Severe hypercapnia associated with metabolic alkalosis due to pyloric stenosis

Postoperative apnea after pyloromyotomy for infantile hypertrophic pyloric stenosis

Objective

Infantile hypertrophic pyloric stenosis (IHPS), which causes gastric outlet obstruction and hypochloremic hypokalemic metabolic alkalosis, could pose a risk of postoperative apnea in patients. The aim of this study is to evaluate the incidence of postoperative apnea in babies admitted to a tertiary-level pediatric surgical center in Milano, Italy with diagnosis of IHPS in 2010–2019. The secondary objective is to evaluate the risk factors for postoperative apnea.

Methods

This is a single-center, retrospective, observational cohort study. All patients admitted to our institution with diagnosis of IHPS during the study period were enrolled. Demographic and surgical variables, along with blood gas parameters, were obtained from the population. Postoperative apnea was defined as a respiratory pause longer than 15 s or a respiratory pause lasting less than 15 s, but associated with either bradycardia (heart rate <120 per minute), desaturation (SatO2 <90%), cyanosis, or hypotonia. Occurrence was obtained from nursing charts and was recorded as a no/yes dichotomous variable.

Results

Of 122 patients, 12 (9.84%) experienced apnea and 110 (90.16%) did not. Using univariate analysis, we found that only postoperative hemoglobin was significantly different between the groups (p=0.03). No significant multivariable model was better than this univariate model for prediction of apnea.

Conclusions

Postoperative anemia, possibly due to hemodilution, increased the risk of postoperative apnea. It could be hypothesized that anemia can be added as another apnea-contributing factor in a population at risk due to metabolic changes.

Respiratory problems owing to severe metabolic alkalosis in infants presenting with hypertrophic pyloric stenosis

OBJECTIVE

Uncorrected metabolic alkalosis in infantile hypertrophic pyloric stenosis (IHPS) could lead to perioperative apnea. However, the precise incidence of preoperative respiratory problems and the association with metabolic alkalosis are unknown. Therefore, we aimed to determine the incidence of preoperative respiratory problems in IHPS and to assess the association with metabolic alkalosis.

METHODS

We retrospectively reviewed all patients diagnosed with IHPS during 2007-2017. Respiratory problems were classified as present or absent. With multivariate logistic regression we analyzed the association between bicarbonate and respiratory problems, corrected for gestational age and birth weight.

RESULTS

We included 459 infants, of whom 23 developed preoperative respiratory problems (5.0%). Infants with preoperative respiratory problems were more often female (43.5% vs. 13.3% p = 0.001) and had significantly higher median serum levels of bicarbonate (32.0 mmol/L vs. 30.0 mmol/L), base excess (6.5 mmol/L vs. 5.3 mmol/L) and pCO2 (6.4 kPa vs. 5.9 kPa), compared to infants without respiratory problems. Multivariate analysis of serum bicarbonate and presence of respiratory problems showed an OR of 2.18 per 10 mmol/L (95% CI 1.21-4.71) (p = 0.009). The optimal bicarbonate cutoff point was 25.7 mmol/L (sensitivity 100%, specificity 13.4%).

CONCLUSION

IHPS with metabolic alkalosis potentially results in preoperative respiratory problems. A lower bicarbonate target before surgery might be recommended and respiratory monitoring should be considered.

LEVEL OF EVIDENCE

Level IV.

Perioperative apnea in infants with hypertrophic pyloric stenosis: A systematic review

BACKGROUND

Infantile hypertrophic pyloric stenosis (IHPS) leads to excessive vomiting and metabolic alkalosis, which may subsequently cause apnea. Although it is generally assumed that metabolic derangements should be corrected prior to surgery to prevent apnea, the exact incidence of perioperative apneas in infants with IHPS and the association with metabolic alkalosis are unknown. We performed this systematic review to assess the incidence of apnea in infants with IHPS and to verify the possible association between apnea and metabolic alkalosis.

METHODS

We searched MEDLINE, Embase, and Cochrane library to identify studies regarding infants with metabolic alkalosis, respiratory problems, and hypertrophic pyloric stenosis. We conducted a descriptive synthesis of the findings of the included studies.

RESULTS

Thirteen studies were included for analysis. Six studies described preoperative apnea, three studies described postoperative apnea, and four studies described both. All studies were of low quality or had other research questions. We found an incidence of 27% of preoperative and 0.2%-16% of postoperative apnea, respectively. None of the studies examined the association between apnea and metabolic alkalosis in infants with IHPS.

CONCLUSIONS

Infants with IHPS may have a risk to develop perioperative apnea. However, the incidence rates should be interpreted with caution because of the low quality and quantity of the studies. Therefore, further studies are required to determine the incidence of perioperative apnea in infants with IHPS. The precise underlying mechanism of apnea in these infants is still unknown, and the role of metabolic alkalosis should be further evaluated.

Alkalosis-induced respiratory depression from infantile hypertrophic pyloric stenosis

We report an infant with apnea due to infantile hypertrophic pyloric stenosis. The distinct mechanism of compensatory respiratory depression of severe metabolic acidosis is implicated.

Severe hypercapnia associated with a non-respiratory alkalosis

A case of hypoventilation in response to a non-respiratory alkalosis is presented. It is postulated that the degree of hypoventilation encountered was a normal response and that a fall in intracellular hydrogen ion concentration was responsible for the hypoventilation. This explains why the alkalosis associated with potassium deficiency is not associated with hypoventilation since the intracellular hydrogen ion concentration then remains constant. The renal response in this condition is responsible for maintaining the alkalosis and seems to be aimed at sodium conservation and hence plasma volume control rather than defence of acid-base balance.

A diagram to facilitate the understanding and therapy of mixed acid base disorders

A diagram based on in-vivo relationships between arterial hydrogen ion activity (H+) and carbon dioxide tension (PCO2) in primary abnormalities of acid base homeostasis is presented. It is designed to facilitate the interpretation of pH data by including the 95% confidence limits described in patients with simple metabolic and respiratory acid base disorders. These bands have been formulated from observation of simple acid base abnormalities and indicate the appropriate respiratory or renal compensatory response to the primary pH defect. A plot which falls outside these limits therefore indicates the presence of a mixed acid base disorder. The diagram presents a physiological approach to clinical disorders of pH regulation demonstrating maintenance of intra-cellular fluid homeostasis during primary extracellular fluid disturbances. Diagnostic and therapeutic advantages are further illustrated and discussed in six case reports.