NAVD88 height (Meters) - EPSG:5703

WKT

VERTCS["NAVD_1988", 
	VDATUM["North_American_Vertical_Datum_1988"], 
	PARAMETER["Vertical_Shift", 0.0], 
	PARAMETER["Direction", 1.0], 
	UNIT["Meter", 1.0]]

WKT2

VERTCRS["NAVD_1988", 
	VDATUM["North_American_Vertical_Datum_1988"], 
	CS[vertical, 1], 
	AXIS["Gravity-related height (H)", up, 
		LENGTHUNIT["Meter", 1.0]], 
	ID["EPSG", "5703"]]

Data from @esri/proj-codes

{
  "wkid": 5703,
  "latestWkid": 5703,
  "macro": "PE_VCS_NAVD_1988",
  "name": "NAVD_1988",
  "wkt": "VERTCS[\"NAVD_1988\",VDATUM[\"North_American_Vertical_Datum_1988\"],PARAMETER[\"Vertical_Shift\",0.0],PARAMETER[\"Direction\",1.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "VERTCRS[\"NAVD_1988\",VDATUM[\"North_American_Vertical_Datum_1988\"],CS[vertical,1],AXIS[\"Gravity-related height (H)\",up,LENGTHUNIT[\"Meter\",1.0]],ID[\"EPSG\",\"5703\"]]",
  "description": "NAVD88 height (Meters)",
  "authority": "EPSG",
  "version": "6.15(9.3.0.0)",
  "deprecated": "no",
  "areaname": "North America - Mexico and USA - onshore",
  "extent": {
    "slat": 14.51,
    "nlat": 71.4,
    "llon": 172.42,
    "rlon": -66.91
  }
}