6±118.2	0.144
Net fluid balance (ml)	1148.2±291.8	591.3±398.4	0.14a

^at-Test (assuming equal variances). IQR=interquartile range, PEEP=positive end-expiratory pressure, SD=standard deviation

Table 3.

Multivariate logistic regression to predict pulmonary congestion

Variable	Odds ratio	95% CI	P
Blood and blood products (ml)	1.0019	0.9943 to 1.0096	0.624
Crystalloids (ml)	0.9966	0.9925 to 1.0007	0.102
Duration of surgery (h)	6.7439	1.1205 to 40.5875	0.037
Haemoglobin (g/dl)	2.3765	0.6070 to 9.3041	0.213
Net balance (ml)	1.0063	1.0003 to 1.0122	0.038

Using Cox and Snell R² and Nagelkerke R². CI=confidence interval

DISCUSSION

We observed the prevalence of lung congestion in patients undergoing general anaesthesia with various IV fluid administrations as 8.5%, as detected by LUS in the immediate postoperative period. An interplay of prolonged duration of surgery, large-volume intraoperative fluid administration and large net balance of fluid lead to perioperative lung congestion.

Pulmonary congestion depends on factors like preexisting cardiac disease, renal disease, hypoproteinemia, perioperative fluid administration, anaphylaxis in the intraoperative period, acute lung injury and post-extubation negative pressure pulmonary oedema.[1,9] Administration of a large volume of fluid damages the capillary glycocalyx and causes a fluid shift into the interstitial space,[5] leading to the development of interstitial oedema. We identified three significant parameters in the participants with positive LUS signs of lung congestion. They are the volume of crystalloid infusion, net fluid balance and the duration of surgery.

Analysis of the volume of crystalloid administration between the two groups, using t-test (assuming equal variances), showed a significant difference (P = 0.024) with 150% more crystalloids administered in participants who developed congestion than those who did not [Table 2]. As stated, large-volume fluid administration is a known risk factor for pulmonary oedema. A retrospective analysis of 13 patients by Arieff[10] determined excessive fluid administration as a cause of pulmonary oedema in the postoperative period. Arieff[10] reported that administering a net volume of 67 ml/kg/day led to the development of pulmonary oedema. In our study, no participants were observed for more than 1 h post-extubation, so the net fluid balance for 24 h could not be determined. However, no participants had more than 28 ml/kg of net fluid balance till the observation was completed. The LUS signs of interstitial oedema, B lines, appear before the occurrence of alveolar oedema and correspond to the flat portion of the Starling curve, where further fluid administration will lead to the development of alveolar oedema. In the present study, the volume of fluid administration and net fluid balance was significantly higher (P > 0.05) in participants who developed interstitial congestion of the lungs. However, none crossed the limit described by Arieff[10] for the occurrence of pulmonary oedema. It could not be determined if net fluid balance and total fluid administration alone would cause interstitial oedema in our subjects, as described in referenced literature and studies. A similar volume of fluid administration and resultant net fluid balance were also obtained in some participants who did not develop interstitial oedema. When the duration of surgery was analysed, it was also significantly longer in the participants who developed LUS signs of interstitial oedema. Long duration of surgery (>3 h) is associated with various postoperative pulmonary complications.[11] Participants who developed interstitial oedema were subjected to a considerably longer duration of surgery than those who did not [Table 2]. The prolonged duration of surgery alone cannot be attributed as a cause of interstitial oedema, as some participants who were subjected to a similar surgery period did not develop interstitial oedema. The appearance of interstitial oedema in the setting of excessive fluid administration and high net volume of fluid in a long-duration surgery can also be attributed to the shearing forces generated by positive pressure ventilation. All three significant factors seem to be a major driver for the development of interstitial lung congestion in the study cases, and no single factor alone seems to be an independent cause. The participants who developed interstitial oedema were subjected to a longer duration of surgery, more fluids and had a higher net fluid balance till the end of the observation period compared to the participants who did not. Further studies are needed to establish the impact of individual factors in the development of pulmonary congestion in surgeries under general anaesthesia.

None of the participants developed signs and symptoms of pulmonary oedema in the PACU and the postoperative ward during follow-up. No ultrasound examination or other imaging was done during the follow-up, so the assumed resolution of interstitial oedema diagnosed in the postoperative period could not be ascertained. The study was limited by its sample size; a larger sample size will be needed to better represent a larger population and obtain accurate results.

CONCLUSION

The prevalence of postoperative lung congestion in patients undergoing general anaesthesia with various IV fluid administrations is 8.5%. An interplay of prolonged duration of surgery, large-volume intraoperative fluid administration and large net balance of fluid lead to perioperative lung congestion. Lung USG can detect lung congestion even before the clinical appearance of signs and symptoms of pulmonary congestion, which can then guide fluid administration.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.