Influence of altitude on cerebral and splanchnic oxygen saturation in critically ill children during air ambulance transport

Abstract

Objective: The aim of the current study was to investigate how cerebral and splanchnic oxygen saturation (rSO2-C and rSO2-A) in critically ill children transported in air ambulance was affected by flight with cabin pressurization corresponding to ≥ 5000 feet. A second aim was to investigate any differences between cyanotic and non-cyanotic children in relation to cerebral and splanchnic oxygen saturation during flight ≥ 5000 feet. The variability of the cerebral and splanchnic Near Infrared Spectroscopy (NIRS) sensors was evaluated.

Design: NIRS was used to measure rSO2-C and rSO2-A during transport of critically ill children in air ambulance. rSO2 data was collected and stored by the NIRS monitor and extracted and analyzed off-line after the transport. Prior to evaluation of the NIRS signals all zero and floor-effect values were removed.

Setting: The Pediatric Intensive Care Unit (PICU) at Astrid Lindgren Children's Hospital, Karolinska University Hospital in Stockholm, Sweden.

Patients: In total, 44 critically ill children scheduled for inter-hospital transport by a specialized pediatric transport team were included in the study between January 2014 and January 2019 (convenience sampling).

Intervention: No interventions were conducted.

Measurements: All study patients were monitored with a cerebral NIRS-sensor placed over the forehead and an abdominal NIRS-sensor placed in the infra-umbilical area for cerebral and splanchnic regional oxygen saturation monitoring, rSO2-C and rSO2-A, respectively.

Main results: Complete rSO2-C and rSO2-A data was obtained in 39 patients. Median age was 12 days. Cyanotic congenital heart malformations were present in 9 patients (23%). In 22 patients (56%) rSO2-C decreased at altitude ≥ 5000 feet and in 24 patients (61%) rSO2-A decreased at altitude ≥ 5000 feet compared to baseline (p<0.0001). In 25 patients (64%) the rSO2-C/rSO2-A ratio was greater at altitude ≥ 5000 feet than at baseline. A ratio ≥ 1 was seen in 77% of patients at altitude ≥ 5000 feet compared to in 67% of patients at baseline.

Conclusion: Both cerebral and splanchnic oxygen saturation decreased at altitude ≥ 5000 feet compared to baseline. In most patients, both cyanotic and non-cyanotic, cerebral oxygen saturation was preserved more than splanchnic oxygen saturation.

Fig 1. Recruitment process of study participants.

NIRS = Near-infrared Spectroscopy. CDH = Congenital Diaphragmatic Hernia.

Fig 2. Coefficient of variation demonstrating the scatter for rSO₂-C and rSO₂-A in each patient before flight, at altitude ≥ 5000 feet and after flight.

All recorded values after all zero values and floor effect values were removed are used. Red dots = rSO₂-C, Blue dots = rSO₂-A.

Fig 3. The median values of rSO₂-C and rSO₂-A.

Data were derived from all recorded values, determined for rSO₂-C and rSO₂-A in each individual patient at baseline, at altitude ≥ 5000 feet and after flight. 3A: rSO₂-C in non-cyanotic patients, 3B: rSO₂-A in non-cyanotic patients, 3C: rSO₂-C in cyanotic patients and 3D: rSO₂-A in cyanotic patients.

Fig 4. Changes in SpO₂, rSO₂-C and rSO₂-A with an increase in FiO₂ illustrated for nine patients who required additional oxygen during flight.

The influence of altitude on rSO₂-C, rSO₂-A and pulse oximetry for 3 different patients was visualized after smoothing with 20 neighbours. The graphs reveal different characteristic patterns of reacting to altitude (Fig 5A–5C).

Fig 5. Different characteristic patterns of reacting to altitude in 3 different patients.

rSO₂-C was higher, at the same level and lower than rSO₂-A in Fig 5A (Patient 17), 5B (Patient 21) and 5C (Patient 16), respectively. The NIRS curves were smoothed by the Savitzky–Golay filtering method (20 neighbours) [16].